Mechanical Properties of a Sintered Asymmetric Particle Ingrowth Coating

Mechanical integrity and frictional stability are important for the safety and efficacy of any porous ingrowth coating. This study evaluates mechanical characteristics including tensile attachment strength, static shear strength, and friction of a sintered asymmetric particle porous coating (STIKTITE™, Smith & Nephew, Memphis, TN) compared to other clinically available porous ingrowth coatings.

Tensile attachment strength (n=154) was determined following ASTM F1147 at a strain rate of 2.5mm/min. Shear attachment (n=5) was evaluated by ASTM F1044. Linear dynamic friction coefficient (n=3) values were determined using a friction and wear testing machine (OrthoPod, AMTI, Watertown, MA) with a vertical normal load of 44N and contact pressure of 0.15MPa against bone analog[1]. Samples were compared to tantalum foam (Trabecular Metal™, Zimmer, Warsaw IN) wire EDM'd from tibial trays and fixed to a solid stub with FM1000 adhesive (n=2), and conventional sintered spherical titanium bead coated coupons.

Average (±standard deviation) static tensile attachment strength for the asymmetric particle porous coating over a two-year production period was 7.35±1.31ksi. This value was approximately twice that reported for another clinically available asymmetric titanium ingrowth structure (3.49ksi; Regenerex™, Biomet, Warsaw, IN)[2], exceeded values reported for tantalum foam (5.02±1.29ksi[3]), and was over twice the minimum (2.9ksi) recommended by the FDA[4]. The average shear strength (5.56±0.51ksi) was almost twice that recommended by the FDA (2.9ksi)[4]. Maximum friction coefficient (1.14±0.07) was comparable to tantalum foam (1.11±0.03) and was significantly higher (p<0.05) than conventional sintered spherical titanium beads (0.55±0.08).

The superior mechanical integrity and high interfacial friction of the asymmetric particle porous coating evaluated here should lead to improved implant stability, which is consistent with clinical data showing less micromotion than conventional sintered bead porous coatings[5].

1.Gilmour, WBC 2008, 464

2.Levine, Adv. Eng. Mat. 10:9, 2008.

3.Medlin, ASTM STP 1471, 2006.

4.FDA Guidance Document 827, April 28, 2004.

5.Bourne, Orthopedics 31(12):92-6, 2008.