Affiliations: [a] Department of Orthopaedic Surgery, University of Texas Southwestern Medical Center, Dallas, TX, USA | [b] Biomaterials for Osseointegration and Novel Engineering Laboratory, Department of Bioengineering, University of Texas at Dallas, Richardson, TX, USA | [c] Department of Orthopaedic Surgery, University of North Texas Health Science Center, Fort Worth, TX, USA | [d] Department of Materials Science and Engineering, University of North Texas, Denton, TX, USA
Correspondence:
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Corresponding author: Victor Kosmopoulos, Department of Orthopaedic Surgery, University of North Texas Health Science Center, 3400 Camp Bowie Blvd., Fort Worth, TX 76107, USA. E-mail:[email protected]
Abstract: BACKGROUND: Stable femoral fixation during uncemented total hip arthroplasty
is critical to allow for subsequent osseointegration of the prosthesis.
Varying stem designs provide surgeons with multiple options to gain femoral
fixation. OBJECTIVE: The purpose of this study was to compare the initial fixation
stability of cylindrical and tapered stem implants using two different
underreaming techniques (press-fit conditions) for revision total hip
arthroplasty (THA). METHODS: A finite element femur model was created from three-dimensional
computed tomography images simulating a trabecular bone defect commonly
observed in revision THA. Two 18-mm generic femoral hip implants were
modeled using the same geometry, differing only in that one had a
cylindrical stem and the other had a 2 degree tapered stem. Surgery was
simulated using a 0.05-mm and 0.01-mm press-fit and tested with a
physiologically relevant loading protocol. RESULTS: Mean contact pressure was influenced more by the surgical technique
than by the stem geometry. The 0.05-mm press-fit condition resulted in the
highest contact pressures for both the cylindrical (27.35 MPa) and tapered
(20.99 MPa) stems. Changing the press-fit to 0.01-mm greatly decreased the
contact pressure by 79.8% and 78.5% for the cylindrical (5.53 MPa) and
tapered (4.52 MPa) models, respectively. The cylindrical stem geometry
consistently showed less relative micromotion at all the cross-sections
sampled as compared to the tapered stem regardless of press-fit condition. CONCLUSIONS: This finite element analysis study demonstrates that tapered
stem results in lower average contact pressure and greater micromotion at
the implant-bone interface than a cylindrical stem geometry. More studies
are needed to establish how these different stem geometries perform in such
non-ideal conditions encountered in revision THA cases where less bone stock
is available.
Keywords: Finite element analysis, total hip replacement, mechanics, arthroplasty, orthopaedics
