Image‐based design and 3D‐metal printing of a rat hip implant for use in a clinically representative model of joint replacement

: The aim of this study was to obtain micro-computed tomography derived measurements of the rat proximal femur, to create parameterized rat hip implants that could be surgically installed in a clinically representative small animal model of joint replacement. The proximal femoral anatomy of N=25 rats (male, Sprague-Dawley, 390-605g) was quantified. Key measurements were used to parameterize computer-aided design models of monoblock rat femoral implants. Linear regression analysis was used to determine if rat hip dimensions could be predicted from animal weight. A correlation analysis was used to determine how implants could be scaled to create a range of sizes. Additive manufacturing (3D printing) was used to create implants in medical-grade metal alloys. Linear regressions comparing rat weight to Femoral Head Diameter and Neck-Head Axis Length revealed a significant non-zero slope (p<0.05). Pearson's correlation analysis revealed five significant correlations between key measurements in the rat femur (p<0.05). Implants were installed into both cadaveric and live animals; iterative design modifications were made to prototypes based on these surgical findings. Animals were able to tolerate installation of implants, and were observed ambulating on their affected limbs post-operatively. Clinical Statement of Significance: We have developed a preclinical rat hip hemiarthroplasty model using image-based and iterative design techniques to create 3D-metal printed implants in medical-grade metal alloys. Our findings support further development of this model for use as a low-cost translational test platform for preclinical orthopaedic research into areas such as osseointegration, metal-on-cartilage wear and peri-prosthetic joint infection. This article is protected by copyright. All rights reserved.