Correlation Between Psychological Readiness, Knee Function, and Isokinetic Performance After Anterior Cruciate Ligament Reconstruction (ACLR) Using Peroneus Longus Tendon Graft (PL-ACL-2025)

Rationale and Objectives Anterior cruciate ligament reconstruction (ACLR) using a Peroneus Longus autograft is increasingly adopted; however, return-to-sport (RTS) decisions often emphasize strength or hop metrics while under-weighting psychological readiness. This single-center case-control study evaluates whether athletes who meet a predefined RTS test battery ("RTS-ready") differ from athletes who do not ("RTS-not-ready") in psychological readiness, knee function, isokinetic performance, hamstring-to-quadriceps (H/Q) strength ratio, and dynamic postural control/core endurance. The central hypothesis is that an integrated profile (physical + psychological) characterizes RTS-ready athletes and can inform safer, individualized RTS decisions after ACLR with Peroneus Longus.

Design and Setting Observational, case-control, cross-sectional assessment conducted in a university sports rehabilitation laboratory. Participants attend a single evaluation visit between 6 and 9 months post-ACLR after completing a standardized postoperative rehabilitation pathway. Group assignment (Case = RTS-ready; Control = RTS-not-ready) is determined by performance on the prespecified RTS battery during the same visit.

Participants Key inclusion and exclusion criteria (e.g., male recreational athletes in cutting/jumping sports; primary unilateral ACLR with Peroneus Longus autograft; exclusion of revision/multi-ligament injuries, significant pain or ROM limitation) are listed in the Eligibility Criteria section and are not repeated here.

Procedures and Test Order

All testing is performed in a single session by trained assessors after informed consent and a brief familiarization to minimize learning effects. To standardize workload and reduce fatigue and order effects, assessments proceed as follows:

Self-report instruments: psychological readiness and knee function questionnaires (validated Arabic versions).

Standardized warm-up: 5-10 minutes of low-intensity cycling followed by dynamic lower-limb mobility.

Isokinetic strength testing: HUMAC NORM dynamometer with standardized positioning (seating/strapping), axis alignment to the lateral femoral condyle, and knee range of motion set to approximately 0-90°. After practice trials, peak concentric torque for quadriceps and hamstrings is recorded at 60°/s, 120°/s, and 240°/s per manufacturer guidelines and lab SOPs. Rest intervals of at least 60-90 seconds are provided between sets. Limb Symmetry Index (LSI) is calculated as (involved/uninvolved) × 100 for each parameter. The H/Q ratio is calculated as peak hamstring torque divided by peak quadriceps torque at each speed.

Functional performance tests: single-leg hop for distance (best of three valid trials per limb; hands on hips; controlled landing), Y-Balance Test (anterior, posteromedial, posterolateral reaches normalized to limb length), and prone plank (time to task failure using standardized termination criteria).

Vital signs and knee discomfort are monitored throughout; testing is stopped if predefined safety thresholds are exceeded.

RTS Battery and Group Assignment The RTS battery used for group assignment (e.g., LSI thresholds for isokinetic quadriceps/hamstrings, single-leg hop LSI, and IKDC threshold) is defined in the Outcome Measures section. Participants meeting all criteria are classified as RTS-ready (Case), otherwise RTS-not-ready (Control). Assessors collecting raw measurements remain blinded to RTS labels until all tests are completed and the RTS algorithm is applied.

Quality Control and Bias Minimization The dynamometer undergoes daily calibration verification and periodic full calibration per manufacturer schedule. Scripted instructions and standardized verbal encouragement are used. Equipment setup (seat/backrest angles, lever arm length, strap positions) is recorded to ensure consistency. Any protocol deviations, adverse events, or premature terminations are documented. Data are double-entered and range-checked prior to analysis.

Outcomes Primary and secondary outcomes (psychological readiness, knee function, isokinetic peak torque/LSI, H/Q ratio, hop performance, Y-Balance, and core endurance), including instruments, scoring ranges, directionality, and time frame (single visit at 6-9 months post-op), are fully specified in the Outcome Measures section of this record.

Sample Size and Statistical Analysis A priori sample-size estimation targeted 80% power (two-sided α = 0.05) to detect a moderate between-group effect size in the primary outcomes; detailed parameters are provided in the Statistical Analysis Plan (if uploaded). Data will be screened for normality (e.g., Shapiro-Wilk) and outliers; continuous variables will be summarized as mean ± SD (or median [IQR] if non-normal), categorical variables as counts (%). Between-group comparisons will use independent-samples t-tests (or Mann-Whitney U where assumptions are violated) and chi-square or Fisher's exact tests for categorical variables. Exploratory multivariable logistic regression will estimate the independent association of psychological readiness, strength (LSI), H/Q ratio, and functional tests with RTS status while adjusting for potential confounders (e.g., age, BMI, time since surgery). Effect sizes (Cohen's d or odds ratios with 95% CIs) will be reported. Missing data will be handled with complete-case analysis; if >5% of a primary outcome is missing, sensitivity analyses will be performed. Statistical significance is set at p < 0.05. Analyses will be conducted using SPSS (Version 29.0).

Ethics and Safety The study complies with the Declaration of Helsinki and has Institutional Review Board approval. Written informed consent is obtained before participation. The procedures are non-invasive and considered minimal risk; predefined stop rules are applied for pain or adverse symptoms.

Expected Impact By integrating psychological readiness with objective strength and functional performance, this study aims to refine RTS decision-making after ACLR using Peroneus Longus autografts, potentially reducing re-injury risk and enabling more individualized rehabilitation progressions.