Cartilage tube formation by perichondrium: a new concept for tracheal reconstruction

Polymeric implant materials for the reconstruction of tracheal and pharyngeal mucosal defects in head and neck surgery

The existing therapeutical options for the tracheal and pharyngeal reconstruction by use of implant materials are described. Inspite of a multitude of options and the availability of very different materials none of these methods applied for tracheal reconstruction were successfully introduced into the clinical routine. Essential problems are insufficiencies of anastomoses, stenoses, lack of mucociliary clearance and vascularisation. The advances in Tissue Engineering (TE) offer new therapeutical options also in the field of the reconstructive surgery of the trachea. In pharyngeal reconstruction far reaching developments cannot be recognized at the moment which would allow to give a prognosis of their success in clinical application. A new polymeric implant material consisting of multiblock copolymers was applied in our own work which was regarded as a promising material for the reconstruction of the upper aerodigestive tract (ADT) due to its physicochemical characteristics. In order to test this material for applications in the ADT under extreme chemical, enzymatical, bacterial and mechanical conditions we applied it for the reconstruction of a complete defect of the gastric wall in an animal model. In none of the animals tested either gastrointestinal complications or negative systemic events occurred, however, there was a multilayered regeneration of the gastric wall implying a regular structured mucosa.

In future the advanced stem cell technology will allow further progress in the reconstruction of different kind of tissues also in the field of head and neck surgery following the principles of Tissue Engineering.

Anatomical 3D Fiber-Deposited Scaffolds for Tissue Engineering: Designing a Neotrachea

The advantage of using anatomically shaped scaffolds as compared to modeled designs was investigated and assessed in terms of cartilage formation in an artificial tracheal construct. Scaffolds were rapid prototyped with a technique named three-dimensional fiber deposition (3DF). Anatomical scaffolds were fabricated from a patient-derived computerized tomography dataset, and compared to cylindrical and toroidal tubular scaffolds. Lewis rat tracheal chondrocytes were seeded on 3DF scaffolds and cultured for 21 days. The 3-(4,5-dimethylthiazol-2yl)-2,5-dyphenyltetrazolium bromide (MTT) and sulfated glycosaminoglycan (GAG) assays were performed to measure the relative number of cells and the extracellular matrix (ECM) formed. After 3 weeks of culture, the anatomical scaffolds revealed a significant increase in ECM synthesis and a higher degree of differentiation as shown by the GAG/MTT ratio and by scanning electron microscopy analysis. Interestingly, a lower scaffold's pore volume and porosity resulted in more tissue formation and a better cell differentiation, as evidenced by GAG and GAG/MTT values. Scaffolds were compliant and did not show any signs of luminal obstruction in vitro. These results may promote anatomical scaffolds as functional matrices for tissue regeneration not only to help regain the original shape, but also for their improved capacity to support larger tissue formation.

Tracheal replacements: part 1

In this review, we summarize the history of tracheal reconstruction and replacement as well as progress in current tracheal substitutes. In Part 1, we cover the historical highlights of grafts, flaps, tube construction, and tissue transplants and address the progress made in tracheal stenting as a means of temporary tracheal support. This is followed in Part 2 by an analysis of solid and porous tracheal prostheses in experimental and clinical trials. We conclude Part 2 with a summary of recent efforts toward generating a bioengineered trachea. Finally, we provide an algorithm on the spectrum of options available for tracheal replacement.

SIS with tissue-cultured allogenic cartilages patch tracheoplasty in a rabbit model for tracheal defect

CONCLUSIONS

In the rabbit model, small intestinal submucosa (SIS) compounded with tissue-cultured allogenic cartilages appeared to be an efficacious method for the patch repair of partial circumferential tracheal defects instead of autologous grafts. SIS appears to be a safe and promising means of facilitating neovascularization and tissue regeneration. The long-term use of SIS and tissue-cultured allogenic cartilages warrants further investigation.

