Bone mineralization at the callotasis site after completion of lengthening

Bone Regenerate Evaluation Methods

Since its introduction by Ilizarov, the distraction osteogenesis technique has been used to treat trauma-related conditions, infections, bone tumors, and congenital diseases, either as methods of bone transport or elongation. One of the major dilemmas for the orthopedic surgeon who performs osteogenic distraction is establishing a reproducible method of assessing the progression of the osteogenesis, enabling the early detection of regenerate failures, in order to effectively interfere during treatment, and to determine the appropriate time to remove the external fixator. Several quantitative monitoring methods to evaluate the structural recovery and biomechanical properties of the bone regenerate at different stages, as well as the bone healing process, are under study. These methods can reveal data on bone metabolism, stiffness, bone mineral content, and bone mineral density. The present review comprehensively summarizes the most recent techniques to assess bone healing during osteogenic distraction, including conventional radiography and pixel values in digital radiology, ultrasonography, bone densitometry and scintigraphy, quantitative computed tomography, biomechanical evaluation, biochemical markers, and mathematical models. We believe it is crucial to know the different methods currently available, and we understand that using several monitoring methods simultaneously can be an ideal solution, pointing to a future direction in the follow-up of osteogenic distraction.

Early Weight-bearing Accelerates Regenerate Bone Mineralisation: A Pilot Study Comparing Two Post-operative Weight-bearing Protocols Following Intramedullary Limb Lengthening Using the Pixel Value Ratio

Introduction

Limb lengthening is increasingly accomplished by internal lengthening nails. Previous versions of the magnetic lengthening nails made from titanium alloy allowed limited weight-bearing. In contrast, the newer nails made of stainless steel allow increased weight-bearing. An objective comparison of the rate of healing of the regenerate bone based on the weight-bearing capabilities of these two types of lengthening nails has not been evaluated. The hypothesis for the study is that earlier commencement of full weight-bearing in patients treated with the stainless steel STRYDE® nail will lead to faster healing of the regenerate bone during intramedullary limb lengthening compared with those treated with the titanium PRECICE® nail.

Materials and methods

Thirty patients, divided into two groups of 15 each, underwent antegrade intramedullary lengthening of the femur using a magnetic lengthening nail between May 2017 and November 2020. The pixel value ratio (PVR) obtained from serial digital radiographs was used to quantitatively determine the regenerate bone's mineralisation rate. We compared the rate of healing of the regenerate bone in both groups of patients using the PVR.

Results

Patients treated with the STRYDE® nail achieved unassisted full weight-bearing significantly earlier than patients treated with the PRECICE® nail (12 weeks vs 17 weeks for STRYDE® and PRECICE® nail-lengthened patients, respectively, p = 0.003). There was no difference in the PVR between both groups of patients at the time of full weight-bearing (p = 0.0857). However, patients treated with the STRYDE® nail attained a PVR of 1 significantly earlier than those treated with the PRECICE® nail (0.0317).

Conclusion

The STRYDE® nail provides an earlier return of function and full weight-bearing compared with the PRECICE® lengthening nail. Earlier commencement of weight-bearing ambulation leads to more rapid mineralisation of the regenerate bone in patients undergoing intramedullary limb lengthening.

How to cite this article

Bafor A, Duncan ME, Iobst CA, et al. Early Weight-bearing Accelerates Regenerate Bone Mineralisation: A Pilot Study Comparing Two Post-operative Weight-bearing Protocols Following Intramedullary Limb Lengthening Using the Pixel Value Ratio. Strategies Trauma Limb Reconstr 2022;17(3):148-152.

Evaluating the Utility of the Pixel Value Ratio in the Determination of Time to Full Weight-bearing in Patients Undergoing Intramedullary Limb Lengthening

Introduction

Limb lengthening using intramedullary nails is an increasingly popular method of achieving limb length equalisation. Currently, the decision regarding when to commence full weight-bearing (FWB) remains largely subjective. Objective criteria for determining the proper timing of FWB would be helpful to limb lengthening surgeons. This study examines using the pixel value ratio (PVR) as an objective method to determine the time to FWB for patients being lengthened with an intramedullary nail.

