NPOS Member Blog Post #1 - Written by Michael Vessely, MD
Total knee arthroplasty – is it time to reconsider the use of an all-polyethylene tibial component?

Metal-backed modular (MB) tibial components are most commonly used in total knee arthroplasty (TKA) today. The Australian, England and Wales, and Norwegian total joint registries report that in less than 10% of the TKAs implanted in their countries were all-polyethylene (AP) tibial components used (1).

The advantages of MB tibial components are reported to include intra-operative flexibility, ability to perform an insert exchange at the time of any subsequent procedure, decreased inventory needed, and better distribution of symmetric loading forces when compared to AP designs.

There are some data to suggest we might question whether MB components are superior to AP components. Two posters at the most recent meeting of the American Association of Hip and Knee Surgeons looked at results from their registries with respect to this question.

The first poster reported data from a community based registry on TKAs implanted between 1991 and 2014 (2). Fifteen surgeons implanted 1,126 TKAs with an AP tibial component and sixty-seven surgeons implanted 12,923 TKAs with a MB tibial component during this time period. Only unilateral TKA cases with the diagnosis of osteoarthritis were included. Kaplan-Meier survival analysis revealed cumulative revision rates of 2.3% in the AP, and 5.4% in the MB groups. Cox regression analysis showed a 51.9% decrease in the risk of revision for AP group after adjusting for other explanatory variables (p= 0.019).

The second poster reported on data from the Mayo Clinic total joint registry on 32,354 TKAs implanted over a 34-year period (3). Tibial components implanted were 20,952 MB (65%), 7,657 monoblock metal-backed (MMB) (24%), and 3715 AP (11%). The MB and MMB patients were significantly younger. The 30-year survivorship rates reported were 83% for AP, 64% for MB, and 53% for MMB components. The AP component group also had significantly lower rates of infection, tibial osteolysis, periprosthetic fracture, and tibial component loosening.

Similar results for AP tibial components have been reported by the Kaiser Permanente total joint registry. Their results did include groups stratified by age (4).
These results are thought provoking. Personally I am wondering if it is time for me to reconsider AP tibial components for TKA.

REFERENCES

1.    Turow, A., et.al.  Knee replacement survival rates with all-polyethylene or metal-backed tibial components- what do the registries say? JISRF Reconstructive Review 3(2), September, 2013.
2.    Comfort, TK, et.al. Long-term survival of the All-poly Tibial in a Community Based Registry. Poster #72, AAHKS Annual meeting, Dallas, TX, 2015.
3.    Houdek, TH, et.al. Metal or Modularity: Why do Metal Backed Tibias Have Inferior Outcomes to All-Polyethylene Tibial Components. Poster #92, AAHKS Annual meeting, Dallas, TX, 2015.
4.    Mohan, V, et.al. Monoblock all-polyethylene tibial components have a lower risk of early revision than metal-backed modular components. Acta Orthop 84(6): 530-536, 2013.