Loma Linda University

Enrollment Information
Call us at: 909-558-1000

Faculty Directory
  
Paul Williams, MS
Publications    Book Review - Scholarly Journals--Published
  • Tateiwa, T., I. C. Clarke, P. A. Williams, J. Garino, M. Manaka, T. Shishido, K. Yamamoto and A. Imakiire (2008). "Ceramic total hip arthroplasty in the United States: safety and risk issues revisited." Am J Orthop 37(2): E26-31. ( 1/2008 )
  Scholarly Journals--Published
  • Williams PA, Brown CM, Tsukamoto R, Clarke IC (2010). Polyethylene wear debris produced in a knee simulator model: effect of crosslinking and counterface material. J Biomed Mater Res B Appl Biomater; 92(1):78-85. ( 1/2010 )
  • Sorimachi T, Clarke I. C., Williams P. A , Gustafson A, Yamamoto K (2009). Third-body abrasive wear challenge of 32 mm conventional and 44 mm highly crosslinked polyethylene liners in a hip simulator model. Proc Inst Mech Eng H 223(5):607-23. ( 9/2009 )
  • Williams, P. A. and I. C. Clarke (2009). "Understanding polyethylene wear mechanisms by modeling of debris size distributions." Wear - 17th International Conference on Wear of Materials 267(1-4): 646-652. ( 6/2009 )
  • Kubo, K., I. C. Clarke, T. Sorimachi, P. A. Williams, T. K. Donaldson and K. Yamamoto (2009). "Aggressive 3rd-body wear challenge to highly crosslinked polyethylene: A hip simulator model." Wear - 17th International Conference on Wear of Materials 267(5-8): 734-742. ( 6/2009 )
  • Clarke, I. C., D. D. Green, P. A. Williams, K. Kubo, G. Pezzotti, A. Lombardi, A. Turnbull and T. K. Donaldson (2009). "Hip-simulator wear studies of an alumina-matrix composite (AMC) ceramic compared to retrieval studies of AMC balls with 1-7 years follow-up." Wear - 17th International Conference on Wear of Materials 267(5-8): 702-709. ( 6/2009 )
  • Bowsher JG, Donaldson TK, Williams PA, Clarke IC (2008). Surface damage after multiple dislocations of a 38-mm-diameter, metal-on-metal hip prosthesis. J Arthroplasty 23(7): 1090-6 ( 7/2008 )
  • Tsukamoto, R., P. A. Williams, H. Shoji, K. Hirakawa, K. Yamamoto, M. Tsukamoto and I. C. Clarke (2008). "Wear in molded tibial inserts: knee simulator study of H1900 and GUR1050 polyethylenes." J Biomed Mater Res B Appl Biomater 85(2): 314-9. ( 2/2008 - 1/2008 )
  • Tsukamoto R, Williams PA, Shoji H, Hirakawa K, Yamamoto K, Tsukamoto M, Clarke IC (2008). “Wear of sequentially enhanced 9-Mrad polyethylene in 10 million cycle knee simulation study.” J Biomed Mater Res B Appl Biomater 86(1): 119-24. ( 1/2008 )
  • Tsukamoto R, Williams PA, Clarke IC, Pezzotti G, Shoji H, Akagi M, Yamamoto K (2008). “Y-TZP zirconia run against highly crosslinked UHMWPE tibial inserts: knee simulator wear and phase-transformation studies.” J Biomed Mater Res B Appl Biomater 86(1):145-53. ( 1/2008 )
  • Bowsher JG, Williams PA, Clarke IC, Green DD, Donaldson TK (2008). "Severe" wear challenge to 36 mm mechanically enhanced highly crosslinked polyethylene hip liners. J Biomed Mater Res B Appl Biomater 86(1):253-63. ( 1/2008 )
  • Williams, P., K. Yamamoto, H. Oonishi and I. Clarke. "Highly crosslinked polyethylenes in hip replacements: improved wear performance or paradox?." Tribology Transactions 50.2 (2007): 277-290. ( 1/2007 )
    The lubrication and wear of artificial joints are important issues for their longevity. Bone loss caused by the biological response (osteolysis) to the wear debris leads to implant loosening and eventual failure of the device. Various studies have shown that the size, shape, and number of particles are important factors in the osteolytic response to wear debris. It has been demonstrated that both submicronsize particles and long fibrils can stimulate macrophage responses. This paper examines the clinical and laboratory data on highly crosslinked polyethylene (XLPE) regarding implant wear and particulate debris. In simulator studies, total hip replacements have shown greatly reduced wear with XLPE cups compared with conventional polyethylene (PE) and short-term clinical studies of XLPE have now also shown reduced levels of wear. However, simulator studies have also demonstrated that adverse wear conditions can partially or completely negate the wear advantage of XLPE. Additionally, it has been shown that the XLPE debris particles are smaller than conventional PE. In a paradoxical manner, the decreased wear of XLPE should decrease the osteolytic potential, but the decreased debris size may have the potential to increase the biological activity. Therefore, the longterm clinical performance of XLPE is not clear at this time. Long-term clinical follow-ups will be needed to determine the actual benefit of XLPE in patients.
