title: Dissociation of modular humeral head components: a biomechanical and implant retrieval study.
abstract: In vivo dissociation of the Morse-taper of shoulder arthroplasty modular humeral components has been reported. The incidence of this complication appears to be approximately 1:1000. The objective of this study was to identify conditions that might affect the Morse-taper interface strength in humeral components. Mechanical tests were performed to load and dissociate humeral heads from the humeral stems (titanium). The effect of loading rate, load amplitude, and number of impactions was investigated. Dissociation force was measured after the taper was contaminated with water, oil, blood, and bone cement particles. The mean dissociation force after two impactions with a mallet was 2926 +/- 955 N. Dissociation force was linearly proportional to impaction force. Repetitive loading beyond two impactions did not significantly increase taper strength. Contamination of the taper with as little as 0.4 ml of fluid could prevent fixation of the taper.
authors.affiliation: University of New Mexico Health Sciences Center, Department of Orthopaedics 87131-5296, USA.
authors.forename: F T
authors.initials: FT
authors.lastname: Blevins
authors.forename: X
authors.initials: X
authors.lastname: Deng
authors.forename: P A
authors.initials: PA
authors.lastname: Torzilli
authors.forename: D
authors.initials: D
authors.lastname: Dines
authors.forename: R F
authors.initials: RF
authors.lastname: Warren
mesh_terms: D001696:Biomechanical Phenomena; D004868:Equipment Failure; D006801:Humans; D006811:Humerus; D007595:Joint Prosthesis / Q000009:adverse effects*; D008422:Materials Testing; D012785:Shoulder Joint / Q000601:surgery*