Additive manufactured osseointegrated screws with hierarchical design

Bone screws are devices used to fix implants or bones to bones.However,conventional screws are mechanically fixed with thread and often face long-term failure due to poor osseointegration.To improve osseointegration,screws are evolving from solid and smooth to porous and rough.Additive manufacturing(AM)offers a high degree of manufacturing freedom,enabling the preparation of predesigned screws that are porous and rough.This paper provides an overview of the problems currently faced by bone screws:long-term loosening and screw breakage.Next,advances in osseointegrated screws are summarized hierarchically(sub-micro,micro,and macro).At the sub-microscale level,we describe surface-modification techniques for enhancing osseointegration.At the micro level,we summarize the micro-design parameters that affect the mechanical and biological properties of porous osseointegrated screws,including porosity,pore size,and pore shape.In addition,we highlight three promising pore shapes:triply periodic minimal surface,auxetic structure with negative Poisson ratio,and the Voronoi structure.At the macro level,we outline the strategies of graded design,gradient design,and topology optimization design to improve the mechanical strength of porous osseointegrated screws.Simultaneously,this paper outlines advances in AM technology for enhancing the mechanical properties of porous osseointegrated screws.AM osseointegrated screws with hierarchical design are expected to provide excellent long-term fixation and the required mechanical strength.

Biomechanical effects of posterior lumbar interbody fusion with vertical placement of pedicle screws compared to traditional placement

BACKGROUND The pedicle screw technique is widely employed for vertebral body fixation in the treatment of spinal disorders.However,traditional screw placement methods require the dissection of paraspinal muscles and the insertion of pedicle screws at specific transverse section angles(TSA).Larger TSA angles require more force to pull the muscle tissue,which can increase the risk of surgical trauma and ischemic injury to the lumbar muscles.AIM To study the feasibility of zero-degree TSA vertical pedicle screw technique in the lumbosacral segment.METHODS Finite element models of vertebral bodies and pedicle screw-rod systems were established for the L4-S1 spinal segments.A standard axial load of 500 N and a rotational torque of 10 N/m were applied.Simulated screw pull-out experiment was conducted to observe pedicle screw resistance to pull-out,maximum stress,load-displacement ratio,maximum stress in vertebral bodies,load-displacement ratio in vertebral bodies,and the stress distribution in pedicle screws and vertebral bodies.Differences between the 0-degree and 17-degree TSA were compared.RESULTS At 0-degree TSA,the screw pull-out force decreased by 11.35%compared to that at 17-degree TSA(P<0.05).At 0-degree and 17-degree TSA,the stress range in the screw-rod system was 335.1-657.5 MPa and 242.8-648.5 MPa,separately,which were below the fracture threshold for the screw-rod system(924 MPa).At 0-degree and 17-degree TSA,the stress range in the vertebral bodies was 68.45-78.91 MPa and 39.08-72.73 MPa,separately,which were below the typical bone yield stress range for vertebral bodies(110-125 MPa).At 0-degree TSA,the load-displacement ratio for the vertebral bodies and pedicle screws was slightly lower compared to that at 17-degree TSA,indicating slightly lower stability(P<0.05).CONCLUSION The safety and stability of 0-degree TSA are slightly lower,but the risks of screw-rod system fracture,vertebral body fracture,and rupture are within acceptable limits.

Comparative study of intertrochanteric fracture fixation using proximal femoral nail with and without distal interlocking screws

