What causes Osteoporosis Fracture in the spine?
Osteoporosis Fractures are fractures of the vertebral bodies which occur in Osteoporosis. The vertebral body is normally box shaped with strong walls of cortical bone and light weight centres of Cancellous bone. Cancellous bone consists of a honeycomb of bone spars with bone marrow between.
In Osteoporosis the coating of bone on the spars thins, leaving them brittle and less capable of carrying load and resisting loading or injury, resulting in inward collapse of the vertebral box. Because of the support from the facet joints at the back of the spine, the overload on the vertebra usually causes the front of the box to collapse into a wedge.
Osteopaenia (also spelt Osteopenia in the USA) is an allied condition where not only do the spars loose their bone coating but the number of spars reduces. Again the vertebral body is less able to withstand normal or excess load resulting in vertebral body wedge fractures.
What are the symptoms?
The main symptom is back pain at the level of the fracture. This is attended by loss of posture and angulation at the fracture level as the vertebral body collapses in to the wedge configuration. The onset of pain and angulation may be sudden when the collapse is rapid but it may be of gradual onset over a period of days. More than one vertebral body may be involved.
The commonest levels to be involved are the 8th Thoracic to the 2nd Lumbar vertebrae. However these fractures can occur at almost any level.
What actually causes the pain?
The sources of the pain may be several. It may occur from the micro-fractures in the vertebral body that precede the full internal collapse. Some pain may occur from the distortion of the tissues that surround the vertebral body itself or from distortion of the Posterior Longitudinal Ligament which passes over the back of the vertebra. More rarely distortion of adjacent exiting or exited spinal nerves may cause pain to radiate around the rib cage or in to the abdominal wall. As the abnormal flexed posture develops pain or discomfort occurs over the protruding spines of the back and eventually from the abnormal overstrain imposed upon the levels below.
How is the diagnosis made?
The presence of increasing back pain in the thoracic or upper lumbar spine should raise the question of impending or actual vertebral body collapse. In a patient with a history of Osteoporosis in the form of widespread bone pain or previous limb fractures the likelihood of osteoporotic vertebral fracture makes the diagnosis more likely. However other causes of vertebral body fracture such as vertebrae weakened by the presence of cancer deposits in the bone must be ruled out. The most effective diagnostic tool is the MRI scan for this demonstrates the reaction in the vertebra undergoing collapse and in the adjacent vertebrae. It indicates whether the fracture is recent or old and may indicate whether adjacent levels are likely to be at risk of such collapse.
What are the treatment options?
The general status of the patient’s bones is best estimated by a CAT scan and where appropriate pharmacological treatment of the Osteoporosis should be started or where the Osteoporosis is a consequence of other causes such as parathyroid, thyroid or kidney disease then these problems should be addressed.
The treatment is still a matter of controversy admixed with financial resource considerations. There are many physicians who will treat just the underlying Osteoporosis. Amongst those of an interventionist persuasion the choices involve:
- Vertebroplasty: This involves injecting a plastic agent in to the collapsed vertebral body to stabilise the fracture and to prevent further collapse. This technique does not correct the angulation and runs the risk of leakage of the plastic into the veins, lungs, heart and brain and posteriorly in to the spinal canal and paralysis. This technique can be performed under local anaesthetic in the elderly to reduce anaesthetic risk.
- Balloon Kyphoplasty: This involves inserting a balloon into the fractured vertebral body from the back and elevating the fracture thus correcting some of the postural deformity. By compressing the surrounding fracture site and reducing the requirement for high pressures the risk of leakage of the plastic in to the veins, lungs, heart and brain and posteriorly into the spinal canal and paralysis is minimised. This technique can be performed under local anaesthetic in the elderly to reduce anaesthetic risk. The technique requires more sophisticated equipment and is more expensive than Vertebroplasty.
- Implant fixation: This is rarely used in common Osteoporosis because the bones are unlikely to be strong enough to transmit the load to the metal scaffolding without loosening of the implants or fracture of the bones. This technique is reserved for rarer forms of Osteoporosis where the cause can be reversed and the progress is not yet too advanced.
- The number of vertebrae to treat: The conservative school will reserve treatment to the collapsed vertebra. The more interventionist school will stabilise the adjacent vertebrae especially where the MRI scan shows signs of reaction within the vertebral body because there is an incidence of fracture occurring in the adjacent vertebrae over the ensuing 3 years.
- The timing of treatment: Where there is existing active reaction within the fracture site shown on the MRI scan, then surgeons will consider performing a Balloon Kyphoplasty. If a fracture has been observed for longer than 3 months intervention is unlikely to be indicated.
What proof is there of successful treatment?
Both Vertebroplasty and Balloon Kyphoplasty effect immediate relief of symptoms in almost all cases. Where this does not occur then this may indicate that adjacent vertebrae may be causal or pain may be arising from local complication occasioned by leakage of the plastic filler on to adjacent structures.
The degree of sustained correction of angulation effected by Balloon Kyphoplasty is questioned by some authorities because of further collapse may occur around the plastic filler post-operatively. However on the operating table and in the medium term postoperative period most patients evidence significant correction of the angulation. This should serve to reduce the strain on adjacent levels and their collapse allowing medical treatment to further curb or contain the Osteoporosis process. Whilst the technique is more expensive than Vertebroplasty, this unit prefers Balloon Kyphoplasty for the benefits laid out above and the reduced risk to the patient of systemic complications and paralysis.