MR image analysis of pedal osteomyelitis: Distribution, patterns of spread, and frequency of associated ulceration and septic arthritis

PURPOSE: To evaluate the anatomic distribution of pedal osteomyelitis and septic arthritis in a large patient group with advanced pedal infection and to compare ulcer location with the distribution of osteomyelitis and septic arthritis. MATERIALS AND METHODS: Contrast material-enhanced magnetic resonance (MR) imaging findings were reviewed for 161 feet in 51 women and 107 men (82% of whom had diabetes mellitus) who were suspected of having osteomyelitis and who underwent tissue diagnosis. Location of skin ulceration and presence of osteomyelitis (indicated by means of low T1-weighted signal intensity, high T2-weighted signal intensity, and contrast enhancement) and septic arthritis (indicated by synovial enhancement and adjacent cellulitis) were evaluated by two musculoskeletal radiologists. RESULTS: In the forefoot, osteomyelitis occurred most frequently at the fifth metatarsal (n = 24), first metatarsal (n = 21), and first distal phalanx (n = 15). In the hindfoot, the calcaneus (n = 21) was involved most frequently. Osteomyelitis was directly adjacent to skin ulcers or surgical defects in all cases but one. Spread of osteomyelitis to adjacent bones in the forefoot occurred in 26 (16%) bones. Evidence of septic arthritis on MR images was present in 53 (33%) feet and involved most frequently the fifth (n = 13) and first (n = 8) metatarsophalangeal joints. CONCLUSION: Pedal osteomyelitis results almost exclusively from contiguous infections and occurs most frequently around the fifth and first metatarsophalangeal joints. One-third of patients with advanced pedal infection show evidence of septic arthritis on MR images.