Unreamed or RIA reamed nailing: an experimental sheep study using comparative histological assessment of affected bone tissue in an acute fracture model.

The purpose of the present study was to evaluate the Reamer/Irrigator/Aspirator (RIA), a reaming system designed to incorporate the advantages of irrigation and suction for every day clinical use. The evaluation process was focused on the displacement of the medullary content and its impact on cortical perfusion. The results of the RIA reamed nailing were compared to conventional non-reamed nailing (NRN). The tibia of the sheep was used as an acute fracture model. The fracture and nailing procedure was followed by intravital staining with Procion red. The effects on cortical perfusion (Procion red staining) were addressed in polymer embedded sections and cryosections. Sudan III stained cryosections were evaluated with respect to the cortical fat distribution. After irrigation and suction minute amounts of fat were observed in the cortex, whereas after non-reamed nailing the endosteal third of the cortical bone was penetrated with fat. Non-reamed nailing acutely showed better perfusion in the endosteal tenth and periosteal third of the cortical bone, after irrigation and suction reaming perfusion was preserved to a lesser degree. Irrigation and suction significantly reduces fat intravasation, and thus the danger of system-wide damage. Therefore, the Reamer/Irrigator/Aspirator is as efficient as its experimental predecessors.

Fat extravasation due to unreamed and experimentally reamed intramedullary nailing of the sheep femur.

AIM: To compare systemic fat extravasation in unreamed and experimentally reamed nailing. METHODS: An osteotomy was created in the proximal third of the femoral shaft in 16 sheep, and intramedullary pressure increase and fat extravasation were monitored for the two nailing techniques. RESULTS: The highest intramedullary pressures, median 2700 mm Hg, and highest percentages of fat extravasation, peaking at almost 90% of fat, were found for the unreamed nailing technique. The values for the reamed group were significantly lower. CONCLUSIONS: The extravasation of intramedullary fat can be attributed to the great increase in intramedullary pressure that occurs during unreamed nailing. Correctly performed intramedullary reaming with the new reaming system produces lower pressures and much less systemic fat extravasation, reducing the risk for fat embolism.

Mechanical and radiological assessment of the influence of rhTGFbeta-3 on bone regeneration in a segmental defect in the ovine tibia: pilot study.

Limitations in the use of autologous bone graft, which is the gold standard therapy in bone defect healing, drive the search for alternative treatments. In this study the influence of rhTGFbeta-3 on mechanical and radiological parameters of a healing bone defect in the sheep tibia was assessed. In the sheep, an 18-mm long osteoperiosteal defect in the tibia was treated by rhTGFbeta-3 seeded on a poly(L/DL-lactide) carrier (n = 4). In a second group (n = 4), the defect was treated by the carrier only, in a third group (n = 4) by autologous cancellous bone graft, and in a fourth group (n = 2) the defect remained blank. The healing process of the defect was assessed by weekly in vivo stiffness measurements and radiology as well as by quantitative computed tomographic assessment of bone mineral density (BMD) every 4 weeks. The duration of the experiment was 12 weeks under loading conditions. In the bone graft group, a marginally significant higher increase in stiffness was observed than in the PLA/rhTGFbeta-3 group (p = 0.06) and a significantly higher increase than in the PLA-only group (p = 0.03). The radiographic as well as the computed tomographic evaluation yielded significant differences between the groups (p = 0.03), indicating the bone graft treatment (bone/per area, 83%; BMD, 0.57 g/cm(3)) performing better than the PLA/rhTGFbeta-3 (38%; 0.23 g/cm(3)) and the PLA-only treatment (2.5%; 0.09 g/cm(3)), respectively. Regarding the mechanical and radiological parameters assessed in this study, we conclude that rhTGFbeta-3 has a promoting effect on bone regeneration. However, under the conditions of this study, this effect does not reach the potential of autologous cancellous bone graft transplantation.

Osteopromotion by a beta-tricalcium phosphate/bone marrow hybrid implant for use in spine surgery.

