Stripping Torque Research Articles

Dynamic Torque Limitation vs Static Torque Limitation for Bone Screws in Pig Bone

Abstract Correctly torquing bone screws is important to achieve good patient outcomes. An automated system has been previously proposed that may allow more objective torquing of bone screws. Here the system is tested vs. a static torque limit in pig bone. 5 screws were first inserted until stripping to calibrate the dynamic and static limits. Then 6 were inserted limited to 80% of the mean stripping torque. Then 7 were inserted using 80% of the dynamic model-predicted stripping torque. The pull-out strength of the dynamic and static insertions were compared and no statistically significant difference was found. Future work should consider at using larger screws and different bone samples, with more repetitions to try and obtain a statistically significant result.

Sustainable additive manufacturing of interference screws made from eco-friendly filament for anterior cruciate ligament reconstruction

Additive manufacturing (AM) is a sustainable manufacturing approach because it can lower emissions and have a lower negative impact on the environment. 3D-printed interference screws from poly-lactic acid, eco-friendly filament, by fused deposition modelling (FDM), were fabricated with different process parameters. The most popular technique for reconstructing the anterior cruciate ligament is interference screw fixation. This study considered the role of the AM sustainability paradigm in terms of material input for FDM and product manufacturing. This study considered the role of the AM sustainability paradigm in terms of material input for FDM and process efficiency by investigating the effect of the AM process parameters, such as printing temperature (PT), printing speed (PS), and infill percentage (IP) on the density and stripping torque (ST). Later, the degradation profile of the screw was analyzed using the weight loss of screws. The experimental design of the fully factorial design was with two levels for each process parameter. The significant process parameters and their interactions were through statistical analysis of the resulting design. Results have shown that PT, PS, and IP significantly influenced the density and ST of 3D-printed interference screws. In five weeks, 3D-printed interference screws started to lose weight.

Effects of Exposure Time and Temperature on Screw Driving Torques in Heat-Treated Anatolian Black Pine and Sessile Oak Wood

This study aimed to investigate the characteristics of screw driving torques in heat-treated Anatolian black pine and sessile oak wood. The wood samples were subjected to heat under atmospheric pressure at three different temperatures (130, 180 and 230 °C) and two different exposure time levels (2 and 8 h). Screw driving torques of seating and stripping torque (SET and STT) was performed on all samples. The process of screw driving had two main torques, one of which was the seating torque defined as the torque required to clamp parts and the other one was the stripping torque defined as the maximum torque right before the screw strips in the material and the torque drops suddenly because of the formed screw threads being stripped in wood material. Results show that, in both wood species, the SET and STT values decreased due to the increase in heat treatment temperature and exposure time compared to the control groups.

Variations in non-locking screw insertion conditions generate unpredictable changes to achieved fixation tightness and stripping rates

BackgroundScrews are the most commonly inserted orthopaedic implants. However, several variables related to screw insertion and tightening have not been evaluated. This study aimed firstly to assess the effect of insertion variables on screw tightness, secondly to improve methodologies used by researchers when testing screw insertion techniques and thirdly to assess for any learning or fatigue effects when inserting screws. MethodsTwo surgeons tightened a total of 2280 non-locking, 3.5 mm cortical screws, with 120 screws inserted to what they felt to be optimum tightness whilst varying each of the following factors: different screwdrivers for measuring torque, screwdriver orientation, gloves usage, dominant/non-dominant hand usage, awareness to the applied torque (blinded, unblinded and re-blinded), four bone densities and seven cortical thicknesses. Screws were tightened to failure to determine stripping torque, which was used to calculate screw tightness – ratio between stopping and stripping torque. FindingsScrew tightness increased with glove usage, being blinded to the applied torque and with denser artificial bone and with thinner cortices. Considering all the insertions performed, the two surgeons stopped tightening screws at difference values of tightness ((77% versus 66% (p < 0.001)). A learning effect was observed with some parameters including sterile gloves usage and non-dominant hand application. InterpretationDifferent insertion conditions frequently changed screw tightness for both surgeons. Given the influence of screw tightness on fixation stability, the variables investigated within this study should be carefully reported and controlled when performing biomechanical testing alongside practicing screw insertion under different conditions during surgical training.