Materials and methods

A retrospective chart review of 42 patients who underwent unilateral lengthening of the femur was undertaken. The PVR of all four cortices of the regenerate bone was monitored throughout the distraction and consolidation stages to determine the ratio at the time of FWB.

Results

Clinically and radiologically determined FWB was achieved at a mean time of 125.7 ± 30.1 days from surgery. The mean PVR at the time of FWB was 0.94. The medial cortex healed fastest with a mean PVR of 0.96, while the posterior cortex healed slowest with a mean PVR of 0.92.

Conclusion

The PVR is a quick and reliable method to objectively assess the state of healing of the regenerate bone during distraction osteogenesis. We observed that there were no adverse effects when subjects commenced FWB when three out of the four cortices had a PVR of at least 0.93.

How to cite this article

Bafor A, Duncan ME, Iobst CA. Evaluating the Utility of the Pixel Value Ratio in the Determination of Time to Full Weight-bearing in Patients Undergoing Intramedullary Limb Lengthening. Strategies Trauma Limb Reconstr 2020;15(2):74-78.

Daily subcutaneous Teriparatide injection increased bone mineral density of newly formed bone after tibia distraction osteogenesis, a randomized study

Long bone defects are often treated by bone segment transport with the Ilizarov method requiring months spent with fixator mounted until bony consolidation of the newly formed bone. Shortening of consolidation would allow earlier fixator removal and earlier return to work. In pre-clinical studies parathyroid hormone, increased bone mineral density and mechanical properties of regenerate bone formed during distraction osteogenesis. Clinical studies showed that Teriparatide accelerated fracture healing in patients with osteoporotic fracture of the pelvis, hip, wrist and shoulder. We hypothesized that rhPTH(1-34) (Teriparatide) administered to patients who had undergone distraction osteogenesis, would increase mineralization of the regenerate formed during the consolidation phase. Sixteen patients with tibial defects after infection, underwent bone segment transport and at the time of docking the transport segment, were randomized to 8 weeks treatment with daily subcutaneous 0.20-μg Teriparatide injection followed by 8 weeks with no treatment, or to 8 weeks with no treatment followed by 8 weeks with daily subcutaneous 0.20 μg Teriparatide injection. Bone mineral density (BMD) of the regenerate was measured at the time of docking, 8 weeks after docking and 16 weeks after docking with DEXA. Functional evaluation was performed after one year. The design was a cross-over study. Overall BMD increased 0.14 g/cm² in 8 weeks without treatment and 0.33 g/cm² under Teriparatide treatment. After adjustment for a potential phase difference, 8 weeks of Teriparatide treatment led to an additional 0.19 g/cm² BMD increase (95%-CI:[0.11,0.28], p < 0.001). The ratio of the BMD increase between the two treatments was 0.33/0.14 = 2.43 (CI: [1.21,3.65]). Teriparatide treatment during the consolidation phase of distraction osteogenesis doubled the mineralization rate of the regenerate when compared to no treatment.

Serial bone mineral density ratio measurement for fixator removal in tibia distraction osteogenesis and need of a supportive method using the pixel value ratio

Distraction osteogenesis is one of the common procedures for limb lengthening. However, attempts are being made constantly to establish objective guidelines for early and safe removal of a fixator using a sensitive and quantitative measurement technique. Dual-energy X-ray absorptiometry (DEXA) has been evaluated in the past for understanding callus stiffness, and the present study is a step further in this direction. The purpose of this study was to evaluate the correlation between bone mineral density ratio (BMDR) obtained by a DEXA scan and the pixel value ratio (PVR) on plain digital radiographs at each cortex and various callus pathways and callus shapes as described by Ru-Li's classification. A retrospective analysis of 40 tibial segments in 23 patients operated upon for various indications for limb lengthening was carried out. There were 11 male and 12 female patients with a mean age of 18 years. The Ilizarov method was applied after monofocal osteotomy, and distraction and consolidation were monitored using digital radiographs and DEXA scanning. BMDR was positively correlated with PVR, and the optimal BMDR for removal of the fixator was found to be 0.511. PVR of all cortices, except the anterior cortex, showed significant positive correlation with BMDR of the regenerate. There was good correlation between BMDR and PVR in the homogenous or heterogenous pathway according to callus shape and pathway. Thus, this study shows that BMD measurement can provide an objective and noninvasive method for assessing the rate of new bone formation during tibial distraction osteogenesis. It can thus function as an effective adjunct to measure callus stiffness, along with PVR, using digital radiographs, especially in cases in which callus maturation and stiffness is doubtful. Further studies especially dealing with callus progression through the lucent pathway as well as those dealing with regenerate fractures may be needed to conclusively prove the efficacy of this method for measurement of callus maturation.

