Mid-term outcomes of modern cementless total knee arthroplasty and patient selection in 2024

Overcoming tibial baseplate loosening

One of the disadvantages of the early cementless TKAs was tibial baseplate loosening [9]. Higher rates of tibial loosening were shown on radiostereometric analysis when compared to cemented baseplates at 5 years [9]. One method to overcome the issues of loosening was to change the design of the tibial baseplates, and this in conjunction with advancements in creation of porous surfaces and 3D printing techniques has led to new implant designs. These include 3D porous metal implants, where the pore size and density varies to improve biocompatibility [9]. A more recent introduction is an implant with a novel modular cementless tibial component comprising a highly porous 3D-printed titanium coating [10]. In addition to the advanced porous surface, another modification applied to this cementless implant is the addition of a triangular keel and four cruciform pegs which are coated only at the base [10]. Bhimji et al [12] assessed the outcomes of a modular titanium with a tibial monoblock baseplate with two hexagonal pegs and found that the modular design may lead to better initial fixation and longer stability. The authors noted that more rocking motions were experienced by the monoblock baseplate with the two hexagonal pegs, leaving it susceptible to more liftoff than the comparative plate [12]. Furthermore, they explained that the keel provided a larger surface area making it better able to resist the moment-induced motion [12].

Promising short-term results

Another study comparing cementless with cemented cruciate-retaining single-radius design TKA implants also used the tibial baseplate comprising a highly porous 3D-printed titanium coating, triangular keel and four cruciform pegs described above in the cementless TKA [8]. This cementless implant had almost identical short-term results as the cemented version [8]; indeed, improvements in the Oxford Knee Scores (OKS) from preoperatively to a mean of 1.4 ± 0.5 years postoperatively were very similar [8]. Furthermore, there were no implant failures during the follow-up period [8]. This study was able to demonstrate that the cementless version of the implant was comparable with its cemented forerunner [8]. Additionally, good short-term outcomes of cementless TKA were found in one study comparing cementless with cemented TKAs using the same single-radius design implants [13]. In this large study, there were no statistically significant differences in risk of revision for aseptic or septic failure in the cementless TKAs: In the cementless TKA group, the rate of aseptic revision was 1.0% and in the cemented TKA group it was 0.57% (P =.19) [13]. The authors stated that the aseptic failures occurring in the cementless group were happening in the early postoperative period, which indicated that failure of osseointegration was the main factor leading to the failure [13].

The cementless and cemented single-radius design TKA was again the subject of another study assessing short-term outcomes, with the cementless version using again the titanium-coated tibial baseplate with triangular keel and cruciform pegs described above [1]. Here the mean implants were followed up for 31.6 months, which provides a longer follow-up than that reported by Nam et al [8]. No implant revisions were reported in the cementless TKA group, with only four revisions being performed in the cemented group. This led to an all-cause revision rate of 0.0% for the cementless vs 1.3% for the cemented group [1]. Thus, at up to 2 years postoperatively, the all-cause survival rate was 100% in the cementless vs 98.7% in the cemented group [1]. Furthermore, no tibial tray subsidence was found in either the cemented or the cementless groups [1]. “With this encouraging data”, Masri explains, “we have expanded our use of cementless TKA without any increase in adverse outcomes”.

Excellent mid-term survivorship

The good short-term results obtained with the cementless single-radius design TKA implants with titanium-coated tibial baseplate with triangular keel and cruciform pegs are also maintained in the midterm. Restrepo et al [14] assessed outcomes at 4–6.8-year follow-ups and found an overall revision rate of 2.94% in the cementless TKA, with an overall survivorship of 97.06% and survivorship for aseptic loosening as the endpoint of 98.40%. Interestingly, here the 3D-printed tibial baseplate had a survivorship of 99.5% [14]. Good implant survivorship has also been shown at 5-year follow-ups for TKAs with 3D-printed cementless tibial baseplates; Nam et al [15] found 98.9% survivorship for these implants compared with 9.3% for an aggregated cementless group and 98.4% in a cemented knee groups. The revision rates for the cementless TKA group were also low at 0.31% per year compared with 0.40% and 0.34% per year in the other two groups, respectively [14].
Longer-term follow-up of cementless designs was evaluated by Hegarty et al [16]. Here, the follow-up of a cementless TKA with a modern tibial tray design was extended to 10 years in their prospective, randomized controlled single-blinded study. This study compared two tray designs, one was the rotating platform TKA tibial tray with a fully porous-coated central step, and the other was the rotating platform TKA tibial tray with a distally polished central stem and four peripheral fixation pegs. This latter tray was also enhanced through the addition of a sprayed 30–55 µm layer of HA on the undersurface of the tibial plateau, the four pegs, and the proximal 2 mm of the central cone [16]. Both of these tibial trays were used together with the same coated femoral component [16]. These two different cementless TKA designs achieved excellent mid-term results. Survivorship was 100% at 10-year follow-ups for the implants with the added HA and four pegs, and 98.85% for the implants with only the porous coating [16].

