Screw Size Research Articles

Experimental behaviour and numerical modelling of timber-timber composite (TTC) joints

Push-out tests were conducted on 15 groups of symmetric timber-timber composite (TTC) joints with coach screw shear connectors. The push-out test results were used to characterise load-slip, peak load carrying capacity and failure mode of the composite shear connection between timber slab made of cross laminated timber (CLT) and timber beams/joists made of laminated veneer lumber (LVL) and/or glued laminated timber (GLT). Effect of coach screw size, type of engineered wood product (i.e. LVL-to-CLT and/or GLT-to-CLT), GLT grade, thickness of the CLT slab and orientation of load with respect to the outermost layer of CLT on the structural behaviour of the TTC joints were studied. In addition to the TTC connection tests, embedment strength of the LVL, CLT and GLT and bending yield strength of the screws were experimentally determined and the results were incorporated into a versatile nonlinear beam on inelastic foundation finite element (FE) model to capture the full range load-slip response of the TTC connection. The nonlinear FE models (including material and geometrical nonlinearities) were validated against the test data produced in this study and available in the literature and it was shown that the proposed nonlinear FE model can accurately predict the load-slip, stiffness and peak load carrying capacity of the TTC joints with screw shear connectors. The ultimate strength of the TTC joints were also estimated by modified European yield model (EYM) and comparison of the experimental peak load with EYM and FE predictions demonstrated the significant influence of the rope effect on the full range load-slip response and ultimate load carrying capacity of the TTC joints with dowel shear connectors.

The study of screw placement parameters for Ogawa type I acromial fractures by 3D simulation

BackgroundAcromial fractures are rare and there is no consensus on fixation, but an increasing number of studies have reported using two screws to fix Ogawa type I acromial fractures. The objective of this study was to obtain the ideal length, diameter, insertion point, and angle of the screw using a novel 3D simulation.MethodsThe scapular CT data of 100 individuals were obtained to reconstruct 3D models. The transparency of the 3D model was then downgraded along the axial perspective (the view perpendicular to the cross section of the acromion axis) to find the maximum translucent area. Two virtual screws were placed at the anterior edge of the acromion until they penetrated the posterior cortical bon. The largest diameters and lengths of the screw were measured, and the direction and insertion point of the screw were observed.ResultsThe mean maximum lengths of the medial and lateral screws were 43.33 ± 6.17 mm and 39.23 ± 6.01 mm, respectively. The mean maximum diameters of the medial and lateral screws were 4.71 ± 1.23 mm and 4.97 ± 1.07 mm, respectively. Differences in screw length, diameter, and insertion point between males and females were found. The differences in screw angle between sexes were not statistically significant.ConclusionsBased on a 3D model test, we recommend the size, entry points, and angles of screws for Ogawa type I acromial fractures, providing valuable guidance for clinical work. More accurate screw parameters can be obtained preoperatively by establishing an individualized 3D model.

Development of program-driven plug-in for conical counter-rotating twin screw based on SolidWorks

Abstract Owing to the existence of the cone angle, the size of a conical counter-rotating twin screw continuously changes along the axis, so it is not easy to model using SolidWorks. In this study, the parametric design of the modeling process is completed based on the Visual Basic language and a program-driven method. Finally, the SolidWorks program plug-in and user interface are developed to complete the automatic generation of the three-dimensional model of a conical counter-rotating twin screw.

Possible Association of Pedicle Screw Diameter on Pseudoarthrosis Rate After Transforaminal Lumbar Interbody Fusion

Although pedicle screw sizes may affect the rate of bone union after lumbar fusion surgery, there is currently no supportive clinical evidence. Eighty-five patients older than 50 years who underwent single-level L4/5 transforaminal lumbar interbody fusion with posterior pedicle screw (PS) fixation were analyzed. Patients with factors that potentially inhibit bone fusion, such as Parkinson disease, were excluded. Bone union was assessed using computed tomography and dynamic radiographs 1 year after surgery. Explanatory factors considered included sex, age, smoking, bone density, material of the cage, PS diameter (PSD), relative PS length, theoretical maximum PSD (PSDmax), which was defined as the maximum diameter of the screw that may be inserted without breaking cortical bone around the pedicle, and the filling index, which was defined as the difference between the cross-sectional area of maximum PS and actual PS (PSDmaxˆ 2 - PSD ˆ 2). Japanese Orthopaedic Association scores before and 1 year after surgery were evaluated as a clinical outcome. Nineteen levels were diagnosed as pseudoarthrosis. A multivariate logistic regression analysis identified a larger filling index (P= 0.016) and older age (P= 0.047) as risk factors for pseudoarthrosis. The Japanese Orthopaedic Association score 1 year after surgery and its recovery rate were significantly worse in patients with pseudoarthrosis than in those with fusion. The selection of an appropriately sized screw is important for achieving rigid fusion after transforaminal lumbar interbody fusion. Preoperative planning using multiplanar reconstruction computed tomography is an important approach for ensuring good clinical results.

