The use of computed tomography to quantitate bone formation after distraction epiphysiolysis in the rabbit

Qualitative assesement of newly formed bone after distraction osteogenesis of mandible in patients with facial asymmetry using 3 dimensional computed tomography

Introduction

Distraction osteogenesis is a surgical technique of new bone formation between the osteotomized bone segments with the help of gradual incremental traction. As distraction osteogenesis is slow biologic process, soft tissue changes gradually follow the new bone formation. Mandibular distraction is one of the accepted modalities to treat the triad of TMJ ankylosis, obstructive sleep apnoea & micrognathia and also for facial asymmetry cases like hemifacial microsomia, mandibular hypoplasia etc. After the distraction osteogenesis, some relapse has been noticed in patients. Therefore, this study was conducted to assess the quality of the newly formed bone after distraction osteogenesis of mandible using 3 dimensional computed tomography (3DCT Scan) to evaluate its relation with relapse if any.

Objectives

1) To objectively analyse the quality of bone formed after mandibular distraction osteogenesis.2) To observe the site & architecture of newly formed bone after distraction is complete.

Material and methods

Total 5 patients of facial asymmetry reported to the Department of Oral and Maxillofacial Surgery were enrolled. Distraction osteogenesis of mandible was carried out in all the patients. Radiographic analysis (CT Scan) was done after 1 year of surgery for further planning and management of deformity. The non-distracted site was considered as a control side and it was compared with newly formed bone at distraction site. The standard & universally accepted radio density measuring Hounsfield Unit (HU) in 3DCT scan was calculated in axial,coronal, sagittal sections from distraction site and it was compared with non-distraction site, as Hounsfield unit is considered as a standard tool for measuring the bone density to evaluate the quality as well as quantity of newly formed bone.

Results

The total mean Hounsfield Unit of distracted site of all three sections was 359.8 HU and non-distracted site was 545.2 HU. Statistical analysis was carried out using students paired ttest and p value was obtained which was <0.01 suggestive of statistically significant difference between the quality of bone in distracted site and non-distracted site.

Conclusion

The findings of our study concluded that the quality of bone formed after distraction osteogenesis was satisfactory but it was less mineralized with less dense trabecular pattern compared to non-distracted bone region of mandible which leads to some relapse. Therefore it was advisable to reinforce the distracted bone segment by cutting the activation arm of distractor itself or mini plate or reconstruction plate to prevent relapse.

Evaluation of distracted mandibular bone using computed tomography scan and ultrasonography: technical note

OBJECTIVES

Distraction osteogenesis is considered an important reconstruction armamentarium in the management of mandibular deformities and deficiency disorders. The duration of the consolidation period is still a debatable issue among the clinicians. Evaluation of the newly formed bone is the cornerstone for terminating the consolidation period safely. The aim of this study is to find a more conservative protocol for the evaluation of callus distraction by monitoring bone healing using two different examination tools: ultrasonography and dental CT.

METHODS

Four adult patients (three women and one man) underwent mandibular distraction (using two intraoral and two extraoral devices). The latency period was 5-7 days and the distraction was at a rate of 2 mm per day, with 12-14 weeks of consolidation. All patients were evaluated during activation, 3 months, 6 months and 1 year post-distraction. Evaluation included clinical examination, plain radiographs, CT and ultrasonography examinations.

RESULTS

Ultrasonographic examination of the healing callus revealed four different phases of maturation. These phases were similar to the degree of tissue calcification as measured by CT. Tissue density across the distraction wound at the time of distractor removal (12-14 weeks) was equal to or less than one-third of normal bone density.

CONCLUSIONS

Clinical monitoring of mandibular distraction wounds can be successfully achieved through frequent use of ultrasonographic examinations. Standardization of ultrasonography based on CT findings will expand the reliability of ultrasound in monitoring callus maturation. An algorithm for evaluation of distraction wound healing is suggested.

Correlation of pQCT bone strength index with mechanical testing in distraction osteogenesis

