Bedside Ultrasound of a Painful Finger: Kanavel’s Fifth Sign?

A 44 year-old male presents to the emergency department with a chief complaint of right index finger pain, worsening over 2 weeks. He reports squeezing pus out of his finger 4 days prior to arrival with temporary relief of symptoms. He also reports a history of multiple previous infections in the same finger.

His vital signs are normal. His right index finger is held in slight flexion and shows uniform swelling. It is mildly erythematous and warm (Figure 1). Passive finger extension and palpation of the flexor surface elicit mild pain. Although all four of Kanavel’s Cardinal signs are present, they are not as intense as would be expected for typical flexor tenosynovitis.

Figure 1.  Swollen index finger.

A bedside ultrasound of the finger was performed with a high-frequency linear probe using the water bath technique (described below). A significant amount of fluid was seen surrounding the flexor tendon that was absent in an unaffected finger (Figures 2 and 3). A hand consult was called, the images were shown, and the patient was promptly taken to the operating room for flexor tenosynovitis. A large amount of purulent material was drained during the procedure. Cultures grew methicillin-sensitive Staphylococcus aureus.

Figure 2.  Flexor tenosynovitis. MP = middle phalanx; PP = proximal phalanx.

Figure 3.  Normal finger. MP = middle phalanx; PP = proximal phalanx.

The water bath technique is useful in the evaluation of small parts such as hands and feet, particularly when looking for fluid or foreign bodies. Most ultrasound probes are completely waterproof. The technique is safe for both the patient and the equipment. In this case, the hand is placed in a basin of water. The probe is submerged and held a few centimeters above the volar surface of the finger. As water is the perfect medium for transmitting sound waves, no gel is necessary. The finger is scanned in two planes (Figure 4).

Figure 4.  Water bath technique.