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


CONCLUSIONS
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.
Orthopaedic Engineering, The University of Edinburgh, Edinburgh, UK. noel.conlisk@ed.ac.uk.|School of Clinical Sciences, The University of Edinburgh, Edinburgh, UK. noel.conlisk@ed.ac.uk.|Institute for Bioengineering, The University of Edinburgh, Faraday Building, The King's Buildings, Edinburgh, EH9 3JL, UK. noel.conlisk@ed.ac.uk.
Noel
http://orcid.org/0000-0002-0465-6213
N
Conlisk
Orthopaedic Engineering, The University of Edinburgh, Edinburgh, UK.|Department of Orthopaedics, New Royal Infirmary of Edinburgh, Old Dalkeith Road, Little France, Edinburgh, UK.
Colin R
CR
Howie
Orthopaedic Engineering, The University of Edinburgh, Edinburgh, UK.|School of Engineering, The University of Edinburgh, Edinburgh, UK.|Institute for Bioengineering, The University of Edinburgh, Faraday Building, The King's Buildings, Edinburgh, EH9 3JL, UK.
Pankaj
P
Pankaj
D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation* / Q000379:methods; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D005264:Femoral Fractures / Q000209:etiology / Q000517:prevention & control*; D005269:Femur / Q000601:surgery*; D020342:Finite Element Analysis; D006801:Humans; D007720:Knee Prosthesis; D008953:Models, Anatomic; D057068:Periprosthetic Fractures / Q000209:etiology / Q000517:prevention & control*; D012306:Risk
Distal femur; Finite element; Optimum stem length; Periprosthetic stress; Total knee arthroplasty