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Posterior Cruciate Ligament Injury
Updated: Jan 12, 2010
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.1 The radiographs belowdemonstrate the results of suchinjuries, comparing a normal knee with one that has a damaged PCL.
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.
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.
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.2
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
As demonstrated in the images below, 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.3 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.
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.
An additional view of the posterior cruciate ligament broad origin and insertion in a knee pending anterior cruciate ligament reconstruction.
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.4 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
The recovery phase discussed here encompasses treatment from 2-12 weeks. The goal of this phase, in higher-grade injuries, is to advance weight bearing and achieve a normal gait pattern, along with a progression of functional strengthening and ROM. For those patients who undergo graft reconstruction, it is especially important to protect the graft during this period, as it is at its weakest state in the healing process.
Nonoperative rehabilitation (weeks 2-12)
- Only patients with grade III injuries should continue to wear a brace (0-60°) until at least the third week of therapy. Shortly thereafter, the patient may be fitted for a functional knee brace.
- Weight bearing may be progressed as tolerated, and the crutches may be discontinued at approximately 2-3 weeks.
- At 2-3 weeks, the exercises performed in the acute phase should be progressed with light resistance as tolerated. Stationary bicycling may be recommended for improving ROM. Aquatic exercises may be recommended to improve ROM and strengthening. As the patient progresses into weeks 3-6, the exercises may be progressed to include closed kinetic chain (CKC) exercises (eg, leg press, mini squats, stair stepper, step-ups). Resistance may be increased on the bicycle as tolerated. At 8-12 weeks, the strengthening exercises should be progressed and a light jogging program may be initiated.
Operative rehabilitation (weeks 2-12)
- The patient gradually should improve ROM (0-130°) during this time. Passive stretching is used as necessary to regain mobility. Patellar mobilization continues to be important. Modalities may be continued as needed for pain and swelling.
- Weight bearing is progressed as tolerated, and crutches are discontinued at the discretion of the physician.
- At 4-6 weeks, the patient may be fitted for a functional knee brace.
- Strengthening exercises may be progressed to include CKC exercises. Aquatic resistance training may be initiated during the later part of this phase.
The maintenance phase (4 mo to 1 y) is the final phase of rehabilitation. This phase prepares the athlete for return to competition. Goals are focused on increasing strength, power, and endurance.
Nonoperative rehabilitation (4-9 mo)
- Strengthening and proprioception exercises are continued and progressed as tolerated. Plyometrics and sport-specific training should be initiated and accelerated as tolerated.
- A running program is developed, and agility drills are incorporated.
- An isokinetic test and a KT-2000 test should be performed at 3-month, 6-month, 9-month, and 12-month follow-up visits.
- The athlete may return to sporting activities when isokinetic and functional tests are satisfactory (determined by the physician), in addition to satisfactory clinical examination findings. The patient should not return to competitive sports until full quadriceps strength has been reestablished.
- Prospective long-term follow-up studies comparing operative versus nonoperative outcomes are lacking. However, nonoperative treatment has demonstrated the following results:
- After completing the rehabilitation program, 68% of patients return to their previous level of competitive function.
- Radiographic signs of arthritis show up in 31% of patients.
- At the time of arthrotomy, 64% of patients had degenerative medial compartment changes.
- Significant degenerative changes developed in 44% of patients.
- In patients with PCL deficiency for more than 5 years, 77.8% develop medial femoral condyle degenerative cartilage lesions and 46.7% develop patellar cartilage degeneration.17
- Operative intervention is required in 42% of patients.
Operative rehabilitation (4 mo to 1 y)
- Functional strengthening, as well as balance and proprioception, is progressed.
- Light jogging may be progressed to running and various agility drills as tolerated. Advanced plyometrics and sports-specific training should be incorporated.
- Isokinetic strength and KT-2000 testing often are performed; however, the necessity of these tests has not been validated to affect outcome.
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 (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.
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- 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.
- 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.
- 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 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.
- 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.
A subsequent, prospective study with a mean follow-up of 5.4 years found that 50% of athletes with isolated posterior laxity returned to the same sport at the same or higher level of performance and that 33% returned to the same sport at a lower level of performance (no patient had greater than grade II injuries). In addition, the grade of laxity noted on physical examination did not change over the course of follow-up, and the grade of laxity did not correlate with radiographic joint-space narrowing.
