Reports in the surgical literature of low-energy (LE) knee dislocations (KDs) in obese patients have been increasing in recent decades. Little is known about the risk factors for KD by LE mechanisms and the outcomes of these patients compared with those with high-energy (HE) trauma. All complete KDs presenting to the emergency department of a large urban level I trauma center were reviewed. Patient demographics, body mass index (BMI), injury mechanism, associated neurovascular injuries, and vascular repairs required were recorded. Risk factors for KD and concomitant injuries were compared between HE dislocations (defined as motor vehicle accidents) and LE dislocations (defined as low energy falls or sports injuries). Between January 1995 and April 2012, there were 53 patients with KD, of which 28 (52.8%) had HE injuries and 25 had LE injuries, with 18 (34.0%) of the latter group classified as obese (BMI >30 kg/m2; Table). LE KDs in obese patients were associated with increased rates of concomitant arterial and nerve injuries compared with both HE KD patients and nonobese LE KD patients (P = .04 and P < .001, respectively). The rates of arterial and nerve injuries were greatest in the most obese (BMI > 40 kg/m2; P = .01 and P < .001, respectively). Despite the isolated nature of their injury, obese patients with LE KD stayed in hospital just as long as multisystem trauma, HE KD patients and significantly longer than non-obese LE KD patients. During a 17-year period, LE KD in the obese represented an increasing proportion and eventual majority of all KDs at our institution (P = .02).TableKnee dislocations and associated injuries by mechanism and body mass index (BMI; kg/m2)CharacteristicHigh-energy (n = 28)Low-energyBMI <30BMI >30BMI >40(n = 7)(n = 18)(n = 13)Isolated extremity injury, No. (%)12 (42.9)5 (71.4)18 (100)13 (100)Any vascular injury, No. (%)3 (10.7)0 (0)6 (33.3)5 (38.5)Popliteal repair, No. (%)2 (7.1)0 (0)5 (27.8)5 (38.5)Nerve injury, No. (%)2 (7.1)1 (14.3)9 (50.0)7 (53.9)Length of stay, mean ± SD days11.4 ± 15.93.7 ± 3.08.1 ± 9.39.2 ± 10.8SD, standard deviation. Open table in a new tab SD, standard deviation. LE KDs in obese patients are becoming increasingly prevalent. These patients are more likely to have vascular and nerve injuries and are more likely to require open vascular repair than patients with HE trauma or nonobese patients with LE KD. The epidemic of obesity in the United States presents unique challenges in the management of KD.