Vertebra S4

The sacral vertebra S4 (4th sacral vertebra) is part of the sacrum, which is formed by the fusion of five sacral vertebrae. The sacrum stabilizes the lumbar spine at the lumbosacral angle. The S4 vertebra is located near the caudal end of the sacrum, just above the sacrococcygeal junction.

Anatomically, the sacrum features both anterior and posterior sacral foramina. The posterior sacral foramen (PSF) at the S4 level allows the exit of sensory fibers. The intermediate crests, formed from the fused articular processes of the sacral vertebrae, narrow and form the sacral cornua caudally, which are landmarks for the sacrococcygeal hiatus and lie just medial to the S4 PSF.

The sacral canal, which houses the cauda equina, decreases in diameter as it progresses caudally, ending at the sacral hiatus. The anterior sacral foramen (ASF) communicates with the sacral canal through the intervertebral foramina, bordered by the pedicles and the fused winged sacral transverse processes.