Mechanical evaluation of a 4-mm cancellous "rescue" screw in osteoporotic cortical bone: a cadaveric study

Augmented screwdrivers can increase the performance of orthopaedic surgeons compared with use of normal screwdrivers

Orthopaedic screws insertion can be trivialised as a simple procedure, however it is frequently performed poorly. Limited work exists defining how well surgeons insert screws or whether augmented screwdrivers can aid surgeons to reduce stripping rates and optimise tightness. We aimed to establish the performance of surgeons inserting screws and whether this be improved with screwdriver augmentation. 302 orthopaedic surgeons tightened 10 non-locking screws to what they determined to be optimum tightness into artificial bone sheets. The confidence in the screw purchase was given (1-10). A further 10 screws were tightened, using an augmented screwdriver that indicated when a predetermined optimum tightness was reached. The tightness for unstripped insertions under normal conditions and with the augmented screwdriver were 81% (95% CI 79-82%)(n = 1275) and 70% (95% CI 69-72%)(n = 2577) (p < 0.001). The stripping rates were 58% (95% CI 54-61%) and 15% (95% CI 12-17%) respectively (p < 0.001). The confidences when using the normal and augmented screwdrivers respectively were 7.2 and 7.1 in unstripped insertions and 6.2 and 6.5 in stripped insertions. Performance improved with an augmented screwdriver, both in reduced stripping rates and greater accuracy in detecting stripping. Augmenting screwdrivers to indicate optimum tightness offer potentially enormous clinical benefits by improving screw fixation.

Salvaging Pull-Out Strength in a Previously Stripped Screw Site: A Comparison of Three Rescue Techniques

Screw stripping during bone fixation is a common occurrence during operations that results in decreased holding capacity and bone healing. We aimed to evaluate the rescue of the stripped screw site using screws of different dimensions. Five screw configurations were tested on cadaveric specimens for pull-out strength (POS). The configurations included a control screw tightened without stripping, a configuration voluntarily stripped and left in place, and three more configurations in which the stripped screws were replaced by a different screw with either increased overall length, diameter, or thread length. Each configuration was tested five times, with each screw tested once. The POS of the control screw, measured to be 153.6 ± 27 N, was higher than the POS measured after stripping and leaving the screw in place (57.1 ± 18 N, p = 0.001). The replacement of the stripped screw resulted in a POS of 158.4 ± 64 N for the screw of larger diameter, while the screws of the same diameter but increased length or those with extended thread length yielded POS values of 138.4 ± 42 and 185.7 ± 48 N, respectively. Screw stripping is a frequent intraoperative complication that, according to our findings, cannot be addressed by leaving the screw in place. The holding capacity of a stripped screw implanted in cancellous bone can successfully be restored with a different screw of either larger diameter, longer length, or extended thread length.

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

BACKGROUND

Screws 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.

METHODS

Two 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.

FINDINGS

Screw 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.

INTERPRETATION

Different 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.

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

AIMS

To devise a method to quantify and optimize tightness when inserting cortical screws, based on bone characterization and screw geometry.

METHODS

Cortical 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.

RESULTS

Cortical 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).

CONCLUSION

Screw 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.

Surgical performance when inserting non-locking screws: a systematic review

Billions of screws are inserted by surgeons each year, making them the most commonly inserted implant. When using non-locking screws, insertion technique is decided by the surgeon, including how much to tighten each screw. The aims of this study were to assess, through a systematic review, the screw tightness and rate of material stripping produced by surgeons and the effect of different variables related to screw insertion.

Twelve studies were included, with 260 surgeons inserting a total of 2793 screws; an average of 11 screws each, although only 1510 screws have been inserted by 145 surgeons where tightness was measured – average tightness was 78±10% for cortical (n = 1079) and 80±6% for cancellous screw insertions (n = 431).

