When a long bone fracture is repaired by internal fixation with plates and screws:
Precise fracture reduction and fixation allows the fracture to heal bone-to-bone without the soft callus formation and endochondral ossification, which are characteristic of closed fracture management. However, internal reduction does not prevent delayed union, especially when infection or poor blood supply are present.
Which of the following is FALSE regarding healing of full-thickness injuries of the GI tract?
The submucosa lies radially and circumferentially outside of these layers, is composed of abundant collagenous and elastic fibers, and supports neural and vascular structures. The submucosa is the layer that imparts the greatest tensile strength and greatest suture-holding capacity, a characteristic that should be kept in mind during surgical repair of the GI tract. Additionally, serosal healing is essential for quickly achieving a watertight seal from the luminal side of the bowel. The importance of the serosa is underscored by the significantly higher rates of anastomotic failure observed clinically in segments of bowel that are extraperitoneal and lack serosa (ie, the esophagus and rectum).
The early integrity of the anastomosis is dependent on formation of a fibrin seal on the serosal side, which achieves watertightness, and on the suture-holding capacity of the intestinal wall, particularly the submucosal layer. There is a significant decrease in marginal strength during the first week due to an early and marked collagenolysis. The lysis of collagen is carried out by collagenase derived from neutrophils, macrophages, and intraluminal bacteria. Collagenase activity occurs early in the healing process, and during the first 3 to 5 days collagen breakdown far exceeds collagen synthesis. The integrity of the anastomosis represents equilibrium between collagen lysis, which occurs early, and collagen synthesis, which takes a few days to initiate. Collagen synthesis in the GI tract is carried out by both fibroblasts and smooth muscle cells.
Steroids impair wound healing by:
The major effect of steroids is to inhibit the inflammatory phase of wound healing (angiogenesis, neutrophil and macrophage migration, and fibroblast proliferation) and the release of lysosomal enzymes. The stronger the anti-inflammatory effect of the steroid compound used, the greater the inhibitory effect on wound healing. Steroids used after the first 3 to 4 days postinjury do not affect wound healing as severely as when they are used in the immediate postoperative period. Therefore if possible, their use should be delayed or, alternatively, forms with lesser anti-inflammatory effects should be administered.
In addition to their effect on collagen synthesis, steroids also inhibit epithelialization and contraction and contribute to increased rates of wound infection, regardless of the time of administration. Steroid-delayed healing of cutaneous wounds can be stimulated to epithelialize by topical application of vitamin A. Collagen synthesis of steroid-treated wounds also can be stimulated by vitamin A.
What type of nerve injury involves disruption of axonal continuity with preserved Schwann cell basal lamina?
There are three types of nerve injuries: neurapraxia (focal demyelination), axonotmesis (interruption of axonal continuity but preservation of Schwann cell basal lamina), and neurotmesis (complete transection). Following all types of injury, the nerve ends progress through a predictable pattern of changes involving three crucial steps:
Phagocytes remove the degenerating axons and myelin sheath from the distal stump (Wallerian degeneration). Regenerating axonal sprouts extend from the proximal stump and probe the distal stump and the surrounding tissues. Schwann cells ensheathe and help in remyelinating the regenerating axons. Functional units are formed when the regenerating axons connect with the appropriate end targets.
The major cause of impaired wound healing is:
All the factors listed impair wound healing, but local infection is the major problem. The surgeon should make every effort to remove all devitalized tissue and leave a clean wound for closure.
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