STUDY DESIGN: Experimental animal study. OBJECTIVE.: Evaluate osteopromotive properties of a beta-tricalcium phosphate (TCP) implant with different osteogenic substances in an animal study. SUMMARY OF BACKGROUND DATA: Current research in spine surgery is focusing on resorbable bone implants because of the high morbidity after iliac crest graft harvesting. Therefore, several osteoconductive scaffolds are combined with osteoinductive substances. METHODS: In 14 sheep, a critical size defect was performed on both tibiae. The sheep were randomized into 3 groups (4 sheep each) and a control group (2 sheep). In the treatment groups, the defects were filled with the beta-TCP scaffold impregnated with either venous blood, bone marrow from sternal aspiration, or a concentrated mononuclear cell suspension derived from sternal bone marrow aspiration. The sheep in each group were euthanized 6 and 12 weeks after the operation; the investigation included quantitative computerized tomography and histology. RESULTS: The best bone formation occurred in the bone marrow group after 6 and 12 weeks, whereas no difference was found between the cell and venous blood groups. Only the bone marrow group showed bone formation inside the scaffold after 6 weeks. We conclude that a beta-TCP scaffold filled with bone marrow aspiration creates a biologic resorbable bone substitute with high osteopromoting capacity. Surprisingly, no better bone formation occurred in the concentrated cells group, which may be a result of technical reasons and needs to be further evaluated. CONCLUSIONS: The combination of beta-TCP and bone marrow has superior osteopromotive properties to venous blood or concentrated mononuclear cells and can be used effectively as a substitute to iliac crest graft.

Influence of copolymer composition of polylactide implants on cranial bone regeneration.

Biodegradable polymers have become useful auxiliary materials for the functional and structural restoration of bone deficiencies. Commercial implants from poly(L/DL-lactide) 70:30 are used clinically for fracture fixation in regions of low load. Implants manufactured from poly(L/DL-lactide) 80:20 are currently being investigated experimentally. The higher degree of crystallinity results in a higher chemical strength and loading capacity which promises advantages for long-term implantation. In this study implants from these two copolymers were applied to promote bone regeneration of bilateral, full thickness, circular cranial defects in 16 adult New Zealand white rabbits. The defects were covered with melt extruded and laser cut polylactide burr hole covers epicranially and endocranially in direct contact to the dura. The defect spaces were kept open with a spacer which created a hollow chamber. Both materials were implanted in each animal. Bone seeking fluorochromes were used to assess the pattern of bone growth. After eight weeks bone regeneration in the defects was assessed radiologically, histologically and by fluorescence microscopy. During the eight weeks observation period the application of a hollow chamber design resulted in almost complete cranial defect healing, whereby the copolymer composition had no effect on the amount or the morphology of the regenerate. The dura mater showed no adverse tissue reactions during these early stages of implantation. Eight weeks is only a short period in the lifetime of the tested polymers and complete bone regeneration can only be expected after complete polymer degradation. Long-term studies or accelerated degradation studies are required to confirm the expected advantages of poly(L/DL-lactide) 80:20.

Early dural reaction to polylactide in cranial defects in rabbits.

Restoring the bone integrity to injured calvariae remains a challenge to surgeons. In this study, the dural biocompatibility of biodegradable poly-L/DL-lactide 80/20 and 70/30 defect covers, designed for guided bone regeneration, was assessed. In each of the 16 test rabbits, bilateral (8.3 mm) cranial defects were created. The different covers were applied to one defect each in every rabbit and consisted of three parts: an epicranial cover, a spacer, and a dural cover. All defects had closed after 8 weeks due to new bone formation. A few giant cells were found at the cover-to-dura interface in equal numbers for both covers. Dural bone formation was present in 15 of 16 rabbits and progressed unhindered by the defect cover or its early degradation products.

Possible problems of moulding the regenerate in mandibular distraction osteogenesis -- experimental aspects in a canine model.

