Histological examination of regenerated bone through craniofacial bone distraction in clinical studies

The process of bone formation by distraction osteogenesis of the craniofacial bone has been studied in animals. To our knowledge there are no published findings in which histological examination of craniofacial distraction in humans has been reported. Specimens were obtained from 10 patients who underwent craniofacial distraction: 2 patients who underwent mandibular distraction, 7 patients who underwent midface distraction, and 1 patient who underwent nasal bone distraction. These specimens were examined histologically. The results revealed that 8 of 10 patients exhibited new bone formation. No cartilaginous callus formation was observed in any of the specimens, which strongly suggests that new bone was produced by intramembranous ossification during human craniofacial bone distraction.

Mechanical tension-stress induces expression of bone morphogenetic protein (BMP)-2 and BMP-4, but not BMP-6, BMP-7, and GDF-5 mRNA, during distraction osteogenesis

Bone lengthening with osteotomy and gradual distraction was achieved in 57 rats, and the effect of mechanical tension-stress on gene expression of bone morphogenetic proteins (BMPs) was investigated by in situ hybridization and Northern blot analysis using probes of BMP-2, BMP-4, BMP-6, BMP-7, and growth/differentiation factor (GDF)-5. There was a lag phase for 7 days after femoral osteotomy until gradual distraction was carried out for 21 days at a rate of 0. 25 mm/12 h using a small external fixator. The signals of the above BMPs mRNA were not detected in the intact rat bone but they were induced after osteotomy except those for BMP-7. By 4 days after osteotomy, BMP-2 and BMP-4 mRNAs were detected in chondrogenic precursor cells in the subperiosteal immature callus. BMP-6 and GDF-5 mRNA were detected in more differentiated cells in chondroid bone. By 7 days after osteotomy, cartilaginous external callus and bony endosteal callus were formed. Meanwhile, the signals of BMP-2 and BMP-4 mRNAs declined to preoperative levels, whereas the signals of BMP-6 and GDF-5 mRNAs were rather elevated. As distraction was started, the callus elongated and eventually separated into proximal and distal segments forming a fibrous interzone in the middle. Expression of BMP-2 and BMP-4 mRNAs was markedly induced at this stage. Their signals were detected widely among chondrogenic and osteogenic cells and their precursor cells sustaining mechanical tension-stress at the fibrous interzone. BMP-6 and GDF-5 mRNAs were detected exclusively in chondrogenic cells at both ends of the fibrous interzone, where endochondral ossification occurred. But neither mRNA was detected in terminally differentiated hypertrophic chondrocytes. As distraction advanced, the cartilage was progressively resorbed from both ends and new bone was formed directly by intramembranous ossification. There was no new cartilage formation in the advanced stage of distraction. The signals of BMP-6 and GDF-5 mRNA declined by this stage, while those of BMP-2 and BMP-4 were maintained at high level for as long as distraction was continued. After completion of distraction, the fibrous interzone fused and the lengthened segment was consolidated. BMP-2, BMP-4, BMP-6, nor GDF-5 was expressed at this stage. The signals of BMP-7 were not detected throughout the experiment. The present results suggest that excellent and uninterrupted bone formation during distraction osteogenesis owes to enhanced expression of BMP-2 and BMP-4 genes by mechanical tension-stress. Abundant gene products of BMP-2 and BMP-4 could induce in situ bone formation by paracrine and autocrine mechanisms.

[Current trends and problems in the measurement of limb loading parameters during transosseous osteosynthesis using external fixation devices]

The problem in question is whether it is reasonable to equip a conventional limb external fixation apparatus with means for the diagnosis of loading parameters: the forces and displacement of the opposite supporting elements of the apparatus. It is assumed that during distraction osteogenesis it is expedient to apply load to the limb by the load rate only at the initial stage of callus regeneration (the plastic or slightly elastic mechanical state) while the most effective way to do so is to act force at later stages. A number of functions derived from the modified parameters which might aid a physician to choose the optimum limb loading parameters at different stages of treatment were considered by using as example a hypothetical ring-type apparatus equipped with means for continuous measurement of current forces applied to the apparatus and current displacements of opposite ring blocks. Specifications for the measuring system of loading parameters were defined by using an Ilizarov apparatus as an example and why possible rough measurement errors may occur is revealed. The paper shows it necessary to develop methods for calculation of parasitic deformations, i.e. those of the loaded elements of the apparatus for the evaluation of the reciprocal displacement of bone fragments.

Stimulation of bone formation by recombinant fibroblast growth factor-2 in callotasis bone lengthening of rabbits

Bone lengthening by callotasis is one of the most useful methods not only for the treatment of short extremities but also for extensive bone defects; however, the procedure takes a long time especially for the consolidation of the distracted callus. In this study, effects of a single local injection of recombinant human fibroblast growth factor-2 (FGF-2 or basic FGF) on callotasis bone lengthening were examined in rabbits. Ten days after the osteotomy at the middle of the tibia and the installment of an external fixator, the osteotomized site was distracted at a rate of 1.4 mm/day for 7 days, resulting in 9.8 mm lengthening. On the final day of distraction, 200 microg of FGF-2 in 150 microl of saline solution or vehicle alone was injected into the center of the distracted callus. Injection of FGF-2 increased bone formation at the distracted callus radiologically and histologically. A significant effect on bone mineral content (BMC) at the callus was observed as early as 2 weeks, and FGF-2 increased the BMC about twofold at 5 weeks after a normal remodeling process. We conclude that the callotasis method in combination with FGF-2 injection at the consolidation step could be clinically beneficial to shorten the bone lengthening period.

Reduced gap strains induce changes in bone regeneration during distraction

A bilateral New Zealand white rabbit model of distraction osteogenesis (DO) was used to investigate the relationship between strain environment and bone regeneration during limb lengthening. In seven (n = 7) rabbits, a stiffener was applied to the fixator on one side to reduce strains within the gap tissue after lengthening was completed. Animals were euthanized six days later and their distraction zones were harvested and analyzed for changes in new bone volume and architecture. Nonlinear finite element analyses (FEA) were performed to predict changes in the gap strain environment. FEA results predicted a nearly uniform sevenfold decrease in average strain measures within the distraction zone. No change in total average new bone volume and significant decreases in both bone volume fraction (BV/TV) and trabecular thickness (Tb.Th) were observed in tibiae in which gap strains were reduced experimentally, compared to contralateral controls. These results suggest that fixator stiffening influenced the architecture but not the amount of newly formed bone. This animal model of distraction might be used to study the mechanisms by which strain fields affect events in bone repair and regeneration, such as cell proliferation, precursor tissue differentiation, and altered growth factor and nutrient delivery to tissues.

