The pelvic x-ray shows
a right sided hip effusion in this skeletally immature patient. There is bulging of the right gluteal fat pad indicative of presence of a hip effusion, where as the left gluteal fat pad is normal.
This subtle sign on plain hip x-ray is very useful finding in a case with suspected hip effusion due to any cause when an ultrasound is not immediately available. Word of caution – absence of this sign on plain imaging does not mean there is no hip effusion.
Case closure – the patient had signs of sepsis with high inflammatory markers and was diagnosed with staphylococcal right hip septic arthritis on further investigations.
Further reading https://pubs.rsna.org/doi/pdf/10.1148/radiographics.20.suppl_1.g00oc06s3#:~:text=of%20the%20left%20hip%20shows%20that%20the%20gluteal%2C,hip%20pain%20in%20the%20setting%20of%20a%20normal-ap-