Quadriceps Strength Recovery Trajectories Associate with Pre-Operative Predictors but not Clinical Outcomes Following ACL Reconstruction

Purpose: Quadriceps weakness following anterior cruciate ligament reconstruction (ACLR) is common, however distinct longitudinal strength trajectories not have been examined. This study aimed to i) identify strength trajectories measured pre-operatively to 12 months post-ACLR, and determine associations with ii) pre-operative demographics, patient-reported outcomes (PROs: Knee Injury and Osteoarthritis Outcome Score [KOOS], Tegner, Marx) and ACLR concomitant surgeries, and iii) clinical outcomes post-ACLR including cartilage compositional changes (via magnetic resonance imaging [MRI] T1ρ relaxation times) and 12-month KOOS. Methods: Isometric quadriceps strength was measured bilaterally pre-operatively and at 4, 6, and 12 months. Group trajectory modeling characterized longitudinal strength recovery in ACLR and uninvolved limbs, which were combined to define dual-limb recovery patterns. Tibiofemoral and patellofemoral cartilage composition was measured pre-operatively and at 12 months post-ACLR. Dirichlet regressions examined associations between trajectories and demographics, surgeries, PROs, and cartilage changes. Results: 59 participants were included (58% female; age, 21.9 ± 4.7y; BMI, 24.55 ± 3.7kg/m 2 ). Three combined trajectories were identified: bilaterally weak (51%), which demonstrated uninvolved limb strength declines and failure to recover ACLR limb pre-operative strength; bilaterally strong (38%), which demonstrated minimal uninvolved limb declines and ACLR limb pre-operative strength recovery; and weak uninvolved, strong ACLR limb (12%). Lower pre-injury Tegner scores associated with bilaterally weak membership (p = 0.01), where probability increased from 0.27 (score of 10) to 0.61 (score of 0). Medial meniscectomy associated most with bilaterally weak membership (p<.001, 0.86 probability). No associations were found between trajectories and clinical outcomes. Conclusions: While individuals who failed to restore ACLR limb strength demonstrated bilateral quadriceps weakness pre-operatively, persons who demonstrated greater pre-operative bilateral strength recovered ACLR limb strength. Medial meniscectomy associated with an inability to restore quadriceps strength.