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Determination of Correct Implant Size in Radial Head Arthroplasty to Avoid Overlengthening

¹ Hand and Upper Limb Centre, St. Joseph's Health Care, 268 Grosvenor Street, London, ON N6A 4L6, Canada. E-mail address for G.S. Athwal: gathwal{at}uwo.ca

Investigation performed at the Hand and Upper Limb Centre, St. Joseph's Health Care, University of Western Ontario, London, Ontario, Canada

Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from the Canadian Orthopaedic Foundation Alexandra Kirkley Young Investigator Award, and less than $10,000 from Wright Medical Technology. In addition, one or more of the authors or a member of his or her immediate family received, in any one year, payments or other benefits of less than $10,000 or a commitment or agreement to provide such benefits from a commercial entity (Wright Medical Technology). Also, a commercial entity (Wright Medical Technology) paid or directed in any one year, or agreed to pay or direct, benefits in excess of $10,000 to a research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which one or more of the authors, or a member of his or her immediate family, is affiliated or associated.

Methods: Radial head implants of varying thicknesses were inserted into seven cadaver specimens, which were then assessed clinically and radiographically. Eight stages were examined: the intact specimen (stage 1); repair of the lateral collateral ligament (stage 2); radial head resection with repair of the lateral collateral ligament (stage 3); insertion of an implant of the correct thickness (stage 4); and insertion of an implant that resulted in radial overlengthening of 2 mm (stage 5), 4 mm (stage 6), 6 mm (stage 7), or 8 mm (stage 8). The specimens were tested with and without muscle loading to simulate resting muscle tone and surgical paralysis, respectively. At each stage, radiographs were made to measure the ulnohumeral joint space and the lateral ulnohumeral joint was visually assessed.

Results: We identified no difference, with regard to medial ulnohumeral joint incongruity as seen radiographically, among stages 1 through 6 during the tests with muscle loading. A significant difference in medial ulnohumeral joint incongruity was found in stages 7 (p = 0.003) and 8 (p < 0.001). The clinical (visually assessed) lateral ulnohumeral joint space gap was negligible in stages 1 through 4 but increased significantly at all stages involving overlengthening (gross gap, 0.9 mm with 2 mm of overlengthening [p = 0.005], 2.3 mm with 4 mm of overlengthening [p < 0.001], 3.4 mm with 6 mm [p < 0.001], and 4.7 mm with 8 mm [p < 0.001]).

Conclusions: Incongruity of the medial ulnohumeral joint becomes apparent radiographically only after overlengthening of the radius by 6 mm. Intraoperative visualization of a gap in the lateral ulnohumeral joint is a reliable indicator of overlengthening following the insertion of a radial head prosthesis.

Clinical Relevance: This in vitro study indicates that the clinical (visual) observation of a lateral ulnohumeral joint gap is a reliable indicator of overlengthening following implantation of a radial head prosthesis. In contrast, radiographic measurements are relatively insensitive and cannot reliably demonstrate overlengthening of <6 mm.

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