THE CAUSE OF CRPS

Clearly, a substantial number of patients are at risk for and will develop CRPS each year. What then is the precipitating factor of this disabling syndrome? CRPS may develop after a traumatic injury or without any obvious trigger event. A chart review by Birklein et al. of 145 patients in 2000, suggested 41.3% of cases were due to fractures, 32% from soft tissue injuries, 9% due to surgeries, and 17.7% from minor traumas and lesions.^41-43 In the Duman study from 2006, which included 168 patients from two hospitals, the percentage of CRPS from fractures was 55.3%, from soft tissue trauma was 28%, and 16.7% from incisive injuries.⁴⁴ A review of 140 cases at the Mayo Clinic over a two year period also noted 65% from external trauma including 28.6% after soft tissue trauma, 20% after fractures, and 16.4% of those cases were a result of surgery.⁴⁵ In the majority of pediatric cases, CRPS follows a soft tissue or joint injury.⁴⁶ It is perceivable that the aforementioned 55-65% of trauma cases including sprains, fractures and surgery also involved damage to the soft tissues including ligaments. If we were to imagine the force required to break a bone, we could also appreciate that the ligaments supporting the joints would also be injured. Connelly et al. comments, “It should be emphasized that the energy of injury is transferred to the soft tissue as well as to the bone. It is easy to forget this when we mistakenly emphasize the radiograph in our acute evaluation of injuries. Soft tissue injury occurs directly when an object impacts it and occurs indirectly when it is stretched, twisted, or torn at the instant of injury. The soft tissue envelope is the key to understanding most problems in fracture care.”⁴⁷ The injured soft tissue includes the ligaments and tendons. Ligaments are bands of flexible, tough, dense white fibrous connective tissue which attach one bone to another bone. Tendons are bands of dense fibrous tissue forming the termination of a muscle and attaching the muscle to the bone.⁴⁸ Ligaments stabilize and support the joints through their full range of motion, therefore an injury to the ligament negatively affects the joint mechanics.⁴⁹ Is it possible that this ligament injury is involved in the subsequent development of some forms of CRPS?

It has been noted that the majority of CRPS cases occur after orthopedic procedures.⁵⁰ To further delineate the frequency of CRPS as far as fractures, a study of 109 patients indicated an incidence of CRPS at 25-37% after wrist fractures.^{51, 52} In the group of 145 patients with CRPS, 42% had previous fractures.^{53, 54} In the second de Mos study of 186 CRPS patients, a fracture was the most common precipitating injury in 49% of the cases.⁵⁵ As far as surgery, the estimates include 2.3-4% after arthroscopic knee surgery, 2.1-5% after carpal tunnel surgery, 13.6% after ankle surgery, 0.8-13% after total knee arthroplasty, and 7-37% after wrist fractures.⁵⁶ Reuben noted that the development of CRPS is a common complication after fasciectomy for Dupuytreen contracture giving an estimate of 4.5-40%.^{57, 58} (See Figure 4.)

As stated earlier, these fractures and surgeries cause soft tissue damage involving the ligaments. (The reverse is also true; weakness of the ligaments could have caused the bony structure to be susceptible to fracture.) Blood supply to bone is excellent, whereas blood supply to ligament tissue is poor. If the blood vessels supplying blood to the ligaments are sheered by fracture or surgery, this further impedes the ability of the ligaments to heal. (See Figure 5.) The ligaments (and other soft tissues) not healed, sets up a perpetual cascade leading to CRPS. We will continue to explore the role of ligament injury and the development of CRPS later in this article.

Figure 5. How trauma leads to poor healing of ligaments.