Return to sports following ACL reconstruction: prospective analysis of functional stability 3 months postoperatively in 280 patients
Authors: Zantop Thore , Terai Shozaburo , Warminski Przemyslaw , Zantop Christian 
Published: September 2020

Introduction: For the last years, the terms return to play and return to competition after ACL reconstruction have been spread. Recent literature does not provide sufficient information on the approach to identify knee joint conditions that are likely to result in a recurrent injury following ACL reconstruction. Aim of this study is therefore to prospectively investigate the functional stability after ACL reconstruction by one single surgeon 3 months postoperatively. Hypotheses: The functional stability after ACL reconstruction 3 months postoperatively can safely be assessed using a multi-factorial testing analysis. Methods: All patients of the year 2018 diagnosed with a primary ACL instability and treated by one single surgeon were enrolled and prospectively assessed. Follow-up at 12 weeks postoperatively was performed using a functional “return-to-sports” analysis including isokinetic and isometric strength measurement (quad/ham ratio, BTE-primus), postural stability tests (MTF balance score), tapping test (force plate, Bertec) and a 3d-motion analysis (myomotion, Noraxon) during bilateral drop jumps and single leg hop tests (uni- and bilateral drop-jump, bilateral Counter Movement-Jump, Single-Leg Hop for Distance). Agility was assessed using speed chase (Speedcort system, Globalspeed). Jump height and distance were recorded by infra-red measuring device (Optogait, Microgate, Italy). Motion analysis to determine the quality of landing and jumping mechanisms using a real time 3d-avatar (myomotion, Noraxon) were investigated during a speedcourt and jump analysis. Contributed to the early time onset of functional analysis, any abnormalty in the bilateral jump tests or refusal of the jump test by the patient led to non-performance to the jump test with the postoperative leg. Statistical analysis were performed using a Wilcoxon-Rank-Sum-Test (p<0.05). Results: At analylsis date of 404 primary ACL reconstruction of the year 2018 a total of 324 patients particated in the functional analysis at three months postoperatively. During the “return-to-sports” no giving way symptoms or recurrent instability was to be recorded. BMI was 25,3 (+/-4,1) and 25,9 (+/-3,7) for female and male patients, respectively. Approximately 40% of all patients were able to perfom single legged jump tests. Three months postoperatively, the perfomance of the ACL reconstructed knee was significantly lower than the intact contralateral leg. Isometric and isokinetic strength analysis showed significantly lower peak maximal force for quadriceps and hamstrings compared to the intact contralateral side. No significant differences were seen in the analysis of the postural stability analysis. Even though the contact forces were significantly different between the intact leg and the postoperative leg, there was no significant differences between the quantitate analysis of the jump height and distance in the dimensions jumping and agility. As a parameter of functional valgus instability the medial knee displacement according to Krosshaug et al. 2016 was severely high, however there was no statistical significant difference to the intact leg. Conclusion: This study shows that a functional analysis at an early timepoint following ACL reconstruction reveals high abnormalities with regard to the quality of the landing mechanism. To further contribute to the high number of recurrent instabilities in the young athlete below 20 years of age, this may be crucial to intervene avoiding a medial knee displacement. To accomplish this, all patients were supported with specific training-protocols for further rehabilitation of the lower extremity. These protocols were individually set-up, however in nearly all patients a specific emphasize was on strengthening of the hip external rotators.