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ReviewVolume 84, Issue 4p671-681April 2015

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Ultrasound of the elbow with emphasis on detailed assessment of ligaments, tendons, and nerves

Highlights

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Medial and lateral tendons: the different muscles forming these tendons can be followed up to the insertion. The imaging anatomy is reviewed.

•

Medial and lateral ligaments: the anatomy is complex and specialized imaging planes and arm positions are necessary for accurate assessment.

•

Biceps tendon: the anatomy of the distal biceps and lacertus fibrosus are discussed and illustrated with cadaveric correlation.

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US imaging of the nerves about the elbow and visualization of the possible compression points is discussed.

Abstract

The high resolution and dynamic capability of ultrasound make it an excellent tool for assessment of superficial structures. The ligaments, tendons, and nerves about the elbow can be fully eval‎uated with ultrasound. The medial collateral ligament consists of an anterior and posterior band that can easily be identified. The lateral ligament complex consists of the radial collateral ligament, ulnar insertion of the annular ligament, and lateral ulnar collateral ligament, easily identified with specialized probe positioning. The lateral ulnar collateral ligament can best be seen in the cobra position. On ultrasound medial elbow tendons can be followed nearly up to their common insertion. The pronator teres, flexor carpi radialis, palmaris longus, and flexor digitorum superficialis can be identified. The laterally located brachioradialis and extensor carpi radialis longus insert on the supracondylar ridge. The other lateral tendons can be followed up to their common insertion on the lateral epicondyle. The extensor digitorum, extensor carpi radialis brevis, extensor digiti minimi, and extensor carpi ulnaris can be differentiated. The distal biceps tendon is commonly bifid. For a complete assessment of the distal biceps tendon specialized views are necessary. These include an anterior axial approach, medial and lateral approach, and cobra position. In the cubital tunnel the ulnar nerve is covered by the ligament of Osborne. Slightly more distally the ulnar nerve courses between the two heads of the flexor carpi ulnaris. An accessory muscle, the anconeus epitrochlearis can cover the ulnar nerve at the cubital tunnel, and is easily identified on ultrasound. The radial nerve divides in a superficial sensory branch and a deep motor branch. The motor branch, the posterior interosseous nerve, courses under the arcade of Frohse where it enters the supinator muscle. At the level of the dorsal wrist the posterior interosseous nerve is located at the deep aspect of the extensor tendons. The median nerve may be compressed at various sites, including the lacertus fibrosis, between the pronator teres heads, and the sublimis bridge. These compression sites can be identified with ultrasound.

초록

초음파의 높은 해상도와 동적 능력은 표면 구조물의 평가에 우수한 도구로 활용됩니다.

팔꿈치 주변의 인대, 힘줄, 신경은

초음파를 통해 완전히 평가될 수 있습니다.

내측 측부 인대는 전방과 후방 띠로 구성되어 있으며

쉽게 식별 가능합니다.

외측 인대 복합체는

방사측 측부 인대, 고리 인대의 척골 부착부, 외측 척골 측부 인대로 구성되며,

특수 프로브 위치 조정으로 쉽게 식별 가능합니다.

측방 척골 측부 인대는

코브라 자세에서 가장 잘 관찰됩니다.

초음파에서 내측 팔꿈치 힘줄은

공통 부착부까지 거의 추적할 수 있습니다.

회전근개, 요골 손목 굴곡근, 장지근, 손가락 굴곡근 표층이

식별됩니다.

측방에 위치한 상완요골근과 요골 손목 신근 장근은

상과돌기 능선부에 부착됩니다.

다른 측부 힘줄은

측부 상과돌기까지 추적할 수 있습니다.

손가락 신근, 손목 신근 단근, 소지 신근,

그리고 척골 손목 신근을 구분할 수 있습니다.

이두근의 원위부 힘줄은

일반적으로 분열되어 있습니다.

