Chronic ACL Deficiency

For Medical Students

What It Tests

A chronically deficient knee has had months or years to adapt, and the examination tests both the laxity and the consequences of living with it.

The laxity is usually easier to demonstrate than acutely, because the patient is no longer guarding and the knee is not swollen.

The consequences are what matter more: muscle wasting, secondary meniscal and cartilage injury, and in time alignment change. 4.3.9 covers muscle wasting.

How It Is Performed

Observe the gait, because a chronically deficient knee may show a quadriceps avoidance pattern or a varus thrust. 4.4.3 covers quadriceps avoidance gait.

Measure thigh circumference or compare it visually, since quadriceps wasting is common and is the main modifiable finding.

Perform the Lachman test, which should be easier and more convincing than in an acute knee. 4.10.4 covers it.

Perform the pivot shift, which is now obtainable and is the test that correlates with the patient's symptom. 4.10.6 covers it.

Examine the menisci and the joint lines deliberately, because secondary injury is common and changes the plan. 4.9.1 covers the meniscal presentation.

What a Positive Means

A clear Lachman with a soft endpoint confirms the deficiency and says nothing about whether it troubles the patient.

A positive pivot shift in a chronically deficient knee corresponds more closely to the patient's complaint than the Lachman does, which is why it is worth obtaining.

Quadriceps wasting indicates both a disuse consequence and a treatable contributor to instability.

Joint line tenderness or mechanical symptoms raise a secondary meniscal tear, which is common in chronic deficiency and often the reason for presentation.

A varus thrust during gait raises a lateral side component or established degenerative change. 4.5.7 covers dynamic alignment.

MRCS Level

What a Positive Means

The reasoning expected is that a deficient knee is not a static finding but a trajectory.

The ligament does not heal, so the laxity persists, and the question is what the laxity has done to the rest of the joint.

Secondary meniscal tears accumulate, because the abnormal translation loads the posterior horn of the medial meniscus repeatedly. 3.5.8 covers contact mechanics after injury.

Cartilage damage follows the meniscal loss, and the sequence is why a long-deficient knee looks different from a recently injured one.

Gait adaptation is also a finding rather than a compensation to be corrected: a quadriceps avoidance pattern reduces the load the ligament would resist, and it appears in a minority of deficient knees rather than most. 3.14.9 covers that correction.

How Good It Is

The examination performs better in a chronic knee than in an acute one for laxity, and that difference is large.

The Lachman test is reliable here and the pivot shift becomes obtainable, which makes the chronic examination the most informative awake assessment available short of anaesthesia.

It performs poorly at the question that matters, which is whether this patient needs reconstruction, because that depends on their symptoms and demands rather than on their laxity grade. 4.10.1 covers the history.

It performs well at detecting the secondary injuries, and that is where the examination earns its place in a chronic knee.

FRCS Level

How Good It Is

At decision level the chronic examination contributes the secondary findings and the alignment, and the history contributes the indication.

A chronically deficient knee with a repairable meniscal tear is a stronger case for surgery than one with laxity alone, because there is something to repair.

A chronically deficient knee with established degenerative change and malalignment is a different operation, and may be a realignment rather than a reconstruction. 4.20.4 covers osteotomy assessment.

Quadriceps deficit should be addressed before reconstruction rather than after, because a knee with better quadriceps function before surgery does better after it. 4.2.34 covers rehabilitation.

A patient who has adapted successfully, has no secondary injury and does not want to return to pivoting is reasonably managed without surgery, and 3.17.1 sets out why that balance is genuine.

Where It Misleads

The commonest error is reconstructing on the strength of the laxity in a patient whose function is acceptable.

The second is missing the secondary meniscal tear, which is frequently the actual reason they presented. 4.9.1 covers it.

The third is missing the alignment, because a varus deficient knee that is reconstructed without realignment loads the graft abnormally. 4.5.2 covers varus alignment.

And treating quadriceps wasting as a consequence to be managed afterwards rather than a problem to be fixed first.

Fellowship Level

Where It Misleads

In referred practice the long-deficient knee is frequently presented as a reconstruction candidate when the assessment that matters is whether reconstruction is still appropriate.

The three findings that argue against it are established degenerative change, a deficient meniscus, and malalignment, and all three are assessable in clinic. 4.9.10 covers deficiency.

The patient who has coped for twenty years and now presents with pain rather than instability usually has degenerative disease, and reconstructing their ligament treats the wrong problem. 4.18.2 covers established disease.

The patient who has coped and now presents with instability during a changed occupation or activity has a genuine new indication.

Separating those two is a history task and the examination's role is to establish what the joint can still tolerate. 4.2.1 covers the pain history.

No figure here supports these claims, under decision 023.