Posterior crutiate ligament injuries

Can I damage this ligament easily?

The posterior cruciate ligament is the largest ligament in the knee and therefore is not torn as often as are the other ligaments (the anterior cruciate or medial collateral ligaments). It is also implied that a larger force is required to injure this ligament.

How does this particular ligament become injured?

The ligament can be injured in isolation or in combination with other ligaments. When damaged in isolation this can occur in one of two ways. Firstly, as is generally the case in sport, the knee can be flexed up (bent) beyond its normal limits. Secondly, a dashboard type injury may be sustained in which a direct blow to the upper tibia (shinbone) with the knee flexed, drives the tibia posteriorly (backwards) behind the femur (thighbone), thus exceeding the limits normally set by this ligament.

The ligament may also be torn in association with other ligaments, often the anterior cruciate and one of the collateral (side) ligaments. This generally is a direct impact injury of considerable force and fortunately is not common. When it occurs however, it represents a form of true knee dislocation.

The normal anatomy is depicted above. The cruciate ligaments and the collateral ligaments provide stability to the joint. The menisci (meniscal cartilages) function as shock absorbers and they also enhance joint lubrication and nutrition of the articular cartilage as well as providing some stability to the knee joint. The articular cartilage lines the inside of the knee joint and allows for its smooth movement.

Unlike the anterior cruciate ligament, injuries to the posterior cruciate ligament are usually not associated with a popping or tearing sensation in the knee. Also as the ligament is outside the actual cavity of the knee joint there may not be much swelling within the joint itself. Again, unlike the anterior cruciate ligament, the ligament is frequently only partially torn and is less often associated with tears of the meniscal cartilages.

Despite the size of the posterior cruciate ligament, in general, the injury is less significant to the stability of the knee than is an injury to the anterior cruciate ligaments. The knee usually does not give way and often, with a good rehabilitation programme to strengthen ther quadriceps muscle (muscle at the front of the thigh), a good functional knee can result. Unfortunately however, some patients do develop problems of increased wear under the patella (kneecap), which is due to the posterior sag of the tibia. This is difficult to prevent and because it is not possible to predict or get this, early operation is not generally recommended. The other complication that is seen, again unpredictably and unfortunately less commonly is wear and tear arthritis of the inner half of the knee. This is also is not sufficiently common to advocate an early operation in most people.

POSTERIOR CRUCIATE LIGAMENT RECONSTRUCTION

As the ligament does not heal well and is not readily repairable sometimes reconstruction is considered. This may be done soon after the injury in cases where other ligaments have also been torn and where it is considered that the posterior cruciate ligament is essential to act as a restraint against which other ligaments can work to control the stability of the knee and to prevent it from giving way.

It is also possible to reconstruct this ligament at a later date and this generally occurs either when the absence of this ligament alone is thought to be the cause of the knee instability (which is uncommon) or when the anterior cruciate ligament has to be reconstructed and this requires a good posterior cruciate ligament to function properly.

Reconstruction of the posterior cruciate ligament is probably the most difficult and demanding operation in knee surgery today and whilst our knowledge of this ligament has greatly increased in recent years, only recently with the advent of newer techniques has the operation started to become successful. Because of this difficulty and because of the problem of achieving consistently good results this operation is currently reserved for the more severely injured knees.

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