Dynamic Assessment

For Medical Students

What It Tests

Dynamic assessment tests what the knee does under load and during movement, rather than what it permits on a couch.

That matters because the patient's complaint is about movement, and every other test in this chapter is static.

It covers gait, single leg stance and squat, hopping, and the landing and cutting movements the injury occurred during. 4.4.1 covers normal gait.

How It Is Performed

Watch the patient walk, looking for a quadriceps avoidance pattern, a varus thrust or a reduced stance time. 4.4.3 covers quadriceps avoidance gait.

Ask for a single leg stance and then a single leg squat, watching the knee for inward collapse and the pelvis for a drop. 4.21.1 covers the single leg squat.

Ask for a hop if the knee is stable enough, comparing distance and quality with the other side. 4.21.2 covers the single leg hop.

Ask for a step down from a low step, which loads the extensor mechanism eccentrically.

Stop at the point where the task is unsafe, and record what they could and could not do rather than persisting.

What a Positive Means

Inward collapse of the knee during a single leg squat indicates poor control at the hip and trunk rather than ligament laxity, and it is modifiable. 4.4.9 covers single leg landing assessment.

A quadriceps avoidance gait indicates an adaptation to the deficiency and appears in a minority of deficient knees rather than most. 3.14.9 covers that correction.

A varus thrust indicates lateral side laxity or degenerative change and changes the operation. 4.5.7 covers dynamic alignment.

A large side to side difference in hop distance indicates a functional deficit that predicts difficulty returning to sport. 4.21.7 covers return to sport testing.

A patient who performs everything symmetrically and well has a functionally good knee whatever their laxity grade.

MRCS Level

How It Is Performed

In a viva the expected sequence is gait, single leg stance, single leg squat, then hop if appropriate, with a statement about safety.

The candidate should say what each task is looking for rather than simply naming the tasks.

Say that these tests assess the whole limb rather than the ligament, and that a finding here frequently points at the hip or the trunk. 4.1.2 covers examining above and below.

Say that you would record the performance in comparable terms, because the value of these tests is largely in repeating them. 4.1.8 covers the record.

What a Positive Means

The reasoning expected is that dynamic valgus is produced by the hip and trunk rather than by the knee, so a knee collapsing inwards is reporting about the segment above it. 3.12.7 covers dynamic valgus.

That is why a patient with a reconstructed, stable knee can still collapse on landing, and why rehabilitation addresses the hip.

It also explains the screening problem: frontal plane landing assessment has not predicted injury consistently, while the training it selects for does reduce injury rates. 3.14.8 sets out that pair.

So a dynamic finding is a target for rehabilitation rather than a prediction about this patient, and the distinction matters when counselling.

How Good It Is

Dynamic assessment performs well for function and poorly for structure, which is the inverse of the static tests.

It is the only part of this chapter that measures what the patient is complaining about directly, other than the pivot shift.

It is reliable when the tasks are standardised and recorded, and unreliable when described impressionistically.

It does not diagnose a ruptured ligament and should not be used to, which is why it sits alongside the laxity tests rather than replacing them.

No figures appear, under decision 023.

FRCS Level

How Good It Is

At decision level dynamic assessment contributes to two decisions the static tests cannot inform.

Whether the patient is functionally impaired, which determines whether anything needs doing, and whether they are ready to return, which determines when. 4.21.8 covers return to play decisions.

It also identifies the modifiable contributors, which is the most useful thing in a patient whose laxity is fixed: hip control, quadriceps strength and landing mechanics are all trainable.

A varus thrust is the one dynamic finding that changes the operation rather than the rehabilitation, because it raises realignment alongside reconstruction. 4.20.4 covers osteotomy assessment.

A patient who performs well dynamically with a lax knee is a candidate for non-operative management, and this assessment is what identifies them.

Where It Misleads

The commonest error is omitting it, which leaves the assessment entirely static in a patient whose complaint is dynamic.

The second is describing it impressionistically, which makes it non-comparable and therefore nearly useless at the next visit.

The third is interpreting dynamic valgus as a knee problem when it is a hip and trunk problem.

And using a dynamic screening finding to predict injury in an individual, which the evidence does not support. 3.14.8 covers the point.

Fellowship Level

Where It Misleads

At this level dynamic assessment frequently answers the question the static tests cannot, which is why a patient with a technically sound reconstruction is not better.

A stable graft with poor single leg control, a hop deficit and reduced confidence is a rehabilitation problem, and that group is larger than the structural failures. 4.22.6 covers the instrument.

A stable graft with good dynamic performance and persistent giving way on pivoting is a rotational problem, and the static tests will have missed it. 4.10.9 covers it.

So the dynamic assessment separates the two commonest causes of a disappointing reconstruction, which no other part of this chapter does.

The limitation is that none of these tasks is standardised across clinics, so a comparison with another unit's assessment is usually not possible, and the comparison that matters is with the patient's own other leg and their own earlier performance.

No figure here supports these claims, under decision 023.