Distraction osteogenesis using a longitudinal corticotomy

PURPOSE

The purpose of this study was to evaluate whether the use of a longitudinal corticotomy (S-Z osteotomy) results in more rapid consolidation following distraction osteogenesis of short tibiae.

METHODS

Sixty-seven lengthening procedures were performed in 51 patients ranging in age from nine to 38 (mean 25) years. Diagnoses included short stature (32 tibiae), postpolio limb deformity (22 tibiae), osteomyelitis (three tibiae), trauma (two tibiae) and other diagnoses (eight tibiae). Forty-five lengthenings were performed via a longitudinal corticotomy, and 22 were performed via a transverse corticotomy. Patients were followed until consolidation of the regenerated bone was noted radiographically (consolidation time). The healing index (consolidation time per centimetre of lengthening) was calculated for each patient and compared between groups.

RESULTS

The healing index was significantly lower in the S-Z group (30.8 ± 9.6 days/cm) than in the transverse corticotomy group (46.8 ± 20.2 days/cm) (p < 0.0001). Mean lengthening was 6.6 (range 2.5-12.5) cm in the S-Z group and 5.8 (range 2.0-12.0) cm in the transverse group (p = 0.28). Mean consolidation time was 6.3 ± 2.8 (range 3-16) months in the S-Z group and 8.1 ± 3.8 (range 3-13.5) months in the transverse group (p = 0.03).

CONCLUSION

The S-Z osteotomy safely reduces consolidation time of regenerative bone during distraction osteogenesis in the tibia relative to a transverse corticotomy.

Callus features of regenerate fracture cases in femoral lengthening in achondroplasia

OBJECTIVE

We studied the callus features seen in cases of regenerate fracture in femoral lengthening using a monolateral fixator in achondroplasia to determine whether callus types and shapes can predict the probability of callus fracture.

MATERIALS AND METHODS

The radiographs of 28 cases of femoral lengthening in 14 patients, 14 cases of callus fracture, and 14 cases without callus fracture were retrospectively analyzed by four observers and classified into different shapes and types in concordance with the Ru Li classification.

RESULTS

The average lengthening of 9.4 cm (range 7.5-11.8 cm) was achieved, which was 41% (range 30-55%) of the original length and the average timing of callus fracture was 470 days (range 440-545 days) after surgery in the callus fracture group. While the average lengthening of 9.1 cm (range 8-9.7 cm) was achieved, this was 30% (range 28-32%) of the original length in the group of patients without callus fracture. The callus was atypically shaped, there was a 48% average (range 30-72%) reduction of the callus width compared with the natural width of the femur, and a lucent pathway was present in all cases of regenerate fracture.

CONCLUSION

A lucent pathway was seen in all fracture cases with concave, lateral, and atypical shapes, and there was more than 30% lengthening and 30% reduction of the callus width compared with the natural width of the femur, which are the warning signs for regenerate fractures. These signs help the surgeon to predict the outcome and guide him in planning for any additional interventions. The Ru Li classification is an effective method for the evaluation of the chance of callus fracture.

Rh-BMP-2 in distraction osteogenesis: dose effect and premature consolidation

We asked whether locally applied recombinant-bone morphogenic protein-2 (rh-BMP-2) with a type I collagen carrier could enhance the consolidation phase in distraction osteogenesis and whether a dose effect could be reported. We performed unilateral transverse osteotomy of the tibia in 15 immature male rabbits. In Group I (five rabbits), 750 microg of rh-BMP-2 on the type I collagen sponge (Inductos, Medtronic) was locally applied on the day of osteotomy; the Group II animals (five rabbits) received 375 microg of the drug and the Group III (control group, five rabbits) had no local application. After 7 days, 3 weeks of distraction was begun at a rate of 0.5 mm/12 h. Starting week 2 of distraction, we assessed radiographic, ultrasonographic, and densitometric parameters once per week. Animals were sacrificed after a 3-week consolidation period. Radiographic evaluation revealed increased regenerate ossification in the rh-BMP-2 groups compared with the control group. The bone mineral content was significantly higher in the rh-BMP-2 treated groups at each time point. A dose effect is shown as densitometric parameters were significantly higher between Groups I and II. 3/5 of the Group I treated animals developed a premature bony union in the regenerate resulting in premature fusion and incomplete distraction.

