Pulsed electromagnetic stimulation of regenerate bone in lengthening procedures

Distraction osteogenesis for limb lengthening represents the treatment of choice in patients with small stature or limb length discrepancies. Bone lengthening and callus formation requires a long therapy. Pulsed electromagnetic fields (PEMF) are normally used to enhance osteogenesis in patients with non-unions. In this study we investigated whether pulsed electromagnetic fields could be used effectively to encourage callus formation and maturation during limb lengthening procedures. Thirty patients underwent bilateral bone lengthening of the humerus, femur or tibia. At day 10 after surgery, PEMF stimulation was started on one side, for 8 hours/day. Stimulated distraction sites exhibited earlier callus formation and progression, and a higher callus density compared to non-stimulated sites. External fixation could be removed on average one month earlier in PEMF stimulated bones. Our results show that the use of pulsed electromagnetic fields stimulation during limb lengthening allows shortening the time of use of the external fixation.     

Callus formation in femur and tibia during leg lengthening:7 patients examined with DXA

We examined the callus formation during leg lengthening in 7 achondroplastic patients who underwent 3 bilateral femoral and 4 bilateral tibial lengthenings. Bone mineral content and bone mineral density (BMD) in the lengthened callus space were evaluated every 1 or 2 weeks for 10 weeks after the start of distraction using dual energy X-ray absorptiometry.

The mean rate of callus mineralization in femurs (0.64 g/wk) was higher than in tibias (0.22 g/wk). The mean BMD at 10 weeks after the start was 0.35 g/ cm² in the femur and 0.14 g/cm² in the tibia. Different rates of callus formation in different kinds of long tubular bones have not been reported previously.     

Comparison between upper and lower limb lengthening in patients with achondroplasia: a retrospective study

Lengthening of the humerus is now an established technique. We compared the complications of humeral lengthening with those of femoral lengthening and investigated whether or not the callus formation in the humerus proceeds at a higher rate than that in the femur. A total of 24 humeral and 24 femoral lengthenings were performed on 12 patients with achondroplasia. We measured the pixel value ratio (PVR) of the lengthened area on radiographs and each radiograph was analysed for the shape, type and density of the callus. The quality of life (QOL) of the patients after humeral lengthening was compared with that prior to surgery. The complication rate per segment of humerus and femur was 0.87% and 1.37%, respectively. In the humerus the PVR was significantly higher than that of the femur. Lower limbs were associated with an increased incidence of concave, lateral and central callus shapes. Humeral lengthening had a lower complication rate than lower-limb lengthening, and QOL increased significantly after humeral lengthening. Callus formation in the humerus during the distraction period proceeded at a significantly higher rate than that in the femur. These findings indicate that humeral lengthening has an important role in the management of patients with achondroplasia.     

Bone Mass in Female Cross-Country Skiers: Relationship Between Muscle Strength and Different BMD Sites

In this cross-sectional study, bone mass and muscle strength of the thigh were investigated in 16 Caucasian female cross-country skiers, age 16.2 ± 0.3 years, that had been ski-training for 6.4 ± 1.8 years (range 3–9 years) and were now training for 6.3 ± 2.4 hours/week (range 3–12 hours). They were compared with 16 nonactive females, age 16.4 ± 0.7 years. The groups were matched according to age, weight, height, and pubertal status. Areal bone mineral density (BMD) was measured using dual energy X-ray absorptiometry, in the total body, head, both total humerus and humerus diaphyses, spine, and in the right femoral neck, greater trochanter, femoral diaphysis, distal femur, proximal tibia, and tibia diaphysis. Bone mineral apparent density (BMAD) was also calculated for the femoral neck and humerus diaphyses. Isokinetic muscle strength of the quadricep and hamstring muscles was measured in an isokinetic dynamometer. Compared with the controls, the cross-country skiing group had significantly higher BMD in the right whole humerus (6.9%), left whole humerus (9.2%), left humerus diaphysis (8.1%), femoral neck (8.9%), greater trochanter (9.3%), femur diaphysis (7.6%), and BMAD of the femoral neck (+19.4%). In the nonactive group there were significant side-to-side differences in BMD of the whole humeri, humerus diaphyses, and BMAD of the humerus diaphyses (3.1%, 5.4%, and 8.8% higher in the right arm, respectively). No such differences were found in the cross-country skiing group. Lean body mass was significantly higher in the cross-country skiers (21.7%), and fat mass (−25.5%) and body fat percent (−28.0%) were significantly lower compared with the nonactive group. There were, however, no significant differences in concentric peak torque of the thigh muscles between the two groups. Stepwise regression analyses revealed that BMI was the best predictor of several sites in the nonactive group. In the cross-country group, on the other hand, muscle strength was a strong predictor of BMD, both at adjacent and more distant BMD sites. In conclusion, it seems that this type of endurance training is associated with a site-specific higher bone mass that may be associated with the type and magnitude of loading during off-season and during the main sports activity, cross-country skiing. Received: 4 May 1998 / Accepted: 8 March 2000     

