Osteoarthritis (OA) is a chronic joint disease, the most common musculoskeletal complaint worldwide, and is associated with significant health and welfare costs. Previous research indicates that co-activation of muscles may lead to the onset of knee OA. Therefore, investigation of muscle recruitment patterns and neuromuscular efficiency in healthy individuals compared to patients with knee OA in simple closed chain exercises using electromyography (EMG), motion analysis system and force plates may lead to a better understanding of how knee OA develops (6). The present studies chosen were in the frontal plane while performing lateral step up and step down tasks for a 4 inch and 8 inch step height. In the stepping tasks it was discovered that there is a greater magnitude EMG and ground reaction force (GRF) for 8 inch rather than a 4 inch step. Additionally, a higher activation of gluteus medius, gluteus maximus and quadriceps muscles (rectus femoris , vastus lateralis , vastus medius) was revealed in both the stepping tasks.

Functional activities in daily life often require shifting body weight toward one limb, from a more even double leg stance. Stability of the knee is challenged in people with total knee replacement (TKR) when weight shifting also includes transverse plane rotation. Our study utilized a novel approach in order to facilitate transfer of load to one extremity during squatting or extending in double-stance. The objective of this study was to identify strategies utilized by individuals with TKR in double-stance transferring load during rotation and flexion. Twelve subjects of an ongoing study were selected (6 TKR, 6 healthy). Each subject completed a custom crossover button push task where rotation, flexion, extension of the knee were utilized. Each subject performed two crossover reaching tasks, a High to Low (H2L) and Low to High (L2H). The subject stood on two AMTI force platforms obtaining ground reaction force, which were then converted to lead force ratios. Knee flexion angles were also recorded. The TKR subjects had less ratio throughout the L2H movement compared to healthy. In contrast, the TKR subjects had a greater load transfer throughout the H2L compared to healthy. Large variation at mid-flexion in TKR subjects suggested possible difficulty in maintaining positional stability during these tasks. The TKR subjects maintained more of an extended knee, suggesting rotation was achieved by a strategy and knee extension is a more ‘stable’. Early identification and correction of these strategies could improve TKR success and return to activities of daily living that involve flexion and rotation.

INTRODUCTION: Articulating metallic implants have a detrimental influence on medical imaging. Polyetheretherketone (PEEK) is already used as a structural implant material in the spine, has the stiffness to provide a stable implant-bone interface and is suitably radiolucent. The purpose of the present study is to further examine the pin-on-plate wear of various PEEK-PEEK pairings and the effects of varied lubricant properties, reinforcement orientation, and pin contact radii. METHODS: Wear testing of self mating unfilled PEEK Optima (OPT) and carbon fiber reinforced (CFR) PEEK provided by Invibio Ltd. was performed using a six station OrthoPOD™ pin on disc apparatus (AMTI). A crossing path motion was achieved with a pin rotation of 87° and oscillation of the plate resulting in a stroke length of 17 mm applied at a frequency of 1 Hz. Two lubricant protein concentrations were used; 12 g/L, and 6 g/L. RESULTS: From 0.25–1.0 Mc OPT exhibited a steady state wear rate of 0.094 mm3Mc-1, compared to 0.170 mm3Mc-1 for CFR. When the protein concentration of the lubricant was reduced from 12 to 6 gL-1, the wear rate of OPT increased significantly while the wear rate of CFR increased slightly to 0.254 mm3Mc-1. DISCUSSION: The present study seems to show a weak correlation between protein concentration and wear for the CFR specimens. Parallel fiber orientation at the contact area and/or reduced contact radius appeared to increase to run-in wear in CFR. The effects of protein concentration is important as different implant applications will observe varying lubrication properties with a lower protein concentration expected in the spinal disc space compared to a synovial joint.

The annulus fibrosus (AF) of the intervertebral disc is subjected to multidirectional loads which are resisted by collagen fibers in its alternating (+/-) 30° lamellae. Engineering a functional replacement for the AF will likely necessitate replication of this multi- lamellar structure. Electrospinning has been used to generate scaffolds for AF tissue engineering that can direct alignment of cells and deposited matrix. Previously, it has been shown that these scaffolds can be used to construct single and multi-lamellar structures that replicate the AF anatomic form and uniaxial mechanical function. Additionally, these constructs provide a model for analysis of AF structure-function relationships, including inter-lamellar shear stiffening. However, previous studies only tested constructs under uniaxial tension; biaxial mechanical testing allows for evaluation in a more physiologic loading regime. In this study, the effect of lamellar orientation on the biaxial mechanics of engineered AF was investigated. This provides an understanding of the mechanical properties as well as insight into native tissue structure-function relationships.