Clinical History
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.
Imaging Findings
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.
Discussion
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).
Differential Diagnosis List
A Neuropathic hip Joint with Loose-Body Formation
Final Diagnosis
A Neuropathic hip Joint with Loose-Body Formation