Mechanical Load-To-Shear Failure of Cemented Patellar Components in Well-Functioning Postmortem Total Knee...

Area of Science:

• Orthopedic Surgery
• Biomedical Engineering
• Materials Science

Background:

• Shear forces on the patella can cause loosening and failure in total knee arthroplasty (TKA).
• Understanding factors influencing patellar component failure is crucial for improving TKA outcomes.

Purpose of the Study:

• To evaluate the mechanical load-to-shear failure of cemented patellar components in well-functioning postmortem TKAs.
• To determine the influence of clinical and radiographic factors on load-to-shear failure in TKA.

Main Methods:

• 22 patellae from well-functioning postmortem TKAs (mean implantation duration 9.1 years) were analyzed.
• All-polyethylene 3-peg onlay patellar designs were subjected to isolated shear stress until failure.
• Univariate and multivariable linear regression models analyzed factors influencing load-to-shear failure.

Main Results:

• Mean load-to-shear failure was 1,881 ± 621 N.
• Failures occurred at the bone-cement or implant-cement interfaces; no peg-implant junction failures were observed.
• Higher bone volume fraction correlated with increased load-to-failure, while higher BMI, longer implantation duration, and greater implant coverage correlated with decreased load-to-failure.

Conclusions:

• Cemented patellar buttons in well-functioning TKAs demonstrated higher load-to-shear failure than previously reported.
• Inverse association found between bony coverage by the patellar button and shear strength.
• Consideration of smaller patellar button sizes may enhance construct shear strength in TKA.