Quadriceps Strength After Anterior Cruciate Ligament Reconstruction: Mechanisms of Weakness and Evidence-Based Rehabilitation Strategies

Impairment of quadriceps strength is a frequent and clinically important problem after anterior cruciate ligament (ACL) injury and reconstruction. This dysfunction reflects muscular, neural, surgical, and rehabilitation-related mechanisms and is not solely attributable to muscle atrophy. Despite restoration of joint stability, quadriceps weakness can persist and contribute to delayed functional recovery and reduced readiness to return to sport. A comprehensive assessment should integrate clinical examination, objective isometric or isokinetic strength testing, rate of force development, functional performance, quality of movement, imaging investigations, and patient-reported and psychological measures. Rehabilitation should be initiated preoperatively and continue postoperatively with a focus on control of effusion and restoration of extension, early quadriceps activation, progressive resistance exercise, appropriate open-chain loading followed by eccentric, plyometric, and sport-specific training. Neuromuscular electrical stimulation has supportive evidence as an adjunct, and blood-flow restriction training may be useful when higher loads may not yet be tolerated. This narrative review summarizes current evidence on the mechanisms and rehabilitation of quadriceps weakness after ACL injury and ACL reconstruction, highlighting clinically relevant strategies for restoring strength and neuromuscular function.