A 3D printed cast for minimally invasive transfer of distal radius osteotomy: a cadaver study.

PURPOSE: In corrective osteotomy of the distal radius, patient-specific 3D printed surgical guides or optical navigation systems are often used to navigate the surgical saw. The purpose of this cadaver study is to present and evaluate a novel cast-based guiding system to transfer the virtually planned corrective osteotomy of the distal radius. METHODS: We developed a cast-based guiding system composed of a cast featuring two drilling slots as well as an external cutting guide that was used to orient the surgical saw for osteotomy in the preoperatively planned position. The device was tested on five cadaver specimens with different body fat percentages. A repositioning experiment was performed to assess the precision of replacing an arm in the cast. Accuracy and precision of drilling and cutting using the proposed cast-based guiding system were evaluated using the same five cadaver arms. CT imaging was used to quantify the positioning errors in 3D. RESULTS: For normal-weight cadavers, the resulting total translation and rotation repositioning errors were ± 2 mm and ± 2°. Across the five performed surgeries, the median accuracy and Inter Quartile Ranges (IQR) of pre-operatively planned drilling trajectories were 4.3° (IQR = 2.4°) and 3.1 mm (IQR = 4.9 mm). Median rotational and translational errors in transferring the pre-operatively planned osteotomy plane were and 3.9° (IQR = 4.5°) and 2.6 mm (IQR = 4.2 mm), respectively. CONCLUSION: For normal weight arm specimens, navigation of corrective osteotomy via a cast-based guide resulted in transfer errors comparable to those using invasive surgical guides. The promising positioning capabilities justify further investigating whether the method could ultimately be used in a clinical setting, which could especially be of interest when used with less invasive osteosynthesis material.

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

PURPOSE: 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 ([Formula: see text]) were reduced for implants (([Formula: see text]) = 2.2 min) and guides (([Formula: see text]) = 1.0 min) compared to the standard (([Formula: see text]) = 13 min and ([Formula: see text]) = 8 min) and the partially customized (([Formula: see text]) = 6.5 min and ([Formula: see text]) = 6.0 min) commercially available alternatives. Mouse and keyboard activities were reduced (median count of strokes and clicks during implant design (([Formula: see text]) = 53, and guide design (([Formula: see text]) = 27) compared to using standard software (([Formula: see text]) = 559 and ([Formula: see text]) = 380) and customized commercial software (([Formula: see text]) = 217 and ([Formula: see text]) = 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.

Biomechanical considerations in the design of patient-specific fixation plates for the distal radius.

Use of patient-specific fixation plates is promising in corrective osteotomy of the distal radius. So far, custom plates were mostly shaped to closely fit onto the bone surface and ensure accurate positioning of bone segments, however, without considering the biomechanical needs for bone healing. In this study, we investigated how custom plates can be optimized to stimulate callus formation under daily loading conditions. We calculated implant stress distributions, axial screw forces, and interfragmentary strains via finite element analysis (FEA) and compared these parameters for a corrective distal radius osteotomy model fixated by standard and custom plates. We then evaluated these parameters in a modified custom plate design with alternative screw configuration, plate size, and thickness on 5 radii models. Compared to initial design, in the modified custom plate, the maximum stress was reduced, especially under torsional load (- 31%). Under bending load, implants with 1.9-mm thickness induced an average strain (median = 2.14%, IQR = 0.2) in the recommended range (2-10%) to promote callus formation. Optimizing the plate shape, width, and thickness in order to keep the fixation stable while guaranteeing sufficient strain to enhance callus formation can be considered as a design criteria for future, less invasive, custom distal radius plates. Graphical abstract ᅟ.

Positioning error of custom 3D-printed surgical guides for the radius: influence of fitting location and guide design.

PURPOSE: Utilization of 3D-printed patient-specific surgical guides is a promising navigation approach for orthopedic surgery. However, navigation errors can arise if the guide is not correctly positioned at the planned bone location, compromising the surgical outcome. Quantitative measurements of guide positioning errors are rarely reported and have never been related to guide design and underlying bone anatomy. In this study, the positioning accuracy of a standard and an extended guide design with lateral extension is evaluated at different fitting locations (distal, mid-shaft and proximal) on the volar side of the radius. METHODS: Four operators placed the surgical guides on 3D-printed radius models obtained from the CT scans of six patients. For each radius model, every operator positioned two guide designs on the three fitting locations. The residual positioning error was quantified with a CT-based image analysis method in terms of the mean target registration error (mTRE), total translation error ([Formula: see text]) and total rotation error ([Formula: see text]) by comparing the actual guide position with the preoperatively planned position. Three generalized linear regression models were constructed to evaluate if the fitting location and the guide design affected mTRE, [Formula: see text] and [Formula: see text]. RESULTS: mTRE, [Formula: see text] and [Formula: see text] were significantly higher for mid-shaft guides ([Formula: see text]) compared to distal guides. The guide extension significantly improved the target registration and translational accuracy in all the volar radius locations ([Formula: see text]). However, in the mid-shaft region, the guide extension yielded an increased total rotational error ([Formula: see text]). CONCLUSION: Our study demonstrates that positioning accuracy depends on the fitting location and on the guide design. In distal and proximal radial regions, the accuracy of guides with lateral extension is higher than standard guides and is therefore recommended for future use.