Radiostereometric analysis of newer cementless total knee arthroplasty designs

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With the increasing number of patients undergoing total knee arthroplasty (TKA) and the significant economic burden associated with revision surgery, prolonging the longevity of TKA implants has become a key driver of innovation in orthopedic surgery. While cemented TKA is still considered the gold standard, the past decade has witnessed a renewed interest in cementless TKA. As evidenced by recent radiostereometric analysis (RSA) studies, modern cementless designs hold promise in extending the lifespan of TKA implants.

In the third of our three-part series, using RSA results from recent TKA studies, David F Dalury from the University of Maryland St Joseph Medical Center will lead us in taking a closer look at the latest advancements of cementless TKA and the significance of RSA data in predicting long-term implant survival.

David F Dalury

University of Maryland St Joseph Medical Center, Baltimore, Maryland, USA

Member AO Recon Education Forum

Optimizing total knee arthroplasty (TKA): the role of RSA measurements

The resurgence of cementless total knee arthroplasty

With the global aging population, the demand for TKA is steadily increasing [1]. The fixation of a knee prosthesis can be cemented, cementless, or hybrid. Cemented fixation is still widely regarded as the reference standard for TKA, with excellent clinical outcomes and implant longevity of up to 20 years [2–4]. Cemented implants rely on primary bone fixation achieved through cement interdigitation into trabecular bone. However, there are concerns regarding long-term failure of cemented TKA due to loss of cement-bone interlock and debonding at the cement-implant interface, particularly in younger, obese, and active patients [5, 6]. The most common cause of late TKA failure is aseptic loosening due to cumulative mechanical stress, abrasion from cement debris, or trabecular resorption [3].

With a growing population of younger, more physically active patients seeking TKA [7], the possibility of long-lasting biological fixation and prolonged implant survival has reignited interest in cementless TKA. Cementless TKA, as opposed to cemented TKA, relies on osseointegration for fixation [8]. This approach aims to provide a more physiological bond between bone and implant, resulting in improved stability and preservation of bone stock for future revisions [4, 5].

First-generation cementless TKA implants faced multiple design-related complications, particularly early aseptic loosening of the tibial component. This loosening was primarily due to factors such as osteolysis, inadequate bone ingrowth into the tibial tray, and micromotion at the bone-implant interface, leading to subsidence—the sinking of the prosthesis into its host bone [9]. However, new designs and, more recently, the integration of 3-dimensional (3D) printing have vastly improved their performance [4]. As introduced in Part 2, modern cementless implants rely on highly porous or roughened surfaces to facilitate bone formation and employ optimized component design to provide a better mechanical interlock, reducing initial micromotion.

Several different modern implants are now available for use in TKA. The latest 3D-printed components are designed to improve the bone-to-metal connection and feature an enhanced porous structure to promote better bone ingrowth, along with peripheral pegs to increase the contact surface area and reduce early micromotion. Some designs exhibit biomechanical properties, such as high compressive strength and elastic modulus, that are very close to those of trabecular bone [10]. These features are thought to facilitate fixation to the host bone, thereby promoting bone ingrowth and increase implant longevity [9–12].

Radiostereometric analysis as a surrogate marker for long-term implant survival

The latest cementless TKA implants have shown promising outcomes in RSA studies. Radiostereometric analysis is a highly accurate imaging technique used to predict implant stability. During the surgical procedure, small radiopaque tantalum markers are implanted in both the bone and the implants. Following surgery, stereoscopic x-rays are taken using a calibration cage with established reference points (Figure 1). These images reveal the positions of the tantalum beads, and when analyzed with an RSA software, they allow surgeons to accurately calculate micromotion between the implant and the bone in three dimensions. By conducting repeated measurements at different time points, RSA allows quantitative analysis of implant migration over time [13]. Given the documented correlation between implant micromotion and the risk of long-term aseptic loosening [14], RSA has emerged as the method of choice for assessing the performance of TKA implants.

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  • Role of RSA measurements
  • Radiostereometric analysis – long-term implant survival
  • Maximum total point motion migration
  • Radiostereometric analysis outcomes
  • RSA outcomes of new generation 3D cementless TKA
  • Limiting factors for cementless implants
  • Conclusion
Part 1 | Historic registry data for cementless total knee arthroplasty (TKA)
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AO Recon - Outcomes of modern cementless TKA
Part 2 | Mid-term outcomes of modern cementless total knee arthroplasty and patient selection in 2024
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AO Recon resources

Contributing experts

This series of articles was created with the support of the following specialists (in alphabetical order):

David F Dalury

University of Maryland St Joseph Medical Center, Baltimore, Maryland, USA

Member AO Recon Education Forum

Bassam Masri

Department of Orthopaedics, University of British Columbia, Vancouver, Canada

Chairperson AO Recon Education Forum and Member AO Recon Steering Board

 

G. A. Sheridan

Gerard A Sheridan

Department of Orthopaedic Surgery, University of Galway, Galway, Ireland

This article was written by Chiara Cianciolo, AO Innovation Translation Center, Clinical Science, Switzerland.

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