Factors Associated With the Accuracy of Depth Gauge Measurements

Background: It is important to select appropriate screws in orthopedic surgeries, as excessively long or too short a screw may results failure of the surgeries. This study explored factors that affect the accuracy of measurements in terms of the experience of the surgeons, passage of drilled holes and different depth gauges.Methods: Holes were drilled into fresh porcine femurs with skin in three passages, straight drilling through the metaphysis, straight drilling through the diaphysis, and angled drilling through the diaphysis. Surgeons with different surgical experiences measured the holes with the same depth gauge and using a vernier caliper as gold standard. The length of selected screws, and the time each surgeon spent were recorded. The measurement accuracy was compared based on the experiences of the surgeons and the passage of drilled holes. Further, parameters of depth gauges and 12-mm cortical bone screws from five different manufacturers were measured.Results: A total of 13 surgeons participated in 585 measurements in this study, and each surgeon completed 45 measurements. For the surgeons in the senior, intermediate, and junior groups, the average time spent in measurements was 689, 833, and 785 s with an accuracy of 57.0, 42.2, and 31.5%, respectively. The accuracy and measurement efficiency were significantly different among the groups of surgeons (P < 0.001). The accuracy of measurements was 45.1% for straight metaphyseal drilling, 43.6% for straight diaphyseal drilling, and 33.3% for angled diaphyseal drilling (P = 0.036). Parameters of depth gauges and screws varied among different manufacturers.Conclusion: Both observer factor and objective factors could affect the accuracy of depth gauge measurement. Increased surgeon's experience was associated with improvements in the accuracy rate and measurement efficiency of drilled holes based on the depth gauge. The accuracy rate varied with hole passages, being the lowest for angled drilled holes.

PREPARATION AND NUMERICAL SIMULATIONS OF DRUG-LOADED HYDROXYAPATITE BIOMATERIALS

To meet the challenge of regenerating bone lost to disease or trauma, biodegradable scaffolds are being investigated as a way to regenerate bone without the need for an auto- or allograft. Herein, we prepared poly (lactic acid) (PLA)/chitosan(CS)/nano-hydroxyapatite biomaterials through solution polymerization and solvent volatilization. Cefadroxil was used as a model drug for loading on biomaterials using supercritical carbon dioxide. In addition, we investigated the in vitro drug release effect, and the in vitro release results showed that the drug could release more than 73% of the drug load within 48[Formula: see text]h. This excellent drug release property could allow continuous drug use at the wound site, further broadening its application in the medical field. A three-dimensional finite element (FE) model of bone screws was established, and the mechanical properties of the screws were numerically calculated. The stress and deformation of the bone screws under different external conditions were simulated. The bending simulation showed that the screw can withstand the maximum deformation of 0.418[Formula: see text]mm and equivalent stress of 566.94[Formula: see text]MPa at a force of 700 N. The maximum equivalent stress of the screw reached 321.84[Formula: see text]MPa, and the corresponding torque was 779.68 N[Formula: see text]mm when the torsion angle was gradually increased to 30[Formula: see text]. The fabricated material has excellent mechanical properties and can be used for bone repair. This study provides a new direction for preparing drug-loaded polymer biomaterials and developing new materials for bone repair.

A Novel Screw Drive for Allogenic Headless Position Screws for Use in Osteosynthesis—A Finite-Element Analysis

Due to their osteoconductive properties, allogenic bone screws made of human cortical bone have advantages regarding rehabilitation compared to other materials such as stainless steel or titanium. Since conventional screw drives like hexagonal or hexalobular drives are difficult to manufacture in headless allogenic screws, an easy-to-manufacture screw drive is needed. In this paper, we present a simple drive for headless allogenic bone screws that allows the screw to be fully inserted. Since the screw drive is completely internal, no threads are removed. In order to prove the mechanical strength, we performed simulations of the new drive using the Finite-Element method (FEM), validated the simulations with a prototype screw, tested the novel screw drive experimentally and compared the simulations with conventional drives. The validation with the prototype showed that our simulations provided valid results. Furthermore, the simulations of the new screw drive showed good performance in terms of mechanical strength in allogenic screws compared to conventional screw drives. The presented screw drive is simple and easy to manufacture and is therefore suitable for headless allogenic bone screws where conventional drives are difficult to manufacture.