Joining polymer parts with self-tapping screws: an improvement of the screw thread geometry

In the present article, the influence of the self-tapping screw’s geometry during the thread forming processes in polymer types used in several industries was studied and analysed using experimental measurement and the finite element method. A number of parameters, such as assembly, type of materials and geometry, were studied. Several commercial screw topologies were also studied, and it was demonstrated that the geometry of the self-tapping screws could be optimised. A new geometry was proposed and then compared against the commercial self-tapping screws. The proposed screw obtained a smaller installation torque and a greater stripping torque, which resulted in a greater clamp load in the self-tapping joining. The clamp load loss due to relaxation was reduced up to 10% compared to the best existing geometry.

Effects of pilot hole diameter and depth on screw driving torques in plywood

Factors affecting screw driving torques in plywood were investigated in this work. The factors were number of layers (7 and 9), pilot hole diameter (3.0 and 3.5 mm), pilot hole depth (60 and 80% of the thickness of specimen), and thickness of the metal plate (7.5 and 10 mm). Screw driving torques were studied in oriented strandboard, medium-density fiberboard, particleboard, and some wood-plastic composites. There is no such information about screw driving torques in plywood (PW). Therefore, this study focused on the plywood made of aspen (Populus tremula L.). The mean seating torque (SET) values ranged from 0.31 to 0.69 N∙m, whereas mean stripping torque (STT) values ranged from 0.50 to 4.7 N∙m. The ratios of STT/SET were between 2 and 5 in PW with seven layers, whereas the ratios were between 4 and 7 in PW with nine layers. The results indicated that the four main effects of SET and STT were statistically significant with p-values of ˂ 0.0001.

Stripping torques in human bone can be reliably predicted prior to screw insertion with optimum tightness being found between 70% and 80% of the maximum.

AimsTo devise a method to quantify and optimize tightness when inserting cortical screws, based on bone characterization and screw geometry.MethodsCortical human cadaveric diaphyseal tibiae screw holes (n = 20) underwent destructive testing to firstly establish the relationship between cortical thickness and experimental stripping torque (Tstr), and secondly to calibrate an equation to predict Tstr. Using the equation’s predictions, 3.5 mm screws were inserted (n = 66) to targeted torques representing 40% to 100% of Tstr, with recording of compression generated during tightening. Once the target torque had been achieved, immediate pullout testing was performed.ResultsCortical thickness predicted Tstr (R2 = 0.862; p < 0.001) as did an equation based on tensile yield stress, bone-screw friction coefficient, and screw geometries (R2 = 0.894; p < 0.001). Compression increased with screw tightness up to 80% of the maximum (R2 = 0.495; p < 0.001). Beyond 80%, further tightening generated no increase in compression. Pullout force did not change with variations in submaximal tightness beyond 40% of Tstr (R2 = 0.014; p = 0.175).ConclusionScrew tightening between 70% and 80% of the predicted maximum generated optimum compression and pullout forces. Further tightening did not considerably increase compression, made no difference to pullout, and increased the risk of the screw holes being stripped. While further work is needed for development of intraoperative methods for accurate and reliable prediction of the maximum tightness for a screw, this work justifies insertion torque being considerably below the maximum.Cite this article: Bone Joint Res 2020;9(8):493–500.

Effects of Countersink Hole on Driving Torques of Screw in Joints Constructed of Medium Density Fiberboard

Aim of study: The aim of this study was to investigate the effect of&#x0D; countersink along with some other factors affecting screw driving torques in&#x0D; joints made of medium density fiberboard (MDF). There is limited research has&#x0D; been done in the field of screw driving torques in wood based composites. In&#x0D; all of these studies, the specimen consisted of a single wood-based composite&#x0D; material and metal plate which was used for the consistency of the screw&#x0D; driving data. However, in this study, the screw driving torques were obtained&#x0D; by the specimens consisted of two MDF testing blocks jointed by a screw.&#x0D; &#x0D; Material and Method: In general, there were two main screw driving&#x0D; torques; seating torque (SET) and stripping torque (STT). The MDF testing&#x0D; blocks had dimension of 150 mm long × 75 mm wide and two different thicknesses&#x0D; were used. For upper testing block, 8-mm-thick MDF and for lower testing block,&#x0D; 18-mm-thick MDF were used. Torques measurements were obtained by an adjustable&#x0D; torque screwdriver. Factors were embedded screw orientation (face-to-face and face-to-side),&#x0D; pilot-hole diameter (2.5 and 3.0 mm), pilot-hole depth (12 and 16 mm) and&#x0D; countersink type (with and without countersink).&#x0D; &#x0D; Main results: The results of statistical analysis indicated that the&#x0D; four-way interaction among the embedded screw orientation, screw length,&#x0D; countersink type and pilot-hole diameter was significant on the mean SET and&#x0D; STT in the MDF joints.&#x0D; &#x0D; Highlights: This study will help MDF manufacturers to understand&#x0D; the screw performance of their products in terms of screw driving torques.

