Shear wave elastography for assessing lower extremity muscle stiffness after anterior cruciate ligament reconstruction: A systematic review.
Marczak J, Lightle C, Brooks A, Kyriazi M, Chong W, Martinez J et al. · Clinical biomechanics (Bristol, Avon) · 2026
Background: Anterior cruciate ligament reconstruction (ACLR) restores passive joint stability, yet athletes who meet strength benchmarks may still land stiffly, hesitate to push off, and re-injure. Muscle stiffness governs how rapidly force is transmitted to the joint, and shear wave elastography (SWE) quantifies it muscle by muscle, but SWE
Findings: after ACLR have not been synthesized.
Methods: Scopus, PubMed, SPORTDiscus, and CINAHL were searched through November 2025 following PRISMA 2020. Eligible studies compared SWE-derived lower-extremity muscle stiffness after ACLR with contralateral limbs or controls. Two reviewers independently screened, extracted data, and appraised quality (Downs and Black).
Findings were synthesized narratively with Hedges' g (95% confidence intervals) where data permitted.
Findings were synthesized narratively with Hedges' g (95% confidence intervals) where data permitted. Findings Six studies (173 ACLR participants, 79 controls; quality poor to good) were included. Reduced passive vastus medialis shear modulus was consistently observed in operative limbs (g - 1.10 to -1.21 versus controls) and was associated with quadriceps strength, knee function, and landing biomechanics. Semitendinosus stiffness was reduced after hamstring tendon harvest (g - 1.29 to -1.64) but not at mid-belly after return to sport. Longitudinal deficits persisted at three months; active-contraction
Findings were synthesized narratively with Hedges' g (95% confidence intervals) where data permitted. Findings Six studies (173 ACLR participants, 79 controls; quality poor to good) were included. Reduced passive vastus medialis shear modulus was consistently observed in operative limbs (g - 1.10 to -1.21 versus controls) and was associated with quadriceps strength, knee function, and landing biomechanics. Semitendinosus stiffness was reduced after hamstring tendon harvest (g - 1.29 to -1.64) but not at mid-belly after return to sport. Longitudinal deficits persisted at three months; active-contraction findings conflicted. No study sampled the distal vastus medialis obliquus or the distal hamstring musculotendinous region. Interpretation SWE detects muscle-specific mechanical deficits that relate to function beyond strength: a compliant vastus medialis offers a mechanical explanation for the strong patient who lands stiffly, and reduced semitendinosus stiffness marks donor-site morbidity. Standardized protocols that sample clinically relevant regions and follow patients to return to sport are needed before SWE can guide rehabilitation.