Radiological features of the carpometacarpal joint in hamate body fracture on anteroposterior hand X-ray image.

Background: Hamate body fractures are rare and can be overlooked due to the diagnostic difficulty on X-ray. We focused on the carpometacarpal joint space width (CMC-JSW) and examined the features of this fracture on versatile anteroposterior hand X-ray images, initially taken for hand trauma cases.

Methods: Ten patients (nine males and one female; mean age, 34 years) diagnosed with a hamate body fracture on CT in our facility between January 2013 and October 2023 were included in this study. The fracture types were dorsal type in six cases and shear type in four cases. The 4th and 5th CMC-JSWs were measured on anteroposterior hand radiography and CT sagittal sections. If the metacarpal and hamate bones appeared to overlap due to depression, the width was expressed as a negative value (overlap sign). CMC-JSWs were compared between the types or unaffected sides using the Mann-Whitney U test. The correlation with X-ray and CT measurements was analyzed using the Spearman test.

Results: The average CMC-JSWs (IV: -0.52 mm, V: -1.33 mm) in hamate body fractures on X-ray were minus and these values were significantly lower than unaffected side (IV: 1.51 mm, V: 1.48 mm) (p < 0.05, p < 0.001). CMC-JSW (IV: -1.64 mm) and CMC-JSW (V: -2.70 mm) of dorsal type were significantly lower than shear type (IV: 1.17 mm, V: 0.72 mm) (p < 0.05). CMC-JSW values on X-ray were positively correlated with those on CT (IV: ρ = 0.796, V: ρ = 0927).

Conclusions: Decreased CMC-JSW, correlated with CT sagittal sections, and "overlap sign" on anteroposterior hand X-ray were possible radiological characteristics of hamate body fracture. Care should be taken to avoid overlooking shear-type fractures because of subtle CMC-JSW decreases.