Scar Formation and Ligament Healing

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 theformation of a scar. This scar tissue is weaker. [Key Points] 5) Ligament healing is characterized by the formation and remodeling of scartissue that is weaker than normal ligament owing to alterations in biochemicalcomposition and structural organization. The scars have a greater amount ofinferior strength tissue compared with that of normal ligaments. 6) Ligaments are composed of: 70% water25% 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, allowingthe ligament to accommodate greater physiologic forces. If forces beyond thisrange are applied, progressive sequential failure of fibers occur, leading to completedisruption of the ligament. 9) Ligaments and ligament scars have the ability to biomechanically adapt tochanges in length or force (viscoelastic behavior, creep). [Adjustment?] 10) Ligaments are dynamic participants in joint function, helping to balancecompressive and tensile forces. 11) Ligaments are part of a neurophysiological mechanism involved with jointfunction. They contain specialized neurological receptors that play a role in aproprioceptive ligamentomuscular reflex loop. [Subluxation] 12) There is evidence that autonomic nerves control blood flow in normal andhealing ligaments. Regulation of blood flow could be an important mechanism forinflammation or repair in ligaments and periarticular tissues. [Key Point] 13) Ligament healing culminates in the formation of a scar that bridges the tornends. 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 debrisand 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 yearsleading to better collagen alignment. 14) The structural strength and stiffness, stress and tissue quality continue toimprove up to 12 months after injury, but after that time only relatively smallincreases are made. However, the material properties of the ligament scar do notreturn to normal even after 2 years. 15) Residual scar tissue behaves with abnormal biomechanical, biochemical andultrastructural properties. 16) The return of joint function after injury does not mean that the ligament hashealed. [Very Important] 17) Motion in stable joints improves the biomechanical properties of healingligaments compared with immobilization of joints. The mechanism presumablyinvolves the application of controlled forces; too little or too much force isdetrimental. [Very Important] [Adjustment?] 18) Clinically, it can be difficult to accurately classify ligament injuries as stableor unstable. 19) Biomechanically, ligament scars are weaker because of inferior materialquality. 20) Ligament healing in what may be considered to be the best case scenario ischaracterized by a scar material with inferior tissue quality, with changes inbiochemical and histologic properties, that does not regenerate a normal ligamenteven 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 chiropractorsthat treat spinal trauma patients: * Even healed ligament injury leaves residual weakness and altered proprioception. * The altered proprioception function of injured and healed ligaments not onlyalters joint protective reflex muscle tone, but also alters the autonomic control ofblood flow, which further impairs the ligament healing. [Not to mention that alters the autonomic control of blood flow has the potential to adversely affect systemichealth including immunology]. * Controlled motion [chiropractic adjustment] is the best approach to enhancethe quality of ligament healing, especially in the remodeling phase.