[Laboratory monitoring of distraction bone formation]

The course of the early period of bone formation during distraction osteosynthesis can be safely, rapidly, and objectively monitored and predicted by hematological and immunological parameters (lymphocytes, rosette-forming cells, monocytes, immunoglobulin A, heterophilic hemagglutinins), which are tested before and after surgery on days 1 and 7-10 and on day 10 of distraction.

Complications following metatarsal lengthening by callus distraction for brachymetatarsia

We performed six metatarsal lengthenings in four patients for brachymetatarsia of the fourth toe by callus distraction from 1991 to 1995. Healing was achieved in all cases. The average amount of lengthening was 30% (range, 15-41%) of the original length. The average healing index was 82 days/cm (range, 66-113 days/cm). After the operation, range of movement of the metatarsophalangeal joint decreased in all cases (120 degrees before and 57 degrees after surgery). In two cases in which the lengthening exceeded 40% of the original length, stiffness of the joint (20 degrees and 0 degrees each) and joint deformity occurred. These two cases also had angulation of the metatarsal. Corrective osteotomy and release surgery was performed in one case. Angulation of the metatarsal was corrected, but the range of movement of the joint did not much recover after surgery. Another case was left untreated because the patient had no complaints. In metatarsal lengthening by callus distraction, the amount of lengthening should not exceed 40% of the original length.

Effect of lengthening rate on angiogenesis during distraction osteogenesis

This study investigated the angiogenic response to four varying rates (0.3, 0.7, 1.3, and 2.7 mm/day) of distraction in a rabbit model of leg-lengthening. Immunostaining was performed with use of specific antibodies to type-IV collagen and endothelial cell antigen to examine semiquantitatively the presence of blood vessels in the developing tissues. With use of the Chalkley counting method, the greatest number of positive-staining blood vessel cells was found in the central fibrous zone of the groups that underwent lengthening at 0.7 and 1.3 mm/day compared with any other zone in any group (p < 0.05, t test). There were no statistical differences in the positive labeling indices in the mineralization front and the new bone zone adjacent to the mineralization front in any of the groups. However, the decrease in the number of positive-staining blood vessel cells in the new bone zone distant to the mineralization front compared with any other zone in any group was statistically significant. The results suggest that during distraction osteogenesis, the precursor cells of new capillaries were present in abundance within the fibrous interzone. These cells connected into the capillary network at the junction of the mineralization front and the fibrous zone. The angiogenic response was weaker in the more mature regions within the new bone zones. A slow rate of distraction (0.3 mm/day) did not maximally stimulate angiogenesis in the central fibrous zone, whereas high rates (2.7 mm/day) appeared to impair this response. In this model of distraction osteogenesis, the vascularization process in the central fibrous zone was maximally stimulated at distraction rates of 0.7 and 1.3 mm/day.

A comparison of gradual distraction techniques for modification of the midface in growing sheep

The authors carried out experiments to advance the midface in growing sheep using a distraction force across the zygomaticomaxillary sutures. They wished to assess the possibility of performing distraction osteogenesis across intact sutures as well as distraction after Le Fort osteotomies. Their results demonstrate that the technique of gradual distraction after osteotomy is successful in the growing animal. Bilateral distraction across intact sutures did not advance the midface or change the dental relationship. Unilateral distraction was successful in angulating the midface away from the distracting force in the intact growing animal. Alternating unilateral distraction or "waltzing" was surprisingly effective in advancing the midface in one of the animals studied and may become applicable in some craniofacial deformities. In all intact animals there was some expansion of the zygomaticomaxillary suture as well as a substantial migration of the distraction devices through the bone.

[Complex reconstruction of the area of the maxilla and mid-face after radical tumor surgery]

The esthetic and functional restoration of facial defects is always a daunting challenge. The advent of free vascularized tissue transfers in combination with oral implants enables the surgeon to attain a high level of flexibility in the treatment of such defects. Due to its anatomical properties, the osteocutaneous scapula flap qualifies to a high degree for reconstruction purposes in the midfacial area. From July 1990 to February 1997, reconstruction of complex facial defects after oncologic surgery was performed in 17 patients using free vascularized tissue transfer. In four cases, a free scapula flap was used. Advantages and disadvantages of this technique are illustrated in these patients. Complete oral rehabilitation requires bony continuity of the jaws and stable dentition. To attain this goal, additional grafting procedures are required in most cases when insertion of oral implants is planned. As for the soft tissues, the problem of measuring the amount of tissue needed often leads to an overcorrection, requiring several debulking procedures.

Mandibular lengthening by distraction osteogenesis in children--a one-year follow-up study

OBJECTIVE

The present study was undertaken to document whether mandibular length could be increased by distraction osteogenesis in children and what happens to the mandibular position 1 year after the distraction.

METHODS

Five patients with hemifacial microsomia (four unilateral, one bilateral) had distraction osteogenesis performed to lengthen the mandible. All patients had cephalometric and panoramic radiographs obtained before and 3, 6, and 12 months after the distraction osteogenesis.

RESULTS

The total mandibular length (Co-Gn) on the affected side was increased by 11.2 mm after the distraction and remained stable during a 1-year observation period. However, the increased mandibular length tended to move the chin downward (8 mm) more than forward (2 mm) during the same period.

CONCLUSIONS

Distraction osteogensis can be used to lengthen the hypoplastic mandible. However, most of the increased mandibular length moved the chin downward more than forward.

Angiogenesis during mandibular distraction osteogenesis

Recruitment of a blood supply is critical for successful bone induction and fracture healing. Despite the clinical success of distraction osteogenesis (DO), an analysis of angiogenesis during membranous bone DO has not been performed. The purpose of this study was to evaluate the temporal and spatial pattern of angiogenesis during mandibular DO. The right hemimandible of adult male rats was osteotomized, and a customized distraction device was applied. Following a 3-day latency period, distraction was begun at a rate of 0.25 mm twice daily for 6 days (3.0 mm total; 12% increase in mandibular length). Three animals each were sacrificed on days 2, 4, and 6 of distraction (D1, D2, and D3 respectively), or after 1, 2, or 4 weeks of consolidation (C1, C2, and C3 respectively). Two experienced pathologists reviewed the regenerate histology, and angiogenesis was assessed by counting the number of blood vessels per intermediate-power field (IPF). Statistical analysis was performed using analysis of variance, with p < or = 0.05 considered significant. Results demonstrate that mandibular DO was associated with an intense vascular response during the early stages of distraction (D1). On average, 31.5+/-7.9 vessels were noted in each IPF examined during this time point. The number of blood vessels in the distraction regenerate decreased significantly during the later distraction time points, with approximately 14.0+/-2.0 and 14.7+/-3.5 blood vessels per IPF in sections obtained after days 4 and 6 of distraction (D2, D3) respectively. However, blood vessels at these time points took on a more mature histological pattern. During the consolidation period, the number of blood vessels noted in the regenerate decreased with 8.0+/-2.6, 9.3+/-2.1, and 4.0+/-2.0 vessels per IPF in sections obtained after 1, 2, or 4 weeks of consolidation (C1, C2, C3) respectively (p < 0.05 compared with vessel counts during the earliest distraction time point). This study demonstrates for the first time that an intense vascular response associated with mandibular DO occurs primarily during the early stages of distraction. The authors hypothesize that as distraction continues, newly formed vessels likely undergo consolidation, thus forming more mature vessels capable of withstanding distraction forces. Future studies will assess the effects of therapeutic interventions designed to increase angiogenesis during DO on bony regenerate formation.

