Differential diagnosis of hip pain in children referred to a specialist bone tumour service

Objective: To determine the differential diagnosis of bone lesions causing hip pain in children and the association between radiographic features of aggression and MRI appearances with final diagnosis. Methods: Retrospective review of children with hip pain referred to a specialist musculoskeletal oncology service between September 2018 and December 2020. Patient demographics, lesion location, the radiographic and MRI features, and the final diagnosis, which was made either by image- guided biopsy, surgical curettage or based on typical imaging features were recorded. Statistical analysis examined the association between the LodwickMadewell score (determined from available radiographs) and MRI findings with final diagnosis. Results: Fifty- nine patients were included, 40 males and 19 females with mean age 10.9 years, (range 3-16 years). Final diagnoses were based on histology in 24 (40.7%) cases and imaging in 35 (59.3%) cases. Eighteen lesions (30.5%) were classed as nonneoplastic, 31 (52.5%) as benign and 10 (16.9%) as malignant, of which four were primary bone sarcomas. There was a significant association between the LodwickMadewell score and final diagnosis (p < 0.001). On MRI, bone marrow oedema, presence of a focal lesion, bone expansion and the presence of an extraosseous mass were all significantly associated with final diagnostic classification. Conclusion: The differential diagnosis of hip pain in children presenting to a bone tumour service is wide. Most cases are due to benign or nonneoplastic conditions, with only 10 out of 59 children having a malignant lesion. Radiography complemented by MRI plays a major role in differentiating nonneoplastic, benign neoplastic and malignant lesions and in determining the requirement for needle biopsy. Advances in knowledge: This is the first study to consider how imaging features relate to diagnosis in suspected paediatric hip tumours. Use of this information can help in determining which cases should undergo needle biopsy.