BACKGROUND

Tracheal defect reparation remains a challenging surgical problem that can require reconstruction using autologous grafts or artificial stents. This study was performed to evaluate the efficacy of SIS, a biocompatible, acellular matrix, compounded with different tissue-cultured allogenic cartilages, in the repair of a critical-size tracheal defect.

MATERIALS AND METHODS

A full-thickness defect (4 x 8 mm) was created in tracheal rings four to six in adult rabbits. A piece of 8-ply SIS sandwiched in thyroid cartilage, auricular cartilage, or without cartilage, respectively (designated experiment 1, 2, or 3, respectively), was sutured to the edges of the defect with interrupted 4-0 polypropylene sutures. In control animals, the defect was closed with lamina praetrachealis. All animals were followed until signs of dyspnea became apparent or for 4 or 12 weeks. After follow-up and euthanasia, the trachea was harvested and prepared for histologic evaluation using conventional techniques.

RESULTS

All animals tolerated the procedure well but two animals in group 1 (n=5), three in group 2 (n=5), and one in group 3 (n=5) had stridor after operation and expired within <1 month with different degrees of obstruction. The other animals in these groups and the control animals (n =3) all survived >1 month. Histologically, neovascularization of the patch was noted with moderate inflammation. The surface of the SIS patch was covered with a lining of ciliated epithelial cells. The tissue-cultured allogenic cartilages degraded to some extent.

Tracheal matrices, obtained by a detergent-enzymatic method, support in vitro the adhesion of chondrocytes and tracheal epithelial cells

Several attempts have been performed to achieve a suitable tracheal replacement for the treatment of different conditions characterized by a lack of sufficient tissue for surgical reconstruction. Actually, tracheal homografts can induce long-term stenosis and their growth potential is not known. Thus, in this work porcine tracheal matrices have been obtained by a detergent-enzymatic method. The treatment decreased the antigenicity of matrices which were able to support the in vitro adhesion of both chondrocytes and tracheal epithelial cells. On the contrary, only few cells were observed in tracheal matrices prepared with formalin, Thimerosal, and acetone, suggesting that the long-term stenosis occurring in vivo is probably because of an insufficient cell ingrowth. In summary, our results indicate that the detergent-enzymatic method allows us to obtain tracheal matrices which can function as a promising support to achieve an in vitro tissue-engineered cell-matrix construct.

Fetal tissue engineering: in utero tracheal augmentation in an ovine model

BACKGROUND/PURPOSE

This study was aimed at comparing fetal tissue engineering with autologous free grafting in an ovine model of in utero tracheal repair.

METHODS

Chondrocytes were isolated from both elastic and hyaline cartilage specimens harvested from fetal lambs and expanded in vitro. Cells were seeded dynamically onto biodegradable scaffolds, which then were maintained in a rotating bioreactor for 6 to 8 weeks. Constructs subsequently were implanted into fetal tracheas (n = 15), in a heterologous fashion (group I). In group II, fetuses (n = 5) received autologous free grafts of elastic cartilage harvested from the ear as tracheal implants. In vivo specimens were harvested for histologic analysis at different time-points postimplantation.

RESULTS

In the 12 of 15 surviving fetuses of group I, all constructs were found to resemble normal hyaline cartilage, engraft well despite their heterologous origin, and display time-dependent epithelialization derived from the native trachea. All autologous free grafts were engrafted and epithelialized at birth, retaining histologic characteristics of elastic cartilage, but were more deformed than engineered constructs. Of the lambs allowed to reach term, 5 of 5 in the engineered group and 4 of 5 in the free graft group could breathe spontaneously.

CONCLUSIONS

(1) Tissue-engineered cartilage, as well as autologous free grafts, can be implanted successfully into the fetal trachea, resulting in engraftment and function. (2) Engineered cartilage provides enhanced structural support after implantation into the fetal trachea when compared with free grafts. Prenatal tracheoplasty may prove useful for the treatment of severe congenital tracheal malformations.

