후방십자인대의 two bundle(두개의 다발) 기능 탐구 - 정리해야

[문형철]

인대의 조성, 기능, 생체역학적 기능, 치유, 치유를 위한 최적의 재생자극의 탐구 중

인대의 기능 탐구방법 중 

하나의 인대에 여러개의 기능을 하는 다발(bundle)이 있다. 

세밀한 인대의 기능을 이해하기 위해서는 반드시 각 bundle의 기능을 알야야 한다.

예를들어 후방십자인대는 두개의 기능적 다발(two finctional bundle)로 되어 있다. 

1) anterolateral bundle(ALB)

2) posteromedial bundle(PMB)

최적 재생자극

최적 움직임 회복 운동을 시행하는 동안 올바른 방향과 올바른 힘이 얼마나 중요한가를 보여주는 논문이다.....

panic bird..

미리 알아야 할 내용들

1. 인대의 조성

# 인대는 GAGs, collagen fiber, 소량의 elastic fiber, fibroblast, capillary vessel, nerve로 구성

2. 인대의 기능

# bone to bone 고정

# type 3 mechanoreceptor가 있어 움직임의 방향(direction)과 진폭(ampulitude)를 모니터링하여 중추신경으로 전달하는 역할

3. 인대 손상후 치유

# 염증기(3일), 증식기(proliferation 1일~3주), remodeling phase

# cross bridge를 올바른 배열로 바꾸어야(올바른 힘과 방향 자극)

# 인대 고유기능 회복

# 인대 손상후 문제는 bone to bone fixation을 제대로 못해주는 axity!

4. 예를 들어 후방십자인대의 생체역학적 기능

# 2개의 bundle로 구성

# meniscofemoral ligament와 부착되어 있음. 

# 두개의 인대는 외측반원팔의 후각에 부착되어 있음. 

후방십자인대 2개의 bundle 그리고 meniscofemoral ligament.pdf

 Abstract : This paper describes the anatomy of the posterior cruciate ligament (PCL) and the meniscofemoral ligaments (MFLs). The fibres of the PCL may be split into two functional bundles; the anterolateral bundle (ALB) and the  posteromedial bundle (PMB), relating to their femoral attachments. 

- 이 논문은 후방십자인대, meniscofemoral ligament의 해부학적 묘사

- 후방십자인대 섬유는 두가지 기능적 다발로 나누어짐. anterolateral bundle와 posteromedial bundle

The tibial attachment is relatively compact, with the ALB anterior to the PLB. These bundles are not isometric: the

ALB is tightest in the mid-arc of knee flexion, the PMB is tight at both extension and deep flexion. At least one MFL is present in 93% of knees. 

- ALB와 PMB는 길이가 같지 않음. ALB 무릎굴곡의 중간 아크에서 제일 타이트하고, PMB는 신전과 완전굴곡에서 타이트함. 

- MFL는 무읖의 93%에서 존재함. 

On the femur, the anterior MFL attaches distal to the PCL, close to the articular cartilage; the posterior MFL attaches proximal to the PCL. They both attach distally to the posterior horn of the lateral meniscus. Their slanting orientation

allows the MFLs to resist tibial posterior drawer.

- 대퇴골에서 전방 MFL은 후방십자인대 distal 부위에 부착, 관절연골 근처에 부착하고, 후방 MFL은 후방십자인대 proximal부위에 부착함.

- MFL은 외측 반월판의 후각에 부착함. 

Introduction

This anatomical paper describes the posterior cruciate ligament (PCL) and the meniscofemoral ligaments (MFLs). It describes the bony attachments of the ligaments, their fibre anatomy, and the patterns of tightening and slackening of the ligament fibres during knee flexion–extension. This description can be tied in with other texts that describe the function of these structures.

- 후방십자인대와 MFL 묘사에 대한 논문

- 인대의 뼈 부착부, 그것들의 섬유 해부구조, 무릎굴곡신전동안 인대섬유의 짧아짐과 늘어남 탐구.

