#cortical bone

coritcal bone – structure and space maintenance cancellous bone – increase surface area for osteoblasts to deposit

Demineralized 

AlloStem Cellular Bone Allograft – AlloStem is partially demineralized allograft bone combined with adipose derived mesenchymal stem cells  Use

Puros Demineralized Bone Matrix (DBM) Putty by Zimmer – DBX Putty by Dentsply Regenaformby Exactech – DFDBA Cortical…

(TOP) Scout radiograph of the tibia illustrating the standard ultradistal and distal scan regions. A single scan slice is shown along with example output from the standard clinical evaluation, the extended cortical analysis, and the cortical pore topology analysis at the ultradistal tibia region.

(MIDDLE) Depiction of the cortical laminar analysis procedure. A small section of a tibial cross-sectional slice is shown. Left: Pores (black) are shown in full with lines depicting boundaries between laminar regions. Center: Pore skeletons are assigned to a single layer (endosteal pores in red, midcortical pores in blue, periosteal pores in green). Right: Full pores are assigned to a layer according to the location of their skeletons. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

(BOTTOM) Time-series line plots of the percentage change in ultradistal tibia biomechanical parameters for the disuse limb (black square) and the contralateral limb (white square). The 6 week disuse period is represented by the gray shaded region between the baseline and F/U #1 time-points. Error lines represent standard deviations. *p < 0.05 versus baseline.

Take home message:  “In summary, we have quantified longitudinal changes in the trabecular and cortical compartments of the distal tibia in a disuse cohort. Dramatic changes in cortical microstructure were accompanied by significant biomechanical deterioration in this cohort.”

   The influence of disuse on bone microstructure and mechanics assessed by HR-pQCT

Galateia J. Kazakia, Willy Tjong, Jasmine A. Nirody, Andrew J. Burghardt, Julio Carballido-Gamioa,

Janina M. Patsch, Thomas Link, Brian T. Feeley, C. Benjamin Ma

http://dx.doi.org/10.1016/j.bone.2014.02.014

Abstract: Numerous clinical cohorts are exposed to reduced skeletal loading and associated bone loss, including surgical patients, stroke and spinal cord injury victims, and women on bed rest during pregnancy. In this context, understanding disuse-related bone loss is critical to developing interventions to prevent fractures and the associated morbidity, mortality, and cost to the health care system. The aim of this pilot study was to use high-resolution peripheral QCT (HR-pQCT) to examine changes in trabecular and cortical microstructure and biomechanics during a period of non weight bearing (WB) and during recovery following return to normal WB. Surgical patients requiring a 6-week non WB period (n = 12, 34.8 ± 7.7 yrs) were scanned at the affected and contralateral tibia prior to surgery, after the 6-week non WB period, and 6 and 13 weeks after returning to full WB.

At the affected ultradistal tibia, integral vBMD (including both trabecular and cortical compartments) decreased with respect to baseline (− 1.2%), trabecular number increased (+ 5.6%), while trabecular thickness (− 5.4%), separation (− 4.6%), and heterogeneity (− 7.2%) decreased (all p < 0.05). Six weeks after return to full WB, trabecular structure measures reverted to baseline levels. In contrast, integral vBMD continued to decrease after 6 (− 2.0%, p < 0.05) and 13 weeks (− 2.5%, p = 0.07) of full WB. At the affected distal site, the disuse period resulted in increased porosity (+ 16.1%, p < 0.005), which remained elevated after 6 weeks (+ 16.8%, p < 0.01) and after 13 weeks (+ 16.2%, p < 0.05). A novel topological analysis applied to the distal tibia cortex demonstrated increased number of canals with surface topology (“slabs” + 21.7%, p < 0.01) and curve topology (“tubes” + 15.0%, p < 0.05) as well as increased number of canal junctions (+ 21.4%, p < 0.05) following the disuse period. Porosity increased uniformly through increases in both pore size and number. Finite element analysis at the ultradistal tibia showed decreased stiffness and failure load (− 2.8% and − 2.4%, p < 0.01) following non WB. These biomechanical predictions remained depressed following 6 and 13 weeks of full WB. Finite element analysis at the distal site followed similar trends.

Our results suggest that detectable microstructural and biomechanical degradation occurs – particularly within the cortical compartment – as a result of non WB and persists following return to normal loading. A better understanding of these microstructural changes and their short- and long-term influence on biomechanics may have clinical relevance in the context of disuse-related fracture prevention.

Introduction:

“The skeleton is highly responsive to its mechanical environment, adjusting bothmacro-  and microstructure in response to altered loading patterns.”

“In lower extremity injuries requiring a period of immobilization, aBMD [areal bone mineral density] decrement persists for 10 years or longer and results in a 37% increased fracture incidence compared to the unaffected limb. Thus, bone loss due to a period of reduced loading is a risk factor for subsequent fractures. Understanding the mechanisms associated with disuse related bone loss is critical to developing interventions to prevent fractures and the associatedmorbidity, mortality, and cost to the health care system.”

 “High-resolution peripheral quantitative computed tomography (HR-pQCT) provides quantitative characterization of bone density, geometry, and microstructure within both trabecular and cortical compartments. Combinedwithfinite element (FE) analysis, HR-pQCT is capable of estimating the effect of disuse-related deterioration of bone density, geometry, and microstructure on bone strength.”