An average of 26% of all inserted screws irreparably damaged and stripped screw holes, reducing the construct pullout strength. Furthermore, awareness of bone stripping is very poor, meaning that screws must be considerably overtightened before a surgeon will typically detect it.

Variation between individual surgeons’ ability to optimally insert screws was seen, with some surgeons stripping more than 90% of samples and others hardly any. Contradictory findings were seen for the relationship between the tightness achieved and bone density.

The optimum tightness for screws remains unknown, thus subjectively chosen screw tightness, which varies greatly, remains without an established target to generate the best possible construct for any given situation. Work is needed to establish these targets, and to develop methods to accurately and repeatably achieve them.

Cite this article: EFORT Open Rev 2020;5:26-36. DOI: 10.1302/2058-5241.5.180066

Osteoporotic Distal Fibula Fractures in the Elderly: How To Fix Them

Osteoporotic fractures of the distal fibula in elderly patients is a challenge to manage. Non-operative management has a poor outcome so operative management is preferred. There are a variety of options for operative management such as locked plate systems, anti-glide plate construct, dual plating constructs, fibula nail, plate with tibial pro-fibular screws, and injectable bone cement (polymethylmethacrylate (PMMA), calcium phosphate). However, no clear guidelines exist for the operative management of osteoporotic distal fibula fractures. The surgeon should detect osteoporotic fractures early to make the best use of resources and avoid complications such as implant failure.

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

BACKGROUND

Millions 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.

METHODS

Longitudinal 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 (T_str) for a further 170 samples. Screw-bone compression generated during insertion was measured, followed immediately by axial pullout testing.

FINDINGS

Screw-bone compression increased linearly with applied torque up to 80% of T_str (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.

INTERPRETATION

Increasing screw tightness beyond 80% of the maximum did not increase screw-bone compression. Variations in torques below T_str, 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.

Biomechanical and histologic assessment of a novel screw retention technology in an ovine lumbar fusion model

BACKGROUND CONTEXT

Screw loosening is a prevalent failure mode in orthopedic hardware, particularly in osteoporotic bone or revision procedures where the screw-bone engagement is limited.

PURPOSE

The objective of this study was to evaluate the efficacy of a novel screw retention technology (SRT) in an ovine lumbar fusion model.

STUDY DESIGN/SETTING

This was a biomechanical, radiographic, and histologic study utilizing an ovine lumbar spine model.

METHODS

In total, 54 (n=54) sheep lumbar spines (L₂-L₃) underwent posterior lumbar fusion (PLF) via pedicle screw fixation, connecting rod, and bone graft. Following three experimental variants were investigated: positive control (ideal clinical scenario), negative control (simulation of compromised screw holes), and SRT treatments. Biomechanical and histologic analyses of the functional spinal unit (FSU) were determined as a function of healing time (0, 3, and 12 months postoperative).

RESULTS

Screw pull-out, screw break-out, and FSU stability of the SRT treatments were generally equivalent to the positive control group and considerably better than the negative control group. Histomorphology of the SRT treatment screw region of interest (ROI) observed an increase in bone percentage and decrease in void space during healing, consistent with ingrowth at the implant interface. The PLF ROI observed similar bone percentage throughout healing between the SRT treatment and positive control. Less bone formation was observed for the negative control.

CONCLUSIONS

The results of this study demonstrate that the SRT improved screw retention and afforded effective FSU stabilization to achieve solid fusion in an otherwise compromised fixation scenario in a large animal model.

The "Open-Envelope" Approach: A Limited Open Approach for Calcaneal Fracture Fixation

BACKGROUND

Minimally invasive surgery (MIS) has a significant and evolving role in the treatment of displaced intra articular calcaneal fractures (DIACFs), but there is limited literature on this subject. The objective was hence to assess the clinicoradiological outcomes of DIACFs fixed with an innovative open-envelope MIS technique.