BACKGROUND Intertrochanteric(IT)fracture is one of the most common fractures seen in an orthopaedic practice.Proximal femoral nailing(PFN)is a common modality of fixing IT femur fracture.We retrospectively studied whether a PFN with two proximal lag screws can be done without distal interlocking screws in the 31-A1 and 31-A2 fracture patterns according to the Arbeitsgemeinschaft für Osteosynthesefragen/Orthopaedic Trauma Association(AO/OTA)guidelines for IT femur fractures.AIM To compare the outcomes of IT fractures(AO/OTA 31-A1 and 31-A2)treated by PFN with and without distal interlocking screws.METHODS We carried out a retrospective study of 140 patients in a tertiary care centre who had AO/OTA type 31-A1 and 31-A2 IT fractures.We divided the patients into two groups,in which one of the groups received distal interlocking screws(group 1)and the other group did not(group 2).The subjects were followed up for a mean period of 14 mo and assessed for radiological union time,fracture site collapse,mechanical stability of implant,and complications associated with the PFN with distal interlocking and without distal interlocking.Then,the results were compared.RESULTS PFN without distal interlocking screws has several advantages and gives better results over PFN with distal interlocking screws in the AO/OTA 31-A2 fracture pattern.However,similar results were observed in both groups with the fracture pattern AO/OTA 31-A1.In patients with fracture pattern AO/OTA 31-A2 treated by PFN without distal interlocking screws,there were minimal proximal lockrelated complications and no risk of distal interlock-related complications.The operative time,IITV radiation time and time to radiological union were reduced.These patients also had better rotational alignment of the proximal femur,and the anatomy of the proximal femur was well maintained.It was also noted that in the cases where distal interlocking was performed,there was a gradual decrease in neck shaft angle,which led to varus collapse and failure of bone-implant construct in 21.40%.CONCLUSION In fracture pattern AO/OTA 31-A2,PFN without distal interlocking had better results and less complications than PFN with distal interlocking.

Application of the Guiding Template Designed by Three-dimensional Printing Data for the Insertion of Sacroiliac Screws:a New Clinical Technique

This study is aimed to explore the clinical application of the guiding template designed by three-dimensional printing data for the insertion of sacroiliac screws.A retrospective study of 7 cases (from July 2016 to December 2016),in which the guiding template printed by the three-dimensional printing technique was used for the insertion of sacroiliac screws of patients with posterior ring injuries of pelvis,was performed.Totally,4 males and 3 females were included in template group,aged from 38to 65years old (mean 50.86±8.90).Of them,5 had sacral fractures (3 with Denis type Ⅰ and 2 with type Ⅱ)and 2 the separation of sacroiliac joint.Guiding templates were firstly made by the three-dimensional printing technique based on the pre-operative CT data. Surgical operations for the stabilization of pelvic ring by applying the guiding templates were carried out.A group of 8 patients with sacroiliac injuries treated by percutaneous sacroiliac screws were analyzed as a control group retrospectively.The time of each screw insertion,volume of intra-operative blood loss,and the exposure to X ray were analyzed and the Matta's radiological criteria were used to evaluate the reduction quality.The Majeed score was used to evaluate postoperative living quality.The visual analogue scale (VAS)was applied at different time points to judge pain relief of coccydynia.All the 7 patients in the template group were closely followed up radiographically and clinically for 14 to 20 months,mean (16.57±2.44)months.Totally 9 sacroiliac screws for the S 1 and S2 vertebra were inserted in the 7 patients.The time length for each screw insertion ranged from 450 to 870 s,mean (690.56±135.68)s,and the number of times of exposure to X ray were 4 to 8,mean (5.78±1.20).The intra-operative blood loss ranged from 45to 120 mL,mean (75±23.32)mL.According to Matta's radiology criteria,the fracture and dislocation reduction were excellent in 6cases and good in 1.The pre-operative VAS score ranged from 5.2 to 8.1,mean (7.13±1.00).The average one-week/six-month post-operative VAS was (5.33±0.78)and (1.33±0.66),respectively (P<0.05 when compared with pre-operative VAS).The 12-month post-operative Majeed score ranged from 86 to 92,mean (90.29±2.21).The three-dimensional printed guiding template for sacroiliac screw insertion,which could significantly shorten the operation time,provide a satisfied outcome of the stabilization of the pelvic ring,and protect doctors and patients from X-ray exposure,might be a practical and valuable new clinical technique.

