Scar Formation and Ligament Healing [Surgical Biology for the Clinician]

Canadian Journal of Surgery December 1998; Vol. 41; No. 6; pp. 425-429 Kevin Hildebrand, MD and Cyril Frank, MD KEY POINTS FROM THIS ARTICLE 1) Ligaments are fibrous connective tissues that provide stability to joints. 2) Ligaments have a vascular network with an accompanying nerve supply. 3) Ligaments also participate in joint proprioception. [Key Point] 4) Injuries to ligaments induce a healing response that is characterized by the formation of a scar. This scar tissue is weaker. [Key Points] 5) Ligament healing is characterized by the formation and remodeling of scar tissue that is weaker than normal ligament owing to alterations in biochemical composition and structural organization. The scars have a greater amount of inferior strength tissue compared with that of normal ligaments. 6) Ligaments are composed of: 70% water 25% collagen protein 05% other matrix components 7) Ligament collagen fibers are arranged longitudinally but not in parallel. 8) When forces to the ligament are increased more fibers are recruited, allowing the ligament to accommodate greater physiologic forces. If forces beyond this range are applied, progressive sequential failure of fibers occur, leading to complete disruption of the ligament. 9) Ligaments and ligament scars have the ability to biomechanically adapt to changes in length or force (viscoelastic behavior, creep). [Adjustment?] 10) Ligaments are dynamic participants in joint function, helping to balance compressive and tensile forces. 11) Ligaments are part of a neurophysiological mechanism involved with joint function. They contain specialized neurological receptors that play a role in a proprioceptive ligamentomuscular reflex loop. [Subluxation] 12) There is evidence that autonomic nerves control blood flow in normal and healing ligaments. Regulation of blood flow could be an important mechanism for inflammation or repair in ligaments and periarticular tissues. [Key Point] 13) Ligament healing culminates in the formation of a scar that bridges the torn ends. Ligament healing follows these steps: A)) A fibrin clot is formed within minutes. B)) An inflammatory response ensues over the next 3-5 days, removing debris and attracting fibroblasts. C)) For the next 6 weeks, the fibroblasts produce a collagen matrix. D)) The healing tissue is remodeled over the next several months and years leading to better collagen alignment. 14) The structural strength and stiffness, stress and tissue quality continue to improve up to 12 months after injury, but after that time only relatively small increases are made. However, the material properties of the ligament scar do not return to normal even after 2 years. 15) Residual scar tissue behaves with abnormal biomechanical, biochemical and ultrastructural properties. 16) The return of joint function after injury does not mean that the ligament has healed. [Very Important] 17) Motion in stable joints improves the biomechanical properties of healing ligaments compared with immobilization of joints. The mechanism presumably involves the application of controlled forces; too little or too much force is detrimental. [Very Important] [Adjustment?] 18) Clinically, it can be difficult to accurately classify ligament injuries as stable or unstable. 19) Biomechanically, ligament scars are weaker because of inferior material quality. 20) Ligament healing in what may be considered to be the best case scenario is characterized by a scar material with inferior tissue quality, with changes in biochemical and histologic properties, that does not regenerate a normal ligament even after 2 years of healing. 21) The ligament scar affects the associated joint function. [Key Point] COMMENTS FROM DAN MURPHY These concepts on ligament repair have important applications for chiropractors that treat spinal trauma patients: * Even healed ligament injury leaves residual weakness and altered proprioception. * The altered proprioception function of injured and healed ligaments not only alters joint protective reflex muscle tone, but also alters the autonomic control of blood flow, which further impairs the ligament healing. [Not to mention that alters the autonomic control of blood flow has the potential to adversely affect systemic health including immunology]. * Controlled motion [chiropractic adjustment] is the best approach to enhance the quality of ligament healing, especially in the remodeling phase.