Problems with the spine such as osteoporosis can lead to back pain.
The human back is composed of a complex structure of muscles, ligaments, tendons, disks, and bones, which work together to support the body and enable us to move around.

The segments of the spine are cushioned with cartilage-like pads called disks.

Problems with any of these components can lead to back pain. In some cases of back pain, its cause remains unclear.

Damage can result from strain, medical conditions, and poor posture, among others.

Strain
Back pain commonly stems from strain, tension, or injury. Frequent causes of back pain are:

strained muscles or ligaments
a muscle spasm
muscle tension
damaged disks
injuries, fractures, or falls
Activities that can lead to strains or spasms include:

lifting something improperly
lifting something that is too heavy
making an abrupt and awkward movement
Structural problems
A number of structural problems may also result in back pain.

Ruptured disks: Each vertebra in the spine is cushioned by disks. If the disk ruptures there will be more pressure on a nerve, resulting in back pain.
Bulging disks: In much the same way as ruptured disks, a bulging disk can result in more pressure on a nerve.
Sciatica: A sharp and shooting pain travels through the buttock and down the back of the leg, caused by a bulging or herniated disk pressing on a nerve.
Arthritis: Osteoarthritis can cause problems with the joints in the hips, lower back, and other places. In some cases, the space around the spinal cord narrows. This is known as spinal stenosis.
Abnormal curvature of the spine: If the spine curves in an unusual way, back pain can result. An example is scoliosis, in which the spine curves to the side.
Osteoporosis: Bones, including the vertebrae of the spine, become brittle and porous, making compression fractures more likely.
Kidney problems: Kidney stones or kidney infection can cause back pain.
Movement and posture
Back pain can also result from some everyday activities or poor posture.

Examples include:

twisting
coughing or sneezing
muscle tension
over-stretching
bending awkwardly or for long periods
pushing, pulling, lifting, or carrying something
standing or sitting for long periods
straining the neck forward, such as when driving or using a computer
long driving sessions without a break, even when not hunched
sleeping on a mattress that does not support the body and keep the spine straight
Other causes
Some medical conditions can lead to back pain.

Cauda equina syndrome: The cauda equine is a bundle of spinal nerve roots that arise from the lower end of the spinal cord. Symptoms include a dull pain in the lower back and upper buttocks, as well as numbness in the buttocks, genitalia, and thighs. There are sometimes bowel and bladder function disturbances.
Cancer of the spine: A tumor on the spine may press against a nerve, resulting in back pain.
Infection of the spine: A fever and a tender, warm area on the back could be due to an infection of the spine.
Other infections: Pelvic inflammatory disease, bladder, or kidney infections may also lead to back pain.
Sleep disorders: Individuals with sleep disorders are more likely to experience back pain, compared with others.
Shingles: An infection that can affect the nerves may lead to back pain. This depends on which nerves are affected.