Septic arthritis of the pubic symphysis

Description

A seamstress aged 57 years presented with fever and pubic pain radiating to the hips. She had recently been treated for Staphylococcus aureus bacteraemia of unclear source. MRI revealed gadolinium enhancement of the pubic symphysis (PS). Small fluid collections consistent with infection were present in the PS and right obturator externus muscle (figures 1 and 2), but when aspiration was attempted, its size had reduced and was deemed undrainable. Blood cultures were sterile, and transoesophageal echocardiography was negative for valvular vegetations. The patient completed 8 weeks of intravenous vancomycin for septic arthritis of PS and obturator pyomyositis, with clinical and radiological resolution. She is well after 3 years of follow-up.

Figure 1.

Coronal T2-weighted magnetic resonance image showing signal intensification in the pubic symphysis and right obturator externus muscle with interconnected fluid collections and hypointense peripheral rim.

Figure 2.

Axial T2-weighted magnetic resonance image showing the right obturator externus muscle pyomyositis and oedema of adjacent tissues.

Approximately 200 cases of septic arthritis of PS have been reported and were frequently associated with prior gynaecological/urological surgery or pelvic malignancy.^{1 2} Insidious symptoms often delay the diagnosis; therefore, clinicians should consider this entity in patients presenting with pubic, groin or abdominal pain that increases on ambulation, and acute onset of fever.² In our patient, repetitive stress of PS from sitting cross-legged while sewing may have caused frequent microtrauma, leading to osteitis pubis and, in the setting of transient bacteraemia, septic arthritis.³ Despite MRI being the most sensitive imaging test, only aspiration (ie, microorganism isolation) provides the ultimate proof of the presence of infection. Staphylococcus aureus is the most frequently isolated organism and the selected empirical antibiotic should have antistaphylococcal activity.² Despite long-course intravenous antibiotherapy, >50% of cases require surgical debridement.² When adequate treatment is instituted, most individuals recover completely.

Learning points.

• Septic arthritis of the pubic symphysis is a rare cause of pubic and hip pain.

• Long delays between the symptom onset and diagnosis are frequent and therefore awareness is paramount for early case detection.

• Long-course antibiotherapy is required and, in some cases, may preclude the need for surgical debridement.