Conventional Lag Screw Research Articles

Evaluation of the Efficay of Computer Guided Lag Screw Fixation in Comparison to Conventional Lag Screw Fixation in Anterior Mandibular Fractures. Randomized Clinical Trial (RCT)

Background and Objective: This study aimed to compare the use of computer guided technology to placelag screws in anterior mandibular fracture in comparison to convectional techniqueMaterials and Method: This study included twenty-six patients divided into two equal groups, wherefixation in group A utilized computer guided patient specific guide to fix anterior mandibular fractures usinglag screws. In group B anterior mandibular fractures were fixed using lag screws in the conventional way.Both groups were compared in terms of stability and the need of auxiliary fixation devices.Results: Both techniques showed uneventful healing and showing insignificant difference between themconcerning stability and the need for auxiliary fixation device.Conclusion: Although the use of computer guided technology didn’t offer significant advantage over theconventional technique yet it provides more easy and reliable way especially for beginners introduced tothe technique.

Analysis of an in-house technique for temporary mandibulotomy and its impact on postoperative radiotherapy

The purpose of this study was to describe a newly developed procedure for temporary mandibulotomy and subsequent osteosynthesis. Clinical outcomes were evaluated, including complications and the impact on postoperative treatment, particularly postoperative radiotherapy. Twenty-four patients underwent temporary mandibulotomies for the surgical resection of malignancies located in the posterior oral or oropharyngeal region. All were treated with postoperative radiotherapy. An angulated median mandibulotomy was followed by osteosynthesis with three anchor screws directed towards the inferior aspect of the mandible. Anchor screws are modified conventional lag screws that include an additional biconcave washer. This modification prevents the screw heads from cracking into the cancellous bone during tightening, improving their biomechanical qualities considerably. Insertion of screws at any angle to the bony surface therefore becomes possible, which is a precondition for this technique. Minor complications occurred in two patients in the early postoperative period. However, complications causing bony non-union, leading to postponed postoperative radiotherapy were not noted in this cohort.

Biomechanical comparison of Kangli hollow screws with sliding compression locking plate system and conventional cannulated lag screws for fixation of type Pauwels III femoral neck fracture

Objective To compare the biomechanical performance of Kangli hollow screws with sliding compression locking plate system (KHS) and conventional cannulated lag screws for fixation of type Pauwels III femoral neck fracture. Methods 7 cadaveric femurs were selected, vertical fractures (Pauwels III fracture, at 70° to the horizontal) were artificially conducted in these cadaveric proximal femurs by an orthopaedic surgeon and fixed by KHS screws with plate system or conventional cannulated lag screws. Samples were positioned at 75° of the femoral shaft to the horizontal, embedded in the mould and fixed in the experimental console. Optical sensors were set at the femoral neck around the osteotomy line. Then the loading were input in the vertical, horizontal lateral direction and rotating direction around the femoral neck axis, the maximal and minimal values between the fractured fragments and the corresponding values of the loading were recorded. The values of stiffness in three directions were calculated and compared. The CT data of the left femur of a 25 year-old healthy male volunteer was input into the corresponding software and vertical femoral neck fracture model was generated. Two finite element analysis models were obtained after the fracture being fixed using these two different implants, and the Von Mises stress distribution on the femur, implants and the interface between the fractured fragments and the relative motion between the fractured fragments were compared. Results In the vertical, horizontal lateral direction and rotating direction around the femoral neck axis, the stiffness of the KHS were 3 904±1 148 N/mm, 4 324±1 234 N/mm and 11.45±4.95 N·m/° respectively, higher than those of the CSs method with the values of 3 020±1 150 N/mm, 3 020±854 N/mm and 6.53±4.83 N·m/° respectively. The differences between the two groups were statistically significant (t=2.7194, 4.7694 and 2.9424; P=0.0347, 0.0050 and 0.0423). In the finite element analysis test, the maximal Von Mises stress values distributing on the femur and the screws in the KHS group were 40.1 MPa and 126.4 MPa, and those in the CSs group were 98.1 MPa and 145.5 MPa respectively, and both values of the former were lower than the latter. But the Von Mises stress value on the interface between the fractured fragments in the KHS group was 14.37 MPa, which was much higher than that in the CSs groupwhich was 9.39 MPa. The gap at the fracture site of the CSs fixation model was dramatically larger than that of KHS fixation model. Conclusion The KHS screws and plate system could provide better immobilization effect for vertical femoral neck fracture compared to the cannulated lag screws. The risk of the screws failure was lower and the fracture union would be easier to obtained by the fixation of KHS screws with plate system. Key words: Femoral neck fractures; Fracture fixation, internal; Biomechanics; Finite element analysis

