| Background The goal of a lower limb prosthesis is to restore the abilities of the intact limb for an individual with lower limb amputation. Daily ambulation includes many maneuvers such as turning, and twisting, which require a component of transverse plane mobility. It has been shown that the inclusion of a transverse plane adapter could reduce peak torsional loads on the residual limb and may alleviate soft tissue damage, increase comfort, and improve mobility level for a lower limb amputee. However, currently available transverse plane adaptors only allow for a single stiffness setting and do not allow for variation to accommodate the maneuvers of everyday ambulation. The specific aims of this research were to determine the transverse plane stiffness that minimizes the transverse plane moment applied to the residual limb of lower limb amputees during different ambulatory activities and identify a user's preferred transverse plane stiffness during different ambulatory activities at different speeds. Three tasks were performed to achieve these aims. First, proof of concept human subject performance tests were conducted using the first-generation prototype (VSTA I). Next, a second-generation prototype (VSTA II) was developed using more refined design criteria gleaned from the testing of the VSTA I. Third, the VSTA II was used to perform preference testing with human subjects during different ambulatory activities at varying walking speeds. First Generation VSTA Design (VSTA I).;Design of the VSTA I focused primarily on existing transverse rotation adapter devices and the capabilities of other prototypes in recent literature. The VSTA I is a device that allows for variable stiffness in transverse plane about its central axis. Variation of the VSTA I is accomplished by an electric motor adjusting the position of a lever arm via an ACME lead screw. The change in position of the lever arm in relation to a central torsion spring effectively varies the mechanical advantage by modifying the lever arm length. This allows for infinitely variable stiffness between 0.10 Nm/° and fully locked.;Mechanical bench testing was performed on the VSTA I via a servo-hydraulic material test machine. The VSTA I was run through its full range of motion (+/-- 30°) at both 0.5 °/s and 60°/s at four static stiffness settings: 0.10, 0.33, 0.64, and 1.17 Nm/°. It was found that the VSTA I was not direction or rate dependent and was capable of stiffness variation between 0.12-0.91 Nm/°, with a rotational range of +/-30°.;The first generation VSTA (VSTA I) was used to completed pilot testing on human subject individuals with lower limb amputation. These tests conducted participants through simulated activities of daily living that focused on turning and twisting maneuvers. These included straight walking, 90° turns (spin and step), 180° turns, standing reach, and the L-Test of Functional Mobility. Testing was performed at three constant settings of the VSTA I (compliant: 0.30 Nm/°, intermediate: 0.57 Nm/°, stiff: 0.91 Nm/°). Evaluation of the testing focused primarily on peak transverse plane moments during each maneuver. It was hypothesized that reduced transverse plane loading on the residual limb relates to decreased transverse plane stiffness. Additionally, the self-selected walking speed and L-Test time of each subject was used as an indicator of mobility. Results indicated that activities requiring high levels of transverse plane motion (90° spin and 180° turns) had significantly reduced peak transverse plane moments at the socket when walking with the compliant transverse plane stiffness as compared to the stiff setting. Additionally, use of the VSTA resulted in no measurable loss of mobility at self-selected walking speeds between the three settings. These preliminary results indicate that a transverse rotation adapter with variable stiffness capability could be useful for a lower limb amputee to help reduce stresses at the socket-limb interface. Testing of the VSTA I also resulted in an updated set of design requirements. It was found that the VSTA I was too heavy, causing fatigue, and too tall, restricting subject population. It also lacked an onboard controller, and suffered from internal deflections that limited its stiffness capabilities.;Given the lessons learned during the testing of the VSTA I, a new and improved VSTA II has been designed. The VSTA II features a 42% reduction in height and 51% reduction in mass compared to the VSTA I with an intended finite stiffness variability from 0.30 Nm/° to 1.25 Nm/°, in five 0.25 Nm/° increments. Stiffness variation is enabled by five independent spring subunits that can be combined in parallel to create different, linear, stiffness settings. It also features an onboard controller that can control the stiffness states, and record rotational displacement and stiffness setting during use. (Abstract shortened by ProQuest.). |
