eMedicine Specialties > Sports Medicine > Knee

Posterior Cruciate Ligament Injury

Charles S Peterson, MD, Consulting Staff, Arizona Sports Medicine Center
Thomas Agesen, MD, Assistant Clinical Professor, UMDNJ, New Jersey Medical School; Consulting Staff, Department of Physical Medicine and Rehabilitation, Mountainside Hospital, Summit Overlook Hospital; Janos P Ertl, MD, Clinical Assistant Professor, Department of Orthopedic Surgery, Chief of Orthopedic Trauma, University of California at Davis; Director of Amputee Clinic, Kaiser Hospital; Gyorgy Kovacs, MD, Department of Orthopedic Surgery, Consulting Surgeon, GOC Clinic
Contributor Information and Disclosures

Updated: Dec 22, 2006

Introduction

Background

The posterior cruciate ligament (PCL) is described as the primary stabilizer of the knee by many authors. PCL injuries are less common than anterior cruciate ligament (ACL) injuries, and they often go unrecognized. The PCL is broader and stronger than the ACL and has a tensile strength of 2000 N. Injury most often occurs when a force is applied to the anterior aspect of the proximal tibia when the knee is flexed. Hyperextension and rotational or varus/valgus stress mechanisms also may be responsible for PCL tears. Injuries may be isolated or combined with other ligamentous injuries. A PCL tear can result in varying degrees of disability, from no impairment to severe impairment.  PCL injury has been overly simplified, and the functional disability of PCL injury may be underestimated (Wang, 2002). 

The primary function of the PCL is to prevent posterior translation of the tibia on the femur. The PCL also plays a role as a central axis controlling and imparting rotational stability to the knee. This injury has received little attention in the past, compared with the ACL; however, this emphasis on the ACL has stimulated increased interest in the treatment of PCL injuries. Controversy regarding treatment of isolated PCL injuries exists in the literature, with recommendations supporting both operative and nonoperative therapy. Current management of PCL injuries unfortunately can yield relatively poor clinical outcomes, whether surgically or conservatively treated (Margheritini, 2002).

Frequency

United States

True incidence in the United States is unknown. In National Football League predraft physical examinations, a 2% incidence of isolated, asymptomatic, and unknown PCL injuries was found; operated, isolated, and combined PCL injuries were reported at an incidence of 3.5-20%. On the KT-1000 stress test examination, a 7% incidence of PCL injuries was found, of which 40% were isolated and unidirectional and 60% were multidirectional.

Functional Anatomy

The PCL originates from the intercondylar notch of the femur on the roof of the medial femoral condyle. The insertion is central on the posterior aspect of the tibial plateau, on a depression between the tibial plateaus, extending 1 cm below the articular surface (Sheps, 2005). The ligament is composed of a larger anterolateral bundle and a smaller posteromedial bundle. The anterior component is tightest in the midarc of flexion and the posterior fibers are tight in extension and deep flexion.

In addition, variable anterior and posterior meniscofemoral ligaments of Humphrey and Wrisberg attach distally and proximally to the PCL, respectively. The meniscofemoral ligaments attach distally to the posterior horn of the lateral meniscus, in a slanting orientation, providing resistance to the tibial posterior drawer (Amis, 2006). The PCL is an extrasynovial structure that lies behind the intra-articular portion of the knee. The primary function of the PCL is to resist posterior displacement of the tibia in relation to the femur; its secondary function is to prevent hyperextension and limit internal and varus/valgus rotation.

Sport Specific Biomechanics

Disruption may occur with forced hyperextension while the foot is planted in dorsiflexion. A force applied to the anteromedial aspect of the knee, as during a football tackle, results in a posteriorly directed force and a varus hyperextension force, leading to PCL and posterolateral capsular ruptures.

Clinical

History

• Knowledge of the mechanism of injury is helpful. The following 4 mechanisms of PCL injury are recognized:
• • A posteriorly directed force on a flexed knee, eg, the anterior aspect of the flexed knee striking a dashboard, may cause PCL injury.
  • 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.
  • Hyperextension alone may lead to an avulsion injury of the PCL from the origin. This kind of injury may be amenable to repair.
  • 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:
• • A semiflexed position, as with ascending or descending stairs or an incline
  • Starting a run
  • Lifting a load
  • 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

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:

• Minimal to no pain
• Minimal hemarthrosis
• Usually full or functional range of motion (ROM)
• Contusion over the anterior tibia
• Posterior tibial sag
• • To observe posterior tibial sag, place patient supine and put 90° 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.
  • 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.
• 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).
• Positive quadriceps active test
• • During the quadriceps active test, the patient is placed supine with the knee flexed to 90° 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.
• 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.
• 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.
• 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.
• 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.

Causes

Possible causes of PCL injuries include the following:

• Football injuries
• Running injuries
• Motor vehicle accidents
• Falls onto a flexed knee

References

• Anterior Cruciate Ligament Injury
• Lateral Collateral Knee Ligament Injury
• Medial Collateral Knee Ligament Injury
• Meniscus Injuries
• Talofibular Ligament Injury

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