Biomechanical Comparison between Preloaded Position Screw and Lag Screw Fixations for Their Compressive Effects in a Porcine Rib Fracture Model.

The aim of this study was to compare the compressive effect between preloaded position screws and lag screws in fracture fixation. Pairs of semi-cylindrical bone fragments were created on a porcine rib model to simulate fractured bones. The compressive forces of fracture fixation generated by preloaded position screws (P group) and conventional lag screws (L group) were recorded by a film stress sensor. In the P group, a pair of Angus bone holding forceps was used to compress the interfragmentary interface until reaching the preloading force of 1.3 MPa. Similar preloading procedure was applied on lag screw fixations to explore its potential of additional compressive force. With 1.3 MPa preloading force and 0.2 Nm screw insertion torque force, the interfragmentary compressive force of P group was similar to that of L group. When the insertion torque force was increased to 0.4 Nm, all screws in the L group failed due to thread stripping. When screws in the P group were installed under 0.4 Nm torque and in the L group under 0.2 Nm torque, the P group generated significantly greater compressive force. With preloading device applied on lag screw installation, it did not further increase the interfragmentary compressive force. Compared with lag screws, preloaded position screws tolerated greater torque in screw installation and provided greater interfragmentary compressive force. The study suggests the applicability of preloaded position screws in fracture fixation requiring interfragmentary compression.

Torsional stiffness after subtalar arthrodesis using second generation headless compression screws: Biomechanical comparison of 2-screw and 3-screw fixation

BackgroundSubtalar joint arthrodesis is a common operative treatment for symptomatic subtalar arthrosis. Because excessive relative motion between the talus and calcaneus can delay or prohibit fusion, fixation should be optimized, particularly in patients at risk for subtalar arthrodesis nonunion. Tapered, fully-threaded, variable pitch screws are gaining popularity for this application, but the mechanical properties of joints fixed with these screws have not been characterized completely. We quantified the torsion resistance of 2-screw and 3-screw subtalar joint fixation using this type of screw. MethodsTen pairs of cadaveric subtalar joints were prepared for arthrodesis and fixed using Acutrak 2–7.5 screws. One specimen from each pair was fixed with two diverging posterior screws, and the contralateral joint was fixed using two posterior screws and a third screw directed through the anterior calcaneus into the talar neck. Internal and external torsional loads were applied and joint rotation and torsional stiffness were measured at two torque levels. FindingsInternal rotation was significantly less in specimens fixed with three screws. No difference was detectable between 2-screw and 3-screw fixation in external rotation or torsional stiffness in either rotation direction. Both 2-screw and 3-screw fixation exhibited torsion resistance surpassing that reported previously for subtalar joints fixed with two diverging conventional lag screws. InterpretationPerformance of the tapered, fully threaded, variable pitch screws exceeded that of conventional lag screws regardless of whether two or three screws were used. Additional resistance to internal rotation afforded by a third screw placed anteriorly may offer some advantage in patients at risk for nonunion.

Compressive Force With 2-Screw and 3-Screw Subtalar Joint Arthrodesis With Headless Compression Screws.

