The three criteria that define 'medically cleared'

'Medically cleared to return to sport' after ACL reconstruction is not a date on a calendar, and it is not simply a surgeon concluding that the knee looks structurally sound. Under the most widely referenced framework in current practice — the Melbourne ACL Rehabilitation Guide, developed by Randall Cooper and Mick Hughes at Olympic Park Sports Medicine Centre — clearance means passing three distinct criteria at the same time.

The limb symmetry index (LSI) is the ratio that runs through all three: it compares the operated leg's output to the uninjured leg, expressed as a percentage. A score of 100% means both sides are equal.

The three criteria that must all be met simultaneously are:

• Strength symmetry — quadriceps and hamstring LSI of ≥90–95%, measured on fixed dynamometry, not estimated from bodyweight exercises or clinical impression.
• Functional performance — a single-leg hop test battery showing ≥90–95% LSI across standardised distance and performance tests.
• Psychological readiness — a score of ≥80 on the ACL-RSI (ACL Return to Sport after Injury) scale, a validated questionnaire assessing confidence, emotions, and perceived risk.

The Melbourne Protocol also sets a minimum floor of nine months post-surgery. This is not a target date for automatic discharge — it reflects the biology of graft ligamentisation, a remodelling process that takes considerably longer than soft-tissue healing alone. Meeting all three criteria before nine months does not constitute clearance; equally, reaching nine months without meeting the criteria does not.

Passing two of the three domains is not clearance. The threshold is simultaneous passage across all three.

Why nine months became the evidence-based minimum

The numbers behind the nine-month floor are stark. Research published in the British Journal of Sports Medicine found that athletes who returned to pivoting sport before that point faced a sevenfold higher ACL reinjury rate than those who waited beyond it. Grindem and colleagues went further: each additional month of delay reduces the reinjury rate by approximately 51%, meaning the protective benefit compounds with every month added.

Large-scale long-term data reinforce why this matters in practice. Winkler and colleagues (2025) followed 1,392 adolescent athletes over nearly a decade and found that 30% suffered a second ACL injury within 24 months of returning to sport — a figure that persists even when initial return appeared successful.

There is also a distinction worth holding in mind before setting expectations. Between 71% and 83% of athletes return to some form of sport after reconstruction, but only 55–65% reach their pre-injury competitive level. The gap — potentially more than 20 percentage points — is clinically significant when the goal is competition rather than participation.

Individual outcomes vary, and population-level figures do not predict any single athlete's trajectory. But the direction of the evidence is consistent: returning before the graft has undergone adequate biological remodelling, however recovered the knee may feel subjectively, substantially raises the risk of a second injury — and a second, more complex rehabilitation.

The team behind your clearance decision

Clearance is not one person's call. In a properly structured return-to-sport process, at least four distinct roles contribute — and none is interchangeable with another.

The orthopaedic surgeon is responsible for structural and biological milestones: confirming graft integrity, ruling out complications, and judging whether the knee has healed sufficiently to tolerate progressive loading. What the surgeon does not hold is the functional performance dataset accumulated across months of rehabilitation.

That data belongs to the physiotherapist. Strength readings, hop test results, phase-by-phase progressions — the physio has tracked these longitudinally and is best placed to interpret whether the numbers genuinely reflect readiness rather than a good day in the gym.

A sports medicine doctor or team physician reviews overall health status and coordinates input from across the team, particularly in elite or multi-practitioner settings where the athlete's care spans several professionals.

The fourth contributor is the athlete. The ACL-RSI questionnaire — the psychological readiness measure described earlier — is a formal clearance gate, not a courtesy conversation at the end of an appointment. A score below the accepted threshold means the criteria are not met, regardless of what the strength or hop data show. The athlete's self-assessment has the same gate-keeping status as the objective tests.

For younger athletes, parental or guardian confirmation of psychological readiness and informed consent is an explicit part of the process, not an informal add-on.

Each role is non-substitutable: structural confidence cannot replace functional evidence, and neither can substitute for the athlete's own reported readiness.