Distraction osteogenesis is an established method of treatment of non-unions and limb length discrepancies. Despite improvements in surgical techniques and fixation devices there is still a considerable possibility of failure of the regenerate bone after frame removal. The hypothesis of the present experimental study was that a noninvasive bone strength marker, the strength-strain index (SSI) measured by peripheral quantitative computerized tomography (pQCT), could be significantly correlated with a biomechanical bone strength index, the maximum load at bone failure (F(max)), assessed in a three-point bending test. The right tibias of fifteen male New Zealand White rabbits were subjected to gradual lengthening using an external fixator. At the end of the consolidation phase (55th day) the animals were sacrificed and the lengthened tibiae were collected free of soft tissue, after removal of the lengthener, for immediate scanning and mechanical testing. The values of cortical bone mineral density, cortical bone area, and the corresponding SSIy, as measured by pQCT, were assessed for statistically significant correlation relative to the values of the F(max) and stiffness as evaluated by the three-point bending test were assessed. SSIy showed a statistically significant positive correlation with the maximum load (F(max)) with a correlation value R=0.846 (p<0.001), and it was a good predictor of F(max) since it was able to describe the 71.6% of variability of F(max)(R2=0.716). Furthermore, cortical bone area appeared to be highly correlated with F(max) (p<0.005), but it was a less efficient predictor of F(max) (R2=0.471). There was, also, a statistically significant correlation between SSIy and bone stiffness as assessed in the 3-point bending test (p<0.005). In conclusion, the present study reveals that the SSI can be used as a sensitive index of adequate consolidation of the regenerate bone, possibly able to reduce mechanical failure due to premature frame removal. In clinical relevance, the aforementioned hypothesis should be applied in studies of human populations and possible confirmation of its validity would establish pQCT as a valuable diagnostic tool not only in distraction osteogenesis but also in other techniques of bone healing.

Assessment of the distraction regenerate using three-dimensional quantitative computer tomography

This study presents a new method for objective assessment of the distraction regenerate using three-dimensional quantitative computer tomography (3D-QCT). The distraction specimens of 16 sheep that underwent bifocal cranial distraction osteogenesis to reconstruct a critical size defect were used to evaluate this method. To analyse the validity of this method the results were compared to conventional quantitative computer tomography (QCT). Squared correlation coefficients (r(2)) according to Sackett showed a high reliability (r(2) > 70% for the total DO regenerate, DO Regions 2-4). Method comparison according to Bland-Altman (< or =6.25% of measurements out of 95% limits of agreement) showed that three-dimensional computer tomography based bone densitometry is valid for future DO research.

Assessment of bone formation in a porcine mandibular distraction wound by computed tomography

The purpose of this study was to document the progression of bone formation in a porcine mandibular distraction wound, at various distraction rates and fixation times, using three-dimensional computed tomography. Bone formation was assessed in a 0-day latency model (n=24 minipigs) using distraction rates of 1, 2, or 4 mm/day to create a 12 mm distraction gap. Animals were sacrificed at 0, 8, 16, or 24 days fixation. For experimental and control sides, three-dimensional data from computed tomographic scans were used to calculate the percent bone volume in the regions of interest. Standardized plain radiographs were used to evaluate bone formation with a semiquantitative scale: 0, 1, 2, 3. Mean percent bone volume and radiographic bone fill scores (pooled sample) increased with fixation time from 16.8% and 0.17 at 0 days, to 64% and 2.0 at 24 days fixation. Mandibles distracted at 1mm/day had higher CT values and bone fill scores than mandibles distracted at 2 or 4 mm/day. At 24 days fixation, the maximum percent bone volume (64%--1 mm/day; 24 days fixation) remained below control values (81.3%). The results of this study indicate that despite high bone fill scores on plain radiographs, the highest percent CT bone volume achieved in this model was 64%.

Calcitonin administration in a rabbit distraction osteogenesis model

The effect of salmon calcitonin on the maturation of the regenerate bone was assessed in an experimental model in rabbits. Twenty-six New Zealand White male rabbits, approximately 5 months old and weighing 3 to 3.5 kg, were subjected to a mid-diaphyseal tibial osteotomy. After 5 days, the right tibia was lengthened gradually at a rate of 0.375 mm every 12 hours, for 10 days. Ten international units of salmon calcitonin were administered daily subcutaneously to the study group (14 animals), whereas the animals of the control group (12 animals) were injected with a placebo, for the duration of the experiment. The bone mineral density of the regenerate bone was assessed on Days 20, 35, 45, and 55 of the experiment, in both groups, using dual energy xray absorptiometry. No statistical significant difference was found in the dual energy xray absorptiometry measurements between the study and control groups regarding the change of the bone mineral density of the new bone relative to a preoperative baseline measurement. Characteristic time-related changes were observed in the bone mineral density of the regenerate bone during its maturation, which proved to be identical in both groups. It seems that the administration of calcitonin does not enhance regenerate bone mineralization rate and tendency during bone lengthening.

Correlation of biomechanical stiffness with plain radiographic and ultrasound data in an experimental mandibular distraction wound

The aim of this study was to determine the stiffness of a porcine mandibular distraction wound at the end of neutral fixation.Twenty-four Yucatan minipigs underwent unilateral mandibular distraction: zero-day latency, rates of 1, 2, and 4 mm per day, distraction gap of 12 mm. Radiographic and ultrasound bone fill scores at 0, 8, 16 and 24 days of neutral fixation were used to evaluate interval healing. At sacrifice, biomechanical stiffness was determined using an Instron machine to produce a downward force of 2 mm/min at the premolar occlusal surface. Force (kilo-Newton, kN) and displacement (mm) were recorded at a rate of 10,000 points/second. Stiffness across the distraction wound, plain radiographic and ultrasound bone fill scores all increased with duration of neutral fixation and were highest for the 1 mm per day group at all time points. At the end of fixation, even in the most clinically stable group, stiffness across the distraction wound was only 25.5% of control.Despite clinical stability and high bone fill scores by X-ray and ultrasound, the distraction wound did not achieve normal stiffness at the end of neutral fixation in this model. This may have implications for the management of patients who undergo large movements by distraction.

