Association between early IKDC-SKF recovery trajectories and long-term symptom acceptability after primary ACL reconstruction: a retrospective cohort study

Abstract Purpose To identify early International Knee Documentation Committee Subjective Knee Form (IKDC-SKF) recovery trajectories during the first 2 years after primary anterior cruciate ligament reconstruction (ACLR), examine their association with long-term Patient Acceptable Symptom State (PASS) at minimum 10-year follow-up, and explore whether trajectory membership added information beyond the absolute 2-year IKDC-SKF score. Methods This single-center retrospective longitudinal cohort included 256 patients (93.0% male) who underwent primary arthroscopic ACLR with hamstring tendon autograft and had IKDC-SKF scores at 6 months, 1 year, 2 years, and minimum 10-year follow-up. Latent class mixed-effects trajectory modeling used the three early postoperative time points. Logistic regression estimated adjusted PASS probabilities and risk differences (RDs). Internal model performance was assessed with bootstrap optimism correction. Results Three trajectories were identified: favorable recovery ( n = 142), gradual recovery ( n = 75), and poor/delayed recovery ( n = 39). Long-term IKDC-SKF PASS was achieved by 129/142 (90.8%), 45/75 (60.0%), and 11/39 (28.2%) patients, respectively. Adjusted PASS probabilities were 90.6%, 60.5%, and 29.6%; compared with favorable recovery, adjusted RDs were −30.1% (95% CI, −42.7% to −18.2%) for gradual recovery and −61.0% (95% CI, −76.5% to −44.1%) for poor/delayed recovery. After inclusion of the 2-year IKDC-SKF score, trajectory membership remained associated with PASS, but changes in optimism-corrected performance were small (AUC, 0.891 to 0.902; Brier score, 0.117 to 0.113). Conclusion Early IKDC-SKF recovery trajectories were associated with long-term symptom acceptability after primary ACLR. Trajectory membership remained associated with outcome after accounting for the 2-year IKDC-SKF score, but its incremental contribution to overall model performance was limited. Trajectory classification should therefore be considered an exploratory longitudinal marker rather than a validated standalone prognostic tool. Level of evidence Level III, retrospective cohort study.