The occurrence of revisions in cemented versus cementless TKAs was further analyzed in a metaanalysis of randomized controlled trials comparing these two TKA fixations [17]. This metaanalysis was able to show positive results in that no significant difference was found between the cementless tibial fixations and the cemented versions in terms of revision rate. Furthermore, the authors looked to see whether there was a difference in survivorship between the two types of fixation in younger patients (< 60 years old): again, no significant difference was found [17]. Finally, an evaluation based on follow-up also revealed no significant difference in revision rates in the short, mid, or long term [17]. Looking at the younger population, Sheridan et al [18] also found aseptic revision rates as low as 0.8% at a median of 10.7-year follow-up in a cementless TKA cohort aged less than 55 years.

Although there are few studies with mid-term follow-ups of cementless TKAs, it can be seen that good or even excellent survivorship is obtained with these modern implant designs. Furthermore, good outcomes are even observed in a younger population [18], which is important given the changing demographic of the TKA population. As Masri notes, “with these encouraging results, one can only extrapolate from our experience with cementless hip implants. Once osseointegration is confirmed, fixation becomes permanent, thus eliminating the risk of late loosening. Time will tell whether the small risk of early ingrowth failure will surpass the risk of late loosening seen with cemented implants.”

Good mid-term clinical outcomes achieved with cementless fixation

Aside from these promising mid-term TKA results reported above, other factors are important in achieving good results in TKA. In order to assess the clinical outcomes of TKA, diverse measures are used, such as an assessment of pain using a Visual Analogue Scale [16], the Oxford Knee Score (OKS), American Knee Society Score (AKS), or the Short Form-12 (SF-12) score.

Hegarty et al [16], in their assessment of the modern rotating platform TKAs with the tibial tray with a porous coating or one with added HA and four pegs, found no differences in pain between these two cementless designs in both the short (6 months) and mid to long term (10 years). Additionally, there were no differences in any patient-reported outcomes based on the OKS, AKS, or SF-12 scores [16]. Significant improvements in patient-reported outcome measures from preoperatively to postoperatively were also found using a 3D-printed cementless total knee system [14]. For a more comprehensive assessment of the mid-term results on function and pain, the metaanalysis of randomized controlled trials by Chen at al [17] showed a benefit of cementless TKAs; indeed, the authors concluded that better knee scores and less pain, as well as comparable complications and revision rates may be achieved with cementless tibial fixation compared with cemented in cruciate-retaining TKAs.

Patient selection

Now that longer-term data supporting the use of cementless TKAs is starting to emerge in the literature, some questions around who would benefit the most from cementless TKAs remain to be answered. As mentioned earlier, TKA is no longer primarily indicated in older patients; a shift towards younger more active patients has occurred [19]. Thus, the good survivorship noted above is beneficial, particularly if the patient population receiving a TKA is younger (Table 1).

Salem et al [19] reviewed a number of studies evaluating outcomes of cementless TKAs in younger patients (Table 1). As the results showed, cementless TKA was successful in the younger population. Obesity is also known as a risk for increased complications following TKA and the optimal method of fixation is still debated [19]. Salem et al noted that the data from studies on obese patients led them to conclude that implant survival may be increased in obese patients when cementless TKA systems are used, citing the potential durable long-term biological fixation as the influencing factor [19]. A closer evaluation of the influence of body mass index (BMI) on survivorship of modern-design cementless TKAs, using data from an institutional registry, found that BMI did not influence survivorship, nor functional outcomes. The authors cited the improved biological fixation at the bone-implant interface as a possible reason [21]. As Masri explains, “with encouraging data about cementless TKA survivorship regardless of age or BMI, it is our hope that this technology will balance the playing field and equalize the results of TKA regardless of age or BMI”.

Conclusion

The advent of modern cementless TKA offers both good or even excellent survivorship, even in younger patients; this, coupled with shorter operating times and a potential overall cost saving [8], makes it a suitable option in a diverse patient population. In particular, younger, more active, and obese patients, for whom cemented fixation yields inferior survivorship, are better suited for cementless fixation in TKA. As Masri notes, “surgeons who are very facile with cemented fixation may be reluctant to switch to cementless fixation, which is understandable. However, as they start to gain confidence with cementless fixation, their appetite for this approach will improve, and this technology will become more important in their practice”.