Background: The risk of subsequent anterior cruciate ligament injury to either knee after surgery based on sex, age, and activity has not been extensively studied.
Hypotheses: Women have a higher incidence of anterior cruciate ligament injury to the contralateral knee after surgery than men but do not have a difference in injuries to the reconstructed knee. Young, competitive athletes have a higher incidence of injury than older patients. The time to return to full activities does not affect injury rate.
Study design: Cohort study (prognosis); Level of evidence, 2.
Methods: The authors prospectively followed 1820 patients after primary anterior cruciate ligament reconstruction to determine if patients suffered an injury to either knee within 5 years after surgery. Subsequent injury was evaluated based on sex, age, and activity level.
Results: Minimum 5-year follow-up was obtained on 1415 patients (78%). Seventy-five patients (5.3%) had an injury to the contralateral knee, and 61 patients (4.3%) suffered an injury to the reconstructed knee (P = .2185). Women suffered more injuries (7.8%) to the contralateral normal knee than men (3.7%; P < .001) but not more injuries to the reconstructed knee (4.3% vs 4.1%; P = .5543). The risk of subsequent injury to either knee was 17% for patients <18 years old, 7% for patients aged 18 to 25 years, and 4% for patients older than 25 years. There was no difference in injury rate between patients who returned before and after 6 months postoperatively.
Conclusion: Women have a higher incidence of anterior cruciate ligament injury to the contralateral knee than men after reconstruction. The incidence of injury to either knee after reconstruction is associated with younger age and higher activity level, but returning to full activities before 6 months postoperatively does not increase the risk of subsequent injury.