Healio
Healio
December 01, 2008
8 min read
Save

Comparison of Mid-term Clinical Outcomes After Primary Total Hip Arthroplasty With Oxinium vs Cobalt Chrome Femoral Heads

Abstract

The purpose of this investigation was to assess the midterm clinical outcomes after implantation of Oxinium (OX) vs cobalt-chrome (CC) femoral heads. Primary total hip arthroplasty (THA) procedures were performed in 100 patients. After randomization, half of the patients received OX femoral heads and half received CC femoral heads. At a minimum follow-up of 2-years, stem survival was 98% for both groups. The mean Harris Hip score was 92 for OX and 92.5 for CC, with mean WOMAC scores of 84.9 and 87, respectively. For SF-12, the OX group had mean physical and mental component scores of 45.2 and 53.8 and the CC group 49.2 and 52.6, respectively. At a minimum follow-up of 2 years, clinical outcomes for THA procedures using OX and CC femoral heads appear equivalent.

The use of metal-on-polyethylene articulations was a key development in establishing total hip arthroplasty (THA) as a successful and reproducible treatment for end-stage osteoarthritis (OA).1-3 As a result of this success, indications for THA were expanded to accommodate younger, more active patients diagnosed with OA.4 However, these patients typically place higher demand on the metal-on-polyethylene articulation, accelerating implant wear.4,5 The resulting accumulation of wear particles has been shown to increase revision risk due to progressive osteolysis.1,4,6,7

To ensure implant durability in relatively younger patients, there is a need for alternative, wear-resistant bearing surfaces.4 Ceramic femoral heads have been widely used due to superior wet-ability and relatively low friction compared with traditional metallic cobalt-chrome (CC) heads.1,8,9 Moreover, ceramic femoral heads are harder and thus more resistant to abrasive scratching.10 Together, these material characteristics allow for significantly less polyethylene wear particle generation.11-14 This reduction in wear may help maintain proper implant fixation by limiting periprosthetic osteolysis, thus improving implant survival.15,16

Despite positive wear characteristics, there is significant risk of implant fracture associated with the use of ceramic femoral heads.1,4,17 To address this risk, considerable research has been carried out to develop more durable bearing alternatives. Oxidized zirconium (Oxinium; Smith & Nephew, Inc, Memphis, Tenn) is a relatively new material that features an oxidized ceramic surface chemically bonded to a hard metallic substrate. This material possesses the reduced polyethylene wear characteristics of a ceramic, without the increased risk of implant fracture.18-20

Although the use of Oxinium (OX) in THA is promising, additional research is necessary to establish its safety and effectiveness in vivo. The purpose of this investigation was to assess early clinical outcomes after primary THA with OX vs CC femoral heads.

Materials and Methods

Institutional Review Board approval was obtained for this study. One hundred primary THA procedures were performed prospectively in 100 patients. Patients included 52 men, and mean age at the time of surgery was 51 years (SD, 11; range, 19-76). Seventy-six patients presented with a primary diagnosis of osteoarthritis, 14 with advanced avascular necrosis, 7 with developmental hip dysplasia, and 3 with rheumatoid arthritis.

Surgery was performed by 1 of 3 staff surgeons with patients in the lateral decubitus position Two surgeons used a posterior approach to the hip, and 1 surgeon used the anterolateral approach. Each patient received perioperative prophylactic antibiotics and low-molecular-weight heparin deep vein thrombosis prophylaxis.

Using sealed envelope randomization, patients were divided into 2 groups. Group 1 consisted of 50 patients, each receiving primary THA implants with an Oxinium femoral head. Mean age of patients was 51 years (SD, 10.8; range, 22-74), with 26 men. The anterolateral approach to the hip was used in 17 patients and the posterior approach in 33. Forty-six patients received an Echelon stem (Smith & Nephew, Inc), whereas the remaining 4 patients received a Synergy stem (Smith & Nephew, Inc). The acetabular components were press fit, uncemented Reflection cups (Smith & Nephew, Inc), paired with either standard polyethylene (22 cases) or highly cross-linked polyethylene (28 cases) (XLPE, Smith & Nephew, Inc).

Group 2 also consisted of 50 patients. In this group again each patient received primary THA implants; however with a CC femoral head. Demographics were similar, with mean age of 51 years (SD, 11.0; range, 19-76), and with 26 men. The anterolateral approach to the hip was used in 5 patients and the posterior approach in 45. Thirty patients received an Echelon stem (Smith & Nephew, Inc), whereas the remaining 20 patients received a Synergy stem. The acetabular components were press fit, uncemented Reflection cups (Smith & Nephew, Inc), paired with either standard polyethylene (31 cases) or highly cross-linked polyethylene (19 cases) (XLPE).