이두근의 원위부 힘줄을 완전히 평가하려면 특수한 시야가 필요합니다. 이는 전방 축 방향 접근, 내측 및 측방 접근, 그리고 코브라 자세를 포함합니다. 상완골의 굴곡근 터널에서 척골 신경은 오스본 인대에 의해 덮여 있습니다. 약간 더 원위부에서는 척골 신경이 척골 손목 굴곡근의 두 머리 사이를 지나갑니다. 부가적인 근육인 안코네우스 에피트로클레아리스는 굴곡근 터널에서 척골 신경을 덮을 수 있으며, 초음파에서 쉽게 식별됩니다. 방사 신경은 표면 감각 분지와 깊은 운동 분지로 분할됩니다. 운동 분지인 후방 간골 신경은 Frohse의 아치 아래를 지나 supinator 근육으로 들어갑니다. 손등 수준에서 후방 간골 신경은 extensor 힘줄의 깊은 부분에 위치합니다. 정중 신경은 lacertus fibrosis, pronator teres 근육의 두 머리 사이, sublimis 다리 등 다양한 부위에서 압박될 수 있습니다. 이러한 압박 부위는 초음파로 식별 가능합니다.

Keywords

1 Introduction

Ultrasound is often used to assess soft tissue structures about joints [1]. Ultrasound offers some advantages over MR, owing to its higher resolution. This allows better depiction of fine nerve branches and better appreciation of subtle alterations in the fibrillar echotexture of tendons and ligaments. Because ultrasound is dynamic, the integrity and continuity of tendons and ligaments can be assessed in real time in positions of stress. Comparison with the asymptomatic side is possible and may help diagnose subtle abnormalities. Finally power Doppler is valuable in diagnosing tendinopathies such as tennis or golfers elbow. A disadvantage of ultrasound is that it is operator dependent and may be technically difficult. This disadvantage can be overcome by proper training.

In this work we discuss the detailed ultrasound anatomy of tendons, ligaments and nerves about the elbow, using cadaveric correlation. We include tips and tricks for eval‎uating difficult anatomic structures.

2 Discussion

2.1 Medial ligaments

The ulnar collateral ligament (UCL) forms the major restraint to valgus stress [1,2]. It is commonly injured in the setting of throwing injuries and sports. The UCL consists of an anterior, posterior and transverse band (Fig. 1). The anterior band is mechanically the most important. To image the anterior band the elbow should be put in slight flexion as this allows optimal alignment of the ultrasound probe along the course of the ligament. An excellent trick is to hook the 2nd to 4th fingers of the operator behind the medial epicondyle from an anterior approach and let the probe slide onto the fingers from anteriorly. The probe is then positioned along the course of the ligament (Fig. 2).

1. 소개

초음파는 관절 주변의 연부 조직 구조를 평가하는 데 자주 사용됩니다 [1]. 초음파는 MR에 비해 높은 해상도를 갖추고 있어 미세한 신경 분지를 더 명확히 묘사하고 힘줄과 인대의 섬유질 에코 텍스처의 미묘한 변화를 더 잘 파악할 수 있습니다. 초음파는 동적이기 때문에 힘줄과 인대의 완전성과 연속성을 스트레스 상태에서 실시간으로 평가할 수 있습니다. 무증상 측과의 비교가 가능하며, 미묘한 이상을 진단하는 데 도움이 될 수 있습니다. 마지막으로 파워 도플러는 테니스 엘보우나 골퍼 엘보우와 같은 건병증 진단에 유용합니다. 초음파의 단점은 조작자에 의존적이며 기술적으로 어려울 수 있다는 점입니다. 이 단점은 적절한 훈련을 통해 극복될 수 있습니다.

본 연구에서는 시체 해부학적 상관관계를 바탕으로 팔꿈치 주변의 건, 인대 및 신경의 상세한 초음파 해부학을 논의합니다. 어려운 해부학적 구조를 평가하기 위한 팁과 요령도 포함되어 있습니다.

