Regenerate healing outcomes in unilateral mandibular distraction osteogenesis using quantitative histomorphometry

Abstract

Background: The authors' goal was to ascertain regenerate bone-healing metrics using quantitative histomorphometry at a single consolidation period.

Methods: Rats underwent either mandibular distraction osteogenesis (n = 7) or partially reduced fractures (n = 7); their contralateral mandibles were used as controls (n = 11). External fixators were secured and unilateral osteotomies performed, followed by either mandibular distraction osteogenesis (4 days' latency, then 0.3 mm every 12 hours for 8 days; 5.1 mm) or partially reduced fractures (fixed immediately postoperatively; 2.1 mm); both groups underwent 4 weeks of consolidation. After tissue processing, bone volume/tissue volume ratio, osteoid volume/tissue volume ratio, and osteocyte count per high-power field were analyzed by means of quantitative histomorphometry.

Results: Contralateral mandibles had statistically greater bone volume/tissue volume ratio and osteocyte count per high-power field compared with both mandibular distraction osteogenesis and partially reduced fractures by almost 50 percent, whereas osteoid volume/tissue volume ratio was statistically greater in both mandibular distraction osteogenesis specimens and partially reduced fractures compared with contralateral mandibles. No statistical difference in bone volume/tissue volume ratio, osteoid volume/tissue volume ratio, or osteocyte count per high-power field was found between mandibular distraction osteogenesis specimens and partially reduced fractures.

Conclusions: The authors' findings demonstrate significantly decreased bone quantity and maturity in mandibular distraction osteogenesis specimens and partially reduced fractures compared with contralateral mandibles using the clinically analogous protocols. If these results are extrapolated clinically, treatment strategies may require modification to ensure reliable, predictable, and improved outcomes.

Fig.1

(Above) Sagittal image of mandibular distraction osteogenesis specimen from a microcomputed to mographic scan, oriented with the posterior aspect/condyle on the left, showing region-of-interest placement over the regenerate using anatomical and surgical landmarks. All histologic sections were oriented similarly. (Below) Region-of-interest template placed on a 7-μm sagittal mandibular distraction osteogenesis stained paraffin section analogous to region-of-interest template calibrated from previous microcomputed to mographic scan and placed using the same methodology to ensure uniform placement between independent reviewers.

Fig. 2

(Above) Mandibular distraction osteogenesis paraffin section uploaded as a TIFF file on a computer used for color thresholding. Turquoise-stained bone within the bright green framed region of interest was manually thresholded using Bio-quant software and now appears fuchsia. (Below) The same mandibular distraction osteogenesis paraffin section as TIFF file on computer showing osteoid/nonmineralized matrix that stains red/pink is now presenting as red with yellow borders within the region of interest, after it was color thresholded using Bioquant software for the osteoid volume/tissue volume calculation.

Fig. 3

Point counting osteocytes required 16× magnification and division of the region of interest into high-power fields of 295×366 μm. This image is a high-power field from a mandibular distraction osteogenesis specimen. At 16× magnification in both mandibular distraction osteogenesis specimens and partially reduced fractures, we readily distinguished the flattened osteoblasts at the periphery of the osteoid islands, abutting the bridges of bone within the region of interest. The mature, spindle-shaped osteocytes were easily visualized within their spacious lacunae surrounded by waves of blue woven bone.

Fig. 4

(Left) Seven-micron paraffin section of a partially reduced fracture shows indiscrete osteotomy edges and still shows the separation of newly formed turquoise woven bone in the fracture region from the mature lamellar bone outside the region of interest. (Right) Seven-micron paraffin section of a partially reduced fracture at 4× magnification reveals osteoblasts at the periphery of the mineralized bone, and osteoid islands (red) scattered throughout the thick lattice of turquoise-stained bone.

Fig. 5

(Left) Seven-micron mandibular distraction osteogenesis (DO) paraffin section at 1.6× magnification shows islands of pink/red osteoid scattered within the turquoise lattice of newly formed woven bone. (Right) Seven-micron mandibular distraction osteogenesis paraffin section at 4× magnification delineates the red osteoidcanalswithosteoblastsflowingrandomlythroughtheturquoisebridgesofwovenbone.Noapparent axial or centripetal vector of osteoid production or mineralization can be discerned.

Fig. 6

Graph comparing mandibular distraction osteogenesis specimens, partially reduced fractures, and contralateral mandibles along the x axis by their percentage of bone volume/tissue volume (TV) on the y axis. The bone volume/tissue volume ratio for contralateral mandibles was statistically greater (*p<0.05) than the bone volume/tissue volume ratio for both surgical groups, yet there was no statistical difference in the bone volume/tissue volume ratio between the mandibular distraction osteogenesis and partially reduced fractures groups.

Fig. 7

This graph reveals no statistical difference in the percentage of osteoid volume/tissue volume (TV) ratio between the mandibular distraction osteogenesis and partially reduced fracture groups. However, the percentage of osteoid volume/tissue volume was statistically less in the contralateral mandible group (*p<0.05) compared with either surgical group.

Fig. 8

(Above) A random high-power field from a partially reduced fracture specimen at 16× magnification displays spindle-shaped osteocytes within their lacunae, surrounded by a sea of turquoise/blue woven bone bridge and the adjacent osteoid. (Below) A randomly selected high-power field from a mandibular distraction osteogenesis specimen at 16× magnification reveals a pattern of osteocytes within turquoise/blue woven bone bridge and adjacent red osteoid similar to that of the high-power field from the partially reduced fracture specimen.

Fig. 9

Graph illustrating that no statistically significant difference in osteocyte count per high-power field (HPF) was found between the mandibular distraction osteogenesis and partially reduced fracture groups. However, the contralateral mandible group had a significantly greater osteocyte count per high-power field (*p<0.05) when compared with both surgical groups.