Abstract
A statement of the purposes of the study
This study examined the stability of two different hexapod frames at increasing strut angles and the possible use of an additional strut to aid stability.
Introduction
Hexapod frames have certain advantages over standard circular frames, however disadvantages include a rattle and instability at some strut angles. This could be particularly important when larger diameter rings are used over a shorter distance resulting in lower ring strut angles such as in the femur.
Method
A standard hexapod frame was constructed with identical diameter rings for each manufacturer (Taylor Spatial, Orthosolutions). The stability of each frame was tested using a Zwick/Roell Z005 table top materials testing machine, which applied 4 cyclical loads of maximum strain 200 N. This process was performed twice. The frame configuration was then modified with increasing strut angles from 15°–70°. The Taylor Spatial Frame was retested with the addition of a seventh strut.
Results
Frame stability significantly deteriorated with shorter struts. This was particularly apparent at angles less than 35 degrees. Stiffness was significantly improved with the addition of a seventh strut. This was especially important for angles less than 35 degrees where displacement was reduced by up to 2 mm.
Conclusions
Ring-strut angle plays a significant factor in hexapod frame stability. Stability can be improved with the addition of a seventh strut. This may be particularly important in the paediatric community and in frame around the thigh were a larger ring may increase the strut angle.