Biomechanical comparison of distal locking screws for distal tibia fracture intramedullary nailing

Background: Newer generation intramedullary (IM) tibial nails provide several distal interlocking screw options. The objectives were to determine: 1) if the new oblique interlocking option provides superior stability, 2) which screw orientation/ configuration is the most biomechanically stable, and 3) if three distal interlocking screws provide better stability. Methods: A preliminary experiment was performed in torsion, compression, and bending tests with four different screw configurations: (I) one medial-to-lateral and one oblique, (II) two me-dial-to-lateral, (III) one medial-to-lateral and one anterior-to-posterior, and (IV) one medial-to-lateral, one anterior-to-posterior and one oblique in simu-lated distal metaphyseal fracture tibiae. Twenty- four Synthes EXPERT tibial IM nails were used for six specimens of each screw configuration. Parts I and II, tibial IM nails were locked with 5.0 mm in-terlocking screws into simulated distal tibiae (PVC and composite analogue tibia). Part III, the two most stable configurations were tested using five pairs of simulated cadaveric distal tibiae metaphy-seal fractures. Results: Significant differences were attributable to distal screw orientation for intrame- dullary nailing of distal tibia fractures. Configura-tions II and IV were found to be more stable than the other two configurations. No significant differ-ence was detected in construct stability in all modes of testing between Configurations II and IV. Dis-cussion: Configuration I did not provide superior stability for the distal tibia fracture fixation. Con-figurations II and IV provided equivalent stability. When choosing IM fixation for treatment of distal tibia metaphyseal fractures two medial-to-lateral screws provide the necessary stability for satisfac-tory fixation. Clinical Relevance: This study indi-cated an option for operative treatment of distal metaphyseal tibia fracture fixation where preserva-tion of soft tissue and rigid stabilization are needed.

Nail Holding Performance of Self-Tapping Screws on Masson Pine and Chinese Fir Dimension Lumbers

Screw connection is a type most commonly applied to timber structures.As important commercial tree species in China,Masson pine and Chinese fir have the potential to prepare wood structures.In this study,the effects of the diameter of the self-tapping screw and the guiding bores on the nail holding performance on different sections of Masson pine and Chinese fir dimension lumbers were mainly explored.The results showed that:(1)The nail holding strength of the tangential section was the maximum,followed by that of the radial section,and that of the cross section was the minimum.(2)The nail holding strength of Masson pine was higher than that of Chinese fir.(3)The nail holding strength grew with the increase in the diameter of self-tapping screws,but a large diameter would lead to plastic cracking of the timber,thus further affecting the nail holding strength.Masson pine and Chinese fir reached the maximum nail holding strength when the diameter of self-tapping screws was 3.5 mm.(4)Under a large diameter of screws,prefabricated guiding bores could mitigate timber cracking and improve its nail holding strength.(5)Prefabricated guiding bores were more necessary for the screw connection of Masson pine.The results obtained could provide a scientific basis for the screw connection design of Masson pine and Chinese fir timber structures.

Does the Location of the Cutting Flute of Self-Tapping Screws in Bony Substrate Affect the Removal Torque?

Introduction: An observation was made that when removing self-tapping cortical screws from patients bones, stripping or shearing of the head of the screw occurred more often in screws whose cutting flutes sat in cortical bone compared with screws that had penetrated the distal cortex with flutes exposed. Method: A model was designed to simulate screws with their cutting flutes either in contact with cortical bone or deep to cortical bone. Screws were grouped depending on the location of their cutting flutes and removal torque was measured. Results: Eighteen screws were included in final analysis. There was a statistically significant difference in average initial removal torque and average maximal removal torque with screws with their cutting flutes in substrate requiring significantly more torque to remove. Conclusion: We conclude that self-tapping cortical screws whose cutting flutes sit in cortical substrate require more torque to remove and are therefore more likely to fail. This finding may be used as a guide in pre-operative planning for removal of metalwork from patients.

