Background: Anterior cruciate ligament (ACL) reconstruction remains one of the most common orthopedic surgical interventions, yet optimal rehabilitation protocols remain incompletely defined. While both closed kinetic chain (CKC) and open kinetic chain (OKC) exercises are widely employed in clinical practice, direct comparative evidence regarding their differential efficacy during early rehabilitation phases is limited. Objective: This study aimed to compare the differential effects of CKC versus OKC exercise protocols on knee stability, quadriceps strength, proprioception, and functional performance during early post-ACL reconstruction rehabilitation (weeks 6-12 post-operatively). Methods: A prospective randomized controlled trial was conducted with 60 participants (36 male, 24 female; mean age 28.3 ± 8.5 years) randomly allocated to CKC (n=30) or OKC (n=30) groups. Primary outcome measures included anterior knee laxity measured via Lachman test, quadriceps strength assessed by isokinetic dynamometry at 60°/second, proprioceptive function evaluated through single-leg stance testing, and functional performance determined using the 6-minute walk test and Timed Up-and-Go test. Assessments were conducted at baseline (week 6), mid-intervention (week 9), and post-intervention (week 12) phases. Results: Both interventions produced statistically significant improvements across all outcome measures (p<0.05). The CKC group demonstrated superior knee stability improvements (59.7% reduction from baseline) and enhanced proprioceptive gains (234.1% improvement; p=0.009), whereas the OKC group achieved substantially greater quadriceps strength development (113.2% improvement; p=0.003). Functional performance improvements were comparable between groups (p>0.05). Conclusions: Both CKC and OKC exercise modalities produce clinically meaningful improvements during early ACL rehabilitation, with distinct profiles of benefit. CKC exercises appear more beneficial for stability and proprioceptive restoration, while OKC exercises provide superior isolated strength gains. A combined sequential approach incorporating both modalities is recommended for comprehensive functional restoration.

Keywords: Anterior cruciate ligament reconstruction, closed kinetic chain exercises, open kinetic chain exercises, knee stability, proprioception, quadriceps strength, physical rehabilitation