Tracheal replacement: a critical review

This review discusses the need for tracheal replacement, distinct from resection with primary anastomosis, the requirements for replacement, and the many efforts over the past century to accomplish this goal experimentally and clinically. Approaches have included use of foreign materials, nonviable tissue, autogenous tissue, tissue engineering, and transplantation. Biological problems in each category are noted.

Tissue engineering: a 21st century solution to surgical reconstruction

Tissue engineering has emerged as a rapidly expanding approach to address the organ shortage problem. It is an "interdisciplinary field that applies the principles and methods of engineering and the life sciences toward the development of biological substitutes that can restore, maintain, or improve tissue function." Much progress has been made in the tissue engineering of structures relevant to cardiothoracic surgery, including heart valves, blood vessels, myocardium, esophagus, and trachea.

Prefabrication of an axial bio-synthetic flap for circumferential tracheal defect reconstruction

The aim of this study was to prefabricate an axial bio-synthetic flap for reconstruction of circumferential tracheal defects in a rabbit model. Two series of experiments were performed. In the first set of experiments axial island bio-synthetic flaps were prefabricated. These consisted of an inner island de-epithelialised fasciocutaneous flap from a rabbit's ear and an outer polytetrafluoroethylene vascular graft. The flaps were buried at the base of the rabbit's ear for periods of 1, 2 and 3 weeks (groups A, B and C, respectively), 10 flaps per group. Only one flap in group C failed to survive. Clinical and histological assessment, at the completion of each time period, showed that only the viable flaps of group C developed all the characteristics needed for a tracheal substitute. In the second set of experiments the prefabricated bio-synthetic flaps were transferred to the rabbit's neck by means of microvascular anastomoses. Ten such free flaps were buried at the rabbit's neck for 3 weeks (group D). Eight of the flaps remained viable and all the viable flaps had characteristics similar to those of group C. These results demonstrate the feasibility of creating a prefabricated axial bio-synthetic flap (island or free), over a 3-week period, possessing the characteristics needed for a tracheal substitute in a rabbit model.

Long-term growth of a vascularized auricular perichondrocutaneous flap in laryngotracheal reconstruction

This study addresses the potential for ongoing cartilage proliferation after repair of laryngotracheal stenosis with vascularized perichondrium. We randomly assigned 32 New Zealand white rabbits to 1 of 3 groups: group 1 (early cartilage growth, n = 10), group 2 (long-term cartilage growth after pedicle ligation, n = 11), and group 3 (long-term cartilage growth without pedicle ligation, n = 11). Bilateral auricular perichondrocutaneous flaps were elevated and transposed into full-thickness anterior tracheal wall or anterior cricothyroid membrane defects. Six weeks after elevation of the flap, animals were randomly assigned to undergo ligation of either the right or left vascular pedicle (group 2), with the contralateral auricular flap used as a matched control (group 3). Neochondrogenesis was present at 6 weeks in group 1 (0.74 +/- 0.14 mm, n = 12 ears). Cartilage thickness did not differ between groups 2 and 3 one year after ligation of the vascular pedicle: group 2 (0.48 +/- 0.24 mm, n = 18) versus group 3 (0.42 +/- 0.12 mm); P > 0.05. We conclude that in the rabbit model, chondrogenesis did not appear to be ongoing and did not result in late stenosis of the reconstructed airway. Furthermore, delayed ligation of the vascular pedicle neither inhibited nor stimulated cartilage proliferation.

