DISSOCIATION OF MODULAR HUMERAL HEAD COMPONENTS - A BIOMECHANICAL ANDIMPLANT RETRIEVAL STUDY

In vivo dissociation of the Morse-taper of shoulder arthroplasty modul ar humeral components has been reported. The incidence of this complic ation 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 lo ad 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 cont aminated with water, oil, blood, and bone cement particles. The mean d issociation force after two impactions with a mallet was 2926 +/- 955 N. Dissociation force was linearly proportional to impaction force. Re petitive 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.