MATERIALS AND METHODS

42 closed Sanders Type 2 and 3; DIACFs were included in this study. The Open-envelope approach was developed, which is essentially a limited open, dual incision, modified posterior longitudinal approach allowing excellent visualisation and direct fragment manipulation. The main outcome measures were American Orthopaedic Foot and Ankle Score (AOFAS) hindfoot score and preoperative and postoperative radiological angles.

RESULTS

The Bohler angle improved from a preoperative mean of 14.3° (range 0°-28°) to a postoperative mean of 32.46° (range 22°-42°). The Gissane angle improved from a preoperative mean of 135.83° to a postoperative mean of 128.33°. The postoperative improvement in Bohler and Gissane angles was highly significant (P < 0.001). The AOFAS scores at 6 months were excellent in nine patients, good in 15 patients, and fair in six patients. Three patients had residual valgus deformity of the heel.

CONCLUSIONS

Open-envelope technique minimized soft tissue complications and achieved acceptable radiological reductions with good clinical outcomes.

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

BACKGROUND

Successful 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.

METHODS

We 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.

FINDINGS

Indentation 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).

INTERPRETATION

Reference 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.

Calcaneal Fractures - Should We or Should We not Operate?

The best treatment for displaced, intraarticular fractures of the calcaneum remains controversial. Surgical treatment of these injuries is challenging and have a considerable learning curve. Studies comparing operative with nonoperative treatment including randomized trials and meta-analyses are fraught with a considerable number of confounders including highly variable fracture patterns, soft-tissue conditions, patient characteristics, surgeon experience, limited sensitivity of outcome measures, and rehabilitation protocols. It has become apparent that there is no single treatment that is suitable for all calcaneal fractures. Treatment should be tailored to the individual fracture pathoanatomy, accompanying soft-tissue damage, associated injuries, functional demand, and comorbidities of the patient. If operative treatment is chosen, reconstruction of the overall shape of the calcaneum and joint surfaces are of utmost importance to obtain a good functional result. Despite meticulous reconstruction, primary cartilage damage due to the impact at the time of injury may lead to posttraumatic subtalar arthritis. Even if subtalar fusion becomes necessary, patients benefit from primary anatomical reconstruction of the hindfoot geometry because in situ fusion is easier to perform and associated with better results than corrective fusion for hindfoot deformities in malunited calcaneal fractures. To minimize wound healing problems and stiffness due to scar formation after open reduction and internal fixation (ORIF) through extensile approaches several percutaneous and less invasive procedures through a direct approach over the sinus tarsi have successfully lowered the rates of infections and wound complications while ensuring exact anatomic reduction. There is evidence from multiple studies that malunited displaced calcaneal fractures result in painful arthritis and disabling, three-dimensional foot deformities for the affected patients. The poorest treatment results are reported after open surgical treatment that failed to achieve anatomic reconstruction of the calcaneum and its joints, thus combining the disadvantages of operative and nonoperative treatment. The crucial question, therefore, is not only whether to operate or not but also when and how to operate on calcaneal fractures if surgery is decided.

Influence of the number and position of stripped screws on plate-screw construct biomechanical properties

INTRODUCTION

Screw stripping is a common situation in fracture fixation, particularly in osteopenic bone treatment. Surgeons' perception of screw stripping is relatively poor and the real number of loose screws in every plate-screw construct is unknown. The biomechanical and clinical implications of the different possible screw-stripping situations are also unidentified. In this study, construct stiffness in different scenarios of stripped screws is investigated.

METHOD

A bone surrogate comminuted osteoporotic fracture was fixed with four screws in both sides of the fracture gap in 75 specimens. In four groups, one or two screws closest or distal to the gap were over-tightened and left in place in one part of the construct and the remaining screws were tightened with 0.3N m torque (four groups). In the fifth group (control), all the screws were tightened with 0.3N m torque. Construct stiffness was tested in terms of compression, bending, and torsion for 1000 cycles.