Effect of Bicortical Interfragmentary Screw Size on the Fixation of Metacarpal Shaft Fractures: A 3-Dimensional-Printed Biomechanical Study

PurposeSpiral metacarpal fractures fixed with 2 non-lagged, interfragmentary cortical screws were tested to failure. The effect of screw size (1.2 mm, 1.5 mm, 2.0 mm, and 2.3 mm) on construct strength was tested in 3-point bending.MethodsThree-dimensional-printed metacarpal test models were reproduced from computed tomography scans to reduce the confounding variables of bone density and anatomy, often encountered when using cadavers.ResultsNo significant difference was found between the screw sizes, and the peak failure force was similar. Drill bit fracture and deformation during the insertion of the smallest screw (1.2 mm) as well as model failure during the insertion of the largest screw (2.3 mm) were found in some cases.ConclusionsScrews of 1.5 mm and 2.0 mm in diameter were of sufficient strength and did not have the issues encountered with smaller or larger screws. Concerns from previous authors regarding intraoperative fracture were consistent with the pre-testing failure of some 2.3-mm models.Clinical RelevanceScrews of 1.5 mm or 2 mm appear adequate for the fixation of spiral fracture patterns in metacarpal shafts using bicortical non-lagged technique with a low risk of fixation complications.

Factors Affecting Pedicle Screw Insertional Torque in Spine Deformity Surgery.

Retrospective observational study of consecutive patients. We sought to: (1) clarify the key factors predominantly associated with the insertional torque of pedicle screws; (2) compare the optimal factors for pedicle screw insertion to obtain rigid screw fixation in patients with adult spinal deformity (ASD) and in those with adolescent idiopathic scoliosis (AIS); (3) determine the optimal screw/pedicle ratio (S/P) to obtain rigid pedicle screw fixation. Rigid pedicle screw fixation is mandatory to perform corrections for spinal deformities properly and to allow successful fusion after surgery. The fixation depends mainly on screw position accuracy and patient bone quality. Traditionally, spinal surgeons have decided the screw size, trajectory, and tapping size based on their intuition. Insertional torque has been indicated as useful to predict screw fixation strength, and is correlated with screw pullout strength and frequency of postoperative screw loosening. We compared insertion torque at L1-L3 levels of 324 screws in 68 patients with ASD and 58 screws in 32 patients with AIS. We assessed the association between screw/pedicle ratio and insertion torque by constructing a spline curve. Pedicle and screw diameter correlated positively with insertion torque in patients with either ASD or AIS. The optimal screw/pedicle ratio to obtain rigid pedicle screw fixation in patients with ASD was close to, but less than one, and, by contrast, was about 1 to 1.25 in patients with AIS. We propose the concept of an optimal S/P ratio for obtaining rigid pedicle screw fixation during spinal corrective surgery, which is different for patients with ASD and patients with AIS. The S/P ratio is useful for deciding the appropriate diameter screw for each case in preoperative planning.Level of Evidence: 4.

Evaluation of Withdrawal Resistance of Screw-Type Fasteners Depending on Lead-Hole Size, Grain Direction, Screw Size, Screw Type and Species

