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Quadriceps Arthrogenic Muscle Inhibition: Neural Mechanisms and Treatment Perspectives
David Andrew Rice, BHSc,* and Peter John McNair, PhD†
Objectives: Arthritis, surgery, and traumatic injury of the knee joint are associated with long lasting inability to fully activate the quadriceps muscle, a process known as arthrogenic muscle inhibition (AMI). The goal of this review is to provide a contemporary view of the neural mechanisms responsible for AMI as well as to highlight therapeutic interventions that may help clinicians overcome AMI.
관절염, 수술, 외상 손상 - 대퇴사두근의 완전한 엑티베이션의 장기간 제한 - 관절기원성 근육 억제
Methods: An extensive literature search of electronic databases was conducted including AMED, CINAHL, MEDLINE, OVID, SPORTDiscus, and Scopus.
Results: While AMI is ubiquitous across knee joint pathologies, its severity may vary according to the degree of joint damage, time since injury, and knee joint angle. AMI is caused by a change in the discharge of articular sensory receptors due to factors such as swelling, inflammation, joint laxity, and damage to joint afferents. Spinal reflex pathways that likely contribute to AMI include the group I nonreciprocal (Ib) inhibitory pathway, the flexion reflex, and the gamma-loop. Preliminary evidence suggests that supraspinal pathways may also play an important role. Some of the most promising interventions to counter the effects of AMI include cryotherapy, transcutaneous electrical nerve stimulation, and neuromuscular electrical stimulation. Nonsteroidal anti-inflammatory drugs and intra-articular corticosteroids may also be effective when a strong inflammatory component is present with articular pathology.
부종, 염증, 관절 렉시티, 관절 수용기 손상 -> 1. 관절 감각 수용기의 discharge
/ 2.척추 반사로/ 3. 척추 상위 경로
cryotherapy, TENS, NMES - 효과적인 치료
NSAIDs, 관절 내 스테로이드 주사는 강한 염증일 때 효과
Conclusions: AMI remains a significant barrier to effective rehabilitation in patients with arthritis and following knee injury and surgery. Gaining a better understanding of AMI’s underlying mechanisms will allow the development of improved therapeutic strategies, enhancing the rehabilitation of patients with knee joint pathology.
© 2010 Elsevier Inc. All rights reserved. Semin Arthritis Rheum 40:250-266
Keywords: quadriceps, muscle inhibition, voluntary activation, arthrogenic, knee trauma
Marked weakness of the quadriceps muscles is
typically observed following knee injury, after
knee surgery and in patients with arthritis.
This is partly due to muscle atrophy and partly to ongoing
neural inhibition that prevents the quadriceps from being
fully activated, a process known as arthrogenic muscle
inhibition (AMI). AMI has been linked to articular swelling,
inflammation, pain, joint laxity, and structural damage
(1-4). The relative importance of these factors is not
clearly understood but it is generally accepted that AMI is
caused by a change in the discharge of sensory receptors
from the damaged knee joint (1,2,4-8). Anomalous joint
afferent discharge may have powerful effects on the central
nervous system, influencing the excitability of multiple
spinal and supraspinal pathways that combine to limit
activation of the quadriceps muscles.
Quadriceps AMI has long been of concern to clinicians
as it contributes to muscle atrophy and can delay or even
prevent effective strengthening, hindering rehabilitation
considerably. While mild AMI does not preclude strength
gains (9-11), it is likely to restrict their magnitude as a
portion of the muscle cannot be activated. During the first
few months after injury or surgery, or when joint damage is extensive, AMI may be severe and quadriceps strengthening
protocols can be largely ineffective. Despite resistance
training, quadriceps strength may remain unchanged
or even decline significantly (12-17), an effect
attributed to AMI (12,17). As a result, quadriceps
strength deficits often remain long after the initial joint
trauma (18,19). Persistent quadriceps weakness is clinically
important as it may impair dynamic knee stability
(14,20), physical function (14,21-23), and quality of life
(22), increase the risk of re-injury to the knee joint (24),
and contribute to the development and progression of
osteoarthritis (OA) (25-27).
The objective of this review is to provide the reader
with a deeper understanding of AMI, with a focus on its
potential neural mechanisms and therapeutic interventions
that may help reduce its impact on rehabilitation.
The first section of this article describes the presentation
of AMI, including factors that may influence its severity
and time course. We then review the sensory innervation
of the knee joint and provide an outline of factors that
may alter afferent discharge in the presence of knee damage.
Thereafter, we examine the spinal reflex pathways
that have been implicated in AMI and discuss the potential
influence of supraspinal centers on this process. Finally,
we present the most promising therapeutic interventions
that may help clinicians overcome AMI.
METHODS
To implement the review, an initial search of the literature
was undertaken using a variety of sources including experimental
papers, review papers, and conference proceedings,
as well as a general internet search. From this initial
search an extensive keyword list was developed (eg, quadriceps,
knee extensors, muscle inhibition, voluntary activation,
arthrogenic, arthrogenous, knee injury, knee
trauma, OA, gonarthrosis, rheumatoid arthritis, knee surgery,
joint receptors, articular receptors, afferent, sensory,
neuromuscular, reflex inhibition, interneuron, motoneuron,
supraspinal, swelling, effusion, inflammation, pain,
instability). An initial check of the keyword list was made
again in a number of databases (AMED, CINAHL,
MEDLINE, OVID, SPORTDiscus, and Scopus), where
appropriate additional keywords were added and modifi-
cations to the keyword list were made. This was supplemented
with a review of the bibliographies of past review
papers on AMI, as well as the personal libraries of the
contributing authors. Only peer-reviewed papers published
in the English language were included in this review.
RESULTS
The Presentation of AMI
AMI occurs across a wide range of knee joint pathologies, with significant quadriceps activation deficits observed in patients with OA (11,28,29), rheumatoid arthritis (RA) (9), anterior knee pain (30), patella contusion (31), following anterior cruciate ligament (ACL) rupture (10,32) and reconstruction (33), after meniscal damage (34) and menisectomy (35,36), and in patients who have undergone knee joint arthroplasty (17,37,38). AMI has been quantified using electromyography (EMG), interpolated twitch, or burst superimposition. Interpolated twitch and burst superimposition are the most commonly used methods and rely on electrical stimulation augmenting quadriceps force production during maximum effort contractions, thereby revealing incomplete muscle activation. Interpolated twitch superimposes 1 or multiple electrical stimuli on various levels of muscle contraction, calculating activation failure using the formula: 1 ! (superimposed twitch force at maximum effort/superimposed twitch force at rest). Burst superimposition superimposes a train of stimuli only during maximum contraction and calculates voluntary activation using the formula: maximum effort torque/(maximum effort torque " superimposed stimulus torque). Unfortunately, researchers have used a number of different stimulation parameters (eg, single versus multiple stimuli, different joint angles, estimated versus measured resting twitch force) to quantify AMI, all of which can alter estimates of muscle activation (39). Furthermore, in healthy subjects quadriceps activation has been found to be 8 to 16% higher using burst superimposition compared with interpolated twitch (39), while even interpolated twitch has been suggested to overestimate true activation (40). The heterogeneity and limitations of the methods used to assess AMI make it difficult to compare the absolute magnitude of inhibition across studies and suggest that in many cases the magnitude of AMI may have been underestimated.1 Nevertheless, repeated measures of interpolated twitch and burst superimposition within single studies (ie, using the same stimulus parameters) provide valuable information concerning the time course of AMI and how its severity may vary across different patient groups.
AMI appears to be most severe in the acute stages of joint damage. To investigate the early progression of AMI, Shakespeare and coworkers (36) asked patients to perform maximum effort isometric quadriceps contractions and compared the amplitude of presurgery quadriceps EMG to that recorded at various times in the first 2 weeks after menisectomy. These authors found that EMG amplitude was typically reduced by 50 to 70% in the first few hours post surgery. Over the next 24 hours, inhibition tended to become more severe (80-90%) and by 3 to 4 days was still 70 to 80%. After 10 to 15 days inhibition had subsided somewhat but was still 30 to 50%. Similarly, AMI is enhanced in the first 3 to 4 weeks after total knee joint arthroplasty (TKA). Using burst superimposition, researchers (17,38) have shown that AMI increases substantially from presurgery values of approximately 10% to almost 30% when assessed 3 to 4 weeks after surgery. During the same time period, quadriceps strength decreased by an average of 60% (range, 30-85%), with multiple linear regression analysis suggesting that AMI contributed almost twice as much as muscle atrophy to the observed weakness (38).
