History of ACL Injury

For Medical Students

What It Tests

The history of an anterior cruciate injury tests whether the mechanism, the immediate aftermath and the subsequent function fit a ruptured ligament.

It does that well enough that the diagnosis is usually made before the examination, which is unusual in the knee. 4.2.16 covers non-contact mechanisms.

It also establishes something no test in this chapter can: whether the patient is functionally unstable, which is the symptom an operation treats. 4.2.2 covers instability.

How It Is Performed

Ask what the knee was doing: a planted foot with a change of direction, a landing, or a hyperextension.

Ask whether anything hit the knee, since a non-contact mechanism points here and a contact one widens the differential. 4.2.17 covers contact injury.

Ask whether they heard or felt a pop, and whether they could carry on.

Ask how quickly the knee swelled, pressing for hours. 4.2.3 covers swelling.

Then ask about function since: whether the knee gives way, during what, and what they have stopped doing. 4.2.6 covers giving way.

What a Positive Means

Four features together are close to diagnostic: a non-contact pivoting or landing mechanism, a pop, immediate swelling, and inability to continue.

Each one alone is weaker. The pop is absent in a substantial proportion of genuine ruptures, so its absence excludes little.

Immediate swelling means blood in the joint and narrows the differential to a short list. 4.8.7 covers acute haemarthrosis.

Giving way on a turn rather than a step points to rotational instability and therefore to this ligament rather than the extensor mechanism. 4.10.9 covers rotation.

A patient who has given up pivoting activities and no longer gives way has adapted rather than recovered.

MRCS Level

What a Positive Means

The reasoning expected is from the mechanism to the structures loaded, which Section 3 supplies. 3.7.14 covers injury mechanisms.

A planted foot with internal femoral rotation loads the ligament and the anterolateral structures together, so an isolated injury is less common than the teaching implies.

Valgus collapse on landing adds the medial structures. 4.12.7 covers separating them.

The same mechanism produces meniscal injury, and a peripheral tear in a young knee has a repair window defined by the date of injury. 4.9.9 covers roots.

So the history's job extends beyond the cruciate: it predicts the associated injuries that the examination then has to look for deliberately.

How Good It Is

For functional instability the history outperforms every test in this chapter and the imaging as well, and the reason is that laxity and instability are different things.

A knee with substantial measured laxity that has never given way is not functionally unstable. A knee with modest laxity that gives way during work is.

The examination measures the first and only the patient can report the second.

For the diagnosis of rupture the history performs well and the examination performs better, so the two are complementary rather than competing.

For grading and for the associated injuries the history is weak and the examination and imaging carry it.

FRCS Level

How Good It Is

At decision level the history determines whether to reconstruct more than the examination does, which is worth stating plainly in a chapter of tests.

The feature that most supports reconstruction is instability during an activity the patient cannot avoid, because that is the symptom surgery addresses.

Instability only during a sport the patient has already given up is a different conversation, and the honest version includes not reconstructing. 3.17.1 covers the balance the literature supports.

The date of injury determines what else is available: a repairable meniscal tear has a window and a delay converts a repair into a resection. 4.2.9 covers onset.

A deteriorating frequency of episodes, or episodes during progressively less demanding activities, indicates a knee that is getting worse and matters more than the current count.

Where It Misleads

The commonest error is under-reporting, where a patient has silently stopped everything that provokes the symptom. Ask what they no longer do.

The second is over-reporting, where a painful degenerate knee buckles from pain inhibition and is offered a reconstruction for laxity it does not have. 4.2.2 covers the distinction.

The third is accepting a non-contact label from the referral without asking, since patients and clinicians both use contact loosely.

And attributing a new episode with swelling in a known deficient knee to the deficiency, when it usually means a new meniscal or chondral injury.

Fellowship Level

Where It Misleads

In referred practice the history has usually been taken and the useful question is different: what has changed, and does the current symptom resemble the original one.

A returned original symptom after a defined event suggests graft failure. A new symptom during pivoting suggests a rotational component never addressed. 4.10.12 covers revision assessment.

A knee that was never confident, in a patient with a stable graft, is a rehabilitation and confidence problem rather than a structural one, and this group is larger than the structural failures. 4.22.6 covers the instrument.

The history of the rehabilitation is therefore part of the history of the knee, and it is frequently absent from the referral. 4.2.34 covers it.

The honest limit is that no claim on this page about which features discriminate is supported by a figure here, under decision 023.