Medial Meniscus Versus MCL Injury

For Medical Students

What It Tests

A painful medial knee after a twisting injury is either a meniscal tear, a medial ligament injury, or both, and the examination's job is to say which.

The two structures sit on top of each other. The medial ligament crosses the joint line and the meniscus sits in it, so tenderness in that region belongs to either. 3.9.4 covers the attachment between them.

What separates them is not where it hurts but what provokes it: valgus load points at the ligament and rotation under compression points at the meniscus.

How It Is Performed

Palpate carefully and record the level rather than the side. Tenderness above or below the joint line along the ligament's course is ligamentous; tenderness in the joint line itself is meniscal or deep ligamentous. 4.9.2 covers joint line tenderness.

Perform valgus stress at thirty degrees and in extension, and note both the opening and whether the manoeuvre reproduces the pain. 4.12.1 covers the test.

Perform a meniscal provocation test, rotating the flexed knee under compression, and note whether that reproduces the pain. 4.9.3 covers the McMurray test.

Ask about mechanical symptoms, because catching, locking and a sense of something moving belong to the meniscus and not to the ligament. 4.2.5 covers locking.

Ask about the mechanism, since a valgus blow points at the ligament and a twisting injury on a loaded knee points at the meniscus. 4.2.18 covers twisting injury.

What a Positive Means

Increased valgus opening indicates a ligament injury, whatever else is present, because the meniscus does not produce valgus laxity.

Pain reproduced by valgus stress without increased opening is a ligament sprain and is the common finding in a mild injury.

Pain reproduced by rotation under compression, with normal valgus stress, indicates the meniscus.

Both patterns in the same knee means both structures, which is common after a valgus twisting injury and is the answer rather than a diagnostic failure.

An effusion that develops over hours suits a meniscal tear and one that is immediate suits a cruciate injury, so the timing of the swelling helps although it does not separate these two. 4.2.3 covers swelling.

MRCS Level

How It Is Performed

In a viva this is the discrimination the examiner is testing when the history is a twisting injury with medial pain, and the answer is a sequence rather than a single test.

The expected points are the palpation level, valgus stress at both angles with attention to pain as well as laxity, a meniscal provocation test, mechanical symptoms, and the mechanism.

Say that you would ask whether the knee has given way as well as whether it has locked, because the two symptoms point at different structures. 4.2.6 covers giving way.

Say that you would examine the cruciates, since a combined cruciate, medial and meniscal injury is a recognised pattern after a valgus twisting mechanism. 3.9.10 covers it.

Say that magnetic resonance imaging answers the question the examination cannot in the acutely painful knee, and that it is a reasonable investigation rather than an admission. 4.1.6 covers that relationship.

What a Positive Means

The reasoning expected is that the meniscus is loaded by compression with rotation and the ligament by valgus, so the provocation that reproduces the pain names the structure taking the load. 3.9.1 covers valgus stability.

The deep ligament complicates that division, because it attaches to the meniscus and is loaded by both, which is why the joint line finding is shared. 4.12.4 covers it.

A meniscal tear with an intact ligament gives mechanical symptoms and no laxity; a ligament injury with an intact meniscus gives laxity and no mechanical symptoms; and the middle cases are real rather than diagnostic failures.

A posterior horn tear and a posteromedial corner injury both give posteromedial tenderness, and separating those two is harder than separating the main structures. 4.12.5 covers the corner.

How Good It Is

The examination separates these two well when one of them is clearly injured and poorly when both are, which is the common situation after the mechanism that causes either.

Valgus laxity is the most useful single finding, because it is specific: the meniscus cannot produce it.

Mechanical symptoms are the most useful historical finding, for the same reason: the ligament does not produce them.

The provocation tests are less reliable in the acutely painful knee, where almost anything reproduces the pain, and that is where the examination most often has to defer.

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 discrimination matters because the two structures have opposite treatment logic. The ligament heals and is braced; the meniscus does not heal reliably and may need repairing within a window.

That asymmetry means the cost of the two errors is unequal. Calling a meniscal tear a ligament sprain delays a repair; calling a ligament sprain a meniscal tear produces an unnecessary arthroscopy.

In a combined injury the sequence follows the window. The repairable meniscal tear sets the timing and the medial ligament is protected around it, rather than the other way round.

The examination's contribution is to decide who needs imaging urgently rather than to make the diagnosis, and that is a reasonable use of it.

A chronic medial knee with both a residual laxity and joint line tenderness needs the question of early compartment change asked as well, because the answer changes the treatment more than either structure does. 4.9.11 covers meniscal examination in osteoarthritis.

Where It Misleads

The commonest error is stopping at joint line tenderness, which belongs to both structures and names neither.

The second is treating a reproduced pain on valgus stress as laxity, which converts a sprain into a graded injury.

The third is attributing mechanical symptoms to the ligament, which does not produce them.

The fourth is forgetting that both can be injured, and writing a letter that names one when the examination found evidence of both.

The fifth is examining a knee too painful to examine and recording the result rather than recording that the examination could not be completed. 4.1.8 covers the record.

Fellowship Level

Where It Misleads

In referred practice this discrimination usually arrives already made and usually made wrong in one specific way: the ligament was blamed and the meniscus was the problem.

The pattern is a patient braced for a medial ligament injury who at three months has a knee that catches, which is a meniscal tear that was never provoked because the knee was too painful at the time. 4.2.5 covers locking.

The reverse happens after arthroscopy, where a normal meniscus was found and the persisting pain is a posteromedial corner that nobody tested. 4.12.5 covers that assessment.

A meniscal root avulsion gives medial pain, a normal valgus examination and rapid compartment change, and it is missed by both of the usual framings. 4.9.9 covers root tears.

Meniscal extrusion with an intact meniscus produces the same picture through a meniscotibial separation, which is a deep ligament problem presenting as a meniscal one. 4.12.4 covers it.

In the chronic knee the useful question stops being which structure and becomes whether the compartment is still worth preserving, and the examination that answers it is alignment and compartment loading rather than either of the tests on this page. 4.11.5 covers dynamic assessment.