AMI는 급성기에 가장 심하게 발현됨 - EMG진폭 조사에서, 반월상연골절제술 후 몇 시간동안 50-70% 감소, 24시간 후 더욱 심해져 80-90% 감소, 3-4일 간 여전히 70-80% 감소됨. 10일에서 15일 후 30-50% 감소로 다소 완화.
There is evidence that with time the severity of AMI lessens. For instance, Snyder-Mackler and coworkers (41) found that 9 of 12 patients with a subacute, isolated ACL tear (average of 3 months post injury) had significant quadriceps inhibition but that no inhibition was present in patients with a chronic ACL rupture (average of 2 years postinjury). Furthermore, Urbach and coworkers (33) have shown that the magnitude of AMI is reduced in the long term following ACL reconstruction. Before surgery (average of 13 months post injury) patients demonstrated mean quadriceps activation deficits 16% greater than matched controls with no history of knee injury. Eighteen months postsurgery quadriceps activation had improved significantly to be 6% lower than controls. Similarly, 18 months after unicompartmental knee arthroplasty,Machner and coworkers (37) observed a reduction in AMI to 18% from presurgery quadriceps activation deficits that were, on average, 28%. Over a longer time frame, Berth and coworkers (42) found that AMI improved from #15% presurgery to #6% by 33 months after TKA.
아급성기 - 손상 3개월 환자는 대퇴사두근 억제가 나타났고, 손상 2년된 환자는 나타나지 않았다. 수술 전 16%감소 에서 술 후 18개월 6%감소로 개선됨, 술후 18개월, 28%에서 18%로 감소 폭 낮아짐. 술 후 33개월에 15%에서 6%감소로 개선.
However, in the medium term (up to 6 months after joint damage) clear reductions in AMI do not always occur with time. Following knee arthroscopy, Suter and coworkers (34) found no significant change in the magnitude of AMI when patients were assessed presurgery and 6 weeks and 6 months postsurgery. More recently, Berth and coworkers (43) compared the recovery from 2 different surgical approaches for TKA (subvastus versus midvastus approach). Across both groups, AMI remained unchanged (15-20%) from presurgery to 3 and 6 months postsurgery.
그러나 중간기(수상 후 6개월 까지) 명확한 AMI감소가 항상 나타나는것은 아님. 관절경 술 후 6주와 6개월에서는 차이가 없었음. TKR후 3개월 과 6개월 사이에 15-20%감소됨이 변하지 않았다는 보고도 있음.
Thus, based on the available evidence, it appears as if AMI is most severe in the first few days after joint damage before reducing somewhat, plateauing in the medium term (up to 6 months), and then slowly declining in the longer term (18-33 months). However, it is apparent that notable levels of AMI may still be present months and in many cases years after joint damage. To further highlight this point, Becker and coworkers (35) have shown that residual levels of AMI (approximately 8% compared with healthy, age-matched controls) remain a mean of 4 years after arthroscopic menisectomy, despite no radiological or clinical evidence of further joint degeneration.
종합해 보면 ; AMI는 손상 후 첫 며칠간 가장 심하고, 6개월까지 유지되고, 18-33개월까지 서서히 감소함.
그러나, 많은 케이스에서 손상 후 수개월에서 수년간 여전히 주목할만한 수준의 AMI가 나타난다. 관절경 반월상 연골 절제술 후 평균 4년간은 대략 8% 감소 수준의 AMI는 계속 나타난다. 비록 방사선학적 혹은 임상적 관절 퇴행의 근거가 없더라도.
Following acute injury, the severity of AMI varies according to the extent of joint damage (2,32,44). Among patients with isolated ACL ruptures, relatively small quadriceps activation deficits may be seen following injury with AMI ranging from 3 to 8% when tested a mean of 6 weeks to 31 months post injury (10,32,45,46). In contrast, patients with ACL ruptured with additional joint damage (ligamentous, capsular, meniscal, and/or bony) demonstrate AMI of 15 to 41% several months or in some cases years after joint damage (12,32). The relationship between joint damage and AMI is less clear in patients with chronic joint disease. In patients with OA, Pap and coworkers (47) assessed the magnitude of quadriceps AMI in relation to joint damage, scored retrospectively according to the extent of cartilage degeneration observed during articular surgery. Quadriceps activation deficits were found to be higher in subjects with moderate (stage II) joint damage (19%) compared with those with greater (stage IV) deterioration (12%).
급성 손상에 이어지는 AMI의 심각도는 관절 손상 정도에 따라 다양하다. ACL단독 손상에서는 3-8%의 비교적 가벼운 AMI가 나타나는 반면, ACL을 동반한 주위 구조물이 추가로 다친 경우는 15-41%의 심한 AMI가 나타남. 그러나 만성환자에 있어서는 손상 정도와 AMI관계는 명확치 않음.
In patients with OA, researchers (21,48) have reported a significant relationship between gender and the magnitude of AMI, with inhibition tending to be more severe in women. In contrast, among ACL-injured subjects no such relationship has been found (32,45). There does not appear to be a significant relationship between age and the severity of quadriceps inhibition in patients with ACL injuries or OA (21,32).
OA환자에 있어서는 여성에 있어서 AMI가 심하게 나타남. 대조적으로, ACL손상은 성별 차이가 없음. 나이는 OA든 ACL손상이는 의미있는 관계는 없음.
Importantly, AMI often occurs bilaterally after unilateral knee trauma or pathology. Bilateral inhibition has been observed in patients with isolated ACL ruptures (10,32,33,45,46), extensive traumatic knee injuries (12,32), OA (11,34,37), anterior knee pain (30), and following ACL reconstruction (33), partial menisectomy (35), and knee arthroplasty (37). AMI in the contralateral limb is typically less severe than that in the injured limb. However, quadriceps activation deficits as high as 16 to 24% have been documented in the uninjured limb among patients with extensive traumatic knee injuries (12,32), anterior knee pain (30), and after knee arthroplasty (37). Similar to the injured side, contralateral AMI may persist for up to 4 years after joint damage (35). These findings highlight the need to ensure a bilateral approach to rehabilitation and suggest that caution be applied when attempting to quantify quadriceps weakness by comparing the injured to the uninjured limb. Both clinicians and researchers should be aware that in many cases these comparisons may substantially underestimate quadriceps strength deficits associated with knee joint pathology (32).
AMI는 종종 한쪽의 외상이나 병리 후에 양측으로 나타나기도 함. 보통 손상 받은 쪽 보다는 약하게 나타남.
Sensory Innervation of the Knee Joint
To better understand the mechanisms involved in AMI it is important to appreciate the range of sensory receptors within the knee joint and their function. Sensory receptors within the knee joint can be divided into 2 major classes, those that are innervated by large, myelinated afferent fibers (group II afferents), and those that are innervated by thinly myelinated or unmyelinated afferents (group III and IV afferents) (49). Group II afferents terminate in corpuscular nerve endings that are activated by mechanical stimuli such as stretch and pressure (49-51). Most of these nerve endings are highly sensitive, with low firing thresholds, and include Ruffini endings, Paciniform corpuscles, and Golgi tendon organ-like endings. The proportion of group II afferents in the knee joint is relatively small. While precise data from the human knee are not available, as few as 16% of sensory fibers are thought to be of group II origin in the cat’s knee joint (51).
그룹2 afferents와 그룹3-4 afferents로 나뉜다. 그룹2는 신장과 압박과 같은 기계적 자극. 이러한 nerve ending은 민감하고 역치가 낮으며 Ruffini, Pacini ending, Golgi tendon organ-like ending과 관련된다. 이러한 그룹2가 관절에서 차지하는 비율은 상대적으로 작다. 고양이에서는 16%정도이다.
The large majority of afferent fibers innervating the
knee joint are high-threshold, lightly myelinated (group
III) or unmyelinated (group IV) fibers (49,51,52). In humans,
#70% of fibers in the articular branch of the tibial
nerve, the largest articular nerve supplying the knee joint,
are reported to be group IV, unmyelinated afferents (52).
