Samer Adeeb

Biomechanical analysis of proximal humeral fixation using locking plate fixation with an intramedullary fibular allograft.

BACKGROUND Loss of locking plate fixation has been reported in proximal humeral fractures, particularly in older patients with poor bone density. In such fractures, the medial support between the humeral head and shaft is occasionally missing, resulting in varus collapse of the construct. A biomechanical study was performed to understand the behaviour of the interface of these fractures fixed with a locking plate fixation with and without augmentation. The augmentation consisted of an intramedullary fibular allograft (bone peg) that has been reported for use in these fractures. METHODS Six embalmed pairs of specimens were utilized; each pair of specimens had one humerus repaired with the locking plate fixation, and the other humerus repaired with the plate fixation and bone peg. The constructs were tested in bending to determine the relative movement between the humeral head and the shaft under bending loads, and the failure loads of both constructs. Digital Imaging Correlation was used to determine the relative movement. FINDINGS The bone peg increased the failure load of the constructs by 1.72 (SD 0.54) times (P=0.02). The relative movement was measured by comparing the initial stiffness of both constructs. Initial stiffness of the construct was increased 3.84 (SD 1.92) times (P=0.005) with the use of the bone peg. INTERPRETATION The intramedullary bone peg significantly decreases the relative movement at the interface. Further studies are needed to accurately determine the effect this reduction has on the healing process, and overall clinical result.

Compositional and Material Properties of Rat Bone after Bisphosphonate and/or Strontium Ranelate Drug Treatment

PURPOSE We investigated elemental strontium and/or bisphosphonate drug incorporation upon the compositional and biomechanical properties of vertebral bone, in a rat model of Osteoporosis secondary to ovariectomy. METHODS Six month old female rats were ovariectomized (OVX) and divided into untreated OVX-Vehicle, OVX-RIS (Risedronate bisphosphonate [BP] treated), OVX-SrR (Strontium Ranelate [Protos®] treated), combination OVX-RIS+SrR, and sham-operated controls. After 16 weeks of treatment, rats were euthanized and lumbar vertebra were dissected. Micro-Computed Tomography (micro-CT), Electron Probe Micro-Analysis (EPMA), mechanical testing in compression and nano-indentation testing were then undertaken to evaluate bone morphometry, elemental composition, material properties and strength. RESULTS Bone Volume was significantly reduced in the OVX-Vehicle (133±10 mm(3)) compared with OVX-RIS (169±22 mm(3)), OVX-SrR (145±2 mm(3)), and OVX-RIS+SrR (172±8 mm(3)). EPMA mapped elemental Sr deposition to the periosteal surface of cortical bone (50-100 µm thick), endosteal trabecular surfaces (20 µm thick), as well as to both vertebral growth plates. The atomic ratios of (Ca+Sr)/P were significantly reduced with SrR treatment (2.4%-6.6%), indicating Sr incorporation into bone mineral. No significant differences were measured in vertebral bone reduced modulus by nano-indentation. Conversely, all BP-dosed groups had significantly increased structural bone strength. CONCLUSIONS Thus, we conclude that BP drugs dominate the conservation of trabecular geometry and structural strength in OP rats, whereas Sr drugs likely influence bone volume and material composition locally.

On the load-sharing along the ligamentous lumbosacral spine in flexed and extended postures: Finite element study.

A harmonic synergy between the load-bearing and stabilizing components of the spine is necessary to maintain its normal function. This study aimed to investigate the load-sharing along the ligamentous lumbosacral spine under sagittal loading. A 3D nonlinear detailed Finite Element (FE) model of lumbosacral spine with realistic geometry was developed and validated using wide range of numerical and experimental (in-vivo and in-vitro) data. The model was subjected to 500 N compressive Follower Load (FL) combined with 7.5 Nm flexion (FLX) or extension (EXT) moments. Load-sharing was expressed as percentage of total internal force/moment developed along the spine that each spinal component carried. These internal forces and moments were determined at the discs centres and included the applied load and the resisting forces in the ligaments and facet joints. The contribution of the facet joints and ligaments in supporting bending moments produced additional forces and moments in the discs. The intervertebral discs carried up to 81% and 68% of the total internal force in case of FL combined with FLX and EXT, respectively. The ligaments withstood up to 67% and 81% of the total internal moment in cases of FL combined with EXT and FLX, respectively. Contribution of the facet joints in resisting internal force and moment was noticeable at levels L4-S1 only particularly in case of FL combined with EXT and reached up 29% and 52% of the internal moment and force, respectively. This study demonstrated that spinal load-sharing depended on applied load and varied along the spine.

