Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon
MBBS(UK), FRCS(EDIN), FAM(SING), FHKCOS(ORTHO)

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Posterior cruciate ligament injuries

PCL tears of the knee are not very common; they constitute only 5-10% of all major knee ligament tears.

Anatomy
The PCL has an average width of 0.5 in (13 mm) and length of 1.5 in (38 mm). It is fan-shaped, being narrowest in the midportion and fanning out superiorly and, to a lesser extent, inferiorly. The PCL originates on the posterior surface of the tibia and passes superiorly and anteriomedially to insert on the lateral wall of the medial femoral condyle. The PCL consists of a larger anterior band which is taut in flexion and relaxed in extension, and a smaller posterior band which is taut in extension and relaxed in flexion. In 70-100% of knees there is either an anterior or a posterior meniscofemoral ligament (passing from the meniscus to the femur). The posterior meniscofemoral ligament is called the ligament of Wrisberg and is more frequently present than the ligament of Humphrey, which is the anterior meniscofemoral ligament. It should be pointed out that the PCL is an intra-articular ligament (inside the joint), but has an extra-articular (outside the joint) distal insertion.

Biomechanics and function
The PCL is stronger than the ACL. The PCL is relatively taut in extreme extension, but it becomes more slack when the knee is flexed, being most relaxed at about 30° of flexion. With increasing knee angle, the PCL begins to tighten again, being maximally taut in full flexion. The PCL provides 95% of the strength to prevent the posterior movement of the tibia in relation to the femur. Secondary stabilizers are the posterior lateral capsule, popliteus muscle and tendon, MCL, posteromedial capsule, LCL, and midmedial capsule. The proposed functions of the PCL are to resist posterior drawer forces, to resist hyperextension, to limit internal rotation, to limit hyperflexion, and to prevent varus and valgus.

Mechanism of injury
A posteriorly directed force on the upper front of a flexed knee, such as a dashboard injury in a motor vehicle accident, is the most common cause of a PCL injury. In soccer, a player may receive a blow to the anterior proximal surface of the tibia while attempting to slide-tackle an opponent, and thereby force the tibia posteriorly to cause a PCL tear (The PCL may also tear from a fall on a flexed knee while the foot is in plantar flexion. An isolated PCL tear may also occur when the athlete’s knee is forced to hyperflex while the foot is in dorsiflexion. Another mechanism of an acute PCL injury is a sudden, unexpected hyperextension of the knee.Injuries to the PCL are often avulsions and disruptions of the tibial insertion, which have been said to
occur most typically in dashboard and hyperextension injuries. An avulsion from the tibial attachment is more frequent in growing individuals than in adults.

Diagnosis
In athletes with an acute isolated PCL injury, there is only a mild hemarthrosis. Typically there is an increase in pain with flexion beyond 90°. Generally, the swelling and the pain are less than in ACL
injuries. In patients with symptomatic chronic PCL deficiency, there is often patellofemoral pain and recurrent instability to support the diagnosis.

There are several tests that indicate a PCL injury.
– The posterior sag sign is a straight posterior increased displacement of the tibia when the knee is flexed 70-90°.that 90% complained of pain with activities, and 50% had difficulties walking 6 years after injury. Longterm reports with over 15 years’ follow-up indicate osteoarthritis in 80%. This outcome may be activity related. There is patellofemoral osteoarthritis in 62% of cases after 15 years. Poor outcome is correlated with chondromalacia, meniscus injury, quadriceps hypotrophy and degenerative changes in the knee. The proposed natural history in PCL-deficient knees is as follows:
– functional adaptations: 3–18 months;
– functional tolerance with some osteoarthritis development: 15–20 years;
– osteoarthritic deterioration of the knee after 25 years.

Treatment
PCL injuries with bony avulsion
In dislocated PCL bone avulsions, open reduction and internal fixation is the method of choice. Excellent results can be achieved after reattachment with sutures through drill holes or by fixation with screws. Early controlled mobilization in a knee brace is usually possible.
Isolated intrasubstance tears Nonoperative treatment with aggressive rehabilitation is often used for isolated PCL injuries, especially if
the posterior translation is less than 0.4 in (10mm). Conservative treatment includes a brace or splint for comfort for up to 2 weeks, and then early functional rehabilitation. Quadriceps strengthening is important and can compensate for functional PCL disability. Studies indicate that injured knees of conservatively treated athletes may remain posteriorly more lax than the uninjured knee, but the great majority of athletes seem to be functionally stable and are often asymptomatic. Return to full activity following an isolated PCL
injury is possible within 2–8 weeks of injury. The short-term outcome is usually acceptable if a strong quadriceps function can be maintained. If the posterior translation is not prevented with quadriceps activity, the late outcome may be medial compartment and patellofemoral osteoarthritis. Surgical treatment of acute PCL injuries is controversial. If the posterior translation on a drawer test is
more than 0.4 in (10mm), surgery should be considered because it is then likely that secondary stabilizers also have been injured. The indication for surgery is increased if the PCL tear is combined with other ligamentous injuries. The surgical technique is the same as for chronic PCL instability.

Chronic PCL instability
If the athlete in spite of vigorous muscle rehabilitation has functional symptoms of ‘giving way’ or discomfort, or more than 0.4 in (10mm) posterior laxity on the posterior drawer test, surgery should be
seriously considered. Many surgical techniques have been described. The majority have failed fully to prevent some remaining objective clinical posterior instability, with some patients having a persistent
posterior drawer or sag compared with the normal contralateral knee.

The most commonly used grafts for PCL reconstruction are:
1. the patellar or quadriceps tendon from the injured knee;
2. an allograft (graft from a cadaver); today, Achilles tendon allograft is mostly used;
3. augmentation of the existing PCL with the hamstring tendons.

An arthroscopically assisted technique is most commonly used; this is technically demanding and great attention to detail is necessary.
Early motion is usually allowed after PCL surgery, but is usually limited to 0–60° during the first few weeks. Partial weightbearing is usually recommended for 8–10 days and thereafter as tolerated. Isometric
quadriceps exercises are started within the first few days, followed by straight-leg raising as soon as possible. Hamstring muscles should be activated later. Functional activities should start as soon as possible.
However, there is controversy over the best postoperative rehabilitation protocol.Depending on the sport, 75–85% of patients can return to activity in 4–8 months after surgery.

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