Use of ultrasound to assess healing of a mandibular distraction wound

PURPOSE

A standardized, noninvasive technique to assess healing of the mandibular distraction wound is not available. Current methods include clinical examination, plain radiography, and computed tomography. These imaging techniques are expensive and obligate the patient to serial radiation exposure. In addition, anatomic overlap and metal artifacts may obscure the distraction gap. In contrast, ultrasound has been shown to be a noninvasive, efficient, and inexpensive way to evaluate bone healing. The purpose of this study was to test the feasibility of ultrasound to evaluate an experimental mandibular distraction osteogenesis wound.

MATERIALS AND METHODS

Distraction devices were placed via a submandibular incision into 24 minipigs. The protocol consisted of 0-day latency and distraction rates of 1, 2, or 4 mm/d for a 12-mm gap. The wounds were assessed in vivo after 0, 8, 16, and 24 days of neutral fixation. Ex vivo radiographs were used to estimate bone fill using a semiquantitative score. A semiquantitative ultrasound score was assigned, and the beam penetration depth was measured in millimeters.

RESULTS

In all groups, clinical stability of the distraction wound increased with the duration of fixation. Plain radiographs, taken during neutral fixation, showed that the desired distraction gap was achieved and maintained. The ultrasound score increased with fixation time, whereas beam penetration depth decreased as expected. Ex vivo radiographs showed increasing bone fill score with time and paralleled the ultrasound score.

CONCLUSIONS

The results of this feasibility study indicate that ultrasound is potentially useful for the assessment of bone formation in distraction osteogenesis wounds.

Evaluation of the consolidation period during osteodistraction using computed tomography

The use of distraction osteogenesis offers an alternative approach to the correction of craniofacial deformities. However, little is known with respect to the appropriate length of the consolidation period for the newly formed bone. The objective of this study was to evaluate, by quantitative computed tomography, the regenerate bone produced during osteodistraction of the dog mandible at three different consolidation times. Twelve skeletally mature male beagle dogs were equally separated into three experimental groups. Each dog underwent 10 mm of bilateral distraction osteogenesis to lengthen the mandible. After the distraction period, the bone was allowed to consolidate for 4, 6, or 8 weeks, at which time the animals were sacrificed and the mandibles harvested for computed tomographic imaging. The results demonstrate a significantly lower mean bone density of the regenerate in the 4 week group when compared with either the 6 or 8 week groups (P < .01). There was no significant difference, however, in mean bone density between the 6 and 8 week groups.

Periosteal insulin-like growth factor I and bone formation. Changes during tibial lengthening in rabbits

We investigated changes in periosteal insulin-like growth factor I (IGF-I) during tibial lengthening. In 37 rabbits, an osteotomy of the right middle tibia was made and fixed by a unilateral external fixator. The rabbits were randomized into 6 groups: the tibiae were distracted at 0.5 mm/day up to 4 weeks and the animals killed after 2 weeks, 4 weeks or 6 weeks, for each period there was a control group with no distraction. Periosteal IGF-I was measured by radioimmunoassay and bone formation was quantified by CT scanning. During bone lengthening, CT showed moderate bone formation, while IGF-I was increased. When lengthening was stopped, IGF-I returned to a basal level, and CT scanning showed considerable bone formation. Our study suggests that IGF-I plays a role in an early stage of bone formation.

Effect of direct current stimulation on bone growth after distraction epiphysiolysis of the rabbit tibia

The effect of direct current stimulation on bone formation during limb lengthening was tested in a lower leg lengthening model in the rabbit. Limb lengthening was performed by distraction epiphysiolysis. A specially designed external distraction device was placed at the tibia. The distractor allowed 10 mm of lengthening in 4 weeks. Two weeks after starting the distraction, a platinum electrode was passed through the anterior cortex below the tibial tuberosity and advanced via the medullary cavity so that the tip rested in the elongated zone. Stimulation started at the time of placement of the electrodes and was continued for 3 weeks. The electrode in the elongated zone served as the cathode; the anode was placed subcutaneously. A 20 microA stimulus was selected. A control group received the same treatment without stimulation. Bone formation in the elongated zone was evaluated by histology and scintigraphy. The data from this experiment show that direct current stimulation in the early phase of a limb lengthening procedure had no effect on the extent of bone formation in the elongated zone.