Proposal for an Adaptive Bone Screw Design Based on FEA Studies Exemplified by Pedicle Screw

This paper presents a proposal for a density-adaptive design of bone screws using pedicle screws for spinal fixations as an example. The basis is the analysis and categorization of currently available variants of bone screws, which differ in principle in their thread design because of different application areas (cortical or cancellous bone). These screw variants are investigated in FEA simulations for pullout and bending with regard to occurring stresses. A corresponding simulation model is presented for this purpose. The precise design models for these screws are generated in a CAD system using a self-developed configuration tool. Based on the FEA evaluation, the proposal for a new pedicle screw design, consisting of several thread types merged into each other, is described in detail. By integrating different thread types over the shaft, the respective properties of the bone can thus be optimally utilized.

Lateral migration resistance of screw is essential in evaluating bone screw stability of plate fixation

Conventional evaluation of the stability of bone screws focuses on pullout strength, while neglecting lateral migration resistance. We measured pullout strength and lateral migration resistance of bone screws and determined how these characteristics relate to screw stability of locking plate (LP) and dynamic compression plate (DCP) fixation. Pullout strength and lateral migration resistance of individual bone screws with buttress, square, and triangular thread designs were evaluated in polyurethane foam blocks. The screw types with superior performance in each of these characteristics were selected. LP and DCP fixations were constructed using the selected screws and tested under cyclic craniocaudal and torsional loadings. Subsequently, the association between individual screws’ biomechanical characteristics and fixation stability when applied to plates was established. Screws with triangular threads had superior pullout strength, while screws with square threads demonstrated the highest lateral migration resistance; they were selected for LP and DCP fixations. LPs with square-threaded screws required a larger force and more cycles to trigger the same amount of displacement under both craniocaudal and torsional loadings. Screws with triangular and square threads showed no difference in DCP fixation stability under craniocaudal loading. However, under torsional loading, DCP fixation with triangular-threaded screws demonstrated superior fixation stability. Lateral migration resistance is the primary contributor to locking screw fixation stability when applied to an LP in resisting both craniocaudal and torsional loading. For compression screws applied to a DCP, lateral migration resistance and pullout strength work together to resist craniocaudal loading, while pullout strength is the primary contributor to the ability to resist torsional loading.

Femtosecond Laser-Processing of Pre-Anodized Ti-Based Bone Implants for Cell-Repellent Functionalization

Microstructures and nanostructures can be used to reduce the adhesion of the cells on the auxiliary material. Therefore, the aim of our work was to fabricate laser-induced hierarchical microstructures and nanostructures by femtosecond laser-treatment (wavelength 1040 nm, pulse length 350 fs, repetition rates in the kHz range) to reduce the cell adhesion. Additionally, surface chemistry modification by optimized electrochemical anodization was used to further reduce the cell adhesion. For testing, flat plates and bone screws made of Ti-6Al-4V were used. Bone-forming cells (human osteoblasts from the cell line SAOS-2) were grown on the bone implants and additional test samples for two to three weeks. After the growth period, the cells were characterized by scanning electron microscopy (SEM). While earlier experiments with fibroblasts had shown that femtosecond laser-processing followed by electrochemical anodization had a significant impact on cell adhesion reduction, for osteoblasts the same conditions resulted in an activation of the cells with increased production of extracellular matrix material. Significant reduction of cell adhesion for osteoblasts was only obtained at pre-anodized surfaces. It could be demonstrated that this functionalization by means of femtosecond laser-processing can result in bone screws that hinder the adhesion of osteoblasts.

‘N-Angle’: Clinical Indicator for Predictable Insertion of Ramal Bone Screws

Introduction: The primary concern in the placement of ramal bone screws is the blind nature of the procedure, as there is a thick, mobile layer of soft tissue over the bone; also, the ramus is not a uniplanar structure but is swerving like a propeller blade. The purpose of this study was to evaluate the possibility of establishing clinical guidelines based on visible dental and soft-tissue landmarks for safe, reliable, and accurate insertion of ramal bone screws. Aims and Objectives: Our primary objective was to evaluate the angle formed between the appropriate direction of ramal-implant placement and the line tangential to the buccal surfaces of the first and second permanent molars. Our secondary objective was to evaluate the average distance of the neurovascular bundle from the tip of the bone screw. Materials and Methods: We obtained 80 cone beam computed tomography (CBCT) samples, marked reference lines and points on selected axial and coronal sections, and evaluated the following parameters using the software’s linear- and angular-measurement device: the angle between the appropriate direction of ramal bone screw placement and the line tangential to the buccal surfaces of the first and second permanent molars; and the proximity of the bone screw to the neurovascular bundle. Results: The angle between the constructed line of insertion and the occlusal line, as evaluated from our study, was 19.04 (SD ± 6.89) degrees. The proximity of the neurovascular bundle from the screw is 7.1773 (SD ± 1.73988) mm. Conclusion: We can conclude that ramal bone screws can be placed with a comfortable margin of safety.