Changing presentation of knee dislocation and vascular injury from high-energy trauma to low-energy falls in the morbidly obese.

OBJECTIVE: Reports in the literature of low-energy (LE) knee dislocation (KD) in obese patients have been increasing. This study was undertaken to define the risk factors for KD by LE mechanisms and the outcomes of these patients compared with those with high-energy (HE) trauma.

METHODS: All patients with a complete KD presenting to the emergency department of a large urban level I trauma center were reviewed. Patient information collected included age, sex, weight, height, body mass index (BMI), injury mechanism, neurovascular and orthopedic injuries, and operations performed to treat vascular injuries. Risk factors for KD and concomitant injuries were compared between HE traumatic dislocations and LE dislocations in obese patients (BMI >30 kg/m(2)), including stratification for increasing levels of obesity.

RESULTS: Between January 1995 and April 2012, 53 patients with KD were identified. The mechanism of injury was HE in 28 (53%) and LE in 25 (47%). Of the LE KDs, 18 (72%) were related to obesity (BMI >30 kg/m(2)). Obese patients with LE trauma were more likely to have associated nerve injuries (50% vs 6%; P < .001), vascular injuries requiring intervention (33% vs 9%; P = .048), and vascular surgical repairs (28% vs 6%; P = .038) than patients with HE traumatic dislocations. These rates were highest in the patients with a BMI >40 kg/m(2). Although all LE KDs in the obese involved an isolated extremity, the hospital lengths of stay were comparable to those with HE KDs who frequently had multisystem trauma (8.7 vs 11.4 days). During a 17-year period, LE KDs in the obese represented an increasing proportion, from 17% in 1995 to 2000 up to 53% in 2007 to 2012, and the eventual majority of all KDs at our institution (P = .024).

CONCLUSIONS: LE KDs in obese patients are becoming increasingly prevalent. These patients are more likely to have nerve and vascular injuries and are more likely to undergo vascular repair than patients with HE trauma. The epidemic of obesity in the United States presents unique challenges in the identification and treatment of patients with LE KD and their associated injuries.