Concomitant injuries may not reduce the likelihood of achieving symmetrical muscle function one year after anterior cruciate ligament reconstruction: a prospective observational study based on 263 patients

PURPOSE: A better understanding of patient characteristics and the way common concomitant injuries affect the recovery of muscle function after surgery should help providers to treat patients with anterior cruciate ligament (ACL) injuries. The aim of this study was to determine whether patient characteristics, concomitant injuries and graft choice at ACL reconstruction were associated with symmetrical knee muscle function at one year. The hypothesis was that the presence of concomitant injuries would negatively influence the opportunity to achieve symmetrical knee function at the one-year follow-up. METHODS: Data was extracted from the Swedish National Knee Ligament Register and a rehabilitation outcome register between August 2012 and December 2016. The patients had been evaluated with a battery of tests comprising knee extension and flexion strength, vertical jump, hop for distance and the side-hop test one year after ACL reconstruction. Univariable and multivariable logistic regression analyses were performed with achieving a limb symmetry index (LSI) of ≥ 90% in all tests of muscle function as primary outcome. RESULTS: A total of 263 patients with a mean age of 26.7 ± 10.3 years were included in the study (47% females). No patient demographic or intra-operative predictors were found to be significant when attempting to predict the achievement of a symmetrical muscle function. Lateral meniscus injury and a patellar tendon autograft reduced the odds of achieving an LSI of ≥ 90% in knee extension strength, OR = 0.49 [(95% CI 0.25–0.97), p = 0.039] and OR = 0.30 [(95% CI 0.14–0.67), p = 0.0033] respectively. In addition, reduced odds of recovering knee extension strength were found in older patients, OR = 0.76 [(95% CI 0.60–0.98), p = 0.034]. A higher pre-injury level of physical activity increased the odds of recovering knee flexion strength, OR = 1.14 [(95% CI 1.01–1.29), p = 0.037]. CONCLUSION: Intra-operatively identified concomitant injuries or graft choice did not affect the likelihood of recovering symmetrical performance in five different tests of muscle function one year after ACL reconstruction. However, fewer than one in four patients achieved an LSI of ≥ 90% in all tests. LEVEL OF EVIDENCE: Prospective observational study: Level 2. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s00167-018-4845-2) contains supplementary material, which is available to authorized users.