Osteochondral Lesions

For Medical Students

What It Tests

An osteochondral lesion is a defect involving both the cartilage and the bone beneath it, usually from an acute impaction or a patellar dislocation. 4.2.22 covers the dislocation event.

Examining for it means establishing the mechanism, finding an effusion, and looking for a mechanical symptom, because the fragment may be loose. 4.17.2 covers mechanical symptoms.

It matters because an osteochondral fragment with bone attached can be fixed back, and that window closes, which makes this the most time sensitive diagnosis in the chapter. 4.8.7 covers the presentation it shares.

How It Is Performed

Establish the mechanism and the timing: an acute impaction, a dislocation, or a twisting injury with a sudden tense effusion. 4.2.3 covers swelling as a symptom.

Assess the effusion and its tension, since a tense effusion within hours is blood and an osteochondral injury is on that short differential. 4.8.7 covers it.

Palpate the compartments and the patellar facets, since the commonest sites are a femoral condyle and the patella after a dislocation. 4.6.5 covers patellar tenderness.

Measure the passive extension and record the end feel, since a displaced fragment gives a block. 4.7.5 covers it.

Examine the patella's medial restraint if the mechanism was a dislocation, since the two injuries travel together. 4.15.7 covers that assessment.

What a Positive Means

An acute tense effusion after an impaction or a dislocation raises an osteochondral injury, and that raises the urgency of the imaging rather than waiting for the swelling to settle. 4.8.7 covers it.

A block to extension with a springy end feel indicates a displaced fragment and is urgent. 4.7.5 covers the end feel.

Medial patellar tenderness with a haemarthrosis after a twisting injury indicates a dislocation, and an osteochondral injury should be assumed until the imaging says otherwise. 4.2.22 covers the event.

A normal examination weeks later in a patient with the right mechanism does not exclude the lesion, and the repair window may already have closed. 4.17.1 covers the presentation.

Recurrent effusions and catching months after an injury suggest a fragment that was missed. 4.17.2 covers the symptoms.

MRCS Level

How It Is Performed

In a viva this is the time sensitive diagnosis in the acute knee, and the expected answer links the haemarthrosis to the short differential.

The expected points are the mechanism, the tense effusion, the compartment and patellar palpation, the extension with its end feel, and the patellar restraint assessment.

Say that an acute haemarthrosis has a short differential and that this is on it, which is why the imaging is early rather than delayed. 4.8.7 covers it.

Say that a fragment with bone can be fixed and that a purely cartilaginous one usually cannot, which is why the distinction matters. 4.17.5 covers the cartilage only defect.

Say that the repair window is measured in weeks, which is the reason for the urgency rather than a general preference for speed.

What a Positive Means

The reasoning expected is that bone heals to bone, so a fragment carrying subchondral bone can be fixed and will unite, where cartilage alone will not. 3.5.1 covers contact areas.

That is why the mechanism matters: an impaction or a dislocation shears bone with the cartilage, where a degenerative process delaminates cartilage alone. 4.17.5 covers the second.

A patellar dislocation shears the medial patellar facet or the lateral femoral condyle, which is why those are the sites to palpate after that mechanism. 2.4.5 covers the surgical relevance.

A displaced fragment obstructs the joint, which is the mechanism of the block and the reason the end feel is firm or springy rather than leathery. 4.7.5 covers the reading.

How Good It Is

The examination raises the possibility and does not make the diagnosis, which imaging does, and in this condition the examination's value is the urgency it creates. 4.1.6 covers that relationship.

Its most useful findings are the tense acute effusion and the block, both of which are reliable when present.

It is insensitive. A lesion without a displaced fragment produces an effusion and little else, so the mechanism carries more weight than the findings.

Radiographs miss a purely cartilaginous fragment and show a bony one, which is why the mechanism should drive the cross sectional imaging. 4.1.6 covers it.

No figures appear for any accuracy comparison on this page, under decision 023, and the comparison is the claim being made.

FRCS Level

How Good It Is

At decision level this is the diagnosis in the chapter where delay changes the operation, so the examination's job is to get the imaging done early.

An acute fragment with bone is fixed, and the result of fixation is better than the result of any later reconstruction, which is why the window matters.

A displaced fragment with a block is an urgent arthroscopy regardless of the rest of the assessment. 4.7.5 covers the finding.

A fragment after a patellar dislocation is the commonest version in a young patient, and the patellar assessment and the osteochondral assessment are done together. 4.15.7 covers the first.

A lesion found late, with the fragment absent or unfixable, becomes a cartilage defect problem and the decision changes category. 4.17.5 covers it.

Where It Misleads

The commonest error is waiting for an acute effusion to settle before imaging, which spends the window.

The second is attributing a haemarthrosis to a cruciate rupture by default. 4.8.7 covers that error.

The third is not examining the patella after a twisting injury with a haemarthrosis, which misses the dislocation and its fragment. 4.2.22 covers it.

The fourth is relying on radiographs in a young patient, where a cartilaginous fragment is invisible.

The fifth is reading a normal examination at six weeks as excluding the lesion.

Fellowship Level

Where It Misleads

In referred practice the osteochondral lesion arrives late, and the referral is about what can still be done.

A patient with a fragment that has been loose for months has lost the fixation option, and the decision becomes a cartilage reconstruction one. 4.17.5 covers it.

A patient with a haemarthrosis attributed to a cruciate injury who has an osteochondral fragment has had the wrong diagnosis made from the right finding. 4.8.7 covers the presentation.

A patient with recurrent effusions and catching after a dislocation treated non operatively has a missed fragment, and the history is where that is caught. 4.17.2 covers the symptoms.

A patient with a fixed fragment and persisting pain needs the alignment and the meniscal status assessed, since both determine whether the fixation survives. 4.9.10 covers meniscal deficiency.

In medicolegal work a missed osteochondral fragment after a documented dislocation is the most defensible form of criticism in this chapter, because the mechanism and the window are both well described. 4.23.7 covers that setting.