Bone and joint infections usually occur from (1) contiguous spread from an overlying skin or soft tissue infection or (2) hematogenous spread from a distant site. Infecting microorganisms tend to be unusual compared with the general population, with Candida and gram-negative organisms the most common examples. In IVDUs, osteomyelitic lesions are seen more frequently in the axial skeleton than in the bones of the extremities. 40
Pyogenic infections are the predominant type seen involving bones and joints. In contrast to the general population, in which approximately two-thirds of bony infections are caused by S. aureus, the infecting organisms in an IVDU with osteomyelitis or septic arthritis is more likely to be polymicrobial and involve uncommon organisms, although recent studies have demonstrated an increasing frequency of S. aureus and groups A and G streptococcal bone infections in IVDUs. One also must consider gonococcal arthritis and tenosynovitis because of the high incidence of sexually transmitted diseases in this population. E. corrodens osteomyelitis also has been reported in IVDUs who lick their needles prior to injection. Nonpyogenic organisms may cause osteomyelitis and septic arthritis in IVDUs. Mycobacterial infections usually involve the ribs and vertebral column (Pott's disease). Symptoms include night sweats, fevers, weight loss, and localized pain. These are often associated with systemic involvement of the lungs, CNS, pelvic organs, and adrenal glands. Candida spp. have been reported with incidences as high as 20 percent in osteomyelitis in these patients.41 Candidal infections are postulated to spread hematogenously. Some patients report an initial syndrome of high fever, headache, and myalgia lasting 3 to 4 days, followed by the appearance of metastatic lesions involving the skin, eye (choreoretinitis and endophthalmitis), and the bones and joints several days to weeks later. Rarely, Aspergillus spp. may cause osteomyelitis of the sternum in these patients.40
IVDU-related osteomyelitis is more likely to involve the vertebral column, particularly the lumbar segments. 42 Collected series have tabulated that 53 percent of all bony infections involved the vertebral column, 18 percent involved the sternoclavicular joint, and 17 percent involved the extremities, particularly the hip and knee joints.
Vertebral osteomyelitis usually presents with localized pain and tenderness to palpation over the involved bone. A soft tissue mass may be palpable, which in the case of Candida may not exhibit evidence of inflammation. Symptoms may be present for days in the case of bacterial infections to weeks in the case of fungal or mycobacterial infections. Many patients will exhibit neither fever nor leukocytosis. An elevated ESR is helpful if present, but its absence does not exclude these infections. If present, drainage from contiguous abscesses should be cultured. Biopsy or needle aspiration may be necessary for joint space and bony infections, especially in the case of unusual or fastidious organisms, such as Mycobacterium, Candida, or Eikenella. Appropriate imaging for osteomyelitis will vary with institution; however, MRI and CT are both useful. Patients with osteomyelitis warrant admission. Unless the patient appears septic or coincident endocarditis is a concern, antibiotic administration should be based on culture results. Antibiotic treatment will usually continue for 4 to 6 weeks.
Septic arthritis in the IVDU usually involves the knee or hip. Sternoclavicular infectious arthritis is also well described in this population and, if found, should strongly suggest IVDU. Patients often will note a recent history of trauma to the area, but causality has yet to be proven. Patients will note pain, localized tenderness, and swelling at the sites. The ESR is usually elevated, and fever and leukocytosis are usually present. Up to 80 percent will have normal plain radiographs; however, joint space widening, articular surface erosion, and surrounding soft tissue infection may be noted. Bone scans are often positive early in the process, and these infections also may be delineated with CT or MRI. The most sensitive but nonspecific finding on synovial fluid analysis is a white blood cell count greater than 20,000/mL with a predominance of neutrophils. Gram stain of the synovial fluid may aid in antibiotic selection. Immobilization, physical therapy, therapeutic arthrocentesis, and occasionally open drainage of a septic hip may be warranted.
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