Comparison of lag screws and double Y-shaped miniplates in the fixation of anterior mandibular fractures

BACKGROUNDMandibular fractures constitute about 80.79% of maxillofacial injuries inAlexandria University, either as isolated mandibular fractures or as a part ofpanfacial fractures. The combination of symphyseal and parasymphyseal fracturesrepresent 47.09% of the total mandibular fractures.AIMTo compare the effectiveness of lag screws vs double Y-shaped miniplates in thefixation of anterior mandibular fractures.METHODSThis study is a prospective randomized controlled clinical trial, performed onsixteen patients with anterior mandibular fractures. Patients were divided equallyinto two groups, each consisting of eight patients. Group 1: Underwent openreduction and internal fixation using two lag screws. Group 2: Underwent openreduction and internal fixation using double Y-shaped plates. The followingparameters were assessed: operating time in minutes, pain using a visual analogscale, edema, surgical wound healing for signs and symptoms of infection,occlusion status and stability, maximal mouth opening, and sensory nervefunction. Cone beam computed tomography was performed at 3 and 6 mo tomeasure bone density and assess the progression of fracture healing.RESULTSThe study included 13 males (81.3%) and 3 females (18.8%) aged 26 to 45 years(mean age was 35.69 ± 6.01 years). The cause of trauma was road traffic accidentsin 10 patients (62.5%), interpersonal violence in 3 patients (18.8%) and othercauses in 3 patients (18.8%). The fractures comprised 10 parasymphyseal fractures(62.5%) and 6 symphyseal fractures (37.5%). The values of all parameters were comparable in both groups with no statistically significant difference except forthe mean bone density at 3 mo postoperatively which was 946.38 ± 66.29 in group 1 and 830.36 ± 95.53 in group 2 (P = 0.015).CONCLUSIONBoth lag screws and double Y-shaped miniplates provide favorable means offixation for mandibular fractures in the anterior region. Fractures fixed with lagscrews show greater mean bone density at 3 mo post-operation, indicative ofhigher primary stability and faster early bone healing. Further studies with largersample sizes are required to verify these conclusions.

Crossed Intralaminar Screws for Fusion of the Cervicothoracic Junction and the Thoracic Spine: The Experience in an Iberic Service with Case Series and Review of the Current Literature with Technique Description

The treatment of pathologies in the thoracic spine is a challenge. The periodic failure of pedicle screw insertion and anatomical variations make the search for an alternative to pedicle screws in thoracic spine surgery necessary. The interlaminar crossed screws is a well-known and secure method for fusion in cervical spine, and in thoracic spine there used to be insufficient clinical data to support this technique, until now. We demonstrate in an initial series of 10 cases treated with interlaminar fusion in association of other fusion techniques in the thoracic spine with good results. Objective: Intralaminar screws have been shown to be a biomechanical salvage technique in the thoracic spine, especially in long cervicothoracic, thoracic and thoracolumbar fixation. The goals of this article are to demonstrate our initial experience and the range of indications for thoracic crossed intralaminar screws. Methods: In this article we describe our initial series performed at S&#227o Teot&#243nio Hospital in Viseu, Portugal, and our results, and also provide a comprehensive review of the recent literature in the use of intralaminar crossed fixation.

Posterior Selective Thoracic Fusion in Adolescent Idiopathic Scoliosis Patients:a Comparison of All Pedicle Screws versus Hybrid Instrumentation

Objective To analyze the influence of segmental pedicle screws versus hybrid instrumentation on the correction results in adolescent idiopathic scoliosis patients undergoing posterior selective thoracic fusion. Methods By reviewing the medical records and roentgenograms of adolescent idiopathic scoliosis patients who underwent selective thoracic fusion from February 2000 to January 2007 in our hospital, the patients were divided into 2 groups according to different instrumentation fashions： Group A was hook-screw-rod （hybrid） internal fixation type, Group B was screw-rod （all pedicle screws） internal fixation type, and the screws were used in every segment on the concave side of the thoracic curve. The parameters of the scoliosis were measured and the correction results were analyzed. Results Totally, 48 patients （7 males, 41 females） were included, with an average age of 14.4 years old and a mean follow-up time of 12.3 months. Thirty and 18 patients were assigned to group A and group B, respectively. The mean preoperative coronal Cobb angles of the thoracic curve were 48.8° and 47.4°, respectively. After surgery, they were corrected to 13.7° and 6.8°, respectively. At final follow-up, they were 17.0° and 9.5°, with an average correction rate of 64.6% and 79.0%, respectively, and the correction rate of group B was significantly higher than that of group A （P=0.003）. The mean preoperative coronal Cobb angles of the lumbar curve were 32.6° and 35.2°, respectively. After surgery, they were corrected to 8.6° and 8.3°, respectively. At final follow-up, they were 10.3° and 11.1°, with an average correction rate of 66.8% and 69.9%, respectively, and the correction rate of group B was significantly higher than that of group A （P=0.003）. The correction loss of the thoracic curve and lumbar curve in the 2 groups were 3.1° and 1.8°, 2.4° and 2.4°, respectively. No significant difference was noted （both P〉0.05）. The decompensation rate at final follow-up in these 2 groups were 4% （1/25） and 7.1% （1/14） respectively, with no significant difference （P〉0.05）.