2 토론

2.1 내측 인대

척골 부인대(UCL)는 외반 스트레스에 대한 주요 제지 역할을 합니다 [1,2]. 투구 부상 및 스포츠에서 흔히 손상됩니다. UCL은 전방, 후방 및 횡대(그림 1)로 구성됩니다. 전방대는 기계적으로 가장 중요합니다. 전방 띠를 촬영하려면 팔꿈치를 약간 굴곡시킨 상태에서 초음파 프로브를 인대의 경과 방향과 최적의 정렬을 유지하도록 위치시켜야 합니다. 우수한 팁은 조작자의 2~4번째 손가락을 전방 접근법으로 내측 상과 뒤쪽에 걸고 프로브를 전방에서 손가락 위로 미끄러지게 하는 것입니다. 프로브는 이후 인대의 경과 방향에 따라 위치됩니다(그림 2).

On MR arthrography the distal attachment of the UCL to the ulna should be tightly attached to the sublime tubercle without contrast interposition between the ligament and ulna. On ultrasound, however, the ligament may appear to insert more distally.

In some patients, the proximal insertion of the anterior band may be somewhat broader or multifibrillar and this should not be taken for a sign of abnormality. It may often be difficult on one static image to separate the ligament fibers from the adjacent fatty tissue. Slightly tilting the probe back and forth uses anisotropy to better differentiate the ligament from adjacent fat (Fig. 2). Along the posteromedial aspect of the elbow the posterior band of the UCL can be seen. Probe positioning is similar to that for assessment of the ulnar nerve and the ligament of Osborne (Fig. 3). The posterior band of the UCL spans the humeroulnar joint like a hammock and forms the bottom of the cubital tunnel. The ulnar nerve is located adjacent to it.

The transverse component of the UCL courses between the ulnar insertions of the anterior and posterior bands, and is less important.

2.2 Lateral ligaments

The anatomy of the lateral ligaments is complex (Fig. 4) [2]. The ligaments include the radial collateral ligament (RCL), ulnar insertion of the annular ligament, and lateral ulnar collateral ligament (LUCL). Probe placement for the RCL is similar to that for assessment of the extensor tendons of the elbow in the longitudinal plane (Fig. 5). The concavity in the distal aspect of the humerus is identified for correct probe placement. Various tubercles may be identified on the lateral epicondyle. The radial collateral ligament inserts on the humeral epicondyle in the groove between the anterior and posterior tubercle. From here it courses toward the radial head where it joins the annular ligament. Occasionally it can be separated from the overlying extensor tendons by a delicate hyperechoic line. In the transverse plane anisotropy helps to differentiate the ligament from the overlying tendon (Fig. 6).

The annular ligament forms a band around the radial head [3]. The annular ligament has an ulnar insertion. When the probe is placed in a transverse plane with respect to the radial head the thin fibers of the annular ligament can be seen to insert on the ulna (Fig. 7). The proximal part of the LUCL also inserts on the humerus in the same area as the RCL but somewhat more toward the radial side [4,5]. Typically, however, the LUCL and RCL cannot be separated along their proximal course. Distally the LUCL courses more distally than the RCL and inserts on the supinator crest of the ulna. In this insertion area the ligament typically fans out. To visualize the LUCL we start with the position for the annular insertion which is transverse with regard to the radial head. From this position, the probe is then slightly tilted anteriorly in between the radius and the supinator crest (Fig. 8). Typically a few delicate vascular structures are seen between the LUCL and adjacent muscles, and these vessels constitute an excellent landmark. We prefer to assess the annular insertion and LUCL with the arm in the cobra position. In the cobra position the LUCL is typically much better outlined likely because it is placed under tension (Fig. 8).

Fig. 9 Drawing of medial elbow tendons. Note pronator teres (Pr), flexor carpi radialis (Fcr), Palmaris longus (Pl), flexor digitorum superficialis (Fds), and humeral and ulnar heads (arrows) of the flexor carpi ulnaris (Fcu).

Fig. 10 Short axis view of medial aspect of elbow just before insertion of the flexor tendons on the epicondyle. From anterior to posterior, note pronator teres (PR), flexor carpi radialis (Fcr), Palmaris longus (PA), and flexor digitorum superficialis (Fds).

