Reduction of Osteolysis with Use of Marathon Cross-Linked Polyethylene

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1 1487 COPYRIGHT Ó 2008 BY THE JOURNAL OF BONE AND JOINT SURGERY, INCORPORATED Reuction of Osteolysis with Use of Marathon Cross-Linke Polyethylene A Concise Follow-up, at a Minimum of Five Years, of a Previous Report* By Rui G. Bitsch, MD, Travis Loiolt, BA, Christian Heisel, MD, Scott Ball, MD, an Thomas P. Schmalzrie, MD Investigation performe at the Joint Replacement Institute, Los Angeles, California Abstract: We previously reporte wear ata at a minimum of two years following thirty-four total hip replacements with a Marathon cross-linke polyethylene liner an twenty-four replacements with a conventional (gamma-sterilize-in-air) Enuron polyethylene liner. In this current stuy, with sequential five-year raiographs, wear rates were etermine with use of linear regression analysis. The Marathon polyethylene ha average wear rates of 15.4 mm 3 /yr an 8.0 mm 3 / million cycles. The Enuron polyethylene ha average wear rates of 55.5 mm 3 /yr an 29.9 mm 3 /million cycles. The ajuste volumetric wear rate of the Marathon polyethylene was 73% lower than that of the Enuron polyethylene (p = 0.001). Osteolysis evelope in eight of the twenty-four hips with an Enuron liner but was not apparent in any hip with a Marathon liner. Level of Evience: Therapeutic Level III. See Instructions to Authors for a complete escription of levels of evience. Backgroun The occurrence of periprosthetic osteolysis 1 has been relate to the amount an size of polyethylene particles generate from the bearing surfaces of the implant 2. Cross-linking of ultra-high molecular weight polyethylene has been shown to markely reuce wear in laboratory tests an clinical stuies 3-5. Concerns have been expresse, however, that the smaller average size of the cross-linke polyethylene wear particles coul lea to osteolysis 6 espite a lower wear rate 7. We previously compare the wear rate at a minimum of two years after total hip replacements with a Marathon cross-linke polyethylene liner with the wear rate after replacements with a conventional polyethylene (Enuron) liner 8. We are upating that previous report after more than five years of clinical experience. *Original Publication Heisel C, Silva M, ela Rosa MA, Schmalzrie TP. Short-term in vivo wear of cross-linke polyethylene. J Bone Joint Surg Am. 2004;86: Methos Two of the patients with a Marathon liner (DePuy, Warsaw, Iniana) in the original stuy 8 i not return for followup, leaving thirty-two hips in thirty-two patients for evaluation. There were ten men an twenty-two women, with an average age of sixty years (range, twenty-six to eighty-eight years) at the time of the operation. The average boy mass inex was 30.5 kg/m 2 (range, 21.3 to 41.4 kg/m 2 ). The patients were followe for an average of sixty-nine months (range, sixty to eighty-three months). The comparison group consiste of twenty-four hips in twenty-four patients with a conventional gamma-sterilize-in-air polyethylene liner (Enuron; DePuy). There were eleven men an thirteen women with an average age of seventy-four years (range, forty-six to eighty-five years) in this group. The average boy mass inex was 27.3 kg/m 2 (range, 18.6 to 35.2 kg/m 2 ). These patients were followe for an average of seventy months (range, sixty to ninety-three months). Patient activity was assesse postoperatively with use of a computerize two-imensional accelerometer (StepWatch Activity Monitor; Cyma, Seattle, Washington) 9. Linear penetration an volumetric wear were measure on serial anteroposterior raiographs of the pelvis with use of the ege-etection-base computer algorithm of Martell an Beria 10. A linear regression analysis was one to etermine femoral hea penetration an volumetric wear over five years for each hip. The slope of the linear regression line represents the penetration or wear rate, an the intercept point on the orinate Disclosure: In support of their research for or preparation of this work, one or more of the authors receive, in any one year, outsie funing or grants of less than $10,000 from the Piemont Fun