Teaching Case

A paraplegic patient developed increasing pain and spasms around the right hip.Radiographs demonstrated progressive subluxation and destruction of the femoral head.CT scan confirmed these findings and also demonstrated an extensive effusion containing bony debris.

A 28 year old male patient, paraplegic following a T5/6 fracture dislocation sustained from a bicycle accident ten years previously, presented with a twelve month history of pain and increasing spasms around the right hip. Plain radiographs of the pelvis demonstrated supero-lateral subluxation, joint space loss, sclerosis and flattening of the right femoral head with new bone formation around the femoral neck (fig 1a). There was a paralytic type of scoliosis affecting the lumbar spine, concave to the right, with an associated pelvic tilt. Radiographs eight months earlier (fig 1b) showed an intact hip joint with mild flattening of the femoral head and a scoliosis, while radiographs of the hip twelve months earlier (not shown) were normal. A CT examination confirmed the plain film findings, with subluxation of the femoral head and new bone formation along the femoral neck (fig 2a,b). It also demonstrated an extensive effusion, with a redundant capsule inferiorly, containing bony debris gravitating to its dependent part posteriorly (fig 2c). A recent MR of the spine (not shown ) demonstrated a tense syrinx, extending from the level of the spinal cord transection at T6 to the conus.Appearances were unchanged from an MR examination three years previously.

Heterotopic new bone formation is a common complication of paraplegia.The cause is unknown but both local and systemic factors have been implicated(1).The hip is commonly involved and in advanced cases arthrodesis may result from peri-articular osseus bridging. Intra-articular loose bodies, however, are uncommon in paraplegia.They originate from an osteochondral nidus which is shed into the joint either from the bone and covering articular cartilage,for example a destructive arthropathy, or from the synovium,for example synovial osteochondromatosis. The nidus increases in size due to successive accumulation of new bone and cartilage around it, termed “layering” (2). Calcified loose bodies can be identified on plain radiography or CT but purely cartilaginous lesions require the use of intra-articular contrast agents also.Both calcified and uncalcified lesions can also be identified on US and MR. Syringomyelia is a well-recognised cause of neurological deterioration in paraplegia and may be the initiating factor in the development of a neuropathic joint.However,although fragmentation of bone and articular cartilage is a characteristic feature of neuropathic joints, development of intra-articular loose bodies is rare (3) , the majority becoming vascularised by abnormal synovium and absorbed into the peri-articular tissues. The main differential diagnosis of femoral head osteolysis with intra-articular debris and sclerosis is septic arthritis which needs to be excluded (4).