Enabling Technology for Remote Prosthetic Alignment Tuning

ABSTRACT Introduction This research has resulted in a system of sensors and software for effectively adjusting prosthetic alignment with digital numeric control. We called this suite of technologies the Prosthesis Smart Alignment Tool (ProSAT) system. Materials and Methods The ProSAT system has three components: a prosthesis-embedded sensor, an alignment tool, and an Internet-connected alignment expert system application that utilizes machine learning to analyze prosthetic alignment. All components communicate via Bluetooth. Together, they provide for numerically controlled prosthesis alignment adjustment. The ProSAT components help diagnose and guide the correction of very subtle, difficult-to-see imbalances in dynamic gait. The sensor has been cross-validated against kinetic measurement in a gait laboratory, and bench testing was performed to validate the performance of the tool while adjusting a prosthetic socket based on machine learning analyses from the software application. Results The three-dimensional alignment of the prosthetic socket was measured pre- and postadjustment from two fiducial points marked on the anterior surface of the prosthetic socket. A coordinate measuring machine was used to derive an alignment angular offset from vertical for both conditions: pre- and postalignment conditions. Of interest is the difference in the angles between conditions. The ProSAT tool is only controlling the relative change made to the alignment, not an absolute position or orientation. Target alignments were calculated by the machine learning algorithm in the ProSAT software, based on input of kinetic data samples representing the precondition and where a real prosthetic misalignment condition was known a priori. Detected misalignments were converted by the software to a corrective adjustment in the prosthesis alignment being tested. We demonstrated that a user could successfully and quickly achieve target postalignment change within an average of 0.1°. Conclusions The accuracy of a prototype ProSAT system has been validated for controlled alignment changes by a prosthetist. Refinement of the ergonomic form and technical function of the hardware and clinical usability of the mobile software application are currently being completed with benchtop experiments in advance of further human subject testing of alignment efficiency, accuracy, and user experience.

Prosthetic Accuracy Depends on the Design of Patient-Specific Instrumentation: Results of a Retrospective Study Using Three-Dimensional Imaging

To determine accuracy of patient-specific instrumentation (PSI), the preoperative three-dimensional (3D) plan should be superimposed on the postoperative 3D image to compare prosthetic alignment. We aimed to compare prosthetic alignment on a preoperative 3D computed tomography (CT) plan and postoperative 3D-CT image, and evaluate the accuracy of PSI during total knee arthroplasty (TKA). Thirty consecutive knees (30 patients) who underwent TKA using PSI were retrospectively evaluated. The preoperative plan was prepared using 3D CT acquisitions of the hip, knee, and ankle joints. The postoperative 3D CT image obtained 1 week after surgery was superimposed onto the preoperative 3D plan using computer software. Differences in prosthetic alignment between the preoperative and postoperative images were measured using six parameters: coronal, sagittal, and axial alignments of femoral and tibial prostheses. Differences in prosthetic alignment greater than 3 degrees were considered outliers. Two observers performed all measurements. All parameters were repeatedly measured over a 4-week interval. This measurement method's intraobserver and interobserver reliabilities were more than 0.81 (very good). For the femoral and tibial prostheses, absolute differences between the preoperative and postoperative 3D CT images were significantly larger in the sagittal than in the coronal and axial planes (p < 0.001). The outlier rate for the sagittal alignment of femoral and tibial prostheses was significantly higher than that for the alignment of coronal and axial planes (p < 0.001). However, there were no significant differences in the range of motion (ROM) before and after TKA when comparing cases with and without outliers in the sagittal plane. Even though the present study did not reveal any issues with the ROM that depended on the presence of an outlier, accurate verification of prosthetic alignment for individual PSI models may be necessary because the designs, referenced images, and accuracy are different in each model.