Fig. 11 More posterior relative to Fig. 10. Note ulnar nerve (arrowhead) between both heads of the flexor carpi ulnaris (Fcu).

Fig. 12 Dissection of medial aspect of elbow. Note flexor tendon insertion (F), with pronator teres (arrow) located most superiorly. Note flexor carpi ulnaris (Fcu). Humeral and ulnar heads are pointed out by curved arrows.

2.4 Lateral tendons

Various bony tubercles and ridges can be seen on the lateral epicondyle and form important landmarks (Fig. 13). We first identify the extensor tendons in the longitudinal plane (Fig. 14) [1,6,8]. In this plane a concavity can be seen in the humerus where the tendons insert (Fig. 14). This approach is similar to that for the RCL. We then turn the probe in the transverse plane. Although the different tendons form a common insertion, they can be followed separately nearly up to the insertion (Fig. 15). Most anteriorly, the extensor carpi radialis brevis (ERCB) can be easily identified because its lateral edge has a prominent beak like appearance. Toward the medial side the muscle of the ECRB cannot be separated from the extensor carpi radialis longus muscle (ECRL). Superficial to the beak of the ECRB, the muscle belly of the extensor digitorum (ED) can be seen (Fig. 15). Lateral to the ED, a small muscle and tendon can be visualized corresponding to the extensor digiti minimi. Flexing and extending the little finger helps identify this muscle. Lateral to the extensor digiti minimi the extensor carpi ulnaris is seen. Along the lateral epicondyle an anterior, posterior, and superior tubercle can be identified. The insertion of the RCL is located in between the anterior and posterior tubercle. Anisotropy artifact can be used to differentiate it from the tendons (Fig. 6). Along the supracondylar ridge, the insertion of the brachioradialis and extensor carpi radialis longus are seen (Fig. 16).

2.5 Biceps tendon

Investigation of the biceps tendon from an anterior approach may prove quite difficult. To obtain a complete eval‎uation of this tendon we typically combine different approaches [9]. First, we identify the biceps tendon in the transverse plane just above the elbow joint. At this level the biceps tendon is seen adjacent to the brachial artery and median nerve (Fig. 17). This has been termed the ‘BAM’ sign. Distally, the biceps tendon dives into the depth but its insertion is difficult to see with this approach. This approach is useful, however, to identify a bifid biceps tendon (Figs. 18 and 19). If two tendon heads are present, the long head will insert more proximally than the short head [10]. At the level where the biceps tendon is located adjacent to the brachial artery, a thin band like structure can be seen crossing over the artery which corresponds to the lacertus fibrosis (Fig. 20). The lacertus fibrosus runs from lateral to medial and fuses with the superficial flexor fascia. The basilic vein is located just superficial to the lacertus fibrosis and constitutes a good landmark. Because the vein is easily compressed, care should be taken not to exert too much pressure (Fig. 21). The best probe position to investigate the biceps tendon consists of an oblique anteromedial approach (Fig. 22). From this position the radial tuberosity can be seen with the biceps tendon inserting on to it. The radial tuberosity is best seen with supination of the forearm. The brachial artery forms an acoustic window through which the biceps tendon can be visualized. The biceps can also be seen from a lateral approach. The probe is placed in a coronal plane along the lateral aspect of the radius. In this position, the biceps tendon can be followed deep to the supinator muscle. The insertion is difficult to see, however, as it is located behind the radius (Fig. 23). This position is useful to perform a dynamic study of the tendon. The last approach consists of a transverse approach with the forearm in the cobra position (Fig. 24). From this approach, only the insertion of the biceps tendon on the radial tuberosity is seen. Combining the different approaches allows a complete examination of the distal biceps tendon.