Bone lengthening osteogenesis, a combination of intramembranous and endochondral ossification: an experimental study in sheep

We evaluated the morphological features of the newly formed tissue in an experimental model of tibial callotasis lengthening on 24 lambs, aged from 2 to 3 months at the time of operation. A unilateral external fixator prototype Monotube Triax^® (Stryker Howmedica Osteonics, New Jersey) was applied to the left tibia. A percutaneous osteotomy was performed in a minimally traumatic manner using a chisel. Lengthening was started 7 days after surgery and was continued to 30 mm. The 24 animals were randomly divided into three groups of 8 animals each: in Group 1, lengthening took place at a rate of 1 mm/day for 30 days; in Group 2, at a rate of 2 mm/day for 15 days; in Group 3, at a rate of 3 mm/day for 10 days. In each group, 4 animals were killed 2 weeks after end of lengthening, and the other 4 animals at 4 weeks after end of lengthening. To assess bony formation in the distraction area, radiographs were taken every 2 weeks from the day of surgery. To study the process of vascularization, we used Spalteholz’s technique. After killing, the tibia of each animal was harvested, and sections were stained with hematoxylin and eosin, Masson’s trichrome, and Safranin-O. Immunohistochemistry was performed, using specific antibodies to detect collagens I and II, S100 protein, and fibronectin. A combination of intramembranous and endochondral ossification occurred together at the site of distraction. Our study provides a detailed structural characterization of the newly formed tissue in an experimental model of tibial lengthening in sheep and may be useful for further investigations on callotasis.

Objective guidelines for removing an external fixator after tibial lengthening using pixel value ratio: a pilot study

During limb lengthening over an intramedullary nail, decisions regarding external fixator removal and weightbearing depend on the amount of callus seen at the lengthening area on radiographs. However, this method is subjective and objective evaluation of the amount of callus likely would minimize nail or interlocking screw breakage and refracture after fixator removal. We asked how many cortices with full corticalization of the newly formed bone at the lengthening area are needed to allow fixator removal and full weightbearing and how to radiographically determine the stage of corticalization. We retrospectively reviewed 17 patients (34 lengthenings) who underwent bilateral tibial lengthenings over an intramedullary nail. The average gain in length was 7.2 +/- 3.4 cm. We determined the pixel value ratio (ratio of pixel value of regenerate versus the mean pixel value of adjacent bone) of the lengthened area on radiographs. There were no nail or screw breakage and refracture. Partial weightbearing with crutches was permitted when the pixel value ratio was 1 in two cortices and full weightbearing without crutches was permitted when the pixel value ratio was 1 in three cortices. The pixel value ratio on radiographs can be an objective parameter for callus measurement and may provide guidelines for the timing of external fixator removal. We cannot determine from our limited data the minimum pixel value in how many cortices would suggest safe removal, but we can say our criteria were not associated with subsequent refracture.

Bone stiffness in children: part II. Objectives criteria for children to assess healing during leg lengthening

BACKGROUND

The decision when to remove the frame after limb lengthening through standard distraction osteogenesis remains a challenge. Multiple studies have attempted to find objective criteria to assess bone healing after fracture or bone lengthening. However, there is a paucity of such data for the pediatric population. The purpose of this study was to correlate data obtained after dual-energy x-ray absorptiometry (DXA) measurement and bending stiffness in children to find an end-point value for the safe removal of an external fixation device.

