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Posterior Cruciate Ligament (PCL) is one of four major stabilizing ligaments of the knee joint. Functionally, the PCL will restrict posterior movement of the tibia or anterior translation of the femur, or a combination of each. The PCL also acts as a pivot point during flexion and extension of the knee joint resisting extremes of varus, valgus, and axial rotation. Between full extension and 30-40 degrees of flexion the PCL is in a slackened position; between 90 to 120 degrees of flexion the tension on the ligament is greatest. As indicative of its name, the PCL attaches to the posterior aspect of the tibia and can be injured by a direct force to the anterior aspect of the tibia causing a posterior translation in relation to the femur.
A PCL injury is classified from grade I to grade III based on the amount of posterior translation of the tibial plateau in relation to the femoral condyles. This can be determined with the posterior drawer test (see orthopedic testing).
- Grade I: There is laxity in the ligament determined by the posterior translation of the tibia but the tibial plateau remains anterior to the condyle.
- Grade II: There is a partial tear of the ligament indicated by the anterior border of the tibial plateau but sits flush with the femoral condyle.
- Grade III: A complete tear of the PCL is likely when the anterior border of the tibial plateau rests posterior to the femoral condyle.
Two bundles make up the PCL. Proximally the PCL has a larger anteriolateral attachment on the medial condyle of the femur forming the bulk of the ligament. The distal attachment is smaller and posteriomedial to the intercondylar eminence of the tibia in the intercondylar sulcus. This arrangement will prevent the tibia from posterior translation under the femur. The anteriolateral bundle is tight in flexion and the posteriomedial bundle is tight during extension.
The meniscofemoral ligaments of Humphrey and Wrisberg attach to the posterior horn of the lateral meniscus and pass on either side of the PCL to insert into lateral aspect of the medial femoral condyle. Studies report that usually only one of these ligaments is present and can often merge with the site of attachment of the PCL.
PCL injuries are rarely an isolated injury and can be difficult to pinpoint solely from a patient’s subjective information. Typically, specific symptomatic complaints are not present when a patient presents with a PCL-deficient knee. The injury is more subtle and is not reported to be accompanied by a popping or tearing sound during trauma like other knee ligamentous stabilizers such as the ACL or MCL. Immediately post injury there will be swelling and pain in the back of the knee. Pain and feelings of instability can also be noted with kneeling or quick directional changes. Over time a patient with a PCL-deficient knee will complain of pain on the anterior aspect of the knee with deceleration or full striding during running or descending the stairs. Overtime pain can become progressive and more localized to the patellofemoral joint due to arthrokinematic changes that take place.
The reported range of the overall incidence of PCL injuries varies due to the variation of studies available coming from small clinic patient databases. However, there is a consistency stating about 45% of all PCL injuries are due to motor vehicle accidents and the rest as a result of high energy sports injury.
Between 2% and 10% of all PCL injuries involving sports related injuries are isolated PCL tears. Otherwise the PCL is often injured along with other knee structures such as the ACL, meniscus, and posterior-lateral capsule. Current literature suggests the incidence of PCL injuries is sport-specific leading with football and followed by other contact sports such as basketball and soccer.
This video is a dramatic reenactment of a PCL injury
When a patient presents with a PCL-deficiency it is through physical examination where you can rule out or determine a combined injury pattern. The mechanism of injury is specific so getting the description of the injury is helpful. If the injury was due to a motor vehicle accident then the patient was likely a front seat passenger and will report that their knees hit the dashboard. Sports related PCL trauma happens when there is a direct blow to the proximal aspect of the tibia with 90 degree knee flexion. If the athlete hit the ground their foot was generally in plantar flexion allowing the tibia to hit the ground first and the direct force will translate the tibia posterior in relation to the femur. In sports like football and soccer the athletes will report being tackled in the lower leg.
With an acute incident the patient will complain of posterior pain and swelling in the knee joint. They may have pain with sharp movements and a loss of range of motion due to the swelling. The patient will have a positive posterior tibial sag sign and will be positive with the posterior drawer test (see diagnostic testing).
Most injuries to the PCL occur with high force trauma to the proximal tibia when the knee is flexed to 90 degrees. It is often associated with passengers who hit their knees along the dashboard during an automobile accident. Other mechanisms of injury occur during contact sports such as football and soccer however the likelihood of an isolated PCL sports related injury is rare. Falling on a fully flexed knee with the proximal tibia taking the direct force of the fall is a likely cause of PCL rupture. In addition, a PCL injury can result from a large valgus-varus or axial rotation torque to the knee when the knee is flexed and the foot is firmly planted on the ground. Yet another mechanism of PCL injury can occur with severe hyperextension of the knee causing a large gapping of the posterior aspect of the knee joint.
Diagnostic Tests 11
MRI is the routine diagnostic protocol used for detecting PCL tears. However, data is limited regarding the reliability and validity of this test due to available research on the PCL. That being said, patients should be advised as to the possibilities of false positives with MRI testing and to not base a decision for reconstructive surgery on the MRI testing alone.
An x-ray should be taken with an acute injure to rule out fractures of the tibial plateau, femoral condyles, and patella.
Posterior drawer and posterior tibial sag sign are two common tests used by physicians and physical therapists when evaluating the integrity of the PCL.
Posterior Drawer Test
Posterior Tibial Sag Sign
An isolated PCL injury is considered to present with the following criteria:
- A posterior drawer of less than 10mm with the tibia in neutral rotation
- Less than 5 degrees of abnormal rotary laxity at 30 degrees of knee flexion
- No significant collateral injury causing varus-valgus laxity.
Conservative Treatment or Surgery Treatment?
Acute grade I and II isolated PCL injuries are managed non-operatively.
2 to 4 weeks of immobilization in extension to decrease tension on the anterolateral aspect of the ligament to allow for maximum intrinsic healing. The brace is fitted with a pad on the inside at the proximal posterior aspect of the tibia to keep the tibia from translating posterior under the femur.
Week 1 - 6
- Decrease inflammation.
- Exercises are completed in prone to maintain the positioning of the tibia.
- Lying passive flexion to maintain range of motion, and avoidance of hamstrings over activity.
- Electrical quadriceps stimulation
6 Weeks - 6 Months
- Quadriceps strengthening with closed-chain exercises.
6 Months - 12 Months
- Return to sport once full quadriceps strength is regained.
Surgery & Post-op Treatment 14
Surgery candidates include grade III injuries that are isolated or with combined instability patterns. Reconstruction surgery is arthroscopic and involves using a replacement graft for the torn PCL ligament. Typically the surgeon will use bio absorbable screws that will eventually dissolve. An allograft is generally used as the replacement ligament decreasing the surgical time and associated surgical pain involved with using an autograft.
PCL ligament reconstruction surgery protocols can vary depending on the repair. Non-weight bearing is always indicated for at least 6 weeks so that early stress is not applied to the graft.
Post Operative Rehabilitaion Protocol
Robert F. LaPrade, M.D., Assistant Professor, University of Minnesota
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