of the Los Angeles Orthopaeic Hospital Founation an a research grant in excess of $10,000 from the Stiftung Orthopäische Universitätsklinik Heielberg. In aition, one or more of the authors or a member of his or her immeiate family receive, in any one year, payments or other benefits in excess of $10,000 or a commitment or agreement to provie such benefits from a commercial entity (DePuy Orthopaeics). Also, a commercial entity (DePuy) pai or irecte in any one year, or agree to pay or irect, benefits of less than $10,000 to a research fun, founation, ivision, center, clinical practice, or other charitable or nonprofit organization with which one or more of the authors, or a member of his or her immeiate family, is affiliate or associate. J Bone Joint Surg Am. 2008;90: oi: /jbjs.f.00991

2 1488 Fig. 1 Linear regression analyses of femoral hea penetration over time (left) or per million cycles (right). Marathon polyethylene is analyze in the upper figures an Enuron polyethylene, in the lower figures. 2D = two-imensional, an PE = polyethylene. axis represents the isplacement of the femoral heaue to being-in (creep an other conformational changes without removal of material from the bearing surface) 11. The ata in both stuy groups were generate three times by two ifferent observers who were bline to the type of polyethylene that ha been use. Serial anteroposterior an lateral raiographs were evaluate for the presence of osteolytic lesions by three orthopaeic surgeons who were also bline to the type of polyethylene. The presence of osteolysis was assesse in the fourteen zones in the femur escribe by Gruen et al. 12 an the six zones in the acetabulum escribe by DeLee an Charnley 13. A lesion was not consiere to represent osteolysis unless all three surgeons agree on the iagnosis. The ifferences between the two patient groups were evaluate with use of a Stuent t test or a Mann-Whitney U test as require for ifferent types of ata. A p value of 0.05 was consiere significant. Results After a mean uration of follow-up of 5.8 years (range, 5.0 to 7.7 years), no hips ha been revise for any reason. There were no mechanical failures of any bearing surface. The average femoral hea penetration (true wear rate, slope of the linear regression line) was mm/yr (range, to mm/yr; stanareviation = mm/yr; 95% confience interval = to mm/yr) in the hips with a Marathon polyethylene liner an mm/yr (range, to mm/yr; stanareviation = mm/yr; 95% confience interval = to mm/yr) in the hips with an Enuron polyethylene liner. The wear rate (femoral hea penetration) in the Marathon group was 71% lower than that in the Enuron group (p = 0.003). The ajuste femoral hea penetration was mm/million cycles (range, to mm/ million cycles; stanareviation = mm/million cycles; 95% confience interval = to mm/million cycles) in the Marathon group an mm/million cycles (range, to mm/million cycles; stanareviation = mm/ million cycles; 95% confience interval = to mm/ million cycles) in the Enuron group; this represente a 76% reuction in the Marathon group (p = 0.023) (Fig. 1). The average volumetric wear rate was 15.4 mm 3 /yr (range, 0.2 to 88.3 mm 3 /yr; stanareviation = 15.9 mm 3 /yr; 95% confience interval = 8.0 to 22.9 mm 3 /yr) in the hips with a Marathon polyethylene liner an 55.5 mm 3 /yr (range, 5.6 to mm 3 /yr; stanareviation = 54.1 mm 3 /yr; 95% confience interval = 30.9 to 80.2 mm 3 /yr) in the hips with an Enuron polyethylene liner. The volumetric wear rate in the hips with a Marathon liner was 72% lower than that in the hips with an Enuron liner (p < 0.001). The ajuste wear rates were 8.0 mm 3 /million cycles (range, 0.2 to 55.7 mm 3 /million cycles; stanareviation = 15.0 mm 3 /million cycles; 95%

