A ‘Lesbian rule’ was a flexible mason’s rule that could be bent to the curves of an irregular shape so as to measure and reproduce it. So named because they were originally constructed of a pliable kind of lead found on the Greek island of Lesbos. Aristotle mentions the rule in his Nichomachean Ethics as a metaphor for the importance of flexibility in equitable justice:
“For what is itself indefinite can only be measured by an indefinite standard, like the leaden rule used by the Lesbian builder; just as that rule is not rigid but can be bent to the shape of the stone so a special ordinance is made to fit the circumstances of the case.”
The flexicurve is a Lesbian rule – pliable lead encased in rubber or plastic – for the human body, used as a non-invasive means to measure and calculate the Cobb angle of the spine, particularly the curve of the thoracic kyphosis. This technique has the advantage of not requiring a radiograph and thereby avoiding the cost and radiation of such an invasive intervention.
With the patient in a standing position the flexicurve is placed on the back of the spine along the spinous processes of the vertebra. The shape of the curves of the spine are reproduced, with the instrument then placed on a flat surface and the curve reproduced on paper. The relevant angles are measured and calculated, the index being a calculation of width divided by length of the curve.
Description provided by Sarah Marshall of Canada and Glenn Ruscoe of Australia.
References:
Lindsey C and Bookstein NA. 2007. Instructional Video: Kypholordosis Measurement Using the Flexible Curve. APTA Section on Geriatrics.
Tillotson KM and Burton AK. 1991. Noninvasive measurement of lumbar sagittal mobility: an assessment of the flexicurve technique. Spine, 16(1), 29–33.
