Original Cortical Bone Research Articles

Depth of vertebral screw insertion using a cortical bone trajectory technique in lumbar spinal fusion: radiological significance of a long cortical bone trajectory.

Contrary to original cortical bone trajectory (CBT), "long CBT" directed more anteriorly in the vertebral body has recently been recommended because of improved screw fixation and load sharing within the vertebra. However, to the authors' knowledge there has been no report on the clinical significance of the screw length and screw insertion depth used with the long CBT technique. The aim of the present study was to investigate the influence of the screw insertion depth in the vertebra on lumbar spinal fusion using the CBT technique. A total of 101 consecutive patients with L4 degenerative spondylolisthesis who underwent single-level posterior lumbar interbody fusion at L4-5 using the CBT technique were included (mean follow-up 32.9 months). Screw loosening and bone fusion were radiologically assessed to clarify the factors contributing to these outcomes. Investigated factors were as follows: 1) age, 2) sex, 3) body mass index, 4) bone mineral density, 5) intervertebral mobility, 6) screw diameter, 7) screw length, 8) depth of the screw in the vertebral body (%depth), 9) facetectomy, 10) crosslink connector, and 11) cage material. The incidence of screw loosening was 3.1% and bone fusion was achieved in 91.7% of patients. There was no significant factor affecting screw loosening. The %depth in the group with bone fusion [fusion (+)] was significantly higher than that in the group without bone fusion [fusion (-)] (50.3% ± 8.2% vs 37.0% ± 9.5%, respectively; p = 0.001), and multivariate logistic regression analysis revealed that %depth was a significant independent predictor of bone fusion. Receiver operating characteristic curve analysis identified %depth > 39.2% as a predictor of bone fusion (sensitivity 90.9%, specificity 75.0%). This study is, to the authors' knowledge, the first to investigate the significance of the screw insertion depth using the CBT technique. The cutoff value of the screw insertion depth in the vertebral body for achieving bone fusion was 39.2%.

Histological characteristics of advanced peri-implantitis bone defects in humans

BackgroundInflammatory osteolysis is the clinical hallmark of peri-implantitis. The morphology of the remaining peri-implant bone and the level of osseointegration, however, remain unknown. Our aim was to characterize advanced peri-implantitis bone defects in humans.MethodsFour patients (3 female and 1 male) were diagnosed with peri-implantitis. A total of 5 implants with machined surfaces and a mean loading time of 12 ± 6 years were removed due to advanced bone loss. The defect extension, the peri-implant bone density (bone area per tissue area in percentage), bone-to-implant contact (%), and the number of filled and empty osteocyte lacunae were calculated based on undecalcified histological specimens.ResultsThe defect extension was on average 4.2 mm (95% CI 0.8–3.4). Remaining peri-implant bone showed a high density of 85.5% (95% CI 79.1–91.3) and covered in total 74% (95% CI 70.5–77.5) of the implant surface. Filled and empty osteocyte lacunae density was on average 191 and 165/mm2 (95% CI 132–251; 103–225), respectively. Histology further revealed signs of ongoing bone formation and resorption.ConclusionThere are signs that suggest that once the original cortical bone is lost due to peri-implantitis, the remaining apical trabecular bone is reinforced and transformed into cortical bone that might take over the functional load.

An Injured Psittacosaurus (Dinosauria: Ceratopsia) From the Yixian Formation (Liaoning, China): Implications for Psittacosaurus Biology.

We describe a Psittacosaurus specimen from the Lujiatun beds of the Yixian Formation in Liaoning, China with an abnormality on its left fibula. Although a large number of Psittacosaurus specimens are known, only a single example of a pathologic Psittacosaurus has been previously noted. The specific pathology in the current specimen is believed to be a healed fibular fracture as assessed through a combination of gross morphology, microcomputed tomography (microCT), and histology data. The fracture can be identified using microCT, but the degree of remodeling and the stage of fracture repair are best determined histologically. The fracture callus is made up of radially oriented spokes of woven bone in a cartilage matrix and the original cortical bone prior to the fracture has been largely eroded. A transverse histologic section taken at the level of the fracture shows the displacement of the proximal and distal parts of the fibula. The Psittacosaurus appears to have survived the break considering the deposition of circumferential non-pathologic bone at the periosteal surface outside of the callus. The combination of gross morphological description, microCT data, and histologic data allowed for a full diagnosis of the abnormality. While some previous authors have preferred gross morphological description above other methods for assessing paleopathologies, it is evident based on this specimen that an amalgam of techniques provides greater clarity to paleopathology diagnoses. Although this Psittacosaurus lived in an environment with many predators, it was able to survive with a fracture on its hindlimb, which undoubtedly would have impacted its locomotion. Anat Rec, 299:897-906, 2016. © 2016 Wiley Periodicals, Inc.

