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The Effect of Scaphoid Distal Pole Resection on Wrist Biomechanics
Stephen Hioe, DO1; Christopher Jones, MD2; Michael Rivlin, MD2; Megan Jimenez, DO3; Amir Kachooei, MD4;
1Rowan University, Stratford, NJ, 2Thomas Jefferson University Hospital, Philadelphia, PA, 3Inspira, Vineland, NJ, 4Ghaem Hospital, Mashhad University of Medical Sciences, Mashhad, Iran (Islamic Republic of)
Purpose: Distal pole scaphoid resection arthroplasty provides pain relief and maintains motion in the face of chronic scaphoid non-union. This study assesses the biomechanical implications of increasing levels of distal pole scaphoid resection.
Methods: Dorsal ligament-sparing scaphoid exposure was used in each of six fresh frozen cadaveric upper extremities statically affixed to a wooden ballast. Scaphoid resection levels at 25%, 50%, and 75% of the longitudinal length of the scaphoid were made under fluoroscopic imaging. Physiologic axial load through the carpus in grip and pinch were simulated with weights affixed to the wrist and finger flexor and extensor tendons. Simulated grip, pinch, radial and ulnar deviation were performed for the intact scaphoid and for each resection level. The following radiographic parameters were assessed: radiolunate and capitolunate angles, carpal height ratio, 1st metacarpal subsidence ratio, and percentage of ulnar carpal translation. These measurements were statistically analyzed by using repeated measures ANOVA at P<0.05.
Results: Increasing levels of scaphoid resection is associated with a linear increase in radio- and capitolunate angles and a decrease in the distance between the radial styloid and trapezium with simulated radial deviation. Of these, only the radiolunate measurements attained statistical significance. We found no significant differences in 1st metacarpal subsidence or carpal height ratios with scaphoid resection levels up to 75%. We also found increasing percentages of ulnar carpal translation in simulated grip, pinch, and radial deviation with more proximal resection levels. Simulated ulnar deviation showed sequentially decreasing percentages of ulnar carpal translation. Though we observed the prior noted changes in ulnar carpal translation, these measurements did not attain statistical significance.
Conclusion: Overall radiocarpal stability was maintained through resections of up to 75% of the scaphoid. More proximal resection levels showed increasing levels of bony impingement with wrist radial deviation as well as increasing radio and capitolunate angles. In cases involving more proximal levels of distal pole scaphoid resection, a concomitant radial styloidectomy may be considered to avoid radial styloid impingement.
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