Hip Pain

A common presenting complaint in children, closely related to and substantially overlapping with limp in children.

It has the same broad, age-stratified differential diagnosis: transient synovitis, septic arthritis, Legg-Calvé-Perthes disease, slipped capital femoral epiphysis, developmental dysplasia of the hip, and juvenile idiopathic arthritis.

The clinical framework for hip pain as the presenting symptom has two key points. Referred knee pain is a common presentation of underlying hip pathology. Septic arthritis is time-critical and must be distinguished from the far more common, benign transient synovitis.

Diagnostic framework specific to hip pain

• The hip joint has rich sensory innervation, shared in part with the obturator nerve supplying the medial aspect of the knee. This accounts for the well established phenomenon of referred hip pain presenting as knee pain.
• Any child with knee pain and no clear, localised knee examination finding warrants careful examination of the ipsilateral hip. Significant hip pathology may be missed if this referral pattern is not considered.
• Transient synovitis is a benign, self-limiting, generally post-viral inflammatory reaction within the hip joint. It is the commonest cause of acute hip pain and limp in young children.
• Septic arthritis is a genuine orthopaedic emergency requiring urgent joint aspiration and treatment.
• Distinguishing these two is the single most important diagnostic distinction in acute hip pain in a child.
• Structured clinical prediction rules support, but do not entirely replace, careful clinical judgement. They incorporate fever, inability to bear weight, elevated inflammatory markers, and elevated white cell count.
• Age at presentation provides substantial diagnostic guidance. Legg-Calvé-Perthes disease typically presents between four and ten years.
• Slipped capital femoral epiphysis typically presents in adolescence, particularly with obesity and rapid growth.
• Developmental dysplasia of the hip, if undetected in infancy, may present later in early childhood with an abnormal gait rather than overt pain.

• Three features give essential diagnostic guidance: the pattern of onset (acute versus gradual, and any relationship to trauma or intercurrent illness), associated systemic symptoms (fever, malaise, or weight loss), and the pattern of any associated limp or functional limitation. The general principles for limp in children apply.
• Reduced range of hip motion, particularly internal rotation, is a sensitive but non-specific finding. It occurs across the great majority of significant hip pathology in children, including transient synovitis, septic arthritis, Legg-Calvé-Perthes disease, and slipped capital femoral epiphysis.
• Obligate external rotation with hip flexion is particularly characteristic of slipped capital femoral epiphysis.
• Inability or marked reluctance to bear weight, together with fever and systemic upset, is a critical combination. It warrants urgent evaluation to exclude septic arthritis.

• Full clinical assessment is the essential foundation of diagnostic evaluation. It uses the age-stratified framework and red flag screening described for limp in children.
• Hip examination includes internal and external rotation. Consider referred pain where the presenting complaint is knee pain rather than overt hip pain.
• Plain radiography of the pelvis (including both hips for comparison) is an appropriate initial imaging investigation in the great majority of presentations. It supports identification of Legg-Calvé-Perthes disease, slipped capital femoral epiphysis, or, in an infant or young child, developmental dysplasia of the hip.
• Ultrasound is a sensitive investigation for identifying a hip joint effusion. It helps distinguish transient synovitis from septic arthritis, both of which can produce an effusion.
• Where septic arthritis remains a genuine concern, ultrasound-guided joint aspiration allows definitive microbiological assessment.
• Blood testing includes full blood count and inflammatory markers, plus blood cultures where septic arthritis is a concern.
• Structured application of validated clinical prediction rules supports risk stratification in acute hip pain with joint effusion. It directly informs the decision on urgent joint aspiration.

• Management is directed entirely by the underlying diagnosis. It follows the condition-specific principles for transient synovitis, septic arthritis, Legg-Calvé-Perthes disease, slipped capital femoral epiphysis, developmental dysplasia of the hip, and juvenile idiopathic arthritis.
• Any child with hip pain and a significant red flag feature warrants urgent assessment. The key feature is inability to bear weight combined with fever or significant systemic upset.
• Keep a low threshold for orthopaedic referral and joint aspiration, given the time-critical nature of excluding septic arthritis.
• The overarching principle is that septic arthritis must always be actively considered and confidently excluded before a more benign alternative diagnosis is accepted.