CORR Insights^®: The Mark Coventry Award: Trabecular Metal Tibial Components Were Durable and Reliable in Primary Total Knee Arthroplasty: A Randomized Clinical Trial

Where Are We Now?

Cemented TKA is durable, generalizable, and inexpensive compared to new materials like trabecular metal (TM) cementless tibial components. Although TM as a material has been around a long time, its application to cementless tibial components is relatively new. Like any new technology, there is the potential of value, but using it adds some risk, uncertainty, and usually cost. Therefore, we should expect trials justifying the use of new technologies to be adequately powered to study endpoints of interest.

This study adds to the body of knowledge already published on the use of TM tibial components, as summarized by the authors. Taken together, it appears that the early (5- to 10-year) durability and reliability of TM cementless tibial components is most likely no different than cemented implants. This begs the question, however, as to why we should consider using cementless implants in TKA? The potential advantage of better long-term durability in younger patients has not been established. The study was not designed to address its application in younger patients. The patient population in the present study had an average age of 68 years (41 to 85 years of age) with an average BMI of 31.8 kg/m². There have been five randomized controlled trials comparing cemented and cementless TKA using roentgen stereophotogrammetric analysis: Two showed more “displacement” with cementless fixation, but three showed a possible increased risk of loosening with cemented fixation [4]. A recently published longer-term study of 80 patients with bilateral TKA (one cemented, the other cementless) showed equivalent clinical results with 100% survivorship for cemented tibias and 98.7% survivorship for cementless tibias at 17 years [3]. It is becoming increasingly clear that no advantage has been shown for cementless fixation.

In the present study, Dr. Pulido and his colleagues from the Mayo Clinic have reviewed their experience with mono-block TM tibial components in TKA. This is an excellent randomized controlled trial comparing three groups: Fully cemented standard modular implants, fully cemented TM tibial implants, and uncemented TM tibial implants. Their results show no difference at 5 years for “reliability” (Knee Society Scores, ROM, and complications) and “durability” (survivorship). What we know from this study is that in 389 patients spread across three groups at their institution with five surgeons, Pulido and colleagues were unable to show a difference at 5 years. But, this study was only powered to detect a 15% difference in radiolucent zones, which were found to be less in the TM group. It is most likely underpowered to detect clinically significant differences in the usual parameters of durability and function due to having multiple surgeons and three groups. What we do not know is whether, in longer-term studies with larger numbers, a significant difference might be found. Also, we do not know whether their results are applicable to other designs using TM (or other highly porous coatings components) or when other surgeons at other centers use them.

Where Do We Need To Go?

Paraphrasing a song by the Rolling Stones: “You can’t always get what you want. But if you try sometime, you just might find, you get what you need”. What we want for new technologies are long-term studies performed by multiple surgeons at different centers with large enough numbers for statistically relevant comparisons. But this is not only impractical; it is impossible for new technologies. By the time we would get them the technology would no longer be “new”. What we need are additional mid-term randomized controlled trial studies from other centers, preferably showing a benefit over and above what we have been using. This study did not address cost, but in most centers it is likely that the TM tibial components cost more than their traditional cemented counterpart. This added cost may be offset to some degree by avoiding the cost of the cement and mixing equipment. Also, cementless total knee replacement should be faster to perform and thus more attractive to surgeons. However, in an era where payors and consumers are demanding justification of the costs of arthroplasty, to justify the use of porous metal implants in TKA, some benefit will need to be shown (value = benefit/cost).

How Do We Get There?

Experienced surgeons who see potential value in the use of these TM cementless tibial components should use them in adequately powered randomized studies to determine value as well as the durability and reliability at 5 to 10 years and beyond. The difficult question is: Who pays for these studies? Registries may be the answer. As of now, the Australian registry has not shown any advantage of cementless components in TKA. Indeed, the revision rate at 12 years for cementless TKA is slightly higher than cemented (7.3% versus 6.3%) [1]. Perhaps with registries like the new California Joint Replacement Registry [2] that collect Level 3 outcome data, we can get the answers we need. Until mid- to long-term data is available that shows significant benefit in appropriate candidates, widespread adoption of cementless total knee replacement cannot be scientifically or economically justified.