The effect of a unilateral costochondral graft on the growth of the marmoset mandible

Long-Term Outcomes and Growth Analysis of Costochondral Grafts for Hemifacial Microsomia: 24-Year Experience of a Single Surgeon

BACKGROUND

Costochondral grafts (CCGs) can be used in mandibular reconstruction of Kaban-Pruzansky IIB/III hemifacial microsomia (HFM). Their growth is variable, occasionally necessitating secondary surgery. This study examined one surgeon's 24-year experience to better quantify long-term outcomes and surgical care required in CCG reconstruction of HFM mandibles.

METHODS

Serial 3-dimensional computed tomography scans, from preoperative to most recent, were analyzed in patients with a minimum of 4 years of clinical follow-up after CCG reconstruction. Graft/ramus height, length, volume, bilateral mandibular body length, and chin deviation were measured. Changes in measurements were analyzed preoperatively, immediately postoperatively, at the most recent imaging before secondary surgery, and at the most recent imaging overall. Growth rates per measure were calculated using scans after CCG but before secondary surgery.

RESULTS

Thirteen patients were analyzed. Median (SD) clinical follow-up was 10.0 (5.1) years. One patient developed temporomandibular joint ankylosis secondary to stacked-graft malposition, which was repaired without further complications. CCG reconstruction led to immediate improvement in graft/ramus height ( P = 0.03), length ( P = 0.002), and volumetric symmetry ( P = 0.02). No difference was found between graft and native ramus height ( P = 0.4) or length measures ( P = 0.5), whereas graft volume and the affected mandibular body grew significantly more slowly. According to the latest imaging, 63% of patients required secondary surgery, including distraction osteogenesis or orthognathic surgery, due to differential graft or hemimandible growth behavior. Based on the most recent clinical follow-up, this proportion increased to 93%.

CONCLUSIONS

CCGs provide significant short-term mandibular and facial symmetry improvement in HFM IIB/III. Long-term analysis reveals frequent undergrowth requiring secondary intervention to promote and maintain symmetry.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

Analysis of the effect on costochondral graft for TMJ ankylosis with jaw deformities in pediatrics

OBJECTIVES

To evaluate the effects of costochondral grafting (CCG) used for temporomandibular joint ankylosis (TMJA) in growing patients.

MATERIALS AND METHODS

Pediatric patients with TMJA treated by CCG from 2010.5 to 2021.7 were included in the study. CT scans were performed before and after operations with at least 1 year follow-up. The height of the mandibular ramus, menton deviation or retraction, osteotomy gap, etc. were measured by ProPlan CMF1.4 software. CCG growth, resorption, and relapse were evaluated and analyzed with influencing factors such as age, ostectomy gap, etc. by generalized estimating equation.

RESULTS

There were 24 patients (29 joints) with an average age of 6.30 ± 3.13 years in the study. After operation, the mandibular ramus was elongated by 5.97 ± 3.53 mm. Mandibular deviation or retrusion was corrected by 4.82 ± 2.84 mm and 3.76 ± 2.97 mm respectively. After a mean follow-up of 38.91 ± 29.20 months, 58.62% CCG grew (4.18 ± 7.70 mm), 20.69% absorbed (2.23 ± 1.16 mm), and 20.69% re-ankylosed. The re-ankylosis was negatively correlated with the osteotomy gap (OR:0.348,0.172-0.702 95%CI, critical value = 6.10 mm). CCG resorption was positively correlated with the distance of CCG ramus elongation (OR:3.353,1.173-9.586 95%CI, critical value = 7.40 mm).

CONCLUSIONS

An adequate osteotomy gap and CCG ramus elongation distance are the key factors for successful treatment of TMJA with jaw deformities in growing patients.

CLINICAL RELEVANCE

TMJA affects mouth opening and jaw development in pediatric patients. The most common autogenous bone graft for pediatric patients is CCG due to its growth potential, convenient access and easy contouring. Also, it can simultaneously reconstruct the TMJ and improve jaw deformity by lengthening the mandibular ramus. But the growth of CCG is unpredictable. In this study, we explored several factors that may affect the absorption and re-ankylosis of CCG, expecting to provide several suggestions to improve future CCG treatment.

