Bursitis

Types of Bursitis

Inflammatory bursitis is often due to repetitive microtrauma. Recurring injury to the bursa triggers local vasodilatation and increased vascular permeability, ultimately causing the infiltration of extracellular fluid and proteins into the bursa. Inflammation causes synovial cells to multiply and thereby increases fluid production. In the acute setting, early inflammation causes the bursa to become distended. The additional bulk is perceived as foreign by the immune system, and this stimulates further inflammation. In the cases of chronic microtrauma, the bursal wall becomes thickened and the contents of the bursal sac are altered. Rather than synovial fluid, the bursa is filled with granular, brown, inspissated blood and calcifications. Its gritty contents create more friction when bone and tendon move against the bursa.

Hemorrhagic bursitis is characterized by bleeding directly into the bursa. It is typically due to violent trauma inflicted on the overlying tissues, and most commonly occurs at the prepatellar bursa of the knee. Rapid accumulation of blood causes an acute enlargement of the bursa and accompanying pain. The increased bursal mass hinders mobility of the nearby joint.

Infectious bursitis most commonly affects the olecranon and prepatellar bursae. Predisposing factors include diabetes, alcoholism, steroid therapy, uremia, trauma, skin disease, and a history of noninfectious bursitis. Patients will present with extreme tenderness, warmth, and erythema at the site, and there is often evidence of injury to the overlying skin. Infection often occurs from direct introduction of bacteria through traumatic injury or by contiguous spread of cellulitis. Bacterial infection is most commonly due to Staphylococcus aureus and Staphylococcus epidermidis. Roughly 10 percent of cases have been linked to species of Streptococcus. Further support for infectious bursitis includes the presence of lymphadenitis, cellulitis, and fever. The absence of these findings, however, does not rule out infection. Acute swelling and erythema warrant aspiration of the bursa and analysis of the fluid—including cell count, Gram stain, culture, and microscopic evaluation. A bursal fluid white cell count greater than 1,000/mcL is consistent with infection. A measurement greater than 50,000/mcL suggests septic bursitis. Complete laboratory evaluation should also include a complete blood count and erythrocyte sedimentation rate.

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