Transient Synovitis
As mentioned above, developmental dysplasia of the hip is not a common cause of hip pain. If your child suddenly starts experiencing this symptom, what is the most common cause? It is transient synovitis and usually shows up at ages 3 to 10 years.
As the name implies, transient synovitis features inflammation of the synovium. This is the membrane that surrounds the articulation and encloses synovial fluid.
Not much is known about this disease because it is still somewhat rare despite being the most common cause of hip pain in children. However, the inflammation tends to be nonspecific, and the synovial membrane thickens. In an ultrasound, a doctor can see a bulging joint capsule, and the synovial fluid contains more proteoglycans than it should.
Transient synovitis is felt as unilateral pain in the groin or the hip. In some cases, very young children and babies can simply become irritable and increase the rate of crying at night. In some cases, patients do not experience pain and only present with a limp.