JOA - 2026-06-01 - Journal Article
Mechanical Load-To-Shear Failure of Cemented Patellar Components in Well-Functioning Postmortem Total Knee Arthroplasties.
LeBrun DG, Sacher SE, Siljander B, Baral EC, Breighner RE, Potter HG, Hopper RH, Wright TM, Engh CA, Padgett DE
Topics
Key Takeaway
Mean load-to-shear failure of cemented patellar components in well-functioning postmortem TKAs was 1,881 ± 621 N, with failure strength inversely associated with implant-to-bone surface area coverage ratio.
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Summary
This study quantified shear failure loads of cemented all-polyethylene 3-peg onlay patellar components harvested from well-functioning postmortem TKAs and identified clinical and radiographic predictors of failure strength. Twenty-two patellae were loaded to shear failure on a servo-hydraulic test frame; multivariable regression identified bone volume fraction as positively associated and BMI, implantation duration, and implant-to-bone surface area coverage as negatively associated with load-to-failure. Failure occurred at the bone-cement interface (n=9), implant-cement interface (n=7), or both (n=6), with no peg-implant junction failures, and no differences across the three implant designs.
Key Limitation
The postmortem cohort is inherently self-selected for well-functioning TKAs, excluding failed or revised patellar components and introducing survivorship bias that likely overestimates real-world shear strength.
Original Abstract
BACKGROUND
Shear forces on the patella can lead to patellar loosening and failure in total knee arthroplasty (TKA). Our objectives were as follows: (1) evaluate the mechanical load-to-shear failure in a unique cohort of cemented patellar components in well-functioning postmortem TKAs and (2) determine the influence of clinical and radiographic factors on load-to-shear failure.
METHODS
There were 22 patellae that were harvested from well-functioning postmortem TKAs (mean implantation duration 9.1 years [range, 1.7 to 19.6]). There were three all-polyethylene 3-peg onlay patellar designs evaluated. The patellae were evaluated for polyethylene damage, implant-to-bone size ratios, microarchitectural parameters, and implant-cement-bone interface. Patellar specimens were loaded with isolated shear stress using a servo-hydraulic test frame until failure. Univariate and multivariable linear regression models were used to analyze the influence of clinical and radiographic factors on load-to-shear failure.
RESULTS
The mean load-to-shear failure was 1,881 ± 621 N. There were nine patellae that failed at the bone-cement interface, seven that failed at the implant-cement interface, and six that involved both interfaces. There were no failures at the peg-implant junction. On multivariable analyses, load to failure was positively associated with bone volume fraction and negatively associated with body mass index, duration of implantation, and implant-to-bone surface area coverage. Load-to-shear failure was not associated with surface damage or radiographic parameters and did not differ across the three patellar implant designs.
CONCLUSIONS
In this novel cohort of cemented patellar buttons from well-functioning postmortem TKAs, load-to-shear failure was higher than previously reported in buttons cemented in cadaver native patellae. The amount of bony coverage by the patellar button was inversely associated with shear strength after accounting for other pertinent factors. When choosing between two patellar button sizes, surgeons should consider opting for the smaller size, which may improve the maximum shear strength of the patellar construct.