Non-locking screw insertion: No benefit seen if tightness exceeds 80% of the maximum torque

BackgroundMillions of non-locking screws are manually tightened during surgery each year, but their insertion frequently results in overtightening and damage to the surrounding bone. We postulated that by calculating the torque limit of a screw hole, using bone and screw properties, the risk of overtightening during screw insertion could be reduced. Additionally, predicted maximum torque could be used to identify optimum screw torque, as a percentage of the maximum, based on applied compression and residual pullout strength. MethodsLongitudinal cross-sections were taken from juvenile bovine tibial diaphyses, a validated surrogate of human bone, and 3.5 mm cortical non-locking screws were inserted. Fifty-four samples were used to define the association between stripping torque and cortical thickness. The relationship derived enabled prediction of insertion torques representing 40 to 100% of the theoretical stripping torque (Tstr) for a further 170 samples. Screw-bone compression generated during insertion was measured, followed immediately by axial pullout testing. FindingsScrew-bone compression increased linearly with applied torque up to 80% of Tstr (R2 = 0.752, p < 0.001), but beyond this, no significant further compression was generated. After screw insertion, with all screw threads engaged, more tightening did not create any significant (R2 = 0.000, p = 0.498) increase in pullout strength. InterpretationIncreasing screw tightness beyond 80% of the maximum did not increase screw-bone compression. Variations in torques below Tstr, did not affect pullout forces of inserted screws. Further validation of these findings in human bone and creation of clinical guidelines based on this research approach should improve surgical outcomes and reduce operative costs.

Teaching Cortical-Screw Tightening: A Simple, Affordable, Torque-Directed Training Protocol Improves Resident Performance.

Cortical-screw insertion is a fundamental skill in orthopaedic surgery, yet, to our knowledge, no standardized method of teaching this skill exists. The purpose of this study was to evaluate a training protocol that was designed to teach residents how to tighten a cortical screw without causing any stripping. Twenty-five residents and 8 attending surgeons from an orthopaedic residency program tightened cortical screws in a synthetic bone model with a digital torque screwdriver using 3 different techniques: percutaneous; open, dominant hand; and open, nondominant hand. The residents then participated in a training protocol during which each tightened additional screws while receiving real-time torque feedback. During training, the residents targeted 50% to 70% of the stripping torque for each screw. They were assessed at baseline, immediately after training, and at 12 to 15 weeks after training. During each assessment, the percentage of screws that were tightened in the target range and the percentage of stripped screws were recorded. The costs of the training protocol were assessed. After training, all of the residents tightened screws with lower insertional torque compared with their baseline, but only the senior residents tightened more screws in the target range and stripped fewer screws. The attending surgeons, when compared with the residents at baseline, tightened more screws in the target range and tended to strip fewer screws, but these differences were absent at final testing. Costs included $1,927 for durable equipment and an estimated $74 per resident per training session for consumable goods. The senior residents inserted more screws in the target range and stripped fewer screws after participating in this training protocol, but the junior residents did not show significant improvement. Implementation of this training protocol for all residents may improve clinical performance but, because our sample size was limited, additional study is required to assess skill transfer to clinical practice. Cortical-screw tightening is a fundamental skill in orthopaedics, and completion of this torque-directed training protocol may accelerate residents' skill acquisition.

