Distal ulnar neck fracture displacement with forearm rotation: A biomechanical cadaveric study

Management of distal ulnar fractures remains controversial, partly due to its low incidence and operative challenges encountered during surgical fixation. This cadaveric study examined fracture displacement in isolated distal ulnar fractures, specifically AO Muller Q2 and Biyani Type I fracture pattern, during forearm pronosupination.6 fresh frozen cadaveric upper limbs amputated at mid-humerus were used. Soft tissues including proximal and distal radioulnar joints were carefully preserved. Specimens were inspected grossly and radiographically for absence of pathologies. Radiocarpal and midcarpal pinning was performed to facilitate quantification of forearm rotation. 2 markers were each placed proximal and distal to fracture site to quantify fracture displacement. 3-dimensional positional data was recorded using an optoelectronic system (Vicon MX motion capture system).Distance between the 2 markers increased in the proximodistal and radioulnar axis, and decreased in the dorsovolar axis when the forearm was rotated from neutral to 100° pronation. The inverse was observed during supination. Mean aggregate fracture site displacement increased to 9.17 ± 2.78 mm at 100° pronation. Statistically significant increase in aggregate fracture site displacement was observed from 60° pronation onwards. At 100° supination, the aggregate fracture site displacement was 4.58 ± 8.62 mm. When supinating from neutral to 100°, fracture displacement did not increase significantly.

from this study suggest that distal ulnar fractures are potentially stable, particularly in supination. However, unrestricted forearm pronation with inadequate immobilisation might still cause further fracture displacement. Further studies are required to assess distal ulnar fracture stability in vivo before treatment guidelines can be established.