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.     

Leg lengthening by distraction osteogenesis using the Ilizarov apparatus: a novel concept of tibia callus subsidence and its influencing factors

This article studies the incidence and magnitude of delayed callus subsidence, which will also help in study the hypothesis of three cortex corticalisation to determine the time of fixator removal during distraction osteogenesis (DO). Eighty-one tibia segments with mean lengthening of 7.7 ± 2.9 cm were studied with age, gender, skeletal maturity, amount and percentage of lengthening, callus pattern, callus shape, number of cortices seen at the time of fixator removal, bone mineral density (BMD) ratio, and callus diameter ratio analysed for their effect on callus subsidence. All segments had tibia callus subsidence ranging from 4 mm to 3.2 cm with 54% having significant subsidence of more than 1 cm. Multivariate regression analysis revealed only the amount of lengthening and callus patterns to be significant. In conclusion, we can say that tibia callus subsidence is a significant delayed complication and factors affecting it can be used to determine the time of fixator removal.     

Limb lengthening in achondroplasia

Background:Stature lengthening in skeletal dysplasia is a contentious issue. Specific guidelines regarding the age and sequence of surgery, methods and extent of lengthening at each stage are not uniform around the world. Despite the need for multiple surgeries, with their attendant complications, parents demanding stature lengthening are not rare, due to the social bias and psychological effects experienced by these patients. This study describes the outcome and complications of extensive stature lengthening performed at our center.Results:Nine patients aged five to 25 years (mean age 10.2 years) underwent limb lengthening procedures for 18 tibiae, 10 femora and 8 humeri. Four patients underwent bilateral lengthening of all three segments. The mean length gain for the tibia, femur and humerus was 15.4 cm (100.7%), 9.9 cm (52.8%) and 9.6 cm (77.9%), respectively. Healing index was 25.7, 25.6 and 20.6 days/cm, respectively, for the tibia, femur and humerus. An average of 33.3% height gain was attained. Lengthening of both tibia and femur added to projected height achieved as the 3^rd percentile of standard height in three out of four patients. In all, 33 complications were encountered (0.9 complications per segment). Healing index was not affected by age or bone segment.Conclusion:Extensive limb lengthening (more than 50% over initial length) carries significant risk and should be undertaken only after due consideration.     

Effect of High Impact Activity on Bone Mass and Size in Adolescent Females: A Comparative Study Between Two Different Types of Sports

The purpose of this cross-sectional study was to investigate the influence of two different types of weight-bearing activity, muscle strength, and body composition on bone mineral density (BMD), bone mineral content (BMC), and bone area in three different groups of late adolescent girls. The first group consisted of 10 females participating in competitive rope-skipping (age 17.8 ± 0.8 years) training for 6.7 ± 3.1 hours/week; the second group consisted of 15 soccer players (age 17.4 ± 0.8 years) training for 6.1 ± 2.0 hours/week; and the third group consisted of 25 controls (age 17.6 ± 0.8 years) with physical activity of 0.9 ± 1.1 hours/week. The groups were matched for age, height, and weight. BMD (g/cm²), BMC (g), and bone area (cm²) of the total body, lumbar spine, hip, total femur, distal femur, diaphyses of femur and tibia, proximal tibia, and humerus were measured using dual-energy X-ray absorptiometry (DXA). Bone density was also assessed in the radial forearm site of the dominant limb in the rope skippers and in 10 matched controls. The rope skippers had 22% higher BMD at the ultradistal site (P < 0.01). Both high-activity groups had significantly higher BMD (P < 0.05) at most loaded sites compared with the control group. When adjusting for differences in lean mass and starting age of sport-specific training between the activity groups, the rope-skipping group had a higher BMD of the total body, lumbar spine, and right humerus compared with the soccer group. They also had a significantly higher bone area of the total body, total femur, and the proximal femur than both other groups, and a significantly higher bone area of the tibia diaphysis, compared with the soccer group. In a multivariate analysis among all subjects (n = 50), all BMD sites, except the femur diaphysis, distal femur, and proximal tibia, were significantly related to type of physical activity (β= 0.25–0.43, P < 0.05). The bone area values at different sites were strongly related to muscle strength and parameters related to body size [height, weight, lean mass, fat mass, and body mass index (BMI)]. In conclusion, it appears that in late adolescent women, weight-bearing activities are an important determinant for bone density, and high impact activities such as jumping also seem to be associated with a modification of the bone geometry (hence, the bone width) at the loaded sites. Received: 28 June 1999 / Accepted: 22 March 2000     

