Posterior Cruciate Ligament Tear

Anatomy:

The PCL is attached to posterior part of tibial plateau and ascends anteromedially to the medial aspect of the intercondylar notch. It consists of two functional components: the anterolateral and the postero-medial bundles.

In addition to the anterolateral and posteromedial bundles, there are two meniscofemoral ligaments (MFL) closely associated with the PCL: the ligament of Humphry (anterior) and the ligament of Wrisberg (posterior). The importance of the MFL has not been fully characterised, but they are believed to be significant anatomic and biomechanical structures that provide stability to the lateral meniscus.

Up to 60% of PCL injuries have associated disruption of the posterolateral structures (PLS). These consist of a complex system of static and dynamic stabilisers. Static stabilisers include the LCL, the arcuate ligament complex, the posterior horn of the lateral meniscus, and the lateral part of the posterior capsule. Dynamic stabilisers include the popliteus complex, biceps tendon and the ITB. Associated meniscal injury is rare. Assessment for peroneal nerve injury should be performed.

Biomechanics:

The PCL and PLS work synergistically together.

The PCL has a primary function in preventing posterior tibial displacement, and a secondary role in limiting external valgus and varus rotations. Loss of the PCL results in laxity that is fairly small at full extension and most pronounced at 90º of flexion. Combined PCL and PLS section increases posterior tibial translation at all degrees of knee flexion greater than isolated PCL section. The PLS is a secondary restraint to posterior tibial translation, but becomes important in isolated PCL rupture.

The PLS play a primary role in resisting varus and ER forces. Isolated loss of the PLS increases varus and external rotations maximally at 30-45º but has little effect on these rotations at 90º. Combined loss of the PCL and PLS results in increased translation in these rotations at both 30 and 90º.

Incidence of injury:

The PCL is stronger than the ACL and ruptures less frequently. The incidence of PCL rupture seems to be sports-specific, with injuries occurring more frequently in high contact force sports, and less frequently during sports that involve more pivoting and cutting manoeuvres.

Mechanism:

A direct posteriorly directed force applied to the proximal tibia accounts for 50% of injuries e.g. a direct blow to anterior tibia while the knee is slightly flexed. Hyperextension may result in combined injury- and should be carefully assessed. Hyperflexion usually results in a pure PCL injury, and these do well with conservative treatment. Isolated PCL injuries are less common than combined ligamentous injuries, which are more likely to be caused by a posteriorly directed force applied to the tibia, or a varus or valgus force applied to the hyperflexed knee.

Features:

There is often poorly defined pain, mainly posterior. There is usually minimal swelling, and the patient may present with unsteadiness or discomfort. Retro-patellar pain is common, and more longstanding lesions may have medial compartment pain. A lateral supine x-ray should have alignment of the posterior femur and tibia.

Examination:

The most sensitive test is the posterior drawer test. This test should additionally be performed with the tibia held in IR and ER. A reduction of posterior translation with the tibia IR suggests the presence of an isolated rather than combined injury and has been used to support conservative treatment.

Grade I posterior translation of 1-5mm (anterior tibia in front of femoral condyle)

Grade II posterior translation of 5-10mm (anterior tibia back to the level of the femoral condyle)

Grade III posterior translation of >10mm (anterior tibia behind femoral condyle)

Quadriceps active test: Use the same position as for posterior drawer test. In the PCL deficient knee there is a posterior sag that can be drawn anteriorly by active quadriceps contraction.

Posterior sag test: The knee is positioned in 90º flexion, look across horizon of proximal tibia and will see affected side sag or drop back due to gravity (can also flex hips to 90 degrees and support heels to assess- Godfrey test). May be masked by large effusions or quadriceps spasm.

Laxity on reverse Lachmans is also suggestive. The external rotation tight foot angle (ERTFA) or dial test is performed at 30 and 90º of flexion to test the PLS (the reverse pivot can also be used). Perform prone to compare both legs at once. An increased angle at 30º only suggests isolated PLS injury, while increased angle at both 30 and 90º suggests combined injury.

Treatment:

Isolated Grade I and II PCL injuries may be managed conservatively with good results. (The reason for only operating on grade III injuries is that surgery at best restores the knee back to the equivalent of grade I or II laxity and is not typically useful for grade I/II injuries). Return to sport is in about 6-10 weeks.

Conservative treatment for isolated PCL injuries can result in good objective and subjective outcomes.

Long-term outcome studies have shown that chronic, isolated PCL-deficient knees may deteriorate over time. Some patients go on to develop articular cartilage degenerative changes in the medial and patellofemoral compartment.

Indications for surgery include:

Acute displaced avulsions (usually tibial attachment but can also peel off from femoral attachment) which requires an ORIF and screw fixation. The knee is then splinted for 2-6 weeks before rehab is commenced.

Chronic symptomatic instability (usually a grade III injury).

Ongoing pain

Combined injuries- posterolateral (common) or posteromedial (rare).

Rehab:

The emphasis is on closed chain extension exercises including:

Squats

Leg press

Cycling

Stair –stepper exercises

Open chain extension exercises are avoided early. In general, before rehabilitation, a MRI scan is used to assess meniscal pathology. Athletes commonly return to previous level of sport.

Isolated PCL injuries treatment:

Grades 1 and 2 (partial) injuries = conservative

NWB in extension for 3-4/52

Isometric quads and straight leg raises in brace during this time

ROM from 3-4/52

Mobilise as tolerated from 3-4/52

Closed chain quads

Avoid active hamstring exercises until 6-10/52

Acute grade 3 tears

repair before 3/52 (significant scarring from this time)

6/52 NWB

minimise hamstring activity for 4/12 post-surgery

closed chain quads (cycling) from 6-8/52

leg presses and squats from 3/12

jog from 4/12

Chronic posterolateral complex injuries

normal or valgus alignment – anatomic reconstruction

varus alignment – proximal tibial opening wedge osteotomy – tightens up posterior structures.  Assess at 6/12 to see if second stage posterolateral corner reconstruction is required

Chronic posterior instability:

The patient usually complains of a ‘jelly-like’ feeling in the knee, and doesn’t have episodes of giving way, or effusion in the knee. The posterior drawer may be positive. An emphasis should be made on improving quadriceps and calf muscle strength. PCL reconstruction may be required.

Surgical options for PCL reconstruction

Single bundle – traditional (1 femoral tunnel)

Double bundle – new (2 femoral tunnels)

In theory double bundle produces a tighter fix, however we do not yet know the long-term results of this procedure.

Current consensus = if acute injury use single bundle procedure; if chronic instability use double bundle

Graft options: Quads tendon; Patellar tendon; hamstring; allograft