Posterior Cruciate Ligament

It took Ryan Shulman 10 years to discover he had damaged his knee

My visit to the Brisbane Orthopaedic and Sports Medicine Clinic was the culmination of more than 18 months of physiotherapy, general practice and orthopaedic reviews. I had developed an interest in triathlon and wanted to get serious about training, particularly some longer distance running. However, after increasing my training load and intensity I had started to develop a vague pain along the antero-medial joint line in my right knee, as well as spasm in my right popliteus muscle.

I attempted to train through the pain (being a physiotherapist and a doctor the old axiom of ‘do as I say, not as I do’ clearly rings home here). The symptoms worsened to the point where I had to rest from any training that involved my lower limbs. I could not cite any recent incidents or particular training sessions to which I could attribute the onset of the pain. Even back to my high school rugby and basketball days, I’d never had to stop play because of knee pain.

Visits to numerous therapists and my general practitioner resulted in not much more than some trigger-point and anti-inflammatory therapy. I was referred to a local orthopaedic surgeon for assessment. After 15 minutes he seemed as dismayed as I was about the cause of the pain.

An MRI at this time noted some sub-articular oedema in the medial femoral condyle, suggesting past trauma, which as I’ve noted was inconsistent with my history. It was also noted that both the anterior and posterior cruciate ligaments were intact.

I persevered with physiotherapy and antiinflammatories and managed to compete in about five triathlons over the next 12 months. But the pain worsened and I asked for a referral to Peter Myers, a reputable, more experienced knee surgeon who works in Brisbane.

He noted that I had some wasting of my quads on the right and had a subtle loss of flexion range at the right knee. It was when he noted the extra anterior-posterior play of my right knee compared to the left that he asked me when I’d ruptured my posterior cruciate ligament.

The posterior cruciate ligament (PCL)

The posterior cruciate ligament (PCL) consists of two main bundles of fibres that act primarily to prevent posterior translation of the tibia on the femur. It runs from the posterior intercondylar notch of the tibia, medial to the anterior cruciate ligament (ACL), to attach to the lateral surface of the medial condyle. Compared to the ACL, the posterior cruciate ligament (PCL) has a shorter, more central and less oblique course that confers a secondary role of preventing hyperextension and varus/valgus rotation.

The posterolateral corner

The posterolateral corner of the knee (see figure 1) comprises the iliotibial tract, biceps femoris, fibular collateral ligament, the middle third of the lateral capsular ligament, the popliteus muscle complex, and the lateral head of gastrocnemius. Poorly understood by many practitioners, it serves a vital role in preventing external rotation of the knee joint as well as minor roles in antero-posterior translation of the tibia (failure to address a posterolateral corner injury that occurs concurrently with a cruciate injury leads to increased stress on a surgical reconstruction and may ultimately cause graft failure).

Figure 1: the posterolateral corner of the knee

How the posterior cruciate ligament (PCL) gets damaged

Isolated posterior cruciate ligament (PCL) injury is usually caused by a direct antero-posterior force to the tibia when the knee is flexed. Most commonly this occurs in motor vehicle accidents when the tibia strikes the dashboard of a car. However, sports-related injury occurs when an athlete falls on to a flexed knee with the ankle plantarflexed, so that the tibial tuberosity takes the force of the fall. This drives the proximal tibia back, rupturing the posterior cruciate ligament (PCL). Hyperextension and hyperflexion of the knee are also known to cause posterior cruciate ligament (PCL) injury.

Acute injury

These injuries are infrequent and are thus easily missed, as symptoms may be vague and attributed to muscular strains. Clinically there may be abrasions or signs of contact on the front surface of the tibia, bruising at the rear (from capsular rupture) and flexion range limited by pain. Often capsular rupture means there will be no evidence of significant joint effusion. Posterior sag of the affected knee and a positive posterior drawer test are indicative of posterior cruciate ligament (PCL) injury. If the forces were large enough to affect the posterolateral corner, neurovascular symptoms may also be noted. Increased external tibial rotation of the affected knee will demonstrate the degree of injury to the posterolateral structures.

Chronic injury

The literature on the natural history of posterior cruciate ligament (PCL) rupture is varied and confusing. Many patients describe a vague medial to antero-medial joint line pain with or without patellofemoral symptoms. Many, as in my case, will not be able to provide details of their injury, making diagnosis difficult.

