LIGAMENT DAMAGE AND HEALING

As already discussed, most cases of CRPS/RSD occur after some type of trauma to bones, joints and soft tissues. One of the tissues injured in these traumas are ligaments. A ligament connects two bones and is involved in the stability of the joint. A sprain is a stretched or injured ligament. Because ligaments generally have a poor blood supply, incomplete healing is common after injury.¹²³ Motion loss of the joint, connected by the ligament, is also common after injury.^{124, 125} This is increased when multiple ligaments are injured, the joint is dislocated or if surgery or prolonged immobility occurs after the ligament injury.^{126, 127} Prolonged immobilization has detrimental effects on periarticular cartilage, bone, and soft tissues and can lead to more motion loss.^128-130 During immobilization, connective tissues shorten, thereby further decreasing range of motion of the joint.¹³¹ This connective tissue shortening, increases compressive forces between the articular surfaces to three times normal in just four weeks of immobilization.¹³² Degenerative or osteoarthritic changes including atrophy of articular cartilage, increased fibrosis of periarticular tissues, regional bony eburnation, sclerosis and resorption can be found after only two weeks of immobilization.¹³³ The negative effects of periodic short-term immobilization on joints and soft tissues is cumulative.¹³⁴ In one animal study, changes in the joint and soft tissues around the joint can be seen within one week of immobilization, with marked degenerative changes appearing by four weeks. Within 80 days of immobilization, joint mobility was lost and severe destruction of the joint often followed.¹³⁵ Another study showed that even an immobilization period of four days has a cumulative effect in producing joint degeneration, and an interval of four weeks between immobilization periods does not prevent osteoarthritis from developing. In addition, this study showed that immobilization, periodic or continuous, over more than 30 days will lead to progressive joint destruction. The authors concluded that “it can be assumed that all situations which lead to the immobilization of a joint can cause osteoarthritis changes. Of interest, is that all radiology, photography, and histology showed some degree of degenerative changes also in the contralateral nonimmobilized limb.”¹³⁶ Another study found that irreversible changes can occur in the joints after eight weeks of immobilization.¹³⁷

It is easy to assume that when a person is subjected to a force significant enough to fracture a bone, that ligaments close to the fracture site would also be injured. The immobilization that follows, induces destructive changes in the joint, that itself could be painful. Once the cast is removed, for instance, the patient has numerous causes for pain including joint or muscle contractures, as well as failed ligament healing, though the fracture itself healed. Perhaps it is the failed ligament healing that is responsible for the chronic signs and symptoms of CRPS?

Ligaments are extremely sensitive to immobilization, also known as stress deprivation. Gross inspection of the ligaments after stress deprivation shows them to be less glistening and more “woody” on palpation.¹³⁸ Under a microscope the collagen of the ligament is very random and has more degradation. Chemically, the ligaments lose water and glycosaminoglycans (which help maintain structure) so there is a net loss of mass in the ligaments.¹³⁹ On close examination, it is clear that non-healed ligaments (also known as ligament scars) differ in some critical ways from normal ligament tissue. (See Figure 11.)

Ligament healing is a complex process similar to wound healing, but due to the poor vascularity of ligaments, the initial inflammatory phase takes longer than in wound healing.¹⁴⁰ Immobilization influences the appearance and biomechanical properties of ligaments, and early motion has a beneficial effect on ligament function.¹⁴¹ The mechanical stress applied by the functional load with movement improves the reorientation of the collagen fiber bundles, and increases the fibril size and density. In contrast, immobilization is followed by a protracted state of catabolism within the ligament, and the degradation of the structural matrix leads to progressive atrophy and lack of mechanical strength.¹⁴² Negative effects histologically (under a microscope) can be seen in ligaments as early as six days after immobility and proceeded destructive joint changes.¹⁴³ Other research confirms that negative structural changes in the ligaments precedes articular cartilage degeneration.^{144, 145} Knee ligaments immobilized for even a few weeks showed that the ultimate load, linear stiffness, and energy-absorbing capacity of a bone-ligament-bone preparation is reduced to about one third of normal.^{146, 147} Other studies noted a decreased resistance to stretch when ligaments were subjected to immobility.^148-150 Ligaments, with their low resting blood supply, are dependent on substantial increases in blood flow and vascular volume during the initial stages of repair.¹⁵¹ This healing response, however, is greatly compromised with lack of movement. Also, if the small feeder vessels are sheared during an initial injury the ligaments are unable to receive the nutritional support for healing. Effective healing responses are dependent on an adequate blood supply to provide the mediators necessary for tissue repair and to maintain joint homoeostasis during injurious episodes.¹⁵²