INJECTION DRUG USERS BONE JOINT INFECTIONS

Bone and Joint Infections in injection drug users
Bone and joint infections usually occur from either contiguous spread from an overlying skin or soft tissue infection, or secondary to hematogenous spread from a distant site. In contrast to the general population in which S. aureus predominates, infecting microorganisms in the injection drug user tend to be unusual, with Candida and gram-negative organisms the most common. In injection drug users, osteomyelitis is seen more frequently in the axial skeleton than in the extremities.

Pyogenic infections predominate in bones and joints. Earlier studies in injection drug user-related osteomyelitis or septic arthritis found a high likelihood of polymicrobial or uncommon organisms; however, recent studies demonstrate an increasing frequency of S. aureus and Streptococcus groups A and G bone infections in injection drug users. Because of the high incidence sexually transmitted diseases in this population, gonococcal arthritis and tenosynovitis should also be considered. E. corrodens osteomyelitis has been reported in injection drug users who lick their needles prior to injection.

Nonpyogenic organisms may cause osteomyelitis and septic arthritis in injection drug users. Mycobacterial infections usually involve the ribs and vertebral column (Pott disease). These infections present with night sweats, fevers, weight loss, and localized pain. Candida spp. has been reported in as high as 20 percent of injection drug user-related osteomyelitis patients. Candidal infections are postulated to be hematogenous in origin. Some patients report an initial flulike syndrome lasting 3 to 4 days, followed by the appearance of metastatic lesions involving the skin, eye (chorioretinitis and endophthalmitis), and the bones and joints several days to weeks later. Rarely, Aspergillus spp. may cause osteomyelitis of the sternum in injection drug users.

injection drug user-related osteomyelitis involves the vertebral column in approximately 50 percent of cases, particularly the lumbar segments, followed by the sternoclavicular joint in approximately 18 percent of cases, and the extremities, particularly around the hip and knee joints, in 17 percent of cases. Vertebral osteomyelitis usually presents with localized pain and tenderness to palpation over the involved bone and a soft tissue mass may be palpable. Symptoms may be present for days in the case of bacterial infections to weeks in the case of fungal or mycobacterial infections.

Many patients both fever and leukocytosis and an elevated erythrocyte sedimentation rate (ESR) and C-reactive protein are helpful, if present, but their absence does not exclude these infections. Drainage from contiguous abscesses should be cultured. Biopsy or needle aspiration of joint space and bony infections may be necessary, especially in the case of unusual or fastidious organisms, such as Mycobacterium, Candida, or Eikenella. Appropriate imaging for osteomyelitis will vary by institution; however, MRI, CT, and radionuclide bone scans are used. Patients with osteomyelitis warrant admission. Unless the patient appears septic or coincident endocarditis is a concern, antibiotic administration should be based on culture results and is typically required for 4 to 6 weeks.

Septic arthritis in the injection drug user usually involves the knee or hip. Sternoclavicular infectious arthritis, well described in this population, strongly suggests injection drug user. Patients often will note a recent history of trauma to the area, but causality has yet to be proven. Patients will describe pain, localized tenderness, and swelling at the sites.

The ESR is usually elevated, and fever and leukocytosis may be present. Up to 80 percent of patients 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/ L, with a neutrophil predominance. Synovial fluid Gram stain may aid in antibiotic selection. Immobilization, physical therapy, therapeutic arthrocentesis, and occasionally open drainage may be warranted.