Primary obturator internus and obturator externus pyomyositis

Abstract

Background: Pyomyositis is a rare condition in immune competent patients and is usually seen in tropical countries. Pyomyositis of obturator muscles in particular is an extremely rare condition, which causes hip pain and mimics septic arthritis.

Case report: This is a case report of a 9-year-old boy without an underlying disease or a compromised immune system, who presented with knee pain that progressed to hip pain and inability to bear weight. He was diagnosed initially with septic arthritis of the hip and underwent unnecessary hip exploration surgery. Magnetic resonance imaging scan was performed postoperatively and showed pyomyositis of obturator internus and obturator externus muscles. He was managed medically and had a good outcome.

Conclusions: A greater awareness of this emergency condition is necessary to prevent misdiagnosis, unnecessary surgical intervention, and to avoid the devastating possible complications of delayed diagnosis.

Keywords: obturator externus; obturator internus; obturator pyomyositis; primary pyomyositis; septic arthritis.

Figure 1

AP radiograph of the pelvis at presentation showing the left hip joint in external rotation, abduction and mild flexion.

Figure 2

T1 weighted image MRI, with IV gadolinium of the pelvis at the level of the greater trochanter showing edematous changes in the obturator internus muscle (star) along with central necrosis (arrow) with ring enhancement suggestive of pyomyositis

Figure 3

T1 weighted image MRI, with IV gadolinium of the pelvis at the level of the lesser trochanter showing edematous changes in the obturator externus muscle (star) along with central necrosis (arrow) suggestive of pyomyositis.