Original article
Biomechanical comparison of component position and hardware failure in the reverse shoulder prosthesis

https://doi.org/10.1016/j.jse.2005.11.008Get rights and content

There has been renewed interest in reverse shoulder arthroplasty for the treatment of glenohumeral arthritis with concomitant rotator cuff deficiency. Failure of the prosthesis at the glenoid attachment site remains a concern. The purpose of this study was to examine glenoid component stability with regard to the angle of implantation. This investigation entailed a biomechanical analysis to evaluate forces and micromotion in glenoid components attached to 12 polyurethane blocks at −15°, 0°, and +15° of superior and inferior tilt. The 15° inferior tilt had the most uniform compressive forces and the least amount of tensile forces and micromotion when compared with the 0° and 15° superiorly tilted baseplate. Our results suggest that implantation with an inferior tilt will reduce the incidence of mechanical failure of the glenoid component in a reverse shoulder prosthesis.

Section snippets

Materials and methods

An apparatus was developed to simulate abduction of the humerus through 60° of abduction (Figure 1). A movable sled with a 500-lb load cell (model LCH-500; Omega Engineering, Stamford, CT) was connected via a cable through a series of pulleys to the distal portion of a steel pipe used to simulate the humerus. The angle of abduction (± 0.01°) was measured by use of an electronic goniometer (Greenleaf Medical, Palo Alto, CA) attached via a ring that moved with the steel pipe. At approximately

Results

Table I summarizes the biomechanical data. Both superior and inferior forces under the baseplate increased when going from an inferior inclination to a superior inclination (Figure 2). The type of force, though, changed when going from an inferior inclination to a superior inclination. The inferior transducer in the inferior inclination showed a progression from a lesser compressive force to a greater compressive force. The same held true for the normal inclination, although the magnitude of

Discussion

Laboratory testing provides a biomechanical basis for rational clinical decision making. We can infer, by looking at results obtained by use of high-density polyethylene blocks, that glenoid component positioning may affect the stability of the baseplate-bone interface. Implants with 15° of inferior tilt had the most uniform compressive forces and the least micromotion when compared with the 0° and 15° superiorly tilted baseplate. These results indicate that an inferior tilt of approximately

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