The role of fracture reduction and plate position in the aetiology of flexor pollicis longus tendon rupture after volar plate fixation of distal radius fractures.

BACKGROUND: Flexor pollicis longus (FPL) rupture has been described as complication following volar plating for distal radius fractures. It has been hypothesised that this is due to plate prominence. The aim of the study was to investigate the relationship between sub-optimal plate position and fracture reduction on plate prominence. METHODS: Plate prominence was measured in two experimental models. In the first, the effect of plate position was investigated using 18 fresh frozen cadavers with prominence being measured using a micrometer. In the second study, the effect of fracture reduction on plate prominence was investigated using similar methodology with simulated mal-reductions on dry bone models. RESULTS: The results of the first study showed a significant increase in lift-off for three plates (DVR, Synthes Universal and Acu-Loc), if the plates were moved distally or proximally from the anatomical position. Similar increases in prominence were also seen with rotational mal-positions. The results of the second study showed a statistically significant effect on plate prominence for even a 5° mal-reduction (p = 0.001) with worsening lift-off with increasing mal-reduction. These changes are significantly different from baseline and also significantly different to the lift-off recorded with mal-reductions 5° better and worse. Mal-reductions also necessitate more proximal placement of the plate to avoid screw penetration of the articular surface, and each 5° increment is significantly different from baseline. CONCLUSIONS: The results show a statistically and clinically significant effect of both plate position and fracture reduction on plate prominence and support the theory that both contribute to the aetiology of post-operative FPL rupture.