Biomechanical modeling of acetabular component polyethylene stresses, fracture risk, and wear rate following press-fit implantation.
Press-fit implantation may result in acetabular component deformation between the ischial-ilial columns ("pinching"). The biomechanical and clinical consequences of liner pinching due to press-fit implantation have not been well studied. We compared the effects of pinching on the polyethylene fracture risk, potential wear rate, and stresses for two different thickness liners using computational methods. Line-to-line ("no pinch") reaming and 2 mm underreaming press fit ("pinch") conditions were examined for Trident cups with X3 polyethylene liner wall thicknesses of 5.9 mm (36E) and 3.8 mm (40E). Press-fit cup deformations were measured from a foam block configuration. A hybrid material model, calibrated to experimentally determined stress-strain behavior of sequentially annealed polyethylene, was applied to the computational model. Molecular chain stretch did not exceed the fracture threshold in any cases. Nominal shell pinch of 0.28 mm was estimated to increase the volumetric wear rate by 70% for both cups and peak contact stresses by 140 and 170% for the 5.9 and 3.8 mm-thick liners, respectively. Although pinching increases liner stresses, polyethylene fracture is highly unlikely, and the volumetric wear rates are likely to be low compared to conventional polyethylene.
Ong
Kevin L
KL
Exponent Inc., 3401 Market St., Suite 300, Philadelphia, Pennsylvania 19104, USA. kong@exponent.com
Rundell
Steve
S
Liepins
Imants
I
Laurent
Ryan
R
Markel
David
D
Kurtz
Steven M
SM
D000077:Acetabulum; D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation* / Q000379:methods; D019544:Equipment Failure Analysis; D020342:Finite Element Analysis; D006622:Hip Prosthesis; D006801:Humans; D011095:Polyethylenes; D011474:Prosthesis Design; D011475:Prosthesis Failure; D013314:Stress, Mechanical
D011095:Polyethylenes