Group III and IV afferents terminate in free nerve endings,
responding to strong mechanical, thermal, and
chemical stimuli. Their major function appears to be as
nociceptors, signaling actual or potential damage to joint
structures. However, it may be that a portion of free nerve
endings also function as mechanoreceptors as experiments
in the cat have found that approximately 55% of
group III and 20% of group IV afferents tested are activated
by nonpainful, passive movements and local mechanical
stimulation of the knee joint (53,54).
주로 그룹3,4 섬유이다. tibial nerve의 관절 분지의 70%가 그룹4. free nerve ending에서 종지하고, 강한 기계적, 온도, 화학적 자극에 반응한다. 주요 기능은 nociceptor,
Changes in Afferent Discharge Due to Joint Damage
A number of factors have been identified that may alter
afferent discharge from the knee joint in patients with
arthritis or following knee injury and surgery (Fig. 1).
These include swelling, inflammation, joint laxity, and a
loss of output from articular sensory receptors due to
structural damage (2-4,53)
1. Swelling
Swelling is often perennial in arthritic conditions and can also continue long after the acute phase of knee injury and surgery. Despite aspiration of acute hemarthrosis, swelling has been shown to persist for an average of 3 months after ACL rupture and for 12 months following ACL reconstruction (55). Swelling causes significant quadriceps AMI, even in the absence of factors such as inflammation, pain, and structural damage. This has been repeatedly demonstrated by infusing fluid into undamaged knee joints. Direct recordings from articular nerves in animals have shown that swelling significantly increases both the firing frequency and the recruitment of group II afferents (56-60). Moderate levels of joint infusion rarely evoke pain (1,61-64), making it unlikely that a significant Figure 1 Schematic diagram summarizing the proposed mechanisms contributing to quadriceps arthrogenic muscle inhibition (AMI). Solid lines are mechanisms with stronger evidence to support their existence. D.A. Rice and P.J. McNair 253 number of group III and IV afferents are stimulated by swelling alone. However, as some of these fibers can be activated by mechanical stimulation (53,54), a portion may increase their discharge in response to swelling, particularly at higher intra-articular pressures or in the presence of inflammation (53,65).
부종은 명확하게 대퇴사두근 AMI를 유발 - 염증, 통증, 구조 손상 같은 요소가 없다하더라도..
By infusing fluid into human knee joints, researchers have shown that swelling reduces quadriceps EMG activity (1,63,66-69), Hoffmann reflex (H-reflex) amplitude (7,8,61,70-72), and force output (62,64,69,73-75). The potency of swelling’s effect is revealed by the finding that as little as 10 mL of fluid may cause notable inhibition (1,64,76), while infusions between 20 and 60 mL are capable of reducing maximum isokinetic quadriceps torque by 30 to 40% (62,64). Several lines of evidence suggest that swelling’s inhibitory effect is mediated by joint afferents. Injecting local anesthetic into swollen joints largely abolishes AMI (8,64) and an infusion as large as 300 mL failed to provoke inhibition in a patient with Charcot neuropathy of the knee (1). Astonishingly, a recent case study (77) has reported absolute increases in quadriceps torque of approximately 400% 1 to 2 hours after aspirating 150 mL of synovial fluid from an acutely injured knee joint. From the results presented, this appears to represent almost a 50% (from #13% to #60%) increase in the quadriceps strength ratio between the injured and uninjured limbs.
10mL면 확연한 억제를 야기
In swollen knee joints particularly, there is a close relationship between intra-articular pressure (IAP) and the discharge of articular afferents. In the presence of swelling, IAP is raised across all joint angles (74,78,79). Even in the resting position, an effusion as small as 5 mL is sufficient to lift IAP above atmospheric pressure (64). In the swollen knee, passive movement of the joint produces a characteristic U-shaped curve, with peaks in IAP occurring in full extension and at end range flexion, with a decrease in mid range (74,78,80,81). The modulation of IAP with joint angle becomes progressively more pronounced with greater volumes of effusion (57,64,74). Similarly, direct recordings from animals have shown that as the knee is moved toward the extremes of motion, in both extension and flexion, joint afferent discharge increases significantly (54,82,83), a pattern that becomes exaggerated in the presence of an effusion (57).
5mL면 유의한 IAP를 높임.
Given the relationships presented above, it is perhaps not surprising that the magnitude of AMI has been found to vary with joint angle. Greater inhibition occurs toward the extremes of joint motion, where IAP and afferent discharge are greatest (74,77,84-87). In acutely injured knee joints, quadriceps inhibition is significantly greater in full extension (87) and toward end range flexion (77) than in mid range. In patients with chronic, perennial effusions, it has been demonstrated that AMI is greater in full extension than in 90° of flexion (84). Even in the absence of a clinically detectable effusion, patients may exhibit more than double the amount of AMI in full extension when compared with 30 to 40° of knee flexion in the first few days following menisectomy (85,86).
초기 손상에, 대퇴사두근은 완전 신전상태와, 굴곡 중간보다 끝으로 갈수록 제한이 심하게 된다.
만성 환자의 지속되는 부종이 있을 때는 90도 굴곡 보다는 완전 신전 때 더 제한된다.
보통 뚜렷한 부종이 없더라도 환자들은 30-40도 굴곡 상태보다 완전 신정 상태에서 두배 정도의 AMI를 나타낸다.
In summary, swelling raises IAP and increases the discharge
of group II afferents from the knee. Swelling has a
strong inhibitory effect on the quadriceps and even small,
clinically undetectable effusions may cause significant
AMI. Thus, clinicians should make every effort to minimize
the swelling associated with joint pathology. Furthermore,
the magnitude of AMI is modulated according
to joint angle and the greater the level of effusion, the
stronger the relationship between joint angle and inhibition
is likely to be. For these reasons, in the acute stages
after injury or surgery, isometric quadriceps exercises
should be performed in 30 to 50° of knee flexion, where
IAP is lowest (64,74,88). This is likely to maximize activation
of the quadriceps, allowing more effective strengthening
of the muscle to take place (74,76).
그래서, 손상 혹은 수술 후 급성기에서는, 대퇴사두근 등척운동은 30-50도 굴곡 상태에서 시행해야한다.
2. Inflammation
While swelling clearly has the potential to cause severe AMI, it is not solely responsible for this process. In patients with RA, the combination of aspiration and intraarticular corticosteroid injection has been found to increase quadriceps peak torque and EMG amplitude by approximately 30% after 14 days, an effect attributed to a reduction in AMI (89). Torque increased by 8.8 Nm immediately after aspiration but by a much larger 21 Nm 14 days after corticosteroid injection, suggesting that decreased inflammation due to the corticosteroid may have played an important role in reducing AMI. Similarly, Fahrer and coworkers (90) showed that after aspirating OA knee joints, subsequent infusion of local anesthetic led to further increases in quadriceps activation. These findings suggest the involvement of other non-pressuremediated afferent impulses in the genesis of AMI.
AMI 생성에 있어, 압력적인 요소가 아닌 afferent impulses.