KINEMATICS OF 3-DOF PYRAMID MANIPULATOR BY PRINCIPAL SCREWS

Kinematics of a 3 RPS parallel pyramid manipulator are investigated by principal screw. Firstly, the principal screws are identified by quadric degeneration. The planar conics representing the relations between the pitches and the three linear inputs are described, and the three dimensional distribution of the axes of all the twists is illustrated. Finally, a numerical example is given successfully.

Modeling and application of thermal contact resistance of ball screws

Aiming at determining the thermal contact resistance of ball screws,a new analytical method combining the minimum excess principle with the MB fractal theory is proposed to estimate thermal contact resistance of ball screws considering microscopic fractal characteristics of contact surfaces.The minimum excess principle is employed for normal stress analysis.Moreover,the MB fractal theory is adopted for thermal contact resistance.The effectiveness of the proposed method is validated by self-designed experiment.The comparison between theoretical and experimental results demonstrates that thermal contact resistance of ball screws can be obtained by the proposed method.On this basis,effects of fractal parameters on thermal contact resistance of ball screws are discussed.Moreover,effects of the axial load on thermal contact resistance of ball screws are also analyzed.The conclusion can be drawn that the thermal contact resistance decreases along with the fractal dimension D increase and it increases along with the scale parameter G increase,and thermal contact resistance of ball screws is retained almost constant along with axial load increase before the preload of the right nut turns into zero in value.The application of the proposed method is also conducted and validated by the temperature measurement on a self-designed test bed.

Cortical bone trajectory screws in the treatment of lumbar degenerative disc disease in patients with osteoporosis

Lumbar degenerative disc disease(DDD)in the elderly population remains a global health problem,especially in patients with osteoporosis.Osteoporosis in the elderly can cause failure of internal fixation.Cortical bone trajectory(CBT)is an effective,safe and minimally invasive technique for the treatment of lumbar DDD in patients with osteoporosis.In this review,we analyzed the anatomy,biomechanics,and advantages of the CBT technique in lumbar DDD and revision surgery.Additionally,the clinical trials and case reports,indications,advancements and limitations of this technique were further discussed and reviewed.Finally,we concluded that the CBT technique can be a practical,effective and safe alternative to traditional pedicle screw fixation,especially in DDD patients with osteoporosis.

Acetabular components with or without screws in total hip arthroplasty

AIM To compare the operation time, blood loss, and early outcomes of acetabular components with and without the screw.METHODS Thirty patients who underwent cementless acetabular component with or without screw and whose follow-up exceeded one year period in total hip arthroplasty were evaluated. A posterior approach was used in all surgical procedures by one experienced surgeon. Demographic data, operation time, intra-and postoperative blood loss volume, follow-up clinical score, cup migration, and osteolysis were recorded. The Kolmogorov-Smirnov test was performed for testing the normality of study data. Mann-Whitney U test was used to analyze the intergroup differences. A P-value of ≤ 0.05 was considered statistically significant.RESULTS Acetabular components were used in 16(53.3%) patients with screw and 14(46.7%) without screw. After one year of follow-up, an osteolytic lesion of 3 mm was found in only one patient in the screw group. No cup migrationwas encountered. Intra-group mean Harris hip score significantly increased, but there was no significant intergroup difference. While the mean operation time of the screw group was 121.8 min(range; 95-140), it was 102.7 min(range; 80-120) in the no-screw group, and this difference was statistically significant(P = 0.002). The mean intraoperative/postoperative, and total blood loss were 556.6 mL(range: 350-800)/423.3 mL(range: 250-600), and 983.3 mL(range: 600-1350), respectively in the screw group; and 527 mL(range: 400-700)/456 mL(range: 230-600), and 983 mL(range: 630-1250), respectively in the no-screw group. The blood loss difference between the two groups was not significant. In the screw group, the operation time was 19.1 min longer than the no-screw group, and this difference was statistically significant.CONCLUSION Acetabular components with or without screw have similar results, but the use of screw increases the operation time significantly, while not changing the blood loss volume.

