History
Knowledge of the mechanism of injury is helpful. The following 4 mechanisms of PCL injury are recognized:
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A posteriorly directed force on a flexed knee, eg, the anterior aspect of the flexed knee striking a dashboard, may cause PCL injury.
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A fall onto a flexed knee with the foot in plantar flexion and the tibial tubercle striking the ground first, directing a posterior force to the proximal tibia, may result in injury to the PCL.
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Hyperextension alone may lead to an avulsion injury of the PCL from the origin. This kind of injury may be amenable to repair.
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An anterior force to the anterior tibia in a hyperextended knee with the foot planted results in combined injury to the knee ligaments along with knee dislocation.
In chronic PCL tears, discomfort may be experienced with the following positions or activities:
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A semiflexed position, as with ascending or descending stairs or an incline
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Starting a run
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Lifting a load
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Walking longer distances
Retropatellar pain symptoms may be reported as a result of posterior tibial sagging.
Swelling and stiffness may be reported in cases of chondral damage.
Individuals may describe a sensation of instability when walking on uneven ground
Medial joint line pain may be reported.
Physical Examination
In the acute stage of isolated PCL injuries, symptoms usually are vague and minimal. The following physical examination findings are common in individuals who have sustained PCL injuries:
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Minimal to no pain
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Minimal hemarthrosis
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Usually full or functional range of motion (ROM)
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Contusion over the anterior tibia
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Posterior tibial sag
To observe posterior tibial sag (seen in the images below), place patient supine and put 90 º of flexion at the knee and hip. In such a position, gravity pulls posteriorly on the tibia, and in the case of PCL disruption, the tibia falls even or behind the femoral condyles. Comparison should be made to the opposite knee.
The posterior tibial sag sign. The photo on the left demonstrates the clinical finding of the posterior tibial sag sign. A line drawn parallel to the patella accentuates the posterior tibial sag. The photo on the right demonstrates the quadriceps active drawer test described by Daniels. With the knee in 70-90° of flexion, the extensor mechanism is contracted, pulling the tibia anteriorly into a reduced position.
A close-up view of a posterior tibial sag with an incompetent posterior cruciate ligament.
Grade I injury is indicated when side-to-side asymmetry exists but the tibial plateau is anterior to the femoral condyles. Grade II injury occurs when the tibial plateau is even with the femoral condyles, and grade III injury occurs when the tibial plateau falls behind the femoral condyles.
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Posterior sag sign during extension
The patient is supine on the examining table, with the examiner at the end of the table. The examiner supports both of the patient's heels simultaneously with legs in full extension.
If a posterior sag can be seen on the injured side compared to the other side, there usually is an injury to the PCL and some secondary restraint (ie, medial collateral ligament [MCL], lateral collateral ligament [LCL], posterolateral corner).
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Positive quadriceps active test
During the quadriceps active test, the patient is placed supine with the knee flexed to 90 º and the foot placed flat on the examining table.
If an individual with an intact PCL is in such a position with the quadriceps relaxed, the tibia is 10 mm anterior to the femoral condyles. If there is a PCL disruption, gravity pulls the tibia even or behind the femoral condyles, with the quadriceps relaxed. The examiner restrains the ankle from moving, and the patient is asked to contract the quadriceps. In individuals who have a deficient PCL, the tibia moves forward; if the tibia moves forward more than 2 mm, the quadriceps active test is positive.
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Findings of the posterior drawer test
The posterior drawer test is considered the most useful for documenting PCL injury.
The patient is placed supine with both knees flexed to 90° and the feet in neutral rotation placed flat on the table (examiner must compare side-to-side difference). As mentioned previously, in such a position the tibial plateau should be about 10 mm anterior to the femoral condyles.
The examiner imparts a posterior force to the proximal tibia, and if the tibia can be displaced 0-5 mm or if there is side-to-side asymmetry, a grade I injury is indicated. If the tibia can be displaced 5-10 mm or the tibial plateau can move posteriorly even with femoral condyles, a grade II injury is indicated. If the tibia can be moved more than 10 mm posteriorly or the tibial plateau moves behind the femoral condyles, a grade III injury is indicated.