Another study involving MRI follow-up imaging found that all low-grade and midgrade PCL injuries healed with continuity, and 19 of 22 high-grade injuries healed (4 healed with normal contour; 15 healed with continuity and altered morphology). In many cases that involve less severe PCL tears, patients are recommended to undergo conservative therapy with a progressive rehabilitation program. However, if the patient continues to experience chronic pain and instability despite therapy and functional bracing, a PCL reconstruction may be required. The choice of which route of treatment depends on the severity of the specific injury, whether the PCL injury is isolated or in combination with other ligamentous or meniscal damage, the activity level and goals of the patient, and the individual physician preference. The stages of physical therapy are discussed here and are broken into the following 2 types of rehabilitation: nonoperative and operative (ie, PCL reconstruction).
Nonoperative rehabilitation (day 1 to week 2)
Many isolated PCL injuries are missed at the time of the initial injury. The patient often cannot remember injuring the knee and often seeks medical attention at a later time. The pain, degree of swelling, and disability associated with ACL and MCL injuries is often missing from the patient’s history. Many are able to walk with normal gait immediately after the injury, and the soft endpoint of the posterior drawer test is firm by 2-3 weeks after injury (though more laxity is noted when compared to the uninjured knee). With higher-grade injuries, usually grade III +/- other ligamentous injury, the patient typically seeks medical attention immediately. In such cases, the physician should order an MRI to evaluate all the knee ligaments and assess for subchondral injury or further intra-articular pathology.
The goal of the rehabilitation for individuals undergoing a conservative program is to control the initial inflammatory phase and regain ROM with muscle function as quickly as possible.
- Apply the rest, ice, compression, and elevation (RICE) method several times a day, in addition to any other modalities incorporated by the physical therapist to control pain and swelling (eg, electrical stimulation, cold whirlpool).
- Patients with grade I and grade II injuries can bear weight as tolerated immediately, though some may require axillary crutches initially. Axillary crutches and a long leg brace are recommended for grade III injuries and with other associated ligamentous laxity (ie, posterolateral corner injury) or intra-articular damage.
- Functional electrical stimulation (FES) may be used to stimulate the quadriceps muscle, but it is probably necessary only if the quadriceps muscle is shut down secondary to pain.
- The physical therapist should instruct the patient in exercises for quadriceps and hip strengthening (eg, quadriceps sets, straight leg raises, hip abduction/adduction, multiangle quadriceps isometrics).
- At this time, all open kinetic chain (OKC) hamstring exercises should be avoided since they impart posterior tibial translation at the knee.
Operative rehabilitation (day 1 to week 2)
Several different techniques may be used to reconstruct the PCL, so the treatment protocol is determined by the individual physician and the type of graft used in surgery.
- Postoperatively, it is very important to control pain and swelling through the use of cold therapy, compression, and elevation.
- The patient may bear weight as tolerated on the operated limb with the use of 2 crutches and a long leg brace.
- Patellar mobility is important, and the patient should be instructed in self-mobilization exercises for the patella, scar, and soft tissues surrounding the kneecap to prevent fibrosis.
- ROM should be initiated (0-90°), emphasizing full passive knee extension. Other examples of exercises that may be initiated include quadriceps sets, ankle pumps, straight leg raises, and upper body strengthening.
Causes
Possible causes of PCL injuries include the following:
- Football injuries
- Running injuries
- Motor vehicle accidents
- Falls onto a flexed knee
More on Posterior Cruciate Ligament Injury |
 Overview: Posterior Cruciate Ligament Injury |
| Differential Diagnoses & Workup: Posterior Cruciate Ligament Injury |
| Treatment & Medication: Posterior Cruciate Ligament Injury |
| Follow-up: Posterior Cruciate Ligament Injury |
| Multimedia: Posterior Cruciate Ligament Injury |
| References |
| Further Reading |
| Next Page » |
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Further Reading
Clinical guidelines:
Knee & leg (acute & chronic). Work Loss Data Institute - Public For Profit Organization. 2003 (revised 2008 May 7). 289 pages. NGC:006561
Review criteria for knee surgery. Washington State Department of Labor and Industries - State/Local Government Agency [U.S.]. 1991 Jan (revised 2004 Jan). 7 pages. NGC:003482
Keywords
posterior cruciate ligament injury, cruciate ligament, knee ligament, ligament injury, posterior cruciate ligament, anterior cruciate ligament, ligament tear, cruciate ligament injury, PCL injury, PCL tear, torn PCL, torn cruciate ligament, posterior knee instability, posterior laxity of the knee