Low-intensity pulsed ultrasound accelerates maturation of callus in patients treated with opening-wedge high tibial osteotomy by hemicallotasis

BACKGROUND: Opening-wedge high tibial osteotomy by hemicallotasis for osteoarthritis in the medial compartment of the knee requires external fixation for a long time, until callus maturation is complete. The aim of this study was to determine if low-intensity pulsed ultrasound would accelerate callus maturation when applied after distraction to limbs treated with opening-wedge high tibial osteotomy by hemicallotasis. METHODS: Twenty-one patients with symmetric grades of osteoarthritis and similar degrees of varus deformity in the two knees underwent bilateral one-stage opening-wedge high tibial osteotomy by hemicallotasis. After completion of distraction, the bone mineral density of the distraction callus was measured. Then, one randomly selected limb was subjected to ultrasound treatment for twenty minutes daily until removal of the external fixator. The contralateral limb was left untreated to serve as the control. After four weeks of treatment, bone mineral density was measured again. RESULTS: During the four-week treatment period, the mean increase in callus bone mineral density was significantly greater in the ultrasound-treated tibiae (0.20 +/- 0.12 g/cm(2)) than in the control tibiae (0.13 +/- 0.10 g/cm(2)) (p = 0.02, unpaired t test). In eighteen patients the increase in the bone mineral density was greater in the ultrasound-treated limb than in the control limb, whereas in three patients the increase was greater in the control limb. CONCLUSIONS: We found that low-intensity pulsed ultrasound applied during the consolidation phase of distraction osteogenesis accelerates callus maturation after opening-wedge high tibial osteotomy by hemicallotasis in elderly patients.     

Growth retardation after experimental limb lengthening by epiphyseal distraction

Growth retardation occurring as a result of limb lengthening by epiphyseal distraction in two animal species was quantified by using femur or tibia as the experimental bone. The growth plate subjected to distraction appeared radiolucent after the lengthening procedure but was less distinct and had reduced height as compared with the control. In seven of 22 animals, the growth plate of the lengthened bone appeared to close earlier than in the control. After lengthening, bilateral longitudinal growth was evaluated semiquantitatively from radiographs until growth had ceased or residual growth was negligible. Growth retardation was consistently experienced in all animals, with an average reduction in growth potential of each study ranging from 40 to 70%. The results show that epiphyseal distraction is a valid method of limb lengthening, but it appears to have a consistently harmful effect on the growth plate and should be used clinically only in patients close to maturity.     

Quantitative assessment of callus distraction using dual energy X-ray absorptiometry

Summary. Bone mineralisation during and after limb lengthening procedures on the femur or tibia using unilateral fixators has been monitored quantitatively using dual energy X-ray absorptiometry (DEXA). We measured the bone mineral density (BMD) prospectively in the newly formed callus, in the bone adjacent to the callus and in the proximal femur. In twenty-one patients we showed a typical course with a peak value at 4 – 6 weeks after beginning distraction and a minimum value at maximum distraction. In the consolidation period the BMD in the distraction gap increased until the fixator was removed. The BMD in the regenerated bone increased faster in the regions of interest (ROI) opposite the fixator compared to those near it. Dynamisation caused more homogeneous regeneration equalising V _BMD in the different ROIs. The BMD in the proximal femur of the leg which was operated on decreased to 67% and in the opposite leg to 87% of the preoperative value. DEXA provides a precise and quantitative assessment of callus and bone mineralisation during limb lengthening and helps in understanding what is happening during these procedures.

