Acute Haemarthrosis

For Medical Students

What It Tests

An acute haemarthrosis is a tense effusion appearing within hours of an injury, and its significance is that blood comes from a vascular structure.

The differential is short. A cruciate rupture, an osteochondral fracture, a peripheral meniscal tear, a patellar dislocation and an intra-articular fracture account for most of them. 4.2.22 covers the dislocation event.

The timing is what makes the diagnosis. A tense effusion within hours is blood; an effusion appearing over a day or two is synovial fluid and a different differential. 4.2.3 covers swelling as a symptom.

How It Is Performed

Establish the timing precisely: how long after the injury the knee swelled, and how quickly.

Assess the effusion's size and tension, since a tense effusion is the characteristic finding. 4.8.6 covers ballottement.

Assess the range, which will be limited by the tension, and record that the effusion was present when it was measured. 4.8.2 covers the significance.

Examine the ligaments, accepting that the examination is less reliable in this setting and that guarding produces false reassurance. 4.10.4 covers the Lachman test.

Examine for a patellar dislocation: medial retinacular tenderness, apprehension and a palpable defect. 4.6.5 covers patellar tenderness.

What a Positive Means

A tense effusion within hours of an injury indicates blood and therefore a structural injury, even if the ligament examination appears normal.

A normal ligament examination in an acute haemarthrosis is not reassurance, because guarding reduces every translational finding. 4.14.6 covers the setting that removes it.

Medial retinacular tenderness with a haemarthrosis after a twisting injury indicates a patellar dislocation, which is the diagnosis most often missed in this group. 4.2.22 covers the event.

A haemarthrosis with a mechanical block to extension indicates a displaced fragment or a displaced meniscal tear, which is urgent. 4.9.8 covers mechanical locking.

A haemarthrosis with a palpable fat globule on aspiration indicates an intra-articular fracture, which changes the management entirely.

MRCS Level

How It Is Performed

In a viva the acute haemarthrosis is a standard station and the differential is the answer, with the timing as the reasoning.

The expected points are the timing, the tension, the limited range, the ligament examination with its caveat, and the patellar assessment.

Say the differential list without being prompted, because that is the content of the question.

Say that a normal ligament examination here is unreliable, and say what you would do about it: a repeat examination when the effusion settles, or an examination under anaesthesia. 4.14.6 covers it.

Say that you would image the knee, since a fracture and an osteochondral injury are both in the differential and neither is a clinical diagnosis. 4.1.6 covers that relationship.

What a Positive Means

The reasoning expected is that the structures capable of producing a rapid haemarthrosis are vascular, so the differential is anatomical rather than statistical. 4.8.1 covers normal fluid physiology.

The anterior cruciate has a blood supply and a synovial covering, which is why its rupture bleeds, and it is the commonest cause in a young patient. 2.7.1 covers its anatomy where that chapter exists.

The peripheral third of the meniscus is vascular and the inner part is not, which is why a peripheral tear bleeds and a central one does not. 2.5.3 covers the vascular supply.

A patellar dislocation tears the medial retinaculum and often causes an osteochondral injury, which is why it produces a haemarthrosis and why it is missed when the patella has reduced spontaneously. 4.2.22 covers the event.

How Good It Is

The clinical diagnosis of a haemarthrosis from the timing and the tension is reliable, and the diagnosis of its cause from the examination is not.

The examination in this setting fails towards false reassurance, because guarding reduces the translational findings, which is the most important limitation on the page. 4.13.4 covers the assessment that suffers most.

Imaging and, where appropriate, aspiration add what the examination cannot, which makes this a presentation where the examination's job is to establish urgency rather than diagnosis. 4.1.6 covers that relationship.

The timing is obtained from the history, so the history is the diagnostic instrument here rather than the hands. 4.2.3 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 the haemarthrosis establishes urgency, and the urgency is what protects the treatable diagnoses in the differential.

An osteochondral fragment is repairable acutely and not later, which is the clearest time dependent diagnosis in this group.

A displaced meniscal tear with a block is repairable acutely, and the window matters. 4.9.8 covers mechanical locking.

A patellar dislocation with an osteochondral injury needs identifying before the effusion settles and the diagnosis is attributed to something else. 4.2.22 covers the event.

A cruciate rupture is not urgent, which makes it the one diagnosis in the differential that can wait, and recognising that prevents an unnecessary rush. 4.10.2 covers the acute knee.

Where It Misleads

The commonest error is concluding a normal examination from a guarding effused knee.

The second is attributing a haemarthrosis to a cruciate rupture by default and missing the time dependent diagnoses.

The third is not imaging the knee.

The fourth is missing a patellar dislocation that reduced spontaneously, since the history may not mention it. 4.2.22 covers it.

The fifth is recording a range and a laxity grade without noting the haemarthrosis. 4.1.8 covers the record.

Fellowship Level

Where It Misleads

In referred practice the acute haemarthrosis has usually already been managed, and the referral concerns what was missed in it.

A patient with a haemarthrosis attributed to a cruciate rupture who turns out to have had a patellar dislocation has a different problem and a different operation. 4.2.22 covers the event.

A patient with an osteochondral fragment identified late has lost the repair window, and that loss is usually traceable to the imaging rather than to the examination.

A patient whose ligament examination was normal acutely and abnormal at six weeks did not change, and the first examination was unreliable. 4.14.6 covers the alternative.

A patient with a recurrent haemarthrosis without injury has a vascular or haematological cause, and that is a different pathway from anything in this section. 4.8.8 covers chronic effusions.

In medicolegal work the recorded timing of an acute effusion is the single most useful fact in these cases, and a vague entry is one of the commonest weaknesses in a record. 4.23.7 covers that setting.