Causes

There is no single cause of CRPS and it is unclear why some people develop CRPS while others with similar trauma do not.

In more than 90 percent of cases, CRPS is triggered by trauma or injury to a part of the body in which the thinnest sensory and autonomic nerve fibers are damaged.

These small nerve fibers—which lack insulating thick myelin sheaths (a protective coating, like insulation that surrounds a wire)—transmit pain, itching, and temperature sensations and control the small blood vessels and health of almost all surrounding cells.

Most CRPS is caused by damage to, or dysfunction of, injured peripheral sensory neurons, which then has secondary effects on the spinal cord and brain. The central nervous system is composed of the brain and spinal cord; the peripheral nervous system involves nerve signaling from the brain and spinal cord to all other parts of the body.

• Fractures. This is the most common cause, particularly ankle and wrist fractures. Nerves can become injured from a displaced or splintered bone, or pressure from a tight cast. Very tight or painful casts must be immediately cut off and replaced to prevent this complication.
• Surgery. A surgical incision, retractors, positioning, sutures, or postoperative scarring can cause nerve injury. Sometimes the cause can be identified and repaired, but CRPS can develop even after surgery goes well. Carpal tunnel surgery and total Knee Arthroplasty are particularly risky procedures with a higher than normal rate of post-surgical CRPS.
• Sprains/strains. Injuries that cause connective tissue ruptures to muscle, ligaments or tendons, can permit excessive joint movement that stretches and damages nearby nerves.
• Strokes. Patients that suffer strokes and have residual nerve damage with reduced limb mobility have an increased risk of CRPS.
• Lesser injuries such as burns or cuts. These are the visible signs of injuries that may also have damaged underlying nerves.
• Limb immobilization (often from casting). In addition to rarely pressing on nerves and restricting blood flow to the hands and feet as above, casts force prolonged disuse of a limb and deprive it of sensory input. After a cast is removed neurons need time to readapt to normal signaling. Also, the use of tight constriction tourniquets to reduce blood loss during limb surgery may lead to nerve damage and increase the likelihood of CRPS.
• In rare cases, simple penetrations, such as from a minor cut or needle stick, can accidentally pierce a superficial sensory nerve and initiate CRPS. A nerve specialist can locate the injured nerve by mapping the sensory changes on the skin. Ideally, larger penetrating nerve injuries are surgically repaired immediately to permit damaged nerve fibers to regrow and reconnect with target tissues.

• Less than 10% of individuals with CRPS report no known injury or trauma. Here, the cause is often an undiagnosed internal nerve injury. These include nerve rubbing or tethering against hard internal structures or scars. Tiny clots sometimes block blood flow to a nerve

Poor circulation can impede nerve and tissue healing. Damage to the small fibers that control blood flow causes many symptoms of CRPS. Blood vessels in the affected limb can dilate (open wider) to leak fluid into the surrounding tissue, causing red, swollen skin.

This reduced blood flow can deprive underlying muscles and deeper tissues of oxygen and nutrients, which can cause muscle weakness and joint pain. When skin blood vessels over-constrict, the skin becomes cold, white, gray, or bluish.

CRPS typically develops in the limbs because circulation is constrained there. Arterial blood pumped down to the hands and feet must fight gravity to return upwards in the veins to the heart.

C-fiber damage can impede this, permitting blood fluids to remain in the limb where the swelling then further blocks return blood flow. Slowed circulation impedes the delivery of oxygen and nutrients needed for healing and sometimes causes the spreading of cellular injury. Breaking the cycle by reducing limb swelling and restoring circulation is often the key that permits recovery to begin.

There are ways above and beyond drug therapy to reduce the symptoms and pain of CRPS.

• Elevating limbs: People should keep CRPS-affected arms and legs elevated when resting or sleeping to help excess fluid return to the heart.
• Physical activity: Exercise every day, even if only for 10-15 minutes. It is critical to improving circulation and oxygenation. Physical therapists experienced in CRPS can help devise an exercise regimen.
• Compression: For some individuals, compression stockings, gloves or sleeves can limit the swelling, particularly when standing. Note: TJ found that wearing an extended Copper-Fit glove or wrapping his affected wrist in an ace bandage helpful.