3 1489 Fig. 2 Location of the osteolytic lesions, accoring to the zones escribe by Gruen et al. 12 an by DeLee an Charnley 13, in the patients with an Enuron polyethylene liner. The number of patients with osteolysis an the mean iameter of the lesions are isplaye. confience interval = 1.0 to 15.0 mm 3 /million cycles) an 29.9 mm 3 /million cycles (range, 4.4 to mm 3 /million cycles; stanareviation = 28.7 mm 3 /million cycles; 95% confience interval = 17.5 to 42.3 mm 3 /million cycles), respectively, a 73% reuction in the Marathon group (p = 0.001). There was a slightly higher average isplacement of the femoral heaue to being-in in the Enuron group. The ifference was not significant (p = 0.435) (Fig. 1). Hips with a Marathon polyethylene liner showe an average isplacement of the femoral heaue to creep an other conformational changes without removal of material from the bearing surface (intercept point on the orinate) of mm (range, to mm; stanareviation = mm; 95% confience interval = to mm), whereas the hips with the Enuron polyethylene liner ha an average being-in of mm (range, to mm; stanareviation = mm; 95% confience interval = to mm). The mean activity of the patients with the Marathon liner was 1.86 million cycles/yr (range, 0.76 to 3.91 million cycles/yr; stanareviation = 0.94 million cycles/yr; 95% confience interval = 1.42 to 2.30 million cycles/yr). This was slightly lower than the mean activity of the patients with the Enuron liner, which was 1.98 million cycles/yr (range, 0.63 to 4.30 million cycles/yr; stanareviation = 0.88 million cycles/yr; 95% confience interval = 1.60 to 2.36 million cycles/yr) (p = 0.683). Negative wear ata were seen in the wear calculations of seven patients in the Marathon group an in three in the Enuron group. These cases were exclue from the calculation of mean values. Osteolysis Osteolysis was not raiographically apparent to any of the three observers in any of the thirty-two hips with a Marathon liner. Eight of the twenty-four hips with an Enuron liner emonstrate osteolysis in at least one zone. Classic, scallope osteolytic lesions were seen in proximal Gruen zones 1, 2, 7, 8, an 14 in four, two, seven, six, an seven hips, respectively, with an Enuron polyethylene liner (Fig. 2). Pelvic osteolysis was seen in zone I in one hip an in zone II in another hip in the Enuron group. The Enuron liners in the hips with osteolysis showe an average femoral hea penetration of mm/yr (range, to mm/yr; stanareviation = mm/yr; 95% confience interval = to mm/yr) an an average volumetric wear rate of mm 3 /yr (range, 29.8 to mm 3 /yr; stanareviation = 75.0 mm 3 /yr; 95% confience interval = 42.3 to mm 3 /yr). The linear wear rate was approximately 2.7 times higher an the volumetric rate was approximately 3.5 times higher than the values for the Enuron liners in the hips without osteolysis, which ha an average femoral hea penetration of mm/yr (range, to mm/yr; stanareviation = mm/yr; 95% confience interval = to mm/yr) (p = 0.010) an an average volumetric wear rate of 29.8 mm 3 /yr (range, 5.6 to 64.5 mm 3 /yr; stanareviation = 18.6 mm 3 /yr; 95% confience interval = 19.5 to 40.2 mm 3 /yr) (p = 0.004). The mean activity of the patients with osteolysis was 2.28 million cycles/yr (range, 0.63 to 4.31 million cycles/yr; stanar eviation = 1.25 million cycles/yr; 95% confience in-

4 1490 terval = 1.23 to 3.32 million cycles/yr). This was only slightly higher than the mean activity of the remaining patients in the Enuron group, which was 1.83 million cycles/yr (range, 0.93 to 2.83 million cycles/yr; stanareviation = 0.59 million cycles/yr; 95% confience interval = 1.47 to 2.13 million cycles/yr) (p = 0.426). Discussion Our previous raiographic stuy emonstrate, at a minimum of two years postoperatively, wear rates of 53.3 mm 3 / million cycles for Enuron liners an 15 mm 3 /million cycles for Marathon liners, a 72% reuction for the Marathon liners 8. The wear rates of both types of polyethylene were lower in the five-year stuy: 29.9 mm 3 /million cycles for the Enuron liners an 8.0 mm 3 /million cycles for the Marathon liners, which was also a 73% reuction for the Marathon liners. The five-year femoral hea penetration rate of mm/yr for the Enuron liners is at the lower en of what has been reporte with this type of polyethylene 14-16, although there was a wie range of measure wear in both groups. Engh et al. reporte a reuction in the mean wear rate of 95% for Marathon liners compare with Enuron liners (0.01 ± 0.12 mm/yr compare with 0.19 ± 0.12 mm/yr) 17. McKellop et al. foun a reuction in the mean wear rate of