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Résumé. Le processus de la minéralisation peut précisément être étudié d’une manière quantitative pendant et après la distraction du cal au moyen de l’absorptiométrie en énergie-binaire (DEXA) en créant une petite radioexposition. Des patients (n = 21) avec une distraction du cal, auxquels nous avons mesuré prospectivement la densité minérale de l’os (bone mineral density = BMD) dans et autour du cal nouvellement formé, étaient traités avec des fixateurs externes unilatéraux. La minéralisation a montré une courbe typique avec une première pointe de valeur [0,365 +/– 0,196 g/cm ² (30,9% de la première valeur)] à 4 – 6 semaines après le début de la distraction. Une valeur minimale apparut à la distraction maximale. Dans la période de consolidation la BMD est montèe jusqu’au moment de l’enlèvement du fixateur à 1,020 +/– 0,234 g/cm² (87%). La minéralisation du cal, mésurée grace à la technique des ?regions of interest (ROIs)?, augmenté plus vite aux ROIs éloignées qu’aux ROIs très proches du fixateur. De la dynamisation du fixateur résulte une vitesse de minéralisation plus homogène. Nous considérons la DEXA comme une méthode précise pour étudier les processus de la minéralisation et du développement du cal pendant la distraction avec un fixateur unilatéral. En tenant compte des limites de la technique, la DEXA – qui nous livre des valeurs quantitatives – nous aide à comprendre ce qui se passe pendant la distraction.

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Accepted: 11 July 1996     

Lower extremity lengthening by Wagner's method and by callus distraction

Fifty-three patients underwent 64 lengthenings of the femur or tibia by the Wagner technique or by the callus distraction method. Thirty-six femoral and 28 tibial segments were lengthened. Simultaneous lengthening of the femur and tibia was performed in seven limbs. Three segments underwent repeat lengthenings. The average length gained by the Wagner method was 5.1 cm in the femur and 5.4 cm in the tibia. Length gains by callus distraction were 4.9 cm in the femur and 4.5 cm in the tibia. Complication rates were fewer and less severe with callus distraction. The number of operations, days of hospitalization, and length of total treatment were less in patients operated on with the callus distraction method than in those who underwent the Wagner technique.     

Monitoring of bone formation during distraction osteogenesis via osteocalcin: a time sequence study in dogs

 The aim of the current study was to analyze the osteocalcin level and radiographic density during distraction osteogenesis in order to investigate the role of osteocalcin in monitoring bone formation during callus distraction. Lengthening of the right tibia by 25% was performed in 12 beagle dogs by callus distraction after osteotomy and application of a ring fixator. Distraction was started on the 5th postoperative day, with a distraction rate of 0.5 mm twice a day, and was ended after 25 days. Blood samples and x-rays of the callus distraction segment were obtained preoperatively and once a week until day 55 after operation. A digital radiograph analysis system was used to determine the bone density of the callus distraction segments. The serum parameters of osteocalcin were evaluated by radioimmunoassay. The radiographic bone densities during the distraction phase increased during the distraction period and markedly increased during the consolidation period. A similar trend was observed for osteocalcin, whereby the coefficient of correlation between these two parameters was, on average, 0.68 ± 0.11. However, the radiographic bone density measurements, as well as the osteocalcin levels, showed large variation between different animals. Therefore, our results suggest that valuable information about bone formation during distraction osteogenesis can be obtained via serum osteocalcin levels, even though it seems that time sequence monitoring is more favorable than the determination of absolute values. Received: January 16, 2002 / Accepted: April 10, 2002     

The value of ultrasonography in monitoring limb lengthening]

The authors attempted to assess the value of ultrasound for monitoring of the new bone formation at the site of distraction in patients undergoing limb lengthening after Bastiani. Twenty patients were assessed; 12 cases of femur lengthening and 8 cases of tibia lengthening. It was found, that ultrasound allowed to detect the new bone formation visible as hyperechogenic foci as soon as 4 to 14 days postoperatively, while regular radiology showed this only 4 to 8 weeks after operation. Detection of the new bone formation at the site of lengthening permits, in authors opinion, to choose an optimal onset of distraction and its pace according to the speed of bone formation. Regular ultrasound monitoring prevents premature bone union or disintegration of the newly generated bone in case of to slow or to fast distraction respectively. In two cases sonography early demonstrated cystic changes at the location of distraction. It also permits detection of an axial displacement of the fragments of bone in every case.     