Joint compression is an essential element of successful arthrodesis. Although subtalar joint compression generated by conventional screws has been quantified in the laboratory, compression obtainable with headless screws that rely on variable thread pitch to achieve bony contact has not been assessed. This study measured subtalar joint compression achieved by 2 posteriorly placed contemporary headless, variable-pitch screws, and quantified additional compression gained by placing a third screw anteriorly. Ten, unpaired fresh-frozen cadaveric subtalar joints were fixed sequentially using 2 diverging posterior screws (one directed into the talar dome, the other into the talar neck), 2 parallel posterior screws (both ending in the talar dome), and 2 parallel screws with an additional anterior screw inserted from the plantar calcaneus into the talar neck. Joint compression was quantified directly during screw insertion using a novel custom-built measuring device. The mean compression generated by 2 diverging posterior screws was 246 N. Two parallel posterior screws produced 294 N of compression, and augmentation of that construct with a third, anterior screw increased compression to 345 N (P < .05). Compression subsequent to 2-screw fixation was slightly less than that reported previously for subtalar joint fixation with 2 conventional lag screws, but was comparable when a third screw was added. Under controlled testing conditions, 2 tapered, variable-pitch screws generated somewhat less compression than previously reported for 2-screw fixation with conventional headed screws. A third screw placed anteriorly increased compression significantly. Because headless screws are advantageous where prominent screw heads are problematic, such as the load-bearing surface of the foot, their effectiveness compared to other screws should be established to provide an objective basis for screw selection. Augmenting fixation with an anterior screw may be desirable when conditions for fusion are suboptimal.

Comparison of tip apex distance and cut-out complications between helical blades and lag screws in intertrochanteric fractures among the elderly: a meta-analysis

PurposeTo investigate whether helical blade implant systems have advantages in terms of tip apex distance (TAD) and cut-out rate in comparison to conventional lag screws for intertrochanteric fractures in a geriatric population. MethodsRelevant articles were sourced from the MEDLINE, Embase, Ovid and Cochrane Library databases from inception through March 2015. All randomized controlled trials (RCTs) comparing outcomes between helical blade and lag screw implant systems were selected. Mean TAD values and reported cut-out complications were noted. Each author independently assessed the relevance of the enrolled studies and the quality of the extracted data. Data were analyzed using R software. ResultsTen studies including 1831 patients were eligible for this review, seven of which were included in a combined analysis of dichotomous outcomes and five in a combined analysis of continuous outcomes. The results revealed that, compared with lag screw implantations, the use of helical blades led to a lower rate of cut-out complications (95% CI: 0.28–0.96, P=0.036). Patients who experienced cut-out complications had a significantly greater tip apex distance (95% CI: 0.68–1.34, P<0.001). However, the actual tip apex distances were similar between the screw group and blade group (95% CI: −0.44–0.79, P=0.58). ConclusionsNo difference in TAD values was found between blades and screws. In addition, the cut-out risk in the blade-design group was lower than that of the screw group. Therefore, TAD is not an accurate predictor of cut-out risk.

A biomechanical study of a novel expansive double-threaded bi-directional compression screw for internal fixation of type II odontoid fractures

Objective To measure and compare the biomechanical performance and anti-bending strength of conventional cannulated lag screw (CLS) versus our self-designed expansive double-threaded bi-directional compression screw (EDBCS) in fixation of type Ⅱ odontoid fracture. Methods Models of type Ⅱ odontoid fracture were created in 10 Chinese cadaveric specimens of axis which were then randomly subjected to fixation with either CLS or EDBCS (n = 5). Torsional stiffness and shear stiffness before and after fixation of type Ⅱ odontoid fracture were measured in all specimens. CLS and EDBCS were compared in terms of biomechanical performance in fixation. The 2 kinds of screws were also compared in terms of anti-bending strength by three-point bending test. Results The torsional stiffness and shear stiffness of CLS and the torsional stiffness of EDBCS after fixation were significantly decreased compared with before fixation (P < 0. 05). The torsional stiffness and shear stiffness of EDBCS were significantly larger than those of CLS (P < 0. 05). The maximal anti-bending strength of EDBCS (652. 3 ±0. 1 N) was significantly higher than that of CLS (576. 7 ±25. 0 N) (t = 2. 984, P = 0. 035). Conclusion Since EDBCS has better biomechanical performance in fixation of type II odontoid fracture than CLS, it may result in better fixation of the fracture theoretically. Key words: Fascia dentata; Fracture fixation, internal; Bone screws; Biomechanics

