Available literature and quality of the evidence

While there have been multiple randomized controlled trials (RCTs) assessing the survival of uncemented versus cemented TKA, most are too small to determine implant survival between groups. To address the limitations of these smaller studies, five meta‐analyses have been performed including a Cochrane review that provide some clarity, but each has limitations to answer the question of survival. Multiple national joint registries provide the clearest information on real‐world use of cemented and uncemented TKA, but these are limited based on the granularity of the data within the registries.

Findings

When performed well and with consistent subject matter, meta‐analyses can provide strong recommendations. The Cochrane review by Nakama et al. (level I) focused principally on the fixation and stability of cemented and uncemented tibial components as assessed by radiostereometric analysis (RSA) in three RCTs at two years.⁵ RSA is a high‐resolution radiographic technique that compares the position of radio‐dense implants to small marker beads embedded in the bone to assess relative motion between implant and bone. Early continuous migration of the mean total point motion of the implant relative to bone of >0.2 mm at two years has been associated with a high risk of early loosening and implant failure.⁶ The review found the overall movement of cemented tibial implants was less than uncemented, but that uncemented implants were at lower risk of future aseptic loosening with a risk ratio (RR) of implant instability to bone versus cement fixation (RR = 0.47; 95% confidence interval [CI]: 0.24–0.92; p = 0.03).⁵ They found that the uncemented implants tended to move a small amount early and then stabilize. Most cemented tibial components were stable, but those that were not stable never stabilized and continued to migrate. In reviewing clinical outcomes, Gandhi et al. reviewed 15 studies that were a mix of RCTs and cohort studies (level II).⁷ They found that the combined odds ratio (OR) for failure due to aseptic loosening for the uncemented group was 4.2 (95% CI: 2.7–6.5; p <0.001). However, when they only assessed the five RCTs in the review, there was no statistical difference (level I) between fixation types. They concluded that there was improved survival of the cemented compared to uncemented implants. Mont et al. (level II) described a similar phenomenon in their 37 study review with uncemented implants with an OR 1.8 (95% CI: 1.1–3.1) of failure with all study types assessed, but with no survival difference found when only the five RCTS (level I) were assessed.⁸ Wang et al. reviewed nine studies (level II) which were a mix of RCT and case series and reported ORs of 3.41 (95% CI: 1.83–6.35) at five years and 4.73 (95% CI: 2.07–10.79) in favor of cemented fixation over uncemented.⁹ Voigt et al. reviewed 14 RCTs (level I) and used both survival and implant instability by RSA as a marker or failure and found no difference between fixation methods at either 5 or 8–10 years.¹⁰ Survival with cement TKA fixation appears better, but despite the rigors of meta‐analysis methods the results are not entirely conclusive.

National joint registry data are a powerful tool that can attest to real‐world use of implants. While causality can be difficult to prove with registries, their massive scale can lead to strong conclusions. Unlike the meta‐analyses, the registries have been consistent in their overall finding that uncemented TKAs have reduced survival as compared to cemented TKAs with relative risks ranging from 1.1 to 1.9.¹¹–¹⁵ All of the registries recognize that younger patients undergoing TKA have higher revision rates and that the trend in the use of uncemented TKA is in younger patients. As a result, age is a confounder in the assessment of uncemented TKA survival and is controlled for in the analysis by the different registries. While the overall survival is reduced, sub‐analysis within the registries demonstrates some interesting findings. The New Zealand registry reported on only three uncemented knee designs with one design accounting for 78% of the uncemented volume (level II).¹³ While the survival of the predominant design was worse than the mean survival of cemented designs, the remaining two uncemented designs did not differ suggesting that the single poorly performing design skewed the results for the uncemented group as a whole. The Swedish Registry (level II) found that, after controlling for confounders, that the relative risk of failure for of a TKA with an uncemented tibial component was 1.6 (95% CI: 1.3–1.9) times higher than for cemented tibial components.¹⁵

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