Biomechanical Research On The Methods Of Preventing Chest Wall Deformity After Costal Cartilage Harvesting

BackgroundCostal cartilage grafts have been widely used in plastic surgery techniques such as auricular reconstruction,rhinoplasty,and craniofacial orthopedics.Chest wall deformity after auricular reconstruction has been a concern because of the high incidence attributed to large amount of costal cartilage harvested and an early age at operation.To prevent this complication,Kawanabe presented a new method of costal cartilage harvest and claimed that there was absolutely no postoperative chest wall deformity with this method.However,despite meticulous donor-site management and reconstruction according to the Kawanabe method,some author concluded that this method did not totally prevent early donor-site deformity especially in growing patients.Therefore,preventing the chest wall deformity after costal cartilage harvesting is still an area of research focus.According to the literature,biomechanical factors might be related to the chest wall deformity.However,most researches are focused on the tissue regeneration of costal cartilage,the relevant biomechanical researches are few.Investigating the intervening measures from the biomechanical view will help to provide new ideas and methods for preventing chest wall deformity after costal cartilage harvesting.Objectives1.To establish an animal model for investigating the repairing of costal cartilage defects.To evaluate the effects of different methods(reimplantation of cartilage blocks,reimplantation of cartilage strips and nonreimplantation)of dealing with costal cartilage defects to the morphology and tissue structure of reconstructed segments at the site of defects.2.To evaluate the effects of different methods(reimplantation of cartilage blocks,reimplantation of cartilage strips and nonreimplantation)of dealing with costal cartilage defects to the biomechanical properties of reconstructed segments at the site of defects.3.To evaluate whether restricting breathing movement through wearing elastic chest belt within half a year postoperatively could decrease the incidence of chest wall deformity after costal cartilage harvesting.Methods1.Twelve New Zealand white rabbits were randomized into two groups.A segment of costal cartilage of 15mm was harvested from bilateral fifth and sixth ribs with the perichondrium preserved intact in situ.The perichondrium was sutured to form a perichondrial pocket and dealt with nonreimplantation/reimplantation of cartilage blocks(left/right,5th rib),reimplantation of cartilage strips/reimplantation of cartilage blocks(left/right,6th rib).The amount reimplanted in each site was about 1/4 of the harvested cartilage.The diameter of the blocks/strips was about 0.5mm.The rabbits of either group were sacrificed at 16weeks and 24weeks postoperatively.The morphology and sizes of the reconstructed segments were evaluated and compared bilaterally.Histological examination was carried out to evaluate the tissue structure of the reconstructed segments.2.A three-point bending test was carried out to evaluate the biomechanical properties of the reconstructed segments.Effects of different treatments to the biomechanical properties of the reconstructed segments was assessed and compared.3.Assessing the contour of chests of the patients receiving the third-stage operation of auricular reconstruction,1 year after costal cartilage harvesting with history collection and physical examination.Summarizing and comparing the incidence of costal wall deformity by whether wearing elastic chest belt or not within half a year postoperatively.Results1.An animal mordel for investigating the repairing of costal cartilage defects was established.At 16th and 24th week postoperatively,the width of reconstructed segments was not different significantly between two sides of the same rib level(P>0.05).The reconstructed segments at 24th week was thinner than that at 16th week,the difference was statistically significant(P<0.05).Fibrous tissues were in majority in the donor site,and no regeneration of hyaline cartilage was observed.The tissue structure of the reconstructed segments was remarkably different with various treatment to the donor sites.2.At 16th and 24th weeks postoperatively,the modulus of elasticity in static bending of all reconstructed segments was lower than normal costal cartilage,the reconstructed segments with nonreimplantation was higher than that with reimplantation of cartilage blocks but was lower than that with reimplantation of cartilage strips.All the differences were statistically significant(P<0.05).In the aspects of stress-strain relationship and stress relaxation,the reconstructed segments with nonreimplantation were superior to that with reimplantation of cartilage blocks but inferior to that with reimplantation of cartilage strips.1.Thirty-eight eligible patients were enrolled in the study.The incidence of chest wall deformity in patients wearing chest elastic chest belt as requested for half a year was lower(64.7%vs.95.2%),and the difference was statistically significant(P=0.031).Conclusions1.In the early stage after costal cartilage harvesting,the defects of costal cartilage was mainly reconstructed by fibrous tissues which became mature and atrophy with time.The reimplanted autogenous costal cartilage could survive but the role of inducing regeneration of hyaline cartilage was not confirmed.Sufficient tissue would fill the defects after costal cartilage harvesting and the morphology and sizes of the reconstructed segments were not related to reimplantation of autogenous cartilage or not,when the amount of cartilage reimplanted was 1/4 of the original volume.However,remarkable differences were observed in the reconstructed segments with reimplanted different shape of autogenous cartilage or not,and might be the reason of the differences in biomechanical properties.2.In the early stage after costal cartilage harvesting,the biomechanical properties of the reconstructed segments were significantly inferior to the normal cartilage but would improve with time.Reimplantation of cartilage blocks(1/4 of the original volume)would not improve biomechanical properties of the donor site.The biomechanical properties of donor site with reimplantation of cartilage strips(1/4 of the original volume)were not as good as normal cartilages,but were significantly superior to that with reimplantation of cartilage blocks and nonreimplantation.3.Restricting breathing movement through wearing elastic chest belt within half a year postoperatively could decrease the incidence of chest wall deformity following costal cartilage harvesting through decreasing the traction force caused by respiratory muscles and intrathoracic negative pressure.