A 65-year-old man presented to the ED with a complaint of right hip pain. He reported a history of chronic pain to the hip, which is usually controlled with NSAIDs. His pain had increased over the past week, and it did not respond to his typical regimen.
He denied any trauma, and his medical history is significant for diabetes mellitus. His blood pressure is 110/80 mm Hg, heart rate is 90 bpm, respiratory rate is 12 bpm, and temperature is 100.5°F. His physical exam is significant for diffuse tenderness to the right hip. No obvious deformity is visible, and he is holding his hip in slight flexion. He is resistant to any movement of the hip secondary to severe pain.
X-rays of the hip show no acute changes. Blood work reveals a normal CBC, with ESR pending.
Bedside ultrasounds of the right and left hips are shown. An arthrocentesis of the right hip was performed based on these findings, revealing a WBC of 100,000 with polymorphonuclear leukocyte predominance.
Septic arthritis can be a challenging diagnosis for emergency physicians. A septic joint is classically described as appearing swollen, erythematous, and warm, with significantly reduced range of motion. These findings may be easily apparent, especially when superficial joints such as the knee or ankle are affected. Diagnosing septic arthritis in other joints, particularly the hip, can be especially challenging because the characteristic findings are not easily apparent.
Identifying an effusion in the hip is the first hurdle when considering a diagnosis of septic arthritis. CT and MRI can be used, but they have significant drawbacks. Bedside ultrasound is a rapid, reliable technique that can be used in conjunction with the physical exam to confirm the presence of an effusion quickly in patients suspected of having septic arthritis.
The images here demonstrate the sonographic view of a normal hip joint when compared with an image of an effusion. Both views were obtained with a high frequency transducer, which allows for sufficient resolution to elucidate the anatomy of the hip. Occasionally, a low-frequency transducer must be used in obese patients to obtain sufficient depth to evaluate the joint space. The transducer is placed in-line with the femoral neck at roughly the level of the inguinal ligament. It is typically placed along an oblique axis, with the indicator pointing toward the pubic symphsis.
The femoral neck and head are the best initial landmarks to identify. They will appear bright white, and are easily recognizable by their characteristic shapes. (Arrow, Figure 1.) The capsule surrounding the hip joint is visible as a relatively bright white ligament arcing over the femoral neck and head. (Arrowhead, Figure 1). Minimal fluid should be visible in the space between the capsule and bony structures. A joint effusion is easily identified as a collection of black fluid within the potential space between the bony structures of the hip and the joint capsule. (Arrow, Figure 2).
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