MILWAUKEE – The obesity epidemic in the United States is bringing Americans to their knees, literally.
A growing number of obese patients are presenting to the emergency department with low-energy (LE) knee dislocations (KDs) caused by slips and falls simply from standing or from a single step.
Despite the isolated nature of their injuries, this new cohort of LE patients stayed in the hospital just as long as multisystem trauma patients with KDs resulting from high-energy injuries like car or motorcycle collisions and more than twice as long as nonobese patients with traditional low-energy knee dislocations from sports injuries.
Obese patients with low-energy KDs are more likely to have vascular and nerve injuries and to require open arterial procedures than are patients with high-energy trauma or nonobese patients with LE knee dislocations, Dr. Andrew Georgiadis explained at the annual meeting of the Midwestern Vascular Surgical Society.
He noted that knee dislocation involves progressive hyperextension of the knee, and that, at 30 degrees of hyperextension, the posterior knee capsule is rent, and at 50 degrees, the popliteal artery actually fails.
Dr. Georgiadis and his surgical colleagues have been studying this phenomenon at Detroit’s Henry Ford Hospital, where, over a 17-year period, the proportion of low-energy KDs in the obese has risen from 17% in 1995-2000 to 33% in 2001-2006 and now represents the majority (53%) of all KDs in the hospital.
Among 53 KD patients treated between January 1995 and April 2012, 28 had high-energy injuries and 25 had low-energy injuries, of which 18 were obese and 7 nonobese. Five of the obese patients had a BMI of at least 30 kg/m2 or less than 40 kg/m2, while the remaining 13 had a BMI of more than 40 kg/m2.
When compared with the high-energy and LE non-obese patients, LE obese patients were significantly more likely to have a vascular injury (33% vs. 9%), vascular repair (28% vs. 6%), and nerve injury (50% vs. 6%), said Dr. Georgiadis, an orthopedic surgery resident at Henry Ford.
These rates were even higher in the morbidly obese (BMI over 40 kg/m2) at 39%, 39%, and 54%.
Although there were only seven arterial repairs in the entire series, five of these patients had "massive BMIs" between 42-69 kg/m2 and "they all had seemingly innocuous trauma, they all had transected arteries, they all had a vein graft bypass, and all of them had some early complication related to their procedure," he said.
Those complications included wound breakdown, early return to the operating room for a fasciotomy, graft occlusion requiring early thrombectomy/revision, and rhabdomyolysis/limb loss in a patient with a prolonged diagnosis.
When asked by the audience why the grafts thrombosed early, Dr. Georgiadis replied, "I think technical difficulty is really at the heart of all these things. And remember, these are patients who are probably being diagnosed later than someone who is crushed between two buses, so there are a lot of factors combining in these cases."
LE obese patients stayed in the hospital for an average of 8.1 days, which was comparable with the 11.4 days in the high-energy KD patients, of whom only 43% had isolated injuries, and significantly longer than the 3.7 days for non-obese LE patients, he said.
Given the increasing prevalence of obese low-energy KD patients, "we should probably have heightened awareness of this injury, especially at tertiary care centers, to avoid the morbidity of neurovascular injury and the consequences of delayed recognition," Dr. Georgiadis said.
A quick glimpse at the literature suggests that the ever-expanding American is not the only one at risk of obesity-related KDs.
Four cases of knee dislocation were recently reported by Morriston Hospital in Swansea, Wales – all in morbidly obese women (BMI range of 35-41) who experienced a simple mechanical fall from standing. The four cases occurred over the course of 1 year, and all had multiple knee ligament rupture on MRI. One case also had peroneal nerve palsy, according to the article, entitled "Dislocation of the Knee: An Epidemic in Waiting?"
Dr. Georgiadis reported no conflicts of interest.