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. 2018 May;26(5):1420-1428.
doi: 10.1007/s00167-016-4367-8. Epub 2016 Nov 3.

Optimum stem length for mitigation of periprosthetic fracture risk following primary total knee arthroplasty: a finite element study

Noel Conlisk  1   2   3 , Colin R Howie  4   5 , Pankaj Pankaj  4   6   7
Affiliations

Optimum stem length for mitigation of periprosthetic fracture risk following primary total knee arthroplasty: a finite element study

Noel Conlisk et al. Knee Surg Sports Traumatol Arthrosc. 2018 May.

Abstract

Purpose: Due to age-related changes to the material properties and thinning of the cortical bone structure, older patients with osteoporosis may be at greater risk of femoral fracture following total knee arthroplasty. This study investigates whether there is a potential role for stemmed prostheses in such scenarios to help mitigate peri-implant fracture risk, and if so what should the optimum stem length be to balance surgical bone loss with reduced fracture risk.

Methods: Finite element models of the distal femur implanted with four different implant types: a posterior stabilising implant, a total stabilising implant with short stem (12 mm × 50 mm), a TS implant with medium stem (12 mm × 75 mm), and a TS implant with long stem (12 mm × 100 mm), were developed and analysed in this study. Osteoporotic properties were applied to the implanted femurs and the periprosthetic stresses and strains of each were recorded.

Results: All stem lengths examined were found to lead to a reduction in periprosthetic stress in comparison with a primary stemless implant, with short-, medium-, and long-stemmed implants leading to an 11, 26, and 29% reduction in stress, respectively.

Conclusion: The results of this study show that periprosthetic stress and therefore fracture risk in old osteoporotic patients may be reduced through the use of stemmed femoral components. Of the three stems investigated, a medium-length stem is found to represent the best balance between bone preservation at the time of surgery and reduction in periprosthetic stress following implantation.

Keywords: Distal femur; Finite element; Optimum stem length; Periprosthetic stress; Total knee arthroplasty.

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Conflict of interest statement

Conflict of interest

None.

Funding

Financial support from the Lothian University Hospitals NHS Trust Brown and Ireland Estates Fund and The University of Edinburgh is gratefully acknowledged, although they had no part in the conception, analysis or reporting of results.

Ethical approval

Not required.

Informed consent

None.

Figures

Fig. 1
Fig. 1
Image of all four implant types investigated in this study, a a posterior stabilising (PS) implant, b a total stabilising implant (TS) with short stem (12 mm × 50 mm), c a TS implant with medium stem (12 mm × 75 mm) and d a TS implant with long stem (12 mm × 100 mm)
Fig. 2
Fig. 2
Semi-transparent rendering of a a femur implanted with 50-mm stem, b a femur implanted with 75-mm stem and c a femur implanted with 100-mm stem, with cement, bone and prosthesis regions indicated through the colour coded legend at the bottom
Fig. 3
Fig. 3
a Arrangement of forces at the distal femur, and b contact areas over which they are applied for 48° flexion
Fig. 4
Fig. 4
Showing a the location of each of the transverse sections through the femur, b the resulting plots of von Mises stress and c equivalent strain at the transverse sections for all cases investigated
Fig. 5
Fig. 5
a von Mises stress and b equivalent strain at each of the points of interest for varying stem length
See this image and copyright information in PMC

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