The Effect of Distal Pole Scaphoid Resection on Wrist Biomechanics:

BackhroundsDistal pole scaphoid resection arthroplasty (DPSR) provides pain relief and maintainsmotion in the face of chronic scaphoid non-union with limited degenerative arthritis.This study assesses the biomechanical implications of increasing levels of distal polescaphoid resection.MethodsDorsally based exposure was used in each of six fresh frozen cadaveric upperextremities statically affixed to a wooden ballast. Scaphoid resection levels at%50 ,%25, and %75 of the longitudinal length of the scaphoid were made underfluoroscopic imaging. Physiologic axial load through the carpus in grip and pinch weresimulated with weights affixed to the wrist and finger flexor and extensor tendons.Simulated grip, pinch, radial and ulnar deviation were performed for the intactscaphoid and for each resection level. The following radiographic parameters wereassessed: radiolunate and capitolunate angles, carpal height ratio, 1st metacarpalsubsidence ratio, and percentage of ulnar carpal translation. These measurementswere statistically analyzed by using repeated measures ANOVA at P <0.05. ResultsIncreasing levels of scaphoid resection is associated with a linear increase in radioandcapitolunate angles and a decrease in the distance between the radial styloidand trapezium with simulated radial deviation. Of these, only the radiolunatemeasurements attained statistical significance. We found no significant differencesin 1st metacarpal subsidence or carpal height ratios with scaphoid resection levels upto %75. We also found increasing percentages of ulnar carpal translation in simulatedgrip, pinch, and radial deviation with more proximal resection level. Simulated ulnardeviation showed sequentially decreasing percentages of ulnar carpal translation.Though we observed the prior noted changes in ulnar carpal translation, thesemeasurements did not attain statistical significance.ConclusionsMore proximal resection levels showed increasing levels of bony impingement withwrist radial deviation as well as increasing radio and capitolunate angles. While ourstudy demonstrates changes in ulnar carpal translation with increasing scaphoidsectioning levels, these values did not reach statistical significance. However, weobserved that ulnar carpal translation with simulated wrist radial deviation worsenedradiographic radial styloid impingement. In cases involving more proximal levels ofdistal pole scaphoid resection, a concomitant radial styloidectomy may be consideredto avoid radial styloid impingement.