Planning the Restoration of View and Balance in Ankylosing Spondylitis

Patients with ankylosing spondylitis (AS; Bechterew’s disease) may develop severe kyphotic deformities of the spine with strong medical, psychological, and social impairments. Due to the rigidity of the spine, surgical correction is the only option to effectively restore horizontal view and spinal balance. It is not trivial, though, to select the level and amount of correction and to predict the outcome of the surgery. This is partly due to the large variety of sagittal deformations and compensation strategies exposed by AS patients, partly also to a lacking definition of good spinal balance and view angle. In the following, it is argued that a well-balanced spine has a fundament in a sacral endplate angle of 40° with respect to the horizon. Further, it is suggested to use the so-called Frankfort horizontal to define the natural cranium position and view angle. Given the circumstance that the spine is a rigid rod, deformities resulting from AS can precisely be quantified. Also, elementary goniometry can be used to plan optimal view angle and spinal balance. However, the question is: what is a good spinal balance? This has to be established in a broad clinical follow-up study; the analytical tools presented here will be helpful in finding the relevant parameters in an accurate way.