Impact of bisphosphonate drug burden in alveolar bone during orthodontic tooth movement in a rat model: A pilot study

INTRODUCTION The aim of this pilot study was to investigate the effect of long-term bisphosphonate drug use (bone burden) on orthodontic tooth movement in a rat model. METHODS Sprague Dawley rats were used for orthodontic protraction of the maxillary first molars with nickel-titanium coil springs and temporary anchorage devices as anchorage. Four groups of 5 rats each were included in the study; the first 2 groups were dosed with alendronate or a vehicle during concurrent orthodontic tooth movement. The third and fourth groups were pretreated for 3 months with alendronate or vehicle injections, and bisphosphonate drug treatment was discontinued before orthodontic tooth movement. Tooth movement measurements were obtained at 0, 4, and 8 weeks using high-resolution in-vivo microcomputed tomography, and the tissues were analyzed with histology and dynamic labeling of bone turnover. RESULTS Appreciable tooth movement was achieved during the 8-week duration of this study with nickel-titanium coil springs and temporary anchorage devices. Both bisphosphonate treatment groups exhibited reduced tooth movement compared with the vehicle-dosed controls with a tendency toward more severe reduction in the bisphosphonate predosed group. Concurrent dosing of the bisphosphonate drug resulted in 56% and 65% reductions in tooth protraction at the 4-week and 8-week times, respectively. The impact of bisphosphonate bone burden in retarding tooth movement was even greater, with 77% and 86% reductions in tooth movement at 4 and 8 weeks, respectively. CONCLUSIONS In this study, we used a robust rat model of orthodontic tooth movement with temporary anchorage devices. It has provided evidence that the bone burden of previous bisphosphonate use will significantly inhibit orthodontic tooth movement.

Symmetry analysis of talus bone: A Geometric morphometric approach

Objective The main object of this study was to use a geometric morphometric approach to quantify the left-right symmetry of talus bones. Methods Analysis was carried out using CT scan images of 11 pairs of intact tali. Two important geometric parameters, volume and surface area, were quantified for left and right talus bones. The geometric shape variations between the right and left talus bones were also measured using deviation analysis. Furthermore, location of asymmetry in the geometric shapes were identified. Results Numerical results showed that talus bones are bilaterally symmetrical in nature, and the difference between the surface area of the left and right talus bones was less than 7.5%. Similarly, the difference in the volume of both bones was less than 7.5%. Results of the three-dimensional (3D) deviation analyses demonstrated the mean deviation between left and right talus bones were in the range of -0.74 mm to 0.62 mm. It was observed that in eight of 11 subjects, the deviation in symmetry occurred in regions that are clinically less important during talus surgery. Conclusions We conclude that left and right talus bones of intact human ankle joints show a strong degree of symmetry. The results of this study may have significance with respect to talus surgery, and in investigating traumatic talus injury where the geometric shape of the contralateral talus can be used as control. Cite this article: Bone Joint Res 2014;3:139–45.

Locking plate fixation of proximal humeral fractures with impaction of the fracture site to restore medial column support: a biomechanical study

BACKGROUND Despite the advent of locking plate techniques, proximal humeral fracture fixation can fail due to varus collapse, especially in osteoporotic bone with medial cortex comminution. This study investigated the effect of restoring the integrity of the medial column by fracture impaction and shaft medialization with locking plate fixation. This construct was compared with a traditional locking plate construct under conditions of varus cyclical loading. MATERIALS AND METHODS Proximal humeral fractures with medial comminution were simulated by performing wedge-shaped osteotomies at the surgical neck in cadaveric specimens and removing 1 cm of medial cortex. For each cadaver (n = 6), 1 humeral fracture was fixed with a traditional locking plate construct. The other was fixed with the locking plate construct plus fracture impaction and shaft medialization, resulting in medial column restoration. The humeral head was immobilized, and a repetitive, varus force was applied to the humeral shaft until construct collapse or until 25,000 cycles were completed. RESULTS None of the constructs with fracture impaction collapsed, whereas 5 of 6 of the nonaugmented constructs collapsed before reaching 25,000 cycles (P = .008). Collapse of the 5 nonimpacted constructs that failed occurred after an average of 11,470 ± 3589 cycles. CONCLUSION Fracture impaction increased the ability of the locking plate to withstand repetitive varus loading. This technique provides a construct biomechanically superior to locking plate fixation alone.

FEM Simulation of Non-Progressive Growth from Asymmetric Loading and Vicious Cycle Theory: Scoliosis Study Proof of Concept

Scoliosis affects about 1-3% of the adolescent population, with 80% of cases being idiopathic. There is currently a lack of understanding regarding the biomechanics of scoliosis, current treatment methods can be further improved with a greater understanding of scoliosis growth patterns. The objective of this study is to develop a finite element model that can respond to loads in a similar fashion as current spine biomechanics models and apply it to scoliosis growth. Using CT images of a non-scoliotic individual, a finite element model of the L3-L4 vertebra was created. By applying asymmetric loading in accordance to the ‘vicious cycle’ theory and through the use of a growth modulation equation it is possible to determine the amount of growth each region of the vertebra will undergo; therefore predict scoliosis growth over a period of time. This study seeks to demonstrate how improved anatomy can expand researchers current knowledge of scoliosis.

