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Distal Radioulnar Joint Reaction Force After Ulnar Shortening: Diaphyseal Osteotomy vs Wafer Resection
Colin D. Canham, MD 1 Michael J. Schreck, MD1; Noorullah Maqsoodi, BS2; Mark Olles, PhD2; John C. Elfar, MD1
1Department of Orthopaedic Surgery, University of Rochester, Rochester, NY; 2Department of Mechanical Engineering, Rochester Institute of Technology, Rochester, NY

Introduction: Prior studies have demonstrated ulnar shortening alters distal radioulnar joint (DRUJ) mechanics. In previous work, we developed a novel method of measuring joint reaction force (JRF) at the DRUJ that preserves peri-articular soft tissues. Prior methods of measuring DRUJ JRF required disruption of these important stabilizing structures. The purpose of this study was to apply this method to compare how ulnar diaphyseal shortening and wafer resection affect DRUJ JRF. Our hypothesis was ulnar shortening osteotomy would increase DRUJ JRF more than wafer resection.

Methods: Based on pilot data, a sample size of 7 was required to detect a 30% increase in DRUJ JRF with 83% power. Eight fresh frozen human cadaveric arms were obtained. Under fluoroscopic guidance, a threaded pin was inserted into the lateral radius orthogonal to the DRUJ and a second pin was placed in the medial ulna coaxial to the radial pin. Each arm was mounted onto a mechanical tensile testing machine with the wrist in neutral rotation using a custom fixture. A distracting force was applied across the DRUJ while force and displacement were simultaneously measured, generating a force-displacement curve. Data sets were entered into a computer and a polynomial was generated and solved to determine the inflection point representing the JRF. Each ulna was then shortened by 3 mm using a standard ulnar diaphyseal osteotomy and fixed with a slotted compression plate that allowed for subsequent re-lengthening. JRF was determined as above. The ulnae were re-lengthened to their original length to re-establish normal anatomy and return JRF to baseline prior to performing wafer resection. Wafer resection was then performed with removal of a 3 mm wafer. JRF was again calculated. JRF between the 4 conditions (baseline, diaphyseal, re-lengthened and wafer) were compared using a linear mixed model with Bonferroni correction.

Results: Average baseline DRUJ JRF was 7.172.52 N and 10.302.66 N after diaphyseal shortening osteotomy, (p<0.0015). Average JRF after re-lengthening the ulna was 6.862.24 N and 6.681.87 N after wafer resection (p>0.05). There were no differences in JRF between baseline, re-lengthened, and wafer resection conditions. A representative force-displacement curve for the 4 conditions is shown in figure 1.

Conclusions: DRUJ JRF increases significantly after ulnar diaphyseal shortening osteotomy and does not increase after ulnar wafer resection.

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