Effect of rate of distraction on loss of range of joint movement, muscle stiffness, and intramuscular connective tissue content during surgical limb-lengthening: a study in the rabbit

Surgical lengthening of limbs often results in loss of range of joint movement and this has been shown to be associated with an increase in passive tension and an increase in collagen content of the muscles. In this study, we have investigated the length/tension properties and the connective tissue component of muscle distracted at three different rates in order to determine whether low rates of distraction would enable the connective tissue component, as well as the contractile component (number of serial sarcomeres), to adapt more completely to the increased functional length of the muscle and thus lead to improved range of joint movement. It was found that loss of range of movement varied with rate of distraction. At the low rate, there was no change in the passive tension or collagen content compared to muscles from sham-operated animals, and range of movement was significantly greater than at the other rates. At the medium rate, although the muscles showed good adaptation in terms of serial sarcomere number, passive tension and collagen content was increased and range of movement reduced, indicating that changes in the connective tissue component are important factors in loss of joint movement. In the case of muscle distracted at a high rate, failure of the muscle fibres to add on sufficient sarcomeres, combined with changes in the connective tissue, resulted in almost total loss of joint movement.

Optimal time for distraction osteogenesis in limbs with nerve repairs: experimental study in the rat

The optimal period of time between peripheral-nerve repair and initiation of limb lengthening procedures has never been precisely determined. In the clinical setting, the surgeon must decide how long the repaired nerves should be allowed to heal before subjecting them to the forces created by the limb-lengthening process. The authors designed a study to quantify and qualify the effects of different recovery periods between initial nerve repair and subsequent limb-lengthening via distraction osteogenesis. Forty-two Sprague-Dawley male rats were randomized in two different categories of nerve repair: end-to-end and nerve grafts. At 4, 8 and 12 weeks after nerve reconstruction, the femur was submitted to limb-lengthening at a rate of 1 mm/day (0.25 mm every 6 hr). Sciatic Function Index (SFI) evaluation indicated that the impact of distraction was detrimental in the grafted nerves, although they maintained their electrical and morphologic properties at comparable levels to the non-distracted nerves. Nerves with direct coaptation presented an overall superior regeneration pattern. The findings in end-to-end repairs distracted at 8 weeks and those of grafted nerves at 12 weeks were comparable to those in distracted normal nerves. The morphology of the distracted nerves appeared to be more organized than that observed in the non-distracted nerves.

Clinical update--the teeth and the maxillary sinus: the mutual impact of clinical procedures, disease conditions and their treatment implications. Part 2. Odontogenic sinus disease and elective clinical procedures involving the maxillary antrum: diagnosis and management

Although odontogenic sinusitis is a rare entity when compared to sinus disease of rhinogenic origin, it is extremely important to identify a dental aetiology when it occurs. The offending tooth or teeth would thus require endodontic treatment or extraction, and the sinus disease carefully assessed and appropriately managed. Aetiology and presentation of oro-antral fistulae are also discussed and guidelines for the management of this complication are recommended. Certain lesions such as cysts and tumours may involve the jaws and hence the maxillary antrum; some of these, such as a radicular cyst are quite common, but the rarer ones are included for completeness. Surgical techniques are continuously evolving to optimise form and function of the jaws, and when applied to the maxilla there may be some impact on nasal and sinus function. The advent, and now proven success, of osseointegrated jaw implants have brought with them innovations and refinements of bone grafting techniques, and more recently distraction osteogenesis for augmentation. Maxillary osteotomies for surgical orthodontics, and to facilitate prosthodontic treatment are briefly mentioned, as most of these inevitably involve the antrum and/or nose. This paper discusses, in summary form, important aspects of clinical dental practice which may involve the maxillary antrum. It is thus a broad overview of certain pathologic conditions and elective surgical procedures which have relevance to both medical and dental practitioners.

Molecular signaling in bone fracture healing and distraction osteogenesis

The process of fracture healing has been described in detail in many histological studies. Recent work has focused on the mechanisms by which growth and differentiation factors regulate the fracture healing process. Rapid progress in skeletal cellular and molecular biology has led to the identification of many signaling molecules associated with the formation of skeletal tissues, including members of the transforming growth factor-beta (TGF-beta) superfamily and the insulin-like growth factor (IGF) family. Increasing evidence indicates that they are critical regulators of cellular proliferation, differentiation, extracellular matrix biosynthesis and mineralization. Limb lengthening procedure (distraction osteogenesis) is a relevant model to investigate the in vivo correlation between mechanical stimulation and biological responses as the callus is stretched by a proper rate and rhythm of mechanical strain. This model also provides additional insights into the molecular and cellular events during bone fracture repair. TGF-beta 1 was significantly increased in both the distracted callus and the fracture callus. The increased level of TGF-beta 1, together with a low concentration of calcium and an enhanced level of collagen synthesis, was maintained in the distracted callus as long as mechanical strain was applied. Less mineralization is also associated with a low level of osteocalcin production. These observations provide further insights into the molecular basis for the cellular events during distraction osteogenesis.

Primary leiomyosarcoma of the mandible in a 7-year-old girl: report of a case and review of the literature

Leiomyosarcoma is a malignant neoplasm of smooth muscle origin that manifests itself uncommonly in the oral cavity because of the paucity of smooth muscle in that location. To the best of our knowledge, only 10 cases of leiomyosarcoma primary to the jawbones have been reported in the English language literature. We report the first pediatric case of leiomyosarcoma arising from the mandible. Facial asymmetry and swelling were accompanied by a rapidly growing exophytic soft tissue mass that caused buccal displacement of the mandibular left permanent first molar. The lesion, observed radiographically as an extensive ill-defined area of osteolytic alveolar destruction, perforated the lingual cortex, displaced the inferior alveolar nerve canal inferiorly, and produced a "floating-in-air" appearance of the first molar. Diagnosis of leiomyosarcoma was made after initial incisional biopsy of the lesion. A 5-cm segmental mandibulectomy and supraomohyoid neck dissection were followed by reconstruction with a dynamic mandibular reconstruction plate and placement of a multidimensional mandibular distraction device in a transport rectangle of bone to promote bifocal distraction osteogenesis. Forty millimeters of distraction (the technical limit of the device) were performed; this was followed by terminal iliac crest bone grafting. Seventeen months after the definitive surgical procedure, the patient remains free of disease.

