Obesity Increases the Physical and Financial Cost of Knee Dislocation

    A new study of more than 19,000 knee dislocation cases in the US between 2000 and 2012 provides a painful indication of how the nation’s obesity epidemic is changing the risk, severity, and cost of a traumatic injury.

    “Obesity greatly increases the complications and costs of care,” said lead author Joey P. Johnson, MD, orthopedic trauma fellow at the Warren Alpert Medical School of Brown University and a physician at Rhode Island Hospital. “As the rate of obesity increases, the rate of knee dislocations increases. The total number of patients who are obese is increasing, so we are seeing more of these problems.”

    Addressing obesity, said co-author Christopher T. Born, MD, a professor of orthopaedics at Brown University, could therefore help reverse the trends in the data reported in the Journal of Orthopaedic Trauma.

    Dr. Johnson and his colleagues were inspired to investigate the role of obesity in knee dislocation because of what they’ve observed clinically over the last 5 years: an increase in knee dislocations among obese patients, with an increased risk of vascular injury to the knee.

    Moreover, they have seen an increase in “low-energy” causes of dislocations, especially among obese patients. A few years ago, for example, Dr. Johnson saw a patient who experienced a knee dislocation after stepping off a ladder while hanging curtains.

    To better understand the issue, the researchers analyzed records in the Nationwide Inpatient Sample, a database of patients who’ve had hospital stays. Over the study period, they found that obese or morbidly obese patients made up an increasing share of knee dislocation patients, rising to 19% of patients in 2012, compared with just 8% in 2000.

    Vascular injury is a particularly severe complication because if undiscovered and untreated, it can lead to amputation of the leg. The team’s calculations from the data revealed that the odds of vascular injury during a knee dislocation were twice as high among obese or morbidly obese people than among normal-weight people.

    Dr. Johnson said this finding is particularly insidious because a common clinical assumption is that vascular injury might be less likely among people suffering a low-energy knee dislocation. The study’s findings suggest that physicians should be especially vigilant about vascular injury in obese knee dislocation patients, regardless of the cause.

    The stakes, Dr. Johnson added, could be the leg itself. “You don’t want to be fooled,” he said. “That patient could lose the leg, and their life could be changed forever.”

    In addition to increased incidence and the likelihood of vascular injury, the researchers examined the costs of care. Patients with vascular injury, which was twice as likely among obese patients, stayed in the hospital for an average of 15.3 days, while patients without vascular injury stayed for an average of 7.4 days. Average hospitalization costs were $131,478 for patients with vascular injury versus $60,241 for patients without vascular damage.


    Johnson JP, Kleiner J, Klinge SA, McClure PK, Hayda RA, Born CT. Increased incidence of vascular injury in obese patients with knee dislocations. J Orthop Trauma. 2017 Oct 23. doi: 10.1097/BOT.0000000000001027. [Epub ahead of print]