Contralateral knee hyperextension is associated with increased anterior tibial translation and fewer meniscal injuries in the anterior cruciate ligament-injured knee

PURPOSE: To investigate the influence of hyperextension of the contralateral healthy knee on anterior tibial translation (ATT) and the presence of associated injuries in the anterior cruciate ligament (ACL)-injured knee. METHODS: A local patient data register containing the surgical and clinical data of patients undergoing ACL reconstruction was analyzed. Patients were divided into groups according to the degree of hyperextension of the contralateral knee: normal (Group A ≤ 0°), mild (Group B 1°–5°), moderate (Group C 6°–10°), and severe (Group D > 10°). The ATT was measured in both knees preoperatively and 6 months postoperatively using the KT-1000 arthrometer. The presence of associated meniscal and cartilage injuries was noted. Using multivariate analysis, Groups B, C, and D were compared with Group A, using this group as a reference. RESULTS: A total of 10,957 patients were available in the register and 8502 (Group A n = 4335, Group B n = 3331, Group C n = 771, Group D n = 65) were included in the final analysis. Groups B (10.3 mm; 95% CI 0.06–0.042, p < 0.0001) and C (10.6 mm; 95% CI 0.23–0.89, p = 0.006) showed significantly greater preoperative ATT in the injured knee compared with the control group (10.1 mm). Moreover, at the 6-month follow-up, greater ATT was observed for Groups B (8.5 mm; 95% CI 0.13–0.45, p < 0.0001), C (8.5 mm; 95% CI 0.02–0.60, p = 0.035), and D (9.1 mm; 95% CI − 0.08–1.77, p = 0.082) compared with Group A (8.2 mm). Meniscal injuries were less frequent in patients with contralateral hyperextension [Group B 903 (27.1%) p < 0.0001, Group C 208 (27.0%) p = 0.0003, and Group D 12 (18.5%), 0.012] compared with the control group [Group A 1479 (34.1%)]. CONCLUSION: Contralateral knee hyperextension is associated with greater pre- and postoperative ATT in the ACL-injured knee. In patients with contralateral knee hyperextension, concomitant injuries to the menisci are less frequent. Surgeons should consider grafts with superior properties regarding postoperative anteroposterior laxity to patients with contralateral knee hyperextension. LEVEL OF EVIDENCE: Retrospective cohort study, Level IV