METHODS

We investigated 16 consecutive children aged between 5.5 and 16.7 years who had 22 lengthenings by callotasis. Twelve femurs and 10 tibiae were lengthened with a monoplane Orthofix external fixator. Fifty simultaneous measurements of bending bone stiffness measured with an Orthometer and DXA scans (bone mineral content [BMC], bone mineral density, volumetric bone mineral density, BMC/1 cm, Area/1 cm, BMC/1 cm, Area) were obtained during healing process. Four femoral fractures were reported after the removal of the external fixation device. Linear regression analysis was used to calculate the squared correlation coefficients for the relation between the DXA scans and the mechanical tests measuring bone stiffness.

RESULTS

The bone stiffness measurement of the intact bone was compared with consecutive measurements of the bone stiffness of the regenerate, and it was expressed as a percentage (coefficient). We compared the BMC of the regenerate with the same bone area of the opposite limb. The best correlation was observed for anteroposterior (AP) bone stiffness coefficient and BMC coefficient (R = 0.82). The linear equation was BMC coefficient = 0.5 x AP stiffness coefficient + 30. The end point of 75% of BMC of the regenerate corresponds to 75% of the AP stiffness on DXA scanning; this is the time when we should consider safe removal of the fixator.

CONCLUSIONS

Our method of comparing bone stiffness and DXA measurements gives an objective healing end point for every patient irrespective of his or her size. This method could allow noninvasive measurement of the end point and identified at-risk population of children, reducing regenerate fracture after bone lengthening.

Quantitative assessment of mineralization in distraction osteogenesis

OBJECTIVES

The most important decision in distraction osteogenesis is the timing of fixator removal. Various methods have been tried, such as radiographic appearance of callus and bone mineral density (BMD) assessment, but none has acquired gold standard status. The purpose of this study was to develop another objective method of assessment of callus stiffness to help clinicians in taking the most important decision of when to remove the fixator.

MATERIALS AND METHODS

We made a retrospective study of 70 patients to compare the BMD ratio and pixel value ratio. These ratios were calculated at the time of fixator removal, and Pearson's coefficient of correlation was used to show the comparability. Inter- and intra-observer variability of the new method was also tested.

RESULTS

Good correlation was found between BMD ratio and pixel value ratio, with a Pearson's coefficient of correlation of 0.79. The interobserver variability was also low, with high intra-observer reproducibility, suggesting that this test was simple to perform.

CONCLUSION

Pixel value ratio is a good method for assessing callus stiffness, and it can be used to judge the timing of fixator removal.

Callus patterns in femur lengthening using a monolateral external fixator

OBJECTIVE

We studied the callus pattern seen in femoral lengthening using monolateral external fixator to determine whether callus types and shapes can predict the final outcome of the procedure.

MATERIAL AND METHODS

The radiographs of 41 cases of femoral lengthening (33 unilateral and 8 bilateral) in 33 patients with a mean age 11.9 years (range 4-22 years) were retrospectively analysed by four observers and classified into different shapes and types in concordance with the Ru Li classification. The classification was tested for concurrence and reproducibility by inter-observer studies.

RESULTS

An average of 6.2 cm of lengthening (range 3-10.8) was achieved with an external fixator index of 36.5 (range 20.9-55.3). The fusiform type of callus (fixator index 32.04, maturation index 21.6) showed the best result followed by the cylinder type of callus (fixator index 35.7, maturation index 22.3) and the lateral type of callus (fixator index 33.2, maturation index 21.5). However, the concave type of callus showed poor results with a fixator index of 49.4 and a maturation index of 37.1. The homogeneous path showed the best results (fixator index 30.4, maturation index 18.6). The heterogeneous path also showed good results (fixator index 36.4, maturation index 23.9). The mixed path (fixator index 42.5, maturation index 30.8) and the lucent path (fixator index 45.1, maturation index 32.8) showed poor results.

CONCLUSION

Analysis of the callus pattern helps the surgeon to predict the outcome of the procedure and guide him in planning any additional interventions if necessary.

Cross-sectional anatomy in postdistraction osteogenesis tibia

BACKGROUND

Although the early period of distraction osteogenesis has been extensively investigated, there are few data describing the appearance of medium-term bone regeneration.

METHOD

We investigated 10 adults with magnetic resonance imaging scans. Seven of them underwent bone transport, and three had tibial lengthening. The mean follow-up was 28 months after removal of the external fixator. The values were compared with those of the contralateral tibia, which acted as a control.

