Anterior Cruciate Ligament

The anterior cruciate ligament is made up of two bands of fibres lying centrally within the knee joint passing from the front (anterior) to the back (posterior) of the knee. It is commonly damaged in sports such as football, and skiing and is a frequent cause of disability. In partial ruptures there is a potential for resolution. In complete ruptures, some cases will regain stability as a result of the torn end of the ACL finding a new attachment to the PCL. In others stability can be maintained by strengthening the hamstring muscles which partly take over the function of the ACL. However in a third or more of cases stability remains impaired and an ACL reconstruction is indicated. Unfortunately it is not possible to pull the fibres of the ACL back together as it’s such a short ligament in quite a confined space. The only sensible way to proceed is to remove the frayed ends and replace the ligament with new tissue.


Posterior Cruciate Ligament 

The posterior cruciate ligament is considerably thicker and stronger than the ACL and is also made up of two bundles of fibres. These pass forwards from the back (posterior) to the front (anterior) of the knee. It is attached at its lower end to quite a broad area of the back of the upper tibia. This is its posterior attachment. From there it leads upwards and forwards ending up attached to the inner part of the medial femoral condyle which forms its anterior attachment. The two bundles of fibres are aligned so that one band becomes tight in rather more flexion and the other band becomes tight in more extended positions of the knee. Like the ACL the PCL contributes to stabilisation of knee movements so that the joint surfaces of the tibia remain properly aligned to the femur in all stages of knee bend. Without it the tibia becomes unstable in relation to the femur and tends to slide backwards under load. posterior cruciate ligament.

Posterior cruciate ligament injuries are much less common than tears of the anterior cruciate ligament. Where it ruptures alone, posterior cruciate ligament injuries usually do very well with conservative treatment. However it is unusual for it to rupture alone and usually other structure such as the postero-lateral corner are also damaged and where multi-ligament injuries occur they generally require surgical reconstruction.


Medial Collateral Ligament

The medial collateral ligament is on the inner (medial) side of the knee. It is quite a wide ligament that passes from the medial aspect of the upper tibia at a point 4 to 5 cm below the knee. From there it passes upwards to join the medial femoral condyle quite far around the side of the condyle. It also has two bands. The superficial layer which is heavier and broader and a deep layer which is much thinner and which attached to the medial meniscus. The MCL controls sideways movements of the knee and without it the knee tends to give way on the inner side that is the knee goes into a valgus (knock knee) alignment under certain types of loading.

Medial collateral ligament injuries usually do very well treated conservatively and most will settle with support in a knee brace and physiotherapy to maintain knee mobility and muscle power. In rare cases the ligament is so badly damaged that surgical repair is required. However this is usually deferred to assess the extent of natural healing before a decision on surgery is made.


Lateral Collateral Ligament

The lateral collateral ligament is on outer (lateral) side of the knee and is sometimes called the fibular collateral ligament. It is more rounded and slimmer than the MCL and stands further away from the joint than the the MCL which runs quite close to the underlying bone. It is attached at its lower end to the head of the fibula and at its upper end to the lateral femoral condyle slightly towards the back of the condyle. The LCL controls sideways movements of the knee and without it the knee tends to give way on the lateral side, that is, the knee goes into a varus (bow leg) alignment under certain types of loading. It also contributes to the posterolateral corner ligament complex.


Postero-Lateral Corner

The structures of the postero-lateral corner jointly act as a check ligament to control movement of the lateral side of the knee joint. Another name for these structures is the postero-lateral complex reflecting the fact that there are a number of structures that contribute to it. The three main structures involved are the LCL, the popliteus tendon, and the popliteo-fibular ligament. The bony shape of the lateral side of the knee makes it inherently more unstable than the medial side and additional stability is provided by the PLC to control sideways movement, and a combination of external rotation and backwards movement of the outer side of the upper tibia. Without the PLC, the knee tends to be rotationally unstable, that is there is an excessive twisting movement of the tibia under certain types of loading.

A tear of the postero-lateral corner can result in significant rotational instability of the knee and when this occurs surgical reconstruction is often required.


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