Physiologic Preoperative Knee Hyperextension Is Not Associated With Postoperative Laxity, Subjective Knee Function, or Revision Surgery After ACL Reconstruction With Hamstring Tendon Autografts

Background: There is concern that physiologic knee hyperextension may be associated with inferior outcomes after anterior cruciate ligament reconstruction (ACLR) using hamstring tendon (HT) autografts. Purpose: To assess whether there is an association between contralateral passive preoperative knee hyperextension (≤−5°) and postoperative anterior knee laxity, subjective knee function, or revision surgery after ACLR using HT autografts. Study Design: Cohort study; Level of evidence, 3. Methods: Patients without concomitant ligament injuries who underwent primary ACLR using an HT autograft at Capio Artro Clinic, Stockholm, Sweden, between January 1, 2005, and December 31, 2018, were identified. The cohort was dichotomized into the hyperextension group (≤−5°) and the no hyperextension group (>–5°) depending on preoperative contralateral passive knee extension degree. Anterior knee laxity (KT-1000 arthrometer; 134 N) was assessed preoperatively and at 6 months postoperatively. The Knee injury and Osteoarthritis Outcome Score (KOOS) was collected preoperatively and at 1, 2, and 5 years postoperatively. Patients who underwent revision ACLR at any institution in Sweden within 5 years of the primary surgery were identified in the Swedish National Knee Ligament Registry. Results: A total of 6104 patients (53.5% male) for whom knee range of motion measurements were available were identified (hyperextension group [≤−5°]: 2350 [38.5%]; mean extension, −6.1°± 2.3° [range, −20° to −5°]; no hyperextension group [>−5°]: 3754 [61.5%]; mean extension, 0°± 1.4° [range, −4° to 15°]). There were no intergroup differences in anterior knee laxity preoperatively (hyperextension group, 3.6 ± 2.8 mm; no hyperextension group, 3.7 ± 2.7 mm; P = .24) or postoperatively (hyperextension group, 1.8 ± 2.3 mm; no hyperextension group, 1.8 ± 2.2 mm; P = .41). The only significant but nonclinically relevant intergroup differences were seen in the KOOS Symptoms subscale at the 1-year follow-up (hyperextension group, 81.4 ± 16.0; no hyperextension group, 80.3 ± 16.5; P = .03) and in the Sport and Recreation subscale at the 5-year follow-up (hyperextension group, 73.0 ± 25.6; no hyperextension group, 75.7 ± 24.3; P = .02). No other significant intergroup differences were noted preoperatively or at 1, 2, or 5 years postoperatively in any of the KOOS subscales. The overall revision ACLR rate at ≤5 years after the primary surgery was 4.9% (302 of 6104 patients). The hazard for revision ACLR in the no hyperextension group (4.5%; 170 of 3754 patients) was not significantly different from that in the hyperextension group (5.6%; 132 of 2350 patients) (hazard ratio, 0.89; 95% CI, 0.71 to −1.12; P = .34). A subsequent subanalysis showed that the hazard of revision ACLR in patients with no hyperextension was not significantly different from that of patients with ≤−10° of extension (5.8%; 27 of 467 patients) (hazard ratio, 0.91; 95% CI, 0.61 to 1.36; P = .65). Conclusion: Preoperative passive contralateral knee hyperextension (≤−5°) was not associated with postoperative anterior knee laxity, subjective knee function, or revision surgery ≤5 years after ACLR using HT autografts. Therefore, the presence of knee hyperextension alone should not be considered a contraindication per se for the use of HT autografts in ACLR.