Controversial Aspects of Diagnostics and Therapy of Arthritis of the Temporomandibular Joint in Rheumatoid and Juvenile Idiopathic Arthritis-An Analysis of Evidence- and Consensus-Based Recommendations Based on an Interdisciplinary Guideline Project

Introduction: Due to potentially severe sequelae (impaired growth, condylar resorption, and ankylosis) early diagnosis of chronic rheumatic arthritis of the temporomandibular joint (TMJ) and timely onset of therapy are essential. Aim: Owing to very limited evidence the aim of the study was to identify and discuss controversial topics in the guideline development to promote further focused research. Methods: Through a systematic literature search, 394 out of 3771 publications were included in a German interdisciplinary guideline draft. Two workgroups (1: oral and maxillofacial surgery, 2: interdisciplinary) voted on 77 recommendations/statements, in 2 independent anonymized and blinded consensus phases (Delphi process). Results: The voting results were relatively homogenous, except for a greater proportion of abstentions amongst the interdisciplinary group (p < 0.001). Eighty-four percent of recommendations/statements were approved in the first round, 89% with strong consensus. Fourteen recommendations/statements (18.2%) required a prolonged consensus phase and further discussion. Discussion: Contrast-enhanced MRI was confirmed as the method of choice for the diagnosis of TMJ arthritis. Intraarticular corticosteroid injection is to be limited to therapy-refractory cases and single injection only. In adults, alloplastic joint replacement is preferable to autologous replacement. In children/adolescents, autologous reconstruction may be performed lacking viable alternatives. Alloplastic options are currently still considered experimental.

Evaluation of Success of Transport Disc Distraction Osteogenesis and Costochondral Graft for Ramus Condyle Unit Reconstruction in Pediatric Temporomandibular Joint Ankylosis

PURPOSE

The costochondral graft (CCG) is considered the reference standard for pediatric temporomandibular joint reconstruction. It has the disadvantages of unpredictable growth, donor site morbidity, and the need for intermaxillary fixation. It has been reported that transport disk distraction osteogenesis (TDDO) can result in the formation of a neocondyle and disc. We performed a randomized trial to measure and compare clinically relevant outcomes of ramus-condyle unit (RCU) reconstruction using CCG and TDDO for pediatric temporomandibular joint ankylosis (TMJA).

MATERIALS AND METHODS

In the present randomized controlled trial (block randomization with a variable block size), pediatric patients with unilateral, nonrecurrent TMJA aged 3 to 16 years who had presented to our unit from December 2015 to June 2017 were enrolled. Instead of temporalis myofascial flap interposition, a buccal fat pad was used to fill the gap created by osteoarthrectomy. The primary outcome parameter was mouth opening. A mouth opening of at least 25 mm at the median follow-up point was considered success. The secondary outcome parameters were occlusion, laterotrusion, protrusion, reankylosis, neocondyle, chin deviation, facial asymmetry, midline shift, and neo-disc formation. Data were analyzed using the independent t test and rank sum test.

RESULTS

A total of 24 patients were enrolled in the CCG and TDDO groups (n = 12 in each group). Trauma (40.9%) was the most common etiology with a slight male preponderance (59.09%). The mean age was 10.32 ± 2.85 years. The average distraction achieved in the TDDO group was 10.42 mm. The median follow-up duration was 31.5 months (range, 24 to 39 months). The mean preoperative maximal incisal opening had improved from 8.5 ± 4.1 and 9.5 ± 7.1 mm in the CCG and TDDO groups preoperatively to 35.7 ± 2.7 and 34.4 ± 8.9 mm, respectively, at the median follow-up point (P < .005). RCU reconstruction with both modalities resulted in improvement in all the parameters; however, the intergroup comparison showed statistically non-significant differences. No reankylosis or open bite was found. The 3-hour delayed gadolinium-enhanced magnetic resonance imaging scan showed successful neo-disc formation.

CONCLUSIONS

Similar success can be achieved in RCU reconstruction using either CCG or TDDO for pediatric TMJA. Both techniques have some advantages and disadvantages. RCU reconstruction using CCG or TDDO results in formation of a neocondyle, maintenance of occlusion, and correction of facial asymmetry.

Ankylosis of the Temporomandibular Joint and Reconstruction With a Costochondral Graft in a Patient With Juvenile Idiopathic Arthritis

Juvenile idiopathic arthritis (JIA), the most common inflammatory autoimmune rheumatic disease in children, consists of a heterogeneous group of diseases with 7 distinct subtypes. Involvement of the temporomandibular joint (TMJ) in JIA varies from 17% to 87%, and can alter craniofacial growth due to damage to the condylar growth center. This study was a literature review and clinical report of bilateral ankylosis of the TMJ in a 13-year-old patient with polyarticular JIA. Temporomandibular joint reconstruction with a costochondral graft was carried out. The surgery was uneventful and the patient developed a mouth opening of 40 mm during the postoperative period of 24 months. The authors concluded that treatment of TMJ ankylosis should be surgical with removal of the ankylotic mass, and when necessary, joint reconstruction in patients undergoing a growth phase. Costochondral graft is still the gold standard due to its biological similarity and growth potential in patients with JIA. Research and early diagnosis of TMJ diseases should be carried out, because the earlier the identification of the disease, the better the chances of reducing its devastating effects, thus avoiding the worst possible outcome: TMJ ankylosis.

