Trapeziometacarpal joint prosthesis revision has been widely reported, mainly due to loosening of the trapezium cup. Our hypothesis is that current prostheses do not sufficiently respect the kinematics of this joint. CT scan acquisitions enabled us to determine the position of the first metacarpal relative to the trapezium in three different characteristic postures, in subjects in different stages of arthrosis. A CAD model of a current prosthesis was inserted into the numerical 3D model of the joint under the different postures. In the numerical model, we observe penetration of the cup by the head of the prosthesis. This virtual penetration could, in vivo, amount to overstressing the prosthetic elements, which would lead to loosening of the cup or of the metacarpal stem and luxation of the prosthesis.

Background/Purpose: Falls onto outstretched hands are the second most common sports injury and one of the leading causes of upper extremity injury. Injury risk and severity depends on forces being transmitted through the palmar surface to the upper extremity. Although the magnitude and distribution of forces depend on the soft tissue response of the palm, thein vivoproperties of palmar tissue have not been characterized. The purpose of this study was to characterize the large deformation palmar soft tissue properties.Methods: In vivodynamic indentations were conducted on 15 young adults (21–29 years) to quantify the soft tissue characteristics of over the trapezium. The effects of loading rate, joint position, tissue thickness and sex on soft tissue responses were assessed.Results: Energy absorbed by the soft tissue and peak force were affected by loading rate and joint angle. Energy absorbed was 1.7–2.8 times higher and the peak force was 2–2.75 times higher at high rate loading than quasistatic rates. Males had greater energy absorbed than females but not at all wrist positions. Damping characteristics were the highest in the group with the thickest soft tissue while damping characteristics were the lowest in group with the thinnest soft tissues.Conclusion: Palmar tissue response changes with joint position, loading rate, sex, and tissue thickness. Accurately capturing these tissue responses is important for developing effective simulations of fall and injury biomechanics and assessing the effectiveness of injury prevention strategies.

Total prosthesis, which preserves strength and respects trapeziometacarpal (TMC) joint range of motion, is a surgical option considered for the TMC joint replacement. With the usual ball-and-socket design, patients obtain faster pain relief, stronger grip function, and shorter convalescence than with trapeziectomy. However, prostheses currently used have led to various early complications, especially in active and young patients. Revisions are most often due to the loosening of the trapezium cup and of the metacarpal stem and to the luxation of the first metacarpal bone. The short lifespan of these devices suggests the difficulty of designing a prosthesis that respects the complex anatomy and motions of the TMC joint. Early implant failure may reflect the fact that the current devices do not exactly replicate the true kinematics. The aim of this chapter will be to shed light mechanical explanations for TMC prosthesis failures in regard to the complex kinematics of the joint.

In vivo characteristics of palmar soft tissue can be used to improve the accuracy of human models to explore and simulate a range of contact scenarios. Tissue characteristics can help to assess injury prevention strategies and designing technologies that depend on quantified physical contacts such as prosthetics, wearables, and assistive devices. In this study, a simplified quasi-linear viscoelastic (QLV) model was developed to quantify large deformation, in vivo soft tissue relaxation characteristics of the palm. We conducted relaxation tests on 11 young adults (6 males, 5 females, 18 < age < 30, mean age: 25 ± 4 yr) and 9 older adults (6 males, 3 females, age > 50, mean age: 61.5 ± 11.5 yr) using a 3 mm indenter to a depth of 50% of each participant's soft tissue thickness. The relaxation parameters of the QLV model were found to differ with age and sex, emphasizing the importance of using targeted material models to represent palmar soft tissue mechanics. Older adults showed on average 2.3-fold longer relaxation time constant compared to younger adults. It took 1.2-fold longer for young males to reach equilibrium than for young females; however, young females had a higher level of relaxation (36%) than young males (33%). Differences in specific QLV model parameters, P₁, P₂, and α were also found between age and sex groups. QLV characteristics differentiated by age and sex, add biofidelity to computational models which can provide a better representation of the diversity of tissue properties in the population.

Background/Objectives: Lower-limb amputation significantly impacts autonomy and daily functioning. Microprocessor-controlled prosthetic knees (MPKs) improve mobility, safety, and quality of life compared with non-microprocessor prosthetic knees (nMPKs). Despite general benefits, differences among MPK models remain unclear. The goal of this investigation was to evaluate functional mobility and patient-reported outcomes in active transfemoral amputees using a new MPK (PROTEOR QUATTRO) compared with existing MPKs. Methods: In this multicenter cross-over clinical trial, active transfemoral amputees were assessed using patient-specific functional scales (PSFS), standardized locomotor capacity tests (6MWT, 10mWT, HAI, SAI) and satisfaction and quality-of-life questionnaires (PEQ-A, SF-36, ESAT). Biomechanical data collection was performed during walking test, to examine gait symmetry indices. Results: The QUATTRO MPK was associated with significantly higher PSFS scores, reflecting higher self-rated ability in performing chosen daily life activities compared with patient’s current prosthesis. Standardized locomotor tests revealed comparable performance between devices. Biomechanical analyses showed similar symmetry indices for QUATTRO and other MPKs. Patient-reported outcomes showed an improvement in physical health with QUATTRO, while overall satisfaction remained similar. Conclusions: QUATTRO improved patient-perceived ability to perform meaningful daily-life activities while maintaining comparable performance on standardized locomotor tests. These results highlight the importance of patient-centered assessments in identifying functional benefits that may guide individualized prosthetic prescriptions for active transfemoral amputees.