Obesity tied to serious complications after knee injuries

Knee dislocations are becoming more common among obese people, and these patients are more likely than normal-weight individuals to develop blood vessel damage that can lead to amputations, a recent study suggests.

Knee dislocations happen when the patella, or kneecap, slips out of its normal position, often as a result of trauma, intense exercise or physically challenging work. But for obese people, knee dislocations are often due not to trauma or excessive force but to strain from carrying excess body weight.

For the current study, researchers examined data on more than 19,000 knee dislocations from 2000 to 2012, including almost 2,300 injuries sustained by overweight and obese people.

The proportion of patients hospitalized with knee dislocations who were also obese rose from 8 percent at the start of the study period to 19 percent by the end, the study found.

Obese people were also about twice as likely as normal-weight patients to have vascular injury, or blood vessel damage, the study also found.

“The effects of obesity go far beyond the effects on general health that are well known,” said lead study author Dr. Joey Johnson of the Warren Alpert Medical School at Brown University in Providence, Rhode Island.

Because the study also found the risk of vascular injury rose with increasing degrees of obesity, patients may benefit from losing weight even when they can’t shed enough pounds to stop being obese, Johnson said by email.

Overall, just 1,075 patients, or about 6 percent, had vascular injuries during the study, researchers report in the Journal of Orthopaedic Trauma.

Compared to non-obese patients, people with severe obesity were more than twice as likely to have vascular injury. Patients with less extreme obesity were still 77 percent more likely to have vascular injury than non-obese individuals.

Obese patients also typically had longer and more costly hospital stays than non-obese people.

With a vascular injury, patients were hospitalized for around 15 days, compared to only about 7 days without vascular injury.

Average hospitalization costs were $131,478 for vascular injury cases compared to $60,241 for patients without vascular damage, the study also found.

About 2 percent of obese patients had amputations. This wasn’t meaningfully different from non-obese people after researchers accounted for whether patients had vascular injury.

The study wasn’t a controlled experiment designed to prove whether or how obesity directly causes knee dislocations or vascular injuries.

Another limitation is the reliance on billing codes to identify obese patients, which might under-represent the overall rate of obesity in the study, the authors note. Researchers also lacked data on long-term patient outcomes.

Even so, the findings add to evidence that knee dislocations and vascular damage can be worse for obese individuals, said Dr. Alexandra Gersing, a researcher at the University of California, San Francisco, who wasn’t involved in the study.

While weight loss is a good way to help avoid these issues, even without losing weight there are things people can do, Gersing said by email.

“In obese individuals that are not able to lose weight, knee stability can be increased by increasing the strength of muscles surrounding the knee joint,” Gersing advised. “Knee stability can thereby be improved up to a certain extent in order to prevent knee dislocations and consequently the associated vascular injury.”