CORR Insights®: What Is the Long-term (27- to 32-year) Survivorship of an Uncemented Tapered Titanium Femoral Component and Survival in Patients Younger Than 50 Years?

Where Are We Now?

We now are in the fourth decade since cementless femoral fixation was developed. In part, cementless fixation was developed in response to what was perceived as “cement disease,” which in most patients was likely periprosthetic osteolysis and subsequent stem loosening related to polyethylene debris. Since the introduction of cementless femoral fixation in the 1980s, a plethora of stem designs have been developed such that cementless stems currently dominate the marketplace in most areas globally.

Although long-term data (that is, into the third and fourth decade) are limited to small series of patients from single institutions, the results have generally been satisfactory. One limitation, of course, is that most such studies report necessarily on first-generation implant designs that are either infrequently used or have undergone substantial design changes [3, 5, 6, 9, 10]. However, national joint registries and institutional databases both have demonstrated excellent results with more-contemporary designs at 15 to 20 years after surgery [1, 8].

In this issue of Clinical Orthopaedics and Related Research®, Streit et al. [11] reported good long-term (27- to 32-year) results of a specific first-generation, tapered, collarless, grit-blasted, titanium alloy cementless stem that is still clinically used today, making this series unusual among those with such complete and long follow-up. They focused on patients younger than 50 years at the index surgery and demonstrated that the stem continued to function well into the fourth decade despite the poor performance of the cup design and the use of non-crosslinked polyethylene. With respect to the femoral stem’s performance, relatively few patients had aseptic loosening (occurring in the second decade in stems deemed to be undersized), with periprosthetic fracture being the main cause of late failure. Although there are limitations to long-term, retrospective studies like this, when viewed alongside the national joint registry data, both clearly support the ongoing use of cementless stem fixation for THA.

Where Do We Need To Go?

Despite the success (and wide adoption) of cementless femoral fixation, many unanswered questions remain. First, it is unclear whether there is an “optimal design” for cementless femoral fixation. There has been enormous variability in the stem material (cobalt-chrome or various titanium alloys), stem geometry (cylindrical or various taper shapes), surface finish of the stem, type and location of any porous coating, and length of the stem. In particular, during the past decade, the minimum length of stem needed to achieve reliable long-term fixation has been examined with an increased interest in so-called “short stems” [4]. The trunnion design is also part of the femoral stem system. In this regard, several stem designs have been problematic, leading in some systems to premature revisions, despite reliable stem fixation [12]. Although titanium alloy tapered stems are the most-common design currently implanted, virtually every combination of the aforementioned design variables shows clinical success at 15 to 20 years of follow-up [1, 8]. Therefore, it is unclear whether any one specific stem design is clearly superior to the others. Furthermore, the importance of the insertion technique of the stem, whether it involves the use of a straight reamer followed by a broach or a broach-only technique, is not known.

Other unanswered questions include the role of the surgical approach, particularly, whether the direct anterior approach may be associated with a higher risk of early stem failure (resulting from failure to osseointegrate or perioperative fracture) with certain femoral stem designs [7]. In addition, it is not known whether the patient’s weightbearing status immediately after surgery influences the long-term results. Most long-term studies report on series in which partial weightbearing was the standard protocol at the time, while most surgeons today allow their patients full weightbearing after cementless THA.

Additionally, it is unclear whether cementless fixation is the best choice for every patient choosing to undergo THA. Good evidence suggests that for patients over the age of 75 years, cemented fixation is associated with a substantially lower risk of revision [2]. However, cementless femoral fixation for elderly patients remains popular in many parts of the world, perhaps owing to the ease of stem insertion and the time-saving benefits it may afford. Lastly, it is unclear whether there is any way to mitigate the long-term risks associated with cementless femoral fixation (such as aseptic loosening or periprosthetic fracture), which are likely a function of inexorable changes in bone quality and morphology associated with aging.

How Do We Get There?

Clearly, the creation of new randomized controlled trials to compare cemented and cementless femoral fixation or one particular cementless stem design (or insertion technique) to another is not practical, feasible, or required given the current evidence of clinical success with a vast number of cementless stem designs. To demonstrate a clear benefit of one cementless stem over another, a prospective randomized controlled trial would require enormous numbers of patients followed closely for three to four decades.

To obtain the answers that we require, there needs to be ongoing surveillance and reporting of long-term results from existing institutional databases (similar to the study by Streit et al. [11] in this issue), with a focus on more-recent (that is, still in use) cementless stem designs. In particular, the most benefit will come from reporting on the outcomes of contemporary cementless stems when used with modern bearings (specifically, highly cross-linked polyethylene). Although this limits the current follow-up duration to approximately 20 years (because cross-linked polyethylene was introduced in 1999), it removes the effect that an inferior bearing (such as non-cross-linked polyethylene) may have had on the survivorship of the stem or socket.

Perhaps more importantly, there needs to be continued reporting of the long-term results from national joint registries to allow for a comparison between various femoral stem designs. As has been done previously in specific reports within national registry publications [1], the results need to be stratified based on several factors, including stem design, the bearing combination used, trunnion design, and, perhaps most importantly, the age of the patient at the index surgery. This will allow us to determine the superiority of the femoral stem system, if it exists, over three to four decades. Furthermore, it will help clarify whether a specific cementless stem design is appropriate in patients of all ages.

It is likely that a substantial number of stem designs will be successful in the long-term, making it difficult to determine the “ideal” cementless stem design. The overwhelming success of cross-linked polyethylene during the past two decades has resulted in the elimination (so far) of significant periprosthetic osteolysis, which previously undermined the results of THA. Therefore, the type of stem fixation (cemented or cementless) or the specific design of a cementless stem will likely be far less critical to the long-term success of THA than the bearing surface and trunnion design. The ideal cementless stem needs to maintain its osseointegration during the patient’s life while preserving femoral bone stock and being resistant to the effects of age on the proximal femoral bone.