2.6 Ulnar nerve

The ulnar nerve is located in the cubital tunnel, where it is covered by Osborne's ligament (Figs. 25 and 26) [11–13]. The bottom of the cubital tunnel is formed by the posterior band of the ulnar collateral ligament (Fig. 3). The ulnar nerve may be compressed between the humerus and the ligament of Osborne. With a dynamic flexion maneuver, the nerve may sublux but this also may occur in patients without neuropathy. In some patients subluxation represents a significant finding, in particular when nerve thickening is also present. In snapping triceps syndrome not only the ulnar nerve subluxes but also the medial head of the triceps muscle. This finding is important to report since the snapping triceps must also be addressed surgically. Instead of the ligament of Osborne, the anconeus epitrochlearis may be present (Fig. 27). This muscle may cause compression of the nerve although it is not uncommon to observe it in the asymptomatic population. Hence it needs to be correlated with focal nerve thickening.

Distal to the cubital tunnel the ulnar nerve courses between the humeral and ulnar heads of the flexor carpi ulnaris (Fig. 26). A fibrous arch connects both heads of the flexor carpi ulnaris and is designated the arcuate ligament. The arcuate ligament also forms a potential compression area for the ulnar nerve.

The thickness of the ulnar nerve should be thoroughly eval‎uated. Although standard values are less well established than for the median nerve, a value of 8mm2 is usually employed. Focal thickening, a notch sign, and hypervascularity also are important findings [11]. It is not rare for the nerve to be bifid or trifid and in such case the different parts can be measured separately and the sum can be used for assessment of thickness.

2.7 Radial nerve

Along the posterior aspect of the humerus the radial nerve courses in the spiral groove where it may be injured with humeral fractures. The nerve then has an anterolateral course deep to the brachioradialis muscle. Just before the proximal edge of the supinator muscle the radial nerve divides in the superficial radial nerve and the posterior interosseous nerve (Fig. 28) [11]. The superficial radial nerve is a sensory nerve and continuous distally to emerge adjacent to the tendons of the first extensor compartment where it can be easily discerned. In this area Wartenberg syndrome, compression of the radial nerve may occur. The posterior interosseous nerve enters the supinator muscle between its two heads. At the entrance point the nerve is covered by the arcade of Frohse. The arcade of Frohse is a fibrous band; it may be quite well developed in some individuals but nearly absent in others (Figs. 29 and 30). A thick arcade of Frohse is a potential cause of nerve compression. The posterior interosseous nerve is a motor nerve and compression causes the syndrome of finger drop, which should be differentiated from wrist drop that occurs with more proximal lesions of the radial nerve [11–14]. Despite the fact that this branch is a motor nerve it also may cause a pain syndrome that may be difficult to differentiate from pain that occurs with tennis elbow. As a rule of thumb the posterior interosseous nerve should be examined when findings at the level of the extensor tendons are inconclusive. An important sign of neuropathy of the PIN is nerve thickening. Unfortunately no standard values have been described. In addition, it is normal for the nerve to be slightly thicker before it enters the supinator muscle, as it gives off delicate muscle branches once it enters this muscle. This can be well appreciated in the sagittal plane. A significant advantage of ultrasound is also that a comparison with the asymptomatic side can be made.

2.8 Median nerve

At the level of the elbow fold the median nerve can be easily identified by the ‘BAM’ relationship which we discussed previously. From lateral to medial we observe the biceps tendon, brachial artery, and median nerve (Fig. 17). There are many potential compression areas of the median nerve which include the ligament of Struthers, lacertus fibrosus, between the pronator heads, the sublimis bridge, and anterior interosseous nerve compression syndrome [11–13]. The ligament of Struthers consists of a fibrous band that courses from a supracondylar process of the humerus to the medial epicondyle. The lacertus fibrosis has been previously described in the paragraph about the biceps tendon. The size and thickness of the lacertus fibrosis is variable however. It can be quite thin and in that case it would be unlikely for it to cause any compression.

