Implementation of a semiautomatic method to design patient-specific instruments for corrective osteotomy of the radius

\u3cp\u3ePurpose: 3D-printed patient-specific instruments (PSIs), such as surgical guides and implants, show great promise for accurate navigation in surgical correction of post-traumatic deformities of the distal radius. However, existing costs of computer-aided design and manufacturing process prevent everyday surgical use. In this paper, we propose an innovative semiautomatic methodology to streamline the PSIs design. Methods: The new method was implemented as an extension of our existing 3D planning software. It facilitates the design of a regular and smooth implant and a companion guide starting from a user-selected surface on the affected bone. We evaluated the software by designing PSIs starting from preoperative virtual 3D plans of five patients previously treated at our institute for corrective osteotomy. We repeated the design for the same cases also with commercially available software, with and without dedicated customization. We measured design time and tracked user activity during the design process of implants, guides and subsequent modifications. Results: All the designed shapes were considered valid. Median design times (t~) were reduced for implants ((t~ \u3csub\u3eI\u3c/sub\u3e) = 2.2 min) and guides ((t~ \u3csub\u3eG\u3c/sub\u3e) = 1.0 min) compared to the standard ((t~ \u3csub\u3eI\u3c/sub\u3e) = 13 min and (t~ \u3csub\u3eG\u3c/sub\u3e) = 8 min) and the partially customized ((t~ \u3csub\u3eI\u3c/sub\u3e) = 6.5 min and (t~ \u3csub\u3eG\u3c/sub\u3e) = 6.0 min) commercially available alternatives. Mouse and keyboard activities were reduced (median count of strokes and clicks during implant design ((s~ \u3csub\u3eI\u3c/sub\u3e) = 53, and guide design ((s~ \u3csub\u3eG\u3c/sub\u3e) = 27) compared to using standard software ((s~ \u3csub\u3eI\u3c/sub\u3e) = 559 and (s~ \u3csub\u3eG\u3c/sub\u3e) = 380) and customized commercial software ((s~ \u3csub\u3eI\u3c/sub\u3e) = 217 and (s~ \u3csub\u3eG\u3c/sub\u3e) = 180). Conclusion: Our software solution efficiently streamlines the design of PSIs for distal radius malunion. It represents a first step in making 3D-printed PSIs technology more accessible.\u3c/p\u3

On the importance of 3D, geometrically accurate, and subject-specific finite element analysis for evaluation of in-vivo soft tissue loads

Pressure ulcers are a type of local soft tissue injury due to sustained mechanical loading and remain a common issue in patient care. People with spinal cord injury (SCI) are especially at risk of pressure ulcers due to impaired mobility and sensory perception. The development of load improving support structures relies on realistic tissue load evaluation e.g. using finite element analysis (FEA). FEA requires realistic subject-specific mechanical properties and geometries. This study focuses on the effect of geometry. MRI is used for the creation of geometrically accurate models of the human buttock for three able-bodied volunteers and three volunteers with SCI. The effect of geometry on observed internal tissue deformations for each subject is studied by comparing FEA findings for equivalent loading conditions. The large variations found between subjects confirms the importance of subject-specific FEA