 “The goal of this work was to quantify the structural and biomechanical changes occurring in response to a period of disuse and during the subsequent return to normal loading.”

 Methods and materials:

 “Individuals undergoing surgery requiring them to be on crutches for six weeks post-procedure were recruited for the study.”

 “On each side, the tibia was scanned at two locations [TOP]: 1) the standard ultradistal site (for standard trabecular and cortical analysis) and 2) a distal site (for exploratory cortical analysis).”

 “Integral vBMD, representing both trabecular and cortical compartments,was quantified based on the periosteal segmentation. A threshold-based process was used to segment cortical and trabecular regions for compartment-specific measurements of density and structure.

 Analysis:

 “Ct.Po was defined as the fraction of the segmented pore volume over the sum of the pore and cortical bone volume.”

 “A novel skeletonization algorithm was applied to the cortical porosity in order to define the topology of pore structures. Using this algorithm, the cortical pore network was deconstructed into individual elements (canals) with each pore voxel assigned a topological label, allowing for the classification of individual canals as either tubes (representing elements with curve topology, resolvable single canals) or slabs (representing elements with planar surface topology, possibly resulting from canal merging).”

 “The cortical compartment was subdivided into three concentric regions of equal width corresponding to endosteal, midcortical, and periosteal layers [MIDDLE]. To achieve this we performed a series of operations on the cortical volume. First, endosteal and periosteal boundaries were discretized. Second, pairs of points on each boundary were identified. Third, the distance between each pair of points was determined and two points representing the inner and outer boundaries of the midcortical region were located. Fourth, each set of discrete points representing the inner and outer boundaries of the midcortical region were joined into a continuous boundary by a series of dilations followed by a thinning routine.”

 “Total pore number was calculated for each slice as the number of skeleton elements assigned to each layer. Both total pore area and total pore number were normalized by the area of each layer, and reported as means over all slices in the analyzed volume. Average pore area was calculated for each slice as total pore area divided by total pore number, and reported as a mean over all slices.”

 “Linear μFE analysis was performed on all ultradistal and distal tibia images to measure changes in apparent biomechanical properties.”

 Results:

 “Twelve subjects (10 males/2 females) completed the study. One of these 12was imaged only at the first three time-points. At baseline, subjects were 34.8 ± 7.7 years, with a range of 22 to 46 years.”

 “Following the disuse period, all regions at the affected distal site showed an increase in total pore area and total pore number. A significant increase in average pore area was seen in both the midcortical and periosteal layers, though not in the endosteal layer. Six and 13 weeks after return to full WB, all measures remained elevated with respect to baseline.”

 “Biomechanical properties of the tibia were altered significantly after the disuse period [BOTTOM]. After 6 weeks of disuse, decreased stiffness

(−2.8%; p b 0.01) and estimated failure load (−2.4%, p b 0.01) were detected at the affected ultradistal site. Lesser decreases in these parameters were found at the corresponding contralateral site (stiffness: −2.2%, failure load: −1.6%, p b 0.05). Changes persisted following return to full WB. After 13 weeks of full WB, stiffness (−4.8%, p b 0.05) and failure load (−4.6%, p b 0.05) remained significantly lower than baseline at the affected ultradistal site. This pattern was mirrored at the corresponding contralateral site, though at a lesser magnitude (stiffness: −2.6%, failure load, −2.2%; p b 0.05).”

 Discussion:

 “Our results demonstrate that detectable and biomechanically significant microstructural deterioration occurs in response to disuse and persists following return to normal loading. This deterioration is most pronounced and enduring within the cortical compartment”

 “Of the microstructural features investigated, Ct.Powas found to have the greatest and most persistent response to non WB. For comparison, the magnitude of Ct.Po increase over the 6 week non WB period was greater than that seen over a decade (40–50 y) in men and on the order of changes over the peri-menopausal decade (40–50 y) in women.”

 “Total pore area was found to increase uniformly throughout the cortex, within the endosteal, midcortical, as well as periosteal layers. Further, increased porosity was found to occur through an increase in both pore size and pore number. In contrast to the data presented here, our observations in a longitudinal study of a postmenopausal cohort demonstrated increased porosity isolated to the endosteal layer of the cortex by a mechanism of increased pore size only (no increase in pore number). The specific pattern of porosity increase seen in this disuse cohort, therefore, may indicate a unique mechanism of increased porosity.” (ß This is very interesting)

 “The increase in Tb.N and decrease in Tb.Sp and Tb.1/N SD during the disuse period are unexpected results considering the usual pattern of structure changes associated with aging or osteoporosis…suggesting that restricted loading of the lower limb may, at least in the short-term, induce bone loss by a mechanismof trabecular fenestration, increasing Tb.N and homogeneity through a conversion of plates to multiple rod-like trabeculae.”

 “Small but significant changes in trabecular structure and biomechanical parameters were seen for the contralateral side over the non WB period, which may have been initiated by a change in loading pattern due to crutch use. Therefore, the contralateral limb is not an ideal control. Second, since this pilot study did not include plantar pressure or accelerometer data capture, we cannot confirm the complete unloading of the surgical side during the non WB period.”