When a patient presents to the Emergency Department with a single painful joint (e.g. wrist, knee, foot) the attending clinician’s top priority is to determine whether the pain is caused by an injury or if it is non-traumatic in nature. Non-traumatic causes for single joint pain can be either inflammatory or septic. While a systemic disease, such as gout, or an auto-immune disease, may present with a single painful joint, septic arthritis should be ruled out before treatment is offered. This is important because a septic joint is a true medical emergency that should be addressed immediately to avoid life-threatening outcomes.

Unfortunately, septic arthritis can be difficult to diagnose as it can have symptoms that are similar to other, benign types of arthritis. Untreated septic arthritis can cause tissue deterioration and joint destruction, thus markedly limiting mobility. In severe cases it can lead to death. The disease is caused by bacterial infection, often migrated from other parts of the body, settling in the joint. It is most prevalent among young children and adults over 55 years. The incidence is higher among patients with a prosthetic joint or those who suffer from immuno-compromising disorders. (Long et al., 2018)

When giving a history of their ailment, a patient with a painful joint may erroneously link the pain with a minor injury that they suffered recently. The medical team should not take this information at face value, especially if the joint does not exhibit signs of a traumatic injury. Fever is a poor indicator for septic arthritis as other aetiologies can often present with fever as well. Upon examination, telltale signs for septic arthritis include joint pain, swelling, tenderness and limited range of motion. (Carpenter at al., 2011)

One way to differentiate between a septic joint and an inflamed joint is that the former is hot to the touch and very painful, whereas the latter can be better characterised as warm. That said, the differential diagnosis can rarely be made just by obtaining history and conducting the examination. If trauma is not suspected, imaging is likely to also be of little use in these situations, as it will simply show soft tissue swelling. The key to diagnosing what is suspected to be septic arthritis is by obtaining synovial fluid. As this is an invasive procedure, the clinician should be careful in obtaining patient history and observing the joint to ensure that there is indeed cause to suspect a septic joint.

All told, when a patient present to the ED with a single painful joint the attending team should maintain a high suspicion for septic arthritis, until it can be definitively ruled out. One cannot solely rely on patient history and examination. If there are signs that point away from a traumatic injury and toward a diagnosis of septic arthritis (such as sudden onset of pain, a hot and tender joint and extremely limited mobility) a synovial fluid aspiration should be considered for a definitive diagnosis. This way, a clinician can ensure a reasonable level of care for the patient and prevent irreversible damage.