Screw-type fasteners are widely used to make connections between wood members or between wood and steel connectors because they can tolerate the applied loads by withdrawal or shearing. In this study, we evaluated the withdrawal resistances of the screw-type fasteners and analyzed the effects of the lead-hole size, relative grain direction (tangential, radial, and cross-sections) of the wood member, screw diameter, screw type, and species. Two wood species, including domestic larch and imported spruce, and three screw-type fasteners, including domestic lag screws (diameters of 9.46, 7.79, and 6.27 mm), domestic tapping screw (diameter, 6.3 mm), and imported Sherpa screw (diameter, 8.0 mm) were used. To assess the effect of lead-hole size, the lead holes with diameters corresponding to 68.7%, 70.8%, and 74.0% of the shank diameter of the lag screw were predrilled. The lead hole corresponding to 74% of the shank diameter was selected for this study because the smaller lead holes required higher rotational force for installation, which may cause damage in the screw neck, although there was no significant difference in the withdrawal resistance depending on the lead-hole sizes applied in this study. The lag screws installed on the tangential and radial surfaces showed similar withdrawal resistances to each other, which were greater than those installed on the cross-sectional surface. As the lag screw diameter increased from 6.27 mm to 9.46 mm, the withdrawal resistance also increased proportionally. The withdrawal resistance of the tapping screw having a diameter of 6.3 mm was almost 1.6 times higher than that of the lag screw having a similar diameter of 6.27 mm, while that of Sherpa screw having a diameter of 8.0 mm was around 1.4 times higher than that of the lag screw having a similar diameter of 7.79 mm.

Thoracic and lumbar spine pedicle morphology in Japanese patients.

Pedicle morphology is important for intraoperative surgical anatomy and to define pedicle screw design and parameters. However, differences of pedicle size according to ethnicity and gender are not well studied. The purpose of this study is to investigate morphological characteristics of the pedicle in Japanese patients for determining adequate screw size and optimal surgical planning. We investigated thoracic and lumbar pedicle morphology in Japanese patients using computed tomography (CT) measurements and analyzed the standard size of pedicles on upper thoracic to lumbar spine CT images in 227 Japanese patients. Gender had a larger impact on the shape and size of pedicles than racial differences. In the distribution of pedicle width, we calculated the ratio of values less than 4.5mm, that in females resulted to be over 30% for the Th3-Th9 segment, and particularly high, above 60% at Th4 and Th5. Our measurement analysis showed that pedicle morphological parameters in Japanese patients showed tendency to be smaller to those found in other studies, and particularly in female patients, they were statistically significantly smaller. Adequate transpedicular instrumentation for Japanese patients will require smaller size pedicle-related devices that will match our anatomical findings to achieve safe device placement. In addition, serving ethnically non-homogenous patient population can require further to spinal morphometric for precise device selection.

Polymorphic Extreme Clubfoot Deformities in Newborns and their Total Correction by Polyarticular, Poly-Axial, Inclusive Manipulation and Serial Castings-(Evidence Based Patiala Technique)

Wrist arthrodesis is commonly performed to improve wrist position, flexion crease hygiene and appearance in patients with spastic upper limbs. These patients often have smaller bones and large commercially available implants lead to complications such as prominence of plate, pain and periprosthetic fractures. Authors hypothesized that Medartis® distal radius plates will lead to lower complication rates on account of lower profile, variable angle locking construct and smaller screw size.

Seismic force-modification factors for mid-rise wood-frame buildings with shearwalls using wood screws

Wood-screw shearwall (WSS) is generally considered to have limited ductility under seismic load. Conservatively, minimum ductility-related force-modification factor, Rd, of 1.0 and over-strength related force-modification factor, Ro, of 1.3 are used in the National Building Code of Canada for seismic design. In this study, the structural performance of WSS’s with different thicknesses of wood-based panels and sizes of wood screws was investigated by conducting monotonic and cyclic loading tests. The combined force-modification factor RdRo was estimated based on shearwall test results. To verify the estimated modification factors, mid-rise light wood-frame buildings (LWFBs) with different numbers of storeys, wall aspect ratios, magnitudes of gravity and diaphragm flexibilities were designed and analysed numerically. Nonlinear dynamic analyses were performed with 22 scaled Far-Field earthquake time-history records. The seismic response of the mid-rise LWFBs with WSS’s under design hazard level met the design criteria of strength and deformation, and the collapse margin ratios obtained by using a simplified FEMA P695 method complied with the requirements. The study indicates that it is appropriate to use an Rd factor of 1.5 and an Ro factor of 1.7 for seismic design of WSS’s.

Morphometric Analysis of C2 Pedicle in 247 Patients and Proposal for Trajectory and Size of Pedicle Screw.

