An anatomic study on the junctura tendinum in the 4th intermetacarpal space and its clinical implication

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

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.

Predicting Tendon Tissue Grafting Source From the Extensors of Long Fingers: A Systematic Review of Cadaveric Studies

Background: The use of tendon tissue for transfer and grafting is a common practice in hand surgery. Many local tendons are usually used, mainly that of the palmaris longus muscle. However, this tendon could be absent in up to 46%. Extra slips of the extensor digitorum communis (EDC) and extra tendons such as the extensor indicis (EI) and the extensor digiti minimi (EDM) could be valuable sources for tendon tissue. Methods: A systematic review was conducted to quantify the proportion of extra slips in relation to each tendon and extra tendons in relation to each long finger. The aim is to better predict the location of tendon tissue sources on the dorsum of the hand in reconstructive surgery. Results: Based on 39 studies including 7847 hands, the cumulative frequencies of extra slips and extra tendons and the association between double-slip frequency and ancestry were as follows: (1) the little finger showed the highest cumulative frequency of extra slips (96.54%), followed by the ring (37.5%), long (30.6%), and index (9.5%) fingers; (2) the index with its EI and its variants and the little finger with its EDM bear by far the highest cumulative frequency of extra tendons (≈100%); and (3) double slips are found to be rare in Indian populations, most prevalent in Japanese populations, more prevalent in the index and little fingers of Caucasians, and more prevalent in the ring fingers of Middle Eastern populations. Conclusions: Knowledge of the frequencies of extra slips for each long extensor tendon and extra tendons for each long finger along with their prevalence in different populations would improve: (1) location prevision of tendon source for tendon grafting; and (2) surgical planning while supporting a patient-centered approach. Evidence-based hand anatomy would have a major potential to contribute to the practice of an evidence-based hand surgery. Predicting the possible tendon sources that could be present on the dorsum of the hand is thought to be very valuable for hand surgeons. In addition and from an evolutionary perspective, we hypothesized that the observed significantly higher frequency values of the double-slip and triple-slip types of the EDC of the ring finger, EDC of the little finger, and EDM might indicate a natural selection tendency for a higher independence of the former digits in the future evolution of the human hand.