3D Printed patient-specific surgical guide with a lateral hinge protecting K-wire and a soft tissue protecting sleeve for open wedge high tibial osteotomy

Abstract

Open Wedge High Tibial Osteotomy (OWHTO) is an extensively used, effective treatment option for medical conditions such as medial knee osteoarthritis and varus malalignment. The current developments in the 3D printing industry facilitated using 3D printed patient-specific guides (PSSGs), making OWHTO a desirable treatment option. Although the PSSG improves the outcomes (e.g., high accuracy, lower radiation) of the OWHTO, lateral hinge fractures and posterior soft tissue injuries of the tibia are two main risks still present. Therefore, this study aims to facilitate an optimal 3D printed PSSG design with a lateral hinge protecting K-wire and a soft tissue protecting sleeve for OWHTO that can prevent or reduce these two critical risks. For this purpose, first, 3D models were constructed from pre-operative CT images of the cadaver specimens. Afterward, a monopolar osteotomy cut was created at a location where the orthopedic surgeon Tom Piscaer decided on the 3D-constructed models to develop Finite Element (FE) analysis. Using the FE analysis and 3D constructed models, different intact lateral hinge lengths (5 mm, 6 mm, 7 mm, 8 mm, 9 mm, and 10 mm) without apical drill holes were analyzed for relative comparison between six different simulations. The intact hinge length was chosen between 10 mm and 5 mm according to the information in the literature. Von Mises stress was used as an outcome measure. The decrease in distribution and magnitude for the von Mises stress at the lateral side of the tibia and the lateral hinge was used to point out the overall impact of the hinge length reduction. As the intact hinge length decreased, the von Mises stress on the lateral hinge generally decreased. According to the results from FE analysis using a high-quality mesh, leaving a 6 mm intact hinge was determined to be the optimum case among other cases. It reduced the stress around the hinge, maintained sufficient cortical and cancellous bone, had a higher margin of error, and likely reduced the fraction risk. The results of this FE analysis were used to develop the hinge K-wire location on the PSSG. Several PSSG models with soft tissue-protecting sleeves were created. Among these designs, the second and third prototypes (3 prototypes in total) were tested on the cadaver specimens. After the tests, post-operative CT images of the cadavers were taken. From these images, 3D models of the tibia were constructed. Pre- and post-operative 3D models were registered onto each other for measuring the deviation between the planned and obtained osteotomy. This was used to analyze the accurate placement of the PSSG and its effect on the sleeve function. While the translation deviations ranged from 5.2 mm, 2.05 mm, and 7.81 mm, the rotational deviations ranged from 7.04°, 1.55°, and 9.16° for cases 1, 2, and 3, respectively. Two PSSG designs passed the acceptable region for translational malpositioning (lower than 5 mm). Although the malpositioning of the PSSG affected the sleeve position slightly, the cadaver test results showed that the sleeve still protected the tibia's posterior side from soft tissue injuries by stopping the cutting saw at the cutting trajectory due to its lengthy coverage at the posterior side of the tibia. Since the cadavers did not have the necessary soft tissues, it wasn't easy to give a concrete answer. Still, according to the results, the sleeve is expected to ensure soft tissue protection. Using the PSSG with a hinge-protecting K-wire and a soft tissue-protecting sleeve will likely provide lower radiation exposure, shorter operation time, fewer complication risks and lateral hinge fractures, less posterior soft tissue damage, and increased healing.