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 Increased Knee Dislocations in Morbidly Obese Patients Caused by Falls, Slips  

 Low-energy injuries rather than high-energy trauma result in more nerve and vascular injuries  

 EMBARGOED MAY 1, 2013 Contact: Sue Patterson, 970-213-8218 spatterson@vascularsociety.org

​CHICAGO–A new study in the May issue of the Journal of Vascular Surgery® compares low-energy (LE) to high-energy (HE) injuries in obese patients that result in knee dislocation (KD). A LE injury occurs when a patient falls or slips; a HE trauma is the result of motor vehicle accidents and crush injuries.
“Likely a result of the obesity epidemic, there has been a marked increase in the proportion of KD’s related to LE mechanisms in obese patients‚” said Alexander D. Shepard, MD, a vascular surgeon in the department of surgery at Henry Ford Hospital, Detroit, Mich. During a 17-year period, LE KD’s in the obese jumped from 17 percent of all KD’s in 1995 to 2000 up to 53 percent in 2007 to 2012. 
Dr. Shepard said that an LE injury usually happens when an obese person falls from a standing position or walking, rather than from a sports-related injury. “Obese patients can be difficult to diagnose because of body size and the low-velocity nature of their injury,” added Dr. Shepard. “Vascular repair or amputation in the obese can be technically challenging and is associated with more perioperative complications than in the non-obese.” 
Between January 1995 and April 2012, 53 patients who came to the Henry Ford Hospital emergency room with KD were evaluated. Twenty-eight patients were classified as HE and 25 were LE. The proportion of women was significantly higher in the LE group than in the HE group (44 percent vs. 29 percent). 
Of the LE KD cases, 72 percent were related to obesity. Twenty-six of the 53 patients (49 percent) were classified as obese, defined as a body mass index (BMI) of more than 30 kg/m2. Eighteen obese patients (69 percent) were in the LE KD group and eight patients (31 percent) were in the HE KD group. Risk factors for KD and concomitant injuries were compared between HE and LE dislocations in the obese patients.
Obese patients with LE KD had the highest rate of vascular injuries compared with all others (6 of 18 vs. 3 of 35 patients). Morbidly obese patients with LE KD had the highest rate of open vascular repair compared to patients with HE KD or non-obese LE KD (5 of 13 vs. 2 of 35 patients). Obese patients with LE trauma were more likely to have associated nerve injuries (50 percent vs. 6 percent), vascular injuries requiring intervention (33 percent vs. 9 percent) and vascular surgical repairs (28 percent vs. 6 percent) than patients with HE traumatic dislocations. These rates were highest in the patients with a BMI >40 kg/m2. The highest rates of neurovascular compromise have classically been associated with HE blunt trauma.
“In our series we found obese patients with LE KD’s to be uniquely at risk for missed diagnoses while experiencing a high rate of nerve and arterial injury,” said Dr. Shepard. “Even when obese LE KD patients are triaged appropriately and expeditious arterial repair is performed, they experienced higher rates of early wound complications, graft occlusion, and reoperation.” 
“The results of this study also suggest that the suspicion for occult KD should be heightened in any obese patient with knee pain after minor trauma,” noted Dr. Shepard, who added that radiographs should be taken immediately, and frequent serial vascular examinations should be documented by an experienced physician.
“The absence of an evidence-based protocol for workup will delay the diagnosis of concomitant vascular injury which is a distinct challenge because most LE KD’s are evaluated at non-level I trauma centers,” added Dr. Shepard. “A recent survey showed only 55 percent of academic primary care physicians understood the need to assess the vascular integrity of the limb after KD, but only 39 percent were able to identify the popliteal artery as the at-risk vessel.”

About the Society for Vascular Surgery
The Society for Vascular Surgery® (SVS.) is a not-for-profit professional medical society, composed primarily of vascular surgeons, that seeks to advance excellence and innovation in vascular health through education, advocacy, research, and public awareness. SVS. is the national advocate for 4,008 specialty-trained vascular surgeons and other medical professionals who are dedicated to the prevention and cure of vascular disease. Visit its Web site at www.VascularWeb.org​®.

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