Simulator Study of MOM using Steep-cup Flexion - A Clinically Relevant Incorporation of Intermittent Edge-loading
Keywords:hip arthroplasty, MOM bearings, edge loading, simulator, wear
Background: Adverse-wear phenomenon in metal-on-metal (MOM) arthroplasty has been attributed to “edge-loading” of the CoCr cups. Simulator studies of steeply-inclined cups run in the ‘Anatomic-cup’ model represented many variations in design and test parameters with no coherent rationale. We created an algorithm to synthesize MOM test parameters and noted that wear areas typically averaged only 10-15% of cup surface. In contrast, retrievals showed wear areas extending to 60% of cup surface. We hypothesized that MOM wear studies run in the orbital hip simulator with the ‘Inverted-cup’ model would, (i) differentiate normal-loading versus edge-loading, (ii) demonstrate cup wear areas x3.8-times larger than on femoral heads, cover 30% of cup surface, and (iii) double the wear-rates measured in prior Anatomic-cup study.
Methods: Edge-loading occurs when the cup rim is allowed to truncate the habitual wear area that provides optimal tribological conditions. A MOM algorithm was developed to synthesize relevant test parameters. The 60mm MOM bearings donated for this study were run in an orbital hip simulator using the Inverted-cup model. Tests #1 and #2 to one million cycles (1-Mc) duration assessed wear at peak cup inclinations 40° and 50°. Test #3 evaluated edge-loading with peak cup inclinations achieving 70° (5-Mc duration).
Results: Wear areas in Inverted-cups averaged 1663mm2 in tests #1 and 2, were fully contained within cup rims, and covered 30% of cup surface as predicted by algorithm. Test-3 with 70° cup inclination produced the predicted edge-loading with volumetric wear-rates averaging 2mm3/Mc, approximately 5-fold greater wear than prior Anatomic-cup study.
Discussion and Conclusions: Simulator studies of steep-cup mechanisms necessitate production of clinically-relevant wear-patterns such that the biomechanical and tribological functionality is respected. As an aid to steeply-inclined cup analyses, the MOM algorithm allowed integration of confounding test parameters. The algorithm successfully differentiated between “normal” and “edge loaded” cups and the MOM wear areas were as predicted for three cup inclinations. Also as predicted, wear-patterns in Inverted-cup model exactly reversed those of the Anatomic-cup model. Even with only intermittent edge-loading, Test-3 produced 5-fold greater wear than our prior Anatomic study.
Clinical Significance: The Inverted-cup simulator model successfully mobilized the cup to produce larger wear areas that were more representative of those in-vivo and therefore reproduced more realistic test conditions for studies of edge-loaded cups.
ISO 14242-1 (2002) Implants for surgery -- Wear of total hip-joint prostheses -- Part 1: Loading and displacement parameters for wear-testing machines and corresponding environmental conditions for test.
Williams S, Leslie I, Isaac G, Jin Z, Ingham E, Fisher J. Tribology and wear of metal-on-metal hip prostheses: influence of cup angle and head position. J Bone Joint Surg Am. 2008;90 Suppl 3:111-117.
Leslie I, Williams S, Brown C, Isaac G, Jin Z, Ingham E, Fisher J. Effect of bearing size on the long-term wear, wear debris, and ion levels of large diameter metal-on-metal hip replacements-An in vitro study. J Biomed Mater Res B Appl Biomater. 2008;87:163-172.
Lee R, Essner A, Wang A. Tribological considerations in primary and revision metal-on-metal arthroplasty. J Bone Joint Surg Am. 2008;90 Suppl 3:118-124.
McMinn, D. Treacy, R. Lin, K. Pynsent, P. (1996). Metal on metal surface replacement of the hip. Experience of the McMinn prosthesis. Clin. Orthop. 329 Suppl., pgs S89-98.
Amstutz, H. C. Campbell, P. McKellop, H. Schmalzreid, T. P. Gillespie, W. J. Howie, D. Jacobs, J. Medley, J. Merritt, K. Metal on metal total hip replacement workshop consensus document. Clin. Orthop. 329 Suppl., pgs S297-303.
Hart, A. J. Hester, T. Sinclair, K. Powell, J. J. Goodship, A. E. Pele, L. Fersht, N. L. Skinner, J. The association between metal ions from hip resurfacing and reduced T-cell counts (2006). JBJS-Br. 88(4), 449-54.
McLardy-Smith, P. Steffen, R. T. Pandit, H. Murray, D. W. Gill, H. S (2006). Metal-on-metal hip resurfacing: America, where are you? Orthopedics 29:795-6.