Effects of timing of low-intensity pulsed ultrasound on distraction osteogenesis.

We investigated the effects of low-intensity pulsed ultrasound (LIPUS; 30 mW/cm2 spatial and temporal average) on the timing of LIPUS treatment in distraction osteogenesis. Lengthening of the right tibia was performed in 75 male Japanese white rabbits using unilateral fixators (waiting period, 7 days; distraction rate, 1.5 mm/day; distraction period, 7 days). Rabbits were divided into four groups according to the timing of the LIPUS treatment. Control group had no stimulation. Waiting group was treated with a daily 20-min session of LIPUS during a 7-day latency period. Lengthening group was treated during the lengthening period. Maturation group was treated for the first 7 days after completion of distraction. We evaluated the distraction site by radiography and histology every week for 4 weeks. Bone mineral density (BMD) and mechanical strength were tested and microfocus X-ray computed tomography was performed on specimens 2 weeks after completion of distraction. The lengthening group had greater BMD and mechanical strength than the other groups, bone regeneration was enhanced more in the maturation group than in the control or waiting groups. Histologically, endochondral bone formation in the lengthening and the maturation groups occurred earlier than in the control or waiting groups. These results suggest the LIPUS effect is mediated via endochondral pathways. We concluded that LIPUS stimulates bone formation in distraction osteogenesis and is most effective during the lengthening phase.     

Limb lengthening by epiphyseal distraction. An experimental study in the caprine femur

Epiphyseal distraction of the left distal femur was accomplished in 10 goats (aged 3-4.5 months). A modified Hoffmann external fixation device was used as a unilateral distraction frame. A distraction rate of 1.5 mm/day was applied for 5.5 weeks. Epiphysiolysis occurred after 3-7 days of distraction. After the lengthening procedure, the growth plate had reduced in height in eight animals on radiographic examination. In two animals the growth plate was fused. Three animals were killed at 4 (Group 1) and 8 (Group 2) weeks and four animals at 16 (Group 3) weeks after the end of the distraction period. The gain in leg length obtained by distraction was reduced owing to growth retardation in the distal femur of the operated limb. The average final lengthening was 24.9, 19.4, and 13.4% in Groups 1, 2, and 3, respectively. Femur and tibia from both sides were tested mechanically in torsion. Only one femur fractured in the elongation area. All but one elongated femur fractured in the area of the diaphysis subjected to distractional force. The torsional strength of the elongated femur compared with control was reduced to approximately 50% in all groups. The corresponding torsional strength of the tibia on the elongated extremity compared with control was reduced to approximately 75% in all groups. The difference in relative strength of femur compared with that of tibia was statistically significant. This finding can be explained by a stress-protective effect on the femur in the distraction area caused by the external device.     

Prediction of Callus Subsidence in Distraction Osteogenesis Using Callus Formation Scoring System: Preliminary Study

Objective

To develop the scoring system which describes both quality and quantity of callus formation to predict the callus subsidence.

Methods

Forty‐seven bony segments with an average lengthening of 5.17 ± 2.83 cm were included. The score was calculated based on the amount of callus classified in five patterns and the summation with the density of the callus classified in four patterns; the total score was 9. Bony subsidence >10% or >10° angulation were considered significant. We analyzed all of the data to find the most appropriate score that would prevent callus subsidence <10% and prevented angulation of the regeneration bone <10 degrees. Data was analyzed by using the receiver operating characteristic (ROC) curve. An area under the curve of 0.9–1 indicated an excellent test, 0.8–0.9 indicated a good test, 0.7–0.8 indicated a fair test, 0.6–0.7 indicated a poor test, and 0.5–0.6 indicated a fail test. The appropriate score for Ilizarov removal was selected from the highest sensitivity and specificity.