Fixation Strength of Caudal Pedicle Screws after Posterior Lumbar Interbody Fusion with the Modified Cortical Bone Trajectory Screw Method.

Study DesignClinical case series.PurposeIn the posterior lumbar interbody fusion (PLIF) procedure in our institute, the cephalad screw trajectory follows a mediolateral and caudocephalad directed path according to the original cortical bone trajectory (CBT) method. However, the starting point of the caudal screw is at the medial border of the pedicle on an articular surface of the superior articular process, and the trajectory takes a mediolateral path parallel to the cephalad endplate. The incidence of caudal screw loosening after PLIF with this modified CBT screw method was investigated, and significant risk factors for caudal screw loosening were evaluated.Overview of LiteratureA biomechanical study of this modified caudal screw trajectory using the finite element method reported about a 20% increase in uniaxial yield pullout load compared with the traditional trajectory. However, there has been no clinical study concerning the fixation strength of this modified caudal screw trajectory.MethodsThe subjects were 193 consecutive patients who underwent single-level PLIF with modified CBT screw fixation. Caudal screw loosening was checked in computed tomography at 6 months after surgery, and screw loosening was defined as a radiolucency of 1 mm or more at the bone-screw interface.ResultsThe incidence of caudal screw loosening after lumbosacral PLIF (46.2%) was significantly higher than that after floating PLIF (6.0%). No significant differences in sex, brand of the instruments, and diameter and length of the caudal screw were evident between patients with and without caudal screw loosening. Patients with caudal screw loosening were significantly older at the time of surgery than patients without caudal screw loosening.ConclusionsFixation strength of the caudal screw after floating PLIF with this modified CBT screw technique was sufficiently acceptable. Fixation strength after the lumbosacral procedure was not.

The effects of zoledronic acid and dexamethasone on osseointegration of endosseous implants: histological and histomorphometrical evaluation in rats

Bisphosphonates are a widely used class of drugs that prevent bone loss. Several side effects related to bisphosphonate therapy have been reported, including osteonecrosis of the jaws associated with invasive dental procedures and implants placement. To evaluate the influence of intravenous nitrogen-containing BPs in combination with or without dexamethasone on osseointegration of titanium implants placed in an animal model. Twenty-seven male Wistar rats were divided into three groups: group 1 was treated solely with zoledronic acid, group 2 was treated with zoledronic acid and dexamethasone, and group 3 did only receive saline solution injections. Two endosseous implants were placed in each tibia, and three animals from each group were sacrificed at postoperative times of seven, 14, and 28 days. Non-decalcified sections were observed with light microscopy for histological and histomorphometrical analyses. Histomorphometrical analysis using the animals and the implants as unit of measurement revealed no statistically significant difference regarding bone-implant contact and bone density among the three groups. Histological observation revealed that zoledronic acid-treated animals in combination with or without dexamethasone showed expressive less bone remodeling activity at 14 and 28 days after implants placement, compared with control specimens. The studied bisphosphonate regimens did not interfere with the osseointegration of the implants, cortical, or medular bone deposition, but a possible lack of bone remodeling of the original cortical bone may affect long-term osseointegration.

Gene therapy with human osteoprotegerin decreases callus remodeling with limited effects on biomechanical properties

Osteoprotegerin (OPG) is a naturally occurring protein, which prevents bone resorption by inhibition of osteoclastogenesis, function, and survival. Therefore, recombinant OPG may be an attractive drug in the treatment of chronic bone resorptive diseases such as osteoporosis. Gene therapy has the potential to achieve long-term treatment by delivering genes of anti-resorptive proteins to the recipient. The effects of OPG gene therapy on fracture healing have not been described previously. The influence of OPG gene therapy on callus formation, callus tissue structural strength, apparent material properties, and histology of tibia fractures in rats was investigated after 3 weeks and 8 weeks of healing. Intramuscular administration of adeno-associated virus (AAV) vector-mediated OPG resulted in increased levels of OPG in serum of approximately 100 ng/ml throughout the study period. Control animals with fractures received transduction with an AAV reporter gene construct (AAV-enhanced green fluorescent protein (eGFP)), and in this group serum OPG levels remained at baseline (<10 ng/ml). After 3 weeks of healing, AAV-OPG treatment reduced the number of osteoclasts in the callus tissue (33%, P < 0.001). However, AAV-OPG treatment did not influence callus dimensions, callus bone mineral content (BMC), fracture structural strength, or apparent callus tissue material properties. After 8 weeks of healing, AAV-OPG treatment reduced the number of osteoclasts in the callus tissue (31%, P < 0.001) compared with AAV-eGFP fractures. Furthermore, deposition of new woven bone at the fracture line of the original cortical bone was hampered (new woven bone present: in all AAV-eGFP animals, in 41% of AAV-OPG-treated animals, P < 0.001). AAV-OPG treatment also increased callus BMC (18%, P = 0.023) compared with AAV-eGFP fractures. AAV-OPG did not influence callus dimensions, structural strength of the fractures, or ultimate stress, whereas elastic modulus was reduced in the AAV-OPG groups (37%, P = 0.039). The experiment demonstrates that AAV-OPG gene therapy decreases the fracture remodeling, but this does not influence the structural strength of healing fractures.