Efficacy of perichondrium and a trabecular demineralized bone matrix for generating cartilage

A pedicled auricular perichondrial flap wrapped around trabecular demineralized bovine bone matrix can generate an autologous cartilage graft. In earlier experimental studies, it was demonstrated that this graft could be used for nasal and cricoid reconstruction. It was assumed that the vascularization of the perichondrial flap was obligatory, but it was never proven that the flap should be pedicled. Moreover, for clinical use, the dimensions of the auricle would set restrictions to the size of the graft generated. Therefore, the possibility to generate cartilage with a composite graft of a free perichondrial flap wrapped around demineralized bovine bone matrix, by using young New Zealand White rabbits, was studied. This composite graft was implanted at poorly (subcutaneously in the abdominal wall; n = 12), fairly (subcutaneously in the pinna; n = 12), and well-vascularized sites (quadriceps muscle; n = 12). As a control, trabecular demineralized bovine bone matrix was implanted without perichondrial cover. Half of these grafts (n = 6) were harvested after 3 weeks, and the remaining grafts (n = 6) after 6 weeks of implantation. In histologic sections of these grafts, the incidence of cartilage formation was scored. Furthermore, the amount of newly formed cartilage was calculated by computerized histomorphometry. Trabecular demineralized bovine bone matrix without perichondrial cover demonstrated early resorption; no cartilage or bone was formed. In demineralized bovine bone matrix wrapped in perichondrium, early cartilage formed after 3 weeks at well- and fairly vascularized sites. No cartilage could be detected in grafts placed at a poorly vascularized site after 3 weeks; minimal cartilage formed after 6 weeks. In summary, the highest incidence of cartilage formed when trabecular demineralized bovine bone matrix was wrapped either in a pedicled auricular perichondrial flap or in a free perichondrial flap, which was placed at a well-vascularized site. Second, a significantly higher percentage of the total area of the graft was cartilaginized at well-vascularized sites after 3 weeks. The newly generated cartilage contained collagen type II and proteoglycans with hyaluronic acid binding regions, whereas collagen type I was absent, indicating the presence of hyaline cartilage. This study demonstrates that new cartilage suitable for a graft can be generated by free perichondrial flaps, provided that the site of implantation is well vascularized. Consequently, the size of such a graft is no longer limited to the dimensions of the auricle.

Reconstruction of the rabbit trachea with vascularized auricular perichondrium

Success in laryngotracheal reconstruction has been limited, in part, by the lack of an ideal grafting material. Perichondrium is thin, pliable, and highly vascularized and has the ability to generate new cartilage providing rigid support. These qualities make vascularized perichondrium potentially the ideal grafting material for circumferential airway stenosis. A pedicled vascularized flap of auricular perichondrium was used in a rabbit model (n = 39) to reconstruct a near-circumferential tracheal defect without a tracheostomy. A stent was used to support the reconstructed airway for 6 weeks, after which time it was removed by direct laryngoscopy. Animals were observed for an additional 6 weeks prior to sacrifice. Qualitative and quantitative histologic analysis of neochondrogenesis is reported. Vascularized perichondrium and periosteum show promise as potential grafts for reconstruction of circumferential tracheal defects.

Generation of cartilage from auricular and rib free perichondrial grafts around a self-reinforced polyglycolic acid mould in rabbits

The generative potential of free perichondrial grafts from rabbit auricular and rib cartilage around a self-reinforced polyglycolic acid (SR-PGA) rod was examined in eight growing rabbits. A 15 x 15 mm perichondrial graft was dissected away from the posterior side of each auricular cartilage. One graft was wrapped around a 1.1 x 10 mm SR-PGA rod and the other served as a control and was shaped into a tube without an implant. Fifth rib cartilages were then resected subperichondrially on both sides. The remaining perichondrium on the other side was wrapped around a 1.1 x 10 mm SR-PGA rod, while the other served as a control and was shaped into a tube without an implant. All the grafts were placed inside pectoralis major muscles. Grafts were biopsied six weeks postoperatively. Neocartilage formation was seen in all grafts with one exception on both the implant and control sides. It formed a tube-like structure around the implant in four cases after grafting of auricular perichondrium and in three cases after grafting of rib perichondrium. New bone formation was also observed. SR-PGA implants did not seem to disturb the generative potential of perichondrium.