Statistical analysis was conducted using MS Excel, and the statistical software package SPSS (v.13, SPSS Inc, Chicago, Ill). Two-way, repeated-measures ANOVA analyses were conducted comparing differences in clinical outcome scores between the OX and CC groups.

Results

Clinical outcome measures for both the OX and CC groups at a minimum follow-up of 2 years postoperatively were reported. At the time of latest follow-up, stem survival for both groups was 98%. For the OX group, 2 dislocations occurred postoperatively. In addition, infection led to the revision of 1 implant. For the CC group, there was 1 incidence of postoperative dislocation. There was 1 reported stroke, 1 case of infection, and 1 case of stem loosening (Echelon stem) that required revision.

There was a significant improvement in all clinical outcome scores between preoperative and 2-year postoperative periods for both bearing groups (P < .003). There were no significant differences between bearing groups for any of the clinical outcome scores at final follow-up (P > .159). Mean Harris Hip scores (Figure 1) at 2 years postoperatively were 92 and 92.5 for the OX and CC groups, respectively (range, 65-100 OX; 60-100 CC). For SF-12, both the Physical Component Summary scale (PCS) and the Mental Component Summary scale (MCS) were reported (Figures 2 and 3). Mean PCS scores at final follow-up were 45.2 and 49.21 for the OX and CC groups, respectively (range, 27.1-56.7 OX; 26.3-61.8 CC). Mean MCS scores were 53.8 and 52.57 for the OX and CC groups, respectively (range, 39.2-65.5 OX; 34.3-64 CC). WOMAC scores are reported in Figure 4, with final mean scores of 84.9 and 87 for the OX and CC groups, respectively.

Figure 1: Mean Harris Hip scores

Figure 1: Mean Harris Hip scores.


Figure 2: Mean SF-12 scores, PCS

Figure 2: Mean SF-12 scores, Physical Component Summary Scale (PCS).


Figure 3: Mean SF-12 scores, MCS

Figure 3: Mean SF-12 scores, Mental Component Summary Scale (MCS).


Figure 4: Mean WOMAC scores

Figure 4: Mean WOMAC scores.

Discussion

This study reports early clinical outcomes after THA using either OX or CC femoral heads. At a minimum follow-up of 2 years postoperatively, these data suggest that there is no difference between the two groups as assessed by Harris Hip, SF-12, and WOMAC clinical scores. Moreover, there was no radiographic evidence of accelerated wear in either group.

As indicated previously, a focus of contemporary THA is the reduction of implant wear. Oxinium was introduced as an abrasion-resistant material with the reduced polyethylene wear characteristics of a ceramic.18-20 However, because the oxidized articular surface is chemically bonded to the metallic substrate, OX possesses the durability characteristics of metal bearings.18-20 The favorable wear characteristics of OX have been reported previously in the literature,19,21 with 1 investigator reporting a 15-fold reduction in wear coupled with a 4-fold reduction in the generation of polyethylene wear particles.19 Reducing polyethylene wear is of particular clinical relevance because it may limit the risk of periprosthetic osteolysis.15,16

Although there is substantial evidence supporting the improved wear characteristics of OX, there is a relative lack of data regarding general clinical outcomes after implantation. At 2-year follow-up, this study reported no significant differences between the OX and CC groups for the Harris Hip, SF-12, and WOMAC scores. Although additional research is required to corroborate these findings, early data support OX as a low-wear bearing surface that supports good clinical outcomes.

Conclusion

The current data suggest that THA using OX femoral heads is safe and effective. Although initial outcomes appear to be excellent, additional follow-up of the current cohort will be performed to fully assess mid- to long-term clinical outcomes. However, strong clinical outcomes in the short term support the use of OX femoral heads as an effective, low-wear alternative to traditional CC femoral heads.

