Preoperative knee laxity is not associated with subjective knee function or revision surgery after primary anterior cruciate ligament reconstruction: An analysis of 5425 patients

PURPOSE: To determine whether preoperative knee laxity, as measured by the KT-1000 arthrometer, was associated with subjective knee function preoperatively and at 1, 2 and 5 years, or with revision anterior cruciate ligament (ACL) reconstruction (ACLR) within 5 years of the primary surgery. METHODS: Patients who underwent primary ACLR using a hamstring tendon autograft at the Capio Artro Clinic, Stockholm, Sweden, between January 1, 2005, and December 31, 2018, and had no associated ligament injuries, were identified. The KT-1000 arthrometer (134-N) was used to assess knee laxity preoperatively. The Knee injury and Osteoarthritis Outcome Score (KOOS) was obtained preoperatively and at 1-, 2- and 5-year follow-ups. Patients who underwent revision ACLR at any hospital or clinic nationwide within 5 years of their primary surgery were identified via the Swedish Knee Ligament Registry. KOOS subscale scores between groups were compared using analysis of covariance (ANCOVA), while differences in revision ACLR rates were evaluated using Cox regression analysis. RESULTS: A total of 5425 patients (54.0% male) with available preoperative KT-1000 arthrometer measurements were included: side-to-side (STS) ≤ 2 mm, 1833 (33.8%); STS 3-5 mm, 2387 (44.0%); STS > 5 mm, 1205 (22.2%). The only significant differences in subjective knee function among the groups were observed in the preoperative KOOS Symptoms (STS ≤ 2 mm: 75.0 ± 17.4; STS 3-5 mm: 75.1 ± 17.5; STS > 5 mm: 76.4 ± 17.1; P = 0.03) and Pain (STS ≤ 2 mm: 78.9 ± 15.9; STS 3-5 mm: 79.4 ± 15.9; STS > 5 mm: 80.4 ± 15.2; p = 0.02) subscale. No additional significant differences were observed between the groups in any of the KOOS subscales at the preoperative assessment or at the 1-, 2- or 5-year postoperative follow-ups. At 5 years postoperatively, the revision ACLR rates were 4.8% (89/1833) in the STS ≤ 2 mm group, 4.9% (118/2387) in the STS 3-5 mm group and 6.0% (73/1205) in the STS > 5 mm group. The hazard of revision ACLR within 5 years did not differ significantly from the reference group (STS ≤ 2 mm) for either the STS 3-5 mm group (hazard ratio HR, 0.96; 95% confidence interval CI, 0.69-1.35; p = n.s.) or the STS > 5 mm group (HR, 1.19; 95% CI, 0.89-1.60; P = n.s.). The incidence of medial meniscus injury increased progressively across the laxity groups from 20.7% in the STS ≤ 2 mm group, to 25.0% in the STS 3-5 mm group and 31.9% in the STS > 5 mm group. CONCLUSIONS: The degree of preoperative knee laxity, as measured by the KT-1000 arthrometer, was not associated with postoperative subjective knee function or revision ACLR within 5 years of primary surgery. Medial meniscus injuries were associated with greater preoperative knee laxity. The findings of this study suggest that preoperative arthrometric knee laxity should not be considered as a prognostic factor for ACLR outcomes. LEVEL OF EVIDENCE: Level III.