The "Trigonometric Technique" for simple measurement of volar angulation in boxers' fractures

Abstract

Introduction: Subcapital fractures of the 5th metacarpal bone (MCV) represent a common injury. Volar angulation measurement is essential for treatment decision-making and therefore needs a reliable and valid method. The purpose of the present study was to investigate a new technique for volar angulation measurement, called the "Trigonometric Technique" (TT), and to compare the TT with the reference standard based on computed tomography (CT).

Hypothesis: Quantifying volar angulation in MCV neck fractures with the TT shows no difference compared to the angle measured on CT scans.

Material and methods: Fifteen patients (14 men and 1 woman) with a mean age of 37±16years (range, from 16 to 72 years) who suffered MCV neck fracture and met the inclusion and exclusion criteria were selected for this prospective cohort study. Radiologic investigation included simple dorsopalmar (DP) radiographs and CT scans from the injured hand. Volar angulation measurements were performed by three observers at two time points comparing the TT to measurements obtained on CT scans. Intraclass correlation coefficients (ICC) were determined to assess inter- and intra-observer reliability.

Results: The TT showed a mean volar angulation of 39±5 degrees (range, from 26 to 46 degrees) compared to 41±7 degrees (range, from 28 to 54 degrees) on CT measurement, which revealed a significant correlation between the two measurement techniques (R=0.922, p<0.001). Overall, the inter-rater (R=0.977; 95% CI 0.945-0.992) as well as intra-rater (R=0.857; 95% CI 0.739-0.941) reliability for the volar angulation using the TT was excellent.

Conclusion: The TT presented in this study uses plain radiography and trigonometric identities to precisely determine volar angulation in MCV neck fractures. The TT correlates excellently with the obtained volar angulation angles measured on CT scans. We recommend the TT for volar angulation measurement in boxer's fracture as a reliable alternative to the conventional techniques. However, rotational abnormalities may remain undetected and should therefore be ruled out during clinical examination.

Level of evidence: II, study of diagnostic test.

Keywords: Decision-making; Radiographic measurement; Subcapital metacarpal fracture; Trigonometric technique; Volar angulation.