Abstract
Introduction
The Taylor Spatial Frame (TSF) is an hexapod external ring fixation system that can move with six degrees of freedom to correct complex limb deformities. The lengths of the struts between the rings are independently adjusted to correct the deformity. The struts form an acute and obtuse “ring-strut” angle with the ring with the sum of these angles totalling 180°. In the course of a correction schedule a strut may need to be exchanged for one of longer or shorter length. The manufacturer's instructions direct that a temporary seventh strut can be placed in any orientation to ensure stability during the exchange. We have noted several episodes of temporary frame instability during this procedure resulting in discomfort. The aim of this study was to investigate which temporary strut positions gave maximal stability.
Methods
A TSF frame was constructed in a neutral alignment with a neutral strut height of 130mm. Strut 1 (red) was identified for exchange. There were 169 theoretical placement options for the temporary strut that were sequentially tested. Fast-FX™ struts were used. Strut 1 was released and the shortening that occurred was recorded using the strut length gauge. Shortening of over 10mm was considered grossly unstable.
Results
There were 21 stable configurations and 11 unstable configurations. There were 68 mechanically impossible positions. The most important factors for frame stability were the avoidance of temporary strut crossing the strut being exchanged, and matching acute/obtuse “ring-strut” angle orientation of the temporary strut.
Conclusions
This study identifies a positioning rule that ensures maximum stability of a neutral frame during strut changes. It further identifies grossly unstable positions that may result in pain during a change.
