Posterior cruciate ligament (PCL), one of four major ligaments of the knee, is situated at the back of the knee. It connects the thighbone (femur) to the shinbone (tibia). The PCL limits the backward movement of the shinbone.
PCL injuries are very rare and difficult to detect when compared to other knee ligament injuries.
The posterior cruciate ligament is usually injured by a direct impact, such as a motor vehicle accident when the knee forcefully strikes against the dashboard or during sports participation when a twisting injury or overextension of the knee can also cause PCL injury.
Injuries to the PCL are graded based on the severity of injury. In grade I the ligament is mildly damaged and slightly stretched, but the knee joint is stable. In grade II there is a partial tear of the ligament. In grade III there is a complete tear of the ligament and the ligament is divided into two halves making the knee joint unstable.
Patients with PCL injuries usually experience knee pain and swelling immediately after the injury. This may also be associated with instability of the knee joint and knee stiffness that causes limping and difficulty walking.
Diagnosis of a PCL injury is made based on symptoms, medical history, and physical examination of the knee.
The doctor may order a few diagnostic tests such as X-rays and MRI scan. X-rays are useful to rule out avulsion fractures where the PCL tears off a piece of bone with it. An MRI scan is done for better visualization of the soft tissues.
Generally, surgery is considered in patients with a dislocated knee and multiple ligament injuries, including the PCL. Surgery involves reconstruction of the torn ligament using a tissue graft taken from another part of the body, or from a donor.
Surgery is usually carried out with the help of an arthroscope, using a few small incisions. The basic steps involved in PCL reconstruction are as follows:
- The surgeon inspects the knee and removes any remains of the native PCL, using an arthroscopic shaver. Care is taken to preserve the ligament of Wrisberg, if it is intact.
- The donor tendon is harvested from the patellar tendon or the semitendonosis and gracilis tendon.
- The soft tissue around the femur is debrided to assist the insertion of the graft.
- A tunnel is created in the femur at the anatomic attachment site of the anterolateral bundle at the anteromedial wall of the itercondylar notch. This tunnel is drilled about 6-8 mm from the articular surface of medial femoral condyle.
- The tibial attachment site is also prepared by identifying the normal attachment of the PCL, at the bottom of the PCL facet.
- For placing the graft, a tibial tunnel is created to the anatomic insertion of the PCL on the tibia.
- Once the tunnels are drilled, the sharp edges and soft tissues around the exit site of the tunnel are smoothed, with a rasp.
- The tendon allograft is inserted in the femoral tunnel and fixed with a cannulated interference screw.
- The graft is made taut distally by removing any slack in the graft.
- The graft is then fixed to the tibia, with the help of staples.
- After fixation, normal posterior stability of the knee is assessed by employing the posterior drawer test.
- The incision is closed with sutures and covered with sterile dressings.
Patients are advised to maintain the knee in full extension, supported by a knee brace, for a period of 2 to 4 weeks. Patients should not bear any weight on the operated knee. Pillows or other supports are placed under the tibia, for the first two months after surgery, to prevent any posterior subluxation of the tibia.
Weight bearing and rehabilitation is initiated after 8 weeks. Crutches are often required until you regain your normal strength.
Risks and complications
Knee stiffness and residual instability are the most common complications associated with PCL reconstruction. The other possible complications include:
- Blood clots (Deep vein thrombosis)
- Nerve and blood vessel damage
- Failure of the graft
- Loosening of the graft
- Decreased range of motion