Clinical and functional comparison of dynamic hip screws and intramedullary nails for treating proximal femur metastases in older individuals

Objective:To compare the outcomes of dynamic hip screws(DHS)and intramedullary nailing(IMN)in the treatment of extra-capsular metastatic carcinoma of the proximal femur.Methods:A retrospective case analysis method was used to examine data of patients with proximal metastatic cancer of the femur who were treated with internal fixation in Department of Orthopaedics,Beijing Friendship Hospital,from January 2007 to December 2018.Blood loss,postoperative pain,functional score,length of stay,and survival rates were compared,and postoperative complications were assessed.Results:Complete follow-up data were available for 33 patients.The mean follow-up period was 12.2±3.6(range:9-32)months and the average age was 72.3±4.7(range:59-83)years old.There were 20 females and 13 males.Twenty-three patients had undergone IMN and 10 DHS,according to bone defects and the patient’s overall condition.The median survival time was 10 months in the IMN group and 11 months in the DHS group.Duration of surgery(t=-7.366,P<0.001)and length of hospital stay(t=-3.509,P<0.001)differed significantly between the two groups.There was one case of breakage of internal fixation in the IMN group.Conclusions:There was no significant difference between DHS and IMN in terms of surgical efficacy.IMN and DHS were different in terms of surgical time and hospital stay.However,due to the limited number of cases in this study,multi-factor analysis has not been performed and needs to be further verified in future analysis.When developing a surgical plan,it is recommended to consider the patient’s condition and the surgeon’s experience.

A novel technique for sacropelvic fixation using image-guided sacroiliac screws:a case series and biomechanical study

In this study, we sought to assess the safety and accuracy of sacropelvic fixation performed with image-guided sacroiliac screw placement using postoperative computed tomography and X-rays. The sacroiliac screws were placed with navigation in five patients. Intact specimens were mounted onto a six-degrees-of-freedom spine motion simulator. Long lumbosacral constructs using bilateral sacroiliac screws and bilateral S1 pedicle and iliac screws were tested in seven cadaveric spines. Nine sacroiliac screws were well-placed under an image guidance system(IGS);one was placed poorly without IGS with no symptoms. Both fixation techniques significantly reduced range of motion(P<0.05) at L5-S1. The research concluded that rigid lumbosacral fixation can be achieved with sacroiliac screws,and image guidance improves its safety and accuracy. This new technique of image-guided sacroiliac screw insertion should prove useful in many types of fusion to the sacrum, particularly for patients with poor bone quality,complicated anatomy, infection, previous failed fusion and iliac harvesting.

The additon of screws and the axodes of gear pairs

In the light of screw addition, the distribution of instantaneous axes along the common perpendicular of the two screws is determined and all possible sorts of axodes are derived cinematically with the pitch of the relative motion screw in the gear pair as the basis and the transmission ratio i as an independent variable.