Screw diameters are currently available based on the literature available for the Western population. No data are available in such a large number of patients for the Indian population. The aim of this study was to define the average pedicle size available and to determine the angulation for placement of screws for C2 pedicle in the Indian population. We also try to determine the pedicle screw diameter which can be used universally in most Indian patients, considering the pedicle dimensions. Retrospective morphometric analysis of CT scans of 247 patients (152 M, 95 F) was done to calculate the C2 pedicle width (PW), pedicle height (PH), pedicle length (PL), pedicle transverse angle (PTA) and the craniocaudal angulation (CCA) of the C2 pedicle. Mean PW in females was 5.3 mm and in males it was 5.9 mm. This difference was statistically significant. The mean PH in the study population was 8.9 mm, while the mean PL was 29.7 mm. The mean PTA was 40.0 degrees and the CCA was 28.4 degrees. This is a morphometric analysis of the C2 pedicle which provides information for the surgeons to determine the safe site of entry and trajectory for the screw implantation. We conclude that a screw diameter of 2.7 mm can be safely implanted in a vast majority of the patient population.

Impact of Screw Diameter and Length on Pedicle Screw Fixation Strength in Osteoporotic Vertebrae: A Finite Element Analysis.

Study DesignBiomechanical study.PurposeTo quantitatively investigate the effect of screw size on screw fixation in osteoporotic vertebrae with finite element analysis (FEA)Overview of LiteratureOsteoporosis poses a challenge in spinal instrumentation; however, the selection of screw size is directly related to fixation and is closely dependent on each surgeon’s experience and preference.MethodsTotal 1,200 nonlinear FEA with various screw diameters (4.5–7.5 mm) and lengths (30–50 mm) were performed on 25 patients (seven men and 18 women; mean age, 75.2±10.8 years) with osteoporosis. The axial pullout strength, and the vertebral fixation strength of a paired-screw construct against flexion, extension, lateral bending, and axial rotation were examined. Thereafter, we calculated the equivalent stress of the bone-screw interface during nondestructive loading. Then, using diameter parameters (screw diameter or screw fitness in the pedicle [%fill]), and length parameters (screw length or screw depth in the vertebral body [%length]), multiple regression analyses were performed in order to evaluate the factors affecting various fixations.ResultsLarger diameter and longer screws significantly increased the pullout strength and vertebral fixation strength; further, they decreased the equivalent stress around the screws. Multiple regression analyses showed that the actual screw diameter and %length were factors that had a stronger effect on the fixation strength than %fill and the actual screw length. Screw diameter had a greater effect on the resistance to screw pullout and flexion and extension loading (β=0.38–0.43, p<0.01); while the %length had a greater effect on resistance to lateral bending and axial rotation loading (β=0.25–0.36, p<0.01) as well as mechanical stress of the bone-screw interface (β=−0.42, p<0.01).ConclusionsThe screw size should be determined based on the biomechanical behavior of the screws, type of mechanical force applied on the corresponding vertebra, and anatomical limitations.

Finite element and biomechanical analysis of risk factors for implant failure during tension band plating.

ObjectiveTension band plating has recently gained widespread acceptance as a method of correcting angular limb deformities in skeletally immature patients. We examined the role of biomechanics in procedural failure and devised a new method of reducing the rate of implant failure.MethodsIn the biomechanical model, afterload (static or cyclic) was applied to each specimen. The residual stress of the screw combined with different screw sizes and configurations were measured and compared by X-ray diffraction. With regard to static load and similar conditions, the stress distribution was analyzed according to a three-dimensional finite element model.ResultsThe residual stress was close to zero in the static tension group, whereas it was very high in the cyclic load group. The residual stress of screws was significantly lower in the convergent group and parallel group than in the divergent group. The finite element model showed similar results.ConclusionsIn both the finite element analysis and biomechanical tests, the maximum stress of the screw was concentrated at the position where the screws enter the cortex. Cyclic loading is the primary cause of implant failure.

