| Transfer of musculocutaneous flap, characterized by large tissue volume, rich bloodsupply and strong ability to resist infection, is one of the most common methods in plasticand reconstructive surgery. Latissimus dorsi musculocutaneous flap, as one of the mostcommon flaps, can be used for both free and pedicled transplantation for its constantanatomical location and large tissue volume. Historically, in order to study themusculocutaneous flap, rectus abdominis myocutaneous flap and gracilis myocutaneousflap in rat or pig were used as the classical model, and latissimus dorsi myocutaneous flapand deep inferior epigastric perforators of porine were getting popular in recent years. Theblood supply of musculocutaneous flap normally comes from their major pedicled vesselsafter transfer until the formation of neovascularization between the musculocutaneous flapand peripheral wound edge and recipient bed. So that, the pedicle can be ligated timelywithout affecting its viability. This feature of musculocutaneous flap is critical meaningfulfor pedicled and tubular flap. It was frequently used to repairing deep and large soft tissuedefects and chronic wound which is characterized by poor blood supply, malnutrition andsevere infection. In general, security division time of musculocutaneous flap is3to5 weeks postoperation. But we discovered that partial flap was last5weeks postoperation.However, when the pedicled musculocutaneous flap finish its neovascularization is stillunknown.To explore the right time of neovascularization and infer appropriate pedicledivision time after pedicled musculocutaneous flap transfer, our experiment was consistedof three parts. The first part: development of a preliminary experiment model of pedicledlatissimus dorsi musculocutaneous flap. A soft tissue defect, in size4×3cm, was made onrabbit’s head. Skull periosteum was removed to simulated exposed bone wound resultingfrom trauma. Then pedicled latissimus dorsi musculocutaneous flap was transferred torepair the defect, and the major pedicle was ligated at different time after operation. Tissuesamples were harvested for general and histologic evaluation to observe the survival rateand morphological changes of muscle fiber. To test the feasibility of this model and proveexperimental basis for the following research. The second part: establishment of theanimal model with the transfer of pedicled musculocutaneous flap. A size6×8cm softtissue defect was made in abdomen, and the base of defect was covered by a siliconegasket to simulate a wound with poor blood supply. Then pedicled latissimus dorsimusculocutaneous flap was transferred to cover the abdominal defect. To vertify thefeasibility of this model, its survival rate and clinical manifestation was assessed bygeneral and histologic observation. The third part: the exploration of the neovascularizationafter pedicled musculocutaneous flap transferred. To determine optimum pedicle divisiontime, the above model was applied in this experiment, and these pedicles were ligated atdifferent time after operation. Tissue samples were harvested to observe survival rate,morphological changes and the changes in micro vessel density. By assessing the aboveresults, the time needed to finish neovascularization and the optimum pedicle divisiontime can be inferred. This outcomes will provide theoretical basis for clinicalmusculocutaneous flap transfer.Part Ⅰ: Development of a preliminary experiment model with pedicledmusculocutaneous flapObjective To explore the establishment of animal model with rabbit skull exposed and verify the visibility of pedicled latissimus dorsi musculocutaneous flap transplantation torepair wound with poor blood supply.Methods15New Zealand rabbits were chosen randomly as experimental animals. Boneexposed wounds in size4cm×3cm were designed in rabbit calvarium in stageⅠ, whichsimulated bone exposed wound in clinic. Transferring pedicled latissimus dorsimusculocutaneous flap to repair the wound. Ligation surgeries were performed accordingto the different division time(1week,2weeks,3weeks) in stage Ⅱ,5rabbits in eachgroup. Tissue samples were harvested7days postoperation to observe the survival rateand morphological changes in each group.Results All myocutaneous flaps of the three groups survived well without flap loss. HEstaining was consistent with general observation. There is no muscle tissue observed ingroup1w and2w and degeneration muscle in group3w.Conclusion The transfer of pedicled latissimus dorsi musculocutaneous flap withthoracodorsal artery to repair exposed skull wound in rabbit is a viable model ofmusculocutaneous flap transplantation. But the wound of rabbit skull exposed was toosmall, which limited the volume of transferred latissimus dorsi muscle and was difficult tosimulate the repairing of large wound. Furthermore, the transferred flap can independentlysurvive without the pedicle vessel1week postoperation, which is not suitable for theresearch of division time.Part Ⅱ: Establishment of the animal model with pedicled musculocutaneous flapObjective To establish a poor blood supply wound by designing a tissue defect inabdomen and covering with silicon gasket. Transferring pedicled latissimus dorsimusculocutaneous flap to repair the wound and verifying its feasibility.Methods20New Zealand rabbits were chosen randomly as experimental animals.Abdominal wound in size6cm×8cm was designed in rabbit and covered with silicongasket, which simulated poor blood circulation. Transferring pedicled latissimus dorsimusculocutaneous flap to repair the wound. The animals was randomly divided into3weeks group,4weeks group,5weeks group and6weeks group according to samplingtimes,5rabbits in each group. Survival rate, histological examination and micro vessel density were carried out to evaluate the musculocutaneous flap.Results All musculocutaneous flaps in four groups survived well with no flap loss andmuscle appearance ruddy. HE and Masson staining showed the morphology of musclefiber is well. Skeletal muscle fibers are long cylindrical, multi-core, located in the musclecell periphery. The muscle of proximal was better than the distal intra-group. The microvessel density was different between-group(5w>4w>3w>2w) andintra-group(proximal＞middle＞distal), which was statistically significant.Conclusion The transfer of pedicled latissimus dorsi musculocutaneous flap withthoracodorsal artery in rabbit was a feasible model for musculocutaneous flap. This modelwill be especially usefull for detecting the effect of drugs, cells and neovacularization.Part Ⅲ：Exploration of the neovascularization after pedicled musculocutaneous flaptransferredObjective To explore neovascularization and optimum division time of pedicledmusculocutaneous flap transplantation repairing abdominal chronic wound.Methods32New Zealand rabbits were randomly selected as experimental animals.Pedicled latissimus dorsi musculocutaneous flaps were transferred to repair the woundin stage Ⅰ, and ligation surgeries were performed according to the different divisiontime(2weeks,3weeks,4weeks,5weeks) in stage Ⅱ,8rabbits in each group. Tissuesamples were acquired on day7after operation. Musculocutaneous flaps were evaluatedby survival rate, histological examination, micro vessel density and ultrastructureexamination.Results The difference of survival rate between-group5w＞4w＞3w＞2w and the resultwas statistically significant(P<0.05). HE and Masson staining was consistent with generalobservation, the morphology of muscle in group5w was much better than other groupswith muscle appearance ruddy. Skeletal muscle fibers are long cylindrical, multi-corewhich locate in the muscle cell periphery and the muscle of proximal was better than thedistal intra-group. Transmission electron microscopy showed the muscle of5w group hadnormal structure of muscle fiber, mitochondrial cristae and intima visible, Golgi apparatusand endoplasmic reticulum clear. While the group2w and3w had the opposite result showed that mitochondrial volume increasing, cristae swelling disorder, vacuolization,Golgi apparatus and endoplasmic reticulum swelling and glycogen granules increased inmatrix. Transmission electron microscopy showed the ultrastructure of5w group wasbetter than other groups. The micro vessel density was different between-group(5w>4w>3w>2w) and intra-group(proximal＞middle＞distal). The difference wasstatistically significant.Conclusion Musculocutaneous flap needed for5weeks to finish its neovascularization.So the optimum division time is5weeks after operation. But it can be appropriate toshorten the division time if the recipient bed or wound edge with good blood circulation. |
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