Mandibular growth after distraction in patients under 48 months of age

Distraction osteogenesis is an effective technique for reconstruction of the congenitally deficient mandible. However, the age at which it is best performed remains under discussion. Distraction performed at an early age, while possibly allowing the face to develop with a more normal functional matrix, may entail a higher rate of complications. Additionally, it is possible that subsequent asymmetric growth of the mandible may necessitate serial distraction. To address this issue, the clinical records and cephalometric radiographs of all patients less than 48 months of age undergoing mandibular distraction at New York University Medical Center between August of 1989 and August of 1997 were examined. There was a total of 14 patients ranging in age from 19 months to 43 months. Nine patients had a diagnosis of unilateral craniofacial microsomia, three had Treacher Collins syndrome, one had Nager syndrome, and one had bilateral developmental micrognathia. The average amount of distraction was 27 mm (range, 23 to 39 mm) in unilateral cases and 24 mm in bilateral cases (range, 15 to 31 mm). The period of clinical follow-up averaged 32.6 months (range, 12 to 92 months). All patients showed significant improvement in craniofacial appearance, and in four patients, long-term tracheostomy tubes were removed. There were two major complications. In one patient with craniofacial microsomia, there was a relapse in the early postretention phase related to the presence of a dentigerous cyst. This required removal of the cyst and repeat distraction. In the patient with Nager syndrome, a coronoid ankylosis developed requiring surgical release. There were no other major complications. The scars required revision in only two of the patients. Cephalometric analysis of the patients in the study revealed a differential in the rate of growth between the affected and the unaffected side in all cases of craniofacial microsomia. The affected side always grew at a slower rate than the contralateral side after the distraction process was complete. This led to a progressive asymmetry of the rami, clinically expressed by some degree of facial asymmetry and an occlusal cant. For this reason, secondary distraction was required in one patient and is planned in a second. Initial overcorrection of the patient would seem to minimize the likelihood that secondary distraction will be necessary. Distraction osteogenesis for reconstruction of the mandible in this subset of young patients was a safe and effective technique for improving the craniofacial skeletal form and appearance, with minimal associated morbidity. Longer follow-up is necessary to assess the full impact of growth in these cases.

Mechanical modulation of calf tail vertebral growth: implications for scoliosis progression

The purpose of this study was to determine whether compression and distraction applied to adjacent vertebrae in the calf tail could modulate vertebral growth. Seven 6-week-old calves had two pairs of adjacent tail vertebrae instrumented with an Ilizarov external fixator with calibrated springs designed to apply a 30-50-N axial load to the vertebrae. Data were obtained from 17 vertebrae loaded in compression and 4 vertebrae loaded in distraction. Vertebrae adjacent (cranial and caudal) to the instrumented vertebrae served as controls. The length of each vertebra on the postoperative radiograph was subtracted from the length of the same vertebra on the radiograph taken 6 months after the operation to calculate vertebral growth. The vertebrae loaded in compression had a growth rate of 68 +/- 42% of that of the controls. In contrast, the vertebrae loaded in distraction had a growth rate of 123 +/- 78% of that of the controls.

The role of chondrocytes in intramembranous and endochondral ossification during distraction osteogenesis in the rabbit

We have used a rabbit leg-lengthening model for detailed studies of the histology of distraction osteogenesis. Some unusual features of the endochondral ossification that occurs during the rapid transition of cartilage to bone in the regenerate were observed. Histological staining techniques together with immunohistochemistry and nonradioactive in situ mRNA hybridization for cartilage and bone-related molecules have been used to document the presence of an overlapping cartilage-bone phenotype in cells of the cartilage-bone transitional region. In those particular areas, some chondrocytes appeared to be directly transformed into newly formed bone trabeculae which are surrounded by bone matrix. Acid phosphatases were found within the cartilage matrix in some of the cartilage/bone transitional regions and type I collagen mRNA and type II collagen protein were found together in some of the marginal hypertrophic chondrocytes. This study indicates an unusual role of chondrocytes in the process of ossification at a distraction rate of 1.3 mm/day in the rabbit. Further direct evidence is required to prove the hypothesis that the hypertrophic chondrocytes may transdifferentiate into bone cells in this model.

Bone repair techniques, bone graft, and bone graft substitutes

This paper reviews the techniques and materials (bone graft and bone graft substitutes) that currently are used to treat nonunions and bone defects. The techniques reviewed are intramedullary nailing, plating, distraction osteogenesis, and electric stimulation. Bone graft and bone graft substitutes reviewed are as follows: vascularized bone transfers; autogenous bone graft; autogenous bone marrow; dimineralized bone matrix; growth factors; calcium sulphate; calcium phosphates; and allograft. The goal of management of fractures, nonunions, and segmental bony defects, is the return of function as quickly and completely as possible. Techniques and management strategies constantly are evolving to accomplish this goal. This paper reviews the history, indications, and limitations of bone repair techniques, methods of bone grafting, and materials available as bone graft substitutes.

Accelerating bone formation and earlier healing after using demineralized bone matrix for limb lengthening in rabbits

We studied the effects of grafting with demineralized bone matrix during lengthening of the tibia in young Japanese White rabbits. The demineralized bone matrix was made from frozen cortical bone harvested from other rabbits. A 5-mm gap was created in the tibial diaphysis by a subperiosteal osteotomy; a maximum of 20 mm (2-3 mm/day) of tibial lengthening was reached in a week with use of an external fixator. The control group of 20 rabbits did not receive an implant; the group of 21 experimental rabbits received an implant of demineralized bone matrix in the surgical gap. The control group failed to demonstrate radiographic callus 5 weeks after surgery, and nonunion was persistent after 1 year. In the group with demineralized bone matrix, new radiodensity was demonstrated within the lengthening gap at 3 weeks, with a gradual increase in bone density to 85% that of the intact tibia after 12 weeks. Bone union was seen within 1 year for all experimental animals for whom the external fixator was removed 8 weeks after the procedure. These bones showed normal bone structure histologically. The lengthening was carried out at a rapid distraction rate of 2-3 mm/day; therefore, this method allows for satisfactory bone formation at a faster rate than normal.

Midface distraction

Since the initial application of distraction osteogenesis to the human mandible by McCarthy, distraction osteogenesis has been used for gradual lengthening of the midface in children with syndromic craniosynostosis, cleft lip and palate, hemifacial microsomia, and midface hypoplasia from other causes. Both external and internal devices are available that permit midface distraction. The background of midface distraction and the development of a Modular Internal Distraction (MID) system that permits widespread use of easily customized, buried distraction devices throughout the craniofacial region are presented. The relative and potential clinical indications for distraction, treatment planning, patient preparation, and possible surgical orthodontic interactions during distraction, as well as a variety of case examples showing the MID system, are discussed.