Experimental tracheal replacement using tissue-engineered cartilage

The authors tested the feasibility of using tissue-engineered cartilage, grown in the shape of cylinders, for replacing large circumferential defects of the cervical trachea in rats. Chondrocytes obtained from the shoulder of newborn calves were seeded onto a synthetic nonwoven mesh, 100 microns thick, of polyglycolic acid fibers 15 microns in diameter, cut into pieces of 2.5 x 4 cm. Twenty cell-polymer constructs were wrapped around silastic tubes and implanted into 10 nude mice for 4 weeks. Specimens were then excised and evaluated grossly and histologically for the presence of new cartilage, and biomechanically for their ability to resist collapse upon application of negative pressure. Six cylinders of tissue-engineered cartilage were then sutured into large circumferential defects created in the cervical tracheas of nude rats to replace the excised trachea. Implantation of cell-polymer constructs resulted in the formation of cylinders of hyaline cartilage. When placed within the lumen of a segment of bowel denuded of its mucosal lining, the hollow cylinders resisted collapse in all instances upon administration of negative 200 mm Hg pressure. The cartilage was grossly and histologically identical to that from which the cells had been initially isolated. Four of the six animals receiving these cartilage cylinders as tracheal replacements survived the procedure and were able to breathe in an unassisted fashion. Three of these animals never recovered fully from the anesthetic and the operation, and expired at 24, 48, and 72 hours. The fourth animal fully recovered from the procedure, and breathed spontaneously for 1 week, with no apparent limitations. Increasing respiratory distress then developed, and the animal died.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental tracheal tube created with vascularized fascia

An experimental fascial transferable bed was developed in the rabbit model. This tissue is reliable in bringing a viable mucosal graft inside the larynx. A vascular connective tissue sheet with full-thickness mucosa and autogenous cartilage for external support are needed. In this study a tracheal tube was preformed to study the use of autogenous cartilage as support for a circumferential lumen.

Effects of free perichondrial graft replacement of epiphyseal cartilage on bone growth

An experimental study in 24 lambs was carried out to find an alternative tissue for the distal epiphyseal cartilage of the femur. The animals were divided into three groups. In the first group (n = 12) the left femoral distal epiphyseal cartilage was completely removed and replaced by a free perichondrial graft taken from the distal half of the scapula. In the second group (n = 6) the epiphyseal cartilage was removed and was not replaced by any tissue. The third group (n = 6) was used as control. After six months the legs in the first and third groups were of the same normal length while the legs in the second group were significantly shorter. We conclude that free perichondrial graft seems to be able to replace the epiphyseal cartilage and prevent retardation of growth.

Perichondrial microvascular free transfer: creation of a compound flap for laryngeal reconstruction in rabbits

A free revascularized compound perichondrial flap was used over an intralaryngeally placed stent for reconstruction of a frontal laryngeal defect. The microvascular flap replaced the cartilaginous and mucosal defect. Short-term results showed successful reconstruction with a patent airway and viable mucosa. The vascularized sheet of perichondrium was not chosen for its neochondrogenetic effect, but it served as a vascular bed, nourishing the mucous and cartilaginous components in the compound flap. It is suggested that for clinical purposes the reliable fascia forearm flap, which is available in large amounts, can be used as a transferable vascularized bed with a thickness comparable to that of the perichondrial flap.

The role of polyglycolic acid rods in the regeneration of cartilage from perichondrium in rabbits

The role of polyglycolic acid (PGA) rods in the regeneration of cartilage from perichondrium was investigated in 12 growing rabbits. The fifth rib cartilage was resected subperichondrially from both sides. A 10 X 1.5 mm self-reinforced polyglycolic acid (SR-PGA) rod was inserted on one side to replace the resected cartilage and the retained perichondrium was sutured around the implant. On the control side the perichondrium was shaped into a tube without an implant. Samples were taken 4, 12, and 20 weeks after operation. Pronounced neocartilage formation was seen on both sides, and had grown to form a tube around the implant. Also new bone formation was seen in 12 and 20 weeks. Foreign body reaction was seen inside the implants in every animal.