INTRODUCTION: Moulding of the regenerate created by distraction osteogenesis has been shown clinically to be efficient and good enough so that for complex three-dimensional deformities, final adjustments by moulding the regenerate may be part of the treatment plan. This study assessed possible drawbacks of moulding a regenerate, taking into consideration compressive and tensile forces acting simultaneously on the fresh callus. METHOD: Distraction osteogenesis in 15 Beagle mandibles was performed using custom made devices which allowed for lengthening as well as for angulation. After linear distraction of 10 mm, a defined 20 degrees angulation was performed in one step. The position of the fulcrum of the device allowed simultaneously compression and stretching of the regenerated bone. Effects on bone healing were assessed after 6 and 13 weeks of consolidation respectively and compared with a control group where only linear distraction was performed. RESULTS: Radiological and histological investigations demonstrated that no significant differences between the biological behaviour of the compressed and the stretched zones of the regenerate could be found. However, there were signs showing the more critical character of the stretched area. After 6 weeks of consolidation some specimens revealed delayed ossification of the stretched zone. Under stable conditions, this delay was compensated for after 13 weeks of consolidation and complete osseous healing occurred. CONCLUSION: Under stable conditions, a fresh regenerate can be moulded to a considerable extent without permanently endangering osseous healing. Nevertheless tensile forces acting on the regenerate should be minimized to prevent damage to the new bone. This can be achieved by overdistraction prior to callus moulding or by gradually changing the vector of distraction during the lengthening process.

Callus mineralization following distraction osteogenesis of the mandible monitored by scanning acoustic microscopy (SAM).

BACKGROUND: Scanning acoustic microscopy uses ultrasound to analyse histomorphology of tissues with microscopic resolution and delivers data about physical properties of the specimen. MATERIAL AND METHODS: Bony consolidation was monitored by scanning acoustic microscopy in 12 embedded specimens of dog mandibles after distraction osteogenesis. Increasing mineralization was detected by measurements of acoustic impedance (Z). RESULTS: There was a strong correlation between acoustic impedance and time of consolidation. Measurements of the speed of sound (v) provided specific information about non-mineralized zones of the distracted area. Distribution of density in the distracted area could be reconstructed by using the measurements of acoustic impedance and speed of sound. CONCLUSION: The method seems suitable for studying bone remodelling qualitatively and quantitatively.

Cranial defect regeneration in a reserved space.

BACKGROUND: Cranial defects exceeding a certain size do not heal spontaneously and require surgical treatment. The prevention of uncontrolled soft-tissue ingrowth is crucial in the bony healing of such defects. METHODS: Bone regeneration of full-thickness cranial defects was assessed in 16 adult New Zealand White rabbits. A single epicranially placed cover was compared with a hollow chamber with an additional barrier on the dural side. After 8 weeks, bone regeneration in the defects was assessed radiologically, histologically, and by fluorescence microscopy. RESULTS: The hollow chamber design resulted in almost complete cranial defect healing. In contrast, five out of 16 defects covered with a single epicranial burr-hole cover showed hardly any visible bone. Inside the reserved space, there was twice as much bone coverage as compared with burr-hole covers only. CONCLUSIONS: Providing a reserved space for bone regeneration reduces the statistical spread significantly and thus makes the clinical outcome more predictable. Use of a hollow chamber can serve as a useful tool to assess the effect of bone-stimulating factors such as growth factors and bone substitutes. Hollow resorbable implants may offer a new approach in bone regeneration by reducing the need for bone autografting and the associated donor-site morbidity.

Distraction osteogenesis of the canine mandible: the impact of acute callus manipulation on vascularization and early bone formation.

PURPOSE: Manipulations of the newly created regenerate, using adjustable multiplanar devices during distraction osteogenesis or as a 1-step molding procedure at the end of the distraction process, may be necessary to correct the position of the mandible. Treatment of complex deformities may require preplanned major angulation provided by adjustable devices. We sought to assess the effects of molding the fresh regenerate on vascularization and early bone formation within clinically relevant dimensions. MATERIALS AND METHODS: Evaluation of the nature of the problem in mechanical terms was based on a geometrical model, its dimensions chosen with clinical relevance. Custom-made devices, allowing the simultaneous compression and stretching of a regenerate 10 mm long, were fixed bilaterally in the angular region of beagle mandibles (n = 14). Angulation of 20 degrees (n = 7) or 30 degrees (n = 7) was performed immediately after ending the lengthening period, and the animals were killed after a 7-day consolidation period. The vascular system was stained via intravital Procion red infusion and post mortem carbon ink (Deperussol P130; Degussa AG, Frankfurt, Germany) perfusion to assess possible damages. Qualitative and quantitative evaluations of the mineralized tissue were performed with contact radiography, quantified computed tomography, and histologic assessment. RESULTS: The only finding indicating mechanical forces acting on the regenerate was related to orientation of the collagenous fibers. Vascular damage was not observed. Mineralization patterns were identical in both the compressed and the stretched zone. The degree of angulation had no visible impact on early bone formation, even if compression and stretching of the regenerate at a range of 33% to 54% exceeds most clinical requirements. However, the amount of callus formation differed independent of the shaping angle, revealing parameters other than the degree of angulation to be important. CONCLUSIONS: Although the newly forming bone is highly sensitive to nonphysiologic strain during the lengthening process, a completed fresh regenerate, created by distraction osteogenesis, can be manipulated to a considerable extent without endangering early callus formation. Manipulation of the regenerates would provide a precise final result, minimizing the need for secondary corrections and diminishing treatment duration and costs.

