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    Examining TKA Bearing Options for Younger, Active Patients

    More than 700,000 Americans undergo a total knee arthroplasty annual, with the fastest growing segment being younger, active patients ages 50 to 59 years.

    To ensure the longest-lasting knee, what should an orthopaedic surgeon look for in a TKA design?

    Matthew S. Austin, MD, from The Rothman Institute in Philadelphia, Pennsylvania, addressed this issue at ICJR’s annual Winter Hip and Knee Course in Vail, Colorado.

    Femoral Component

    For the femoral component, the debate is between cobalt chromium (CoCr) and oxidized zirconium, Dr. Austin said.

    A bilateral knee study of CoCr and oxidized zirconium implants by Kim et al [1] found no significant differences in outcomes, survivorship, and size of particles at 7.5 years after surgery. However, the oxidized zirconium implants cost 20% to 30% more than the CoCr implants.

    Hui et al [2] also conducted a bilateral knee study comparing the two types of implants, and at the 5-year follow-up, they did not detect any differences in clinical, subjective, or radiologic outcomes.

    Tibial Component

    All-polyethylene vs. Modular Tibial Components

    The advantages of an all-poly component include:

    • Eliminates back-side wear
    • Cost
    • Thicker polyethylene per given tibial resection depth

    The disadvantages include:

    • Less intraoperative flexibility (no stems, thickness, no augment)
    • No “poly change” option in I&D for acute infections

    The use of all-polyethylene tibial components is low: 1.5% or fewer TKAs in the US and 0.6% in the UK.

    Kaiser registry data show the revision rate for all-poly tibial components was significantly lower than the revision rate for metal-backed modular tibial components [3]. This was especially significant in younger patients.

    Two systematic meta-analyses, however, found similar results for aseptic revision for all-poly and metal-backed tibial components. [4,5]

    As Dr. Austin noted, all-poly components cost between $470 and $1,650 less than metal-backed modular components.

    Mobile- vs. Fixed-Bearing Tibial Components

    A meta-analysis by Zeng et al [6] compared mobile- and fixed-bearing tibial components and found no significant difference with regard to:

    • Radiolucent lines
    • Osteolysis
    • Aseptic loosening
    • Survivorship

    Similarly, a meta-analysis by Smith et al found no significant difference in Knee Society Scores between mobile- and fixed-bearing components. [7](JOA 2011)

    Conventional vs. Cross-Linked Polyethylene Tibial Components

    As Dr. Austin noted, most polyethylene components have some degree of cross-linking. Lachiewicz et al [8] compared moderately vs. highly cross-linked polyethylene and found improved simulator wear for highly cross-linked polyethylene. There were concerns about decreased mechanical properties and the possibility of the small wear particles being more biologically active.

    Two recent studies reporting short- and mid-term results, however, concluded that highly cross-linked polyethylene is safe [9] [Hodrick, CORR 2008] and does not introduce new complications [10] [Long, Ortho Clin NA 2012].

    Conclusions

    Dr. Austin concluded that young patients with total knee arthroplasty do well. The procedure improves Knee Society clinical and functional scores, and survivorship rates are excellent at 10 year, although they may fall of at 20 years.

    There is no clear advantage of any particular design or material choice at this point, and in his practice, Dr. Austin typically uses a CoCr femoral component and a monoblock all-polyethylene tibial component made from conventional polyethylene.

    Dr. Austin’s presentation can be found here.

    References

    1. Kim Y-H, Park J-W, Kim J-S. Comparison of the Genesis II total knee replacement with oxidised zirconium and cobalt-chromium femoral components in the same patients. J Bone Joint Surg Br 2012;94-B:1221–7.
    2. Hui C, L, S, J, W, L. Five-year comparison of oxidized zirconium and cobalt-chromium femoral components in total knee arthroplasty: a randomized controlled trial. JBJS 04/2011; 93(7):624-30.
    3. Mohan V, Inacio MCS, RS, D, Paxton EW. Monoblock all-polyethylene tibial components have a lower risk of early revision than metal-backed modular components. A registry study of 27,657 primary total knee arthroplasties. Acta Orthop. Dec 2013; 84(6): 530–536.
    4. Nouta KA, Verra WC, Pijls BG, Schoones JW, Neilissen RGHH. All-polyethylene tibial components are equal to metal-backed components: systematic review and meta-regression. Clin Orthop Relat Res. Dec 2012; 470(12): 3549–3559.
    5. Voigt J, . Cemented all-polyethylene and metal-backed polyethylene tibial components used for primary total knee arthroplasty: a systematic review of the literature and meta-analysis of randomized controlled trials involving 1798 primary total knee implants. J Bone Joint Surg Am. 2011 Oct 5;93(19):1790-8.
    6. Zeng Y,
Shen B, Yang J, Zhou ZK, Kang PD, Pei, FX. Is there reduced polyethylene wear and longer survival when using a mobile-bearing design in total knee replacement? a meta-analysis of randomised and non-randomised controlled trials. Bone Joint J 2013;95-B:1057–63.
    7. Smith H, Jan M, Mahomed NN, Davey JR, Gandhi R. Meta-analysis and systematic review of clinical outcomes comparing mobile bearing and fixed bearing total knee arthroplasty. J Arthroplasty. 2011 Dec;26(8):1205-13
    8. Lachiewicz, PF Geyer, MR. The use of highly cross-linked polyethylene in total knee arthroplasty. J Am Acad Orthop Surg 2011;19: 143-151
    9. Hodrick JT, Severson EP, McAlister DS, Dahl B, Hofmann AA. Highly crosslinked polyethylene is safe for use in total knee arthroplasty. Clin Orthop Relat Res. 2008 Nov;466(11):2806-12. doi: 10.1007/s11999-008-0472-4. Epub 2008 Sep 10.
    10. Long WJ, Levi GS, Scuderi GR. Highly cross-linked polyethylene in posterior stabilized total knee arthroplasty: early results. Orthop Clin North Am. 2012 Nov;43(5):e35-8. Epub 2012 Sep 27.