There are many possible causes of kyphosis, and narrowing down the curve's cause starts with narrowing down what type of kyphosis you have. Remember, there are 2 types: postural kyphosis and structural kyphosis.

Cause of Postural Kyphosis
The cause of postural kyphosis is easy to understand: Poor posture leads to an excessive rounding of the upper back. If you try, you can correct postural kyphosis, just by making a conscious effort to stand up straight and have good posture.

Causes of Structural Kyphosis
The second type of kyphosis, structural kyphosis, can't be corrected with postural work, and its causes are much more varied. The causes of structural kyphosis relate to problems with various structures in the spine.

One type of structural kyphosis is congenital kyphosis. "Congenital" means present at birth, so people with this type of structural kyphosis are born with either missing or incompletely formed parts of the spine. Congenital kyphosis is called a primary kyphosis because it's not related to another cause. During a growth period, a person with a vertebra that has not formed correctly may develop a pronounced kyphotic curve because of the underlying structural problems.

Then there's Scheuermann's kyphosis, also known as Scheuermann's disease. It's also considered a primary kyphosis because it's not caused by another condition. Right now, the medical community isn't exactly sure what causes Scheuermann's kyphosis, but they believe that it has something to do genetics. The condition seems to run in families.

Other possible causes of Scheuermann's kyphosis include interrupted bone growth, height, and weight.

Scheuermann's kyphosis occurs when the front of the spine doesn't grow as fast as the back of the spine. Doctors have found that some children begin to develop this type of kyphosis between the ages of 12 and 15—generally a period of bone growth.

Structural kyphosis can develop because of another spinal problem. This is known as secondary kyphosis; the kyphosis is "secondary to another medical condition" in doctor-speak.

Some conditions that can cause secondary kyphosis are:

• Connective tissue disorders
• Endocrine disease
• Infection
• Muscular dystrophy
• Neurofibromatosis
• Paget's disease
• Polio
• Spina bifida
• Tumors

Some other causes of secondary kyphosis are:

Degenerative Conditions
Over time, parts of our bodies can wear out or degenerate. When that happens, those body parts don't work as well, and this degeneration can lead to kyphosis. Two common degenerative conditions that can cause secondary kyphosis are:

• arthritis: Inflammation of the spinal joints can create spinal instability as your spine loses its ability to move as it should. If you have arthritis in your spine, you may develop kyphosis.
• degenerative disc disease: This spinal condition is generally considered to be age-related; over time, our intervertebral discs can wear out because our spines have to work so hard to cushion our movements. When the discs wear out, other problems can develop. DDD can lead to kyphosis because as the discs thin, the front of the vertebrae begin to tip forward. That makes the spine unstable and as more discs wear out and thin, more vertebrae start to tip, and you'll develop a hyperkyphotic curve.
• osteoporosis: When the bones in the spine weaken because of osteoporosis, you can get vertebral compression fractures. The vertebrae can fracture because of a sudden movement—even a cough can damage osteoporosis-weakened vertebrae—or they can collapse. Several vertebral fractures can cause kyphosis because if it's fractured, the spine can no longer support itself. Vertebrae may lose their normal shape and may begin to look like wedges, causing the vertebrae to collapse on one another and creating a curve in the spine.

Iatrogenic
In Greek, "iatro-" means medicine or physician; "genic" relates to the cause of something. So iatrogenic means that the physician's actions caused something to happen—and that's usually taken in a negative way. Certainly without intending to and with no malice involved, surgeons can sometimes cause a patient to develop an abnormal kyphotic curve following a surgery. This is very, very rare.

• Post-laminectomy kyphosis: If the surgeon is trying to open up more room for your spinal cord or spinal nerves, he or she may do a laminectomy. That's a form of decompression surgery because it takes pressure off—decompresses—the nerves or cord. Perhaps the nerves are being compressed by a herniated disc, a tumor, or a bone spur (osteophyte). The surgeon will remove what's causing your pain and any related structures that could compress the nerve.
  
  In a laminectomy, the surgeon removes part of the lamina, which is somewhat like the roof of your spine. The lamina is located on the posterior side (the backside) of the vertebrae. Usually, the surgeon also has to remove part of the ligament that's on the back of the spine, and that can cause the patient to lose spinal stability. Also, the surgery can weaken the muscles that support the spine. Without strong supporting structures, the spine may start to bend forward—abnormal kyphosis.

Trauma
If you experience a traumatic event—a car accident, a fall, a serious sports injury, etc—the injuries to your vertebrae and supporting soft tissues may cause secondary kyphosis. The following is a list of injuries that, in combination, can cause significant spinal instability and kyphosis.

• Fractures of the posterior (back) elements: The back part of your vertebra is crucial in stabilizing and controlling your movements. If you fracture the lamina (the roof of the vertebrae) or a facet joint (very central to control your vertebral movements), your spine could become so unstable that it will curve forward.
• Torn posterior (back) ligaments: Ligaments on the backside of your vertebrae provide a lot of stability. If they're torn, your spine may start to curve forward too much.
• Loss of supporting muscles: The muscles in your back also have an important job in supporting the spine. If they're torn or injured, they won't be able to provide as much support to the vertebrae. The spine can then start to curve forward too much.
• Compression fractures: These were covered in the osteoporosis section above. In addition to being caused by osteoporosis, compression fractures can happen during a traumatic event that places too much strain and stress on your spine.
  
  Additionally, without the strong supporting structures on the posterior (back) side—the ligaments and muscles—the spine may develop compression fractures. It may collapse on the front side of the spinal column (the anterior side) as it adjusts to the strain. When too many vertebrae collapse (and then start to tip forward because the front part is compressed), you can develop an abnormal kyphotic curve.