However, the long-term pathology is based on the biomechanical changes associated with loss of the posterior cruciate ligament (PCL). Apart from increased stresses on the menisci, collateral ligaments and posterolateral structures, a posterior cruciate ligament (PCL)-deficient knee may result in these main functional difficulties for the athlete:

• Degeneration of the medial femoral condyle
  Restraint of posterior tibial translation is lost, so the medial femoral condyle fails to contact the contoured, shock absorbing posterior medial meniscus and moves forward on to the flat and less forgiving tibial plateau (a ‘fixed’ anterior subluxation of the medial femoral condyle). This decreases the area of contact, thereby increasing the load and predisposing the femur to degenerative chondral damage.
• Patellofemoral degeneration
  Increased posterior tibial translation will also increase the load placed on the patellofemoral joint. As the attachment of the patella tendon is now further back than pre-injury, the resultant force is more compressive which predisposes to degenerative damage to the trochlear groove of the patellofemoral joint.
• Instability
  Reports of instability vary among patients. Usually those with isolated injuries and good quadriceps and hip control report fewer problems.

Imaging

Magnetic resonance imaging (MRI) remains the gold standard in almost all soft-tissue damage, particularly acute injuries. One recent study claims that MRI of posterior cruciate rupture, read by experienced musculoskeletal radiologists, has a diagnostic accuracy of 96%, though the sample size was small and no information was given regarding the nature of the injury (ie acute vs chronic). Most acute cruciate injuries show a pattern of bone bruising that radiologists can use to assist diagnosis. But another study highlighted the decreased accuracy of MRI with chronic posterior cruciate ligament (PCL) injury, with an average diagnostic accuracy of 57%. This was attributed to the process whereby the injured ligament heals (and thus appears intact), but in a lengthened or lax state.

My MRI showed an intact posterior cruciate ligament (PCL), but its laxity wasn’t picked up for 18 months. My MRI also showed chronic medial femoral and patellar trochlear degeneration (but these were not picked up).

Treatment

• Conservative
  If the injury is detected early, conservative management can include a knee brace that maintains knee extension for four to six weeks. This is intended to minimise stresses on the damaged ligament. It should be accompanied by appropriate pain relief, taping, massage and isometric quads exercises to minimise wasting. Rehabilitation involves the isolated training of quadriceps, hip and core stability muscles, with graduated return to activity. Hamstring strengthening should be avoided, particularly in the early stages as the hamstrings act to accentuate the anterior subluxation of the femoral condyle. It is common to encourage hamstring training, as this is part of ACL rehab, but for posterior cruciate ligament (PCL) injury it is a mistake.
• Operative
  Avulsion injuries are indicators for early surgical intervention, with the avulsed fragment being internally fixed and the patient braced post-operatively.

Reconstruction of the posterior cruciate ligament (PCL) is controversial. Whereas reconstruction is used to minimise the degenerative changes that have been shown to develop in an athlete’s ACL-deficient knee, there is little evidence to suggest that repairing the posterior cruciate ligament (PCL) confers such protection. Pain with instability is the primary indicator for posterior cruciate ligament (PCL) reconstruction.

As mentioned above, highly unstable knees (those with posterior cruciate ligament (PCL) and posterolateral corner injuries) need reconstruction of both structures to ensure better outcomes. One- or two-bundle grafts are used, usually from hamstrings, but sometimes from patellar or Achilles tendons. As with ACL reconstruction, physiotherapy plays a role in pre-habilitation as well as working with the surgeon’s preferred post-operative regimen.

My knee

After some consideration I remembered an incident from roughly 10 years previously: I had been tripped during a lunchtime football game. I’d landed on my knee and was sore for a few days, but it was nothing that slowed me down much at age 14.

My knee was relatively stable; I was in pain because of the chondral damage, so I opted for an arthroscope to tidy up the medial condylar and femoral trochlear damage. The femoral damage received microfracture in an attempt to fill the defect, which also meant a much shorter rehab schedule. I did not have a posterior cruciate ligament (PCL) reconstruction.

Just to prove that physiotherapists/ doctors make the worst patients, it took me about six months to really begin working hard on rehab (work and exam commitments – yes, typical excuses). After a further six months of regular quads work including cycling and balance exercises, my pain has almost resolved. I’ve decided to avoid any running training to focus on cycling, given that the offending pathology (posterior cruciate ligament (PCL) laxity) still exists and I want the microfracture treatment to last as long as possible!

Conclusion

While there are likely to be many competitive athletes with posterior cruciate ligament (PCL) laxity, few present for treatment, and even fewer with chronic injuries will be able to give you a good history. Take care to examine the posterior cruciate ligament (PCL) carefully – my injury was more than 10 years old before it was discovered!

Ryan Shulman is a physiotherapist and medical practitioner working at the Princess Alexandra Hospital, Brisbane, Australia. He has a keen interest in sports medicine and orthopaedics

Illustrations by Viv Mullett