Effect of ED-71 on modeling of bone in distraction osteogenesis

We investigated the effect of 2-beta-(3-hydroxypropoxy)-1alpha,25-dihydroxyvitamin D3 (ED-71) on the modeling of bone in distraction osteogenesis. The tibiae of 30 rabbits were lengthened by 10 mm in 10 days. Following osteotomy, ED-71 (0.05 microg/kg) was administered subcutaneously twice a week to the ED-71 group until necropsy. The bone mineral content (BMC) of the lengthened callus was measured by dual-energy X-ray absorptiometry (DXA). Five rabbits per group were killed at 1, 3, and 8 weeks after completion of lengthening, and the lengthened callus was examined histologically and histomorphometrically. Bone volume of the lengthened callus was measured by peripheral quantitative computed tomography (pQCT) at 8 weeks after the completion of lengthening. At all timepoints the BMC in the ED-71 group was significantly higher than that in the untreated group. The mineral apposition rate and bone formation rate were higher in the ED-71 group than in the untreated group at 1 and 3 weeks after the completion of lengthening on the coronal section. In cross sections, the cortical area and width in the ED-71 group showed significantly higher values than in the untreated group at 8 weeks after the completion of lengthening. Both the endosteal osteoid surface and endosteal eroded surface showed no differences between groups. However, the endosteal mineral apposition rate and endosteal bone formation rate were significantly higher in the ED-71 group. At 8 weeks after completion of lengthening, the intracortical area and intracortical BMC were significantly greater in the ED-71 group than in the untreated group, but no significant difference was noted in intracortical BMD. These findings indicate that ED-71 increases callus volume during the early period after the completion of lengthening, resulting in thick cortical bone formation.

Strain-related bone remodeling in distraction osteogenesis of the mandible

Distraction osteogenesis has become a mainstay in craniofacial surgery. However, there are several unresolved problems concerning the biology of bone regeneration. We investigated the biomechanical effects of mandibular lengthening in 32 rabbits on a cellular and histologic level. The mandible was subjected to a corticotomy, held in a neutral position for 4 days, and then lengthened at various strain rates and frequencies for 10 days. Radiographic, histologic, and electron microscopic examinations showed a strain-related bone regeneration. Application of physiologic strain rates (2000 microstrains or 0.2 percent) led to a bridging of the artificial fracture exhibiting woven ossification, whereas at 20,000 microstrains trabecular bone formation was demonstrated. In contrast, hyperphysiologic strain magnitudes (200,000 microstrains and 300,000 microstrains) showed a fibrous tissue formation. Multiple strain applications (10 cycles/day versus 1 cycle/day) increased the width of the distraction gap without changing the stage of bone regeneration. The gradual distraction of bone in physiologic magnitudes at higher frequencies seems to be desirable for a bony differentiation and may help to improve clinical applications.

Rat mandibular distraction osteogenesis: II. Molecular analysis of transforming growth factor beta-1 and osteocalcin gene expression

Distraction osteogenesis is a powerful technique capable of generating viable osseous tissue by the gradual separation of osteotomized bone edges. Although the histologic and ultrastructural changes associated with this process have been extensively delineated, the molecular events governing these changes remain essentially unknown. We have devised a rat model of mandibular distraction osteogenesis that facilitates molecular analysis of this process. Such information has significant clinical implications because it may enable targeted therapeutic manipulations designed to accelerate osseous regeneration. In this study, we have evaluated the expression of transforming growth factor beta-1, a major regulator of osteogenesis during endochondral bone formation and development, and osteocalcin, an abundant noncollagenous extracellular matrix protein implicated in the regulation of mineralization and bone turnover. The right hemimandible of 36 adult male rats was osteotomized, and a customized distraction device was applied. Animals were allowed to recover and, after a 3-day latency period, were distracted at a rate of 0.25 mm twice daily for 6 days followed by a 2- or 4-week consolidation period. Distraction regenerate was harvested after the latency period, days 2, 4, or 6 of distraction, and after 2 or 4 weeks of consolidation and processed for Northern analysis (n = 4 at each time point) and immunohistochemical localization of TGF-beta1 (n = 2 at each time point). Six sham-operated animals (i.e., skin incision without osteotomy) were also killed (immediately postoperatively), and the mandibles were harvested and prepared in a similar fashion. Equal loading and transfer of RNA for Northern analysis was ensured by stripping and probing membranes with a probe against GAPDH (a housekeeping gene). Our results demonstrate that the spatial and temporal patterns of TGF-beta1 mRNA expression and protein production coincide with osteoblast migration, differentiation, and extracellular matrix synthesis. In addition, we demonstrate that TGF-beta1 production may be an important regulator of vasculogenesis during mandibular distraction osteogenesis. Finally, we have shown that osteocalcin gene expression coincides temporally with mineralization during rat mandibular distraction osteogenesis.

Successful distraction osteogenesis across a growing cranial suture without an osteotomy

The application of distraction osteogenesis to the membranous bones of the craniofacial skeleton and its effects on cranial volume and overall skull shape have not been fully studied. This pilot study was designed to compare distraction of a cranial suture in the rabbit model with distraction across an osteotomy and to evaluate the response of the suture both grossly and histologically. Additionally, the need for a period of rigid fixation after distraction was evaluated. Calibrated distraction of either the coronal suture or an osteotomy in the midsection of the parietal bone using an internal distractor (Synthes Maxillofacial, Paoli, Pa.) was studied in juvenile and adult New Zealand White rabbits. Skull growth and distraction were followed by serial cephalograms, and bone biopsies of the distracted sites were obtained after death for histologic evaluation. Craniometric analysis of the skulls was also performed. There was significantly greater mean marker separation in the juvenile suture distraction group (6.6 +/- 0.2 mm; n = 3) than in the control group (2.2 +/- 0.2 mm; p < 0.01). Marker separation was also significantly greater across the parietal osteotomy (6.4 +/- 0.1 mm) than in the sham group (no marker separation). Craniometric data demonstrated the ability of the juvenile skull to distribute the change at the coronal suture throughout the skull to maintain symmetry and minimize disproportion. No distraction was obtained across the adult suture. In the juvenile suture distraction group without a period of stable fixation, a relapse of 17 +/- 6 percent was noted after 1 week, an additional 2.3 +/- 0.5 percent after the second week, and no further change in the third postdistraction week (n = 2; p < 0.01). These results show that in this animal model, distraction osteogenesis can be achieved across a growing cranial suture without an osteotomy or suturectomy and that the degree of distraction and new bone formation is comparable to that across an osteotomy. This suggests that cranial expansion can be obtained in a growing animal without using a more invasive cranial osteotomy. Additionally, the first week after distraction seems to be the most critical time period to maintain stable fixation.

