Modular particle filtering FPGA hardware architecture for brain machine interfaces.

As the computational complexities of neural decoding algorithms for brain machine interfaces (BMI) increase, their implementation through sequential processors becomes prohibitive for real-time applications. This work presents the field programmable gate array (FPGA) as an alternative to sequential processors for BMIs. The reprogrammable hardware architecture of the FPGA provides a near optimal platform for performing parallel computations in real-time. The scalability and reconfigurability of the FPGA accommodates diverse sets of neural ensembles and a variety of decoding algorithms. Throughput is significantly increased by decomposing computations into independent parallel hardware modules on the FPGA. This increase in throughput is demonstrated through a parallel hardware implementation of the auxiliary particle filtering signal processing algorithm.

Parallel field programmable gate array particle filtering architecture for real-time neural signal processing.

Both linear and nonlinear estimation algorithms have been successfully applied as neural decoding techniques in brain machine interfaces. Nonlinear approaches such as Bayesian auxiliary particle filters offer improved estimates over other methodologies seemingly at the expense of computational complexity. Real-time implementation of particle filtering algorithms for neural signal processing may become prohibitive when the number of neurons in the observed ensemble becomes large. By implementing a parallel hardware architecture, filter performance can be improved in terms of throughput over conventional sequential processing. Such an architecture is presented here and its FPGA resource utilization is reported.

Bayesian auxiliary particle filters for estimating neural tuning parameters.

A common challenge in neural engineering is to track the dynamic parameters of neural tuning functions. This work introduces the application of Bayesian auxiliary particle filters for this purpose. Based on Monte-Carlo filtering, Bayesian auxiliary particle filters use adaptive methods to model the prior densities of the state parameters being tracked. The observations used are the neural firing times, modeled here as a Poisson process, and the biological driving signal. The Bayesian auxiliary particle filter was evaluated by simultaneously tracking the three parameters of a hippocampal place cell and compared to a stochastic state point process filter. It is shown that Bayesian auxiliary particle filters are substantially more accurate and robust than alternative methods of state parameter estimation. The effects of time-averaging on parameter estimation are also evaluated.

The effect of an augmentation patella prosthesis versus patelloplasty on revision patellar kinematics and quadriceps tendon force: an ex vivo study.

The purpose of this study was to assess the effect of 2 revision reconstructive interventions on patellofemoral joint mechanics in comparison to control. We flexed 8 cadaver knee specimens from 0 degrees to 60 degrees of flexion in a test rig designed to simulate weight-bearing flexion and extension (Oxford rig). Quadriceps tendon extensor force and patellar kinematics were recorded for control total knee arthroplasty (TKA) (normal primary TKA with patella resurfaced) and then for each of the 2 revision patellar interventions (after patelloplasty of typical revision knee patellar bone defect to leave a simple bony shell, and after TKA with augmentation patella resurfacing). Our results demonstrate that patellar kinematics and quadriceps extensor force are optimized when the patella is reconstructed to normal anteroposterior thickness.

The position of the joint line in relation to the trans-epicondylar axis of the knee: complementary radiologic and computer-based studies.

Two complementary studies that seek to establish the relationship between the length and position of the trans-epicondylar axis (TEAL) of the distal femur and the position of the knee joint line were presented. A radiologic study of 50 patients having computerized axial tomography of the knee showed that there is a good correlation between TEAL and the depths of the femoral condyles distal to the trans-epicondylar axis. A retrospective review of the anatomical data gathered on 99 patients having computer-assisted total knee arthroplasties (TKAs) provided equivalent information. The 2 studies suggest that TEAL determined by the process of registration, as a preliminary to computer-assisted TKA, can be used to predict the position of the joint line using the derived constant k at a value of 3.4. Thus, the joint line of the knee lies at a distance (TEAL / 3.4) expressed in millimeters from the trans-epicondylar axis. This is potentially very useful information during TKA especially where there is extensive femoral bone loss.

Cementing constrained acetabular liners in revision hip replacement: clinical and laboratory observations.

During revision hip arthroplasty, removal of a well-fixed, ingrown metal acetabular component may not be possible. Therefore, a new polyethylene liner can be cemented into the existing shell via the cement locking mechanism. This technique is well recognized, and the cement locking mechanism has proved to be sufficiently strong and durable for clinical use. A constrained polyethylene liner is designed to reduce the risk of hip dislocation by capturing the femoral head. However, there are increased shear forces created at the liner interface as the dislocation is resisted. If a constrained liner is cemented into an ingrown acetabular component, then there is the theoretical risk that these increased shear forces will damage the cement locking mechanism, thus leading to failure of the construct. There are a few clinical series in which a constrained liner has been used with the cement locking mechanism. Overall, the failure rate of the cement locking mechanism is no greater if a constrained liner instead of a standard liner is used. The cement locking mechanism can be strengthened by roughening the backside of a smooth polyethylene liner to improve the cement-polyethylene interface, or by using an all-polyethylene acetabular component that is designed to be used with cement. Whether a smooth metal shell needs to be roughened as well is a matter of debate.