Posterior Cruciate Ligament Pathology
- Author: Matthew Lawless, MD; Chief Editor: Carlos J Lavernia, MD more...
The posterior cruciate ligament (PCL) of the knee has been the subject of many debates. The role of the PCL has become a topic of interest across the subspecialties of trauma, sports medicine, and knee arthroplasty. What, if any, treatment is required for a PCL-deficient knee is still a widely debated topic. See the images below.
The consequences of an isolated PCL injury are poorly understood. PCL reconstruction has been advocated to restore knee kinematics to normal, which decreases the perceived risk of early degenerative joint disease. Although the development of early degenerative disease is controversial and has not been proven with clinical studies, the ability to restore normal knee kinematics with PCL reconstruction has also not been demonstrated in vivo. Thus, the PCL continues to be a topic of research and debate.
History of the Procedure
Many procedures have been described and are mentioned here only for completeness and historical interest. These were nonanatomic reconstructions using transfers of various structures, including the medial head of the gastrocnemius, the popliteus, and the semimembranosus.
Current reconstruction is anatomic with attempts to recreate the posterior cruciate ligament (PCL) in the same manner as is done in anterior cruciate ligament (ACL) reconstruction.
Isolated posterior cruciate ligament (PCL) injuries are defined by the degree of posterior translation of the tibia with respect to the distal femoral condyles with the knee in 90° of flexion. These injuries can be tears in continuity or complete ruptures of the PCL.
Also, 40% of PCL injuries, including grade 1 and grade 2, are isolated injuries. Some have estimated that 51% of PCL injuries are combined with other ligament injuries of the knee, most commonly the medial collateral ligament (MCL).[7, 8, 9] Grade 3 injuries are more likely to be combined injuries. However, many isolated PCL injuries are believed to be undiagnosed. About 2-5% of the participants at a National Football League Combine event were found to have isolated PCL laxity, and most could not recall having a significant injury.
Several mechanisms are responsible for posterior cruciate ligament (PCL) injuries. A direct posterior force on the proximal tibia with the knee flexed is commonly described. This mechanism occurs in dashboard injuries and in falls in which the foot is plantarflexed such that the tibial tubercle strikes the ground first. Hyperextension injuries of the knee are the most common cause of PCL tears from sports participation. Another mechanism related to sports injuries involves the combination of valgus and external rotation forces on a planted but unloaded lower extremity. The axial load of weightbearing is protective.[11, 12]
The posterior cruciate ligament (PCL) is stronger than its counterpart, the anterior cruciate ligament (ACL), and it is less frequently injured.[13, 14] The PCL is the primary restraint to posterior tibial translation between 30° and 90°. At 90°, the PCL accepts 95% of posterior translational forces. The in situ forces of the PCL are 36 N in knee extension and 112 N in knee flexion. Quadriceps and popliteus loading and weightbearing decreases the in situ PCL forces, whereas hamstring loading increases the forces.[17, 18, 19]
Gollehan et al applied a 100 N posterior load to cadaver knees at 90° of flexion and reported that the normal posterior translation was 5 mm. After isolated PCL sectioning, the posterior translation increased to 16 mm, whereas isolated lateral collateral ligament (LCL) and deep ligament complex sectioning increased the posterior translation by less than 3 mm. Sectioning of the PCL combined with sectioning of the LCL and deep ligament complex resulted in 25-30 mm translation; this amount was consistent throughout all positions of knee flexion. The authors concluded that the PCL is the only primary restraint to posterior translation throughout the entire knee range of motion (ROM). Secondary restraints have a decreased role between 60° and 90° of knee flexion. With isolated PCL sectioning, external rotation and varus stability of the knee remained unchanged.
The tensile strength of the PCL is greater than that of the ACL. The ultimate load of the PCL, averaging 1627 N, is also greater than that of the ACL.[14, 21] The contributions to the PCL ultimate load of the anterolateral and posteromedial bundles remains controversial.[21, 22] The stiffness of the PCL averages 204 N/mm.
The importance of the posteromedial bundle in bearing forces throughout knee ROM has been established.[17, 23, 24] Posteromedial-bundle forces have been found to exceed anterolateral-bundle forces in all angles of knee flexion. Codominance of the anterolateral and posteromedial bundles has gained acceptance, instead of anterolateral bundle dominance.