The effect of dynamic prosthetic alignment on the transtibial gait: Analyzing with Opensim

After amputation, fitting of the prosthesis in the adaptation and gait of an individual is crucial. However, this known dynamic alignment process is subjective on the part of the professional who makes said adjustment, compromising the stability of the individual. Therefore, a kinematic model to analyze the effects of dynamic alignment during the transtibial amputees gait in the sagittal plane using Opensim was developed. For this group, the socket position (Flexion and Extension, Abduction and Adduction) and the movements of prosthetic foot (Plantarflexion and Dorsiflexion, Inversion and Eversion) were analyzed. In opensim, the “osim” pilot was amputated incorporating a transtibial prosthesis that was previously modeled in Solid work, with a Matlab script the variation of the position of the prosthesis using inverse kinematics was simulated, results were validated on a subject with wireless sensors for the measurement. The model showed that acceptable gait patterns are found in positive variations between 2 ° and 6° for the socket and 2 ° for the prosthetic foot.

POLYCENTRIC EXOPROSTHETIC KNEE JOINTS – EXTENT OF SHORTENING DURING SWING PHASE

BACKGROUND: An often assumed advantage of polycentric knee joints compared to monocentric ones is the improved ground clearance during swing phase due to the geometric shortening of the lower leg segment (LLS). OBJECTIVE: To investigate whether polycentric knee joints considerably improve ground clearance and to evaluate the influence of prosthetic alignment on the extent of ground clearance. METHODOLOGY: 11 polycentric and 2 monocentric knee joints were attached to a rigid, stationary testing device. Shortening of the LLS and the resulting ground clearance during knee flexion were measured. Prosthetic components were mounted at the same height and the anterior-posterior position was in accordance with the manufacturer's alignment recommendations. FINDINGS: Shortening of up to 14.7 (SD=0.0) mm at the instance of minimal ground clearance during swing phase was measured. One knee joint elongated by 4.4 (SD=0.0) mm. Measurements of the ground clearance demonstrated differences up to 25.4 (SD=0.0) mm. One monocentric knee joint provided more ground clearance when compared to 8 of the polycentric knee joints investigated. CONCLUSION: Only some polycentric knee joints shorten appreciably during swing phase. With an optimized prosthetic alignment and a well-designed swing phase control, a monocentric knee joint may generate greater ground clearance compared to a polycentric knee joint. LAYMAN’S ABSTRACT Tripping is a safety risk for amputees and it is mainly affected by ground clearance during swing phase. An often assumed advantage of polycentric knee joints compared to monocentric ones is the improved ground clearance during swing phase due to the geometric shortening of the lower leg segment (LLS). Based on this statement safety benefits for above knee-amputees due to reduced danger of stumbling are discussed commonly for the entire group of polycentric knee joints. We believe that this statement is not true for all polycentric knee joint designs. Therefore, we analyzed 11 polycentric and two monocentric knee joints in a rigid, stationary testing device with their individual prosthetic alignments according to the manufacturer’s alignment recommendations. Shortening of the LLS and the resulting ground clearance during knee flexion were measured. The results showed shortening effects of up to 15 mm. One knee joint elongated by 4 mm. One monocentric knee joint provided more ground clearance when compared to 8 of the polycentric knee joints investigated. We conclude, that only some polycentric knee joints shorten appreciably during swing phase. With an optimized prosthetic alignment a monocentric knee joint may generate greater ground clearance compared to a polycentric knee joint. Article PDF Link: https://jps.library.utoronto.ca/index.php/cpoj/article/view/33768/26547 How To Cite: Köhler T.M, Bellmann M, Blumentritt S. Polycentric Exoprosthetic Knee Joints – Extent of Shortening during Swing Phase. Canadian Prosthetics & Orthotics Journal. 2020;Volume3, Issue1, No.5. https://doi.org/10.33137/cpoj.v3i1.33768 Corresponding Author: Thomas Maximilian Köhler, MScOttobock: Hermann-Rein-Straße 2a, 37075, Göttingen.E-mail: [email protected]: https://orcid.org/0000-0002-5063-121X