In support of this conjecture, several studies involving animals have examined the effects of inflammation on joint afferent discharge using experimental models of arthritis. These investigations have shown that the induction of inflammation produces potent, long-lasting changes in the sensitivity of articular free nerve endings supplied by group III and IV joint afferents, a process known as peripheral sensitization (53,91,92). The activation threshold of these receptors is lowered so that normal joint movement or nonnoxious mechanical stimulation of articular structures results in notable group III and IV afferent discharge (53,91,92). In addition, these sensory receptors demonstrate increased responsiveness to noxious mechanical stimuli and an augmented spontaneous discharge when the knee joint is held in a static position (53,91,93). Finally, the inflammatory process may activate a number of silent free nerve endings (91,92,94). Usually insensitive to both innocuous and noxious stimuli, the release of inflammatory mediators “awakens” these receptors, substantially lowering their threshold and allowing them to respond to a wide range of mechanical 254 Quadriceps arthrogenic muscle inhibition stimuli (92,95). Collectively, these phenomena greatly enhance the output from group III and IV joint afferents to the central nervous system after joint damage. As most group III and IV joint afferents are considered to be nociceptive, inflammation can be expected to increase pain in conjunction with afferent discharge (96). However, it is important to remember that AMI can occur in the absence of pain. Furthermore, nociceptive afferent output is modulated at multiple spinal and supraspinal sites, all of which can influence pain perception (97). Thus, consciously perceived pain may not closely reflect the motor effects of nociceptive afferent output (eg, muscle inhibition), which may be largely mediated at the spinal level and are subject to their own modulatory in- fluences. This is reflected in the literature, where the relationship between pain and AMI is inconsistent. Among subjects with anterior knee pain, those who rated their knee pain higher on a visual analog scale tended to have higher levels of quadriceps AMI (34). Furthermore, reductions in knee pain have been associated with an increase in quadriceps activation post surgery (98) and in patients with RA (89) and OA (99,100). In contrast, other studies have found a weak relationship between pain and AMI (17,21,30,36,38,44,101). After knee surgery, a 15 mL intra-articular injection of local anesthetic was found to significantly reduce both pain and AMI (36,101). However, if only 10 mL of anesthetic was infused, pain was largely eradicated while AMI remained unchanged. Shakespeare and coworkers (36) further demonstrated that in the first 24 hours after menisectomy, quadriceps activation during a maximum voluntary contraction was typically reduced by 80 to 90% compared with presurgery measures and patients reported severe pain with muscle contraction. However, 3 to 4 days postsurgery pain had decreased to 7/100 on a visual analog scale, yet inhibition was still between 70 and 80%. Two weeks after the operation, when pain was largely absent, AMI was commonly 30 to 50%. Similarly, poor correlations (r2 $ 0.09-0.22) have been found between pain and AMI in patients with OA (21) and after TKA (17,38). Finally, in patients with anterior knee pain, nonsteroidal anti-inflammatory drugs (NSAIDS) have been shown to significantly reduce pain compared with placebo but have no effect on the magnitude of AMI (30).
To summarize, the release of inflammatory mediators
due to arthritis, injury, or surgery substantially increases
joint afferent discharge by sensitizing free nerve endings
innervated by group III and IV afferents. In humans, the
intra-articular injection of local anesthetic or corticosteroid
reduces quadriceps AMI over and above aspiration,
probably by silencing some of these sensory endings.
Many of the group III and IV joint afferents influenced by
peripheral sensitization are involved in nociceptive signaling.
While the presence of knee pain may be associated
with quadriceps inhibition, it appears to be a poor indicator
of the magnitude of AMI. Importantly, substantial
inhibition occurs in the absence of pain and reducing pain
does not necessarily lessen the severity of AMI.
염증 매게물은 free nerve ending을 sensitization시켜 joint afferent discharge를 증가사킴.
3. Joint Laxity
Joint laxity may alter the activation of sensory receptors in
the knee joint. Structural damage or degeneration (eg, to
ligaments, capsule) leads to greater translation of the joint
surfaces during movement that is likely to increase the
activation of mechanoreceptors and nociceptors involved
in signaling the limits of joint motion (2). This has been
demonstrated in animals by surgically transecting the
ACL and directly measuring afferent activity from the
major nerves supplying the knee joint. Following ACL
transection, Gomez-Barrena and colleagues (102,103)
noted significant increases in the transmission of afferent
impulses during a range of standardized movements of
the knee joint. Immediately after transection, GomezBarrena
and coworkers (102) surgically reconstructed the
ACL and repeated articular nerve recordings. Reconstruction
was found to partially reverse these changes, with
overall articular discharge decreasing toward baseline values.
However, differences in afferent discharge were still
noted between normal and ACL reconstructed knee
joints. A recent study by the same researchers (104) suggests
that despite afferent discharge tending to normalize
over time, some differences still persist 9 to 18 months
after reconstruction. While direct comparison to humans
cannot be made, these studies provide evidence that joint
laxity may cause anomalous firing of sensory receptors
during joint movement. Surgical stabilization of the knee
reduces joint laxity and can perhaps normalize afferent
activity to a degree. However, abnormalities in joint afferent
discharge may still be apparent compared with the
uninjured knee, even in the absence of damage to other
joint structures.
관절 렉시티는 무릎 관절의 감각 리셉터의 활성을 변화시킨다. - 관절 모션의 제한 signaling과 관련된, 메카노 리셉터와 노시셉터의 활성을 증가시킴.
재건술 후 9-18개월 까지도 discharge afferents의 약간의 차이는 남는다. 수술적 안정성은 관절 렉시티를 줄이고 afferents 활성을 정상화 시키지만, 손상받지 않는 정상 무릎에 비해서 차이는 존재한다, 비록 다른 구조물의 손상이 없더라도.
4. Damage to Articular Receptors
Joint damage does not unequivocally lead to increased
firing of articular sensory receptors. Trauma to joint
structures (eg, ligaments, joint capsule) may simultaneously
damage the sensory endings located within these
tissues, thus reducing the afferent output from this population
of receptors (2,3,44,105). An anomalous increase
in joint afferent discharge (as with swelling) is strongly
associated with AMI. However, different populations of
joint afferents may have opposing effects on motoneuron
excitability. Experiments involving cats suggest that background
joint afferent discharge has competing excitatory
and inhibitory influences on the quadriceps !-motoneuron
pool and that in the normal, undamaged knee the net
effect may be excitatory (106,107). In support of this
premise, Konishi and coworkers (3,108) have shown that
injecting undamaged human knee joints with 5 mL of
local anesthetic reduces quadriceps force output (!8.8 %
7.3%) and integrated EMG (!17.1 % 11%) during maximum
voluntary isometric contractions. Repeating the
D.A. Rice and P.J. McNair 255
procedure in an ACL-injured population had no such
effect, with quadriceps torque and EMG remaining unchanged.
These observations led Konishi and coworkers
to reiterate previous authors’ suggestions (2,44,105) that
in some cases AMI may arise due to a loss of sensory
output from receptors in the knee joint.
sensory endings에 손상을 줘 afferent output을 감소 시킨다. - 증가된 discharge of afferents는 AMI를 야기.
관절 주위 afferent discharge는 대퇴사두근 알파모토 뉴런의 흥분성과 억제성 경쟁을 하게 되어있고 손상받지 않은 무릎의 넷 이펙트는 흥분성이다. - 5mL의 국소마취제를 정상 무릎에 주입하면 대퇴사두근의 힘은 8%, 근전도 상으로는 17% 저하된다. 그러나 ACL손상 환자군에는 이러한 효과가 나타나지 않는다 ; 즉 몇 경우는 receptor로 부터의 sensory output 감소가 AMI의 원인이 될 수 있다.
Spinal Reflex Pathways Implicated in AMI
Abnormal afferent discharge from the knee may alter the excitability of reflex pathways within the spinal cord, which in turn reduce the excitability of the quadriceps !-motoneuron pool and prevent supraspinal centers from fully activating the muscle (2-4,7,109). Joint afferents project widely to many classes of spinal neurons (110,111) and thus have the potential to influence quadriceps !-motoneuron excitability via multiple, independent pathways. At this time, 3 spinal pathways have been identified that may contribute to AMI (Fig. 1). These are the following:
● Group I nonreciprocal (Ib) inhibitory pathway
● Flexion reflex
● Gamma-loop
비정상적 affernet discharge는 척수의 reflex pathways 흥분성을 변화시킨다. 이는 대퇴사두근 알파모토 뉴런의 흥분성을 감소시키고, 근육의 완전 활성으로 부터 척수이상 센터를 억제한다.
These pathways should not be thought of as mutually
exclusive (4). Instead, it is likely that they are simultaneously
affected by joint pathology, with the sum of their
actions governing the magnitude of AMI. While other
spinal pathways (eg, recurrent inhibition, lumbar propriospinal
pathways) may well be involved in AMI, their role
has not yet been explored in any detail.
1. Group I Nonreciprocal (Ib) Inhibition
Group I nonreciprocal (Ib) interneurons are located in
lamina VI and VII of the spinal cord (110). Their dominant
input is from Ib afferent fibers originating from
Golgi tendon organs located near the musculotendinous
junction. However, Ib interneurons receive widespread
convergent input from a number of peripheral sensory
receptors, including joint afferents (112). Lundberg and
coworkers (113) investigated the link between joint afferent
discharge and Ib interneuron activity by electrically
stimulating the posterior articular nerve of the cat knee
joint at low stimulus intensities. Ib inhibition of extensor
motoneurons was facilitated at 2 distinct latencies, suggesting
the existence of both disynaptic and trisynaptic
excitatory pathways from group II knee joint afferents to
Ib inhibitory interneurons. These findings were later con-
firmed by Harrison and Jankowska (112) using direct,
intracellular recordings from Ib interneurons in the lumbosacral
spinal cord of the cat.