Potential Indications for Tissue Engineering in Temporomandibular Joint Surgery

PURPOSE

Musculoskeletal tissue engineering has advanced to the stage where it has the capability to engineer temporomandibular joint (TMJ) anatomic components. Unfortunately, there is a paucity of literature identifying specific indications for the use of TMJ tissue engineering solutions. The objective of this study was to establish an initial set of indications and contraindications for the use of engineered tissues for replacement of TMJ anatomic components.

FINDINGS

There was consensus among the authors that the management of patients requiring TMJ reconstruction as the result of 1) irreparable condylar trauma, 2) developmental or acquired TMJ pathology in skeletally immature patients, 3) hyperplasia, and 4) documented metal hypersensitivities could be indications for bioengineered condyle and ramus TMJ components. There was consensus that Wilkes stage III internal derangement might be an indication for use of a bioengineered TMJ disc or possibly even a disc-like bioengineered "fossa liner." However, there was some controversy as to whether TMJ arthritic disease (e.g., osteoarthritis) and reconstruction after failed alloplastic devices should be indications. Further research is required to determine whether tissue-engineered TMJ components could be a viable option for such cases. Contraindications for the use of bioengineered TMJ components could include patients with TMJ disorders and multiple failed surgeries, parafunctional oral habits, persistent TMJ infection, TMJ rheumatoid arthritis, and ankylosis unless the underlying pathology can be resolved.

CONCLUSIONS

Biomedical engineers must appreciate the specific indications that might warrant TMJ bioengineered structures, so that they avoid developing technologies in search of problems that might not exist for patients and clinicians. Instead, they should focus on identifying and understanding the problems that need resolution and then tailor technologies to address those specific situations. The aforementioned indications and contraindications are designed to serve as a guide to the next generation of tissue engineers in their strategic development of technologies to address specific clinical issues.

Management of temporomandibular joint ankylosis

Temporomandibular joint (TMJ) ankylosis is a pathologic condition where the mandible is fused to the fossa by bony or fibrotic tissues. This interferes with mastication, speech, oral hygiene, and normal life activities, and can be potentially life threatening when struggling to acquire an airway in an emergency. Trauma is the most common cause of TMJ ankylosis, followed by infection. Diagnosis of TMJ ankylosis is usually made by clinical examination and imaging studies. The management goal in TMJ ankylosis is to increase the patient's mandibular function, correct associated facial deformity, decrease pain, and prevent reankylosis.

[Facial asymmetries and their skeletal component]

The diagnosis and treatment of facial asymmetries is one of the most difficult challenges in orthognathic surgery. In some cases, the involvement of soft tissue defects or, in other cases, an associated basi-cranial asymmetry can complicate the management. The influence of various components of the cephalic end in the development of the face requires a thorough clinical and radiographic examination including the overall posture of the patient. The causes are multiple: congenital, constitutional, acquired with an important esthetic, functional, and psychological and social impact. The classification of these asymmetries can only be incomplete and purely didactic because of the multiplicity of clinical forms. Two elements are mandatory for the diagnosis and surgical treatment: first, the anterior clinical and radiological "craniofacial cross" established from the midline or midplane of the face; second, the clinical and radiological orientation of the maxillary and mandibular occlusal transverse and sagittal planes. The surgical techniques are the same as in conventional orthognathic surgery except for those used for the correction of the vertical posterior dimension of the face: condylectomy, lengthening osteotomy of the mandibular ramus, costochondral graft, and free flap. The contribution of 3D vision of the facial skeleton and its possibilities of measurement have improved the assessment of skeletal structure displacement during surgery. However, traditional radiographic examinations are still useful for pre and postoperative comparison and also to assess results. Computer simulation and computer-assisted surgery should allow achieving better and more stable results because of their reliability and easy access.

Selecting reconstruction option for TMJ ankylosis: a surgeon's dilemma

OBJECTIVES

The aim of this study was to compare the outcome of reconstruction options adopted for the management of temporomandibular joint (TMJ) ankylosis.

