Difference in time-course change in muscle cross-sectional area and knee and ankle functions between Japanese male patients who meet the return-to-sport criteria and those who do not meet it after triple-bundle anterior cruciate ligament reconstruction.

Background: The lower-extremity muscles are the main target of rehabilitation post-anterior cruciate ligament reconstruction (ACLR). This study aimed to investigate time-course changes in the cross-sectional area of lower-extremity muscles (MCSA) amongACLR patients.

Methods: Twenty-seven male patients who underwent ACLRwere included and groupedintoPASS and non-PASS. PASS could achieve a ratio of injured-to-uninjured performance surpassing 90 % in all hop-tests and Lysholm score of ≥ 90. Those who failed to achieve even one of those conditions were designated as non-PASS. About MCSA, magnetic resonance images of the lower extremity on the injured side were obtained. Quadriceps, hamstrings, gastrocnemius, and soleus were manually surroundedatthe slice featuredthe maximal MCSAfor each muscle. Range of motion (ROM) and muscle strength of the knee and anklewere measured. All parameters were measured before surgery (PRE) and at 3, 6, 9, and 12 months post-ACLR(POST3/POST6/POST9/POST12, respectively). Knee stability was measured using KT-1000 in patients who underwent second-look surgery. The significance level was set at 5 %.

Results: At POST12, PASS (n = 14) exhibited greater ankle dorsiflexion ROM, knee extension strength, and ankle plantarflexion strength than non-PASS (n = 13). The interaction of MCSA was not detected, thus both data were integrated into a unified group for post-hoc tests.Quadriceps MCSA at POST12 was significantly larger than that at PRE. Hamstring, gastrocnemius, and soleusMCSAsat POST12did not have significant differences than those at PRE.

Conclusions: Restoration of ankle function and strength may be important for returning to sports.