Langton DJ, Jameson SS, Joyce TJ, Webb J, Nargol AV. The effect of component size and orientation on the concentrations of metal ions after resurfacing arthroplasty of the hip. J Bone Joint Surg Br. 2008;90:1143-1151.
Glyn-Jones, S., Roques, A., Gill, R.Taylor, A., Whitwell, D., Esposito, C., Walter, W., Tuke, M., Murray, D.Metal on metal hip resurfacing arthroplasty-related pseudotumours are associated with increased bearing surface wear, caused by impingement and edge-loading. In 56th Annual Meeting of the ORS, poster #2164, 2010.
Morlock, M. M., Bishop, N. E., Zustin, J., Hahn, M. , Ruther, W. Amling, M. Modes of Implant Failure After Hip Resurfacing: Morphological and Wear Analysis of 267 Retrieval Specimens. J Bone Joint Surg (Am):90;89-95, 2008.
Leslie, I. J. Williams, S. Isaac, G. Ingham, E. Fisher, J. (2009). High cup angle and microseparation increase the wear of hip surface replacements. Clin. Ortho. 467(9), 2259-65.
Hu, XQ Jeffers, J Roques, A Taylor, A Tuke, M.(2011). In vitro wear study of MOM and COM Hip Prostheses with High Cup Angle. In Orthop Res. Soc, poster 1163.
Angadji A, Royle M, Collins SN, Shelton JC. Influence of cup orientation on the wear performance of metal-on-metal hip replacements. Proc Inst Mech Eng H. 2009;223:449-457.
Clarke IC, Donaldson TK, Burgett MD, Smith EJ, Bowsher J, Savisaar C, John A, Lazennec JY, McPherson E, Peters CL. Normal and Adverse Wear Patterns Created In-vivo on MOM Surfaces - a retrieval study representing four vendors. In: Kurtz SM, Greenwald SA, Mihalko WM, Lemons JA, ed. Metal-on-Metal Total Hip Replacement Devices. West Conshohocken, PA: ASTM International; 2013:157-192.
Clarke IC, Lazennec JY. Margin-of-safety Algorithm used with EOS imaging to Interpret MHRA Warning for Small-diameter MOM Hip Arthroplasty. Reconstructive Review. 2015;5:13-21.
Bowsher JG, Clarke IC, Williams PA, Donaldson TK. What is a “normal” wear pattern for metal-on-metal hip bearings? J Biomed Mater Res B Appl Biomater. 2009;91:297-308.
Koper MC, Mathijssen NMC, Claasen HHR, Witt F, M MM, Vehmeijer SBW. Pseudotumor after bilateral ceramic-on-metal total hip arthroplasty. J Bone Joint Surg: JBIS Case connect; 2014.
Chan, F. W. Bobyn, J. D. Medley, J. B. Krygier, J. J. Yue, S. Tanzer, M.(1996). Engineering issues and wear performance of metal on metal hip implants. Clin. Ortho. 333:96-107.
Anissian, H. L. Stark, A. Gustafson, A. Good, V. Clarke, I. C. (2009). Metal-on-metal bearing in hip prosthesis generates 100-fold less wear debris than metal-on-polyethylene. Acta Orthop. Scand. 70(6): 578-82.
Park, S. H. McKellop, H. Lu, B. Chan, F. W. Chiesa, R.(1999). Wear morphology of metal-metal implants: Hip simulator tests compared with clinical retrievals. In “Metasul, A Metal-on-Metal Bearing”, Eds. Rieker, Claude Windler, Markus and Wyss, Urs, Pub: Hans Huber, Berne Switzerland.
How to Cite
Copyright (c) 2017 Ian Clarke, Julia Shelton, John Bowsher, Christina Savisaar, Thomas Donaldson
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.
Copyright and License Agreement:
Authors who publish with the Reconstructive Review agree to the following terms:
- Authors retain copyright and grant the journal right of first publication with the work. Reconstructive Review follows the Creative Commons Attribution-NonCommercial CC BY-NC. This license allows anyone to download works, build upon the material, and share them with others for non-commercial purposes as long as they credit the senior author, Reconstructive Review, and the Joint Implant Surgery & Research Foundation (JISRF). An example credit would be: "Courtesy of (senior author's name), Reconstructive Review, JISRF, Chagrin Falls, Ohio". While works can be downloaded and shared they cannot be used commercially.
- Authors are able to enter into separate, additional contractual arrangements for the non-exclusive distribution of the journal's published version of the work (e.g., post it to an institutional repository or publish it in a book), with an acknowledgement of its initial publication in this journal.
- Authors are permitted and encouraged to post their work online (e.g., in institutional repositories or on their website) prior to and during the submission process, as it can lead to productive exchanges, as well as earlier and greater citation of published work.