Modelling and multi-objective optimization of ultrasonic inserting parameters through fuzzy logic and genetic algorithm

As the usage of plastic components has increased in various industries, the methods for fastening have increased rapidly. When the plastic components are fastened by self-tapping screws or bolts, failure occurs because of stripped threads or plastic creep. In these circumstances, threaded metal inserts provide improved joint performance and ability to assemble and disassemble the components without degrading them. Even though many techniques such as insert moulding, thermal insertion and cold insertion are available for joining thermoplastic material with metal insert, ultrasonic insertion is one of the most preferred processes because of the shorter cycle time usually less than a second, possibility of simultaneous installation of the multiple inserts and large-scale automation possibilities for higher production operations. The technical problems faced by the industries in ultrasonic insertion process are poor insertion quality which affects the function of the product. These problems arise because of the improper selection of insertion parameters. The objective of this paper is to optimize the ultrasonic insertion parameters for improving the quality of joint through non-traditional optimization techniques. Response surface methodology (RSM) is used to design the experiments, and then pullout strength and stripping torque are measured. Data obtained from the measurement are utilized to develop a nonlinear equation between the responses and predictors, and optimal combinations of insertion parameters are found out by fuzzy logic and genetic algorithm (GA) approach. From the confirmatory test, it was observed that the fuzzy logic yields better output results than GA.

EFFECTS OF PILOT HOLE DIAMETER ON SCREW-DRIVING TORQUES IN MEDIUM DENSITY FIBERBOARD

ABSTRACT This study investigated the effects of pilot-hole diameter in medium density fiberboard (MDF) on the characterization of screw-driving torques. The factors investigated were the embedded screw orientation and pilot hole diameter. Based on the curves obtained from screw-driving process, the measurements of the seating torque (SET) and stripping torque (STT) were obtained. The results of statistical analysis indicated that the SET and STT values in MDF were significantly affected by the pilot hole diameter. In the case of driving screws into the side of MDF material, the mean SET ranged from 0.37 to 1.23 N∙m and STT values ranged from 1.18 to 2.68 N∙m whereas for the face specimens, the mean SET ranged from 0.57 to 1.56 N∙m and STT values ranged from 2.89 to 5.41 N∙m.

Local bone quality measurements correlates with maximum screw torque at the femoral diaphysis

BackgroundSuccessful fracture fixation depends critically on the stability of the screw-bone interface. Maximum achievable screw torque reflects the competence of this interface, but it cannot be quantified prior to screw stripping. Typically, the surgeon relies on the patients' bone mineral density and radiographs, along with experience and tactile feedback to assess whether sufficient compression can be generated by the screw and bone. However, the local bone quality would also critically influence the strength of the bone-screw interface. We investigated whether Reference Point Indentation can provide quantitative local bone quality measures that can inform subsequent screw-bone competence. MethodsWe examined the associations between the maximum screw torque that can be achieved using 3.5 mm, 4.5 mm, and 6.5 mm diameter stainless steel screws at the distal femoral metaphysis and mid-diaphysis from 20 cadavers, with the femoral neck bone mineral density and the local measures of bone quality using Reference Point Indentation. FindingsIndentation Distance Increase, a measure of bone's resistance to microfracture, correlated with the maximum screw stripping torque for the 3.5 mm (p < 0.01; R = 0.56) and 4.5 mm diameter stainless steel screws (p < 0.01; R = 0.57) at the femoral diaphysis. At the femoral metaphysis, femoral neck bone mineral density significantly correlated with the maximum screw stripping torque achieved by the 3.5 mm (p < 0.01; R = 0.61), 4.5 mm (p < 0.01; R = 0.51), and 6.5 mm diameter stainless steel screws (p < 0.01; R = 0.56). InterpretationReference Point Indentation can provide localized measurements of bone quality that may better inform surgeons of the competence of the bone-implant interface and improve effectiveness of fixation strategies particularly in patients with compromised bone quality.

Evaluation of osseous integration of titanium orthopedic screws with novel SLA treatment in porcine model