The median nerve can be compressed between the large humeral and small ulnar head of the pronator teres muscle (Fig. 33). The method to identify this compression area is to follow the median nerve distally from the elbow fold. The ulnar artery splits of from the brachial artery and courses medially. When the ulnar artery becomes positioned precisely underneath the median nerve a band-like structure is seen between the median nerve and the ulnar artery. This band like structure corresponds to the short head of the pronator teres muscle. The short head of the pronator teres is variable in size. It may be band-like, a thick muscle belly, or absent.

The next compression area of the median nerve is located more distally and corresponds to the sublimis bridge. The sublimis bridge is a fibrous arch between the radial and humeral heads of the flexor digitorum superficialis muscle (Figs. 34 and 35). As the name indicates, if forms an easily recognizable bridge over the median nerve slightly distal to the pronator teres heads.

Figure viewer

Fig. 34 Drawing of flexor digitorum superficialis muscle. Radial and humeral heads (arrows) of this muscle are seen to form a bridge underneath which the median nerve (M, yellow) courses.

Figure viewer

Fig. 35 Transverse ultrasound. Connection between two heads of flexor digitorum superficialis (arrowheads) referred to as sublimis bridge is seen. Median nerve (arrow) courses deep to it. Insert, probe position.

The anterior interosseous branch of the median nerve splits off from the median nerve. Injury of this nerve causes Kiloh Nevin syndrome with an inability for the patient to pinch between the thumb and 2nd finger. It is a thin branch that may be more difficult to visualize. A good trick, however, is to displace the probe distally until the triangular origin of the flexor muscle for the thumb is brought in view (Fig. 36). Correct identification of this muscle can be confirmed by asking the patient to make movements with his thumb. The anterior interosseous nerve will course just adjacent to the ulnar border of this muscle origin. More distally, the nerve may be seen adjacent to the artery and anterior to the interosseous membrane. A helpful indirect finding indicating neuropathy of the anterior interosseous nerve is fatty atrophy of the pronator quadratus muscle (Fig. 37) [15].

Figure viewer

Fig. 36 Transverse ultrasound image at origin of flexor pollicis muscle (arrows). Note triangular shape. It can be readily identified by asking the patient to move the thumb. Anterior interosseous nerve (short arrow) and artery (longer arrow) course alongside the edge of this muscle. R, radius.

Figure viewer

Fig. 37 Transverse ultrasound image at level of pronator quadratus muscle (arrows) in distal forearm. Atrophy and fatty infiltration of this muscle may occur with anterior interosseous nerve involvement. U, ulna; R, radius. Insert, probe position.

3 Conclusion

Ultrasound is an excellent imaging modality for assessment of ligaments, tendons, and nerves about the elbow. Advantages of ultrasound are its high resolution, its dynamic capability and the ability to compare findings with the asymptomatic side.

In this review, we provide valuable tips and tricks that can be used to depict elbow anatomy. Although the technique is operator dependent and experience is necessary, these tricks may significantly shorten learning curves. For better comprehension of anatomic features of different areas, we included anatomical dissections.

Conflict of interest

The authors have no conflict of interest.

Acknowledgments

We thank Jan Gielen, MD, PhD, Antwerp, Belgium and Tjeerd Jager, MD, Aalsters Stedelijk Ziekenhuis, Aalst, Belgium. We acknowledge Aloka-Hitachi, Belgium for providing an F75 demo ultrasound system.

References

The next compression area of the median nerve is located more distally and corresponds to the sublimis bridge. The sublimis bridge is a fibrous arch between the radial and humeral heads of the flexor digitorum superficialis muscle (Figs. 34 and 35). As the name indicates, if forms an easily recognizable bridge over the median nerve slightly distal to the pronator teres heads.

Figure viewer

Fig. 34 Drawing of flexor digitorum superficialis muscle. Radial and humeral heads (arrows) of this muscle are seen to form a bridge underneath which the median nerve (M, yellow) courses.

Figure viewer

Fig. 35 Transverse ultrasound. Connection between two heads of flexor digitorum superficialis (arrowheads) referred to as sublimis bridge is seen. Median nerve (arrow) courses deep to it. Insert, probe position.

