Ultra-Low Velocity Knee Dislocations: A Challenging Population of Multiligament Knee Injuries

OBJECTIVES: Multiligament knee injuries (MLI) are usually associated with high energy mechanisms such as motor vehicle accidents or sports injuries. However, obese patients are at risk of MLI from simple falls. Termed “ultra-low velocity” (ULV) dislocations, these may be associated with higher associated risks and complications due to the patient’s inherent size. The objectives of this study are to characterize the epidemiology, risk factors, associated neurovascular injuries, and perioperative complications of ULV dislocations to allow surgeons to make informed decisions regarding their care. METHODS: Study Design: Retrospective cohort study. 215 consecutive patients with MLI were identified over a 12 year period. Their charts were reviewed to identify a cohort of patients with mechanisms consistent with ULV dislocation (n=23). This cohort was compared to all MLI. Additionally, ULV patients with neurovascular injury were compared to those without neurovascular injury. Analysis: Means and ranges were calculated for continuous variables (age, BMI) and compared between cohorts using Student’s t test. Frequencies for categorical variables were compared using chi square tests. RESULTS: Compared to all patients with MLI, the ULV cohort had significantly higher BMI, greater prevalence of female gender, and higher rates of both peroneal nerve and popliteal artery injury (Table I). Within the ULV cohort, patients with neurovascular injury demonstrated significantly greater post-operative complications (Table II). There was a trend for higher BMI to be predictive of neurovascular injury in ULV dislocations, but patient numbers limited any additional statistical analysis. CONCLUSION: ULV knee injuries occur in patients with greater BMI, more frequently in females, and with higher rates of concomitant neurovascular injury compared to other MLI. Additionally, a greater incidence of post-operative complications can be expected after ligament reconstruction in this population.