Design of a four-bar latch mechanism and a shear-based rotary viscous damper for single-axis prosthetic knees

With over 30 million people worldwide requiring assistive devices, there is a great need for affordable prosthetic technologies that can enable kinematics close to able-bodied gait. Passive prosthetic knees designed for low-income users have primarily focused on stability and affordability, often at the cost of the high biomechanical performance that is required to replicate able-bodied kinematics. We present the design and preliminary testing of two distinct mechanisms that are novel for passive prosthetic knee applications: the stability module and the damping module. These mechanisms are designed to enable users of single-axis, passive prostheses to walk with close to able-bodied kinematics on level-ground, specifically during the transition from the stance phase to the swing phase of the gait cycle. The stability module was implemented with a latch mounted on a virtual axis of a four-bar linkage, which can be engaged during early stance for stability and disengaged during late stance to initiate knee flexion. The damping module was implemented with a concentric stack of stationary and rotating pairs of plates that shear thin films of high-viscosity silicone oil. For preliminary user-centric validation, a prototype prosthetic knee with the stability module and two dampers (with varying damping coefficients) was tested on a single participant. The stability module enabled smooth transition from stance to swing with timely initiation of knee flexion. An increase in the damping coefficient was found to decrease the peak knee flexion close to the able-bodied range (58-70 deg).

Differences in trochlear groove based on morphometric measurements of three-dimensional reconstruction models between native knees and five different femoral component designs in Chinese subjects

Background: The prosthetic trochlear design is important in postoperative patellofemoral kinematics and knee function. However, little research has been conducted on the differences in trochlear groove between native and prosthetic knees. We aimed to investigate the differences between Chinese native knees and prosthetic knees of five different femoral component designs using three-dimensional computerized quantification of the entire trochlear length.Methods: Virtual total knee arthroplasty was performed using three-dimensional models of 42 healthy Chinese knees matched to the femoral components of five different prosthetic systems by mechanical alignment. The deepest points of the trochlear groove were marked in multiple cross sections for both the native and prosthetic knees. Taking the lower extremity mechanical axis as reference line, the differences in the mediolateral location of the trochlear groove were analyzed between the native and prosthetic knees.Results: From the proximal to the distal end, the native trochlear groove started from 0° cross section and extended laterally and then medially, with its turning point located at 69° cross section. The prosthetic trochlear groove showed a similar medial orientation and extended more proximally, but varied in mediolateral location and the length extending to the intercondylar notch. Compared with the proximal portion of the native trochlear groove, the prosthetic knees extended along a paradoxical orientation and started from a more proximal and lateral position to 3.2 mm in the 0° cross section, with maximal discrepancy. Distally, the prosthetic trochlear grooves were located significantly medial to 2.4 mm in the 69° cross section, with maximal discrepancy.Conclusion: The prosthetic trochlear design varied among the different types and did not conform to the native knee in terms of shape, orientation, and location, which may cause soft tissue tension imbalance and abnormal patellofemoral biomechanics during knee flexion. This study may provide useful information for creating prosthetic trochlear designs that conform with the native knee anatomy to optimize patellofemoral biomechanics and reduce the risk of patellofemoral complications.

Differences in trochlear groove based on morphometric measurements of three-dimensional reconstruction models between native knees and five different femoral component designs in Chinese subjects

Background: The p rosthetic trochlear design is important in postoperative patellofemoral kinematics and knee function. However, little research has been conducted on the differences in trochlear groove between native and prosthetic knees. We aimed to investigate the differences between Chinese native knees and prosthetic knees of five different femoral component designs using three-dimensional computerized quantification Of the entire trochlear length. Methods: Virtual total knee arthroplasty was performed using three-dimensional models of 42 healthy Chinese knees matched to the femoral components of five different prosthe tic systems by mechanical alignment . T he deepest points of the trochlear groove were marked in multiple cross sections for both the native and prosthetic knees . Taking the lower extremity mechanical axis as reference line, the differences in the mediolateral location of the trochlear groove were analyzed between the native and prosthetic knees. Results: From the proximal to the distal end, the native trochlear groove started from 0° cross section and extended laterally and then medially , with its turning point located at 69° cross section . T he prosthetic trochlear groove showed a similar medial orientation and extended more proximally, but varied in mediolateral location and the length extending to the intercondylar notch . Compared with the proximal portion of the native trochlear groove , the prosthetic knee s extended along a paradoxical orientation and started from a more proximal and lateral position to 3.2 mm in the 0° cross section , with maximal discrepancy. Distally, the prosthetic trochlear groove s were located significantly medial to 2.4 mm in the 69° cross section , with maximal discrepancy. Conclusion: The prosthetic trochlear design varie d among the different types and did not conform to the native knee in terms of shape, orientation, and location, which may cause soft tissue tension imbalance and abnormal patellofemoral biomechanics during knee flexion. This study may provide useful information for creating prosthetic trochlear design s that conform with the native knee anatomy to optimize patellofemoral biomechanics and reduce the risk of patellofemoral complications.

Differences between native and prosthetic knees in trochlear groove tracking based on a morphometric measurement of three-dimensional reconstruction models in Chinese people

Background Prosthetic trochlear design is important to ideal postoperative patellofemoral kinematics and knee function. But there has been little research on the differences of trochlear groove trackings between the native and prosthetic knees. We aimed to investigate the differences between native and prosthetic knees through the entire trochlear length by three-dimensional computerized quantification.Methods Virtual total knee arthroplasty was performed, using three-dimensional models of 42 healthy knees that were matched to the femoral components of five different prosthesis systems. Coaxial planes were created along the trochlear groove in 3° increments, and the deepest points of the trochlear groove were marked in each plane. Taking the lower extremity mechanical axis as reference line, the differences in the mediolateral location of the groove tracking were analyzed between the native and prosthetic knees.Results From the proximal to the distal end, the native tracking started from 0° cross section and extended laterally and then medially with its turning point located in 69° cross section, while the prosthetic knees showed medial orientation throughout the trochlear length. Compared with the proximal portion of the native tracking, the prosthetic trackings extended along a paradoxical orientation and started from a more proximal and lateral position, with maximal discrepancy to, 3.2 mm in the 0° cross section. Distally, the prosthetic trackings were located significantly medial, with maximal discrepancy, to 2.4 mm in the 69° cross section.Conclusion The prosthetic trochlear design varies among different types, and does not conform to that of the native knee in terms of shape, orientation, and location, which may cause soft tissue tension imbalance and abnormal patellofemoral biomechanics during knee flexion. This study may be helpful for prosthetic trochlear design that accords with native anatomy so as to optimize patellofemoral biomechanics and decrease the risk of patellofemoral complications.