The internal and external rotation of the foot during the posterior drawer test can assess different structures. If the foot is placed in internal rotation, the PCL and tibial collateral ligaments are tested. If the foot is placed in external rotation, the PCL, LCL, and posterolateral corner are tested. Assessment of the posterolateral corner is paramount with PCL injuries because isolated PCL injuries have a very good prognosis. However, a PCL injury combined with posterolateral corner injury has a less favorable prognosis. The external rotation recurvatum test and the reverse pivot shift test (described below) are used to assess the posterolateral corner.
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Findings of the external rotation recurvatum test: This test is the same as the posterior sag sign described above, except the examiner notices significant subluxation of the lateral tibial plateau.
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Findings of the posterolateral drawer test in 90° of flexion: This test is performed with the patient sitting with thighs supported by the examining table and legs lying off the end of the examining table. In such a position, the knees are at 90° of flexion. The examiner performs a posterior drawer test. If the posterolateral structures are injured, the lateral tibial plateau rotates posteriorly around the axis of the PCL as the posterior force is applied.
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False-positive Lachman test: The Lachman test is performed to assess the integrity of the ACL. In a knee with a deficient PCL, the starting position of the tibial plateau is posterior to normal. Since the starting point is posterior, there seems to be increased anterior laxity. This results in a false-positive Lachman test. The endpoint of the Lachman test is still firm with PCL disruption.
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A normal lateral radiograph of a knee. In a normal knee, a line drawn along the posterior femoral condyle will not intersect the posterior tibial condyle.
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A lateral radiograph of a knee with a posterior cruciate ligament injury. Note that the same line as in the above image will bisect the posterior tibial condyle due to a posterior sag and an incompetent posterior cruciate ligament.
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The posterior tibial sag sign. The photo on the left demonstrates the clinical finding of the posterior tibial sag sign. A line drawn parallel to the patella accentuates the posterior tibial sag. The photo on the right demonstrates the quadriceps active drawer test described by Daniels. With the knee in 70-90° of flexion, the extensor mechanism is contracted, pulling the tibia anteriorly into a reduced position.
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A close-up view of a posterior tibial sag with an incompetent posterior cruciate ligament.
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This MRI of the knee shows a torn posterior cruciate ligament.
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This MRI (coronal section) shows a posterior cruciate ligament tear.
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This transverse MRI shows edema to the torn posterior cruciate ligament.
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A view of the broad origin of the posterior cruciate ligament (PCL) on the medial femoral condyle of a left knee. The anterior cruciate ligament has been removed for surgical reconstruction.
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An additional view of the posterior cruciate ligament broad origin and insertion in a knee pending anterior cruciate ligament reconstruction.
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A right knee pending posterior cruciate ligament (PCL) reconstruction. A minimal notchplasty is completed. Two guide pins are advanced into the medial femoral condyle for tunnel placement to reconstruct the 2 bundles of the PCL.
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The 2 tunnels are created by reaming from outside in; 8- to 9-mm tunnels are made depending on patient size and the graft that will be used.
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Two red Robinson catheters are advanced through the femoral tunnels.
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The catheters have premade holes, which are used for suture retrieval.
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The catheters are advanced and threaded out the posterior knee. In this case, a posterior tibial onlay graft from an Achilles tendon allograft is used. The 2 bundles are secured to the catheters and advanced into the joint through the tunnels.
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The 2 Achilles tendon bundles are secured with a baseball whipstitch, are threaded through the catheter holes, and are advanced into the femoral condyle tunnels.
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Additional view of the placement and advancement of the Achilles allograft.
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Completion and seating of the femoral allograft reconstruction. The 2 bundles are secured or stabilized by suturing over a post and washer. Note the reestablishment of the broad surface area for the reconstructed posterior cruciate ligament origin.
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Completion of the tibial onlay, 2-bundle Achilles tendon allograft/posterior cruciate ligament (PCL) reconstruction. The bony calcaneus remnant is secured to the posterior tibia with 1 or 2 interfragmentary compression screws into a trough into the posterior tibia at the level of the PCL insertion. Care is taken to not penetrate the anterior tibial cortex with these screws. Note the intact original anterior cruciate ligament.