PATIENTS AND METHODS

This retrospective cohort study consisted of a sample of patients with TMJ ankylosis diagnosed clinically and radiologically. Depending upon the reconstruction provided, the cases were divided into 2 groups. Group I includes the cases treated by excision of ankylosed mass and interposition of temporalis myofascial flap. In group II, the cases were treated by excision, temporalis myofascial flap interposition, and reconstruction of ramus condylar unit (RCU). Two different methods of reconstruction were used, costochondral graft (CCG) (group IIa) and distraction osteogenesis (group IIb). The outcome variables were range of jaw motion, overgrowth of CCG, reankylosis, and other complications. Data analyses included appropriate univariate and bivariate statistics.

RESULTS

The average mouth opening achieved in both groups was 36 mm. Failure was observed in 3 patients, 1 from group I and 2 from group IIa. One case of bilateral ankylosis and 2 cases of unilateral ankylosis had recurrence. No overgrowth of CCG was observed.

CONCLUSIONS

In cases with no or minimal mandibular deformity, interpositional arthroplasty with temporalis myofascial flap is a good option without a second surgical wound. However, in younger patients, joint reconstruction with both costochondral graft and distraction osteogenesis of RCU is more appropriate and had similar results. The failure of treatment was due to noncompliance to postsurgical physiotherapy rather than the selection of reconstruction options.

Management of temporomandibular ankylosis--compromise or individualization--a literature review

Temporomandibular joint ankylosis is defined as bony or fibrous adhesion of the anatomic joint components accompanied by a limitation in opening the mouth, causing difficulties with mastication, speaking and oral hygiene as well as inadvertently influencing mandibular growth. Surgical treatment procedures include arthroplasty of the joint cavity with or without a reconstruction and a coronoidectomy, an autogenous costochondral rib graft, distraction osteogenesis and intensive mouth-opening exercise, corrective orthognathic surgery or alloplastic joint prostheses. The authors of this study would like to provide the reader with an evidence-based review of the literature in order to determine the most efficient way to manage TMJ ankylosis and re-ankylosis. The authors have concluded that in order to achieve a satisfactory and durable effective treatment, an individualized approach is necessary in each case.

A protocol for management of temporomandibular joint ankylosis in children

Temporomandibular joint (TMJ) ankylosis in children is a challenging problem. Surgical correction is technically difficult and the incidence of recurrence after treatment is high. The purpose of the present report is to describe the protocol currently used at the Massachusetts General Hospital for the management of TMJ ankylosis in children. It has been our observation that the most common cause of treatment failure is inadequate resection of the ankylotic mass and failure to achieve adequate passive maximal opening in the operating room. The 7-step protocol consists of 1) aggressive excision of the fibrous and/or bony ankylotic mass, 2) coronoidectomy on the affected side, 3) coronoidectomy on the contralateral side, if steps 1 and 2 do not result in a maximal incisal opening greater than 35 mm or to the point of dislocation of the unaffected TMJ, 4) lining of the TMJ with a temporalis myofascial flap or the native disc, if it can be salvaged, 5) reconstruction of the ramus condyle unit with either distraction osteogenesis or costochondral graft and rigid fixation, and 6) early mobilization of the jaw. If distraction osteogenesis is used to reconstruct the ramus condyle unit, mobilization begins the day of the operation. In patients who undergo costochondral graft reconstruction, mobilization begins after 10 days of maxillomandibular fixation. Finally (step 7), all patients receive aggressive physiotherapy. A case series of children with ankylosis treated using this protocol is presented.

Overgrowth of a costochondral graft in reconstruction of the temporomandibular joint

We report the case of a 3-year-old girl with temporomandibular ankylosis, which was treated with a costochondral graft and required two further resections because the grafted tissue had overgrown.

Biomechanical Properties of the Condyle Created by Osteodistraction

A new condyle can be reconstructed by osteodistraction, but the biomechanical properties of the neocondyle remain unknown. This study examined the hypothesis that the biomechanical properties of neocondylar cancellous bone could reach control levels 24 weeks after its creation by osteodistraction. The right mandibular condyles were removed and reconstructed by osteo-distraction in 16 adult goats. Their contralateral condyles served as controls. Microstructural and mechanical properties were examined by microcomputed tomography and mechanical testing. At 24 weeks after distraction, the neocondyle grew larger in size, but the shape and histological features were similar to those of the controls. The cancellous bone of the neocondyle even appeared to be more dense and stiffer in comparison with the control condyle. The results of this study suggest that the neocondyle created by osteodistraction develops nearly normal biomechanical properties for functional loading by 24 weeks after creation.