The anterior interosseous branch of the median nerve splits off from the median nerve. Injury of this nerve causes Kiloh Nevin syndrome with an inability for the patient to pinch between the thumb and 2nd finger. It is a thin branch that may be more difficult to visualize. A good trick, however, is to displace the probe distally until the triangular origin of the flexor muscle for the thumb is brought in view (Fig. 36). Correct identification of this muscle can be confirmed by asking the patient to make movements with his thumb. The anterior interosseous nerve will course just adjacent to the ulnar border of this muscle origin. More distally, the nerve may be seen adjacent to the artery and anterior to the interosseous membrane. A helpful indirect finding indicating neuropathy of the anterior interosseous nerve is fatty atrophy of the pronator quadratus muscle (Fig. 37) [15].

Figure viewer

Fig. 36 Transverse ultrasound image at origin of flexor pollicis muscle (arrows). Note triangular shape. It can be readily identified by asking the patient to move the thumb. Anterior interosseous nerve (short arrow) and artery (longer arrow) course alongside the edge of this muscle. R, radius.

Figure viewer

Fig. 37 Transverse ultrasound image at level of pronator quadratus muscle (arrows) in distal forearm. Atrophy and fatty infiltration of this muscle may occur with anterior interosseous nerve involvement. U, ulna; R, radius. Insert, probe position.

3 Conclusion

Ultrasound is an excellent imaging modality for assessment of ligaments, tendons, and nerves about the elbow. Advantages of ultrasound are its high resolution, its dynamic capability and the ability to compare findings with the asymptomatic side.

In this review, we provide valuable tips and tricks that can be used to depict elbow anatomy. Although the technique is operator dependent and experience is necessary, these tricks may significantly shorten learning curves. For better comprehension of anatomic features of different areas, we included anatomical dissections.

Conflict of interest

The authors have no conflict of interest.

Acknowledgments

We thank Jan Gielen, MD, PhD, Antwerp, Belgium and Tjeerd Jager, MD, Aalsters Stedelijk Ziekenhuis, Aalst, Belgium. We acknowledge Aloka-Hitachi, Belgium for providing an F75 demo ultrasound system.

References

The next compression area of the median nerve is located more distally and corresponds to the sublimis bridge. The sublimis bridge is a fibrous arch between the radial and humeral heads of the flexor digitorum superficialis muscle (Figs. 34 and 35). As the name indicates, if forms an easily recognizable bridge over the median nerve slightly distal to the pronator teres heads.

Figure viewer

Fig. 34 Drawing of flexor digitorum superficialis muscle. Radial and humeral heads (arrows) of this muscle are seen to form a bridge underneath which the median nerve (M, yellow) courses.

Figure viewer

Fig. 35 Transverse ultrasound. Connection between two heads of flexor digitorum superficialis (arrowheads) referred to as sublimis bridge is seen. Median nerve (arrow) courses deep to it. Insert, probe position.

The anterior interosseous branch of the median nerve splits off from the median nerve. Injury of this nerve causes Kiloh Nevin syndrome with an inability for the patient to pinch between the thumb and 2nd finger. It is a thin branch that may be more difficult to visualize. A good trick, however, is to displace the probe distally until the triangular origin of the flexor muscle for the thumb is brought in view (Fig. 36). Correct identification of this muscle can be confirmed by asking the patient to make movements with his thumb. The anterior interosseous nerve will course just adjacent to the ulnar border of this muscle origin. More distally, the nerve may be seen adjacent to the artery and anterior to the interosseous membrane. A helpful indirect finding indicating neuropathy of the anterior interosseous nerve is fatty atrophy of the pronator quadratus muscle (Fig. 37) [15].

Figure viewer

Fig. 36 Transverse ultrasound image at origin of flexor pollicis muscle (arrows). Note triangular shape. It can be readily identified by asking the patient to move the thumb. Anterior interosseous nerve (short arrow) and artery (longer arrow) course alongside the edge of this muscle. R, radius.

