Sacrum and Coccyx Vertebrae Possible Cause of Low Back Pain

The sacrum and coccyx are part of the vertebral spinal column and could contribute to low back pain. They are not like the other bones in the spinal column. The sacrum, also known as the sacral vertebra, sacral spine, and S1 is a large, flat triangular-shaped bone that is between the hip bones and below the last lumbar vertebra known as L5. The coccyx, known as the tailbone, is positioned below the sacrum. The sacrum and coccyx are made up of smaller bones that fuse and grow into a solid bone mass by the age of 30. The sacrum is composed of 5 fused vertebrae known as S1-S5 and 3 to 5 smaller bones that fuse creating the coccyx. Both are weight-bearing bones and are integral to walking, standing, and sitting functions.  

Sacrum and the Lumbosacral Spine

The sacrum forms the back of the pelvis. Along with the coccyx and the two sacroiliac joints make up the pelvic girdle. S1 is at the top of the sacrum and connects to the last lumbar vertebrae L5. Together they create the lumbosacral spine. Where they join forms the lumbosacral curves known as lumbar lordosis and lumbar kyphosis. The curvature works to support the upper body, weight/force distribution maintains spinal balance and flexibility. Lordosis is the inward curve of the spine, but too much can cause swayback that can be associated with spondylolisthesis. Loss of this curve can cause spinal imbalance and can lead to Flatback syndrome.   Kyphosis is the outward curve of the spine. The location of the sacrum at the intersection of the spine and pelvis means it has an important role in the movement of the low back and hips. The sacrum’s joints help to bear weight and help stabilize the spinal column along with the ligaments, tendons, and muscles help support/stabilize joint movement.

Lumbosacral joint

Joint L5 and S1 connect the lumbar spine to the sacrum. The pressure at this meeting point can be massive as the curve of the spine shifts from the lordotic forward curve to a kyphotic backward curve. The L5-S1 region bears weight, absorbs, and distributes the upper body’s weight when moving and resting. Disc herniation and spondylolisthesis are more common at L5-S1 for this reason.

Sacroiliac joints

The sacroiliac joints connect the sacrum to the left and right sides of the pelvis. The range of movement of the sacroiliac joints is minimal compared to other joints like the knees. However, the joints are essential for walking, standing, and stabilization of the hips. Sacroiliitis and sacroiliac joint dysfunction are two spinal disorders related to the joints. Other spinal disorders related to the sacral spine include:

• Sciatica
• Tarlov cysts
• Spinal chordoma, a common type of spine bone cancer

The Coccyx’s Function

The coccyx commonly known as the tailbone is just below the sacrum. It is smaller than the sacrum and has an important weight-bearing function. It helps supports weight while sitting. An example is leaning back while sitting. This motion and position increase the pressure/weight on the coccyx. An injury in this area can cause tailbone pain. Inflammation of the coccyx’s connective tissue that results in tailbone pain that gets worse when sitting is a common symptom. A traumatic event like a fall or auto accident that causes a tailbone fracture can also cause this pain.

Sacral and Coccygeal Nerves

The spinal cord ends at L1-L2, which branches out into the cauda equina, which is a bundle of nerves that looks like a horse’s tail. In the sacrum, there are sacral nerves known as the sacral plexus. Plexus means a network of nerve structures. The sacral and lumbar plexus compose the lumbosacral plexus. This is where the sciatic nerve, which is the largest nerve in the sacral plexus converges into the band. Sciatic nerve compression causes a combination of symptoms known as sciatica. It is very well known for causing low back and leg pain. The coccygeal nerve serves the tailbone. There are five sacral nerves numbered S1 through S5 and are part of the spinal cord.

• S1 supports groin and hip function
• S2 the back of the thighs
• S3 the middle of the buttock area
• S4 and S5 the anus and vagina

Injury or trauma to the sacral spine can cause mild stress fractures to severe bone fractures. These fractures can cause sacral nerve compression and intense pain. Symptoms include:

• Low back pain
• Leg pain
• Bowel dysfunction
• Bladder dysfunction
• Unusual buttock/s or groin sensations
• Osteoporosis or spinal inflammatory arthritis increases the risk for a sacral fracture.

Sacrum and Coccyx Injury Prevention

A doctor or chiropractor, physical therapist are excellent sources for information to help prevent sacrum and coccyx pain. These medical professionals will utilize a patient’s medical history, recommend lifestyle changes and injury prevention guidelines.

• If at risk of developing osteoporosis then a bone mineral density test could be recommended.
• Activities that stress the lower spine should be avoided. Extreme flexing could cause or contribute to low back/leg pain, numbness, and weakness.
• Moderate exercising like walking, jogging, yoga, and strength training all help keep the spine strong, flexible, and healthy.
• The core or abdominal muscles should be strengthened. Proper core muscle strength will stabilize the sacrum.
• Proper posture must be maintained. Avoid slouching as this places added pressure on the lumbosacral spine and the sacroiliac joints.
• Proper body mechanics when engaging in any activity needs to be observed.
• Use leg strength to lift objects.
• Avoid twisting while lifting or holding heavy objects, as this can cause sprain, strain, or serious injury of the lower spine.
• Put on the seat belt. Auto accidents are a major cause of spine trauma. Exercise restraint when driving or riding in any vehicle even a golf cart.

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Sciatica Pain Relief

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