Appropriate sagittal positioning of femoral components in total knee arthroplasty to prevent fracture and loosening

Listen to Simon and Amy discuss the paper 'Appropriate sagittal positioning of femoral components in total knee arthroplasty to prevent fracture and loosening' published in the October 2024 issue of Bone & Joint Research.

Click here to read the paper.

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Transcript

[00:00:00] Welcome back to another episode of AI Talks with Bone & Joint from the publishers of Bone & Joint Research. Today, we're delving into the paper, 'Appropriate sagittal positioning of femoral components in total knee arthroplasty to prevent fracture and loosening', published in October 2024 by Q. Wan, Q. Han, Y. Liu, H. Chen, A. Zhang, X. Zhao, and J. Wang. 

I'm Simon, and with me is my co-host, Amy. 

Hello, Simon, and greetings to all our listeners. This study tackles an important aspect of total knee arthroplasty or TKA, focusing on how to position the femoral components to reduce the chances of fractures and loosening. With the increasing number of TKA procedures the significance of this research is clear.

Yes precisely. Despite TKA's high ten- to 15-year survival rate of over 90%, postoperative issues like periprosthetic fractures and a septic loosening remain troublesome. These issues account for significant proportions of revision surgeries, [00:01:00] 2.6% for fractures and a rather alarming 29.6% for loosening.

Indeed, the study's main goal was to determine the best sagittal placement of the uncemented femoral component in TKA using finite element analysis or FEA. They tested various sagittal positions, from -5 mm causing an anterior notch to +4 mm causing an anterior gap, under both gait and squat loading conditions. They measured Von Mises stress and interface micromotion. 

The findings were intriguing. During gait, different sagittal positions didn't result in excessive Von Mises stress or micromotion. However, under squat conditions, a posterior positioning of -4 to -5 mm, led to stress levels exceeding 150 MPa at the femoral notch, suggesting a possible fracture risk.

Moreover, the study showed that slightly anterior positioning at +1 mm or neutral positioning at 0 mm significantly reduced stress at the femoral notch. These positions also [00:02:00] minimised interface micromotion, crucial for preventing aseptic loosening and ensuring prosthesis stability.

They also noted that while computer navigation improves coronal alignment of the femoral component. It hasn't fully resolved the challenges of accurate sagittal positioning. This can still result in anterior femoral notching, a notable problem with incidences ranging from 3.5% to 29.8%.

Absolutely, and they stressed avoiding anterior notching wherever possible. Notching of more than three millimetres significantly heightens fracture risk, especially during squat conditions. Stress concentrations move from the centre of the notch to its edges as the notching depth increases, which is vital for surgeons to consider during TKA.

Practically speaking, the recommendations were quite clear. Adopting a neutral or slightly anterior sagittal position is beneficial in reducing both stress concentrations and micromotion. This can greatly assist surgeons in achieving better patient outcomes and reducing the [00:03:00] likelihood of complications.

Another key point was the initial stability of uncemented prostheses. The study indicated that under squat loading, the maximum micromotion was substantially higher than during gait, highlighting the importance of avoiding high impact activities like deep squatting in the early postoperative period.

Indeed, ensuring initial stability is essential for the success of uncemented prostheses, as it lays the foundation for strong biological fixation. The study's findings emphasise that a neutral or slightly anterior sagittal positioning aids in achieving this necessary stability, improving long term outcomes.

In conclusion, our discussion today on this paper provided key insights into the biomechanics of TKA. Optimising the femoral component placement by targeting neutral or slightly anterior sagittal positions can markedly reduce the risks of fracture and aseptic loosening. 

Quite right, Amy. It is crucial for the orthopaedic community to heed these findings to enhance surgical results and patient quality of life. Thanks to advanced [00:04:00] techniques like FEA, we gain a deeper understanding of the biomechanics involved, offering invaluable guidance for surgical practices. 

And that wraps up today's episode of AI Talks with Bone & Joint. We hope you found our discussion as enlightening as we did. Join us next time as we continue to explore the latest research and breakthroughs in orthopaedics.

Thank you for listening. Goodbye for now.