Original articleBiomechanical comparison of component position and hardware failure in the 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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