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. 2023 Dec 21;13(1):46.
doi: 10.3390/jcm13010046.

New Insights into Boxer's Knuckle Injury of the Little Finger

Sébastien Durand  1 , Thierry Christen  1 , Jean-Baptiste Ledoux  2 , Romain Baillot  1
Affiliations

New Insights into Boxer's Knuckle Injury of the Little Finger

Sébastien Durand et al. J Clin Med. .

Abstract

Background: The original description of boxer's knuckle injury of the fifth ray mentions that the injury occurs between the extensor digitorum communis (EDC) and the extensor digiti minimi (EDM). Subsequent reports claim similar findings. Anatomical studies show that the EDC of the fifth ray is absent in most patients, while the EDM is generally composed of two slips. We present a modification of the current description of boxer's knuckle injury of the little finger based on the correlation between advanced preoperative 3D imaging and intraoperative findings.

Methods: Five patients were investigated preoperatively using high-resolution ultrasound and 3D tendon reconstruction-based MR arthrography. Surgical exploration identified the lesion site relative to the EDM and EDC.

Results: All patients had two slips of the EDM and no EDC to the fifth ray. The injury appeared as a longitudinal tear of the EDM between its two slips. The mean gap was 7.8 mm (range 4.5-10 mm) on the pathological side vs. 1.3 mm (range 1-2 mm) on the healthy contralateral side.

Conclusions: We believe that previous descriptions of boxer's knuckle of the fifth ray are inaccurate. High-resolution ultrasound and 3D reconstructions based on MR arthrography are reliable diagnostic tools allowing to locate the injury with precision.

Keywords: 3D imaging; MRI; boxer’s knuckle; extensor digiti minimi; tendon injury; ultrasound.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Preoperative high-resolution ultrasound (case 4, 24-year-old female). Transverse/axial ages in B-mode (A), color Doppler (B), sagittal images in B-mode (C) and color Doppler (D) showing hyperemia and (red arrows) gap through the EDM on the pathological side. Contralateral comparative images (E–H).
Figure 2
Figure 2
Representative MR images (case 1, 25-year-old male). Axial T1-weighted on the healthy side (A) and axial fat-suppressed T2-weighted with arthrography on the pathological side (B). MRI revealed a gap between the two tendon slips of the EDM (red arrows) on the pathological side. Using 3D reconstruction based on MRI, the maximum distance between the two tendons of the EDM was 7.2 mm on the injured side (D) and 1.5 mm on the contralateral side (C). The JT of the fourth inter metacarpal space (yellow arrow) was in continuity with the EDM on the pathological and contralateral side.
Figure 3
Figure 3
Preoperative photograph (case 3, 27 year-old male) of the dorsal aspect of the hand showing swelling (white arrow) over the 5th MCP joint (A). Intraoperative photographs showing the gap between the two tendons (red arrows) of the EDM (B) that increases with MCP flexion (C) Results after running suture of the EDM to close the space between the two tendinous slips (D). Note that JT type 3y (yellow arrow) remains attached to the radial tendon of the EDM.
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