Quantitative analysis of radial torsion angle according to location with CT scan.

PURPOSE: Malrotation of the radius following a shaft fracture can lead to persistent pain, limited motion, and adjacent joint instability. This study aimed to evaluate radial torsion patterns by specific location.

METHODS

We included 50 patients with uninjured radii on computed tomography (CT). The torsion measuring zone (TMZ), defined along the longitudinal axis from just proximal to the watershed line to the distal end of the radial tuberosity, was divided into 3 mm intervals, generating cross-sectional images for torsion evaluation. Distal and proximal 30 mm segments were defined as distal end zone (DEZ) and proximal end zone (PEZ), respectively. The area with the largest 30 mm angular difference in distal half was designated the distal shaft torsion zone (DSTZ). The area between the proximal end of DSTZ and distal end of PEZ was the mid-shaft zone (MSZ). Angle change rate was evaluated in each zone, with the DSTZ compared to DEZ, MSZ, and PEZ.

RESULTS

The cohort included 27 men and 23 women, mean age of 54.8 ± 19.6 years. TMZ length was 160.5 ± 16.3 mm, with torsion angle of 49.8 ± 13.3° The angle change rate was 4.6 ± 1.9°/cm in the DEZ and 5.1 ± 3.3°/cm in the PEZ. The centre of the DSTZ was 4.8 ± 1.4 cm from distal end, with an angle change rate of 6.5 ± 1.8°/cm. The MSZ length was 6.7 ± 1.7 cm, with angle change rate of 0.3 ± 1.6°/cm. DSTZ showed significantly higher angle change rates compared to DEZ (P < 0.001) and MSZ (P < 0.001).

CONCLUSION

The DSTZ, located about 5 cm from the distal end, exhibited the most significant torsion, while the MSZ showed minimal torsion. Recognising these torsion patterns will guide proper plate positioning and prevent iatrogenic malrotation during plate osteosynthesis for radius shaft fracture.