As swelling is known to significantly enhance the discharge
of group II afferents, joint effusion may contribute
to AMI by facilitating Ib inhibition of the quadriceps
motoneuron pool. This is supported by the findings of
Iles and coworkers (7), who infused uninjured human
knee joints with saline and used the spatial facilitation
technique to show that swelling enhances Ib inhibition of
the quadriceps H-reflex both at rest and during voluntary
muscle contraction. It is unknown whether an increase in
group III and IV joint afferent discharge also facilitates
the Ib inhibitory pathway. However, this remains a possibility
as electrical stimulation of group III and IV joint
afferents has been shown to excite Ib interneurons in the
cat, probably via polysynaptic pathways (112).
2. Flexion Reflex
The flexion reflex is a polysynaptic pathway that typically
produces a pattern of flexor facilitation and extensor inhibition
(114,115). As such, it has been suggested (4,116)
that enhanced flexion reflex excitability may be partially
responsible for quadriceps AMI. The interneurons involved
in the flexion reflex have not yet been clearly identified.
However, recent evidence from studies involving
animals suggests that wide dynamic range neurons play a
major role in mediating the flexion reflex (117,118).
These interneurons are predominantly located in lamina
V of the dorsal horn and receive convergent input from a
number of peripheral afferent sources, including articular
receptors (111,119). A consequence of articular inflammation
and the resulting barrage of group III and IV
afferent input is that wide dynamic range neurons become
hyperexcitable (120). This process is known as central
sensitization and is characterized by long-lasting plastic
changes in synaptic efficacy (for review see (121)). As a
result, the activation threshold of wide dynamic range
neurons is progressively reduced following the onset of
knee joint inflammation and they demonstrate enhanced
activity in response to innocuous and noxious stimuli applied
to the knee (120). Additionally, as inflammation
develops, there is an expansion of their receptive fields,
with neurons showing a heightened response to mechanical
stimuli from adjacent areas such as the thigh, or even
remote, noninflamed tissue as far afield as the contralateral
limb (120).
In studies involving animals, the induction of knee
arthritis is followed by a corresponding increase in flexion
reflex excitability. Flexor (biceps femoris and semitendinosus)
motoneurons show significantly enhanced responses
to standardized pinching of both the ipsilateral
and the contralateral toes, indicating an enhanced central
excitability of the flexion reflex pathway (122). Remarkably,
at the peak of knee joint inflammation the amplitude
of the electrically induced flexion reflex has been
reported to increase by an average of 545% (SEM %
174%) (109), while the number of flexor motoneurons
responding to local pressure and/or gentle flexion and
extension of the knee increased from 14 to 41%, suggesting
a parallel reduction in flexion reflex threshold (65).
Ferrell and coworkers (109) demonstrated that injecting a
local anesthetic into the inflamed knee returned reflex
intensity back to control values, confirming the role of
articular sensory receptors in this response.
256 Quadriceps arthrogenic muscle inhibition
While evidence from studies involving humans is less
cogent, it is highly probable that the flexion reflex contributes
to quadriceps AMI. Leroux and coworkers (123)
examined the relationship between knee joint pathology
and flexion reflex excitability. Compared with healthy
controls, significantly lower flexion reflex thresholds were
found in patients with anterior knee pain, probably inferring
an amplified excitability of this pathway. Importantly,
these authors showed that activation of the flexion
reflex produced concomitant inhibition of the quadriceps
during isometric contraction of the knee extensors. Recently,
it has been shown that flexion reflex thresholds are
lower in patients with knee OA compared with age- and
gender-matched controls (124). However, no significant
relationship was found between flexion reflex threshold
and the magnitude of AMI, assessed using burst superimposition.
This may be partly due to the insensitivity of
burst superimposition to lower levels of inhibition as surprisingly
only 4 of 20 subjects with OA were found to
have quadriceps activation deficits in this study. Further
research is warranted.
3. Gamma (!)-Loop
The "-loop is a spinal reflex circuit formed when "-motoneurons
innervate primary muscle spindles that in turn transmit
excitatory impulses to the homonymous !-motoneuron
pool via Ia afferent fibers (Fig. 2). Normal function of the
"-loop is necessary to achieve full muscle activation during
voluntary contractions. Thus, impaired transmission
along this pathway may contribute to AMI (3,44,105).
To investigate the importance of the "-loop to muscle
activation, a number of authors have used prolonged vibration
to experimentally attenuate the excitability of Ia
afferent fibers. A vibratory stimulus, applied to the muscle
or its tendon, temporarily blocks transmission in Ia afferent
fibers by increasing presynaptic inhibition, raising the
activation threshold of Ia fibers, and/or causing neurotransmitter
depletion at the Ia afferent terminal ending
(125). In healthy subjects, prolonged vibration (20-30
minutes) causes a reduction in EMG activity (3,126,127),
motor unit firing rates (126), and muscle force output
(3,126-128) during subsequent maximum voluntary contractions.
However, in patients who have ruptured their
ACL, prolonged vibration has no effect on quadriceps
force output or EMG activity. This suggests a deficit in
the transmission of Ia input to the motoneuron pool and
has been termed "-loop dysfunction (3). Similar findings
have been confirmed in patients after ACL reconstruction up
to 20 months postsurgery (129-131). Interestingly, it has
been demonstrated that "-loop dysfunction occurs bilaterally
in ACL-injured and ACL-reconstructed patients
(129,130) but that transmission in the contralateral "-loop
may be (at least partially) restored 18 months after surgery
(129). It is currently unknown whether "-loop dysfunction
contributes to AMI in other knee joint pathologies.
A number of potential neural mechanisms can be considered
to explain "-loop dysfunction. Researchers have
suggested that structural damage to the ACL results in a
loss of excitatory feedback from ligamentous mechanoreceptors
to quadriceps "-motoneurons and/or supraspinal
centers that diminishes !-" coactivation during strong
muscle contractions (3,4,44,105). In support of this conjecture,
Konishi and colleagues (3,108) have shown that
injecting undamaged knee joints with 5 mL of local anesthetic
reduced maximum isometric quadriceps torque
and integrated EMG. However, the same infusion of local
anesthetic into knee joints with an isolated ACL rupture
had no effect on quadriceps torque or EMG. Furthermore,
prolonged vibration of the infrapatellar tendon in
subjects with uninjured but anesthetized knee joints did
Figure 2 Schematic diagram of the "-loop (shaded area). During voluntary muscle contraction, supraspinal centers coactivate the
!-motoneuron and "-motoneuron pools. The "-motoneuron pool in turn innervates muscle spindles via " efferents, enhancing their
firing. Muscle spindles provide a tonic excitatory input to the homonymous !-motoneuron pool via Ia afferent fibers.
D.A. Rice and P.J. McNair 257
not diminish maximum quadriceps force output or EMG
amplitude. These observations led Konishi and coworkers
(3) to conclude that excitatory output from sensory receptors
within the ACL may be critical to the maintenance of
normal "-loop function. Given the relatively sparse innervation
of the ACL compared with other structures in the
knee joint (50,51), this seems unusual. It remains to be
determined if other sensory receptors in the knee joint
could also be involved.
Alternatively, or perhaps concurrently, an increase in
the discharge of nociceptive joint afferents may contribute
to "-loop dysfunction. Scott and coworkers (132)
have shown that low-intensity stimulation of the posterior
articular nerve in the cat, sufficient to activate group II
and III knee joint afferents, has a net excitatory effect on
extensor "-motoneurons of the calf. However, if a second,
high-intensity stimulus (activating group IV joint afferents)
was applied beforehand, the excitatory effect of
group II and III afferents was abolished or reduced. Thus,
the discharge of group IV afferents may suppress the excitatory
effects of low-threshold joint receptors on extensor
"-motoneurons (132). Whether this occurs in humans
is not known.
Finally, transmission in the afferent limb of the quadriceps
"-loop may be impaired by an increase in Ia afferent
presynaptic inhibition. Presynaptic inhibition involves
spinal inhibitory interneurons that project to the synaptic
terminals of Ia afferent fibers, adjusting the quantity of
neurotransmitter released in response to an afferent volley,
thus modulating synaptic efficacy (for review see
(133)). As activity from a wide range of peripheral receptors,
including joint receptors (134), can modify the excitability
of presynaptic inhibitory interneurons, a change
in articular afferent discharge could theoretically impair
quadriceps "-loop function via this mechanism (135).
