PCL INJURY

POSTERIOR CRUCIATE LIGAMENT INJURY

The posterior cruciate ligament (PCL) courses from the posterior intercondylar area of the tibia to the medial condyle of the femur.

It gives dynamic stability to the knee by preventing posterior displacement of the tibia on the femur.

The PCL is an extrasynovial structure composed of a large anterolateral portion and a small posteromedial portion.

The PCL resists 85-100% of posteriorly directed forces at 30 º and 90 º of knee flexion.

The 2 bands of the PCL, the anterolateral band and the posteromedial band, have different tension patterns.

The anterolateral band is under great tension during knee flexion, whereas the posteromedial band is under more tension during knee extension.

PATHOPHYSIOLOGY

Posterior cruciate ligament (PCL) injuries are usually the result of a direct blow to the anterior part of the tibia, with a hyperextension moment at the knee.

Biomechanical studies have shown an increase in PCL force with knee flexion and the application of internal tibial torque, while other studies have shown that PCL-deficient knees have greater external tibial rotation.

Several mechanisms have been implicated in PCL injury, including following:

• Posterior translation of the proximal tibia

• Dashboard injuries in motor vehicle accidents (the most common mechanisms)

• Falling on a flexed knee (the most common injury in sports, particularly in wrestling and football)

• Forced hyperflexion of the knee joint

• A posterior force applied against a hyperextended knee with the foot fixed

• Forced hyperextension of the knee

FREQUENCY

There is a variable incidence of posterior cruciate ligament (PCL) injuries in the US population.

In a retrospective study by Schulz and colleagues, 33% of the injuries were sports related. As many as 20% of all knee ligament injuries

consisted of PCL trauma.

MORTALITY/MORBIDITY

Chronic posterior cruciate ligament (PCL) deficiency can cause or predispose individuals to these pathologies: (1) medial compartment osteoarthritis of the knee, (2) increased risk for meniscal injury, and (3) patellofemoral osteoarthritis.

AGE

In Schulz's study, the mean age at which posterior cruciate ligament (PCL) injury occurred was 27.5 years ± 9.9 years.

CLINICAL

HISTORY

Pain and limited range of motion (ROM) after an injury are the most common symptoms of posterior cruciate ligament (PCL) trauma with associated ligamentous injuries.

The associated ligamentous injuries occur about 95% of the time. In isolated PCL injuries, patients may have symptoms of mild swelling, discomfort, and knee stiffness.

Knee instability is uncommon in injuries isolated to the PCL. Patients with grade 2 injuries are able to perform gait and drop-landing activities.

PHYSICAL

The posterior drawer test performed with the knee at 90 º is the most sensitive test for detecting posterior cruciate ligament (PCL) injury.

The change in the step off from 1 cm (normal) from the medial tibial plateau anterior to the medial femoral condyle is absent, as compared with the healthy knee.

This test is 90% sensitive and 99% specific in the diagnosis of PCL injury.

Grading the injury on examination may be performed by using the following scale:

• Grade I injury - Step off present but decreased (ie, 0-5 mm)

• Grade II injury - 5-10 mm of posterior translation

• Grade III injury - Greater than 10 mm of posterior translation

Decreased ROM may be observed, as compared with the ROM of the other knee. The injured knee may lack only 10-20 º of flexion.

Adjuvant tests can increase the sensitivity for diagnosis of PCL injuries.

These include the quadriceps active test, the dynamic posterior shift test, the posteromedial and posterolateral instability test, the posterolateral drawer test, the reverse pivot shift test, and Godfrey (posterior sag) test.

In the posterior sag test, the patient is asked to flex both knees and hips at 90 º while lying in the supine position. The examiner holds both heels and legs. Posterior tibial translation is an indication of an injured or insufficient PCL.

In the quadriceps active test, the knee is flexed at 60 º and the foot is secured by the physician.

The patient is asked to extend the knee isometrically, and if the PCL is injured or absent, the tibia translates anteriorly from a subluxed position. This motion creates a medial tibial plateau step off. The sensitivity of this test was reported to be 58%, with a specificity of 97%.

In the dynamic posterior shift test, the patient is asked to extend the knee from 90 º of flexion to full extension.

The patient is asked to keep his/her hip at 90 º of flexion. A positive result occurs when the tibia reduces with a click near full extension.

In the reverse pivot shift test, a valgus load is applied to the knee. The foot is also externally rotated while the knee is extended from a flexed position. If the posteriorly subluxated tibial plateau abruptly shifts back to the reduced position, the result is positive. This test is 95% specific but is only 26% sensitive.

