A coincidence, or not?

A 4 year old boy, previously fit and well, presented with a painful right hip. Six days previously, he had fallen off a 2 foot high bed and landed on his right side onto carpeted floor. He complained of pain immediately after and began limping. His temperature was normal and he had no other symptoms. By day 2, his pain worsened and was not weight bearing. The pain did not respond to analgesia. On day 3, he was referred by his GP to the local hospital. Laboratory investigations showed a raised C reactive protein; x ray and ultrasound examinations of his right hip were normal. He was diagnosed with a muscular injury post‐trauma and sent home. He was referred to us on day 6 with worsening constant pain in his right hip, necessitating him being carried around.

On examination, he was pyrexial and tachycardic. He was very miserable. He lay very still and did not want to be moved. He refused to walk and weight bear or move his right leg. On inspection, there were no obvious bruises or injuries. On palpation, he was tender over the right hip. Active and passive movements on the right hip and knee were not tested as he complained of severe pain. His left hip and knee were not tender and the rest of the examination was normal. Blood results showed a high C reactive protein of 137 mg/l and white cell count of 11.7×10⁹/l. An x ray examination of both hips was normal. An ultrasound scan of his right hip showed 4 mm of fluid in the hip joint, which was within the upper limits of normal.

As the clinical severity of his pain did not correspond with the results of the investigations, we proceeded to magnetic resonance imaging (MRI) to rule out osteomyelitis or psoas abscess. Figures 1 and 2 show the MRI scan of his pelvis. There was abnormal signal/fluid in the right iliopsoas, obturator internus, inferior gamellus, between the obturator internus and right ischial tuberosity, which extended anteriorly into the right iliac fossa. There was also a small amount of fluid in the pelvic cavity. A diagnosis of psoas abscess was made.

Figure 1 

Figure 2