Age-related Changes in Marmoset Trabecular and Cortical Bone and Response to Alendronate Therapy Resemble Human Bone Physiology and Architecture

In older humans, bone elongation ceases, periosteal expansion continues, and bone remodeling remains a dominant metabolic process. An appropriate animal model of type I and type II osteoporosis would be a species with sealed growth plates and persistence of bone remodeling. The rat is commonly used as a primary model, but due to delayed epiphyseal closure with continuous modeling and lack of Haversian remodeling, Food and Drug Administration guidelines recommend assessment of bone quality in an additional, non rodent, remodeling species. This study investigated the skeletal characteristics of senescent marmosets to evaluate their suitability as an osteoporosis model. Animals were randomized across three experimental groups; controls for both sexes and marmosets receiving alendronate for either 30 or 60 days (28 microg/kg, sc, twice per week). Outcome measures included serum chemistry and bone biomarkers, DEXA, histomorphometry, micro-computed tomography, and histopathology. Results showed that the adult marmoset skeleton has similar anatomical characteristics to the adult human, including the absence of growth plates, presence of Haversian system, and true remodeling of cancellous and cortical bone. Structural analyses of senescent marmoset cancellous bone demonstrated loss of trabecular mass and architecture similar to skeletal changes described for elderly men and women. Treatment with alendronate improved trabecular volume and number by reducing bone resorption, although bone formation was also reduced through coupling of bone remodeling. The common marmoset may provide a valuable model for research paradigms targeting human bone pathology and osteoporosis due to skeletal features that are similar to age-related changes and response to bisphosphonate therapy reported for humans.

Reconstruction of Mandibular Condyle by Transport Distraction Osteogenesis: Experimental Study in Rhesus Monkey

PURPOSE

This study investigated histomorphologic changes in the newly formed condyle reconstructed by transport distraction osteogenesis through a nonhuman primate model.

MATERIALS AND METHODS

Six adult rhesus monkeys were used in this study. Bilateral condyles and articular discs were extirpated, and the technique of transport distraction osteogenesis was carried out to reconstruct the condyles. X-ray and 3-dimensional (3D) computed tomography (CT) scanning films were taken at various intervals. Two monkeys were killed respectively at 4, 12, and 24 weeks after completion of distraction; the transport segments and the distracted calluses were harvested and processed for histologic examination. The original condyles removed at surgery served as normal control.

RESULTS

Open bite was seen in all animals postoperatively and diminished at the end of distraction. Bone regeneration was perfect in the distraction gap between the transport disc and the pre-existing mandible. The bony transport disc gradually remodeled to a neocondyle that was similar to the original condyle in the appearances and structures. The head of neocondyle was covered with a fibrous cap, which might play the role of an articular disc.

CONCLUSION

A neocondyle with functional shape can be created by transport distraction osteogenesis. This suggests that this technique is an alternative method for reconstruction of the mandibular condyle.

Intraoral distraction osteogenesis for the correction of facial deformities following temporomandibular joint ankylosis: a modified technique

The aim of this study was to evaluate the feasibility of transoral bimaxillary distraction osteogenesis before releasing temporomandibular joint (TMJ) ankylosis using intraoral mandibular distractors. Nine patients (5 males, 4 females) aged 14-35 (mean 19) years were included. A bilateral Le Fort I osteotomy was performed together with a mandibular osteotomy on the affected side(s). An intraoral distractor(s) was inserted in the lower jaw, followed by an intermaxillary fixation (IMF) to maintain preoperative dental occlusion. The distractor was activated, after a latency period of 5-7 days, 2 times daily by 0.5 mm. There followed a consolidation period of 6-8 weeks. TMJ ankylosis was then released via a peri-auricular incision, a gap arthroplasty was performed, and mandibular movement was established after removal of the IMF and distractor. Optimal results were achieved clinically and radiologically with minimal relapse and complications. Apart from minor complaints, the distraction process was smooth and tolerable in all cases. Total mandibular elongation ranged from 17 to 25 mm (20.7 mm). Occlusal canting decreased to 0 degrees in 7 patients and to 1 degree in 2 patients (mean 0.2 degrees). After a mean follow-up period of 17 months, a mean postoperative mouth opening of 34.7 mm was achieved (0.6 mm preoperatively) and no re-ankylosis was detected. Intraoral distraction of a deformed mandible and maxilla before releasing TMJ ankylosis is a feasible and perhaps advantageous technique.