An Anatomical Study of Metacarpal Morphology Utilizing CT Scans: Evaluating Parameters for Antegrade Intramedullary Compression Screw Fixation of Metacarpal Fractures

This study evaluated metacarpal morphology for antegrade placement of intramedullary headless compression screws (IMHCS) for metacarpal fracture fixation. We analyzed 100 hand computed tomography scans to quantify cortical thickness, intramedullary diameter, and metacarpal lengths. In addition, dorsal or ulnar overhang of the metacarpals over their respective carpal bones was measured. We also predicted optimal entry points for guidewire placement at the metacarpal head. The ring finger metacarpal had the narrowest medullary canal width (coronal, 2.8 mm; sagittal, 3.5 mm). Not counting the thumb, the little finger metacarpal had the widest midshaft medullary width of 4.1 mm in the coronal plane and the middle metacarpal was widest in the sagittal plane with canal width of 3.9 mm. On average, there was maximal dorsal overhang at the base of the middle metacarpal (4.2 mm) and maximal ulnar overhang at the base of the small metacarpal (3.9 mm). The optimal entry point for guidewire placement over each metacarpal head was approximately 3.5 to 3.8 mm volar to the dorsal cortex. Minimum IMHCS diameters of 3.5 mm for the ring and 4.0 mm for the index, middle and little fingers are necessary to achieve interference fit within the medullary canal. Minimum screw lengths of 38 mm would be needed to ensure 6 mm fixation past the midshaft of the metacarpals. Antegrade IMHCS for fixation of proximal metacarpal fractures may be most feasible with thumb, middle, and little finger metacarpals because there was larger dorsal or ulnar overhang to allow screw placement without violating the carpometacarpal joints. Our analysis provides a reference guide for intramedullary screw sizes for each metacarpal of the hand to achieve interference fit with fracture fixation. Furthermore, the dorsal and ulnar overhangs of the metacarpal bases suggest the practicality of antegrade IMHCS fixation.

Early Weightbearing after Operative Fixation of Jones Fractures Does Not Delay Union

Category:Lesser Toes; Midfoot/ForefootIntroduction/Purpose:The Jones fracture of the proximal fifth metatarsal metadiaphysis is predisposed to delayed union and nonunion due to a tenuous blood supply. Surgical fixation followed by delayed weightbearing is commonly recommended, though the optimal period of nonweightbearing after surgery is not well defined. In response to more recent literature and in an effort to facilitate functional recovery, the trend in our practice has begun to shift toward earlier weightbearing for all patients after Jones fracture fixation. The purpose of this study is to investigate the effect of earlier weightbearing after surgical fixation of Jones fractures.Methods:All Jones fractures treated with an intramedullary (IM) screw in a large, urban practice from 2012-2018 were identified. We excluded fractures that were chronic in nature and patients with underlying metabolic disease. We defined a delayed union as longer than 12.5 weeks based on published data. Time to weightbearing and early weightbearing (within 1 week of surgery) were investigated as risk factors for delayed union using logistic regression and Fisher exact tests, respectively. The relationship between time to weightbearing and time to union was assessed with Spearman correlation. Additional variables were explored in bivariate analysis: time to surgery from initial presentation; age, sex, chronicity, tobacco use, weight, BMI, screw size; preoperative NSAID use, and postoperative VTE prophylaxis. Multivariate regression analyses were then performed to identify variables independently predictive of delayed union.Results:Forty-one cases were included (17 males, 24 females), all treated with IM fixation. Median age in the sample was 45 years ( IQR, 32-62 years). Overall mean time to union was 10.9 +- 7.0 weeks (range, 4.9-41.4 weeks). There were nine (22.0%) delayed unions. Earlier weightbearing was not significantly predictive of delayed union (OR 1.02; 95% CI, 0.99-1.05; P = 0.211), and the incidence of nonunion was not significantly different between early and delayed weightbearing groups (OR, 1.20; 95% CI, 0.02- 17.54; P > .999). In bivariate analysis, increasing age was associated with increasing risk of delayed union (OR, 1.06; 95% CI, 1.01- 1.12; P = 0.031), and was correlated with time to union (ρ = 0.327, P = 0.037). Mutivariate analaysis demonstarted no significant variables.Conclusion:Our results suggest that earlier weightbearing after internal fixation of Jones fractures is not a risk factor for delayed union and does not significantly alter healing time. These findings are consistent with previously published data, but go further by assessing the effects of time to weightbearing in continuous regression models.

