The Limping Child, a Rare Differential: Pyomyositis of the Iliacus Muscle -A Case Report.

Introduction: The presentation of an unwell child with a short history of a limp is not an uncommon referral to the orthopaedic on-call team. In the acute setting, this is most commonly secondary to trauma or infection. An unusual differential that clinicians should be aware of is pyomyositis of the muscles around the hip joint. The rarity of our case makes this a very interesting one, with only a few other recorded cases within the UK.

Case Report: A 3-year-old Caucasian girl presented to the Paediatric ED, with 6 days' history of general malaise, vomiting, and intermittent pyrexia. 5 days before prior to attendance, she also developed a limp, which progressively worsened until she refused to weight bear on the left side with obvious distress and pain. No history of trauma was reported. According to the parents, she had become more irritable each day. The patient had no significant medical history and no family history of congenital or developmental hip disorders. Her vital signs were in keeping with sepsis as she was tachycardiac (154) and pyrexial (38.1°). The referring GP also recorded a high temperature of 38.9°. Physical examination proved difficult, due to pain. No obvious erythema or swelling was noted around either groin or lower limb. When asked to walk, she held the left hip in flexion and refused to weight bear.

Conclusion: Treatment of pyomyositis is essential to prevent subsequent life-threatening sepsis. Intravenous antibiotics, radiologically guided or surgical drainage of the collection, or debridement may be indicated in the management. Good understanding of the anatomy surrounding the hip joint is vital. The iliopsoas muscle inserts into the lesser trochanter of the hip joint. Therefore, inflammation in the origin or along the track of the muscle can mimic a septic arthritis picture. Radiological modalities, including ultrasound and magnetic resonance imaging, should be considered, particularly when diagnostic doubt exists. Overall, making surgical decisions in such a case can be challenging. We advocate multii-disciplinary approach and seeking further opinions from colleagues if in doubt which should help in providing the best care possible for a child.