Why Should Return to Sport Be Delayed by up to Two Years After ACL Reconstruction? A Narrative Review of the Biological, Surgical and Rehabilitation Evidence

Background: Despite outstanding clinical outcomes are routinely achieved after ACL reconstruction (ACLR), the major current issue is the failure rate (re-rupture or objective clinical instability). Reinjury rates have been reported to be about 6% for ipsilateral graft rupture and 8% for contralateral ACL rupture, with a cumulative reinjury rate of about 20%. Methods: A comprehensive review of the literature was performed to summarize the latest evidence on biological, surgical and rehabilitation aspects of ACLR. Results: It has been demonstrated that young age is a risk factor for ACL graft rupture and so is not passing return-to-play (RTP) testing following ACLR (those who pass the RTP test battery have a one-third reduction in the ACL re-rupture rate). Furthermore, up to 30% of reinjury occurs within two years from ACLR. These data can be explained by numerous pieces of evidence showing that the recovery of proprioception, proper neuromuscular activation and strength, as well as proper biomechanics, remains affected for a long time after surgery (up to two or three years in some cases) despite adequate rehabilitation programs. Conclusions: Clinical evidence, together with biological data on the ligamentization process and the remodeling phase, suggest that return to strenuous sports, especially in younger athletes, should be delayed by at least 18 months or 2 years after ACLR.