Os sacrum (pars caudalis)
The sacrum is formed by the fusion of five sacral vertebrae into a rigid triangular bone. It connects the spine to the pelvis via the sacroiliac joints. The cranial segment (first 2-3 sacral vertebrae) forms the sacral wings (alae) that articulate with the iliac wings. The promontory (cranial edge of S1) forms the lumbosacral angle. The caudal segment (last 2-3 sacral vertebrae) tapers and articulates with the first caudal vertebra. The sacral canal contains the cauda equina nerve roots. The sacral foramina transmit the sacral spinal nerves that contribute to the pudendal and caudal rectal nerves. The sacrum transmits hindlimb thrust to the vertebral column and anchors the pelvis.
Origin: N/A (bone)
Insertion: N/A (bone)
Action: Transmits hindlimb thrust to the vertebral column via the sacroiliac joint; anchors the pelvis
Sacroiliac joint dysfunction, sacral fractures, and cauda equina syndrome can affect function. The sacral spinal cord segments give rise to the nerves of the hindlimb and pelvic organs. Trauma to the sacrum or sacroiliac region can cause significant neurologic or locomotor deficits.
## Overview Cauda equina syndrome is a constellation of neurologic signs caused by disease of the nerve roots that form the cauda equina at the end of the spinal cord. Affected horses show varying co
## Overview Sacrocaudal injury is trauma to the junction between the sacrum and the tail, often from falling backward or the tail being caught. It causes tail paralysis or deviation, pain at the tail
Sudden hindlimb weakness, incontinence, or abnormal tail tone after trauma should be evaluated immediately.
## Overview Cauda equina syndrome is a constellation of neurologic signs caused by disease of the nerve roots that form the cauda equina at the end of the spinal cord. Affected horses show varying combinations of hind-limb weakness, urinary incontinence, fecal retention, and loss of tail tone. Causes include trauma, equine protozoal myeloencephalitis, polyneuritis equi, and space-occupying lesions. ## Causes Trauma to the sacrum, infectious or inflammatory neuritis, protozoal myelitis, and neoplasia can all damage the cauda equina. The specific cause determines treatment and prognosis. ## Diagnosis Neurologic examination demonstrates lower-motor-neuron signs to the tail, anus, bladder, and hind limbs. Rectal examination, cerebrospinal fluid analysis, and advanced imaging help identify the lesion. Testing for Sarcocystis neurona or other infectious agents is often performed. ## Treatment Therapy is directed at the underlying cause when known (antiprotozoal drugs, anti-inflammatories, or surgical decompression). Supportive care includes bladder management, fecal softeners, and prevention of urine scald. ## Recovery and Prognosis Prognosis is guarded and depends on the cause and severity. Some horses with inflammatory disease improve; severe trauma or advanced denervation often leaves permanent deficits. ## Prevention No specific prevention exists beyond minimizing sacral trauma and controlling known infectious risks where possible. Signs include: hindlimb weakness or ataxia; urinary incontinence; fecal retention; reduced tail tone; muscle atrophy of the hindquarters in chronic cases
## Overview Sacrocaudal injury is trauma to the junction between the sacrum and the tail, often from falling backward or the tail being caught. It causes tail paralysis or deviation, pain at the tail base, and swelling. Nerve damage can also affect bladder and rectal function in more severe cases. ## Causes Trauma. ## Diagnosis Clinical examination and radiographs of the sacrocaudal region. ## Treatment Rest and anti-inflammatories for mild injuries. Severe nerve damage has a poor outlook. ## Recovery and Prognosis Variable. Mild cases improve. Complete nerve disruption often leaves permanent deficits. ## Prevention Avoid catching the tail in gates or equipment. Signs include: tail paralysis or deviation; pain at the tail base; swelling
Sacroiliac joint dysfunction, sacral fractures, and cauda equina syndrome can affect function. The sacral spinal cord segments give rise to the nerves of the hindlimb and pelvic organs. Trauma to the sacrum or sacroiliac region can cause significant neurologic or locomotor deficits.
Sudden hindlimb weakness, incontinence, or abnormal tail tone after trauma should be evaluated immediately.
See the Sacrum (Caudal Segment) on our interactive 3D horse model. Open 3D Model