A 67-year-old man with a past medical history of complicated diabetes, hypertension, and hyperlipidemia who presented to the hospital after a fall was found to have methicillin-resistant Staphylococcus aureus (MRSA) bacteremia from endocarditis. He developed wrist pain during his hospital stay, and an initial radiograph showed mild degenerative changes of the wrist. He continued to have worsening right wrist pain, swelling, and soft tissue erythema.
A follow-up radiograph was performed two weeks after the initial radiograph, and it showed interval development of diffuse lucency throughout the carpal bones with severe crowding of the carpal joints. (Photo.) His physicians were concerned about septic joint and infection, especially because the lucency developed so quickly. MRI of the wrist confirmed septic arthritis-osteomyelitis involving the distal radius, all of the carpal bones, and the proximal second-fifth metacarpals.
Osteomyelitis (OM) may occur from hematogenous seeding, contiguous spread from adjacent infected soft tissues, or direct inoculation. Hematogenous OM is usually monomicrobial, but OM from contiguous spread or direct inoculation is usually polymicrobial. Long bones are usually the most affected in children, favoring the metaphysis over epiphysis over joints. (Diagnostic Imaging: Musculoskeletal Non-Traumatic Disease. Philadelphia: Elsevier; 2016.) The most common location in adults is adjacent to any site of ulceration or in the joints themselves.
Complications of untreated OM are severe, and can destroy the epiphyses in children and joints in adults and cause septicemia and death. Most OM is caused by bacterial etiologies, and treatment consists of long-term IV antibiotic treatment tailored to the pathogen. (Overview of Osteomyelitis in Adults. UpToDate.com; April 2017.) Surgery may be necessary if there is evidence of abscess, joint infection, or subperiosteal collections.
The approach to diagnosing OM starts with a plain radiograph, and changes include cortical destruction adjacent to a site of soft tissue ulceration and abrupt loss of joint space or periosteal reaction. It is important to note that changes in OM may not be seen on plain radiographs for one to two weeks, and repeat radiographs should be performed. MRI is the modality of choice to diagnose OM due to high sensitivity and specificity, and should be employed emergently for clinical suspicion of infection because bone changes on x-ray lag behind the infection by 10-20 days. MRI changes include confluent T1 low signal intensity, fluid sensitive sequences that show increased signal intensity within bone and adjacent soft tissues, and enhancement of the bone in contrast-enhanced T1 sequences. (Diagnostic Imaging: Musculoskeletal Non-Traumatic Disease. Philadelphia: Elsevier; 2016.) Multiphase nuclear medicine Tc-99m bone scan may be considered when MRI is not possible, and it will show increased radiotracer uptake on all phases in acute OM. (Diagnostic Imaging: Musculoskeletal Non-Traumatic Disease. Philadelphia: Elsevier; 2016.) Direct tissue sampling is usually obtained to identify the causes and further direct treatment.
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