Establishing a New Bony Landmark for Safe Screw Insertion in Medial Displacement Calcaneal Osteotomy: A Simulation-Based Approach

Category:Hindfoot; OtherIntroduction/Purpose:Medial displacement calcaneal osteotomy (MDCO) is a commonly performed procedure in flatfoot reconstruction. Fixation is often achieved with screws due to its ability to compress across the osteotomy site. Screws are placed via a free-handed technique without direct fluoroscopic visualization, due to difficulty attaining a simultaneous axial calcaneal view. In addition, the posterior calcaneal tuber translates medially after displacement, resulting in altered anatomical geometry. It is therefore important to establish a reliable external bony landmark when performing free-handed interfragmentary fixation in order to avoid potential screw-related complications and to provide better surgical technique and fixation. The purposes of this study are to validate a new external bony landmark and to establish the appropriate trajectory and screw length for free-hand screw fixation in MDCO.Methods:A total of 84 postoperative computed tomography (CT) scans of MDCO in 70 patients were analyzed. The images were reconstructed using a 3-dimensional simulation program (Vworks 4.0, Cybermed). Virtual screw insertion was simulated by aiming towards two bony landmarks: the base of the 5th metatarsal in the axial plane, and the sinus tarsi in the sagittal plane (Figure 1). A grading system was also utilized to classify scenarios in which the screw breached the distal cortical wall: Grade 1 was defined as contact between the virtual screw and the cortex, Grade 2 as the screw approaching the outer margin of the cortex, and Grade 3 as the screw penetrating the outer cortex. The trajectory angle between the screw and the osteotomy, as well as the screw size, were also measured.Results:The average age of patients was 24.5 (range, 19 to 53), and 100% were males. The average displacement of the posterior calcaneal fragment was 7.3+-1.5 mm (range, 3.9 to 13.8). Among the 84 virtual screws, only five (6.0%) breached the medial cortical wall of the osteotomized calcaneus. All medial breaches were Grade 1. None of the virtual screws breached the lateral cortical wall. Mean trajectory angle between the virtual screw and the osteotomy site was 74.9+-6.7˚ (range, 60.0 to 89.8˚). In the perioperative data, estimated maximum screw length by simulation was 55.6+-4.4 mm (range, 50 to 65).Conclusion:Our results suggest that the optimal trajectory of free-handed screw placement can be determined through simulation of calcaneal interfragmentary screw insertion using postoperative CT imaging. Using this simulation technology, we determined a trajectory towards the sinus tarsi on the sagittal plane and the base of the 5th metatarsal on the axial plane to be a reliable external bony landmark for placement of screws in MDCO. These promising results have potential implications in achieving better fixation as well as improving union rates and operative outcomes.

A cadaveric morphometric analysis of coracoid process with reference to the Latarjet procedure using the "congruent arc technique".

Congruent arc Latarjet procedure involves rotating the coracoid process so that its inferior surface is flush with the glenoid face, owing to their matching radius of curvature (ROC). However, there has been no cadaveric study to actually measure and compare the ROC of coracoid with glenoid, especially in Indian population. 44 shoulders were dissected in 24 cadavers to measure usable length of coracoid process, width, height, ROC of coracoid and glenoid as well as ulnar length (as proxy of cadaver height). Critical coracoid height and length were estimated based on screw sizes of 2.7mm, 3.5mm, 4mm and 4.5mm, and pair concordance between height and length calculated. ROC of coracoid and glenoid were compared to measure extent of congruency. The mean usable length of coracoid process, width and height at mid-point were 21.8mm, 13.7mm and 8.6mm, respectively. Out of the different screw sizes, 2.7mm screws were found safe in 82% shoulders. 24 coracoid-glenoid pairs fulfilled the operational definition (≤ 5mm) of congruency while rest 20 were seemingly incongruent chiefly due to coracoid variations, with mean ROC difference 4.13mm (95% CI 1.51-6.74mm). The ulnar length was significantly smaller in the incongruent ROC group (p = 0.0002). The available length as well as height of the transferred coracoid must be considered when deciding optimum diameter fixation screws in Latarjet procedure. Owing to smaller anatomic dimensions of coracoid in Indian population, 2.7-mm screws provide the safest fixation option. Also, the ROC of coracoid and glenoid does not match in substantial proportion of the cadavers. Pre-operative planning should include a CT-based assessment of glenoid and coracoid dimensions to decide the technique of Latarjet procedure and the optimum diameter fixation screws required.