Surface reconstruction of torsos with and without scoliosis.

Visible surface asymmetries such as uneven shoulders, waist and hips, shoulder height differences and a shoulder blade prominence are often the most troublesome features associated with adolescent scoliosis. Treatment considerations are influenced by the severity and changes over time of these asymmetries. Outcomes are judged on how well the asymmetries are improved towards a normal trunk shape. In this paper, a deformable self organizing feature map (SOFM) is used as a geometric surface reconstruction tool to model the torso surface of subjects with and without scoliosis. The proposed parameterization technique provides a means of quantifying the surface asymmetries and assessing the changes due to either natural history or the effects of treatment. For evaluation 10 control subjects without scoliosis and 10 adolescents with scoliosis were scanned and their torsos were reconstructed. This preliminary study demonstrates that in around 5 min a torso scan with 60,000 data points can be transformed into a 2562 nodes mesh using SOFM. The accuracy of the final mesh is around 1.40 mm on average. The high accuracy and speed of this technique, makes it well suitable to be used in a clinical setting to assess surface features of subjects with scoliosis.

3-D Volumetric Evaluation of Human Mandibular Growth

Bone growth is a complex process that is controlled by a multitude of mechanisms that are not fully understood.Most of the current methods employed to measure the growth of bones focus on either studying cadaveric bones from different individuals of different ages, or successive two-dimensional (2D) radiographs. Both techniques have their known limitations. The purpose of this study was to explore a technique for quantifying the three dimensional (3D) growth of an adolescent human mandible over the period of one year utilizing cone beam computed tomography (CBCT) scans taken for regular orthodontic records. Three -dimensional virtual models were created from the CBCT data using mainstream medical imaging software. A comparison between computer-generated surface meshes of successive 3-D virtual models illustrates the magnitude of relative mandible growth. The results of this work are in agreement with previously reported data from human cadaveric studies and implantable marker studies. The presented method provides a new relatively simple basis (utilizing commercially available software) to visualize and evaluate individualized 3D (mandibular) growth in vivo.

Monitoring for idiopathic scoliosis curve progression using surface topography asymmetry analysis of the torso in adolescents

BACKGROUND CONTEXT At first visit and each clinical follow-up session, patients with adolescent idiopathic scoliosis (AIS) undergo radiographic examination, from which the Cobb angle is measured. The cumulative exposure to X-ray radiation justifies efforts in developing noninvasive methods for scoliosis monitoring. PURPOSE To determine the capability of the three-dimensional markerless surface topography (ST) asymmetry analysis to detect ≥5° progression in the spinal curvature in patients with AIS over 1-year follow-up interval. STUDY DESIGN/SETTING Cross-sectional study in a specialized scoliosis clinic. PATIENT SAMPLE In this study, baseline and 1-year follow-up full torso ST scans of 100 patients with AIS were analyzed using three-dimensional markerless asymmetry analysis. OUTCOME MEASURES Patients with ΔCobb≥5° and ΔCobb<5° were categorized into progression and nonprogression groups, respectively. METHODS The ST scan of each full torso was analyzed to calculate the best plane of symmetry by minimizing the distances between the torso and its reflection about the plane of symmetry. Distance between the torso and its reflection was measured and displayed as deviation color maps. The difference of ST measurements between two successive acquisitions was used to determine if the scoliosis has progressed at least 5° or not. The classification tree technique was implemented using the local deformity of the torso in the thoracic-thoracolumbar (T-TL) and lumbar (L) regions to categorize curves into progression and nonprogression groups. The change in maximum deviation and root mean square of the deviations in the torso were the parameters effective in capturing the curve progression. Funding for this research is provided by the Scoliosis Research Society, and Women and Childrens Health Research Institute. RESULTS The classification model detected 85.7% of the progression and 71.6% of the nonprogression cases. The resulting false-negative rate of 4% for T-TL curves, representing the proportion of undetected progressions, confirmed that the technique shows promise to monitor the progression of T-TL scoliosis curves. Although 100% L curves with progression were detected using the deviation color maps of the torsos, because of the small number of analyzed L curves, further research is needed before the efficiency of the method in capturing the L curves with progression is confirmed. CONCLUSIONS Using the developed classification tree for the patients analyzed in this study, 43% of nonprogression cases between two visits would not have to undergo an X-ray examination.