Characterization of Femoral Component Initial Stability and Cortical Strain in a Reduced Stem-Length Design.
Short-stemmed femoral components facilitate reduced exposure surgical techniques while preserving native bone. A clinically successful stem should ideally reduce risk for stress shielding while maintaining adequate primary stability for biological fixation. We asked (1) how stem-length changes cortical strain distribution in the proximal femur in a fit-and-fill geometry and (2) if short-stemmed components exhibit primary stability on par with clinically successful designs.



Cortical strain was assessed via digital image correlation in composite femurs implanted with long, medium, and short metaphyseal fit-and-fill stem designs in a single-leg stance loading model. Strain was compared to a loaded, unimplanted femur. Bone-implant micromotion was then compared with reduced lateral shoulder short stem and short tapered-wedge designs in cyclic axial and torsional testing.



Femurs implanted with short-stemmed components exhibited cortical strain response most closely matching that of the intact femur model, theoretically reducing the potential for proximal stress shielding. In micromotion testing, no difference in primary stability was observed as a function of reduced stem length within the same component design.



Our findings demonstrate that within this fit-and-fill stem design, reduction in stem length improved proximal cortical strain distribution and maintained axial and torsional stability on par with other stem designs in a composite femur model. Short-stemmed implants may accommodate less invasive surgical techniques while facilitating more physiological femoral loading without sacrificing primary implant stability.
Orthopaedic Biomedical Engineering Laboratory, Joint Replacement Surgeons of Indiana Research Foundation, Inc, Mooresville, Indiana.
Scott R
SR
Small
Department of Biology and Biomedical Engineering, Rose-Hulman Institute of Technology, Terre Haute, Indiana.
Sarah E
SE
Hensley
Department of Biology and Biomedical Engineering, Rose-Hulman Institute of Technology, Terre Haute, Indiana.
Paige L
PL
Cook
Department of Biology and Biomedical Engineering, Rose-Hulman Institute of Technology, Terre Haute, Indiana.
Rebecca A
RA
Stevens
Department of Biology and Biomedical Engineering, Rose-Hulman Institute of Technology, Terre Haute, Indiana.
Renee D
RD
Rogge
Orthopaedic Biomedical Engineering Laboratory, Joint Replacement Surgeons of Indiana Research Foundation, Inc, Mooresville, Indiana.
John B
JB
Meding
Orthopaedic Biomedical Engineering Laboratory, Joint Replacement Surgeons of Indiana Research Foundation, Inc, Mooresville, Indiana.
Michael E
ME
Berend
D005269:Femur / Q000502:physiology / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D011474:Prosthesis Design; D013314:Stress, Mechanical
THA; digital image correlation; micromotion; primary stability; short stem