Ultra-low velocity knee dislocations: patient characteristics, complications, and outcomes.
Knee dislocations resulting in multiligament knee injuries (MLIs) are usually associated with high-energy mechanisms such as motor vehicle accidents or sports injuries; however, obese patients are at risk of MLIs from simple falls. Termed "ultra-low velocity" (ULV) dislocations, these injuries occur in obese patients during activities of daily living and may be associated with higher associated risks and complications. Ultra-low velocity knee dislocations occur more commonly in obese female patients, are associated with higher risks of neurovascular injuries, and have more significant perioperative complications compared with other MLIs. Case series; Level of evidence, 4. The records of 215 consecutive patients with MLIs were identified over a 12-year period. Their charts were reviewed to identify a cohort of patients with mechanisms consistent with ULV dislocations (n = 23). This cohort was compared with all patients with MLIs. Additionally, ULV patients with neurovascular injuries were compared with those without neurovascular injuries. The average body mass index (BMI) was significantly higher in the ULV cohort (49.1 kg/m2) compared with all patients with MLIs (34.1 kg/m2). Injuries occurred more commonly in female patients in the ULV cohort (69.6%) compared with all patients with MLIs (24.3%). Peroneal nerve injuries occurred more commonly in the ULV cohort (39.1%) compared with all patients with MLIs (8.4%), as did vascular injuries (28.1% vs. 4.7%, respectively). Postoperative complications were common among all ULV-MLI patients regardless of neurovascular injury status. Seventeen patients (6/12 in the intact group and 11/11 in the neurovascular injury group) had significant complications postoperatively. A significantly higher overall complication rate was noted in the ULV-MLI group (73.9%) compared with the entire MLI cohort (21.4%). Additionally, the ULV-MLI cohort had a higher reoperation rate, wound infection rate, deep venous thrombosis rate, and presence of vascular claudication. Ultra-low velocity knee injuries occur in patients with a greater BMI, more frequently in female patients, and with higher rates of concomitant neurovascular injuries compared with other MLIs. Additionally, a significantly greater incidence of postoperative complications can be expected after ligament reconstruction in this population compared with other MLIs.