Risk of pedicle and spinous process violation during cortical bone trajectory screw placement in the lumbar spine

BackgroundPrevious studies have confirmed the feasibility of the cortical bone trajectory (CBT) technique. However, there are few reports on spinous process violation and screw penetration during the screw insertion. The purpose of this study was to evaluate the incidence of spinous process violation and screw penetration through the pedicle during CBT screw insertion.MethodsComputed tomography (CT) scans with normal lumbar structures were consecutively obtained and three-dimensional (3D) reconstructions of the lumbar spine were created. Bilateral CBT screw placement was simulated on each segment using a screw diameter of 4.5 mm, 5.0 mm, or 5.5 mm. Incidences of these complications were recorded and analyzed.ResultsA total of 90 patients were enrolled. Spinous process violation was observed in 68.3, 53.3, 25.5, 1.7, and 0% from L1 to L5, respectively, using 4.5 mm screws. A significant difference was found among the five segments but this was unconnected to gender or screw diameter. The incidence of screw penetration through the inner wall decreased from L1 to L4; in turn, L1 (16.7–35.5%), L2 (12.7–34.4%), L3 (2.8–23.8%) and L4 (1.1–6.7%). This trend was reversed in L5 (6.7–16.7%). Moreover, screw penetration through the outer wall was rare. The incidence of screw penetration varied with screw size as well as lumbar level, but not with gender.ConclusionsThere are more difficulties of CBT screw fixation in upper lumbar spine. The low rate of screw penetration, using 4.5 mm screws, suggests the safety for CBT fixation in the lumbar spine. Larger screws (5.0 mm or 5.5 mm) are more recommended for use in the lower lumbar spine. Moreover, CBT fixation in L5 deserves greater attention because of the unique morphology of the pedicle.

Femoral interference screw insertion significantly increases graft tension in medial patellofemoral ligament reconstruction.

This study aimed to quantify the effect of interference screw insertion on MPFL graft tension when securing the femoral attachment after patellar fixation. It was hypothesized that interference screw insertion significantly increases graft tension. Ten fresh frozen human cadaveric femurs were utilized to compare graft tension at three different preloading conditions (2N, 5N, 10N) using a tensile testing machine (Admet Inc., Norwood, MA). Each preloading condition was analyzed with varying graft sizes (5-8mm), tunnel diameters (7-9mm), and interference screw sizes (7-9mm). Non-parametric statistical analysis was utilized to compare testing conditions among each other. Graft tension significantly increased after interference screw insertion by 100% to 552%, with 2N preload showing the greatest increase (p < 0.001). Grafts with a larger diameter (7-8mm) had a significantly greater increase in tension than smaller grafts (5-6mm), regardless of preloading conditions (p < 0.001). Interference screw size had no influence on graft tension (n.s.). A graft-tunnel interference (tunnel diameter-graft diameter) fit of 0mm and 1mm significantly increased graft tension for each preloading condition when compared to a slightly looser fit of ≥ 2mm (p < 0.05). Femoral interference screw insertion significantly increases graft tension in MPFL reconstruction even in low preloading conditions, with graft size and graft-tunnel interference fit having a considerably effect on graft tension. Surgeons should be aware of the inadvertent increases in graft tension even in low preloading conditions to mitigate the risk of graft overtensioning.

Influence of bone density, screw size and surgical procedure on orthodontic mini-implant placement – part B: implant stability

This in vitro study aimed to investigate the influence of bone density, implant size, and surgical procedure on the primary stability (PS) of orthodontic mini-implants (OMIs). In total, 640 OMIs of various sizes (2.0 × 7, 2.3 × 7, 2.0 × 11 and 2.3 × 11 mm) were inserted in the artificial bone of different densities (D1–D4). Placement was performed with an insertion angle of 90° or 60° to the bone surface and in 320 cases without predrilling, which resulted in 64 groups. PS was measured on the basis of implant stability quotient (ISQ) and insertion torque (IT). With regard to all possible influencing parameters, the mean PS differed between 39.20 and 60.00 (ISQ), and 10.00 and 39.00 Ncm (IT). The effect of OMI size and surgical procedure was dependent on bone quality. For example, implant size had less effect in high-density bone and was stronger with decreasing density. Overall, implant length had a greater influence than the diameter, and a high correlation was found among both PS measurement techniques. Therefore, a suitable choice of implant size and surgical protocol with regard to bone density can positively influence PS. In principle, ISQ and IT are suitable for measuring OMI stability.