Experimental reconstruction of the canine trachea with a free revascularized small bowel graft

Extensive tracheal stenotic lesions caused by tracheomalacia or neoplasms represent a surgical challenge. Segmental tracheal substitution is sometimes required to obtain radical cure. We present an experimental study of 27 dogs undergoing replacement of the cervical trachea using a vascularized small bowel segment as a tubular graft. A silicone stent was placed in the lumen of the intestinal fragment and was removed the second week after operation. Endoscopic and histological examinations were performed between the first week and second month after operation, and rigidity of the graft was assessed in all cases. No evidence of anastomotic stricture or mucous formation was found. Microscopic examination showed the substitution of bowel mucosa by squamous epithelium as well as the development of connective tissue favoring the fixation of the skeletal muscular structures of the neck to the serous layer of the graft, thus avoiding collapse of the new airway.

The potential of adult human perichondrium to form hyalin cartilage in vitro

The usefulness of adult human perichondrium for the restoration of articular cartilage defects depends on the potential to form hyalin cartilage. In order to evaluate the capacity of adult human perichondrium to form hyalin cartilage in vitro, perichondrium of the rib of eight adult human beings was cultured in vitro. After removal of residual cartilage, perichondrial explants were cultured for 7 or 10 days. The explants were histologically examined using specific stains to prove the presence of glycosaminoglycans (GAGs) normal for hyalin cartilage. Clear differentiation of perichondrial cells towards chondrocytes was noted. The chondrocytes synthesized new matrix substances normally present in hyalin cartilage. This investigation supports the usefulness of adult human rib perichondrium for the restoration of cartilage defects. Due to the enormous potential of the rib perichondrium to form hyalin cartilage in vitro, even defects in joints with a rather thick cartilage layer might be restored using this biological material.

Formation of chondroitin sulphate proteoglycan in cartilage regenerated from free perichondrial graft

Perichondrium from rabbit auricular or rib cartilage was used as a free autogenous graft and transplanted either to the subcutaneous tissue of the back of the rabbit or to an experimental defect in the femur condyles. Outgrowth of new tissue, morphologically indistinguishable from cartilage, was observed after six weeks. Inorganic 35SO4, administered in vivo, was incorporated into the newly formed tissue. The labelled products were isolated, identified, and compared with those obtained from authentic cartilage of auricular, rib or joint surfaces. The products of newly formed cartilage were similar to those of authentic cartilage. The results support earlier morphological findings, indicating that perichondrium from rib cartilage has a better ability to regenerate than auricular perichondrium. The synovial environment seems to have a positive effect on the generation of cartilage.

Repair of subglottic stenosis with a free perichondrial graft

A case of tracheal stenosis was reconstructed, after trough formation, with a chondromucosal flap which was developed by submucous perichondrial grafting. At the first stage, a free perichondrial graft from the pinna was transplanted into the buccal submucosal layer. About 10 months later, when sufficient neocartilage had formed, the chondromucosal composite graft was transferred from the buccal region to the paratracheal subcutaneous region with the mucosa facing deeply. Finally, 4 weeks later the tracheal trough was closed with a composite rotation flap which incorporated the skin, neocartilage and mucosa. The postoperative course was uneventful and a wide tracheal lumen with a firm framework and mucous lining was confirmed by both fibrescopic and radiographic examination.

The development of bone after perichondrial grafting: an experimental study using ear and rib perichondrium in rabbits

The development of bone after perichondrial grafting was investigated using rabbit ear and rib perichondrium. Sixty-four white adult female rabbits were used. Both free and vascularised perichondrial grafts were undertaken. In each case the chondrogenic potential of perichondrium was proved. Furthermore, when the perichondrium was vascularised or grafted in recipient sites having good blood circulation, the development of large areas of bone was observed around the regenerated cartilage.

