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Adventitious bursitis

Case contributed by Dr Bruno Di Muzio

Presentation

Left first metatarsophalangeal diabetic foot ulcer for 3 months. There is pus discharge through a soft tissue. Clinically suspicious for osteomyelitis. Osteomyelitis? Septic arthritis?

Patient Data

Age: 70 years
Gender: Male

Left foot radiographs

X-ray

Prominent soft tissue swelling adjacent to the first metatarsophalangeal joint. There is no adjacent periostitis or cortical erosion to indicate establish osteomyelitis. Deformity of the head of the first metatarsal with loss of joint space is likely related to degenerative changes. If there is an ongoing clinical concern for osteomyelitis, a further assessment with either bone scan or MRI is recommended.

Left Foot MRI

MRI

Well defined subcutaneous mass measuring 27 x 8 x 26 mm, showing intermediate T1 and increased T2 signal, located directly under the first metatarsophalangeal joint. A tiny focal skin breach in continuity with this lesion may represent the mentioned ulcer. There are degenerative changes of the first metatarsophalangeal joint, with joint narrowing, subcortical cyst, and a small amount of joint effusion. The capsuloligamentous complex of this joint is intact, with no extension of the subcutaneous mass lesion/inflammatory process to the joint. The remainder of the foot demonstrates diffuse muscular atrophy, but no relevant findings for this clinical scenario.

Case Discussion

MRI demonstrates features consistent with an adventitious bursa under the 1st MTPJ, that has ruptured cutaneously and may be secondarily infected given the clinical picture. There is no involvement of the underlying joint.

Wound culture has grown: Serratia marcescens and Dermabacter hominis

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