Psychological readiness — a formal gate, not a formality

The ACL-RSI questionnaire covers three distinct areas: how the athlete feels emotionally about the injured knee, their confidence in its physical performance under load, and — the most telling — their appraisal of risk when returning to sport. It is this third domain, risk appraisal, that separates those who ultimately return from those who do not. At 24 months post-surgery, athletes who had returned to sport scored a mean of 55.9 on the risk appraisal subscale; those who had not returned scored 23.8. That gap — more than 30 points — is the most persistent divergence across all three subscales and the one that takes longest to improve with time alone.

The nuance the scale captures runs in both directions. Low scores on risk appraisal reflect fear that may still be clinically protective; a passing threshold of ≥80 overall is set partly because some level of caution is appropriate. But some research suggests that very high psychological readiness scores carry their own concern — athletes who feel entirely confident may underestimate movement risk and adopt patterns that raise, rather than lower, their chance of re-injury. Fear of re-injury is therefore not simply a barrier to clear before returning: at one extreme it blocks readiness; at the other, its absence may contribute to recurrence. The ACL-RSI is designed to capture that range — which is why a clinical conversation exploring all three domains, not just a total score, gives the most complete picture of where an athlete actually stands.

What most athletes actually experience in practice

Knowing what the Melbourne Protocol requires is one thing; knowing whether you are receiving it is another. The honest picture from published research is that full criteria-based clearance — covering strength symmetry, hop performance, psychological readiness, and the nine-month biological window simultaneously — remains far from universal.

An international survey of 476 physiotherapists across Australia, the Netherlands, and France found no consensus on which thresholds should trigger clearance. The most commonly applied limb symmetry index cut-off for both strength and hop testing was 70% — roughly 20 to 25 percentage points below the 90–95% Melbourne standard. Many practitioners also weighted swelling levels (below grade 1+) and pain scores (0–3 out of 10) as primary decision factors, which are useful safety checks but not the same as functional readiness benchmarks.

Beyond thresholds, the underlying methodology varies. Hop test protocols differ across centres in setup, instruction, and how many hops are included, which makes comparison between settings — and the validity of any single 'pass' — harder to judge.

A 2025 neuromuscular review flags a further gap: arthrogenic muscle inhibition (AMI), a pattern of persistent quadriceps inhibition driven by altered nerve feedback, may endure for months or years after surgery yet be invisible to a standard strength-symmetry measure. If the inhibited muscle produces acceptable LSI numbers through compensatory effort, the underlying deficit may go undetected.

None of this means a time-based clearance process is reckless — clinical variation has systemic causes, including resource constraints and absence of accessible dynamometry. But it does mean the process an individual athlete undergoes may differ substantially from the published protocol. Asking your clinical team which thresholds they are using, and how performance is measured, is a reasonable and straightforward question.

Questions worth asking before your clearance appointment

Four direct questions are worth raising before — or during — any clearance appointment.

• What LSI threshold are you using for strength and hop testing, and is it 90% or above? The evidence base sits at ≥90–95%; a cut-off of 70% is common in practice but meaningfully lower than the criteria-based standard.
• Is psychological readiness formally measured, and how? The ACL-RSI, or an equivalent validated tool, should be part of the process — not a brief conversational check at the end of the session.
• Who is involved in the clearance decision? A multidisciplinary process typically includes the surgeon, the physiotherapist who holds the longitudinal performance data, and ideally a sports medicine clinician. Clearance signed off by one person alone may reflect a compressed process.
• Is progression criteria-based or primarily time-driven? If the answer centres on a fixed post-operative date rather than specific benchmarks — strength symmetry, hop performance, readiness score — it is worth asking what happens if those benchmarks have not yet been met.

None of these questions are confrontational. They reflect what the evidence says a thorough process looks like, and any clinical team running one will answer them readily. If clearance feels primarily time-driven and the questions above do not surface a clear criteria-based framework, seeking a second opinion from a sports medicine specialist is a straightforward and reasonable step.