An 11-year-old male patient consulted for left coxalgia of 2 years' evolution with mechanical characteristics that improved with rest. His personal history included Arnold-Chiari malformation, hydrocephalus associated with Dandy Walker malformation treated with ventriculo-peritoneal shunt valve and epilepsy with partial seizures. Physical examination revealed gait dysfunction with an antalgic limp and limb adduction and lumbar hyperlordosis. The hip had 20o flexion with a range of motion of 90o flexion, 20o external rotation, 10o internal rotation, and 20o abduction. Plain radiography showed discrete regional osteopenia ;. CT scan showed oedema and discontinuity of articular cartilage with synovial hypertrophy.

Arthrocentesis was performed under fluoroscopic control under general anaesthesia, but no synovial fluid sample was obtained. The study was complemented with arthrography which confirmed the existence of severe chondrolysis. With a presumptive diagnosis of idiopathic chondrolysis, rest, unloading of the limb with the use of canes and physical rehabilitation were prescribed.
One month later, the hip was infiltrated with hyaluronic acid under radioscopic control. The evolution was torpid with persistence of symptoms despite treatment. Ten months after diagnosis, gentle joint mobilisation was performed under general anaesthesia, confirming movement of the femoral head en bloc with the pelvis, which was assessed as fibrous ankylosis. Due to joint stiffness, the option of periarticular tenotomy was ruled out. A year after diagnosis, joint stiffness improved slightly, so treatment was supplemented with soft tissue traction, with a favourable response in terms of pain control and flexion. The patient used outpatient traction for nocturnal periods, walking with English canes and continued with rehabilitation treatment for 6 months. After this treatment, the flexion attitude disappeared and he was able to lead a normal life without physical activity or prolonged walking, which caused episodes of pain and lameness.
Four years later, concentric loss of 50% of the joint space with effacement of the medial line and local osteopenia was evident. The clinical evolution was favourable with disappearance of pain and almost complete spontaneous progressive recovery of function and mobility over a period of 6 years, as well as partial recovery of joint space. The MRI then showed joint narrowing with subchondral lesions in the femoral head and acetabulum, without signal changes in the medullary on both sides of the joint, with a destructive process of the articular cartilage. MRI was not previously performed due to lack of availability at the centre, but it would have been more appropriate to perform it to make a differential diagnosis.
The range of joint movement at the end of clinical follow-up was -10o for abduction, internal rotation and external rotation with a dysmetry due to a 1 cm shortening of the affected limb.
Currently, after 14 years of follow-up since the onset of symptomatology, the patient is living a normal life, asymptomatic, Trendelenburg (-), symmetrical and painless mobility of both hips (RI 30o, RE 65o), with incomplete recovery of joint space.