Objective: The purpose of this study was to evaluate the incidence, cause, injury patterns, and MRI findings in knee dislocation in patients with normal and increased body mass index and to determine whether obesity interferes with knee MRI examinations.
Materials and methods: A retrospective study of the period from 2000 to 2007 (90 months) was performed at a level 1 trauma center, finding a total of 24 patients who had sustained a knee dislocation.
Results: Twenty-two of the 24 patients underwent surgery and 19 patients had an MRI examination of diagnostic quality before surgery. Of the 24 patients, 11 had a body mass index greater than 25 and had knee dislocation due to low-energy trauma (nine due to a simple fall, two to a noncontact sport). Two of these 11 patients were morbidly obese (body mass index>40). These patients had no injuries to the popliteal tendon and they had no irreversible peroneal nerve injuries. Otherwise, the patients' injuries were in agreement with previous knee dislocation studies. Obesity did not interfere with knee MRI examinations. On the basis of the population served by our trauma center, the annual incidence of knee dislocation due to low-energy trauma in overweight patients is about 1.0 per million.
Conclusion: The annual incidence in obese patients of knee dislocation due to low-energy trauma is not insignificant at a level 1 trauma center. As the prevalence of obesity increases, the injury patterns seen in emergency departments may change. The radiologist should be aware that even after a simple fall, overweight patients may have a knee dislocation.