CAUSES

In Schulz's study, the most common causes of posterior cruciate ligament (PCL) injury were motor vehicle accidents (45%) and athletic injuries (40%), with motorcycle accidents (28%) and soccer-related injuries (25%) making up the main specific causes of such trauma.

Dashboard injuries (35%) and falls on a flexed knee with the foot in plantar flexion (24%) were the most common injury mechanisms.

DIAGNOSIS

LABORATORY STUDIES

·        Complete blood cell (CBC)

CRP

CMP

IMAGING STUDIES

• Magnetic resonance imaging (MRI) has high sensitivity and specificity in the diagnosis of posterior cruciate ligament (PCL) injury. MRI is found to be 80% sensitive and 97% specific in the diagnosis of complete PCL tears. MRI can also yield information about the extent of the injury.

• For direct visualization of the PCL, diagnostic arthroscopy can be performed.

OTHER TESTS

If effusion is present, knee aspiration should be conducted to rule out causes of effusion other than posterior cruciate ligament (PCL) injury.

PROCEDURES

After aspiration of the knee joint, injection with a steroid may be considered if oral medications are not effective in pain management.

HISTOLOGIC FINDINGS

The posterior cruciate ligament (PCL) is composed of type I collagen. Electron microscopy has demonstrated that the mean fibril cross-sectional area decreases in diameter from the proximal to the distal portion of the PCL.

TREATMENT

PHYSICAL THERAPY

The top priority in the rehabilitation of posterior cruciate ligament (PCL) injury is the restoration of knee function to normal or to as close to normal as possible.

       The treatment of PCL injury depends on the grade of the injury.

An isolated injury of grade I or grade II may be treated with physical therapy.

A grade I or grade II injury is usually treated with a brief period of knee splinting in extension, followed by early ROM and a quadriceps and hamstring strengthening program (that is particularly eccentric).

Recovery is quick, and many patients are able to return to normal function in about 4 weeks. Closed kinetic chain exercises and open kinetic chain exercises are recommended.

The use of continuous passive motion (CPM) machines for early knee mobilization is an option. A good outcome is correlated with the maintenance of good quadriceps strength.

The postoperative protocol includes the use of a knee brace in extension, with weight bearing as tolerated for 4 weeks, as well as the use of quadriceps strengthening exercises.

Later, closed chain exercises are performed at 6 weeks, and proprioceptive training is carried out at 12 weeks.

Hamstring exercises are delayed for 4 months to decrease the posterior load on the tibia.

Patients can begin light jogging at 6 months.

Cycling and aerobic exercise can also benefit the patient and can help to restore function.

With a multidisciplinary approach and the use of various modalities, such as ice and heat therapy, a good outcome is expected.

Weight training and proprioceptive techniques also show good results in rehabilitative treatment.

SURGICAL INTERVENTION

Grade III posterior cruciate ligament (PCL) injuries may need surgical intervention.

Tibial avulsion fractures with a PCL injury also require such intervention. Because of the complexity of biomechanical tensions, reproducing the function of the PCL complex is difficult.  

Suture repair of insertion site avulsions is effective if it is performed less than 3 weeks after the injury. Non absorbable sutures are placed through the avulsed ligament and tied over the bone bridge. Unfortunately, the results are often unsatisfactory.

Other surgical techniques can rely on a single or a double reconstruction technique.

In the single bundle reconstruction technique, a hamstring patellar tendon or Achilles allograft is passed through the tibial tunnel into the femoral tunnel in single bundle technique.

Studies have shown that this technique can result in an improvement in the patient's symptoms. In one study, statistically significant improvement (P = .001) from the preoperative condition was found at 2- to 10-year follow-up evaluations.

In the double bundle reconstruction technique, 2 femoral patellar tunnels are used to recreate the functional activity of the 2 bands in the injured PCL. Two grafts are placed. A larger anterolateral graft is placed at 90º of flexion. A posteromedial graft is placed in knee extension to provide posterior stability.

OTHER TREATMENT

If patients who develop knee pain are willing to try acupuncture treatment, this therapy may be considered. However, data do not show long-term relief from acupuncture use.

More research into this modality, including the conduction of double blind, placebo-controlled studies, is needed. Studies have shown that

transcutaneous electrical nerve stimulation (TENS) units and ultrasonographic treatment are effective in pain management.