Brucellosis is an endemic systemic infectious disease, the most common complication is bone and joint involvement. Sacroiliac joint and spinal joint are the most frequently involved sites in adults, but knee joint infection is rare, and acute infectious knee arthritis complicated by acute osteomyelitis is even extremely uncommon in adults. Here, we report two cases of acute septic knee arthritis complicated by acute osteomyelitis caused by Brucella melitensis (B. melitensis).

Both patients had a history of traveling in animal husbandry areas within three months. On clinical examination, their right knee joint was tender, swollen, had limited movement and an effusion was present. Imaging examination showed effusion and synovial thickening of the right knee joint, as well as subchondral bone edema of the distal femur and proximal tibia. Laboratory examination showed that the serum agglutination test (SAT) in both patients were positive (1: 640 and 1: 320) without leukocytosis, although the proportion of lymphocytes, erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) significantly increased. Both patients underwent knee joint aspiration. Real-time polymerase chain reaction (Real-time PCR) analysis of synovial fluid showed that there was B. melitensis, and blood bacterial culture was negative. We determined that two patients had acute brucellosis knee arthritis complicated by acute osteomyelitis. Antibiotic treatment was given during hospitalization consisting of doxycycline (0.1 g po bid) and rifampicin (0.6 g po qd) for six weeks, and the changes of inflammatory indexes were closely monitored. At discharge, the symptoms had completely resolved, imaging abnormalities disappeared, and inflammatory indexes returned to normal. There was no recurrence of the disease at 1-year follow-up.

Acute brucellosis knee arthritis complicated by acute osteomyelitis is a rare but serious complication of brucellosis in adults. There is no obvious specificity of clinical manifestation and imaging examination. Early diagnosis and treatment can prevent the occurrence of knee joint deformity and even pathological fracture. Clinicians should fully consider the possibility of brucellosis where the travel or occupational history is suggestive.

• Acute osteomyelitis
• Brucellosis
• Septic knee arthritis
• Synovitis

Brucellosis is a common global zoonotic disease, which is responsible for a range of clinical manifestations. Fever, sweating and musculoskeletal pains are observed in most patients. The most frequent complication of brucellosis is osteoarticular involvement, with 10% to 85% of patients affected. The sacroiliac (up to 80%) and spinal joints (up to 54%) are the most common affected sites. Spondylitis and spondylodiscitis are the most frequent complications of brucellar spinal involvement. Peripheral arthritis, osteomyelitis, discitis, bursitis and tenosynovitis are other osteoarticular manifestations, but with a lower prevalence. Spinal brucellosis has two forms: focal and diffuse. Epidural abscess is a rare complication of spinal brucellosis but can lead to permanent neurological deficits or even death if not treated promptly. Spondylodiscitis is the most severe form of osteoarticular involvement by brucellosis, and can have single- or multi-focal involvement. Early and appropriate diagnosis and treatment of the disease is important in order to have a successful management of the patients with osteoarticular brucellosis. Brucellosis should be considered as a differential diagnosis for sciatic and back pain, especially in endemic regions. Patients with septic arthritis living in endemic areas also need to be evaluated in terms of brucellosis. Physical examination, laboratory tests and imaging techniques are needed to diagnose the disease. Radiography, computed tomography, magnetic resonance imaging (MRI) and bone scintigraphy are imaging techniques for the diagnosis of osteoarticular brucellosis. MRI is helpful to differentiate between pyogenic spondylitis and brucellar spondylitis. Drug medications (antibiotics) and surgery are the only two options for the treatment and cure of osteoarticular brucellosis.

• Brucellosis
• Brucella
• Osteoarticular manifestations
• Musculoskeletal pain
• Bone
• Joint

• biofilms
• fracture fixation
• prosthesis-related infections
• surgical wound infection