Theoretical considerations for the surgical correction of mandibular deformity in hemifacial microsomia patients using multifocal distraction osteogenesis.

PURPOSE: This theoretical pilot study investigated the geometric changes necessary to normalize the mandibular shape in hemifacial microsomia. Using the mandibular deformity of a 13-year-old patient affected by hemifacial microsomia as an example, we addressed 2 main issues. First, the number of segments needed for adequate reshaping of the deformed mandible is evaluated. Second, the geometry of the intersegmental gaps resulting from reposition of the segments is correlated with established parameters of distraction osteogenesis to theoretically predict the practicability of correction using multifocal distraction osteogenesis. MATERIALS AND METHODS: Virtual surgery was performed on a solid mandible model created from computed tomography (CT) data from a patient with hemifacial microsomia type IIB. In the first step, ideal mandibular reshaping was achieved according to anthropometric standard measurements using 7 osteotomies. By scanning and superimposition of the virtual models and variation of distraction sites and numbers, we assessed the minimal number of osteotomies necessary for optimal correction of the deformity. Geometrical evaluation of the regeneration and assessment of the possibilities of continuous curved distraction were also performed. RESULTS: Three osteotomies were shown to be sufficient for complete mandibular reshaping. Using accepted parameters for distraction osteogenesis, the geometry of the regenerate allows for continuous curved distraction. However, simultaneous movements at several distraction sites result in interfering vector forces, making coordination of multifocal distraction difficult. CONCLUSION: Theoretical assessment of a severe mandibular hypoplasia in hemifacial microsomia revealed the 3-dimensional (3D) complexity of the deformity for corrective procedures, especially distraction osteogenesis. Despite precise planning and transfer of the plan to the patient, multifocal 3D distraction may result in deviations from the planned result. Manipulation of the fresh regeneration may be necessary to correct inaccuracies.

Effect of perforations in burr hole covers on cranial bone regeneration in rabbits.

The reconstruction of bone defects is a significant problem in cranio-maxillofacial surgery. In an effort to avoid the known disadvantages of autogenous bone grafting, alternatives have been investigated. Bone substitute materials, degradable or nondegradable, aim at facilitating bone regeneration, while they take over load-bearing functions for a period of time. In this study, the healing of cranial defects in rabbits was assessed using polylactide guiding covers with and without perforations. Bilateral circular cranial defects were produced in 16 New Zealand white rabbits. The defects were covered with extruded and laser cut polylactide burr hole covers, each animal receiving a perforated burr hole cover on one side and a nonperforated one on the contralateral side. Bone seeking fluorochromes were administered at regular intervals. After an observation period of 8 weeks the amount of bone regeneration in the area of the defects was quantified from contact radiographs, and the dynamics of bone formation were assessed by fluorescence microscopy. Stained sections were used to analyze morphologic differences. No signs of adverse tissue reactions or osteolysis were observed. A bone-guiding function was observed for both covers with or without perforations. Intracranial tissue herniation into the defect hindered the regeneration process. Wide intraindividual and interindividual variation became apparent and average defect filling was only 40% within the 8-week observation period. In this model the perforated covers offered no advantage over nonperforated covers. It can be concluded from this study, that the use of external burr hole covers alone does not guarantee a full thickness regeneration of the cranial defect, but it provides a guiding function for promotion of structured bone regeneration.