The effect of twisting on the spinal discs
Another effect of poor manual handling techniques is wear on the top and bottom of the invertebratal discs. This is usually cause by excessive, repeated twisting at the waist over a prolonged period of time.
As already mentioned, discs are made up of a hard outer cartilage like material but with a softer middle part. If the top of bottom, or both, side of the discs wear too much, the harder outer "casing" can wear away causing the softer core to become exposed.
If the work involved makes it imperative that the worker does twist repeatedly, the only real action open to an employer is to introduce job rotation.