Radiographic Soft Tissue Thickness Differentiating Pyogenic Flexor Tenosynovitis From Other Finger Infections

Purpose: Characteristic swelling has been described as a differentiating sign of pyogenic flexor tenosynovitis (PFT) but has not been validated. We conducted a retrospective study of adults with finger infections to compare radiographic parameters of soft tissue dimensions. Our hypothesis was that in patients with digit infections, radiographic soft tissue thickness measurement would differ between PFT and non-PFT infected digits.

Methods: Patients with a finger infection and radiographic evaluation were identified retrospectively at a large academic medical center and divided into 2 groups: PFT (n = 31) and non-PFT infections (n = 31). We defined PFT as purulence in the tendon sheath or positive culture growth from the sheath at surgery. Non-PFT infections included all other finger infections such as abscesses and cellulitis. A total of 15 radiographic measurements were made on all included digits. Ratios and differences were calculated to characterize the pattern of swelling for each infected finger. Bivariate analysis was performed to identify potential predictor variables between the PFT and non-PFT groups. Logistic regression was performed to reduce confounding and model potential relationships.

Results: Neither presence of diffuse swelling nor the shape of finger swelling distinguished PFT from non-PFT infections. All finger infections resulted in diffuse swelling. Pyogenic flexor tenosynovitis was distinguished by differential volar soft tissue thickness minus dorsal soft tissue thickness on radiographs at the proximal phalanx level (9 ± 1 mm for PFT vs 5 ± 1 mm for non-PFT). This was an independent predictor of PFT. The area under the receiver operating curve was 0.83 (95% confidence interval, 0.73-0.94). A difference between volar and dorsal soft tissue swelling of 7 mm or greater had a positive predictive value of 82% with a sensitivity of 84% and specificity of 74%. A difference of 10 mm predicted PFT infection with 76% probability (95% confidence interval, 73% to 99%).

Conclusions: Pyogenic flexor tenosynovitis may result in uniform finger swelling, but this does not appear to distinguish PFT from other finger infections. Acute PFT swelling is distinguished by differential volar versus dorsal radiographic soft tissue thickness at the level of the proximal phalanx. The term "fusiform swelling" is a misnomer for the appearance of acute PFT because the finger is not spindle-shaped.

Type of study/level of evidence: Diagnostic IV.