Flexor Tenosynovitis

 

Written By: Michael Lin, MD, PGY-1, Edited: Timothy Khowong, MD, MSEd

 

Background:

Flexor tenosynovitis is a critical diagnosis not to miss in the emergency department. It involves an acute infection of the synovial sheath surrounding the flexor tendons, most commonly in the fingers or hand. The infection often results from penetrating trauma, such as a laceration, puncture wound, or bite, which introduces bacteria into the closed tendon sheath. Once inoculated, the infection can rapidly spread along the length of the sheath. 

Because of the risk of rapid progression, flexor tenosynovitis is considered a surgical emergency. Delayed recognition or management can lead to tendon ischemia, necrosis, osteomyelitis, and ultimately permanent functional loss or digital amputation. Prompt diagnosis, early antibiotics, and surgical consultation are critical to preserving hand function and preventing serious complications.

Presentation:

It often presents as a swollen finger that is warm, has overlying erythema, and painful to articulate with both passive and active motions.

Physical examination:

“BEST” Mnemonic or Kanavel Sign

B: Bend finger (i.e., finger held in slight flexion)

E: Extension pain (i.e., pain on passive extension)

S: Sausage-like digit (i.e., fusiform swelling

T: Tenderness along tendon sheath


Other Differentials To Consider:

  • Felon

  • Cellulitis 

  • Septic arthritis

  • Gout/pseudogout 

  • Flexor Tenosynovitis

Workup: 

Labs: 

  • BMP and CBC

  • Inflammatory Marker 

    • ESR 

    • CRP

Imaging:

  • XR 

    • Check for foreign bodies 

  • Ultrasound 

  • MRI 

Ultrasound Tips for Evaluating Flexor Tenosynovitis in the ED

Start by using a high-frequency linear probe and position it in the transverse plane, perpendicular to the long axis of the finger. This orientation provides a clear cross-sectional view of the tendon and surrounding structures.

To improve image quality—particularly in cases where direct probe contact is difficult or painful for the patient—consider using a water bath (with the finger submerged a few centimeters below the surface) or a standoff pad. Both techniques help optimize visualization of superficial structures like tendons.

Next, identify the tendon, which should appear as a band-like, fibrillar structure in cross-section. Scan both transversely and longitudinally to assess for abnormalities.

In cases of flexor tenosynovitis, you’ll typically see an anechoic (black) fluid collection surrounding the tendon sheath, indicating inflammation or infection. This fluid may be subtle, so compare with the contralateral (unaffected) finger when in doubt.

To assess for hyperemia, switch on color Doppler. Increased vascular flow around the tendon is a supportive finding and suggests active inflammation. Normal tendons should not demonstrate vascularity, so the presence of Doppler signal is clinically significant.

Early ultrasound diagnosis can expedite hand surgery consultation and improve outcomes, especially in patients with equivocal physical findings. Keep this quick POCUS approach in mind as part of your bedside evaluation.

Management and Disposition of Flexor Tenosynovitis:

Once flexor tenosynovitis is suspected or confirmed—clinically and/or with ultrasound—prompt treatment is essential. This is a surgical emergency, and delays in care can lead to devastating complications, including tendon necrosis, osteomyelitis, or even amputation.

Initiate empiric IV antibiotics immediately. The standard regimen includes vancomycin for MRSA coverage, combined with either piperacillin-tazobactam (Zosyn) or ceftriaxone to cover gram-negative organisms and anaerobes. In diabetic patients or those with immunocompromising conditions, be sure to include Pseudomonas coverage.

Following antibiotic administration, arrange for an urgent consult with hand surgery or orthopedics. These patients typically require operative irrigation and debridement (I&D) to definitively manage the infection and preserve hand function.

Rapid recognition and action in the ED can make a critical difference in patient outcomes. Always treat suspected flexor tenosynovitis as a limb-threatening emergency.

 
 

Resources:

Dezman, Zachary. “UMEM Educational Pearls.” University of Maryland School of Medicine, 28 Sept. 2015, umem.org/educational_pearls/2880/.

RaaeNielsen, Jennifer. Splinter Series: Kitty Nibble: A Case of the Sausage Finger, ALiEM, 2 Apr. 2021, www.aliem.com/splinter-series-sausage-finger/.

Shih, Jeffrey. “Ultrasound for the Win! 53m with Right Index Finger Swelling .” Https://Www.Aliem.Com/, 12 July 2017, www.aliem.com/ultrasound-win-53m-right-index-finger-swelling/.

Whipple, Teresa. Splinter Series: Point Tender, ALiEM, 23 May 2023, www.aliem.com/splinter-series-point-tender-finger/.

Yoon, Richard. “Pyogenic Flexor Tenosynovitis.” Orthobullets, 20 Feb. 2025, www.orthobullets.com/hand/6105/pyogenic-flexor-tenosynovitis.

 
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