Does the IOFIX improve compression in ankle fusion?

The new IOFIX is an intra-osseous fixation device comprising an "X-post" through which a lag screw passes to apparently improve force distribution across an arthrodesis. We conducted a novel human cadaveric study. Our null hypothesis was no difference in force exists in an ankle arthrodesis model stabilized with the IOFIX or a conventional single lag screw. In ten cadaver ankles a pressure transducer was compressed as an IOFIX and standard single lag screws were alternately compared. The median average force created by the IOFIX was 3.95kg and 2.4kg for the single conventional lag screw (p⩽0.01). The IOFIX improved contact area across the arthrodesis with a median average of 3.41cm(2) compared with 2.42cm(2) in the lag screw group (p⩽0.03). Our results suggest an IOFIX improves force distribution across an ankle arthrodesis compared with a single conventional lag screw.

Does bone compaction around the helical blade of a proximal femoral nail anti-rotation (PFNA) decrease the risk of cut-out?

ObjectivesBecause of the contradictory body of evidence related to the potential benefits of helical blades in trochanteric fracture fixation, we studied the effect of bone compaction resulting from the insertion of a proximal femoral nail anti-rotation (PFNA). MethodsWe developed a subject-specific computational model of a trochanteric fracture (31-A2 in the AO classification) with lack of medial support and varied the bone density to account for variability in bone properties among hip fracture patients.ResultsWe show that for a bone density corresponding to 100% of the bone density of the cadaveric femur, there does not seem to be any advantage in using a PFNA with respect to the risk of blade cut-out. On the other hand, in a more osteoporotic femoral head characterised by a density corresponding to 75% of the initial bone density, local bone compaction around the helical blade provides additional bone purchase, thereby decreasing the risk of cut-out, as quantified by the volume of bone susceptible to yielding.ConclusionsOur findings indicate benefits of using a PFNA over an intramedullary nail with a conventional lag screw and suggest that any clinical trial reporting surgical outcomes regarding the use of helical blades should include a measure of the femoral head bone density as a covariable.

Anchor lag screw vs conventional lag screw in mandibular fractures: A series of 30 cases

Lag screw osteosynthesis is a well proven technique. Its application is limited by the fact that the spherical head of the screw act as wedge. Combining this screw with a bioconcave washer has broadened the range of applications for lag screw osteosynthesis in the maxillofacial region. PurposeThe aim of the study was to compare the efficacy of anchor lag screw with conventional lag screw in anterior mandibular fractures. Patients and methodThirty patients with anterior mandible fractures with no concomitant fractures, infection or extraoral communication, who visited our outpatient Department of Oral and Maxillofacial Surgery, were included in the study after obtaining their informed consent. Patients were randomly divided into two groups; where Group A underwent fixation using conventional lag screw and Group B anchor lag screw. The fixation system used included 2 mm titanium lag screws of sizes 25 mm, 27 mm and 30 mm and 3 mm titanium bioconcave washer. At each follow up visit, clinical data was collected detailing clinical presentation of healing and radiographic findings. ResultsRadiographic features at post surgery evaluation indicated loss of bone contact around the screw head and bone resorption in five patients of Group A, thus causing loosening of lag screw whereas none of the patient in Group B, was found to have any such complication. ConclusionsThe findings support the hypothesis that bioconcave washer aids in holding up the farthest fragment at the interface of the fracture fragment. Application of bioconcave washer provides easy loading of lag screw.