  • Bowsher, Nevelos, Williams, Shelton. "Severe wear challange to 'as-cast' and 'double heat-treated' large-diameter metal-on-metal hip bearings." Proc Inst Mech Eng, Part H 220.2 (2006): 135-143. ( 2/2006 ) Link...
    The wear generation of double-heat-treated and as-cast large-diameter metal-on-metal (MOM) hip bearings was investigated using standard- and 'severe'-gait simulations. The test hypothesis was that double heat treatment would change MOM hip wear compared with the as-cast condition. Two groups of high-carbon MOM bearings of 40 mm diameter were manufactured and subjected to either hot isostatic pressing (HIP) and solution annealing (SA) or no heat treatment (as cast). The results showed no statistical difference between the two groups under both running-in and steady state conditions. Even under the most 'severe'-gait simulation published to date, the mean volumetric wear rates were 2.9 and 3.9 mm3 per 10(6) cycles for the HIP-SA and as-cast bearings respectively, showing a ten-fold increase in wear compared with walking. These differences were not statistically different; therefore our hypothesis was negated. Changes in alloy microstructure do not appear to influence the wear behaviour of high-carbon cast MOM articulations with similar chemical compositions. This is in sharp contrast with the published significance of bearing diameter and radial clearance on the wear of MOM hip bearings.
  • Bowsher, Hussain, Williams, Shelton. "Metal-on-metal hip simulator study of increased wear particle surface area due to 'severe' patient activity." Proc Inst Mech Eng, Part H 220.2 (2006): 279-287. ( 2/2006 ) Link...
    This study investigated changes in metal-on-metal (MOM) hip wear and wear particle characteristics arising from a more aggressive patient activity level compared with normal walking. The test hypothesis was that 'severe'-gait conditions will change wear, wear particle sizes, and morphology owing to a decline in joint lubrication. Four carbon MOM hip bearings 40 mm high were subjected to normal-walking and fast-jogging simulations in an orbital hip joint simulator with 25 per cent alpha-calf serum as a lubricant. Co-Cr-Mo wear particles were extracted using an enzymatic method, and prolate ellipsoid equations were used to estimate particle volume and surface area. Fast-jogging simulations generated a sevenfold increase in volumetric wear, a 33 per cent increase in mean wear particle size, and a threefold increase in the number of larger (needle) particles compared with walking. This resulted in a twentyfold increase in total wear particle surface area per 10(6) cycles compared with walking, thereby confirming our hypothesis. The clinical significance of this result suggests that highly active MOM patients may exhibit greater ion release than less active patients.
  • Shishido, T., K. Yamamoto, S. Tanaka, T. Masaoka, I. C. Clarke and P. Williams. "A Study for a retrieved implant of ceramic-on-ceramic total hip arthroplasty." J Arthroplasty 21.2 (2006): 294-298. ( 2/2006 ) Link...
    A Mittelmeier-type ceramic on ceramic total hip arthroplasty (THA) was retrieved because of aseptic loosening 17 years after implantation. The extent of wear was assessed by scanning electron microscopy. The synovial fluid and the tissue surrounding the implant were also examined. Scanning electron microscopy analysis of the ball head showed that the main wear zone had grade IV wear. The stripe wear zones showed grain pullout regions (grade 5 wear). Pathologically, chronic inflammation was observed in the surrounding tissue. The debris particles in the synovial fluid were polygonal and approximately 3 x 4 microm. Thus, the Mittelmeier-type THA proved excellent wear resistance. Further longevity of ceramic on ceramic THA may indeed become a reality with improvement of the design and quality of alumina.
