Recovery of preoperative absolute muscle strength in the quadriceps or hamstrings at time of return to sport did not affect rate of a second anterior cruciate ligament injury: a registry study

Background Recovery of preoperative absolute muscle strength (PAMS) after anterior cruciate ligament (ACL) reconstuction remains a significant challenge. However, whether recovery of PAMS contributes to an affected rate of second ACL injury has yet to be explored. This study aimed to analyse the rate of a second ACL injury incidence after return to sports (RTS) between patients with ACL reconstruction dependant on the recovery of their PAMS for quadriceps and hamstrings, respectively and in combination, compared to patients who had not. Methods A retrospective cohort study with data from a rehabilitation specific registry were used. Patients who had undergone primary ACL reconstruction, were aged between 15 and 35 years, had performed complete preoperative isokinetic strength tests for quadriceps and hamstrings prior to primary ACL reconstruciton, who had a pre-injury Tegner Activty Scale ≥ 6, had returned to sport after ACL reconstruction and complete isokinetic strength tests for quadriceps and hamstrings at the same time of RTS were included. The main outcome was the rate of second ACL injury after RTS based on recovery of ≥ 90% PAMS for the quadriceps, and hamstrings indivudually, and in combination, or not. Results A total of 190 patients (mean age 22.2 ± 5.2 years, 56.3% women) were included. Thirty-one patients (16.3%) sustained a second ACL injury. There was no difference in rate of second ACL injury between patients who had recovered ≥ 90% of PAMS in their quadriceps, or hamstrings, in both limbs, respectively and in combination, compared to patients who had not. Conclusion Recovery of preoperative absolute muscle strength in the quadriceps and hamstrings respectively and in combination, at time of RTS did not affect the rate of second ACL injury.