However, the evidence supporting this theory is limited
and findings to date are conflicting. Poststimulus time
histograms from single quadriceps motor units have
shown that electrical stimulation of knee joint afferents
before femoral nerve stimulation does not change the amplitude
of the initial, purely monosynaptic component of
the resulting H-reflex response (136). This suggests that
joint afferent discharge does not alter presynaptic inhibition
of quadriceps Ia afferents. In contrast, using a modified
H-reflex protocol, Palmieri and coworkers (135)
found that quadriceps paired reflex depression increased
after experimental knee joint infusion. This finding led
Palmieri and coworkers to conclude that an increase in
presynaptic inhibition may contribute to AMI. However,
this interpretation can be challenged on methodological
grounds and should be considered with caution.
In summary, "-loop dysfunction contributes to AMI in
patients with an ACL rupture and after ACL reconstruction.
There is evidence to suggest that ACL injury disrupts
the flow of excitatory joint afferent output to the
quadriceps "-motoneuron pool and/or supraspinal centers,
attenuating "-motoneuron discharge and, ultimately, Ia
afferentfacilitation of the quadriceps !-motoneuron pool.
A change in joint afferent discharge could theoretically
enhance quadriceps Ia presynaptic inhibition, contributing
to "-loop dysfunction. However, this has yet to be
clearly determined. Future research should investigate the
presence of "-loop dysfunction in other knee joint pathologies
and aim to achieve a stronger understanding of its
underlying neurophysiological causes.
Supraspinal Influences on AMI
Joint afferents are known to have extensive supraspinal as
well as spinal projections (137-141). Research to date has
largely focused on the spinal mechanisms behind AMI.
However, supraspinal centers are highly likely to be affected
by changes in joint afferent discharge. Importantly,
descending pathways have widespread projections to interneurons
and motoneurons at the spinal level (for reviews
see (97,110,111)) and thus have the potential to
strongly influence AMI.
Jt. afferents는 spinal 뿐 아니라 supraspinal까지 projection된다. 하행로는 spinal level에 있는 인터뉴런, 모토뉴런에 광범위하게 projection하고 AMI와 연관이 깊다.
1. Changes in Corticospinal Excitability
Transcranial magnetic stimulation (TMS) of the motor
cortex has recently been used to quantify changes in corticospinal
excitability associated with chronic knee joint
pathology (142,143). Fascinatingly, it was found that
quadriceps corticospinal excitability was higher in patients
with chronic anterior knee pain (average duration,
3.5 years) than in healthy control subjects (143). This was
despite lower quadriceps EMG amplitude during maximal
contractions and diminished patellar tendon reflexes
in subjects with joint pathology. Similarly, Heroux and
Trembly (142) investigated quadriceps corticospinal excitability
in chronic ACL-injured subjects (median time
since injury, 22 months) and found that resting motor
threshold was significantly lower in the injured compared
with the uninjured limb. No significant differences were
found between limbs in healthy control subjects. While
these findings show that corticospinal excitability is increased,
the location of the observed changes (ie, motor
cortex versus motoneuron pool) is not easily determined
using single-pulse TMS. However, as the quadriceps
!-motoneuron pool is likely to be inhibited, it is reasonable
to suggest that chronic knee joint pathology paradoxically
increases excitability in the area of the primary motor
cortex projecting to the quadriceps motoneuron pool.
While speculative, it is possible that enhanced cortical
excitability allows the central nervous system to increase
corticospinal drive to the quadriceps to counteract !-motoneuron
inhibition by spinal reflex pathways.
2. Brainstem Modulation of the Flexion Reflex
Descending brainstem pathways typically exert a tonic
inhibitory control over spinal neurons involved in pain
processing and the flexion reflex, including wide dynamic
range neurons (97,134,144). Injury or inflammation
258 Quadriceps arthrogenic muscle inhibition
greatly enhances descending input from brainstem pathways
that has both inhibitory and facilitatory components
(97,144-148). Thus, it is possible that joint damage leads
to a reduction in the effectiveness of descending inhibition
(4) and/or enhanced descending facilitation to wide
dynamic range neurons, increasing excitability in the flexion
reflex pathway and amplifying AMI.
Investigations in animals have shown that acute arthritis
(3-48 hours) results in a net increase in descending
inhibition to wide dynamic range neurons (144,146-148)
that may help to limit central sensitization of wide dynamic
range neurons and suppress flexion reflex excitability.
However, with time, descending inhibition returns to
baseline levels (146,149), subsiding as early as 1 week after
inflammation commences despite continued hyperalgesia
(149). Likewise, time-dependent changes in the efficacy
of diffuse noxious inhibitory controls (DNICs) have been
observed following the induction of experimental arthritis
in the rat (145). DNICs are considered an endogenous
form of pain control and refer to the widespread, brainstem-mediated
inhibition of spinal and trigeminal wide
dynamic range neurons that is triggered by the stimulation
of peripheral nociceptors. Danziger and colleagues
(145) showed that in the acute stages of arthritis (24-48
hours) DNIC-mediated inhibition of convergent trigeminal
neurons was enhanced compared with control conditions.
However, in animals with chronic arthritis (3-4
weeks), DNIC-mediated inhibition decreased to normal
levels despite continued hyperalgesia. Similarly, a reduction
in the efficacy of DNIC-mediated inhibition has
been noted in humans with chronic OA of the hip (150).
These authors used a pressure algometer to induce graded
mechanical stimulation of the soft tissue overlying the
hip. The threshold for pressure-mediated pain was found
to be significantly lower in arthritic patients compared
with a healthy control group. Ischemic arm pain was then
induced in both groups, a procedure commonly used in
laboratory studies to evoke DNIC-mediated inhibition of
wide dynamic range neurons. As expected, the threshold
for pressure-mediated pain rose significantly in healthy
control subjects. However, in patients with chronic arthritis,
ischemia had no effect on pressure-mediated pain,
suggesting dysfunction in the descending inhibition of
wide dynamic range neurons.
However, in a similar study, Leffler and coworkers
(151) found no evidence for DNIC dysfunction among
subjects with RA. As expected, RA patients had signifi-
cantly lower pressure pain thresholds over their thigh
compared with healthy, age- and gender-matched controls.
In this study, DNIC-mediated inhibition was
evoked by immersing the contralateral hand in a bath of
ice cold water (the cold-pressor test), after which pressure
pain thresholds were reassessed in both groups. After cold
water immersion, pressure pain thresholds increased significantly
in both RA and healthy control subjects, suggesting
preserved function of DNIC-mediated inhibition
in patients with RA. These findings are at odds with the
previous observations in OA patients (150) and experimental
arthritis (145) described above. As suggested by
Leffler and coworkers (151), this discrepancy may relate
to the populations tested (OA versus RA versus animal
models of experimental arthritis), the duration and location
of joint disease, or differences between methods of
inducing pressure pain and DNIC-mediated inhibition.
Nevertheless, the balance of evidence suggests that
chronic joint pathology be associated with dysfunction in
the brainstem modulation of wide dynamic range neurons
involved in pain perception and the flexion reflex
pathway. The net effect of brainstem regulation appears
to be influenced by the stage of joint injury, suggesting a
possible role for brainstem pathways in the maintenance
of flexion reflex hyperexcitability after articular damage
(Fig. 1). In turn, this may contribute to the long-lasting
AMI that is often observed after knee injury, after surgery,
and in patients with arthritis.
3. Reduced Voluntary Effort
Studies investigating changes in quadriceps activation rely
on the motivation of their participants. It has been suggested
that reductions in quadriceps strength and activation
may be partly due to a subconscious adjustment in
voluntary effort, perhaps for fear of damaging or eliciting
pain from the injured joint (4,24,116). this
seems reasonable and a decrease in voluntary effort may
well contribute to reduced quadriceps activation. However,
it should be remembered that a strong reflex component
to AMI has been established by a number of studies
(7,8,61,71). Moreover, Wood and coworkers (64)
found no evidence that a reduction in voluntary effort
contributes to AMI when utilizing an experimental model
of joint effusion. In this study, the knee joint was distended
with different volumes of saline and dextran or
local anesthetic. Subjects were blindfolded throughout
the testing procedure and were kept unaware of the volume
of fluid injected. Both the subjects and the tester
were unaware of the nature of fluid injected. The presence
of saline and dextran within the knee joint caused marked
reductions in maximal isokinetic torque at all velocities
tested. However, subsequent injection of anesthetic almost
completely restored force to pre-effusion values. In
addition, when anesthetic was infused before saline solution,
quadriceps torque remained stable over time. As
subjects were unaware of the nature of fluid injected, the
authors concluded that the observed reductions in quadriceps
activation were due to reflex actions of articular
afferents, not to changes in volition.