Modeling approach for axial contact stiffness of ball screws

Axial stiffness of ball screws has great effects on accuracy of positioning,dynamic characteristic and transmission efficiency. Axial contact stiffness modeling of ball screws is the key problem in dynamic analysis of ball screws. Aiming at obtaining axial stiffness of ball screws considering microscopic fractal characteristics of contact surfaces,a new analytical method is proposed to estimate axial contact stiffness of ball screws and combine the minimum excess principle with Mandelbort( MB)fractal theory in this research. The minimum excess principle is employed to conduct normal stress analysis. And the Mandelbort fractal theory is adopted to obtain contact stiffness in ball screws. The effectiveness of the proposed method is validated by the self-designed experiment. The comparison between theoretical results and experimental results demonstrates that axial contact stiffness of ball screws could be obtained by the proposed method.

Surgical treatment for scoliosis extending to main thoracic spine by key-vertebral-screws technique (KVST)

Objective:To introduce a key-vertebral-screws technique(KVST) in the surgical treatment of scoliosis extending to main thoracic levels, and to find the role of fulcrum bending in predicting the result of surgical treatment for scoliosis by this technique. Methods: Seventeen consecutive patients with scoliosis extending to main thoracic spine,who underwent pure posterior fusion without anterior or posterior release by KVST between January 2004 and July 2005 were evaluated for fulcrum bending flexibility, surgical correction rate, fulcrum bending correction index (FBCI) in main thoracic curves. Universal Spine System (USS) instrumentation was used in 15 cases,Monarch in another 2 cases. The severity of the curves was measured by Cobb's method using Rad Work 6. 0 software. Preoperative standing AP radiographs, preoperative fulcrum bending anterioposterior (AP) radiographs, postoperative standing AP radiographs, and most recent follow-up standing AP radiographs for spine were measured and recorded. All the data were analyzed with two-sample paired t-test by Origin 7. 0 software. Results: Infection and neurological complications were not noted. No major complications were found. Just one case had some axial back pain, which got a full recovery from physiotherapy for 2 weeks. In the X-ray, there was an average correction of 71. 5% of the fused main thoracic curves, which had no significant lose of correction in final follow-up. For the whole fused main thoracic curves, the fulcrum bending flexibility were lower to operation correction rate (P = 0. 013). The average FBCI was 123%. From the data, the more rigid curves (especially fulcrum bending flexibility <50%), the more correction rate operation could get, compared with fulcrum bending flexibility. Conclusion: (1) KVST is a good method in the surgical treatment of thoracic scoliosis, which can get satisfying result with lower medical cost. (2) Fulcrum bending flexibility is lower than operative correction rate by KVST in main thoracic curves (P<0. 05). In the more rigid curves assessed by fulcrum-bending radiograph, the operative corrective could be gained, especially in the curves which FBCI is lower than 50%.

Failure Analysis of Austenitic Stainless Steel Implant Screws and Prospection of Chemical Composition Using Artificial Intelligence

In this work, austenitic stainless steel screws employed in a locking compression plate for veterinarian use were investigated. These types of implants are widely utilized in bone fractures healing. Two surgical screws were extracted due to the observation of slight superficial red rust colorizing on one of the screw implants, visual evidence of probable screw rusting. From the same implant, another screw was extracted simultaneously without visual evidence of rusting. In order to characterize and analyze the different behavior of both screws, the chemical composition was characterized by atomic absorption and energy dispersive X-ray spectroscopy (EDS) coupled to a scanning electron microscope (SEM). Also, the screws were studied by metallography, optical microscopy (OM), Vickers microhardness tests, and SEM analysis. On the other hand, a prospection for alloy chemical composition limits of these types of implants was performed based on the Schaeffler-Delong diagram and the ASTM F-138 standard. To analyze the effect of the chemical composition, heat treatment, microstructure, pitting resistance equivalent number (PRE) and stacking fault energy (SFE), a genetic algorithm (GA) and an artificial neural network (ANN) were used. In accordance with the elemental analysis, the surgical screws do not fulfill the ranges of the chemical composition established by the ASTM F-138 standard. Furthermore, there were found differences between the microstructures of the screws. In regard to the prospection, the results of GA and ANN support the proposed chemical composition region on the Schaeffler-Delong diagram. The corrosion failure was associated with severe plastic deformation and the presence of precipitates. The proposal can minimize the cause of failures in these types of austenitic stainless steel implants.