Association of Persistent Interlimb Kinetic Asymmetry at Return to Sport With Increased Risk of Contralateral Anterior Cruciate Ligament Injury
Orthopaedic journal of sports medicine · 2026
Athletes who pass RTS testing but still show force-plate asymmetry have nearly 1.5x the risk of tearing the other ACL, though this needs validation before changing clearance decisions.
The paper
Cohort study (Level of evidence 3), n=500 patients after primary unilateral ACL reconstruction who completed force-plate biomechanical testing at RTS clearance, followed for a mean of 36 months for contralateral ACL injury.
What they found
24% (120/500) sustained a contralateral ACL injury; each 1-SD increase in interlimb peak vGRF asymmetry at RTS was independently associated with higher risk (adjusted HR 1.47, 95% CI 1.23-1.75, p<.001), and adding kinetic asymmetry to conventional RTS criteria improved discrimination from C-index 0.64 to 0.76.
Study design
This is a single-centre prospective cohort study of 500 patients who underwent primary ACL reconstruction and completed return-to-sport (RTS) testing, followed forward in time to track contralateral ACL injury; it sits above case series and retrospective cohorts but below an RCT or externally validated prognostic model, so it can establish association and risk-stratification but not causation.
Methodology
Interlimb peak vertical ground reaction force (vGRF) asymmetry was captured at a single RTS testing session (likely a jump-landing or hop protocol on force plates), then entered as a continuous predictor in an adjusted Cox proportional-hazards model, with the C-index comparison against conventional RTS criteria calculated within the same derivation sample rather than a held-out or external cohort, so the model is optimistically biased and the 0.64-to-0.76 gain will likely shrink on re-testing elsewhere. Key threats are selection bias, since only patients who actually reached and passed RTS testing were eligible, meaning slower or higher-risk recoveries may be underrepresented; ascertainment bias in confirming contralateral ACL injury, which depends on how consistently re-injury was captured (clinical follow-up and imaging versus patient self-report) across a presumably multi-year follow-up; and residual confounding, since asymmetry likely correlates with unmeasured factors like graft type, sport level, or psychological readiness that also drive re-injury risk. A clinician wanting to reproduce the ascertainment would need the same standardised RTS force-plate protocol and vGRF asymmetry calculation the authors used, not an ad hoc single-leg hop test.
The appraisal
The hazard ratio is statistically robust and the discrimination gain (0.64 to 0.76) is a meaningful jump for a prognostic model, but a single-cohort HR doesn't tell a clinician the actual injury probability for an individual asymmetry value, and without external validation this could shrink substantially in another population. It's a solid association, not yet proof that correcting the asymmetry reduces injury risk, since no intervention was tested.
The gap
No external validation cohort and no data on whether modifying interlimb asymmetry before clearance actually lowers contralateral ACL injury rates; that intervention trial is the missing piece before this changes RTS criteria.
Landmark context
This builds on the well-established literature (Paterno et al. and others) showing biomechanical asymmetries persist despite meeting standard RTS criteria and predict second ACL injury; this paper adds a specific kinetic asymmetry metric and formal risk-prediction modeling (C-index, decision curve analysis) on top of that established association.
What to do Monday
If a clinic already has force-plate capability, this supports incorporating interlimb vGRF asymmetry into RTS testing batteries as an added risk marker, but it shouldn't be used alone to deny or delay clearance since no trial has shown correcting it changes outcomes.
In practice
Applies to ACLR patients nearing RTS who already meet standard clinical/functional criteria (strength symmetry, hop tests) but are being cleared largely on those metrics alone. In clinic, if you have force-plate access, add a single-leg landing/loading asymmetry check (Benchmark Single Leg Jump, comparing peak vGRF and loading rate side to side) as a final data point at the RTS visit; athletes who clear on hop/strength tests but show marked landing asymmetry get flagged for extra loading-based work (eccentric quad/glute capacity, landing mechanics retraining) and a staged rather than blanket return, not an automatic delay since no trial yet shows correcting the asymmetry cuts injury risk. On the S&C floor this is a cue to fold the same asymmetry check into return-to-performance testing days alongside CMJ or hop testing, and to load flagged athletes more conservatively and asymmetrically-aware (limb-specific volume, landing technique cueing) through early return-to-training rather than assuming symmetry once strength benchmarks are hit. Treat the asymmetry figure as a conversation starter and monitoring flag, not a pass/fail gate, since this abstract gives no validated cutoff.
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