Infections of Bursae, Joints, and Bones

Definition

Bursae are the satellite structures that form to protect tissues from bony prominences. The superficial bursae, including the olecranon, prepatellar, infrapatellar, and bursae over the first metatarsophalangeal bunions, are more likely to become infected than are the deep bursae, such as the subacromial, trochanteric, and iliopsoas bursae.

Epidemiology

Olecranon bursitis may occur in as many as 10 in 100,000 persons per year. The majority of cases occur in men, and antecedent trauma to the skin is frequent.

Pathobiology

Septic bursitis of superficial bursae is most commonly due to direct inoculation through the overlying skin; less commonly, it is secondary to overlying cellulitis. Most cases of deep septic bursitis are due to contiguous spread from adjacent infected joints or hematogenous seeding.

Predisposing risk factors for septic bursitis include trauma to the skin. For example, olecranon septic bursitis may occur in plumbers, athletes, and patients with chronic obstructive pulmonary disease (COPD) who frequently lean on their elbows; prepatellar or infrapatellar septic bursitis can occur in housecleaners, gardeners, and carpet layers. At least one third of patients with septic bursitis have an underlying comorbid illness such as diabetes mellitus, rheumatoid arthritis, gout, COPD, or alcohol use disorder.

Clinical Manifestations

In immunocompetent patients, septic bursitis often but not always presents with fever as well as erythema and warmth of the overlying skin; there may be swelling of the bursae. In contrast to patients with septic arthritis, patients with septic bursitis of superficial bursae have intact range of motion of the joints, which may be limited only at the extremes of flexion. Pain on motion of the joint and restriction of joint range of motion are highly suggestive of septic arthritis. Acute phase reactants such as C-reactive protein, the sedimentation rate, and the white blood cell (WBC) count may be elevated.

Diagnosis

Radiography should be performed to look for a foreign body and to evaluate the surrounding bones. Aspiration of bursal fluid is helpful in the diagnosis of patients who have pain, erythema, and/or swelling of an affected area. However, given the risk for contaminating the bursa if the aspiration occurs through cellulitic skin, many clinicians choose to aspirate a bursa only if empirical antimicrobial therapy has failed. Ultrasound or computed tomography (CT) guidance greatly enhances the successful aspiration of superficial bursae. Care must be taken not to violate the joint space when aspirating a bursa to avoid inoculating it.

The leukocyte count of the bursal fluid is generally lower than what is seen in septic arthritis. A leukocyte count greater than 2000/μL has a sensitivity of 94% and a specificity of 79% for superficial (olecranon or prepatellar) bursitis. Bacterial culture and in vitro susceptibilities must be obtained; if additional fluid is available, a Gram stain may be obtained, although its sensitivity may be as low as 15%. The presence of crystals does not exclude the possibility of septic bursitis ( Chapter 252 ). Concomitant bacteremia can occur, and blood cultures should be obtained before the initiation of therapy if possible.

Staphylococcus aureus ( Chapter 267 ), which is the most common cause of septic bursitis, accounts for more than 70% of culture-proven cases, followed by β-hemolytic streptococci. Aerobic gram-negative bacilli, including Escherichia coli, and pseudomonas, are less common causes of septic bursitis. Polymicrobial infection can also occur. Chronic bursitis may be associated with infections due to Brucella spp, atypical mycobacteria, or Mycobacterium tuberculosis, as well as fungi; the presence of these infections should raise the possibility of systemic infection.

Treatment

Prevention

Because superficial septic bursitis is often associated with occasional or avocational activities involving kneeling or resting on the elbows, using protective padding may be helpful.

Prognosis

The optimal duration of therapy is unknown, but prognosis of superficial bursitis is generally excellent. The presence of comorbid conditions, especially conditions associated with deep bursal infections (e.g., including septic arthritis, bacteremia, and osteomyelitis), is associated with more intractable and difficult disease.

Definition

Septic arthritis, which refers to infection of a joint by a microorganism, is associated with increased morbidity and mortality as well as loss of articular integrity and function. Septic arthritis is usually caused by a bacterial infection, but other microorganisms also can cause infections with clinical characteristics that differ from those of bacterial infections.

Nongonococcal Septic Arthritis

Epidemiology

The incidence of septic arthritis affecting native joints is approximately 10 per 100,000 patient years. Among patients presenting with an acutely swollen and painful joint, bacterial pathogens are the most common etiology. Nongonococcal septic arthritis is the most common form of septic arthritis and is somewhat more common in men than in women.

Pathobiology

Staphylococci or streptococci are the most common pathogen to cause septic arthritis, but the microbiology depends on the mechanism of the infection ( Table 251-1 ). Septic arthritis can result from direct inoculation (e.g., accidents, bites, surgery) or by extension from infected bone into an adjacent joint space. Approximately 75% of cases are due to hematogenous spread, particularly in patients who use injection drugs, have indwelling catheters, or are immunocompromised. Iatrogenic septic arthritis due to needle arthrocentesis (is estimated to be between <1/10,000 to 1/3000 procedures) or arthroscopy (estimated to be between 0.0009 to 1.1%) is very rare.

Bacteria causing septic arthritis produce an acute inflammatory reaction in the synovial membrane. Synovial hyperplasia and inflammatory cell immigration, with the release of pro-inflammatory and cartilage-destroying cytokines and proteases, result in damage to cartilage and bone. Bacterial toxins and DNA as well as superantigens, such as those seen in staphylococcal toxic shock syndrome, also damage cartilage and bone.

Risk factors for the development of septic arthritis include penetrating trauma, diabetes, alcohol use disorder, cutaneous ulcers, injection drug use, prosthetic joints, rheumatoid arthritis, osteoarthritis, and low socioeconomic status, as well as advanced age, skin infection, indwelling intravenous catheters, cancer, and immunosuppressive therapies, including biologic response modifiers used in the management of autoimmune diseases such as rheumatoid arthritis and inflammatory bowel disease.