Viscoelastic characterization of mesenchymal gap tissue and consequences for tension accumulation during distraction

Nonlinear viscoelastic analysis was used to characterize the time-dependent behavior of mesenchymal gap tissue generated during distraction osteogenesis. Six (n = 6) lengthened tibiae were harvested from New Zealand white rabbits at 18 days. This gap tissue was subjected to a series of step displacement tests of increasing magnitude, and force relaxation behavior was monitored. Isochrones in stress-strain space were fit to odd cubic functions of strain. An analytic expression, linear in both e and e3, was developed to predict stress accumulation within the gap tissue as a function of time during distraction. Stress relaxation functions were described well by two-term Prony series. The two time constants determined from mechanical testing results were consistent, suggesting the presence of two fundamental physiologic relaxation processes. Gap tissue stresses were predicted to rise considerably during early stages of lengthening when distraction magnitudes exceeded the clinical norm of 0.25 mm. These differences in tension accumulation were less pronounced by the time lengthening was completed. Specifically, these results may in part explain clinical observations of decreased bone regeneration and altered tissue proliferation and differentiation at higher distraction rates. More generally, this work provides a framework for the rigorous characterization of the viscoelastic properties of biologic tissues ordinarily exposed to step strains.

Advancement of the midface using distraction techniques

Fourteen patients underwent Le Fort III midface advancement using distraction techniques. Six have cephalometric documentation extending beyond 1 year postoperatively, and the positions of cephalometric points A and orbitale over time are reported here. Excellent stability of advancement at the occlusal level and some relapse at the level of orbitale are documented. Elimination or diminution of obstructive sleep apnea occurred in all patients so affected, and one of two patients with tracheostomy has been decannulated. Speech effects have been mild or transient. No untoward effects on extraocular muscle function have occurred.

Transplantation of osteoblast-like cells to the distracted callus in rabbits

We carried out limb lengthening in rabbits and then transplanted osteoblast-like cells derived from the tibial periosteum to the centres of distracted callus immediately after distraction had been terminated. Two weeks later the transaxial area ratio at the centre of the distracted callus and the bone mineral density (BMD) were significantly higher in the transplanted group, by 21% and 42%, respectively, than in the non-injected group or the group injected with physiological saline (p < 0.05). Callus BMD as a percentage of density in uninvolved bone was also significantly higher in the transplanted group (p < 0.05) than in the other two groups, by 27% and 20% in the second and fourth weeks, respectively (p < 0.05). Mechanically, the callus in the transplanted group tended to be stronger as shown by the three-point bending test although the difference in fracture strength was not statistically significant. Our results show that transplantation of osteoblast-like cells promotes maturity of the distracted callus as observed at the second and fourth weeks after lengthening. The method appears promising as a means of shortening the consolidation period of callus distraction and decreasing complications during limb lengthening with an external fixator.

The role of transforming growth factor-beta, insulin-like growth factor I, and basic fibroblast growth factor in distraction osteogenesis of the mandible

Distraction osteogenesis is a viable method for regenerating large amounts of bone. In contrast to fracture healing, the mode of bone formation in distraction osteogenesis is primarily intramembranous ossification. The basic biology of the process is still not well understood. The growth factor cascade is likely to play an important role in distraction. This study examines the growth factor cascade in a lengthened ovine mandible model. Twenty-four animals were divided into four groups with varying rates of distraction (1, 2, 3, and 4 mm/day). A unilateral distractor at the angle of the mandible was used. The mandibles were lengthened to 24 mm and fixed for a period of 5 weeks, after which the animals were killed. The sections were probed for transforming growth factor-beta, basic fibroblast growth factor, and insulin-like growth factor I. The growth factors studied were present in all four groups. Transforming growth factor-beta, basic fibroblast growth factor, and insulin-like growth factor I were present in both the bony matrix of the sections and the cytoplasm of the cells, osteoblasts, and a small number of mesenchymal cells. The sections obtained from groups distracted at faster rates showed stronger presence of the growth factors examined by more intense staining. In fracture healing, the localization of transforming growth factor-beta in stage I of healing corresponded with the precise region of intramembranous ossification in stage II. Diffuse presence of transforming growth factor-beta throughout the lengthened region corresponded with the process of intramembranous ossification observed in distraction. In fracture healing, insulin-like growth factor I and basic fibroblast growth factor have been shown to promote proliferation and differentiation of osteoblasts from precursor cells. The intense presence of insulin-like growth factor I and basic fibroblast growth factor in the distracted region may account for osteoblast proliferation and formation from precursor mesenchymal cells. Mechanical strain has been shown to increase the expression of transforming growth factor-beta and insulin-like growth factor I. Distraction may serve as a source of mechanical strain, which may explain, in part, the expression of these growth factors, particularly in the faster groups.

Callotasis in a fasciosteal flap model in rabbits: part II. a new contribution to the concept of distraction osteogenesis

The basis of lengthening bones at their anatomic locations has been defined in detail by many authors. The possibility of distraction osteogenesis in vascularized bone grafts and the role of periosteum was investigated in 35 growing New Zealand White rabbits in four experimental groups: group 1, the scintigraphic assessment group (N = 4); group 2, the distraction group with intact periosteum (N = 15); group 3, the control group without periosteum in the distraction area (N = 6); and group 4, the control group in which the flaps were wrapped in silicone leaves (N = 10). Scintigraphy was used to evaluate the survival of the bone graft. Metatarsal fasciosteal flaps were fixed by external fixators and then subjected to osteotomy. Distraction was started after 10 days of osteotomy and continued at 0.5 mm/24 hr for 10 days, with a total elongation of 4 to 6 mm. Radiological examination at day 10 of starting the distraction, and both radiological and histological examinations at days 15, 20, and 30 were performed. In group 1, positive scintigraphic images of the flaps were obtained. In group 2, progressive calcification was detected radiologically and mixed-type ossification was observed histologically. However, in group 3, distraction failed. Group 4 was excluded from the study due to silicone exposition. The authors demonstrated that vascularized bone segments can be lengthened, and provided information about the importance of periosteum in distraction osteogenesis.

Early decannulation with bilateral mandibular distraction for tracheostomy-dependent patients

Obstructive sleep apnea in the neonatal period may originate from a hypoplastic mandibular framework causing retroposition of the base of the tongue and an inadequate hypopharyngeal space. A tracheotomy in childhood is an effective treatment for obstructive sleep apnea, but it is associated with increased morbidity, management problems, and difficulties in social interaction. Tracheostomy-dependent pediatric patients who underwent mandibular distraction were reviewed to determine the effectiveness of this technique in achieving decannulation. A clinical review was completed to determine the status of the tracheostomy after external, unidirectional distraction in tracheostomy-dependent patients. Expansion of the mandibular framework was analyzed using traditional bony landmarks on predistraction and postdistraction lateral cephalograms. The area of the lower face was analyzed, and changes in the position of the hyoid bone were determined. Four patients with tracheostomies underwent an average of 21.3 mm and 20.8 mm of distraction on the left and right hemimandibles, respectively. The average age at the time of distraction was 2.7 years (range, 2.2 to 3.2 years). All patients underwent successful decannulation at an average of 3.8 months (range, 1.5 to 5.5 months) after completion of distraction. The area of the lower face increased 26.9 percent (range, 12.2 to 53.5 percent) after distraction, and the hyoid bone advanced an average of 14.5 mm (range, 8 to 25 mm). Bilateral mandibular distraction is an effective method of expanding the mandibular framework and concomitantly advancing the base of the tongue. The technique provides a tool for early intervention and decannulation in pediatric patients with indwelling tracheostomies secondary to mandibular deficiencies.