Results

Twenty‐two tibia segments and 25 femur segments were included. The mean of bone lengthening was 5.17 ± 2.83 cm (range, 1.6–13.5 cm) and the mean of percentage lengthening was 16.58% ± 10.03% (range, 4.63%–56.84%). The mean distraction period was 5 months. The average months of follow‐up for measurement of bony subsidence was 4.2 months. Mean subsidence was 21.06% (1.54%–57.44%). The mean of callus subsidence was 1.29 ± 1.17 cm (range, 0.03–4.72 cm). There were 32 segments (68%) with callus subsidence greater than 10% and 15 segments (32%) with subsidence less than 10%. The callus subsidence ranged from 0.3 mm to 4.72 cm, with 68% of bony fragments having significant subsidence. Type 5 callus diameter was statistically significant (P < 0.0001) in preventing callus subsidence compared to the other types. Type 4 callus density was statistically significant in preventing callus subsidence compared to the other types (P < 0.0001). The ROC curve with area under the curve 0.961 and sensitivity 0.933 showed that a callus scoring system score >7.5 was effective in preventing significant callus subsidence. When using score 8 as a result from the ROC curve, 73.3% of bony fragment subsidence was <10% with sensitivity 93.3 and specificity 83.2.

Conclusion

Callus diameter 81%–100% and callus density type 4 could prevent significant callus subsidence. Based on the results of the present study we suggest using callus score > 8 to determine the time of Ilizarov removal.

     

Limb lengthening with a fully implantable mechanical distraction intramedullary nail

AIM: The morbidity of fixator-assisted distraction osteogenesis should be reduced by intramedullary lengthening devices. The ISKD (intramedullary skeletal kinetic distractor) is a new, fully implantable mechanical lengthening nail. In a prospective cohort trial the possibilities and limitations of the device used on femur and tibia are examined. METHODS: 22 patients with a mean age of 25 (range: 16-46) years were treated with an ISKD for femoral (n = 16) and tibial (n = 6) lengthening. The average leg length discrepancy was 48 (range: 25-80) mm. The follow-up was 21 (range: 7-37) months. Clinical and radiological results and complications were evaluated. RESULTS: The results of femoral and tibial applications of the ISKD are different. At the tibia, in three patients a pseudarthrosis occurred and slow callus formation was observed twice. An equinus contracture became evident in 2 patients. At the femur, in one case the lengthening was not accomplished with the device. Five patients were manipulated under anaesthesia at least once to achieve the aim of distraction. Three of these patients received retrograde implantation of the ISKD. An infection or interlocking screw failure was not observed either at the femur or the tibia. CONCLUSION: The ISKD reduces fixator-associated problems but incorporates its own difficulties which are mainly based on the guidance of the device. Careful patient advice in monitoring the lengthening process is mandatory. At the femur 8 cm of lengthening can be achieved but the nail tends to "block". Proper reaming and osteotomy techniques are important. A lengthening of more than 1 mm/day is recommended to prevent early consolidation. At the tibia weak callus formation and soft tissue contractures occur, therefore not more than 4 cm lengthening should be planned, the distraction speed has to be reduced noticeable below 1 mm/day and the initial immobilisation should be for more than a week.     

Dose-dependent effect of low-intensity pulsed ultrasound on callus formation during rapid distraction osteogenesis.

Distraction osteogenesis of bone or callotasis causes poor bone formation when the distraction rate is beyond the optimal rate. Low-intensity pulsed ultrasound was reported to enhance fracture healing, treatment of nonunion, and accelerate bone maturation and remodeling during consolidation stage of distraction osteogenesis. In this study, we evaluated the efficacy of different durations of LIPUS treatments during rapid bone lengthening. After 7-day latent period, osteotomized New Zealand white rabbit tibiae were lengthened at the rate of 2 mm per day for 1 week. Two different LIPUS treatment durations of 20 min and 40 min were selected for treatment groups. Rabbits without treatment served as the control group. Plain X-ray, peripheral quantitative computed tomography (pQCT) and histology were performed to assess bone acquisition in the distraction callus. The results showed that LIPUS increased bone mineral content and volume of the mineralized tissue of distraction callus in a dose-dependent manner. The different regions of distraction callus exhibited various spatial response to LIPUS treatment. Moreover, LIPUS enhanced dose-dependant endochondral formation. Compared with 20-min treatment, the 40-min LIPUS treatment was a more favorable treatment duration for bone regeneration in the distraction callus. In conclusion, LIPUS was able to enhance bone regeneration under rapid distraction, and its effect was dose-dependent.     

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.