No description available.

No description available.

Wear is the number one concern with regards to the longevity of THR (total hip replacement). Therefore, reliable in-vitro prediction of wear is necessary. Thus, the laboratory should first validate their hip simulators with known clinical materials. The limiting factor in hip wear simulation has been the joint fluid analog. Using 100% bovine serum as the joint fluid analog, UHMWPE (ultra-high molecular weight polyethylene) wear-rates have been continually underestimated and PTFE (polytetrafluoroethylene) wear has been overestimated. Therefore, this work investigated the effect of protein concentration in bovine serum on the wear of PTFE and UHMWPE in a biaxial hip joint simulator. Validation criteria were developed based on the clinical findings of: ball size effect of increased wear with increased head size, 6% increase in wear for each millimeter of increased head diameter, clinical wear magnitudes, PTFE/UHWMPE wear-rate ratio and debris morphology. Both materials duplicated the clinical criteria using bovine serum with 10mg/ml of protein concentration. As protein concentration went from 0 to 10mg/ml, wear of both materials increased, however with greater than 10mg/ml protein; a) the rate of increase for PTFE was reduced by 80% and b) the wear of UHMWPE reversed, thus, showing that proteins cause wear. Additionally as the volume of fluid was increased, wear increased. This change in wear with protein concentration and volume was due to a protection of protein precipitate. As protein concentration increased protein precipitation increased and wear was decreased due to a protective layer of precipitates. Furthermore, wear protection was dependent on the amount of protein precipitation which was in turn, dependent on the initial concentration, volume of fluid and time. Therefore, wear in-vitro was dependent on the joint fluid analog. This work proved that the laboratory could duplicate clinical findings using bovine serum with 10mg/ml of protein concentration as the joint fluid analog and thus increase confidence in wear evaluation; taking the first steps to showing reliability of in-vitro THR wear studies.

ABSTRACT The purpose of this study was to determine if there is a relationship between knee integrity and function in patients who have had a total knee replacement. Twenty-two patients were selected at the arthroplasty clinics at the Johannesburg Hospital and Chris Hani Baragwaneth Hospital. This occurred at six weeks following a primary total knee replacement. Twenty-two subjects who participated in the study underwent two tests. The first test measured the patients’ functional ability using the Iowa Level of Assistance (ILOA) Scale. Knee integrity was measured using the Knee Society Knee Score. The two examiners were blinded to each other’s results. The results indicate that there is no relationship between knee integrity measured using the Knee Society Knee Score and function measured using the ILOA Scale (p= 0.19).

Back pain is a common complaint and the origin of this frequently attributed to degenerative disc disease. In the most severe cases, the integrity of the disc and surrounding tissue is lost to such an extent that surgical intervention is necessary. Fusion procedures are commonly used to treat severely degenerated discs. Yet this is known to alter the biomechanics of the operated level, and may create a progression of degenerative decline. Total disc replacement has emerged as a viable treatment but the complexity of the spine is reflected in the clinical results, which trail far behind the success of hip and knee arthroplasty. This may be due to a failure of total disc replacement procedures to restore the natural biomechanics of the spine. The present study has led to the development of a dynamic pre-clinical testing protocol to quantitatively assess the efficacy of disc replacement devices. A six-axis spine simulator was designed and built, and the stiffness matrix testing of porcine lumbar specimens was completed, both with and without an axial preload. Intact specimens were tested, and the testing repeated after a total disc replacement procedure with a DePuy In Motion artificial disc. This is the first study to complete dynamic six-axis spinal testing of this kind. The testing demonstrated the disc replacement device compared favourably with the intact porcine disc both in shear and axial stiffness. However, the low-friction, double ball and socket design of the In Motion device lacks stiffness in the three rotational axes, and it is unstable in lateral bending. Rotations are the primary movements in the spine, and it is crucial if the natural biomechanics are to be restored, that a disc replacement device should replicate the stiffnesses of these axes. The next generation of disc replacement devices feature elastomeric materials that may more closely replicate the natural intervertebral disc. From patents registered with DePuy, this may also be true of the next generation of In Motion disc. This research provides a means to complete standardised performance tests of new spinal devices and lays the foundations for future comparison studies. Additionally, the spine simulator and testing protocol would provide valuable data during the design stage of new total disc replacements, aiding the development of the next generation of artificial discs.

I use a unique dataset of 1,808 mutual fund manager replacements to study the determinants and the subsequent impact of the choice between hiring the successor from within (internal hire) and outside (external hire) the fund family. I find that fund families prefer to replace their top performers with internal hires and bottom performers with external hires. External hires demonstrate superior ability to turn around bottom performing funds, but exhibit inferior ability to maintain the record of top performing funds. I find no cross-sectional difference in post-replacement performance between internal and external successors, indicating fund families, in general, make their replacement decisions optimally. I do, however, find that funds that deviate from the optimal decision have subsequent sub-par performance. Overall, the evidence suggests that portfolio managers play a pivotal role in determining mutual fund performance.

Mechanical low back pain is a disabling condition often associated with degenerative disc disease (DDD). Treatment for DDD includes non-operative pain management, total disc arthroplasty and nucleus pulposus (NP) replacement. A thiol-modified hyaluronan elastin-like polypeptide (TMHA/EP) composite has been under consideration as a NP replacement and has shown promise in vitro. This thesis aims to determine the effects of TMHA/EP composite augmentation on spinal motion segment mechanics in healthy and induced early stage DDD porcine intervertebral discs (IVD). Healthy IVD augmentation on average increased axial compressive stiffness, while bending and rotational stability decreased. Early stage DDD porcine IVD had compromised mechanical integrity in comparison to healthy controls. TMHA/EP augmentation of the mechanically compromised IVDs through two injection techniques worked to restore spinal stability, exhibiting mechanical properties similar to healthy IVDs. This work demonstrates the potential of the injectable TMHA/EP composite in providing initial structural stabilization in early stages of DDD.

Mechanical low back pain is a disabling condition often associated with degenerative disc disease (DDD). Treatment for DDD includes non-operative pain management, total disc arthroplasty and nucleus pulposus (NP) replacement. A thiol-modified hyaluronan elastin-like polypeptide (TMHA/EP) composite has been under consideration as a NP replacement and has shown promise in vitro. This thesis aims to determine the effects of TMHA/EP composite augmentation on spinal motion segment mechanics in healthy and induced early stage DDD porcine intervertebral discs (IVD). Healthy IVD augmentation on average increased axial compressive stiffness, while bending and rotational stability decreased. Early stage DDD porcine IVD had compromised mechanical integrity in comparison to healthy controls. TMHA/EP augmentation of the mechanically compromised IVDs through two injection techniques worked to restore spinal stability, exhibiting mechanical properties similar to healthy IVDs. This work demonstrates the potential of the injectable TMHA/EP composite in providing initial structural stabilization in early stages of DDD.

Thesis (Ph. D.)--Lehigh University, 2004. / Includes vita. Includes bibliographical references (leaves 92-96).

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.