S023015 ラグスクリューの形状と配置が骨頭部の回旋抑制性に与える影響([S02301]整形外科バイオメカニクス(1))

Treatment of proximal femoral fractures is done mainly with femoral nails. An important part of the femoral nail is the Lag-screw. The design of the Lag-screw is known to have significant influence on the rotation of the femoral head. However, the conventional Lag-screw is unable to sufficiently inhibit the rotation of the femoral head. Redesign of the Lag-screw is suggested to resolve this problem. In this study, we propose the design of the Rectangle Double Lag-screw system. In this paper, to examine the validity of our design, we performed torsion tests and an FEM analysis. Results of the comparison of the Rectangle Double Lag-screw system with the conventional Lag-screw system in torsion test and FEM analysis, indicated the validity of our design for inhibiting the rotation of the femoral head.

A soccer player with idiopathic osteonecrosis of the complete lateral talar dome: a case report

We report a 13-year-old soccer player with osteonecrosis of the talus and a large carticular fragment. The defect was revitalized with curettage and drilling and filled with autologous bone graft followed by the fixation of the carticular fragment with two conventional lag screws. Screw placement was such that they could be removed arthroscopically. Healing was uneventful. Eighteen months postoperative hardware was indeed removed arthroscopically. He returned to his former competitive level without restrictions or complaints.

Twin Hook Fixation for Proximal Femoral Fractures

To report results of twin hook fixation for proximal femoral fractures in comparison to those fixed with the conventional lag screw. Between August 2005 and July 2006, 2 men and 15 women aged 74 to 94 (mean, 85) years with proximal femoral fractures underwent open reduction and internal fixation using the twin hook system. The tip-apex distance was compared with that in 20 patients treated with the sliding hip screw between August 2004 and July 2005. In the 17 patients, the hook was inserted into the centre of the femoral head. Bone union was achieved and no intra- or post-operative cut-out or device failure was encountered. In patients using the twin hook and sliding hip screw respectively, the mean tip-apex distance was 22.3 mm and 14.6 mm (p<0.001). Using the twin hook system requires more surgical skill than using the sliding hip screw, because failure to insert the pin into the centre of the femoral head risks intra-articular perforation by the hooks.

Bending Stiffness and Pull-Out Strength of Tapered, Variable Pitch Screws, and 6.5-mm Cancellous Screws in Acute Jones Fractures

Stabilization of fifth metatarsal Jones fractures with intramedullary screws is popular, particularly in athletes, because nonoperative treatment involves prolonged casting and a distinct risk of nonunion or delayed union. Conventional lag screws of various diameters are routinely used for Jones fracture fixation. More recently, tapered, headless, variable pitch screws have become available as an option. These screws have the advantage of not having a protruding screw head, but information regarding their performance in Jones fracture fixation is limited. To determine whether differences exist in the mechanical integrity of fifth metatarsals fixed with each type of screw, this study was designed to compare Jones fracture fixation with 6.5-mm partially-threaded lag screws and headless, tapered, variable pitch compression screws with a 4-mm leading-thread diameter and 5-mm trailing-thread diameter. Simulated Jones fractures were created in 20 matched pairs of fresh-frozen fifth metatarsals. One bone from each pair was stabilized with a tapered, variable pitch screw, and the contralateral with a 6.5-mm partially-threaded cancellous lag screw. The stiffness in lateral-to-medial bending of the resulting constructs and the resistance of the screws to pulling out of the distal fragment were quantified. There was no demonstrable difference in bending stiffness between metatarsals fixed with the two types of screws (p = 0.688). The 6.5-mm screw provided significantly higher resistance to pull-out (p = 0.001). Headless, tapered, variable pitch compression screws of the size tested are not entirely comparable to 6.5-mm lag screws in this application. They are effective in resisting bending but do not offer equivalent resistance to thread pull-out.

