A biomechanical comparison of volar locked plating of intra-articular distal radius fractures: use of 4 versus 7 screws for distal fixation.

PURPOSE: To determine whether the number of distal locking screws significantly affects stability of a cadaveric simulated distal radius fracture fixed with a volar locking plate.

METHODS: We created AO/ASIF type C2 fractures in 10 matched pairs of human fresh-frozen cadaveric wrists and then fixed them using volar locking plates. The number of distal locking screws used was 4 screws or 7 screws in each wrist of the matched pair. We loaded the stabilized fractures cyclically to simulate 6 weeks of postoperative stressing during a therapy protocol and then loaded them to failure. Failure was defined as 2 mm or more of displacement of any fracture fragment as recorded by differential variable reluctance transducers.

RESULTS: No wrists failed during the cyclic loading portion for either the 4- or 7-screw construct. The average initial stiffness of the 7-screw construct was 69 N/mm (± 38) versus 48 N/mm (± 14) for the 4-screw construct. The average failure load for the 7-screw construct was 139 N (± 78) versus 108 N (± 18) for the 4-screw construct. Neither of these differences was statistically significant.

CONCLUSIONS: Although there was a trend toward increased initial stiffness and higher failure load in fractures fixed distally with 7 locking screws, the results were not statistically significant compared with fractures fixed with only 4 screws. Both constructs can withstand forces likely encountered in early therapy protocols.

CLINICAL RELEVANCE: The use of extra distal locking screws when fixing distal radius fractures increases expense and may increase the risk of complications, such as extensor tendon irritation or rupture.