  • Richardson, Clarke, Williams, Donaldson, Oonishi. "Precision and accuarcy in ceramic-on-ceramic wear analyses: influence of simulator test duration." Proc Inst Mech Eng, Part H 219.6 (2005): 401-405. ( 11/2005 ) Link...
    In this, the first report of precision and accuracy in simulator studies, ceramic-ceramic implants with ultra-low wear trends represented a relevant wear model. The effect of test durations was examined in a standard simulator test mode on the quality of the linear regression trends, the average wear estimates, and the amount of noise in the data. Three sets of diametral tolerances were compared in 28 mm diameter alumina implants. The authors' hypothesis was that wear data would be significantly improved with increased test durations. The average wear rates varied little with test duration, the biggest change amounting to only 30 and 15 per cent decreases in the wear estimate by 10 and 14 million cycles respectively. The most satisfactory improvement in the study was the decrease in variance (noise) with increasing duration, +/- 200 per cent at 5 million cycles reduced to +/- 55 per cent at 14 million cycles. The quality of the linear regression coefficients improved 150 per cent by 10 million cycles and 250 per cent by 14 million cycles. Overall the ceramic implants with highest diametral tolerances showed the least wear (15 per cent less, but not statistically significant). However, given such low wear rates for alumina liners, it was unlikely that any differences owing to diametral tolerances would be clinically significant in the typical patient.
  • Brown, Kawanabe, Manaka, Williams, Good, Clarke. "Discerning alumina ball wear from confounding metal transfer artifact." J Biomed Mater Res, B: Appl Biomater 75.2 (2005): 400-404. ( 11/2005 ) Link...
    On dismounting a ceramic femoral ball from its metal trunnion, there is usually a range of gray metallic bands transferred to the trunnion bore inside the ball. This creates an artifact that may compromise detection by weight of the exceedingly low wear rates of ceramic balls. The objective of this study was to compare the weight trending of the metal trunnions and their ceramic balls during conditioning studies. Our hypothesis was that a pretest conditioning protocol would eliminate or greatly reduce the metal transfer artifact. The balls and tapers were placed on a hip simulator under 300-600 load cycles but with no articulation. The balls were then dismounted from the trunnions, and both were cleaned and weighed. This was repeated 6-23 times. We developed a novel hydraulic method for dismounting balls from trunnions that proved to be safe and efficient. There was significant weight loss in the trunnions after the ball removal, but there was no corresponding weight gain in the alumina balls. The weight effect of the metal transfer appeared to have been removed from the balls with our standard cleaning procedures. Therefore, wear rates for alumina balls may be gravimetrically determined without compensating for the metal transfer from trunnion to ball. (c) 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2005.
  • Bowsher, J. G., A. Hussain, P. Williams, J. Nevelos and J. C. Shelton. "Effect of ion implantation on the tribology of metal-on-metal hip prostheses." Journal of Arthroplasty 19.8 (2004): 107-111. ( 12/2004 )
    Nitrogen ion implantation (which considerably hardens the surface of the bearing) may represent one possible method of reducing the wear of metal-on-metal (MOM) hip bearings. Currently there are no ion-implanted MOM bearings used clinically. Therefore a physiological hip simulator test was undertaken using standard test conditions, and the results compared to previous studies using the same methods. N2-ion implantation of high carbon cast Co-Cr-Mo-on-Co-Cr-Mo hip prostheses increased wear by 2-fold during the aggressive running-in phase compared to untreated bearing surfaces, plus showing no wear reductions during steady-state conditions. Although 2 specimens were considered in the current study, it would appear that ion implantation has no clinical benefit for MOM.
  • Bowsher JG, Hussain A, Williams PA, Nevelos J, Shelton JC. "Effect of ion implantation showed no reduction in running-in wear for metal-on-metal hip bearings." J Arthroplasty 19.8 Suppl 3 (2004): 107-111. ( 1/2004 )
    Nitrogen ion implantation (which considerably hardens the surface of the bearing) may represent one possible method of reducing the wear of metal-on-metal (MOM) hip bearings. Currently there are no ion-implanted MOM bearings used clinically. Therefore a physiological hip simulator test was undertaken using standard test conditions, and the results compared to previous studies using the same methods. N2-ion implantation of high carbon cast Co-Cr-Mo-on-Co-Cr-Mo hip prostheses increased wear by 2-fold during the aggressive running-in phase compared to untreated bearing surfaces, plus showing no wear reductions during steady-state conditions. Although 2 specimens were considered in the current study, it would appear that ion implantation has no clinical benefit for MOM.