A biomechanical study on fixation stability with twin hook or lag screw in artificial cancellous bone

The twin hook has been developed as an alternative to the conventional lag screw to be combined with a barrelled side-plate in the treatment of trochanteric hip fractures. With two oppositely directed apical hooks introduced into the subchondral bone of the femoral head, the twin hook provides different stabilising properties to the lag screw. The femoral head purchase of the twin hook and the lag screw were compared in a biomechanical study using artificial cancellous bone, and responses to axial and torsional loading was determined. A distinct yield point in load and torque was noted for the lag screw, representing failure of the laminas supporting the threads. For the twin hook, gradual increase of load and torque occurred during impaction of the bone supporting the hooks. The peak loads and torques were higher for the lag screw, but were similar for both devices after 8 mm deformation. The stiffness was higher for the lag screw, but in counter-clockwise rotation the stiffness for the lag screw was negligible. The twin hook appeared to provide fixation stability comparable to that offered by the lag screw, but with conceivable advantages in terms of a deformation response involving bone impaction and gradually increasing stability.

2D-finite element analyses and histomorphology of lag screws with and without a biconcave washer

For osteosynthesis and for bone transplant fixation in particular, a lag screw with a biconcave washer, the so called “Anchor Screw” (AS) has been introduced in maxillo-facial surgery. Using 2D-finite element analysis (FEA), the v.Mises and the circumferential stresses induced in underlying bone by this AS are analysed and compared to those under a conventional lag screw. The stress distributions below the biconcave washer of the AS were correlated with histomorphological bone reactions after AS osteosynthesis in two tumor patients, retrieved 12 weeks and 19 months after tumor surgery, respectively. Depending on the thickness of cortical bone, the v.Mises stress concentrations below the biconcave washer were lower than under the head of the conventional lag screw (CLS), but with a higher stress maximum concentrated around the rim of the washer. The circumferential stresses were only half as high around the AS, and thus the deformation of bone was reduced. As predicted by FEA, histology showed microcrack formation, but then after minimal resorption, remodelling of bone below the biconcave washer. Stable osteosynthesis could be demonstrated by bony union already after 12 weeks, and, while bone remodelling continued in the healed osteotomy, it had decreased around the screws after 19 months. It can be concluded from the biomechanical principles and the histomorphological findings that the AS appears superior to the CLS.

The self adapting washer for lag screw fixation of mandibular fractures: finite element analysis and preclinical evaluation

Besides rigid fixation, lag screws have distinct advantages compared with plates in appropriate indications in mandibular fractures. However, in current lag screw systems, the relatively small area of the screw head has to transfer the tensile force which can exceed 1000 N in the symphysis, to the thin cortical bone plate. Countersinking, which is obligatory in most systems, will weaken the cortical plate. Finite element analysis (FEA) revealed that load in this situation can exceed the normal tensile strength of metal and bone. Consequently, a new washer was constructed which both increased the supporting surface and did not require countersinking. The washer is self adapting (SAW) to the cortical plate in a defined position, forming a ball and socket joint with the screw head. Using the FEA model, a ten-fold reduction in load on bone and metal was observed with the new washer. In a miniature pig mandibular symphysis fracture model, the clinical applicability and a favourable histological reaction were demonstrated, compared with conventional lag screw designs.

Anterior bone grafting and conventional lag screw fixation to treat scaphoid nonunions

The results of 20 established nonunions of the scaphoid treated with resection of the pseudoarthrosis, anterior cortic-cancellous iliac bone grafting, and conventional lag screw fixation with the ASIF 2.7 mm cortical screw are presented. Union rate was 95% and the average time off work was 8.9 weeks. Review of the relevant literature uniformly shows that the most common reasons for failure are improper internal fixation techniques and/or the absence of bone grafting. Successful treatment of scaphoid nonunions with screw fixation and cast-free after-treatment does not depend on the implant used but rather on careful case selection and precise surgical technique.