- 

The PCL is a very strong ligament, with a maximum tensile load reported in the range 739–1,627 N [13, 16, 18, 19, 22]. This is stronger than the anterior cruciate ligament (ACL) in specimens of similar age. The strength relates to a large cross-sectional area, and the fibres spread out to an extensive femoral attachment.

- 후방십자인대는 매우 강한 인대. 최대 장력부하는 739~1627N

- 전방십자인대보다 훨씬 강함. 강도는 큰 단면적과 연관되고, 섬유는 대퇴골 부착부로 이어짐. 

Because of this, knee flexion–extension causes them to have different patterns of tightening and slackening, and so they become more or less important. This relates to the patterns of damage that are caused by injuries with the knee flexed or extended, and also to the importance of graft tunnel positions and tensioning protocols for restoring tibial posterior laxity to normal.

- 이때문에, 무릎 굴곡-신전은 짧아짐과 이완됨의 서로다른 패턴을 가짐. 그래서 매우 중요함. 

- 이것은 손상의 패턴과 연관되고, 무릎 굴곡 또는 신전과 함께 손상을 야기함. 

The PCL is the primary restraint to tibial posterior draw, contributing approximately 90% of the resistance across most of the arc of knee flexion [4, 20]. Recently, however, there has been increasing knowledge of the role of other structures in providing this function as the knee reaches extension [3]. This helps to explain why an isolated PCL rupture often does not lead to disabling instability, despite the strength of the damaged structure.

- 후방십자인대는 경골이 뒤로 밀리는 것을 막아주고, 무릎굴곡 각도의 저항의 90%를 담당함. 

- 최신 증가된 지식에 의하면 .....

Femoral attachment of the PCL

The femoral attachment of the PCL extends more than 20 mm in an anterior–posterior (AP) direction across the roof and medial side of the femoral intercondylar notch. The PCL attachment is bounded distally by the margin of the articular cartilage of the medial femoral condyle and in general conforms to a ‘half-moon’ shape.

- 후방십자인대의 대퇴부착부는 전후방 방향에서 20mm를 넘고.

- 후방십자인대 부착은 ....

The extent of the attachment is variable, and is influenced by the presence or absence of the MFLs. In the specimen illustrated in Fig. 1 the PCL attachment extends as far posteriorly as it can against the margin of the articular cartilage. In some knees the attachment is more compact than this and does not extend so far posteriorly.

The PCL does not attach solely to the medial side of the femoral intercondylar notch, but also to the roof of the notch. A straight posterior–anterior view reveals that the anterior fibres of the PCL, which are the most lateral part of it, pass in a sagittal plane to the roof of the notch. 

In contrast, the posterior fibres take an oblique path as they pass up to the wall of the femoral condyle medially and down to the tibia laterally. When viewed from the anterior aspect of the flexed knee, the distal aspect of the PCL femoral attachment is revealed in the so-called ‘notch view’ (Fig. 2). It can be seen that the fibres extend in the left knee from approximately 12.00 to 1.00 o’clock, at the top of the notch, back round from approximately the 7.30 to 8.00 o’clock position, which is adjacent to the tibial plateau.

Thus, the entire medial aspect of the femoral intercondylar notch has the PCL attached to it in this view. The anterior meniscofemoral ligament (aMFL) of Humphrey slants across the PCL and also attaches adjacent to the femoral condylar articular cartilage  [1 , 8 ]. When the femoral attachment area of the PCL is viewed in the PCL-deficient knee, it is seen that the bulk

of the attachment area, that corresponds to the anterolateral (AL) fibre bundle, is between the 9.00 o’clock and 12.00 o’clock position in the left knee. 

The attachment also extends further down towards the tibial plateau, that is posteriorly on the femur, as the posteromedial

(PM) fibre bundle area. The shape and size of the anteromedial bundle is consistent in most knees, however, the variability in the size and shape of the PCL is mostly reflected in variations in the PMB size both in mid-substance and its attachment. In some knees, the posterior meniscofemoral ligament (pMFL) is a significant and relatively large structure. This may have some bearing on PCL reconstruction technique, in that one may be able to replace the anterolateral bundle (ALB) alone if the pMFL is substantial and intact. Currently, this is simply a point of conjecture.

