Combined Ligament Injury Assessment

For Medical Students

What It Tests

A combined ligament assessment establishes which of the knee's restraints are deficient, in a knee where more than one of them is.

The reason it is a separate skill rather than a longer list of tests is that the tests interfere with each other. A deficient posterior cruciate changes the anterior drawer, and a deficient corner changes the rotational tests. 4.11.1 covers the first of those.

Before any of that, a knee with multiple ligament injuries may have been dislocated, and a dislocated knee can injure the artery and the nerve. The vascular and neurological examination comes first and is not optional.

How It Is Performed

Examine the circulation first. Feel both foot pulses, compare the two limbs for temperature and colour, and record what you find.

Treat absent or reduced pulses as an arterial injury until it has been excluded properly, rather than as a finding to review later.

Examine the common peroneal nerve next, testing ankle dorsiflexion, great toe extension and sensation over the dorsum of the foot, because this nerve is the one at risk in the posterolateral injury.

Then look for skin dimpling medially, which suggests an irreducible dislocation, and record the limb's resting position.

Only then begin the ligament sequence: inspection and sag, posterior drawer in neutral and in internal rotation, Lachman and anterior drawer, valgus stress at zero and thirty degrees, varus stress at zero and thirty degrees, the dial test at thirty and ninety degrees, and the rotational tests last. 4.12.1 covers valgus stress testing.

Record every test on both knees, because a combined injury is defined by a pattern and a pattern needs a comparison.

What a Positive Means

Increased laxity to a stress at thirty degrees with a firm endpoint at zero suggests the collateral alone; laxity at both suggests the collateral and a cruciate. 4.12.2 covers the assessment in extension.

A positive sag with increased external rotation at thirty degrees but not at ninety suggests the posterolateral corner without the posterior cruciate. 4.13.5 covers the dial test.

Increased external rotation at both thirty and ninety degrees suggests both the corner and the posterior cruciate, which is the combination the reverse pivot shift detects. 4.11.4 covers it.

A third degree posterior drawer should be read as a combined injury until the corner has been examined, because the corner resists the last part of that translation. 4.11.2 covers the grade.

MRCS Level

How It Is Performed

In a viva the multiligament knee is the station where sequence is the answer, and the candidate who starts with the Lachman has already lost the mark.

Say pulses, nerve, skin, then ligaments, and say it in that order without being prompted. 4.1.4 covers the structured approach.

Say that you would repeat the vascular examination rather than record it once, because an arterial injury can declare itself hours after a normal first assessment.

Say that you would examine the hip and the ankle, since a high energy mechanism rarely injures one joint. 4.2.17 covers contact injury.

Say that you would not force a knee that feels grossly unstable into ninety degrees of flexion, and that examination under anaesthesia answers what the clinic cannot. 4.23.1 covers it.

Say that you would document the pattern rather than a list of positive tests, because the pattern is what the operation is planned from. 4.1.8 covers the record.

What a Positive Means

The reasoning expected is that each restraint has a flexion angle and a plane in which it dominates, so the pattern across angles localises the injury in a way that no single test can. 3.8.3 covers bundle function.

The superficial medial ligament dominates valgus restraint at thirty degrees, and laxity in full extension requires a cruciate or the posteromedial corner as well. 4.12.5 covers the posterior oblique ligament.

The lateral collateral dominates varus restraint at thirty degrees, with the same logic applying in extension. 4.13.2 covers it.

External rotation at thirty degrees is resisted principally by the posterolateral corner and at ninety degrees principally by the posterior cruciate, which is why the dial test is read at two angles rather than one. 4.13.5 covers that reading.

Hyperextension and a recurvatum deformity on lifting the great toe implicate the corner rather than either cruciate. 4.13.7 covers the recurvatum test.

How Good It Is

The clinical examination of a multiligament knee localises the injured structures well and grades them poorly, and that combination decides how it is used.

Localisation is what the operation needs, so the examination contributes more to planning in these knees than in any other group in this chapter.

It is unreliable in the acute high energy knee, where pain, guarding and effusion defeat most of the sequence, and that is exactly the knee in which the information is most urgently needed.

Examination under anaesthesia is therefore part of the assessment rather than a luxury, and in these knees it is usually the examination the plan is built on. 4.23.6 covers complex injuries.

Magnetic resonance imaging identifies the torn structures more completely and says less about which laxity matters, so the two are read together rather than one instead of the other. 4.1.6 covers that relationship.

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 combined assessment determines the operation, which is not true of any other examination in this chapter.

Whether the corner is reconstructed alongside the cruciate, whether the medial side is repaired or reconstructed, and whether the knee is staged all follow from the pattern the examination establishes.

The single most consequential finding is an unrecognised posterolateral corner injury, because a cruciate graft placed into a knee with an uncontrolled corner stretches, and that is the commonest avoidable failure in this group. 4.13.4 covers the corner.

Stress radiographs convert the grades into numbers and are worth obtaining where the plan turns on a grade, since the examination's weakness is grading rather than localisation.

Alignment matters as much here as in the chronic knee, because a varus limb loads a lateral reconstruction continuously. 4.11.6 covers that argument.

Where It Misleads

The commonest error is a complete and careful ligament examination with no vascular examination recorded, which is the one omission in this chapter that can cost a limb.

The second is reading each test in isolation rather than as a pattern, which produces a list of positives and no diagnosis.

The third is examining a grossly unstable knee aggressively in the clinic, which is uninformative and occasionally harmful.

The fourth is accepting an imaging report as the assessment. An image names torn structures; the examination says which laxity the patient has, and the operation is planned from the second.

The fifth is examining one knee. In a bilaterally hypermobile patient the uninjured side is the only thing that makes a grade interpretable. 4.23.3 covers those patients.

Fellowship Level

Where It Misleads

In referred and revision practice the combined knee arrives having been operated on once already, and the examination is reconstructing what was missed rather than what was torn.

The commonest finding is a stretched posterior cruciate graft with an uncontrolled corner, and the two are separated by the dial test at thirty and ninety degrees rather than by the drawer. 4.13.5 covers it.

Previous surgery changes what the tests mean. A reconstructed lateral side may be tight in a way that masks rotational laxity, and a healed medial repair can give a firm endpoint over a lax joint. 4.2.30 covers previous surgery.

A knee with multiple reconstructions and persistent instability needs alignment and the tibial slope assessed before any further soft tissue work, because a slope that favours posterior translation will defeat a posterior cruciate graft whatever the technique.

A common peroneal nerve palsy that recovered incompletely changes the dynamic examination permanently, and attributing the resulting gait to ligament laxity is a recognised error in this group. 4.11.5 covers dynamic assessment.

The examination also carries the decision about staging, which no imaging supports. A knee that cannot be examined because of pain and effusion is usually a knee to examine under anaesthesia and stage, and that judgement is clinical. 4.23.6 covers it.