Figure viewer

Fig. 37 Transverse ultrasound image at level of pronator quadratus muscle (arrows) in distal forearm. Atrophy and fatty infiltration of this muscle may occur with anterior interosseous nerve involvement. U, ulna; R, radius. Insert, probe position.

3 Conclusion

Ultrasound is an excellent imaging modality for assessment of ligaments, tendons, and nerves about the elbow. Advantages of ultrasound are its high resolution, its dynamic capability and the ability to compare findings with the asymptomatic side.

In this review, we provide valuable tips and tricks that can be used to depict elbow anatomy. Although the technique is operator dependent and experience is necessary, these tricks may significantly shorten learning curves. For better comprehension of anatomic features of different areas, we included anatomical dissections.

Conflict of interest

The authors have no conflict of interest.

Acknowledgments

We thank Jan Gielen, MD, PhD, Antwerp, Belgium and Tjeerd Jager, MD, Aalsters Stedelijk Ziekenhuis, Aalst, Belgium. We acknowledge Aloka-Hitachi, Belgium for providing an F75 demo ultrasound system.

References

The next compression area of the median nerve is located more distally and corresponds to the sublimis bridge. The sublimis bridge is a fibrous arch between the radial and humeral heads of the flexor digitorum superficialis muscle (Figs. 34 and 35). As the name indicates, if forms an easily recognizable bridge over the median nerve slightly distal to the pronator teres heads.

Figure viewer

Fig. 34 Drawing of flexor digitorum superficialis muscle. Radial and humeral heads (arrows) of this muscle are seen to form a bridge underneath which the median nerve (M, yellow) courses.

Figure viewer

Fig. 35 Transverse ultrasound. Connection between two heads of flexor digitorum superficialis (arrowheads) referred to as sublimis bridge is seen. Median nerve (arrow) courses deep to it. Insert, probe position.

The anterior interosseous branch of the median nerve splits off from the median nerve. Injury of this nerve causes Kiloh Nevin syndrome with an inability for the patient to pinch between the thumb and 2nd finger. It is a thin branch that may be more difficult to visualize. A good trick, however, is to displace the probe distally until the triangular origin of the flexor muscle for the thumb is brought in view (Fig. 36). Correct identification of this muscle can be confirmed by asking the patient to make movements with his thumb. The anterior interosseous nerve will course just adjacent to the ulnar border of this muscle origin. More distally, the nerve may be seen adjacent to the artery and anterior to the interosseous membrane. A helpful indirect finding indicating neuropathy of the anterior interosseous nerve is fatty atrophy of the pronator quadratus muscle (Fig. 37) [15].

Figure viewer

Fig. 36 Transverse ultrasound image at origin of flexor pollicis muscle (arrows). Note triangular shape. It can be readily identified by asking the patient to move the thumb. Anterior interosseous nerve (short arrow) and artery (longer arrow) course alongside the edge of this muscle. R, radius.

Figure viewer

Fig. 37 Transverse ultrasound image at level of pronator quadratus muscle (arrows) in distal forearm. Atrophy and fatty infiltration of this muscle may occur with anterior interosseous nerve involvement. U, ulna; R, radius. Insert, probe position.

3 Conclusion

Ultrasound is an excellent imaging modality for assessment of ligaments, tendons, and nerves about the elbow. Advantages of ultrasound are its high resolution, its dynamic capability and the ability to compare findings with the asymptomatic side.

In this review, we provide valuable tips and tricks that can be used to depict elbow anatomy. Although the technique is operator dependent and experience is necessary, these tricks may significantly shorten learning curves. For better comprehension of anatomic features of different areas, we included anatomical dissections.

Conflict of interest

The authors have no conflict of interest.

Acknowledgments

We thank Jan Gielen, MD, PhD, Antwerp, Belgium and Tjeerd Jager, MD, Aalsters Stedelijk Ziekenhuis, Aalst, Belgium. We acknowledge Aloka-Hitachi, Belgium for providing an F75 demo ultrasound system.

References