up to 85% for Marathon liners in hip simulator tests an reporte that the reuction was epenent on the roughness of the bearing partners 5. The percent reuction is a function of the comparison material, which was not irraiate in either the wear simulator stuy by McKellop et al. or the clinical stuy by Engh et al. Our comparison is probably the most clinically relevant because most conventional polyethylene has been sterilize with gamma irraiation in air, as was the Enuron polyethylene use in the arthroplasties that we stuie. Prostheses with a linear penetration rate of 0.2 mm/yr are categorically associate with an increase risk for osteolysis over ten years 18,19. The three orthopaeic surgeons in our stuy inepenently recognize periprosthetic osteolysis in eight of the twenty-four hips with an Enuron liner, which ha a mean linear penetration rate of mm/yr. Osteolysis was not observe in any of the hips with a Marathon liner. A linear penetration rate of mm/yr (a volumetric wear rate of 15.4 mm 3 /yr), which was the mean for the Marathon liners, is categorically associate with a very low risk of osteolysis over twenty years 9,16,20 an is consistent with the results of other meium-term stuies of crosslinke polyethylene 18,19. There was a wie range of wear an activity ata in both groups because of the ranomness of the patient selection. The aim of the stuy was to obtain a representation of all patients who receive a total hip replacement, an we i not exclue any patient on the basis of boy mass inex, age, or activity level. A unique aspect of our stuy metho is the quantification of iniviual patient activity an the reporting of an ajuste wear rate i.e., the wear per million cycles for a 70-kg patient weight. Quantitative activity assessment with ajustment for both patient activity an weight was the best available means with which to compare these cohorts. Commonly matche variables, such as gener, age, iagnosis, an Charnley class, are actually surrogates for the more funamental variable: the amount of use of the implant. Our metho more irectly assesses that funamental variable. The limitations of raiographic assessment of small amounts of wear with the metho use in our stuy have been recognize 10 an are not unique to our stuy. In the stuy by Engh et al., 32% (twenty-four) of seventy-six hips with a Marathon polyethylene liner ha negative wear rates 17. Methoological limitations relate to image quality, patient positioning, an muscle tone can contribute to outlier ata, incluing apparently negative wear 21,22.With a properly powere stuy, however, such spurious results have little impact on the calculation of mean hea penetration rates. We trie to optimize the accuracy of the metho by not analyzing any raiographs in the early postoperative perio to avoi evaluating patients with poor muscle tone, by having all raiographs performe by the same raiology technician, an by using stanarize patient positioning an the same imaging system. In summary, compare with Enuron polyethylene that was sterilize with gamma irraiation in air, Marathon polyethylene ha a 73% reuction in the ajuste volumetric wear rate. Osteolysis was observe in eight of the twenty-four hips with an Enuron liner but in none of the thirty-two hips with a Marathon liner. Concerns about an increase risk of osteolysis ue to smaller particles from cross-linke polyethylene were not realize at the time of this meium-term follow-up. We will continue to follow this cohort of patients. n Rui G. Bitsch, MD Christian Heisel, MD Stiftung Orthopäische Universitätsklinik, Schlierbacher Lanstrasse 200A, Heielberg, Germany Travis Loiolt, BA Scott Ball, MD Thomas P. Schmalzrie, MD Joint Replacement Institute at Orthopaeic Hospital, 2400 South Flower Street, Los Angeles, CA aress for T.P. Schmalzrie: schmalzrie@earthlink.net References 1. Harris WH. The problem is osteolysis. Clin Orthop Relat Res. 1995;311: Green TR, Fisher J, Matthews JB, Stone MH, Ingham E. Effect of size an ose on bone resorption activity of macrophages by in vitro clinically relevant ultra high molecular weight polyethylene particles. 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