Distraction osteogenesis

Distraction osteogenesis is a surgical technique originally used to lengthen the long bones without bone grafting. An osteotomy is created and by slowly separating the two segments with specially fabricated hardware, the biological distractant will grow with the bone and calcify into mature bone once the appropriate length has been achieved. Distraction techniques have been used in the human facial bone area for the past 10 years. This article reviews the basic uses of distraction osteogenesis, the pros and cons, and possible future techniques.

Changes of callus diameter during axial loading and after fixator removal in leg lengthening

We retrospectively reviewed nine tibial lengthenings in seven achondroplastic patients. The callotasis method was used, and a unilateral type lengthener, either the Dynamic Axial Fixator (Orthofix, Italy; eight legs) or the High Functional Fixator (Matsumoto Co., Japan; one leg), was applied. The distracted length averaged 14.6 (range 10-18) cm. The minimum diameter of the callus was measured using a ruler on anteroposterior and lateral radiographs. The callus diameter ratio (%) was calculated as the callus diameter divided by the original diaphysis diameter. For periods during axial loading and after removal of the fixator in each patient, a single regression line was drawn on the callus diameter ratio data using the least squares method, and the diameter change rate (%/day) was evaluated by inclination of this line. The diameter change rates during axial loading were negative in six legs, but those after fixator removal were positive in all legs, and the latter were significantly greater than the former. The diameter change rates after fixator removal on the anteroposterior radiographs were negatively correlated with the callus diameter ratio at the time of fixator removal (r = 0.84, P = 0.0008). Simple axial loading may not be a sufficient mechanial environment for restoration of the physiological shape, and it is important to be aware that we cannot expect the callus diameter to increase by this means alone.

Rat mandibular distraction osteogenesis: Part I. Histologic and radiographic analysis

The application of distraction osteogenesis to craniofacial surgery has altered the approach and treatment of congenital and acquired craniofacial defects. Although the histologic and ultrastructural changes associated with distraction osteogenesis have been described extensively, relatively little is known about the molecular regulation of this process. The elucidation of the molecular mechanisms of distraction osteogenesis has important clinical implications because it may facilitate the use of recombinant proteins or gene therapy to accelerate bone regeneration. Molecular analysis of distraction osteogenesis has been hindered by the use of large animal models in which only limited genetic information is available. In this study, a rat model of mandibular distraction osteogenesis is described. This report includes a pilot study (n = 50) to develop an appropriate distraction device and to determine the optimal placement of the osteotomy. The study subsequently included 80 animals, 35 of which were distracted at a rate of 0.25 mm per day for 6 days (1.5 mm total) and 35 that were distracted at a rate of 0.25 mm twice per day (3.0 mm total). These animals were killed at various time points (after latency and during the distraction and consolidation periods) and displayed histologic and radiographic findings of membranous bone distraction osteogenesis that were consistent with those in large ,animal and clinical models. In addition, five animals each were acutely lengthened 1.5 mm and 3.0 mm and demonstrated a fibrous nonunion. Furthermore, the utility of this model is demonstrated in the analysis of the molecular mechanisms of distraction osteogenesis by applying the polymerase chain reaction to total cellular RNA isolated from normal and distracted rat mandibles. In conclusion, it is believed that the rat model of distraction osteogenesis has significant advantages over traditional models, including decreased costs and facilitation of molecular analysis.

Pre-surgical CT/FEA for craniofacial distraction: I. Methodology, development, and validation of the cranial finite element model

Recently, surgeons have begun to treat serious congenital craniofacial deformities including craniosynostoses with mechanical devices that gradually distract the skull. As a prospective means of treatment planning for such complex deformities, FE models derived from routine preoperative CT scans (CT/FEA) would provide ideal patient specific engineering analyses. The purpose of this study was to assess the dimensional and predictive accuracy of the CT/FEA process through the development of a 3D model of a dry human calvarium subjected to two-point distraction ex vivo. Comparative skull measurements revealed that CT/FEA construction error did not exceed 1% for transcranial dimensions, and the thickness error did not exceed 8.66% or 0.31 mm. CT/FEA strain predictions for the central region of the skull, between the distraction posts, were not statistically different from homologous gage values at P < 0.05. Peripherally, however, the strain fields were less well behaved and the FE predictions showed only general qualitative agreement with gage recordings.

Effect of distraction osteogenesis on the peripheral nerve: experimental study in the rat

Distraction osteogenesis is the current method of choice for bone lengthening. Despite the gain in experience, various complications are reported, among them, adverse effects on peripheral-nerve function. In order to thoroughly investigate the effect of distraction on neural tissue, a distraction osteogenesis model in the rat was established, using the femur of 30 Sprague-Dawley rats. The animals were randomized in three groups, following different rates of distraction (0.5 mm, 1.0 mm, and 1.5 mm/day) for 50, 25, and 16 days, respectively, so that the final length of distraction was the same in all groups. The mean sciatic function index ranged near normal in all groups. All groups demonstrated decrease of conduction velocity and the area under the curve of the compound action potential, while morphologic alterations consisted of decrease in the number of axons and evidence of active degeneration. Animals in Groups 1 (0.5 mm/day) and 2 (1 mm/day) displayed comparable changes, while in Group 3 animals (1.5 mm/day), changes were significantly more adversely dramatic. The safest and fastest rate of distraction in this rat model was determined to be 1 mm/day.

The use of bone grafts and substitutes in the craniomaxillofacial region

Craniomaxillofacial defects arise from congenital abnormalities or are acquired following trauma or ablative surgery. Various bone grafting techniques have been developed for application in the facial skeleton to assist in the reconstruction of small alveolar deficiencies to more complex, extensive bony defects. Autogenous grafts from different sites vary in volume, stability and contour characteristics. The introduction of allogeneic grafts has further increased the possibilities for hard tissue replacement as have alloplastic substitutes which have been used successfully. Recent advances in bone regeneration in the maxillofacial region using distraction osteogenesis and the recent advent of cell culture techniques have introduced new therapeutic approaches that will provide the foundation for a significant shift in the approach to reconstructive surgery of the facial skeleton.

