Acute monoarthritis: differentiating between crystals sepsis and trauma

Septic arthritis

The most important diagnosis to exclude is septic (infectious) arthritis, which if inadequately treated may cause permanent joint damage, and death in up to 11% of patients.

Septic arthritis usually affects single large joints, most frequently the knee. The patient often presents with systemic symptoms of sepsis (e.g., fever and malaise), as well as the rapid onset of swelling, warmth and local pain in the involved joint. Redness around the joint is an important clue, limiting diagnosis to either infectious or crystal-induced arthritis.

There is increased risk of septic arthritis in those who are older (especially > 80 years), have skin infections, recent joint surgery, a hip or knee prosthesis, rheumatoid arthritis, diabetes mellitus, are immunosuppressed or IV drug users.²

Staphylococcus aureus causes most septic arthritis in adults. Gonococcal infections are a rare but important cause of septic arthritis in sexually active young adults although there is often less associated morbidity due to less articular damage. Occasionally monoarthritis may be caused by other pathogens.

If the patient has septic arthritis admission is usually required for drainage of the joint, management of sepsis syndrome and IV antibiotics.

Crystal-induced arthritis

Gout is caused by precipitation of monosodium urate crystals in the synvovial fluid. Gout predominantly affects the first metatarsophalangeal joints, midfoot, ankles or knees. For further information see BPJ 8.³

Pseudogout is caused by precipitation of calcium pyrophosphate dihydrate crystals and affects mainly the knees and wrists, but can occur in the first metatarsophalangeal and other joints as well. Rarely, calcium oxalate, apatite and lipid crystals may be found.

Trauma-induced arthritis

A painful swollen joint can be caused by joint trauma. It is often associated with mild-to-moderate joint swelling in the absence of erythema, and the pain is characteristically exacerbated on movement and relieved at rest. The pain of traumatic arthritis is felt within seconds to minutes of the trauma, in contrast to the pain of infectious and crystal-induced arthritis which often develops over hours.

Joint aspiration

Although most resources suggest joint aspiration (arthrocentesis) is required in most patients with monoarthritis to confirm etiology, it is not always performed. However, if septic arthritis is suspected on clinical grounds, patients are usually referred to secondary care for joint aspiration and empirical IV antibiotics whilst awaiting culture results.

Joint aspiration in primary care depends on the skill and experience of the practitioner and availability of local secondary services. When performing joint aspiration aseptic technique is crucial to avoid introduction of infection.

Generally joint aspiration will not be required if a patient has classic signs and symptoms of gout, in which case the condition can be treated on clinical grounds.