RESULTS

When one or two screws closest to the gap were stripped, stiffness only decreased by, respectively, 5.7% or 7.6% under compression and 4.7% or 6.7% under bending; however, stiffness in torsion was 15.1% or 32%, respectively, lower than the initial stiffness. When a screw distal to the gap was stripped, the stiffness decreased by 28% under bending and 10% under compression; no change was noted under torsion. When two screws distal to the gap were stripped, the stiffness decreased by 11% in compression, collapsed under bending, and decreased by 8% under torsion.

CONCLUSIONS

Position and number of stripped screws affect the biomechanical properties of a construct in different ways, depending on the acting forces.

Effect of Real-Time Feedback on Screw Placement Into Synthetic Cancellous Bone

OBJECTIVES

The objective of this study is to evaluate whether real-time torque feedback may reduce the occurrence of stripping when inserting nonlocking screws through fracture plates into synthetic cancellous bone.

METHODS

Five attending orthopaedic surgeons and 5 senior level orthopaedic residents inserted 8 screws in each phase. In phase I, screws were inserted without feedback simulating conventional techniques. In phase II, screws were driven with visual torque feedback. In phase III, screws were again inserted with conventional techniques. Comparison of these 3 phases with respect to screw insertion torque, surgeon rank, and perception of stripping was used to establish the effects of feedback.

RESULTS

Seventy-three of 239 screws resulted in stripping. During the first phase, no feedback was provided and the overall strip rate was 41.8%; this decreased to 15% with visual feedback (P < 0.001) and returned to 35% when repeated without feedback. With feedback, a lower average torque was applied over a narrower torque distribution. Residents stripped 40.8% of screws compared with 20.2% for attending surgeons. Surgeons were poor at perceiving whether they stripped.

CONCLUSIONS

Prevention and identification of stripping is influenced by surgeon perception of tactile sensation. This is significantly improved with utilization of real-time visual feedback of a torque versus roll curve. This concept of real-time feedback seems beneficial toward performance in synthetic cancellous bone and may lead to improved fixation in cancellous bone in a surgical setting.

Can high-friction intraannular material increase screw pullout strength in osteoporotic bone?

BACKGROUND

Osteoporotic bone brings unique challenges to orthopaedic surgery, including a higher likelihood of problematic screw stripping in cancellous bone. Currently, there are limited options to satisfactorily repair stripped screws. Additionally, nonstripped screws hold with less purchase in osteoporotic bone.

QUESTIONS/PURPOSES

This study attempts to answer the following questions: (1) Does high-friction intraannular (HFIA) augmentation increase pullout strength in osteoporotic and in severely osteoporotic bone; and (2) can HFIA repair stripped bone thread in osteoporotic and severely osteoporotic bone?

METHODS

We measured screw pullout strength using a synthetic bone model in three groups: (1) predrilled nonstripped control holes as controls; (2) predrilled nonstripped augmented with HFIA; and (3) predrilled stripped holes repaired with HFIA. We tested this in osteoporotic and severely osteoporotic synthetic bone for a total of six test groups. We measured screw pullout force using an electromechanical tensile-testing machine comparing pullout force between the test groups and controls.

RESULTS

HFIA augmentation did not increase pullout force compared with the control group in the osteoporotic bone model (489 ± 175 versus 607 ± 76, respectively; effect size = 0.94 [95% confidence interval {CI}, -1.75 to 0.08], p = 0.06). However, in severely osteoporotic cancellous bone that was augmented, the HFIA material generated more pullout force than the control (51 ± 18 versus 35 ± 16, respectively; effect size = 0.94 [95% CI, -0.02 to 1.82], p = 0.05). In stripped holes, HFIA partially restored pullout strength but remained weaker than controls in both osteoporotic and severely osteoporotic bone models (osteoporotic: 320 ± 59 versus 607 ± 76, respectively; effect size = -4.28 [95% CI, -5.57 to -2.51], p < 0.001; severely osteoporotic: 21 ± 8 versus 35 ± 16, respectively; effect size = -1.13 [95% CI, -2.0 to 0.12], p = 0.027).