RESULTS

All of the cases with bone transport had an increase in the volume of the whole tibia of 15.3%-50.8%. The diameters of the regenerated segments increased significantly (P < 0.0001) in all cases. The mean signal intensity in the regenerate decreased significantly in seven cases (P < 0.0001), which suggested a rise in the content of unhydrated tissue, such as bone and collagen. The cross-sectional area of the transported segment increased in all cases (P < 0.01). Finally, in the patients who underwent bone transport, the docking site was seen to be obstructed by unhydrated tissue.

CONCLUSIONS

Contrary to previous claims, the postdistraction osteogenesis of tibia consists of areas with potentially different biomechanical properties. Recognition of these changes is essential not only for appropriate preoperative counseling but also for considering treatment modalities in case of fracture.

Assessment of distraction regenerate using quantitative bone scintigraphy

In this study, we examined whether quantitative bone scintigraphy can be used to assess new bone formation following distraction osteogenesis (DO). A vertical osteotomy was performed on the right hemimandible of male Sprague-Dawley rats, and a custom-made distraction device was applied. Following the gradual distraction, rats were divided into 2 subgroups, the second and fourth week. Cephalograms were taken and scintigraphic and histomorphometric analysis was performed at the second and fourth week. Scintigraphic findings showed good correlation with histomorphometric results. Results were compared with sham-operated (skin and muscle incision and placement of pin but no osteotomy) and acute distraction (5-mm acute distraction) groups. Scintigraphic mean uptake ratios were significantly higher in the gradual distraction group compared with the sham-operated and acute distraction groups. Quantitative bone scintigraphy is a promising method for the assessment of DO and consolidation. It could offer objective qualitative and quantitative data for the noninvasive evaluation of bony regenerate.

In vivo assessment of regenerate axial stiffness in distraction osteogenesis

This paper presents an in vivo test for assessment of regenerate axial stiffness after the distraction phase of lengthening therapy. The test result supplements radiography in evaluating bone healing and assists in determining when the regenerate stiffness is sufficient for removal of the external fixator. The test is non-invasive and does not require fixator removal. The theoretical basis for the method is that an externally applied load is shared between the fixator and the regenerating bone. The amount of load carried by the regenerate depends on its axial stiffness, which increases with advanced mineralization. By measuring the force in the fixator while applying a known external load to the limb, the load-share ratio between fixator and limb can be assessed. A load-share ratio of 100% indicates that the entire load is carried by the fixator. The ratio decreases as the regenerate structure gradually stiffens. In a clinical trial of 22 individuals with tibial lengthening, the fixator was removed when the load-share ratio dropped below 10%. None of the patients experienced fracture after removal of the fixator.

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.

Greater frequency of distraction accelerates bone formation in open-wedge proximal tibial osteotomy with hemicallotasis

BACKGROUND

In chickens, increased distraction frequency stimulates bone formation in distraction osteogenesis.

PATIENTS AND METHODS

We investigated the effect of two different distraction frequencies on bone formation in the distracted portion, and on the time of removal of the fixator, in open-wedge osteotomies of the proximal tibia with hemicallotasis (HCO). The study included 20 consecutive patients (20 knees) who underwent HCO for medial osteoarthrosis of the knee. 10 knees were distracted at a rate of 0.25 mm four times a day (the 4-step group); and the other 10 knees were distracted at a rate of 0.125 mm eight times a day (the 8-step group).

RESULTS

There were no significant differences in the preoperative FTAs or the correction angles between the two groups. At all intervals until 6 weeks after the completion of distraction, bone mineral density in the distraction gap was significantly higher in the 8-step group than in the 4-step group. The average time in external fixation was 78 (SD 5) days in the 8-step group as compared to 89 (SD 6) days in the 4-step group, a significantly shorter time.

INTERPRETATION

Our findings indicate that an increase in the distraction frequency in HCO provides better bone formation, resulting in a shorter external fixation period.

Predicting duration of Ilizarov frame treatment for tibial lengthening

AIM

To predict duration of treatment for tibial lengthening, as a function of target length increase.

METHOD

Review of case notes and radiographs of patients undergoing Ilizarov method of tibial distraction osteogenesis.

