gms | German Medical Science

Objectives/Interrogation: The deep component of the distal radioulnar ligaments (DRUL) inserts on the ulnar styloid and ulnar fovea and is considered as the most important stabilizer of the distal radioulnar joint (DRUJ). Ulnar styloid fractures (USF) may cause DRUJ instability depending on the fracture size. The aim of this study was to determine the relevant fragment size, leading to a significant increase in dorso-palmar (DP) translation and pronosupination.

Methods: Soft tissue was removed from a total of 8 cadaveric upper extremities (3 female) aged 60 to 77 years (mean: 66.4), preserving the interosseous membrane, extensor carpi ulnaris (ECU), pronator quadratus (PQ), and triangular fibrocartilage complex. The ECU and PQ were both loaded with 5N weight in a custom fixture, which permitted free rotation and DP-translation of the radius around the fixed ulna. For biomechanical testing, DRUJ stability in DP-Translation and pronosupination were evaluated. Four specific points on the DRUJ were chosen, to record the positional change of the DRUJ using a MicroScribe 3DLX. 1Nm of torque was applied to reach an endpoint in Pronosupination. DP-translation was measured in neutral, full pronation and 90° supination with 15 N translation loads. Measurements were repeated for four different ulnar styloid fractures done sequentially in the same specimen: intact, USF of the tip, basal USF and an USF including the fovea. Statistical analysis was performed using a repeated-measures ANOVA and Tukey multiple comparison post hoc tests.

Results and Conclusions: Compared to the intact condition (170.9°), the pronosupination significantly increased after all three fractures (Tip:181.5°, p0.002; base: 184.3°, p<0.001; Fovea: 190.5°, p<0.001). The fovea fracture also showed a significant increase compared to the tip fracture (p=0.031). Total dorso-palmar translation significantly increased in neutral rotation after the fovea fracture (10.0mm) compared to the intact (6.8mm, p=0.002) and tip fracture conditions (7.8mm, p=0.029). There was also a significant increase in dorso-palmar translation in supination from intact (5.8mm) and tip fracture (5.9mm) to the fovea fracture (7.3mm, p<0.001 and 0.002). All tested fracture sizes of the ulnar styloid led to rotational instability of the DRUJ; however, the DRUJ remained stable in dorso-palmar translation unless the ulnar styloid fracture involved the fovea. Styloid fracture repair should be considered in fractures of the ulnar styloid involving the fovea.