Patients with acute posterior cruciate ligament (PCL) injuries have a presentation similar to that of patients with most other knee injuries. Patients with acute isolated PCL injuries often have minimal symptoms consisting of pain, swelling, and instability. In many cases, a near-normal gait pattern is seen. See the image below.
PCL injury should be suspected at the time of physical examination of any acute knee injury. Complete examinations of the contralateral and injured knees should be performed for comparison. If a PCL insufficiency is noted, care must be taken to evaluate the competency of the posterolateral corner.
With acute isolated PCL injuries, patients typically do not have joint-line tenderness. An effusion may or may not be present. Varus, valgus, and rotational stressing reveal no instability.
The posterior drawer test is the most reliable indicator during physical examination for a PCL injury.[26, 27] Positive posterior drawer test results are graded as follows:
Grade 1: Laxity is noted compared with the contralateral knee, but the tibia remains anterior to the anterior aspect of the femoral condyles.
Grade 2: The anterior tibia can be subluxated equal to the anterior aspect of the femoral condyles.
Grade 3: The tibia subluxates posterior to the anterior aspect of the femoral condyles.
With internal rotation, the posterior drawer test may elicit normal results for a PCL-insufficient knee because of the secondary restraint effect of the meniscofemoral ligaments. If more than 10 mm of posterior tibial translation is noted at 90° of knee flexion, a combined PCL and posterolateral corner injury is present. The posterior drawer test result demonstrates more than 10 mm posterior translation at 30° of knee flexion when the posterolateral corner is disrupted, either in isolation or in combination with a PCL injury.
The dial test helps identify an associated or isolated posterolateral corner injury. Greater than 10° of increased external rotation of the leg compared with the contralateral leg at 30° and 90° of knee flexion is a positive finding signifying a posterolateral corner injury with a PCL injury. A posterior lateral corner injury has increased external rotation at 30 º of flexion that (with PCL injury) stays the same or increases at 90 º of flexion, whereas, at 90 º of flexion without a PCL injury, less external rotation occurs. Care must be taken in evaluating a knee with a positive dial test result to note that the lateral tibial plateau is subluxating posteriorly so that anterior subluxation of the medial tibial plateau secondary to an anteriorcruciate ligament(ACL) and/or medial collateral ligament (MCL) disruption is not misinterpreted.
The posterior sag, quadriceps active, external rotation recurvatum, and reverse pivot shift tests also aid in evaluating an acutely injured knee for PCL pathology. See the images below.
See Medical therapy.
The posterior cruciate ligament (PCL) originates from the junction of the femoral notch roof and the medial femoral condyle roughly 1 cm proximal to the articular surface. The insertion of the PCL is on the posterior aspect of the proximal tibia at the fovea, a depression between the tibial plateaus 1 cm distal to the articular surface. The PCL is an intra-articular ligament but remains extrasynovial.[33, 34] The PCL is just medial to the center of the knee and averages 38 mm in length and 13 mm in thickness. At its origin, the PCL averages 32 mm thickness, is narrowest at its mid substance, and then fans out to an average of 13 mm at its insertion. See the images below.
The PCL consists of 2 bundles, the anterolateral and posteromedial bundles. The anterolateral bundle originates anteriorly and inserts laterally. It is largest at the mid substance and is taut in flexion. The posteromedial bundle originates posteriorly and inserts medially. It is tight in extension and contains a small component that is isometric.[35, 36]
The vascular supply of the PCL depends in large part on the middle geniculate artery. A small component of the nutrient supply of the PCL is contributed by the synovium. Capsular branches of the inferior geniculate and popliteal arteries supply the PCL insertion.
Fibers of the posterior articular nerve, a branch of the tibial nerve, are in the posterior capsule and the synovium lining the cruciate ligaments. At the insertion of the cruciate ligaments, Golgi tendon–like organs are found and may play a role in proprioception.[39, 40]
The meniscofemoral ligaments contribute to the function of the PCL. The ligament of Humphrey is less than a third of the size of the PCL. It traverses anterior to the PCL origin and attaches to the posterior horn of the lateral meniscus. The ligament of Wrisberg is nearly half the size of the PCL. It traverses posterior to the PCL origin and inserts onto the posterior horn of the lateral meniscus.
All other ligament laxities, especially the lateral side, should be addressed. Contraindications to posterior cruciate ligament (PCL) reconstruction include active infection and lack of full motion.
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