investigations
Last reviewed 01/2018
A work up of an irritable hip should seek both to exclude alternative diagnoses and to demonstrate confirmatory features.
Haematologic tests such as FBC, WCC, ESR and CRP are usually normal. Throat swab and mid-stream urine specimens rarely reveal an infection.
Radiographs are poor at demonstrating effusions and are frequently normal.
Ultrasound is the most useful investigation and can detect an effusion in 95% of cases where one is present. The anterior hip capsule is displaced 2.5 mm from the femoral head in a normal hip, but by up to 6 mm in an irritable hip. Any effusion must be aspirated and cultured to exclude septic arthritis. However, an effusion is not demonstrable in all cases of irritable hip.