Sonographic Evaluation of Tendinous Mallet Finger to Estimate the Extent of Extension Lag

Abstract

Background: Although several reports have addressed tendinous mallet finger (TMF), they have not identified which method best informs surgeons about the extent of residual extension lag in these patients. We aimed to assess the association between sonographic classification of acute TMF and the degree of extension lag remaining at the final follow-up. Methods: The inclusion criterion was acute TMF with symptom onset within 2 weeks. Thirty-eight patients (23 male and 15 female) participated, with a mean follow-up of 17.1 months (range, 12.3–23.5 months). Range of motion, including extension lag, was measured at both the initial presentation and the final follow-up. All patients were managed conservatively using a finger splint for a period exceeding 6 weeks. Ultrasonography was performed for all participants to assess the severity of terminal extensor tendon injury. Statistical analyses examined the relationship between sonographic type and extension lag at final follow-up. Results: At initial presentation, the mean extension lag was 46.0°, which improved to 17.5° at the last follow-up. TMF cases were categorized into 3 sonographic types (hypo-echoic, thinned, and wavy) based on ultrasound characteristics. A significant difference in extension lag at final follow-up was observed among the TMF groups (p = 0.005). Patients with the wavy type had the greatest mean extension lag, whereas those with the hypo-echoic type had the least mean extension lag, with statistical significance. Conclusions: Sonographic assessment of TMF can aid in predicting residual extension lag in patients with TMF undergoing conservative treatment with a finger splint.