Shoulder joint abduction motion test bench: a new shoulder test bench for in vitro experiments with active muscle force simulation.
BACKGROUND
In our society the average age is increasing, as are the number of proximal humeral head fractures. For fixation of these fractures, an increasing number of implants are available. New fixation devices should be compared biomechanically with established methods in a standardized fashion.


METHODS
The test bench that was designed was intended to simulate abduction motion of the humerus actively induced by muscle forces. We used three pneumatic muscles to apply forces to the tendons of the musculus supraspinatus and the bifid musculus deltoideus. Thus, it was possible to create an active abduction in the scapular plane. Two different fracture models (with and without medial support) were stabilised with an angular stable plate in sawbone models to reproduce a known clinical outcome with the newly designed test setup.


RESULTS
The resultant force acting on the proximal humerus reached approximately 47% BW (per cent body weight), which amounted to 329.0 N (SD: 21.76). The supraspinatus reached maximum forces of 254.7 N (SD: 20.1) and the deltoid muscle 258.9 N (SD: 16.5). Fracture gap instrumentation with medial support resulted in a significantly reduced per-cycle fracture gap motion.


CONCLUSIONS
The performance evaluation showed that the simulator produced predicable, reproducible movements with physiological muscle force magnitudes.
Department for Trauma Surgery, Innsbruck Medical University, Austria. ursula.onder@i-med.ac.at
Ursula
U
Onder
Michael
M
Blauth
Franz
F
Kralinger
Werner
W
Schmoelz
D040761:Biomimetic Materials; D004867:Equipment Design; D019544:Equipment Failure Analysis; D009068:Movement / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology; D012371:Robotics / Q000295:instrumentation*; D012785:Shoulder Joint / Q000502:physiology*