Effect of compliant layers within piezoelectric composites on power generation providing electrical stimulation in low frequency applications.

For patients that use tobacco or have diabetes, bone healing after orthopedic procedures is challenging. Direct current electrical stimulation has shown success clinically to significantly improve bone healing in these difficult-to-fuse populations. Energy harvesting with piezoelectric material has gained popularity in the last decade, but is challenging at low frequencies due to material properties that limit total power generation at these frequencies. Stacked generators have been used to increase power generation at lower voltage levels but have not been widely explored as a load-bearing biomaterial to provide DC stimulation. To match structural compliance levels and increase efficiency of power generation at low frequencies, the effect of compliant layers between piezoelectric discs was investigated. Compliant Layer Adaptive Composite Stacks (CLACS) were manufactured using five PZT discs connected electrically in parallel and stacked mechanically in series with a layer of low modulus epoxy between each disc. The stacks were encapsulated, keeping PZT and overall volume constant. Each stack was electromechanically tested by varying load, frequency, and resistance. As compliant layer thickness increased, power generation increased significantly across all loads, frequencies, and resistances measured. As expected, increase in frequency significantly increased power output for all groups. Similarly, an increase applied peak-to-peak mechanical load also significantly increased power output. The novel use of CLACS for power generation under load and frequencies experienced by typical orthopedic implants could provide an effective method to harvest energy and provide power without the use of a battery in multiple low frequency applications.

In vitro evaluation of biomechanical effects of multiple hemilaminectomies on the canine lumbar vertebral column.

OBJECTIVE: To conduct an in vitro investigation of the biomechanical characteristics of the canine lumbar spinal column in flexion and extension and measure the destabilizing effects of multiple consecutive unilateral and bilateral hemilaminectomies. SAMPLE POPULATION: 30 isolated multisegmental spinal units (L1-L4) from nonhypochondroplastic dogs weighing 15 to 30 kg. PROCEDURES: Physically normal and surgically altered spinal specimens were subjected to 4-point bending in flexion and extension to determine effects of multiple consecutive hemilaminectomies on the basis of analysis of test system load-displacement data. Six groups with 5 spinal columns in each were defined on the basis of the following procedures: hemilaminectomy at L2-L3, 2 adjacent hemilaminectomies at L1-L3, 3 adjacent hemilaminectomies at L1-L4, bilateral hemilaminectomies at L2-L3, 2 bilateral hemilaminectomies at L1-L3, and no hemilaminectomy (intact). Spinal stability before and after surgery was determined in all groups. Each group served as its own control for nondestructive testing. Spinal strength was evaluated through destructive testing to determine deformation at failure, strength to failure, and mode of catastrophic failure. The intact group served as the control for destructive testing. RESULTS: Stability in extreme flexion and extreme extension did not change significantly following any hemilaminectomy procedure. Postoperative stability within the neutral zone was significantly decreased in all groups. Range of motion within the neutral zone was not significantly different from the intact condition in any group. CONCLUSIONS AND CLINICAL RELEVANCE: Multiple hemilaminectomies did not decrease stiffness of the lumbar spinal column during flexion and extension. These results support clinical recommendations regarding multiple consecutive hemilaminectomies in dogs.

Negative pressure intrusion cementing technique for total knee arthroplasty.

Negative pressure intrusion (NPI) is an alternative cementing technique for the tibial baseplate of total knee arthroplasty that uses a suction cannula in the proximal tibia to remove excess fluids and fat before cementing. This technique was compared with standard third-generation positive pressure intrusion (PPI) techniques in an in vitro implantation and analysis of 6 pairs of cadaveric tibiae. Six matched pairs of fresh frozen tibiae were prepared by cutting the tibial surfaces, standard cleaning and surface drying, then performing PPI and NPI on 1 of each pair. No objective differences were noted on radiographs or direct cement depth measurement analysis. Scanning electron micrograph evaluation revealed that the PPI specimens had consistently more voids in the cement-bone composite, and the NPI specimens had consistently narrower empty spaces between bone and cement, resulting in tighter fill in NPI specimens. NPI was shown to enhance characteristics known to improve tensile and shear strength in cement-bone composites.

Effect of bone block removal and patellar prosthesis on stresses in the human patella.

Thermoelastic stress analysis was used to examine stresses on the anterior surface of patellae after patellar bone block excision for autogenous graft anterior cruciate ligament reconstruction. Complications of anterior cruciate ligament injury often lead to degenerative changes in the knee that can require total knee joint replacement. It was hypothesized that stresses in a bone block-compromised patella may be increased even further by insertion of a patellar prosthesis. All patellae were first tested intact and then were retested after a sequence of surgical modifications including patellar prosthesis implantation, tapered bone block excision, square bone block excision, and both shapes of excised bone blocks with a patellar prosthesis in place. Stresses in patellae with bone blocks excised were significantly greater than stresses in intact patellae. The anterior surface stress pattern in the loaded patella was significantly altered by excision of a bone block. There were no significant differences between maximum stress in patellae with tapered and square bone blocks excised. A finite element analysis showed that excision of a larger trapezoid-shaped bone block greatly increased maximum stress levels. Insertion of a patellar prosthesis did not significantly alter stress patterns or maximum stress levels in the patella.

Prevalence of carpal tunnel syndrome and other work-related musculoskeletal problems in cardiac sonographers.

Cardiac sonographers at a regional medical center have experienced carpal tunnel syndrome symptoms and other work-related musculoskeletal injuries. The nationwide incidence of these problems was not known. A questionnaire pertaining to possible causes of work-related injuries was developed and distributed to 225 cardiac sonographers. A 47% response rate was achieved with 72% female respondents. Eighty-six percent reported one or more physical symptoms. Only 3% of respondents had been diagnosed with carpal tunnel syndrome. Posture correlated significantly with other work-related musculoskeletal injuries. High-pressure hand grip correlated significantly with carpal tunnel syndrome symptoms. No other strong relations with physical symptoms were found. The contribution of specific factors to musculoskeletal problems experienced by cardiac sonographers was difficult to determine.

External fixation of unstable Malgaigne fractures: the comparative mechanical performance of a new configuration.

An external fixator has been designed that is rigid enough to eliminate the need for skeletal traction in patients with unstable pelvic-ring fractures. This Wichita frame is similar to the Pittsburgh frame but is stiffened by the use of locked crossbars connecting the side triangles. The frame was tested in cadaveric specimens by techniques previously reported. In addition, finite-element modeling of the various frame designs was performed to ensure that the frame configuration was optimal and to supplement in vitro test results. Multiple variables that can influence frame failure loads were examined.