Cross-education does not improve early and late-phase rehabilitation outcomes after ACL reconstruction: a randomized controlled clinical trial

Purpose: Limited evidence suggests that cross-education affords clinical benefits in the initial 8 weeks after anterior cruciate ligament (ACL) reconstruction, but it is unknown if such cross-education effects are reproducible and still present in later phases of rehabilitation. We examined whether cross-education, as an adjuvant to standard therapy, would accelerate the rehabilitation up to 26 weeks after ACL reconstruction by attenuating quadriceps weakness. Methods: ACL-reconstructed patients were randomized into experimental (n = 22) and control groups (n = 21). Both groups received standard care after ACL reconstruction. In addition, the experimental group strength trained the quadriceps of the non-operated leg during weeks 1–12 after surgery (i.e., cross-education). Self-reported knee function was assessed with the Hughston Clinic Knee score as the primary outcome. Secondary outcomes were maximal quadriceps and hamstring strength and single leg hop distance. All outcomes were measured 29 ± 23 days prior to surgery, as a reference, and at 5-week, 12-week, and 26-week post-surgery. Results: Both groups scored 12% worse on self-reported knee function 5-week post-surgery (95% CI 7–17) and showed 15% improvement 26-week post-surgery (95% CI − 20 to − 10). No cross-education effect was found. Interestingly, males scored 8–10% worse than females at each time point post-surgery. None of 33 secondary outcomes showed a cross-education effect. At 26-week post-surgery, both legs improved maximal quadriceps (5–14%) and hamstring strength (7–18%), and the non-injured leg improved 2% in hop distance. The ACL recovery was not affected by limb dominance and age. Conclusion: 26 weeks of standard care improved self-reported knee function and maximal leg strength relative to pre-surgery and adding cross-education did not further accelerate ACL recovery.