Tibial attachment of the PCL

 Looking down onto the tibial plateau from a proximal viewpoint it is seen that the PCL attachment is relatively compact (Fig. 3 a). It is onto the superior aspect of the posterior tibial ‘shelf’. The attachment is nestled between the posterior horns of the two menisci.

When viewed posteriorly the PCL tibial attachment is seen to extend over the posterior rim of the shelf. Above the shelf the attachment relates mostly to the AL fibre bundle area of the PCL. The attachment of the PM fibre bundle includes the most posterior area above the shelf, and also the area immediately below the shelf (Fig. 3 b). 

The ALB occupies a central area covering almost the entire flat intercondylar surface of the posterior tibial

plateau (‘posterior intercondylar fossa’) from the posterior

edge of the root of the posterior horn of the

medial meniscus to within 2 mm of the posterior rim of

the plateau. Its shape is trapezoidal, wider posteriorly.

The posteromedial bundle (PMB) occupies a central

area of the posterior surface of the tibia from immediately

above the plateau rim. The bundle’s most posterior

and distal attachment occurs distal to the tibial plateau.

Its fibres blend with those of the tibial periosteum and

the attachment of the knee joint capsule to the tibia and

is demarcated by the presence of a small transverse ridge

on the tibia. Superiorly its attachment meets that of the

AL bundle. The overall orientation of the tibial attachment

reflects the path of the fibres of the PMB, slanting

postero-lateral-distally. Thus the PMB attachment is

distal and lateral to the ALB attachment. When the PCL

is intact, the most-posterior fibres pass ‘over the top’ of

the tibial shelf and extend distally and insert into the

distal periosteum close to the attachment area of the popliteus muscle.

The fibre anatomy of the PCL can be divided into

two main fibre bundles: AL and PM [1 , 5 , 12 , 17 , 19 , 23 ].

The split between the two bundles in Fig. 4  has been

created by dissection; this is an artificial division and not

a natural phenomenon. This division between the two

bundles is based on their different tightening and

slackening behaviour during knee flexion and extension.

It can be seen that the ALB attaches mostly to the roof

of the intercondylar notch, while the PMB attaches

mostly to the medial side wall of the notch on to the

medial femoral condyle. There is some overlapping of

the bundles from anterior to posterior, with the PMB

attaching slightly proximal to the ALB. The ALB has a

larger cross-sectional area than the PM, and is much

stronger [19 ]. Although the mid-substance proportions

of the AL and PMBs are considerably different, the

tibial attachments have much more similar areas.

The fibre bundles do not twist around themselves in

the extended knee. Rather, the AL fibres are on the

anterior aspect of the tibial attachment and the PM fibres

are posterior and, therefore, are superficial to the

anterior fibres when the knee is viewed from the posterior

aspect. Because of this arrangement, the anterior

fibres are shortest and the posterior fibres are longest. If

a surgeon performs a single-bundle PCL reconstruction,

aiming to reconstruct the AL fibre bundle, the graft

should be brought up from the tibia underneath (anterior

to) any remnant of the natural PCL. If the graft is

brought out of the tibia into the back of the knee joint

and then to the femur, it will cause a twisted structure

that is not anatomical.

In addition, some anatomists have identified posterior

oblique fibres of the PCL. These may sometimes be

confused with the pMFL of Wrisberg if their distal

attachment is not identified correctly [6 ]. This is because,  like the pMFL, these fibres are situated posteriorly on

the PCL and follow a slanting path, from medial on the

femur to lateral on the tibia, where they attach to the

bone below the level of the posterior horn of the lateral

meniscus (Fig. 4 ). This similarity may cause confusion

between a complete rupture of the PCL with intact

pMFL, and a partial rupture of the PCL.