CONCLUSIONS

HFIA effectively augmented severely osteoporotic bone for screw purchase, but this effect was not seen for osteoporotic bone. In a model simulating both osteoporotic and severely osteoporotic bone, we found that HFIA can be used to repair stripped screw holes, but the resulting construct remains weaker than nonstripped controls.

CLINICAL RELEVANCE

The HFIA material looks promising as a potential solution to stripped screws in osteoporotic bone. However, this material has yet to be tested in human bone. Furthermore, the fine mesh material could be damaged by autoclaving and could break off in vivo causing unknown tissue reactions. We recommend additional testing in a living animal model to better understand how living bone will react to the HFIA material.

Surgeon perception of cancellous screw fixation

OBJECTIVES

The ability of surgeons to optimize screw insertion torque in nonlocking fixation constructs is important for stability, particularly in osteoporotic and cancellous bone. This study evaluated screw torque applied by surgeons during synthetic cancellous fixation. It evaluated the frequency with which screws were stripped by surgeons, factors associated with screw stripping, and ability of surgeons to recognize it.

METHODS

Ten surgeons assembled screw and plate fixation constructs into 3 densities of synthetic cancellous bone while screw insertion torque and axial force were measured. For each screw, the surgeon recorded a subjective rating as to whether or not the screw had been stripped. Screws were then advanced past stripping, and stripped screws were identified by comparing the insertion torque applied by the surgeon to the measured stripping torque.

RESULTS

Surgeons stripped 109 (45.4%) of 240 screws and did not recognize stripping 90.8% of the time when it occurred. The tendency to strip screws was highly variable among individual surgeons (stripping ranging from 16.7% to 83.3%, P < 0.0001) and did not correlate with synthetic bone density in the range tested (P = 0.186) nor with the ranking of surgeons as resident or attending surgeon (P = 0.437). Screws that were correctly recognized as stripped retained a mean 55.0% of maximum torque, less than when stripping was not recognized (79.6%, P = 0.005).

CONCLUSIONS

Surgeon perception is not reliable at preventing and detecting screw stripping at clinical torque levels in synthetic cancellous bone. Less aggressive insertion or standardized methods of insertion may improve the stability of nonlocking screw and plate constructs.

Osteoporotic ankle fractures: an approach to operative management

The incidence of osteoporosis is increasing as the elderly population grows. Because these patients remain active, fragility fractures of the ankle are becoming more common. The literature indicates a relatively high complication rate for non-operative management of ankle fractures in this patient cohort, leading surgeons to face challenges unique to patients with poor bone and skin quality. This article discusses techniques to address osteoporotic ankle fractures and reviews the current literature relevant to this issue.

Salvaging the pullout strength of stripped screws in osteoporotic bone

Our goal was to determine whether the pullout strength of stripped screw holes in osteoporotic bone could be increased with readily available materials from the operating room. We inserted 3.5-mm stainless steel nonlocking self-tapping cortical screws bicortically into 5 osteoporotic humeri. Each screw was first stripped by rotating it 1 full turn past maximum torque. In the control group, the screw was pulled out using an MTS machine (858; MTS Inc, Eden Prairie, Minnesota). In the treatment groups, the screw was removed, the hole was augmented with 1 of the 3 materials (stainless steel wire, polysorb suture, or polyethylene terephthalate glycol plastic sheet), and the screws were replaced and then pulled out. The effect of material on pullout strength was checked for significance (P < .05) using a general linearized latent and mixed model (Stata10; StataCorp, College Station, Texas). The mean (95% confidence interval) pullout strength for the unaugmented hole was 138 N (range 88-189), whereas the holes augmented with plastic, suture, or wire had mean pullout strengths of 255 N (range 177-333), 228 N (range 149-308), and 396 N (range 244-548), respectively. Although wire augmentation resulted in pullout strength that was significantly greater than that of the unaugmented screw, it was still below that of the intact construct.