Rigid external distraction: its application in cleft maxillary deformities

Patients with severe maxillary hypoplasia secondary to congenital facial clefting present numerous challenging problems for the reconstructive surgeon. Traditional surgical/orthodontic approaches for these patients often fall short of expectations, especially for achieving normal facial aesthetics and proportions. The purpose of this paper is to present our clinical experience and cephalometric results with the use of rigid external distraction for the treatment of patients with severe maxillary deficiency. Eighteen consecutive orofacial cleft patients with severe maxillary hypoplasia were treated with maxillary distraction osteogenesis. Criteria for patient selection included severe maxillary hypoplasia with negative overjet of 8 mm or greater, patients with normal mandibular morphology, and patients with full primary dentition or older. There were 10 unilateral cleft lip and palate patients, 6 bilateral cleft lip and palate patients, and 2 patients with severe congenital facial clefting. A maxillary splint was prepared for each patient, and all patients underwent a high Le Fort I maxillary osteotomy. All surgery was performed on either an outpatient or a 23-hour admission basis. No patient required blood transfusions or intermaxillary fixation. Two types of mechanical distraction were utilized in this series. In group 1 (n = 14), the patients underwent rigid external distraction with an external distraction device. In group 2 (n = 4), patients underwent face mask distraction with elastics. There was no surgical morbidity in any of the patients. For the patients in the rigid external distraction group, the mean effective horizontal advancement of the maxilla was 11.7 mm. All of these patients had correction of their negative overjet. For patients in the face mask distraction group, the results were disappointing. The mean effective advancement of the maxilla in this group was only 5.2 mm. In all face mask distraction patients, the initial maxillary hypoplasia was undercorrected. Maxillary distraction osteogenesis with rigid external distraction permits full correction of the midfacial deficiency, including both the skeletal and soft-tissue deficiencies. Rigid external distraction in patients with severe maxillary hypoplasia allows full correction of the deformity through treatment of the affected region only. It offers the distinct advantage of correcting these severe deformities through a minimal procedure. Rigid external distraction has dramatically improved our treatment results for patients with severe cleft maxillary hypoplasia.

Presurgical finite element analysis from routine computed tomography studies for craniofacial distraction: II. An engineering prediction model for gradual correction of asymmetric skull deformities

Finite element analysis from routine computed tomography studies (CT/FEA) allows clinicians to predict the mechanical and anatomic consequences of specific distraction systems before human application. A realistic three-dimensional CT/FEA engineering model of an actual plagiocephalic infant with unicoronal synostosis was developed using 4215 parabolic triangular shell elements and intracranial pressure conditions ranging from 10 to 20 mmHg. The completed finite element analysis model was used to predict the anatomic outcome of multiaxial distraction delivered by hypothetical patterns of rod and node distraction units. The predictions for the various patterns of distraction units were also compared quantitatively with respect to force, stress, strain, and intracranial volume. Best anatomic corrections were achieved with bilateral patterns of distraction units that simultaneously elongated the ipsilateral cranium and shortened the contralateral cranium. Greatest strain levels were experienced within the osteotomy callus, greatest stress levels at the appliance anchorage sites, and the greatest rod force at the ipsilateral lower coronal position.

Mechanobiology of skeletal regeneration

Skeletal regeneration is accomplished by a cascade of biologic processes that may include differentiation of pluripotential tissue, endochondral ossification, and bone remodeling. It has been shown that all these processes are influenced strongly by the local tissue mechanical loading history. This article reviews some of the mechanobiologic principles that are thought to guide the differentiation of mesenchymal tissue into bone, cartilage, or fibrous tissue during the initial phase of regeneration. Cyclic motion and the associated shear stresses cause cell proliferation and the production of a large callus in the early phases of fracture healing. For intermittently imposed loading in the regenerating tissue: (1) direct intramembranous bone formation is permitted in areas of low stress and strain; (2) low to moderate magnitudes of tensile strain and hydrostatic tensile stress may stimulate intramembranous ossification; (3) poor vascularity can promote chondrogenesis in an otherwise osteogenic environment; (4) hydrostatic compressive stress is a stimulus for chondrogenesis; (5) high tensile strain is a stimulus for the net production of fibrous tissue; and (6) tensile strain with a superimposed hydrostatic compressive stress will stimulate the development of fibrocartilage. Finite element models are used to show that the patterns of tissue differentiation observed in fracture healing and distraction osteogenesis can be predicted from these fundamental mechanobiologic concepts. In areas of cartilage formation, subsequent endochondral ossification normally will proceed, but it can be inhibited by intermittent hydrostatic compressive stress and accelerated by octahedral shear stress (or strain). Later, bone remodeling at these sites can be expected to follow the same mechanobiologic adaptation rules as normal bone.

Distraction osteogenesis through high energy fractures

We present a series of three patients with segmental, high energy open tibial fractures with bone loss (2-7 cm), where we have used distraction through a fracture site to replace lost bone. The open fracture was treated by debridement and shortening to eliminate the bone and soft tissue defect. Limb length was restored by distraction instituted through the closed segmental fracture. The length of regenerate formed at the fracture site ranged from 10 to 30 mm. In each case, bone formation at the distracted fracture site was satisfactory and times for regenerate consolidation were similar to those seen in standard corticotomies. These findings suggest that new bone will form in distraction reliably from high-energy fracture sites.

Histochemical and molecular analyses of distraction osteogenesis in a mouse model

A tibial lengthening scheme in the mouse was used to study the molecular and cellular events regulating tissue regeneration during distraction osteogenesis. Here, we report on the surgical technique and frame design and describe the histochemical and molecular aspects of distraction during different phases of treatment. A total of 26 mice were used in this study. The treatment protocol was divided into a latency period of 7 days, a phase of active distraction that lasted 10 days with a distraction rate of 0.42 mm/day, and a maturation phase of 9 days. During latency, the distraction site resembled a stabilized fracture callus on both a histochemical and a molecular level. During active distraction, the gap was characterized by a central fibrous interzone bordered by primary matrix fronts, regenerate bone aligned with the distraction force, parallel columns of vascular sinusoids, and a medullary cavity. Alkaline phosphatase activity was detected in the endosteal and periosteal surfaces of the bone ends. Tartrate resistant acid phosphatase staining revealed that osteoclasts remodeled the bone regenerate as it formed. Collagen type I was expressed in the periosteum and the primary matrix front during distraction, whereas collagen type-II transcripts were localized to discrete regions on the periosteal surfaces, immediately adjacent to the osteotomy ends. Collagen type-II transcripts were not detected in the fibrous interzone. During the maturation phase, cells within the fibrous interzone expressed collagen type I and exhibited abundant alkaline phosphatase activity, suggesting that they had begun to terminally differentiate. Collectively, these data demonstrate the utility of a mouse model to study the molecular and cellular bases for the regeneration and remodeling of tissue.