Ultrasound Probe: POCUS for Flexor Tenosynovitis
Authors: Naila Ghafoor MD, Flor Lema, and Catherine Yu MD (Department of Emergency Medicine, Rutgers NJMS) // Reviewed by: Stephen Alerhand MD (@SAlerhand)
A 21 year-old female with no past medical history presented to the emergency department (ED) with ring finger pain and swelling of her right hand over the past six days. According to the patient, she initially developed a paronychia on the finger one week after getting her nails done. She went to an urgent care center for drainage of the paronychia and was also started on trimethoprim-sulfamethoxazole. She presented to the ED six days later for worsening pain and swelling of her finger despite taking the antibiotic as prescribed. She also noted decreased range of motion as well asmild numbness and tingling of the ring finger.
Vital signs were normal. On exam, the patient’s right fourth digit was edematous and held in flexion (Figure 1). Range of motion testing was limited due to pain elicited with any movement of the digit. Tenderness on palpation was most severe at the distal digit and the overlying skin was erythematous. Laboratory values, including a blood cell count, chemistry panel, erythrocyte sedimentation rate, and C-reactive protein, were within normal range. Plain films showed diffuse soft tissue swelling of the 4th digit with no bone or joint space abnormalities.
Figure 1: Palmar view of the right hand demonstrating the fourth digit held in flexion, with erythema and fusiform swelling.
Given the concern for cellulitis, abscess, and/or flexor tenosynovitis, a point-of-care ultrasound (POCUS) water bath (Figure 2) was performed which showed a hypoechogenic effusion along the tendon sheath in the longitudinal view (Figure 3) (Video 1).
Ultrasound water bath was performed by submerging the patient’s hand in a basin filled with warm water and then placing the high-frequency linear transducer in the water above the affected area. The transducer was not in direct contact with the patient’s skin and the patient was comfortable throughout the evaluation.
Figure 2: Ultrasound water bath using the high-frequency linear transducer.
Figure 3: Linear transducer in longitudinal plane demonstrating peritendinous effusion (red arrows) concerning for tenosynovitis
Video 3: Linear transducer in longitudinal plane demonstrating peritendinous effusion concerning for tenosynovitis
Review of the Literature
Flexor tenosynovitis is the infection of a digit’s flexor tendon sheath and is considered an orthopedic emergency. Clinical diagnosis of this condition is made using the four cardinal Kanavel’s signs: tenderness along the flexor tendon sheath, flexion of the finger, pain with passive extension, and fusiform swelling . Studies have shown that the sensitivity of the Kanavel signs ranges from 91.4% to 97.1% and specificity ranges from 51.3% to 69.2% . As diagnosis is primarily made through history and physical examination findings, a misdiagnosis or delayed diagnosis can have negative consequences including but not limited to: worsened range of motion owing to adhesions, tendon necrosis and rupture, deformity, and loss of limb .
POCUS can be used as a helpful adjunct to history and physical examination findings as shown by two large studies [3, 7], one case series  and several case reports [1, 8, 9]. One large study examining 57 cases of early flexor tenosynovitis found that ultrasound had a 94% sensitivity, 65% specificity, 63% positive predictive value, and 95% negative predictive value in making the diagnosis . Another study showed that out of 12 patients with sonographic evidence of flexor tenosynovitis who underwent surgical drainage, 11 (91.6%) were found to have purulent fluid in the flexor sheath .
POCUS can be used to look for direct signs of flexor tenosynovitis which include a hypoechogenic peritendinous effusion, as well as a thickened synovial sheath that is hypoechogenic and hyperemic (Figures 4 and 5) . This can be especially helpful in the early diagnosis of the condition, when patients are likely to present without all four Kanavel signs . Using an ultrasound water bath technique can help evaluate distal extremity injuries like flexor tenosynovitis. The patient is not exposed to ionizing radiation and the ultrasound transducer does not directly apply pressure to the affected extremity . This minimizes any discomfort and pain to the patient and enhances visualization of the superficial tissue at the proper depth on the machine near the focal zone, especially for the curved surfaces of the fingers .
Figure 4: Peritendinous effusion in the transverse view 
Figure 5: Peritendinous effusion in the longitudinal view 
With the concerning physical exam and POCUS findings, an emergent orthopedic surgery consult was placed and the patient was started on broad-spectrum antibiotics. The patient went to the operating room the same day, where she received an ultrasound-guided irrigation and debridement (I&D). According to the operation note, 200mL of gross purulent fluid was evacuated. She was then taken for an open I&D two days later. Wound cultures grew methicillin-susceptible Staphylococcus aureus, and her antibiotic regimen was narrowed appropriately. The patient never developed leukocytosis, fever, or hemodynamic instability during her 3-day hospital stay. On a follow-up orthopedic clinic visit, the patient was noted to be doing well and the wound healing appropriately.
Early diagnosis of flexor tenosynovitis can be challenging. It can be difficult to differentiate between cellulitis and flexor tenosynovitis if all four Kanavel’s signs are not present. POCUS using an ultrasound water bath can be used as a helpful adjunct to diagnose flexor tenosynovitis by demonstrating peritendinous fluid and thickened synovial sheath.
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