The success of many endosseous implants in orthopaedic and dental applications depends on the surface characteristics, as they affect osseous integration. Previous investigations indicated that a novel large-grit sand-blasted and acid-etched (SLA) titanium (denoted as SLAffinity-Ti) implant had better bone integration than that of a comparably shaped implant with a plasma-sprayed titanium surface. The purpose of the present investigation was to create a SLAffinity surface on pedicle screws and trauma screws and to compare it with the surfaces of a sand-blasted-only implant and commercial implants in terms of bone integration. The cortical bone and spine of twelve minipigs were implanted with 3 and 4 implants, respectively, and the bone integration was evaluated using micro-computed tomography (micro-CT), mechanical tests (pull-out strength and stripping torque), and histological analysis (toluidine blue and hematoxylin and eosin staining) one and three months after implantation. The micro-CT images showed that the gap between the bone and implant was consistently higher in the sand-blasted-only and commercial groups compared to that in the SLAffinity group 1 and 3 months after implantation. Moreover, the bone volume of implant inserted into bone and the percentage of implant inside bone tissue were greater in the SLAffinity screws 1 and 3 months after implantation, as compared to the sand-blasted and commercial screws. In the mechanical tests, the removal torque and pull-out strength (p < 0.05) were higher in the SLAffinity group at 1 and 3 months. The histological results were consistent with mechanical testing, showing that the SLAffinity group had the most mineralized matrix, the most bone formation around the screws, and the most bone cells in bone tissue. These findings indicate that a SLAffinity surface can effectively enhance the holding strength and integration of pedicle screws and cortical screws, promoting early healing and improving outcomes, compared to sand-blasted-only and commercial implants.

Feasibility of detecting orthopaedic screw overtightening using acoustic emission.

A preliminary study of acoustic emission during orthopaedic screw fixation was performed using polyurethane foam as the bone-simulating material. Three sets of screws, a dynamic hip screw, a small fragment screw and a large fragment screw, were investigated, monitoring acoustic-emission activity during the screw tightening. In some specimens, screws were deliberately overtightened in order to investigate the feasibility of detecting the stripping torque in advance. One set of data was supported by load cell measurements to directly measure the axial load through the screw. Data showed that acoustic emission can give good indications of impending screw stripping; such indications are not available to the surgeon at the current state of the art using traditional torque measuring devices, and current practice relies on the surgeon's experience alone. The results suggest that acoustic emission may have the potential to prevent screw overtightening and bone tissue damage, eliminating one of the commonest sources of human error in such scenarios.

Effects of Driving Torques on Direct Screw Withdrawal Resistance in OSB

This study was performed to evaluate effects of driving torques on direct screw withdrawal resistance (DSWR) in wood-based composites. Pilot hole diameters (1.6, 2, 2.4 mm), embedded screw orientations (edge-, end- and face-) and torque levels, that were obtained from the typical driving torque curve among two main driving torques, were selected to test on screw withdrawal resistance. The results of the study showed that the pilot hole diameters were needed to be chosen carefully related to the grain orientation. The screw withdrawal resistance in face-grain orientation had the highest DSWR than the ones in edge- and end- grain orientations. Based on the torque levels selected that the DSWR was lower at the torque level closer to the stripping torque levels in OSB.

Two-Finger Tightness: What Is It? Measuring Torque and Reproducibility in a Simulated Model.

Residents in training are often directed to insert screws using "two-finger tightness" to impart adequate torque but minimize the chance of a screw stripping in bone. This study seeks to quantify and describe two-finger tightness and to assess the variability of its application by residents in training. Cortical bone was simulated using a polyurethane foam block (30-pcf density) that was prepared with predrilled holes for tightening 3.5 × 14-mm long cortical screws and mounted to a custom-built apparatus on a load cell to capture torque data. Thirty-three residents in training, ranging from the first through fifth years of residency, along with 8 staff members, were directed to tighten 6 screws to two-finger tightness in the test block, and peak torque values were recorded. The participants were blinded to their torque values. Stripping torque (2.73 ± 0.56 N·m) was determined from 36 trials and served as a threshold for failed screw placement. The average torques varied substantially with regard to absolute torque values, thus poorly defining two-finger tightness. Junior residents less consistently reproduced torque compared with other groups (0.29 and 0.32, respectively). These data quantify absolute values of two-finger tightness but demonstrate considerable variability in absolute torque values, percentage of stripping torque, and ability to consistently reproduce given torque levels. Increased years in training are weakly correlated with reproducibility, but experience does not seem to affect absolute torque levels. These results question the usefulness of two-finger tightness as a teaching tool and highlight the need for improvement in resident motor skill training and development within a teaching curriculum. Torque measuring devices may be a useful simulation tools for this purpose.

