Moderately Increased Post-Operative Anterior Knee Laxity does not Predict Decreases in Patient-Reported Outcome Scores or Subsequent Knee Surgery between 2 and 6 Years after ACL reconstruction

OBJECTIVES: A primary goal of anterior cruciate ligament reconstruction is to reduce pathologically increased anterior and rotational laxity of the knee. The impact of residual anterior laxity on patient-reported outcomes and the risk of subsequent ipsilateral knee surgery has not been clearly elucidated. The goal of this study is to determine the influence of residual anterior knee laxity on changes in patient-reported outcomes from 2 to 6 years following ACL reconstruction and risk of subsequent ipsilateral knee surgery during that period. METHODS: From a prospective multi-center cohort of patients, 429 patients under age 35 years injured in sports with no history of concomitant ligament surgery, revision ACL surgery, or surgery of the contralateral knee were identified at a minimum 2 years following primary ACL reconstruction. These patients underwent a KT-1000 assessment of anterior knee laxity examination relative to the contralateral normal knee by an independent examiner and completed patient-reported outcome assessments with KOOS and IKDC scores. Patients were followed until the 6-year mark following ACL reconstruction and any ipsilateral knee surgeries performed during this period were noted. Patients completed the same patient-reported outcome assessments at 6 years post-operative. Subsequent surgery risk was calculated and compared between those patients with side-to-side KT-1000 differences between -1 and 2 mm and those with a side-to-side KT-1000 differences between 2 and 6mm. Multiple linear regression models were built to determine the relationship between KT-1000 and 2 to 6 year change in patient-reported outcome score while controlling for age, sex, BMI, smoking status, meniscus and cartilage status, and graft type. RESULTS: Thee hundred seventy-seven patients (87.9%) were available for follow-up at the six year mark post-operative. There were 36 patients with a side to side KT-1000 difference less than -1 mm (tighter than contralateral) that were excluded from the analysis. Side-to-side KT-1000 difference was between -1 and 2 mm (IKDC A) in 153 patients, between 2 and 6 mm (IKDC B) in 162 patients, and greater than 6 mm in 26 patients. Subsequent knee surgery was performed significantly more patients in the IKDC A group (23 of 153 patients, 15%) than in the IKDC B group (13 of 162 patients, 8%) (p = 0.05). Increased side-to-side KT-1000 differences at 2-year post-operative were correlated with decreases in subjective IKDC score (β = -0.67, p = 0.038) and KOOS-sport subscale (β = -0.90, p = 0.029) but not with other KOOS subscales. A 5mm increase in anterior laxity at 2 years would predict a 3.4 point decrease in IKDC subjective score and a 4.5 point decrease in the KOOS sport subscale at 6 years post-operative. CONCLUSION: Three presence of 2 to 6 mm of residual side-to-side KT-1000 difference is not associated with an increased risk of subsequent ipsilateral knee surgery or clinically relevant decrease in patient-reported outcome score up to 6 years following ACL reconstruction.