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

Cementless total knee arthroplasty (TKA) has undergone a rapid evolution over the last few years. Technology has advanced leading to new designs with highly porous surfaces promoting osseointegration at the bone-implant interface. These new generations of cementless TKA designs are now starting to show good short- to midterm outcomes [1].

In this part of the series, Bassam Masri from the Department of Orthopaedics at the University of British Columbia leads us through the technological advancements in cementless TKA designs and their performance in clinical studies, looking at midterm survivorship and clinical outcomes of newer cementless TKA designs.

Updates in cementless total knee arthroplasties

There has been an upsurge in the use of cementless fixation in TKA in recent years evidenced both by the most recent registry data [2–6] and the changing sentiments of an ever-increasing community of surgeons performing TKAs. Indeed, as shown in Part 1 of this series of articles, around one-fifth of TKAs performed in the United States are now cementless, which is a substantial increase compared to 10 years prior [2]. As Masri explains, “at least at our center, the utilization of cementless TKA has increased significantly since 2018, and this has mirrored what other centers and surgeons have done. This is due to the improving results of cementless TKA and will hopefully withstand the test of time.”

With this increasing trend towards using cementless TKAs comes another, more concerning trend, that of the changing demographic now seeking TKA. Patients are more active, younger, and there are also more obese patients requiring TKA [7]. Bearing these factors in mind, it is now necessary to carefully consider the survival of implants as well as the type of fixation used. Cemented fixation, which is traditionally considered to be the gold standard in TKA, allows for immediate stability of the prosthesis and is still the most frequently used method of fixation. In contrast, cementless fixation was previously associated with poorer outcomes and survivorship when compared with cemented implants. The historically poorer performance of cementless TKAs may potentially be attributed to the type of implant designs used at the time [8]. Thankfully, cementless fixation technology and cementless implant design have advanced. Modern implants now include the addition of highly porous surfaces promoting osseointegration, and this has been coupled with parallel advancements in implant fixation strategies [9]. It was previously proposed that a cementless TKA has the potential to preserve bone stock, avoid cement debris, and provide a lasting biological fixation of the implant to the bone through osseointegration [9]. Regarding the latter, it is therefore more unlikely that implant loosening occurs except as a result of lysis or sepsis [9]. This feeds into the desire to provide an implant with a lasting physiological bone fixation, particularly in the younger and more active as well as the obese population.

Advanced implant technology promotes osseointegration

Newer cementless TKA implants have been developed with highly porous surfaces aiming to promote osseointegration to achieve fixation. Here, the osteoblast and mesenchymal cells migrate towards the implant and osseointegration occurs at the implant’s roughened surface achieving durable fixation [10]. The porous surfaces ideally have a minimum pore size of 100 µm taking cell size, migration, and transport into consideration, although pore sizes > 300 µm have been recommended given the new bone and capillary formation that occurs [10]. Additional to the roughened, porous surfaces facilitating osseointegration, these newer surfaces also positively impact primary stability because in the immediate postoperative period, the shear load-bearing capacity at the bone-implant interface is increased [10]. The mechanical “interlock” provided by the porous surface also acts to limit micromotion, an important feature given that the presence of micromotion compromises a change of osseointegration [9].