Cartilage grafts--present status

Cartilage grafts have been in use for almost a century and have proved their usefulness. Many questions about immunology, survival, growth, and role of perichondrium are still debated. We are presenting a review of the literature and of our experimental work on cartilage grafts. Ear cartilage was transplanted from 28 young New Zealand rabbits subcutaneously in the chest walls. The grafts were divided into 1) bare cartilage, 2) perichondrium, 3) cartilage covered with perichondrium on one side, and 4) cartilage covered with perichondrium on both sides. The grafts were measured in length and weight before transplantation, and at 2 and 4 months after transplantation; they were compared to a control piece of cartilage tagged in situ. Histologic examination was performed on all retrieved grafts. Transplanted cartilage survival was good in over 75% of cases; however, cartilage production from perichondrium was minimal and no growth was noticed in any of the grafts.

Experimental laryngeal reconstruction with preformed composite graft

The use of perichondrial grafts for reconstruction of the thyroid cartilage of the larynx was studied in two series of rabbits. In the first pilot study the thyroid cartilage was replaced by a cartilage performed by the neochondrogenic effect of an auricular perichondrial graft set into the defect on a subcutaneous flap. When this transplantation technique proved successful, another series was performed where a laryngeal defect of the thyroid cartilage and the underlying mucosa were replaced by a preformed composite graft. This composite graft consisted of a biological support of newly formed cartilage from the neochondrogenic effect of a free perichondrial graft and mucosal lining made of a retention cyst from a free graft of oral mucosa. The newly formed composite graft was transferred to set into the laryngeal defect on a subcutaneous flap. The reconstruction was successful and all the rabbits survived, with no respiratory distress. The newly formed cartilage offered sufficient support to the reconstructed larynx. The lining formed from the mucosa of the retention cyst consisted of undiffered stratified squamous cells. This lining membrane was sufficient to control the fibrous tissue response and maintain patency of the restored lumen.

[Regeneration of the trachea following partial or total replacement by synthetic resorbable material (polyglactin 910)]

Though longer distances of the trachea and segments of the bronchi can be resected and the blunts be joined by end-to-end anastomosis, the replacement of parts of the wall of the tracheobronchial tree may become necessary. Alloplastic not absorbable material like silicone was not successful because of its disposition to infections and development of stenosis. Absorbable suture material proved to be suitable in tracheal surgery and it was shown that texture of Polyglactin 910 (Vicryl) could even be used for replacement of the aortic wall. We used weaved tubes of 2.5 mm diameter as prostheses of this material. We partly resected the trachea in the throat of 30 rats and in a microsurgical procedure we replaced in 17 animals the whole circumference by the tube shaped prosthesis and in 13 animals a window in the trachea by a patch, cut from such a prosthesis. By pneumonia or granulation in the anastomosis region 11 rats died or had to be sacrificed untimely. The others survived in several periods up to 10 weeks. At the time of autopsy starting after 3 weeks, a newly formed trachea could be demonstrated, which is covered more and more with respiratory epithelium. By light microscopic and scanning microscopic examinations, the development of a new wall, similar to the normal one, was seen. This wall lacks only mucus glands, but contains structures similar to hyaline cartilage. Our absorbable prosthesis cannot prevent the development of stenosis by overshooting granulation in the early postoperative period, but very soon the material is absorbed and replaced by a structure similar to the normal wall. After biodegradation, problems appear by instability of the new tissue, because of collapsing during inspiration. This problem could be solved by covering the prosthesis by an additional supporting scaffold.

Thoracic trauma. Newer concepts

Thoracic trauma induces pulmonary injury by functional as well as by structural damage. Injury at the cellular level causes changes seen 24 to 48 hours after initial trauma. Treatment should be aimed at stabilizing the patient upon initial presentation, and one should be aware of potential problems that may arise as the injury progresses. An animal with tracheobronchial tree injury is usually presented a few days after the initial injury with a client complaint of dyspnea. The only treatment is surgical repair.