PCL tension pattern with knee flexion–extension

A video of the PCL during knee flexion–extension

motion1 clearly shows the movements and tightening–

slackening behaviour of the different structures. There

are three main structures to consider: the ALB, the

PMB, and the MFLs. The importance of the length

changes is that they inform us of the role of each of the

structures in controlling tibial posterior draw laxity, and

how these roles become more or less important as the

knee flexes and extends. The PCL is known to be the

primary restraint to tibial posterior draw across most of

the arc of knee flexion [4, 20].

First, the PMB of the PCL. This is tight and aligned

in a proximal–distal direction in the extended knee

(Fig. 5a). Thus, it is not aligned to withstand tibial

posterior draw, but appears to resist hyperextension.

The PM fibres slacken when the knee starts to flex. In

mid-flexion the PM fibres pass between the medial side

wall of the notch and the AL fibre bundle of the PCL,

where they are slack (Fig. 5b). In deep flexion the PM

fibre attachment moves anteriorly and also upwards

away from the tibial plateau and so the PM fibres then

become tight again (Fig. 5c). Thus, in deep knee flexion

the PM fibre bundle is both tight and well aligned to

withstand tibial posterior draw [20, 23].

The AL fibre bundle is seen to be curved in the sagittal

plane and, therefore, is slack in the extended knee

(Fig. 6a). This curved path is seen clearly in MRI scans

of the extended knee. When the knee flexes, this fibre

bundle becomes tight and also takes a steeper angle

away from the tibial plateau (Fig. 6b). In deep knee

flexion the AL fibre bundle rests against the roof of the

femoral intercondylar notch (Fig. 6c). Its steep orientation

means that it is now less efficient at withstanding

tibial posterior draw.

In deep knee flexion the PCL passes through a narrowing

gap between the posterior aspect of the femur, at

the posterior outlet of the femoral intercondylar notch,

and of the tibial plateau. It is easy to imagine that it may

be nipped or sheared between the bones during hyperflexion,

and that this is a potential injury mechanism

when a person falls on to the tibial tuberosity with the

knee flexed (Fig. 6c).

The above description shows that the fibre bundles of

the PCL undergo significant length changes as the knee

flexes and extends. Thus, the PCL cannot be approximated

by an isometric reconstruction. It has been shown

that an isometric graft over-constrains the knee in

extension, where the bulk of the natural PCL is slack,

and does not tighten enough to control laxity normally

in deep flexion [21]. Because of this, several studies have

examined ‘anatomical’ double-bundle reconstructions

[10, 15, 21]; a review of these [2] has shown that all three

investigations found biomechanical advantages for this

method, although clinical advantages have not been

found.

The other significant functional deduction from the

observations of the fibre bundles is that neither of them

is set up to control tibial posterior draw in the extended

knee; the ALB is slack, and the PMB is not orientated

correctly. This may explain why an isolated PCL rupture

may not cause knee instability; other structures, particularly at the PL and PM aspects, are then acting to

stabilise the extended knee [3 ].

The meniscofemoral ligaments

The aMFL of Humphrey slants across the distal aspect

of the PCL in the flexed knee. It attaches to the femur

distal to the PCL and, therefore, is superficial when

viewed in the flexed knee. It is immediately adjacent to

the articular cartilage, in the 10.00 o’clock position in a

left knee. Its fibres intermingle with those of the PCL

immediately adjacent to their femoral attachment. Its

distal attachment is to the posterior horn of the lateral

meniscus (Fig. 7a). It is difficult to identify this attachment

when the knee is intact; it has been demonstrated

here by excising the ACL, to allow the tibial plateau to

sublux anteriorly. When the PCL is viewed arthroscopically,

the aMFL may be identified by the slanting orientation

of its fibres, which is in contrast to the vertical

orientation of the PCL fibres.

The pMFL of Wrisberg extends between the medial

side wall of the femoral intercondylar notch and the

posterior horn of the lateral meniscus (Fig. 7b). The

femoral attachment is proximal to the PM fibres of the

PCL and so it is superficial to the PCL when viewed

from the posterior aspect. Unlike the aMFL, its femoral

attachment is separate to that of the PCL, so there

is no intermingling of its fibres with those of the PCL.

