Purpose: To investigate the effects of graft source, time since surgery, age, and sex on unilateral and symmetry-based measures of knee extension strength among individuals with ACL reconstruction (ACLR).
Methods: Three hundred and eight individuals aged 13-40 years old with primary, unilateral ACLR in the last 60 months were enrolled in this multi-site clinical measurement study. Participants completed bilateral knee extension maximal voluntary isometric contraction (MVIC) torque assessments which were normalized to body mass (Nm/kg) and limb symmetry indices (LSI) were calculated. The effects of graft source (patellar tendon autograft; hamstring tendon autograft), time since surgery (≤ 12 months; >12 mo.), age (≤ 18 years; >18 years), and sex were evaluated using separate ANCOVAs.
Results: A significant interaction was present between time since surgery and graft source for LSI (P = 0.01) as participants with patellar tendon autografts ≤ 12 months post-ACLR experienced the greatest asymmetry (LSI = 69.2 ± 24.5%). Significant interactions were present between time since surgery and sex for involved limb (P = 0.01) and uninvolved limb MVIC torque (P = 0.05) with females ≤ 12 months post-ACLR being weakest (involved MVIC = 1.81 ± 0.70 N m/kg; uninvolved MVIC = 2.40 ± 0.68 N m/kg). Participants ≤ 18-year-old displayed weaker involved limb (P < 0.001) and contralateral limb (P < 0.001) MVIC torque as compared to participants > 18-year-old during the first year after ACLR.
Conclusions: Graft source, sex, age, and time since surgery effect quadriceps strength and symmetry after ACLR. Surgical and demographic factors should be considered when developing treatment approaches to optimize quadriceps function prior to re-integration into pre-injury levels of physical activity.
Level of evidence: IV.
Keywords: Isometric knee extension strength; Knee-related function; Quadriceps function.