Quantitative Mapping of the Distal Radius to Aid Screw Selection for Volar Plate Fixation and Single-use Distal Radius Kits

BACKGROUND: 

Volar plate fixation is a common surgical fixation method for distal radius fractures. The aim of the study was to perform a large-scale quantitative analysis of intact distal radius anatomy to (1) investigate the demographic and anatomical factors associated with lengths of locking screws for volar plate fixation and (2) determine the optimal screw distribution in a single-use distal radius set for the overall patient cohort, ensuring inclusion of all necessary screws while minimizing waste. 

METHODS: 

CT scans from 198 wrists with an intact distal radius were evaluated. An open-source software module was used to automatically segment the distal radius and assemble a 3-dimensional anatomy for each patient. A quantitative map was computed to represent thickness across the volar surface. Variation in thickness was assessed in quantiles at the articular surface of the distal radius, using multivariate mixed modeling with respect to metaphyseal screw length and patient demographics. 

RESULTS: 

Calculated across the entire patient cohort, the mean (95% percentile range) for each screw position was 10.2 (9.0 to 13.0) mm for the metaphyseal screw, 9.42 (6.7 to 13.8) mm for Qu1, 15.3 (11.4 to 20.5) mm for Qu2, 19.22 (15.6 to 22.3) mm for Qu3, 19.39 (16.2 to 23.0) mm for Qu4, and 16.22 (10.3 to 19.7) for Qu5. Female patients had a smaller mean thickness than male patients at Qu2 (-1.93 mm, P = 0.003), Qu3 (-1.90 mm, P = 0.003), Qu4 (-1.99 mm, P = 0.002), and Qu5 (-2.21 mm, P < 0.001). For every 1 mm decrement in metaphyseal screw length, thickness was estimated to decrease by 0.518 mm ( P < 0.001) at Qu2, 0.462 mm ( P = 0.002) at Qu3, and 0.462 mm ( P = 0.004) at Qu4. 

CONCLUSION: 

A high-resolution, high-fidelity anterior to posterior quantitative thickness map was constructed. This was used to find an effect of sex and metaphyseal screw length on distal locking screw length and an overall 95% percentile distribution of screw lengths.