title: Not all zirconia femoral heads degrade in vivo.
abstract: Degradation of yttria-stabilized zirconia femoral heads in vivo has been linked to increased roughening and even fracture of the femoral head. To determine whether magnesia-stabilized zirconia is better suited to resist degradation, we characterized the monoclinic phase concentration, surface topography, and microhardness of retrieved zirconia femoral heads. From previous work, we expected yttria-stabilized zirconia heads to undergo considerable tetragonal-to-monoclinic phase transformation in vivo, leading to considerably increased roughness and decreased microhardness, whereas magnesia-stabilized zirconia heads would not experience phase transformation and thus would not roughen or exhibit decreased microhardness. We studied seven yttria-stabilized zirconia and 12 magnesia-stabilized zirconia femoral heads. Yttria-stabilized zirconia heads explanted after 5 years exhibited a rough orange peel-like surface under light microscopy and were rougher than magnesia-stabilized zirconia heads (average roughness approximately 20 nm versus 7.5 nm, respectively), likely attributable to increased mono-clinic phase transformation (approximately 37% by weight) caused by low-temperature aging. The microhardness of yttria-stabilized zirconia heads decreased with age, but the relationship was not noteworthy. In contrast, magnesia-stabilized zirconia retrievals showed no change in monoclinic phase concentration, surface roughness, or microhardness with age. The properties of the yttria-stabilized zirconia evaluated in our study deteriorated in vivo, whereas magnesia-stabilized zirconia did not degrade and appears to be a superior biomaterial for bearing in total joint arthroplasty.
authors.affiliation: Missouri Bone and Joint Research Foundation, St Louis, MO 63131, USA. mroy@mobojo.org
authors.forename: Marcel E
authors.initials: ME
authors.lastname: Roy
authors.forename: Leo A
authors.initials: LA
authors.lastname: Whiteside
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Katerberg
authors.forename: Jerry A
authors.initials: JA
authors.lastname: Steiger
authors.forename: Tariqa
authors.initials: T
authors.lastname: Nayfeh
mesh_terms: D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation*; D020878:Device Removal; D019544:Equipment Failure Analysis; D005269:Femur / Q000601:surgery*; D006244:Hardness; D006622:Hip Prosthesis; D006801:Humans; D008277:Magnesium Oxide / Q000737:chemistry*; D011474:Prosthesis Design; D011475:Prosthesis Failure; D012086:Reoperation; D013499:Surface Properties; D013997:Time Factors; D016896:Treatment Outcome; D015019:Yttrium / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*