Copyright © 2009 by The Journal of Bone and Joint Surgery, Inc.
Commentary & Perspective
Commentary & Perspective by
Nicolas Noiseux, MD*,
The University of Iowa Hospitals and Clinics, Iowa City, Iowa
Posted July 2009
In this issue of The Journal,
Dunbar et al. present the results of a prospective randomized controlled study using
radiostereometric analysis to compare the fixation of uncemented Trabecular
Metal (Zimmer, Warsaw, Indiana)
tibial components and cemented tibial implants. Seventy patients were
randomized to receive either a Trabecular Metal uncemented tibia or a cemented
stemmed tibia. Twenty-eight of thirty-seven patients in the Trabecular Metal
group completed the full analysis. At the twenty-four-month follow-up, radiostereometric
analysis revealed that none of these knees were considered to be at high risk
for early loosening, even though nine of the twenty-eight components had migrated
extensively (>1 mm) in the first twelve months but had subsequently stabilized.
In comparison, twenty-one of thirty-three patients with cemented tibias had
complete follow-up, of which four (19%) were deemed to be at high risk for
early loosening at twenty-four months.
The historical results of uncemented tibial components have
been disappointing with regard to the prevalence of midterm and late loosening.
Thus, it is crucial that newer cementless designs, whether they are porous
metal, hydroxyapatite-coated, or otherwise, be subjected to the most rigorous short-term
analysis tools that we possess.
Newer reports comparing cemented and cementless tibial
fixation in total knee arthroplasty have shown improved results for cementless
fixation. In their present study, Dunbar et al. have contributed to this
expanding body of knowledge. Recent randomized controlled trials have shown equivalent
rates of survival for porous-coated compared with cemented total knee
components at fifteen years1, equivalent clinical results (with zero
revisions) with use of hydroxyapatite-coated compared with cemented tibias at
five years2, and superior radiostereometric data at two years for hydroxyapatite-coated
tibias in young recipients of total knee arthroplasty3, which are similar
to the findings for porous metal tibias in this report. Thus, it appears that
certain newer-generation cementless tibial (and femoral) designs are performing
at least as well as cement in the short and medium term under scrupulous
analysis. This includes radiostereometric analysis, Knee Society radiographic score,
and functional scores from such instruments as the Western Ontario
and McMaster Universities (WOMAC) and Short Form-36 (SF-36).
Many knee surgeons are eager to move beyond cement in total
knee replacement. One of the major reasons for this is the desire to offer
reliable and long-lasting fixation to the increasingly younger patients who are
demanding total knee replacements, in whom we know cement has poorer results.
Another benefit would be the technically simpler and quicker revision for those
knees that do loosen in the (hopefully) longer term, provided that the bone
loss is not systematically worse due to a lack of cement. A possible downside
would be losing the ability to include antibiotics in the cement, but the
efficacy of this measure appears to have a relatively small impact and is a
controversial topic in its own right.
This report is a well-performed randomized controlled trial
showing that, with use of radiostereometric analysis, which is currently the
most sensitive tool for predicting early loosening, Trabecular Metal tibial
components performed at least as well as comparable cemented tibias. A few issues
do arise, however, and must be considered. The attrition rate of 30% overall
(twenty-one of seventy patients; 24% in the Trabecular Metal group and 36% in
the cemented group [nine because of difficulties with the radiostereometric
analysis, and twelve because of follow-up issues]) is quite high for a two-year
study. Unfortunately, the attrition in the cemented group resulted in a final number
of subjects that was smaller than the minimum required for the power analysis,
so we cannot with certainty know the ultimate results of the two cohorts.
Overall, the authors provide valuable data regarding the
early performance of Trabecular Metal tibial components. Furthermore, the study
is of value to the readers of JBJS because it is part of the larger spectrum of
thorough, ongoing, and scientifically sound assessment of cementless total knee
implants.
*The author did not receive any outside funding or grants in support of his research for or preparation of this work. Neither he nor a member of his immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity.
References
1. Baker PN, Khaw FM, Kirk LM, Esler CN, Gregg PJ. A randomised controlled trial of cemented versus cementless press-fit condylar total knee replacement. 15-year survival analysis. J Bone Joint Surg Br. 2007;89:1608-14.
2. Beaupré LA, al-Yamani M, Huckell JR, Johnston DW. Hydroxyapatite-coated tibial implants compared with cemented tibial fixation in primary total knee arthroplasty. A randomized trial of outcomes at five years. J Bone Joint Surg Am. 2007;89:2204-11.
3. Nilsson KG, Henricson A, Norgren B, Dalén T. Uncemented HA-coated implant is the optimum fixation for TKA in the young patient. Clin Orthop Relat Res. 2006;448:129-39.
|
