Orthopedic or emergency surgery is often used in the early stage of lower limb trauma [7 - 10],some patients have primary injuries, such as electric burn, severe rolling of skin and soft tissue, vascular injury or local hematoma, fat liquefaction, hematoma infection, etc., which eventually develop into skin necrosis [11-13];
For fracture patients, plate internal fixation is a more common method. However, the bone or steel plate was exposed due to postoperative skin swelling, excessive shear stress, skin necrosis or secondary wound infection, osteomyelitis and other reasons.Some scholars reported that if the wound fails to heal in 4 weeks, it will become a chronic wound. The important characteristic of chronic wound is the stagnation of wound healing process.Once a chronic wound is formed, the tissue repair process stops, the tissue around the wound becomes fibrotic, scarred, and stops growing,The exposed bone, tendon or steel plate can not be effectively covered by tissue, resulting in lasting exposure.For this kind of wound, the traditional repair method is to use various skin flaps.However, in some patients, the steel plate at the suture between the flap edge and the receiving area cracked again, and the steel plate was exposed again.In other patients, the flap healed well in the early stage, but 1 or 2 months after operation, the sinus appeared again on the suture between the flap and the recipient area, the secretion was discharged intermittently, and the sinus orifice showed typical chronic inflammation .The swelling of the flap is an important reason for the re division of the flap and the exposure of bone steel nails in the later stage.Due to the contracture of the flap tissue and the tissue around the wound, the tension between the flap and the wound suture gradually increases,because the suture between the flap and the recipient tissue is a single end-to-end contact,due to the effect of tension, the tissue at the suture becomes thinner and finally splits,in particular, when the suture part crosses the bone or steel plate, there is not enough tissue in the deep layer to provide healing, and the wound will eventually crack again.
In addition, due to the retention of foreign bodies such as dead bone, necrotic and degenerative tendon tissue and steel plate, the ejection reaction of the body also produces inflammatory exudation, which contains the colloidal substances such as proteins in the exudate precipitate and solidify in the foreign body surface and the surrounding spaces to form peptone which becomes a good culture medium for bacteria.Bacteria multiply in large numbers in the above-mentioned areas(Figure 2), release toxins, and further aggravate the inflammatory reaction of the tissue around the wound, so that the wound continues to produce exudate and pus, forming a vicious circle, and the wound can not heal[15-16].After timely wound dressing change and anti-infective treatment, the acute inflammation of the wound was control.Due to the stimulation of chronic inflammation, the tissue around the wound gradually fibrosis, scarring, congestion and blood stasis, thickening, dark purple color, lack of elasticity, poor circulation, which is not conducive to wound repair-.led and turned to chronic wound, the bone plate was exposed or formed one or more sinuses(Fig. 8: A, B, c). After several months or even longer treatment, there was no obviously tending to heal.
In this study,according to the causes of secondary wound with chronic bone exposure,through one-stage expansion, remove the scar skin within a certain range around the wound, remove or remove the sinus wall, scrape the basal granulation tissue, remove the fresh wound bed in combination with VSD culture, change the chronic wound into acute wound, restart the wound healing process, and provide a good foundation for flap healing and wound final healing.a certain width of recipient granulation wound is formed around the wound, which can increase the contact surface between the transplanted flap and the base, so that the blood supply between the flap and the wound can be established quickly,it is conducive to the survival of flap and promote wound healing.
After the wound bed is ready, a second stage debridement is performed.The necrotic bone, periosteum, tendon tissue and peptone on the surface of the plate and bone were removed, and the space around the plate was filled with artificial dermis to completely cover the exposed bone and plate.then the wound was closed with flap.Artificial dermis isolated the contact between body tissue and foreign bodies at an early stage and blocked rejection .The flap and periwound blood vessels can quickly grow into the artificial dermis and close the dead space around the bone plate.proper pressure wrapping of the flap after operation can effectively prevent the possibility of residual dead space and purulent cavity formed by blood accumulation under the flap.The suture between the flap edge and the wound edge tissue was changed from end-to-end plane contact to three-dimensional mortise and tenon contact,this three-dimensional contact increases the contact area between the flap and the tissue around the wound,so that the flap and wound can establish blood supply in an earlier and wider range,the three-dimensional mortise and tenon contact can effectively reduce the risk of skin thinning and cracking at the suture caused by excessive tension caused by flap retraction.Since the bacteria in chronic wounds are mainly low toxic strains , the bacterial content is greatly reduced after twice debridement and cleaning with VSD and alcohol.Fresh wound granulation tissue and flap tissue have reliable blood supply, can completely remove residual bacteria, and significantly reduce the possibility of infection and sinus formation.
When expanding the wound, the scar skin and fibrotic tissue of the outer wall of the steel plate should be excised. If there is a sinus, the outer wall of the sinus should be incision, and the fibrous capsule inside the outer wall and the sinus cavity should be removed. If necessary, make a transverse incision at the bottom of the sinus wall, so that the sinus wall can be loosely attached to the base after the fibrous capsule is removed. If the fibrotic scar of the outer wall of the sinus is so severe that it can not be well attached to the base, it can be removed as appropriate. Free bone fragments should be removed. The necrotic periosteum and tendinous tissue at the base of the wound were also removed as clean as possible. Scratching the aged granulation at the bottom can cause bleeding in the wound, which can lead to fresh wounds, thus activating the wound healing process. The protein-like tissue attached and precipitated in the holes of the steel plate, in the steps formed between the edge of the steel plate and the bone surface, in the gap formed by the incompact adhesion between the steel plate and the bone, and in the gap at the broken end of the bone should be carefully cleaned to remove. During the skin flap transplantation, the denatured and necrotic bone cortex should be chiseled off 1-2mm, the peptone in the steel plate steps and spaces should be removed, and the exposed bone or steel plate should be covered with artificial dermis. The gap between the steps formed at the edge of the steel plate and the bones under the plate should be closely filled, so that the dead space will not remain after the flap transplantation and avoid infection and necrosis caused by effusion under the flap after operation.
Artificial dermis was developed by Yannas and Burke in 1980. It is a membrane artificial skin and a synthetic tissue used to repair skin tissue [25,26]. Suzuki researched and improved the product and developed a new artificial dermis (PELNAC), which is widely used in scar shrinkage repair, excision of wounds caused by tumors, traumatic skin defects, peeling of skin flaps and other reasons,the effect evaluation shows that the good rate is 86%.In recent years,PELNAC has been widely used in some wounds with bone exposure after trauma. When the artificial dermis was transplanted to the wound with poor basal blood supply, the time of local vascularization was delayed than that of the wound with good basal blood supply.In this study, two debridement and VSD were performed to complete the wound bed preparation, so as to form a wide base with good blood supply around the wound, so as to ensure the vascularization of artificial dermis and the healing of flap. The blood supply of the flap is reliable. When the flap covers the artificial dermis, in a short time, the deep layer of the artificial dermis is filled with new collagen, and the sponge structure is replaced by true skin like tissue, so as to quickly complete the embedding process of steel plate or exposed bone.