Time-elapsed screw insertion with microCT imaging

Time-elapsed analysis of bone is an innovative technique that uses sequential image data to analyze bone mechanics under a given loading regime. This paper presents the development of a novel device capable of performing step-wise screw insertion into excised bone specimens, within the microCT environment, whilst simultaneously recording insertion torque, compression under the screw head and rotation angle. The system is computer controlled and screw insertion is performed in incremental steps of insertion torque. A series of screw insertion tests to failure were performed (n=21) to establish a relationship between the torque at head contact and stripping torque (R2=0.89). The test-device was then used to perform step-wise screw insertion, stopping at intervals of 20%, 40%, 60% and 80% between screw head contact and screw stripping. Image data-sets were acquired at each of these time-points as well as at head contact and post-failure. Examination of the image data revealed the trabecular deformation as a result of increased insertion torque was restricted to within 1mm of the outer diameter of the screw thread. Minimal deformation occurred prior to the step between the 80% time-point and post-failure. The device presented has allowed, for the first time, visualization of the micro-mechanical response in the peri-implant bone with increased tightening torque. Further testing on more samples is expected to increase our understanding of the effects of increased tightening torque at the micro-structural level, and the failure mechanisms of trabeculae.

"Turn-of-the-Nut" Method Is Not Appropriate for Use in Cancellous Bone.

The level to which bone screws are tightened is determined subjectively by the operating surgeon. It is likely that the tactile feedback that surgeons rely on is based on localized tissue yielding, which may predispose the screw-bone interface to failure. A limited number of studies have investigated the ratio between clinical tightening torque and stripping torque. The purpose of this study was to measure, for the first time, the ratio between yield torque (T yield) and stripping torque (T max) during screw insertion into the cancellous bone and to compare these torques with clinical levels of tightening reported in the literature. Additionally, a rotational limit was investigated as a potential end point for screw insertion in cancellous bone. A 6.5-mm outer diameter commercial cancellous bone screw was inserted into human femoral head specimens (n = 89). Screws were inserted to failure, while recording insertion torque, compression under the screw head, and rotation angle. The median, interquartile ranges, and coefficient of variation were calculated for each of the following parameters: T yield, T max, T yield/T max, slope, T plateau, and rotation angle. The median ratio of T yield/T max and rotation angle was 85.45% and 96.5 degrees, respectively. The coefficient of variation was greatest for the rotation angle compared with the ratio of T yield/T max (0.37 vs. 0.12). The detection of yield may be a more precise method than the rotation angle in cancellous bone; however, bone-screw constructs that exhibit a T yield close to T max may be more susceptible to stripping during insertion. Future work can identify factors that influence the ratio of T yield/T max may help to reduce the incidence of screw stripping.

Pullout strength of cancellous screws in human femoral heads depends on applied insertion torque, trabecular bone microarchitecture and areal bone mineral density

For cancellous bone screws, the respective roles of the applied insertion torque (TInsert) and of the quality of the host bone (microarchitecture, areal bone mineral density (aBMD)), in contributing to the mechanical holding strength of the bone-screw construct (FPullout), are still unclear. During orthopaedic surgery screws are tightened, typically manually, until adequate compression is attained, depending on surgeons’ manual feel. This corresponds to a subjective insertion torque control, and can lead to variable levels of tightening, including screw stripping. The aim of this study, performed on cancellous screws inserted in human femoral heads, was to investigate which, among the measurements of aBMD, bone microarchitecture, and the applied TInsert, has the strongest correlation with FPullout.Forty six femoral heads were obtained, over which microarchitecture and aBMD were evaluated using micro-computed tomography and dual X-ray absorptiometry. Using an automated micro-mechanical test device, a cancellous screw was inserted in the femoral heads at TInsert set to 55% to 99% of the predicted stripping torque beyond screw head contact, after which FPullout was measured.FPullout exhibited strongest correlations with TInsert (R=0.88, p<0.001), followed by structure model index (SMI, R=−0.81, p<0.001), bone volume fraction (BV/TV, R=0.73, p<0.001) and aBMD (R=0.66, p<0.01). Combinations of TInsert with microarchitectural parameters and/or aBMD did not improve the prediction of FPullout.These results indicate that, for cancellous screws, FPullout depends most strongly on the applied TInsert, followed by microarchitecture and aBMD of the host bone. In trabecular bone, screw tightening increases the holding strength of the screw-bone construct.