Transient synovitis of the hip (a.k.a. Toxic synovitis,Transitory coxitis, Coxitis fugax, Acute transient epiphysitis, Coxitis serosa seu simplex, Phantom hip disease, Observation hip and Irritable hip) is a condition which causes hip pain due to inflammation of the inner lining of the hip joint.

It was first described in 1892, and is a benign, self-limiting condition which usually resolves in a week or so, with or without treatment with NSAIDs (e.g. Paracetamolplugin-autotooltip__plain plugin-autotooltip_bigParacetamol

"Acetaminophen (INN Paracetamol) is one of the most widely used over-the-counter antipyretic and analgesic drugs worldwide. [...] Although discovered more than 100 years ago, and used extensively for ~ 50 years, its mode of action is still unclear)

It usually affects children between the ages of 3 and 10, (around 2 - 3 % ) leading to hip pain and limping. It has been noted that it sometimes follows upper respiratory tract infections - viral and bacterial.

What leads to the inflammation, and why it appears to be mostly restricted to young children, is unknown.

More info : Wikipedia

Also see : Snapping hip syndrome (SHS)plugin-autotooltip__plain plugin-autotooltip_bigSnapping hip syndrome (SHS)

"SHS is a condition characterized by a palpable or audible “snapping” that occurs around the hip with movement. This condition is further described as either internal snapping hip syndrome (ISHS) or external snapping hip syndrome (ESHS). With ISHS, the “snapping” is felt in the anterior hip region and often involves a tight iliopsoas muscle. With ESHS, the sensation is felt over the lateral hip region and often involves a tight iliotibial band (ITB).