Chronic PCL Deficiency

For Medical Students

What It Tests

The examination of a chronically deficient posterior cruciate is looking for two different things: the laxity itself, and what years of that laxity have done to the rest of the joint.

The second is the part that is usually missed. A tibia sitting back changes where the joint surfaces touch, and that change loads the patellofemoral joint and the medial compartment. 3.8.2 covers posterior stability.

A chronic knee is therefore not an acute knee that has had time pass. It is a knee with a second set of findings that the acute knee does not have.

How It Is Performed

Start with the patient standing, and look at alignment from the front and at the knee profile from the side.

Watch the gait for a flexed knee pattern and for a varus thrust, which in a chronic knee can come from the corner or from medial compartment wear. 4.11.5 covers dynamic examination.

Inspect the quadriceps for wasting and measure the thigh circumference on both sides at the same distance above the joint line.

Perform the sag sign, the posterior drawer and the rotational tests in that order, as in any posterior cruciate assessment. 4.11.1 covers the sag.

Then examine the patellofemoral joint and the medial compartment deliberately, including the joint lines, patellar tracking and the response to compression. 4.11.5 covers the loaded assessment.

What a Positive Means

An obvious sag, a third degree drawer and a wasted quadriceps in a patient who walks into the clinic unaided describe a knee that has compensated, and that combination is common.

Anterior knee pain in a chronically deficient knee is the commonest complaint in this group, more common than the instability most clinicians expect. 4.2.1 covers pain.

Medial joint line tenderness with a varus alignment suggests the joint has begun to change, which alters the treatment from a ligament problem to a degenerative one. 4.2.8 covers pain location.

A varus thrust suggests the posterolateral corner, and in a chronic knee it can also mean the corner has stretched over years rather than torn at the time. 4.11.7 covers the combined knee.

MRCS Level

How It Is Performed

In a viva the chronic knee is the station where the examiner is testing whether you look beyond the ligament, and the structured sequence is what earns the mark. 4.1.4 covers that sequence.

The expected points are standing inspection, gait, quadriceps, the three posterior cruciate tests, the rotational tests, and then the patellofemoral and medial compartments.

Say that you would ask what the patient actually cannot do, because in this knee the answer is often pain on stairs rather than instability. 4.2.6 covers giving way.

Say that you would ask about the original injury and how long ago, since a dashboard mechanism or a sporting hyperextension years before is frequently the missing history. 4.2.21 covers the mechanism.

Say that you would record the quadriceps measurement, because it is the finding that most influences what happens next and the one least often written down. 4.1.8 covers the record.

What a Positive Means

The reasoning expected is that posterior subluxation shifts the tibiofemoral contact point and increases patellofemoral contact pressure, which is the mechanism behind the anterior pain.

The same shift increases medial compartment load, which is the mechanism behind the late degenerative change in these knees.

Quadriceps function is the compensating mechanism, so wasting is both a consequence of the injury and a cause of the symptoms, and it is the only part of the picture that treatment can reliably change.

Laxity grade and symptoms correlate poorly in this ligament, which is the single most important thing to know about the chronic knee and the reason a grade is a poor basis for a decision. 4.11.2 covers the grade.

How Good It Is

The examination of a chronic knee is reliable for the laxity and better than imaging for the compensation, because compensation is a behaviour rather than a structure.

It is less reliable for the compartment change, where weight bearing radiographs answer a question the hands cannot. 4.1.6 covers the relationship with imaging.

The quadriceps measurement is the most reproducible useful finding in this assessment and the most frequently omitted.

Comparison with a previous examination is worth more here than in any other part of the chapter, because the question in a chronic knee is almost always whether something has changed. 4.1.8 covers the record that makes it possible.

No figures appear for any of these comparisons, under decision 023, and the comparison is the claim being made.

FRCS Level

How Good It Is

At decision level the chronic knee is where this chapter's argument becomes practical, because the examination that grades the ligament best is the examination that predicts the outcome worst.

The decision in an isolated chronic deficiency rests on function, quadriceps state, alignment and compartment condition, and the drawer grade informs the technique rather than the indication. 4.11.5 covers the functional assessment.

A varus aligned knee with medial compartment change and a deficient posterior cruciate is a realignment problem before it is a ligament problem, and operating on the ligament alone in that knee is a recognised route to failure.

A knee with preserved alignment, a healthy medial compartment and a genuine functional complaint after proper rehabilitation is the knee where reconstruction has the best case.

The corner has to be assessed in every chronic knee, because a stretched corner is far commoner here than in the acute presentation and it is the variable that determines whether anything done to the cruciate survives. 4.11.7 covers it.

Where It Misleads

The commonest error is treating the grade as the severity, when in this ligament the grade and the problem are only loosely connected.

The second is attributing anterior knee pain in these patients to something else, because the pain does not feel like instability and the connection is not obvious at the bedside.

The third is examining the knee and not the limb. Alignment, the hip and the foot all contribute to the thrust and to the compartment load.

The fourth is accepting a patient's account of rehabilitation without establishing what was actually done, since a knee with a wasted quadriceps has usually not completed it.

Fellowship Level

Where It Misleads

In referred practice the chronic posterior cruciate knee arrives under a different label most of the time, and the examination is what relabels it.

Patellofemoral pain in a patient in their thirties with a quiet history of a knee injury in their teens is the classic presentation, and the sag is visible before the knee is touched. 4.11.1 covers it.

A chronic knee with a fixed posterior subluxation that cannot be reduced changes every test in the chapter. The drawer has nowhere to go, the reverse pivot shift cannot shift, and the examination reads as mild in the most deficient knee in the clinic. 4.11.4 covers that failure.

Medial compartment change in a posterior cruciate deficient knee progresses in a pattern that differs from primary osteoarthritis, and the examination finding that gives it away is tenderness that sits more posteriorly on the medial joint line than expected.

A patient who has had a reconstruction years ago, has an acceptable drawer and complains of the same anterior pain they had before it, has usually had a technically adequate operation for a problem that was never a ligament problem. That is the assessment this chapter exists to prevent.

In medicolegal work the chronic knee is where the gap between examination findings and disability is argued, and recording function separately from laxity is what makes an opinion defensible. 4.23.7 covers that setting.