대퇴사두근의 활성은 참가자의 동기에 의존한다는 연구가 있다. 자의적 노력의 잠재의식적 조절에 의함. 예를 들면 손상에 대한 두려움이나 손상된 관절로부터 오는 통증 유발같은 것들에 의해. 그러나 실험적 모델로는 증명이 안된다는 연구가 많다.
Therapeutic Interventions That May Counter AMI
Therapeutic interventions that may counter AMI can be divided into 2 groups, those that modulate joint afferent discharge and those that stimulate the quadriceps muscle directly.
Afferent Modulation
1. Aspiration
In the first 3 to 5 days after menisectomy, aspiration of
fluid from the knee (range, 36-85 mL) has been found to
consistently reduce (although rarely abolish) quadriceps
AMI (24). Similarly, a recent case study showed that aspirating
150 mL of fluid from the knee a week after sustaining
an acute injury produced large increases in quadriceps
strength and activation (77). However, in patients
with chronic inflammatory arthropathies, aspiration may
have no significant effect on AMI (84) or produce moderate
(14-18%) increases in quadriceps strength (73,90).
This may relate to the volume of fluid aspirated in these
studies, which was typically lower than in studies involving
acute injury. Alternatively, it may be that
chronic joint pathology leads to changes in capsular
compliance (56,84) and/or damage to articular receptors
that reduces the afferent response to swelling. Thus, while
aspiration appears to be an effective way to reduce AMI in
patients with an acutely swollen knee joint, its clinical
benefit is questionable in patients with chronic arthritic
joint disease, particularly where effusion is expected to
reoccur within a short time frame.
급성기 부종이 있는 관절에는 효과적임. 만성 환자에게는 유의한 효과는 확인되지 않음.
2. Intra-Articular Corticosteroid Injection
In patients with RA, intra-articular corticosteroid injection
has been shown to increase quadriceps peak torque
and EMG by #30% after 14 days, an effect attributed to
a reduction in AMI (89). However, in OA patients, corticosteroid
injection was found to produce only marginal
improvements in quadriceps strength that did not reach
statistical significance (152). This may be related to the
lack of notable joint inflammation for many patients with
OA. Corticosteroid injection may be more effective in
patients with advanced OA, when inflammation is more
prevalent (153).
염증이 확실한 관절에는 효과적 ; RA는 효과적, OA는 의문 - OA는 상대적으로 염증 환경이 적다.
3. Nonsteroidal Anti-Inflammatory Drugs
There is conflicting evidence regarding the use of NSAIDS
to reduce AMI. Suter and coworkers (30) found that 7
days of NSAIDs (naproxen sodium, 550 mg) taken twice
daily reduced pain but failed to diminish AMI in a group
of patients with anterior knee pain. In contrast, there is
indirect evidence that NSAIDS may help to reduce AMI
after knee surgery. Ogilvie-Harris and coworkers (154)
investigated the effects of twice daily doses of a NSAID
(naproxen sodium, 550 mg) for 6 weeks compared with
placebo after arthroscopic menisectomy. Patients in the
NSAID group had significantly less pain (P & 0.001),
swelling (P & 0.001), and quadriceps atrophy (P $ 0.01)
compared with the placebo group and returned to work or
sport quicker (P # 0.002). Similarly, in a double-blind,
placebo-controlled study, Arvidsson and Eriksson (155)
showed that daily doses of an NSAID (piroxicam, 20 mg)
led to significantly increased isokinetic quadriceps torque
values compared with placebo across a range of joint angular
velocities at 3, 7, 11, and 21 days after open menisectomy.
Finally, while strength was only measured semiquantitatively,
10 days of twice daily NSAIDs (naproxen
sodium, 550 mg) was found to significantly improve
quadriceps strength after arthroscopy compared with placebo
(P & 0.05) (156). Intuitively, it seems reasonable
that NSAIDS may help to reduce AMI, particularly in the
acute stages after joint damage or when there is a strong
inflammatory component to articular pathology. However,
the use of NSAIDs may also have negative consequences.
NSAIDs have been shown to reduce pain but
increase knee joint loading during gait in patients with
OA (157). Furthermore, a recent observational study (158)
reported that OA patients taking diclofenac for '180 days
had a 3.2-fold greater risk of knee joint OA progression
when factors such as age, gender, body mass index, baseline
OA, follow-up time, and dosage were taken into
account.
NSAIDs사용과 AMI를 낮추는 데는 상반된 근거 연구들이 많다. 급성기 혹은 강한 염증 소견에는 효과적이나, OA환자가 걷는 동안 통증은 줄이지만, 관절 부하를 증가시켜 OA를 촉진시킨다는 근거도 있다. - 디클로페낙을 180일 이상 복용한 OA환자는 OA진행에 있어, 3.2배 큰 위험성.
4. Local Anesthetic
Following experimental joint infusion (8,64), menisectomy
(36) and in patients with OA (90), the intra-articular injection
of local anesthetic has been used to partially silence afferent
impulses from the joint, effectively reducing AMI.
However, a more recent study found that while local anesthetic
reduced AMI in patients with OA, the improvements
were not statistically different from placebo (99). Furthermore,
the invasive and short-lasting nature of this treatment
(a few hours) makes it clinically impractical. A number of
injections would have to be administered to achieve an appropriate
therapeutic effect, increasing the risk of sequelae
such as joint infection.
5. Cryotherapy
Like local anesthetic, cryotherapy may temporarily reduce
AMI but has the added benefit of being noninvasive.
Thirty minutes of cryotherapy has been shown to reverse
the decline in quadriceps H-reflex amplitude that is seen
after swelling, an effect that lasts for at least 30 minutes
after the ice is removed from the joint (72). Hopkins (66)
showed that 30 minutes of cryotherapy negated the reductions
in peak torque, power, and quadriceps that
EMG caused by swelling during a semirecumbent stepping
task performed at 36% of maximum intensity. More
recent work (69,159) has established that cryotherapy reduces
AMI during maximum effort voluntary contractions.
Icing experimentally infused knee joints for 20
minutes led to a significant increase in quadriceps peak
torque and muscle fiber conduction velocity compared
with control subjects (P & 0.05) (69). These findings
were notable in that quadriceps torque returned to within
#6% of baseline measures. Similarly, in patients with
OA, 20 minutes of icing was found to significantly reduce
AMI compared with a control condition (159). Thus, if
cryotherapy is applied to the knee joint immediately before quadriceps strengthening, it may provide a therapeutic
window during which more complete activation of
the quadriceps musculature is permitted. Yuktaran and
Kocagil (100) have shown that repeated applications of
ice may lead to improved quadriceps activation in subjects
with chronic OA. In this study, subjects received ice massage
to 4 standard acupoints for a total of 20 minutes per
session, 5 sessions per week for 2 weeks. After the 2-week
treatment period, maximum effort quadriceps strength
was found to improve by 22% compared with the placebo/sham
treatment group’s improvements of #7% (P &
0.001).
국소 마취제처럼 일시적으로 AMI를 줄이지만 침습적이지 않다는 장점이 있다. 30분간의 클라이오테라피로 부종 후 AMI를 줄일 수 있고 이는 적어도 아이싱 제거 후 30분간은 유지된다. 20분의 아이싱으로 AMI를 낮출 수 있다는 다수의 연구.
그래서, 클라이오테라피는 대퇴사두근 강화운동 바로 직전에 적용되야한다. 이렇게 하는 것이 대퇴사두근의 완전한 활성을 허용해 치료 범위를 결정할수 있게 해준다.
한 세션당 20분, 1주에 5 세션을 2주간. - 개선효과.
