Disc Protrusion in the Cat: Ventral Protrusions and Radial Splits

Abstract

SUMMARY Ventral protrusions and radial splits of the intervertebral discs have been investigated in 100 adult cats, 50 being of known age. Forty-eight of the latter were also examined for osteophytes. The ventral protrusions were either diffuse mounds or discrete knobs; clear splits of the annulus usually led towards the protrusion, but the annulus was seldom completely perforated. They were found in 23 cats. Forty-nine discs were affected, most of them (69 per cent) being between T10 and S1. There were no true lateral protrusions. In 15 cats with ventral protrusions there were 189 discs with osteophytes, and 21 of these had a ventral protrusion as well: 12 other discs had ventral protrusions, but no osteophytes. It cannot be said that osteophytes cause ventral protrusions, nor vice versa, but there was some statistical evidence that they may share causal factors in the cervical and lumbar regions. Radial splits consisted of outward distortion or radial rupture of lamellae unaccompanied by protrusion. These were found in 27 cats, affecting 43 discs, most of which (58 per cent) lay between T10 and S1, Ventral splits accounted for 60 per cent, and these occurred mostly between T10 and S1. Dorsal splits (19 per cent) were mainly cervical. Lateral splits (21 per cent) were irregularly scattered. Radial splits may be precursors of protrusions. Radial splits first occurred at 6 years old, ventral protrusions at 10. Over 80 per cent of both were found in cats 14 years old or more; therefore, both are essentially phenomena of senility. The nucleus pulposus was still gelatinous in 20 per cent of discs with ventral protrusions and 9 per cent with radial splits. This casts doubt on the orthodox concept that protrusions originate from degeneration of the nucleus pulposus. The findings suggest that one set of anatomical or biomechanical factors is needed to explain the distribution of dorsal protrusions and another for ventral protrusions. The low incidence of radial splits and ventral protrusions in the first 9 thoracic discs indicates that the conjugal ligament is not the only factor restricting dorsal protrusion in this region.