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