Figure 5c. Osteomyelitis of the first metatarsal head and septic arthritis of the first MTP joint in a 30-year-old woman with systemic lupus erythematosus. (a) Axial T1-weighted MR image shows an area of diffuse low signal intensity within the marrow of the distal first metatarsal bone (arrows). Similar changes were also present within the base of the proximal phalanx of the great toe. (b) Coronal T2-weighted MR image demonstrates a dorsal cutaneous ulcer (arrowheads), dorsal sinus tract (short arrows), high-signal-intensity changes in the soft tissues representing cellulitis, increased signal intensity within the marrow of the metatarsal head (*), and joint effusion (long arrow). (c) Sagittal fat-suppressed T1-weighted MR image reveals intense contrast enhancement of the bone marrow, joint, and soft tissues. Note that the extensor tendon sheath dorsal to the first ray demonstrates both edema and enhancement (arrows), findings that indicate tenosynovitis.