6. Trancutaneous Electrical Nerve Stimulation (TENS)
Following open menisectomy (24) and ACL reconstruction
(98), high-frequency TENS has been shown to increase
quadriceps activation during subsequent maximal
voluntary contractions. Furthermore, Hopkins and coworkers
(160) have found that high-frequency TENS
(120 Hz, pulse width, 0.1 seconds) prevents the decline in
quadriceps H-reflex amplitude seen after the infusion of
fluid into the knee joint. Recently, the application of
high-frequency (150 Hz, pulse width, 0.15 seconds)
TENS to OA knee joints has been shown to significantly
improve quadriceps activation when applied during maximal
voluntary contractions (P & 0.05) (159). The improvement
in quadriceps activation with TENS (#11%)
was greater compared with a matched control group of
OA patients (#1%) who did not receive an intervention
(P & 0.05).
Low-frequency (4 Hz, pulse width, 1 second), acupuncture-like
TENS has been reported to increase quadriceps
force output by 71% in OA patients after 2 weeks
of treatment (20 minutes per day, 5 days per week) (100).
Such large changes in quadriceps strength in just 2 weeks
suggest a substantial improvement in voluntary activation.
It remains unknown whether low-frequency TENS
may be effective in reducing AMI in patients with other
knee joint pathologies.
high-frequency TENS는 대퇴사두근 활성을 증가시킨다.
(120 Hz, pulse width, 0.1 seconds)
(150 Hz, pulse width, 0.15 seconds)
Low-frequency TENS, acupuncture-like TENS
(4 Hz, pulse width, 1 second)
대퇴사두근의 힘을 71%증가 - 총2주 ; 1주에 5번 한번에 20분씩) - OA환자.
어떤 종류의 텐스가 좋은지는 논란.
7. Altering Fluid Distribution/Capsular Compliance
McNair and coworkers (62) showed that infusing 60 mL
of saline and dextrose into undamaged knee joints reduced
quadriceps isokinetic peak torque by approximately
30%. However, peak torque returned to preinjection
levels after a 3- to 4-minute period of submaximal
flexion and extension movements of the knee. Magnetic
resonance imaging scans of the knee joint at each measurement
interval showed that the volume of fluid within
the joint capsule was largely unchanged, suggesting that
submaximal exercise may modulate mechanoreceptor discharge
by increasing the compliance of the joint capsule
and/or by redistributing fluid throughout the knee joint,
reducing local capsular strain (56,62). Thus, in patients
with an effused knee, a series of non-weight-bearing, submaximal
movements of the joint may serve to reduce AMI
before quadriceps strengthening.
60mL의 식염수와 포도당을 건강한 무릎에 주입하면, 대퇴사두근의 피크 토크는 대략 30% 감소한다. 그러나 완전에 준하는(submaximal) 굴곡- 신전 움직임을 하는 동안, 3-4분 후 피크토크는 다시 정상으로 돌아온다. submaximal exercise는
1. capsular compliance를 증가시켜,
2. 무릎 관절의 수액 재분배를 통해 국소 관절 긴장을 줄임으로써,
메카노리셉터의 discharge를 조절한다.
그래서, 무릎 부종이 있는 환자는, 체중부하를 주지 않는 완전에 준하는 관절 움직임은 대퇴사두근 근력운동 전 AMI를 줄일 수 있다.
Muscle Stimulation
1. Neuromuscular Electrical Stimulation (NMES)
The therapeutic advantage of NMES is that it activates the muscle directly, circumventing the inhibited motoneuron pool (4). Thus, while it is unlikely to affect AMI itself, NMES may help to minimize quadriceps atrophy after joint damage, thereby reducing quadriceps weakness. It should be noted that in many cases, voluntary exercise is as effective, if not more effective, than NMES in improving quadriceps strength (for review see (161)). However, there is some evidence (41,162-165) that after knee injury and surgery the combination of NMES and volitional training may achieve greater gains in quadriceps strength when compared with volitional training alone. If isometric protocols are used, NMES may obtain superior results when performed with the knee partially flexed (163) compared with full extension (162). Additionally, the benefits of NMES appear to be dose-dependent, with high-intensity, maximally tolerated stimulations proving more effective than those performed at lower intensities (41,163). A relatively unexplored alternative to NMES is peripheral magnetic stimulation of the quadriceps. Preliminary evidence (166) suggests that magnetic stimulation may be significantly more comfortable and achieve greater quadriceps activation than NMES. Further research is indicated.
NMES가 직접적으로 AMI에 영향을 준다기 보다는, 관절 손상 후 대퇴사두근 위축 최소화를 돕는다.
자발 운동과 NMES를 같이 했을 때, 자발적 운동만 할 때보다 효과적으로 대퇴사두근의 근력을 회복.
NMES의 효과는 dose-dependent해서 높은 강도, 참을 수 있는 최고 자극이 더욱 효과적.
NMES보다는 덜 밝혀졌지만, peripheral magnetic stimulation도 더 편안하고 효과적이라는 보고도 있다.
2. Transcranial Magnetic Stimulation
Urbach and coworkers (167) have shown that TMS improves
quadriceps activation following TKA when it is
applied during maximum voluntary quadriceps contractions.
Statistically significant improvements in quadriceps
peak torque and a trend toward increased voluntary activation
were found to persist up to 60 minutes after 3
single pulses of TMS were applied to the motor cortex.
While improvements were modest (&10% increase in
quadriceps torque), the dose of TMS used in this study
(single treatment session, 3 pulses, 60% of maximum
stimulator output) was low. These findings indicate a
need for further research, investigating the effect of different
stimulation parameters on AMI in subjects with knee
joint pathology and at different stages after joint damage.
The major disadvantage of transcranial magnetic stimulators
is their cost, which may prohibit the widespread use
of this technique in clinical settings.
DISCUSSION
AMI remains a significant barrier to effective rehabilitation in patients with arthritis and following knee injury and surgery. AMI contributes to quadriceps atrophy and prevents full activation of the muscle, playing a major role in the marked quadriceps weakness that is commonly observed in these patients. Moreover, AMI may delay or prevent effective quadriceps strengthening. This is particularly apparent in the first few months after trauma or in the case of extensive joint damage when AMI may be severe and quadriceps strengthening protocols are often ineffective. While the magnitude of AMI appears to diminish with time, it is clear that quadriceps inhibition often persists for months or even years after acute knee injury and surgery. This may lead to long-lasting quadriceps weakness that impairs physical function and increases the risk of further joint damage.
AMI는 효과적인 재활을 방해. - 대퇴사두근의 위축, 대퇴사두근의 근력강화 지연, 방해.
첫 몇 달 동안 뚜렷하게 나타나지만 간혹 수개월 혹으 수년간 지속되기도 함.
AMI is caused by a change in the discharge of sensory receptors in or around the damaged knee joint. Factors that may alter afferent discharge include swelling, inflammation, joint laxity, and damage to articular sensory receptors. Abnormal output from knee joint afferents may alter the excitability of spinal reflex pathways that in turn decrease quadriceps !-motoneuron excitability and prevent full activation of the muscle. To date, 3 major reflex pathways have been implicated in AMI. These are the group I nonreciprocal (Ib) pathway, the flexion reflex, and the "-loop. While it seems likely that each of these plays a role in AMI, the relative importance of these (and possibly other) reflex pathways remains to be discovered and may well vary across different knee joint pathologies. The potential influence of supraspinal centers on AMI is vast but has only just begun to be explored. Preliminary findings suggest that chronic joint pathology paradoxically increases quadriceps motor cortex excitability and may be associated with changes in the modulation of spinal interneurons by descending brainstem pathways.
Some of the most promising interventions to mitigate
the effects of AMI include cryotherapy, TENS, and
NMES. Intra-articular corticosteroids and NSAIDs may
also be effective when a strong inflammatory component
is present with joint pathology. To allow the development
of improved therapeutic strategies, it is important to attain
a greater understanding of AMI’s underlying neural
mechanisms. This will augment current rehabilitation
practice by allowing clinicians to target AMI directly, thus
minimizing muscle atrophy and enhancing quadriceps
strength gains after knee injury, after surgery and in patients
with arthritis.
가장 효과적인 치료는 클라이오테라피, 텐스, NMES.
관절내 스테로이드 주사와 NSAIDs는 강한 염증 소견이 있을 때 효과적임.
첫댓글 감사합니다