Return to sport after ACL reconstruction: what the testing should show

The question that matters after ACL reconstruction is not “how long until I can play?” It is “what does my knee have to be able to do before I play?” The evidence on this is unusually clear, and it argues strongly against returning to sport on the basis of the calendar alone.

What the research shows

The most useful single study is the Delaware–Oslo ACL cohort, published in the British Journal of Sports Medicine in 2016. It followed patients returning to high-demand sport after reconstruction and recorded re-injuries over two years.

• For every month that return to sport was delayed, the re-injury rate fell by 51 per cent, up to nine months. After nine months, waiting longer made no further difference.
• Of the patients who failed the return-to-sport criteria, 38 per cent re-injured. Of those who passed, one patient did.
• For every one per cent improvement in quadriceps strength symmetry, the estimated re-injury rate fell by three per cent.

Time and function both matter. Nine months is the floor, not the finish line. The knee still has to pass the tests.

What the testing should actually include

Quadriceps strength symmetry

Measured against the uninjured side, usually with isokinetic dynamometry or a handheld device with a fixed protocol. The commonly used threshold is 90 per cent. Quadriceps strength is the variable most consistently linked to re-injury, and it is also the one most often assumed rather than measured.

Hamstring strength and the hamstring-to-quadriceps ratio

Particularly relevant where a hamstring autograft was used, since the donor site takes time to recover. The ratio between the two muscle groups matters as well as the absolute numbers.

Hop test battery

Usually four tests: single hop for distance, triple hop, crossover hop and timed six-metre hop, each compared with the other leg. Hop tests capture something strength testing does not: the ability to accept and produce force on one leg at speed.

Movement quality under load

How the knee behaves during a drop landing or a change of direction. Dynamic valgus, the knee collapsing inward, is a risk pattern that will not show up on a strength test.

Psychological readiness

Measured with a validated tool such as the ACL-RSI. Fear of re-injury is a genuine and measurable barrier, and a patient who is physically ready but not psychologically ready is at risk of moving poorly and of not returning at all.

Sport-specific demand

Testing in a gym does not reproduce a contested mark or a change of direction on a wet oval. The last stage of the progression should look like the sport.

Why this is worth doing properly

Second ACL injuries, either a graft rupture or a tear of the other knee, are most common in young athletes returning to pivoting sport, and the great majority occur in the first year back. The testing above is the main tool available for reducing that risk, and it is the reason a nine-to-twelve month timeline is quoted rather than the six months that patients often hear about.

It also changes the conversation with the patient. “Not yet” is a difficult thing to hear. “Your quadriceps is at 78 per cent and we need 90” is something a patient can work with.

How this works in practice

Return-to-sport testing is carried out by physiotherapists and exercise physiologists, not in the surgeon’s rooms. Dr Mooney’s role is to set the expectation early, at the pre-operative consultation rather than at nine months, and to work with the treating therapist so that clearance is a shared decision based on the numbers rather than a date written on a discharge summary.

If you are having ACL reconstruction, ask at the outset which criteria will be used and who will measure them. If you are a therapist in Adelaide and want to discuss a shared protocol for a patient, the rooms are happy to take the call.