Diagnosis and treatment of sacral and coccygeal vertebral lesions

Although minor variations are recognised, the typical vertebral formula of the horse is C7, T18, L6, S5, Cy 15– 21. The sacrum is formed by the fusion of five sacral vertebrae, which is usually completed by 4–5 years of age. The sacrum is triangular shaped (viewed dorsoventrally) with a broad base cranially and a smaller apex caudally. Cranially the sacrum articulates with the caudal aspect of the last lumbar vertebra at the lumbosacral junction. This comprises five articulations including paired lumbar–sacral facet joints, paired intertransverse joints and the lumbosacral joint itself. The pelvic surface of the wing of the sacrum articulates with a corresponding articular surface on the ventral surface of the wing of the ilium forming the sacroiliac joint. The caudally orientated dorsal spinous processes usually remain distinct and the expanded tuberosities at the summits form a prominent dorsal sacral crest. There are both dorsal and larger ventral sacral foraminae to permit passage of the dorsal and ventral rami of the sacral segmental nerves. In the adult horse the end of the spinal cord (conus medullaris) terminates at approximately the level of S1 and is continued caudally by the filum terminale, which reaches the last sacral segments ...