Methods: A sixty-one-year-old woman presented with right knee pain. Imaging demonstrated osteonecrosis, pathologic fracture, and a permeative lesion. A biopsy with irrigation and debridement was performed. Cultures grew Escherichia coli, and histology showed features of malakoplakia, a rare lesion of uncertain etiology usually found in the genitourinary tract. The patient was treated successfully with antibiotics.

Conclusions: Malakoplakia, although rare, should be included in the differential diagnosis of permeative bone lesions, especially in an immunocompromised patient.