It therefore rests on the posterior/superior aspect of the

surface of the PCL. This means that the pMFL is very

deep in the notch when viewed from an anterior portal,

and is usually difficult to identify, because the PCL

hides it. In order to make a positive identification of  the pMFL, it should be noted that it attaches directly

to the posterior horn of the lateral meniscus, whereas

the oblique posterior fibres of the PCL pass down to

the posterior rim of the tibial plateau and so, by definition,

are not menisco femoral. If an MFL is tugged

using a hook, this will cause the lateral meniscus to

move. If that does not occur, then the fibres may be a

remaining part of the PCL after a partial rupture, and

not an MFL.

Not all knees have both of the MFLs present [6 ].

However, when they are present, they embrace the PCL

anteriorly and posteriorly (Fig. 7 c). Because their distal

attachment is to the relatively mobile meniscus, it is

possible for the PCL to be ruptured and for the MFLs to

remain intact. The illustration shows that they may act

as a splint to keep the PCL in position while it heals, and

this anatomical arrangement may be significant in relation

to the conservative treatment of an isolated PCL

rupture.

A review of the published literature shows that the

presence of the MFLs has been sought in a total of

approximately 1,200 knees [6 ]. These studies have found a

preval‎ence of approximately 93% of all knees having at

least one MFL and approximately 50% having both.

 Some studies have reported a higher preval‎ence of pMFL

than others; this may have resulted because of misidentification

of the posterior oblique fibres of the PCL.

The MFLs are variable structures and when present,

their bulk may vary considerably. They have a mean

strength of approximately 300 N and so mechanically

they are equivalent to the PMB of the PCL [7 , 14 ]. Because

of their slanting arrangement from the posterior

horn of the meniscus up to the femoral intercondylar

notch, they are oriented so that they can help to withstand

tibial posterior draw, and this function has been

proven recently [9 ].

It is easy to misdiagnose the posterior oblique fibres of

the PCL as being a posterior MFL. The posterior intracapsular

examination has to extend distally so that the

attachment to either the meniscus or to the tibia can be

identified if these structures are to be differentiated [8 ].

The femoral attachments of the aMFLs and

pMFLs are distal and proximal to the PCL attachment,

respectively. These positions mean that the aMFL is

slack in the extended knee and tightens with knee

flexion, when it is well aligned to withstand tibial posterior

draw. Conversely the pMFL is tight in the extended

knee and slackens with knee flexion, because its

femoral attachment moves down towards the tibial

plateau as the knee flexes.

In a video that shows flexion and extension movement

of a knee that has an aMFL,1  but not a pMFL, the

aMFL is slack in the extended knee and is collapsed

underneath the anterior fibres of the PCL. When the

knee flexes, this structure is seen to straighten out and

tighten. When the knee extends, the aMFL is seen to

buckle and become visibly slack.

Conclusions

This paper has given an overview of the gross anatomy of the PCL and MFLs. The movements and tightening–slackening patterns of the fibre bundles help to explain their differential functions in stabilising the knee, particularly against tibial posterior draw, at different angles of flexion. More detailed description of the behaviour of the ligaments may be found in the references listed below.

In the context of reconstructive surgery, the description of the PCL fibre bundles suggests that double-bundled reconstructions are a logical development, but although there is laboratory evidence to support this idea [2, 10, 15, 21], it has not been supported by reports of superior clinical results. Similarly, although the MFLs have been treated as unimportant vestigial structures, now that their function in helping to control posterior laxity has been demonstrated [9], it suggests that maybe they should be preserved if possible, rather than being treated as a nuisance that gets in the way of a PCL reconstruction. The idea that the embrace of the MFLs around the PCL acts to splint it after an isolated rupture is also attractive as a way to

explain the success of conservative treatment of an isolated PCL rupture.