Observations of the ranges of flexion of the lumbar interbody joints under standardized loading have been made before and after isolated floating fusions were performed. The observed effect was that the movement which had previously occurred at a free disc level was transferred preferentially to discs immediately adjacent to the fusion-usually, but not always, most of this movement being taken up by the disc immediately below the fusion. The implications of these observations for patients on whom a floating spinal fusion is to be performed are discussed. A clinical case is discussed in which a congenital fusion is associated with degeneracy of an immediately neighboring disc.
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