RESULTS

In the 27 cases suitable for analysis, the median age was 29.9 years (13.3 to 72.6 years), and the median distraction was 3.5 cm (1.0 to 7.2 cm). A positive linear relationship (r = 0.7) was demonstrated between the distraction length (x, in cm) and the frame duration (y, in days), according to the equation y = 54x + 94. A negative hyperbolic relationship was also demonstrated between rate of bone healing and distraction length (r = 0.6), with distractions over 3.0 cm healing significantly faster than shorter ones (P < 0.03).

Experimental study of mechanical analysis in mandibular lengthening

In distraction osteogenesis, the assessment of new bone formation and the decision of when to remove the distraction device are very important from clinical viewpoint. The purpose of this study was to measure bone stiffness using a strain gauge during and after mandibular lengthening, and to compare the results with those from radiographic and histological examinations. Twelve adult mongrel dogs served as the experimental subjects. An external distraction device was connected to the mandible, and distraction was started 7 days after operation and continued for 10 consecutive days. The animals underwent strain gauge measurement and radiographic examination of the mandible at the completion of distraction and every 2 weeks until the end of the consolidation period. The animals were then sacrificed at 2, 4, 6, 8, 10, and 12 weeks after completion of the distraction for histologic examinations. There was correlation between the amount of decrease in strain, increase in ratio of radiopacity, and newly formed bone in the distracted area.

Effect of weightbearing on bone formation during distraction osteogenesis

The effect of weightbearing on the bone formation during distraction osteogenesis was studied with 24 goats after standardized osteotomy and distraction. Twelve goats were allowed to bear weight immediately and 12 were not allowed to bear weight. With the pattern of weightbearing documented, the formation of bone was monitored with serial radiographs and the bone forming activity was studied with histologic examination and immunohistochemical study of transforming growth factor-beta 1 expression. The results of the study showed that the bone formation as depicted by radiologic assessment of callus width and mineralized tissue was significantly better in the weightbearing group. Histologic study showed more bone formation qualitatively and quantitatively in the weightbearing group. This study confirmed the beneficial effect of weightbearing activity during distraction osteogenesis. Distraction provides pulsed form stimulation by tension stress across the osteotomy site and initiates osteogenesis while the compression stress exerted by the weightbearing is continuous in daily activities and enhances new bone formation. The clinical practice of early weightbearing during distraction osteogenesis should be reinforced.

Bone mineral content and soft-tissue assessment in limb segments by dual-energy X-ray absorptiometry: optimal scan speed and pixel size

The aim of this study was to define the best scanning parameters to assess bone mineral content (BMC) and bone mineral density (BMD) in specific dual-energy X-ray absorptiometry (DXA) applications, such as those encountered in orthopedics for the measurements of the peripheral skeleton. To simulate soft tissues and bones in a limb, we used simple phantoms made with plastic bottles (500 mL and 1500 mL) filled with tap water and cylinders of hydroxyapatite (HAP) powder set in a polymer at various concentrations (range, 0.150-1.500 g HAP/cm3). Data obtained from 204 measurements of these phantoms with different scanning speeds and pixel sizes showed that the best compromise for obtaining precise measurements in the shortest scan time was a scanning speed of 50 mm/s and a pixel size of 1.5 mm x 1.5 mm.

Bone mineralization gradient at the callotasis site

Thirteen patients (18 lengthenings; mean age at operation, 11.0 years) underwent dual-energy X-ray absorptiometry (DEXA) scanning weekly during the distraction phase, at 2-week intervals until removal of the fixator, and at the time of each outpatient visit after removal of the apparatus for a median of 353 days. The three transverse regions remained significantly different in the 7 achondroplastic patients throughout the study, but the difference among these regions became nonsignificant by fixator removal in the 11 limb length discrepancy (LLD) patients. The most proximal region was significantly more mineralized throughout the study in the achondroplastic patients. The central region became the region of highest mineralization in the LLD patients by week 16 after removal of the fixator. The three longitudinal regions showed significantly different mineralization at all time points except at fixator removal. The central and medial regions always showed the highest mineralization. The mechanical characteristics of the fixator and the biomechanical features of the lengthening site may account for the mineralization gradient reported in this study and should probably be taken into account when planning removal of the fixator and subsequent weight-bearing.