Fabricating Stiffness-Matched Three Dimensional –Printed Metal Implants for Total Wrist Arthroplasty

Abstract

Background Total wrist arthroplasty (TWA) is a motion-sparing treatment for pancarpal arthritis; however, complication rates up to 50% have limited widespread use. Implant micromotion, stress shielding, and periprosthetic osteolysis result in implant failure and revision to arthrodesis. Metal 3-dimensional (3D) printing allows for more accurate matching of surrounding bone biomechanical properties, theoretically reducing periprosthetic osteolysis. Herein, we use computed tomography to characterize the relationship of relative stiffness along the length of the distal radius with patient demographic factors. Methods After institutional review, wrist computed tomography scans at a single institution between 2013 and 2021 were identified. Exclusion criteria were history of radius or carpal trauma or fracture. Collected demographics included age, sex, and comorbidities (including osteoporosis/osteopenia). Scans were analyzed using Materialize Mimics Innovation Suite 24.0 (Leuven, Belgium). Distal radius cortical density (in Hounsfield units) and medullary volume (in cubic millimeters) with relation to distance from the radiocarpal joint were recorded. Average values for each variable were used to 3D-printed distal radius trial components with stiffness matched to bone density by length. Results Thirty-two patients met inclusion criteria. Distal radius cortical bone density progressively increased proximal to the radiocarpal joint, whereas medullary volume decreased; changes in both plateaued 20 mm proximal to the joint. Distal radius material properties differed by age, sex, and comorbidities. Total wrist arthroplasty implants were fabricated to match these variables as proof of concept. Conclusions Distal radius material properties vary along the bone length; conventional implants do not account for this variance. This study showed 3D-printed implants can be created to match bone properties along the length of the implant.