Autogenous coronoid process as a new donor source for reconstruction of mandibular condyle: an experimental study on goats

OBJECTIVE

To evaluate the feasibility and effectiveness of autogenous coronoid process grafts for reconstruction of the mandibular condyle.

STUDY DESIGN

Two groups of 9 goats each were used. Each animal underwent unilateral total condyle and disk removal and was treated by grafting an autogeneous coronoid process. The animals in group A were sacrificed at 4, 12, and 24 weeks after surgical procedure, and their grafted coronoid processes were harvested for histological observation. All animals in group B received 3-dimensional CT scanning examination at different times and were sacrificed at 24 weeks after surgical procedure. The items of ramus height (RH), transverse dimension of the condyle (CT), and posteroanterior dimension of the condyle (CP) were measured for comparison with the operated and nonoperated sides.

RESULTS

Despite the differences in the measurements of RH, CT, and CP between the operated and nonoperated sides, the grafted coronoid process had a similar shape and histological structures to the normal condyle at 24 weeks after surgical procedure. The head of the neocondyle was covered by a cap of fibrous tissue, which might play the role of the articular disc.

CONCLUSIONS

Under the mechanical stimuli of the temporomandibular joint site, the grafted coronoid process could gradually remodel to a neocondyle with functional shape and structure in goats. This animal study suggests that autogenous coronoid process could be considered as a new donor source for reconstruction of the mandibular condyle.

Surgical treatment of osteochondroma of the mandibular condyle in the adult

Five adult patients with temporomandibular joint (TMJ) pain and impaired mandibular function and with clinical and radiographic features of unilateral osteochondroma of the mandibular condyle was included in a 5-year prospective follow-up study. All patients were surgically treated with condylectomy and reshaping of the condylar neck which was then positioned underneath the preserved TMJ disk. The yearly follow-up evaluations comprised measurements of maximum interincisal opening and protrusive movements, assessments of occlusion and TMJ pain as well as tomographic interpretation of recurrent growth. No patient showed recurrence of growth at the 5-year follow-up and mandibular function and occlusion was normalized in all patients. The results indicate that this conservative surgical approach can be recommended for treatment of osteochondroma of the mandibular condyle.

Histology of surgically removed overgrown osteochondral rib grafts

INTRODUCTION

Osteochondral rib grafts are most commonly used for mandibular condylar replacements. However, when used in growing patients, unpredictable growth of the constructed condyle/ramus is a common complication. Clinically two types of overgrowth, linear or exuberant, have been described.

PURPOSE

In order to investigate growth disorders associated with osteochondral rib grafts in children, overgrown grafts were examined histologically.

PATIENTS AND METHODS

The material consisted of seven samples (six patients) of osteochondral rib grafts, that had been removed due to overgrowth.

RESULTS

Examination revealed that the clinical type of overgrowth was not related to any specific microarchitecture, which in itself, showed considerable variation. In three of the samples, a typical endochondral ossification zone was seen and in two others, signs of metaplasia, i.e. a gradual transformation of the cartilage cells into osteocytes, were noted.

CONCLUSIONS

The study reveals that the clinical type of overgrowth, linear or exuberant, cannot be related to any typical histological finding. Furthermore, the findings suggest that local factors, such as mandibular movements and loading of the reconstructed condyle may have an effect on the structure of the osteochondral rib graft, and eventually on its growth.

Distribution of insulin-like growth factor-I mRNA in the mandibular condyle and rib cartilage of the rat during growth

This study makes a molecular biological comparison of primary and secondary cartilage at an early phase of postnatal development. The distribution of insulin-like growth factor-I (IGF-I) mRNA expression in the mandibular condyle and rib cartilage of 1-28-day-old rats was examined after in situ hybridisation using an oligo probe cocktail for IGF-I mRNA. In the condyle, expression was localised to a narrow strip under the articular layer where the cells are undifferentiated. Essentially, no differences were found in IGF-I synthesis within three samples from the same age group or between different age groups. In rib cartilage, IGF-I mRNA was localised within the germinative, proliferative and early hypertrophic cell layers in 1-28-day-old rats. Again, there were no differences in expression among animals of the same age or as a function of age. This pattern of IGF-I mRNA expression indicates that IGF-I synthesis during growth of the mandibular condylar cartilage is different from that of costal cartilage. The findings shed light on the problem of overgrowth often associated with the use of costochondral grafts to replace defective mandibular condyles.