Purpose: Evaluating joint laxity and graft compliance after ACL surgery may be used to quantify biomechanical graft properties during the ligamentization process. This study aimed to analyse the evolvement of joint laxity and graft compliance of short hamstring tendon grafts after ACL reconstruction (ACLR).
Methods: Forty-seven patients that underwent ACLR were retrospectively enrolled. Joint laxity was quantified with a GNRB® arthrometer before surgery, then at 15 days, at 1/3/6/9 months (M1-M9), at 1 year postoperatively and then again at the last mean follow-up (FU) of 14.7 ± 3.0 months. The side-to-side laxity difference (ΔL in mm) was measured at 30 and 60 N at every FU, additionally at 90 N from M3 on and at 134 N from M6 on. The side-to-side compliance difference (ΔC in µm/N) was calculated for each graft.
Results: Mean ΔL and ΔC decreased significantly between preoperative and M1 for all applied forces (at 30 N, ΔL: 0.8 mm, p < 0.0001; ΔC: 25.9 µm/N, p < 0.001). Between M1 and M9, ΔL increased significantly at 30 N (p = 0.02) and 60 N (p < 0.001), while ΔC increased by 15.2 µm/N at 30 N (p = 0.003) and 14.9 µm/N at 60 N (p = 0.001). Between M9 and the last FU, there were no significant differences for ΔL and ΔC.
Conclusion: Joint laxity and graft compliance evolve during the first postoperative year with a phase between the first and ninth postoperative month of relative weakness. According to the established evolvement profile, return to pivoting or contact sports should be considered only after stabilization of joint laxity and graft compliance.
Level of evidence: Retrospective cohort study, Level III.
Keywords: ACL reconstruction; Compliance; GNRB®; Hamstring tendons short graft; Laxity; Ligamentization.