References

  1. Vendittoli PA, Girard J, Lavigne M, Lavoie P, Duval N. Comparison of alumina-alumina to metal-polyethylene bearing surfaces in THA: a randomized study with 4- to 9-years follow-up. Acta Orthop Belg. 2007;73(4):468-477.
  2. Berry DJ, Harmsen WS, Cabanela ME, Morrey BF. Twenty-five-year survivorship of two thousand consecutive primary Charnley total hip replacements: factors affecting survivorship of acetabular and femoral components. J Bone Joint Surg. 2002;84:171-177.
  3. Charnley J. The long term results of low friction arthroplasty of the hip performed as a primary intervention. J Bone Joint Surg. 1972;54:61-76.
  4. Bourne RB, Barrack R, Rorabeck CH, Salehi A, Good V. Arthroplasty options for the young patient. Clin Orthop Relat Res. 2005;441:159-167.
  5. Sychertz CJ, Moon KH, Hasimoto Y, Terefenko KM, Engh CA, Bauer TW. Wear of polyethylene cups in total hip arthroplasty: a study of specimens retrieved post mortem. J Bone Joint Surg. 1996;78:1193-1200.
  6. Amstutz HC, Campbell P, Kossovsky N, Clarke IC. Mechanism and clinical significance of wear debris-induced osteolysis. Clin Orthop Relat Res. 1992;276:7-18.
  7. Schmalzried TP, Jasty M, Harris WH. Periprosthetic bone loss in total hip arthroplasty. Polyethylene wear debris and the concept of the effective joint space. J Bone Joint Surg. 1992;74:849-863.
  8. Dorlot JM, Christel P, Meunier A. Wear analysis of retrieved alumina heads and sockets of hip prostheses. J Biomed Mater Res. 1989;23:299-310.
  9. Dowdy PA, Rorabeck CH, Bourne RB. Uncemented total hip arthroplasty in patients 50 years of age or younger. J Arthroplasty. 1997;12:853-862.
  10. Kusaba A, Kuroki Y. Femoral component wear in retrieved hip prostheses. J Bone Joint Surg Br. 1997;79:331-336.
  11. Gonishi H, Wakitani S, Murata N, et al. Clinical experience with ceramics in total hip replacement. Clin Orthop Relat Res. 2000;379:77-84.
  12. Urban J, Garvin K, Boese C, et al. Ceramic-on-polyethylene bearing surfaces in total hip arthroplasty: Seventeen to twenty-one year results. J Bone Joint Surg. 2001;83:1688-1694.
  13. Yoo J, Kim Y, Yoon K, Koo K, Song W, Kim H. Alumina-on-alumina total hip arthroplasty. J Bone Joint Surg. 2005;87:530-535.
  14. Skinner H. Ceramic bearing surfaces. Clin Orthop Relat Res. 1999;369:83-91.
  15. Orishmo KF, Claus AM, Sychterz CJ, Engh CA. Relationship between polyethylene wear and osteolysis in hips with a second-generation porous-coated cementless cup after seven years of follow-up. J Bone Joint Surg Am. 2003;85:1095-1099.
  16. Ingham E, Fisher J. The role of macrophages in osteolysis of total joint replacement. Biomaterials. 2005;26(11):1271.
  17. Fritsch E, Gleitz M. Ceramic femoral head fractures in total hip arthroplasty. Clin Orthop Relat Res. 1996;328:129-136.
  18. Hunter G, Jones WM, Spector M. Oxidized zirconium. In: Total Knee Arthroplasty. Bellemans J, Ries MD, Victor J, eds. Berlin: Springer; 2005:370.
  19. Good V, Ries M, Barrack R, Widding K, Hunter G, Heuer D. Reduced wear with Oxidized Zirconium femoral heads. J Bone Joint Surg. 2003;85:S105-S110.
  20. Heuer D, Good V, Widding K. Wear performance of damaged oxidized Zr-2.5 Nb modular femoral heads. Trans. 29th Ann. Mtg. Soc. Biomaterials, Minneapolis, MN. 2005;366.
  21. Good V, Widding K, Hunter G, Heuer D. Oxidized zirconium: a potentially longer lasting hip implant. Mater Des. 2005;26:618-622.

Authors

From the Division of Orthopaedics, Department of Surgery, St Michael’s Hospital, Toronto, Ontario, Canada.

Investigation conducted at St Michael’s Hospital, Toronto, Ontario, Canada.

Drs Schemitsch is a consultant for Smith & Nephew and received research grant support from Smith & Nephew. Drs Lewis, Olsen, and Waddell have no relevant financial relationships to disclose. Christopher A. Moore, MS, is an employee of Smith & Nephew, Inc.

The investigators thank Kerry Ann Griffith-Cunningham and Jane Morton from the Division of Orthopedics at St Michael’s Hospital for their kind assistance in the data collection used in this study. They also thank Dr ER Bogoch for providing patients for the study.

Correspondence should be addressed to Peter Lewis, c/o James P. Waddell, MD, FRCSC, St. Michael’s Hospital, 30 Bond Street, Toronto, Ontario, Canada.