6 Intra-articular Loose Body

CASE 6

Intra-articular Loose Body

Anthony G. Ryan and Peter L. Munk

Clinical Presentation

Our patient presented with recurrent pain and locking after a remote trauma.

Figure 6A

Figure 6B

A sagittal T1-weighted image (Fig. 6A) and an axial proton density (PD) fat-saturated image (Fig. 6B) show a very large irregular intra-articular loose body in the superomedial patellar recess secondary to degenerative osteoarthritis. Speckled low density scattered throughout the lesion is evident, consistent with calcifications. Chondromalacia patella is evident on the axial image. Articular surface irregularity and subchondral sclerosis are evident on the sagittal image.

Diagnosis

Intra-articular loose body.

Differential Diagnosis

Solitary loose body:

Chip fracture from trauma (Figs. 6C–6F)
Osteochondral fracture
Usually affecting the knee (Fig. 6G), talus, and elbow. A donor site may be visible.
Severe degenerative joint disease (Figs. 6A, 6B)
Detached osteophyte; usually other signs of degenerative arthritis. The fragments are typically larger and more variable than those found in synovial osteochondromatosis.

Figures 6C Transaxial CT pelvis posttrauma shows a comminuted fracture of the posterosuperior acetabular margin. 6D Same patient as in 6C. Postreduction CT shows two small intra-articular fragments, one medially at the level of the fovea capitis and a second lying posteriorly at the level of the posterior acetabular margin. 6E and 6F Axial and coronal reformat, respectively, of the left hip shows an untreated posttraumatic loose body medial to the femoral head. Erosion and irregularity of the femoral head is evident, as are secondary degenerative changes (articular surface irregularity, superior joint space narrowing, and subchondral sclerosis). 6G Sagittal T2-weighted image of the knee shows a small loose body posterior to the patella. The donor site secondary to an osteochondral defect on the posterior aspect of the patella is not shown.

Multiple loose bodies:

Neuropathic arthropathy (the debris of the six Ds)

Rice bodies (rheumatoid arthritis, seronegative inflammatory arthritis, juvenile rheumatoid arthritis, and tuberculous joints)

Synovial osteochondromatosis (Fig. 6H)

Figure 6H Sagittal T1-weighted image of the knee shows multiple well-defined loose bodies secondary to synovial osteochon-dromatosis posterior to the posterior cruciate ligament.