Periosteal and endosteal reaction to reaming and nailing: the possible role of revascularization on the endosteal anchorage of cementless stems

The reaction of bone to titanium implants of different shapes inserted in the rabbit tibia was investigated with histological and perfusion techniques to determine the pattern of vessel distribution. The experimental implants included full cylindrical rods, hollow rods with holes on the surface and wire mesh rods. In the implanted bones the rods were found to fill a large area of the medullary canal; however, owing to the discrepancy between the shape of the diaphysis and the implant, the endosteal contact was never complete. In an early phase, reactive bone filled the gap between the endosteal and the implant surface; in hollow and wire mesh rods bone had grown inside through the lateral holes or loops of the mesh. Revascularization took place together with remodelling of the endosteal, primary bone to mature lamellar. In full implants a reticle of newly formed vessels developed around the rods; in hollow and wire mesh implants vessels had grown inside the implant itself and the endosteal surface had a more regular profile than in full rods. Wire mesh plugs prevented formation of a peripheral medullary space and showed no encapsulation; wires in contact with or in proximity to the endosteal surface were incorporated by lamellar systems with strong connections with the original cortical bone.

The Effects of Therapeutic Doses of Irradiation on Experimental Bone Graft Incorporation Over a Porous-Coated Segmental Defect Endoprosthesis

The incorporation of autogeneic bone graft into a porous coated segmental endoprosthesis after high-dose irradiation was studied in dogs. A mid-diaphyseal defect was surgically created and then reconstructed with a porous-coated segmental endoprosthesis in 16 dogs. Autogeneic bone grafts were placed over the porous-coated regions of the endoprosthesis and at the endoprosthesis-bone junctions to achieve extracortical fixation. In eight dogs, the reconstructed femora were treated with a time-equivalent dose of 5500 cGy, delivered over a five-week period, beginning three weeks after surgery. In eight dogs, which served as the control group, the reconstructed femora were not irradiated. Dogs were killed 12 weeks after surgery, and the reconstructed femora were evaluated clinically, roentgenographically, mechanically, and histologically. Extracortical bone formation and bone ingrowth into the porous-coated segmental endoprosthesis were significantly inhibited by high-dose irradiation. Nonirradiated reconstructed femora had higher maximum torque at the implant-bone junction than irradiated femora. Nonirradiated femora had significantly greater bone ingrowth within the porous space than irradiated femora. Intracortically, irradiated femora had greater unlabeled bone and less porosity as well as more new bone than nonirradiated femora at 12 weeks postsurgery. Extracortically, irradiated femora had greater original cortical bone and less porosity as well as more new bone than nonirradiated femora at 12 weeks postsurgery. Mineral apposition was less in the irradiated femora from the initiation of radiotherapy to the time of killing five weeks after cessation of irradiation.

Bone healing in rabbits after compression osteosynthesis: a comparative study between the radiological and histological findings

The relationship between the radiological and histological findings was studied in a series of rabbit osteotomies and fractures stabilized with plates with and without longitudinal compression. When compression was employed, the gap varied between 10 and 200 μm and no radiologically visible callus was seen. After 4 weeks the smallest gaps of 10–30 μm were filled histologically with structureless material, while the larger gaps contained ‘cortical’ bone derived from periosteal and endosteal proliferation. The degree of union could not be assessed from X-ray examination, as there was no correlation between the histological and radiological appearances. When no compression was employed, the gap varied between 200–1200 μm; radiologically visible periosteal callus and filling of the gap indicated that consolidation had appeared in four weeks. Gaps of 200–500 μm were filled with bone derived from the periosteum and endosteum of lamellar structure which had invaded the original cortical bone (‘plugging’). When the gaps were more than 500 μm, islands of cartilage and connective tissue were found. In all cases studied, many ‘anchoring osteons’ passed from the endosteal and periosteal callus into the original cortical bone. It is concluded that a ‘compression internal fixation’ of cortical bone will not necessarily secure union, as histologically confirmed, even when the formation of radiologically visible callus is suppressed. The lack of periosteal callus appears to be the result of a small gap and rigid fixation, rather than related to strains induced in the bone.