Scope of the problem

Non-traumatic joint pain is a common presenting complaint for patients in the emergency department, and emergency medicine practitioners should be knowledgeable in the evaluation of the “red hot joint.” While rarely life-threatening, joint pain is important because it may be the harbinger of more serious systemic diseases and infections. Furthermore, even mild diseases of many joints, especially the hands and weight-bearing joints, can result in significant short- and long-term disability. Accurate evaluation and treatment may reduce the severity and duration of disability.

Anatomic essentials

In order to determine the cause of joint pain, one must understand the underlying anatomy of the joint (Figure 27.1). The sources of joint pain may be classified into two major anatomic categories: articular structures (joint capsule and its contents) and periarticular structures (structures superficial to the joint capsule).

A joint is the union of the ends of two or more bones. On each bony surface lies a cushion, the articular cartilage, a compressible matrix of collagen fibers and proteoglycans which serves to prevent bone-on-bone contact. Adherent along the margins of the articular cartilage is a synovial membrane, which creates the synovial cavity. The synovial membrane also secretes high-viscosity synovial fluid, which fills the synovial cavity in order to lubricate the joints and facilitate mobility. A fibrous joint capsule encloses the synovial membrane, thus creating the unit known as the joint space.

The joint is strengthened and supported by ligaments, which are bands of fibrous tissues connecting bones or cartilages.