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.

Improving Footwear Options for Persons With Lower Limb Amputations

Men and women with lower limb amputations struggle with managing the balance between prosthesis alignment and shoe heel rise. A novel prosthetic ankle-feet system is being developed to support a wider range of footwear options for men and women with lower limb amputations. Each rigid foot is customized to fit the footwear of choice and can be rapidly attached to (or released from) an ankle unit which remains attached to the prosthesis. The ankle unit has a mass of 318g and is small enough to fit in the design volume of a 22cm foot across a range of heel rises. The ankle uses elastomeric bumpers arranged in a wiper design to maximize space efficiency. Structural testing has shown that the 3D printed custom Nylon 12 feet withstood 4584N of forefoot loading without failure based on the ISO 10328 loading parameters, indicating suitable strength to support safe human use in the laboratory. The feet have a mass of 446g. Feedback from two women Veterans with lower limb amputations reinforced the importance of improving access to shoes with different heel rises. Future activities will include cyclic fatigue testing, additional weight reduction, and incorporating suggested design refinements.

Intraoperative Radiographic Assessment of Ankle Prosthesis Alignment

Category: Ankle Arthritis Introduction/Purpose: In the last 2 decades, total ankle replacement (TAR) has gained greater acceptance as a treatment option for patients with end-stage ankle osteoarthritis. However, TAR still has a higher failure rate than either hip or knee replacements. One of the most common reasons for TAR failure is malalignment of the prosthesis component which accounts for 15% of all failures. The purpose of this study was to assess ankle prosthesis alignment using intraoperative fluoroscopy images and to compare the results with postoperative weightbearing radiographs. Methods: Sixty-eight primary TARs were performed using the Zimmer trabecular metal implant (37 men and 31 women, mean age of 67.7±8.2 years) from October 2012 to August 2017. Alpha and beta angles were used to assess the alignment of the tibial component in the coronal and sagittal plane, respectively. Gamma angle was used to assess the alignment of the talar component in the sagittal plane. All measurements were performed by two observers (ICC 0.787-0.984). One observer evaluated all images twice at a 6-week interval to determine the intraobserver reliability (ICC 0.858-0.986). Results: There were significant differences between intraoperative and postoperative assessment for all three angles. For the alpha angle, the mean absolute difference was 1.8º±1.5º with a range between 0º and 6º (p = 0.001). For the beta angle, the mean absolute difference was 2.1º±1.5º with a range between 0º and 7º (p = 0.034). For gamma angle, the mean absolute difference was 2.0º±1.5º with a range between 0º and 6º (p = 0.002). The Pearson coefficient for the alpha, beta, and gamma angle was 0.664 (p < 0.001), 0.852 (p < 0.001), and 0.928 (p < 0.001), respectively. Conclusion: In the present study, radiographic assessment of the prosthesis’ component alignment demonstrated significant differences up to 7 degrees. This can be partially explained by the lack of a standardized radiographic technique to obtain fluoroscopic images, difficult identification of anatomic landmarks for intraoperative measurements, and distortion of x-rays using fluoroscopy.

A new prosthetic alignment device to read and record prosthesis alignment data

Prosthetic alignment is an essential process to rehabilitate patients with amputations. This study presents, for the first time, an invented device to read and record prosthesis alignment data. The digital device consists of seven main parts: the trigger, internal shaft, shell, sensor adjustment button, digital display, sliding shell, and tip. The alignment data were read and recorded by the user or a computer to replicate prosthesis adjustment for future use or examine the sequence of changes in alignment and its effect on the posture of the patient. Alignment data were recorded at the anterior/posterior and medial/lateral positions for five patients. Results show the high level of confidence to record alignment data and replicate adjustments. Therefore, the device helps patients readjust their prosthesis by themselves, or prosthetists to perform adjustment for patients and analyze the effects of malalignment.