End Screws Research Articles

Comparison of treatment of volar Barton's fracture with T plate using distal end screws and without distal end screws.

To compare the functional and radiological outcomes of treatment of volar Barton's fractures using T plate with and without distal end screws. This randomized control trial was conducted at the department of Orthopedics, Mayo Hospital, Lahore, Pakistan from December 2021 to May 2022. Total 60 patients (30 in each group) were randomly allocated to either group A (T-Plate with distal end screws) or B (T-Plate without distal end screws). Patients were followed up on day-0, day-14, day-28 and day-90. Assessments of patients were done by Green O'Brien Score for pain, Modified Warden Score for callus formation on radiographs at 12-weeks of follow-up and Stewart Score for displacement of fracture. At 90th day, significant difference was seen in Green O'Brien Score (Excellent score: Group-A: 80% vs. Group-B: 90%, p=0.278) while Stewart scores remained comparable (Excellent Score: Group-A: 93.33% vs. Group-B: 96.67%, p=0.221) between treatment groups. Fracture healing assessed with Modified Warden score for score 4 did not show significant difference between both groups at 90th day. i.e. (Group-A: 96.67% vs. Group-B: 96.67%). However, callus formation assessed with Modified Warden score for score 3 showed significant differences between groups at 90th day. i.e. (Group-A: 53.33% vs. Group-B: 86.67%, p=0.001). Both treatment approaches appear to yield comparable outcomes in terms of clinical assessment, Stewart scores, and fracture healing, with a potential advantage for T-plate without distal end screw in callus formation at the 90th day.Trial registration: IRCT20221231056999N1.

Lumbar Dynamic Stabilization With 2-Stage Surgery: Early Results.

Screw loosening, which is a major problem in dynamic systems, can be easily overcome with 2-stage surgery. In this article, the clinical and radiological results of patients undergoing dynamic stabilization with a Dynesys device in 2 stages are discussed. A total of 10 male and 13 female adult patients were included in this single-center retrospective study conducted between 2018 and 2021. The mean age of the patients was 65.6 years. All of the patients had pain complaints that affected their daily lives. Bone density T scores were determined with the dual-energy x-ray absorptiometry method before patients were admitted for surgery. In the first surgery, Dynesys system pedicle screws were inserted. After 6 months of osteointegration, Dynesys system spacers and elastic bandages were placed. Preoperative, early postoperative, and late postoperative visual analog pain scale (VAS) scores and Oswestry Disability Index (ODI) scores were determined and statistically compared. Patients were followed for an average of 30 months. Complications and recurrence were not observed. Neurological deficits were not observed after patients recovered from anesthesia. Significant improvement was observed in the ODI and VAS parameters in the preoperative (ODI: 66.2%, VAS: 7.8), early postoperative (ODI: 20.3%, VAS: 2.4), and late postoperative (ODI: 6.8% and VAS: 1.1) periods. Symptomatic improvement was seen in all patients. No screw breakage or loosening was detected by radiological evaluation in any of the patients during the 2-year follow-up period. In our experience, the insufficiency of the proximal and distal end screws is eliminated when 2 stages of dynamic system stabilizations are completed after osteointegration of the screws.

Bone resorption triggered by high radial stress: The mechanism of screw loosening in plate fixation of long bone fractures.

Screw loosening is a common complication in plate fixation. However, the underlying mechanism is unclear. This study investigated screw loosening mechanisms by finite element analysis (FEA) simulation and clinical X-ray feature analysis. Two FEA models incorporated bone heterogeneity and orthotropy, representing fracture fixation using dynamic compression plate (DCP) and locking compression plate (LCP), were developed. These models were used to examine the volume of bone exceeding a certain stress value around each screw under physiologically-relevant loading conditions. These damaged bone was then separated and compared by the axial stress and radial stress of each screw. In addition, features of patients' X-ray images showing screw loosening were analyzed to validate the loosening features simulated by the models. The FEA study showed that more damaged bone was found at the central two screws which gradually decreased toward the two end screws in all groups. More bone was damaged by the radial stress of each screw than by the axial stress. The radiological analysis of screw loosening showed that bone loss occurred at the screw closest to the fracture line first then subsequent bone loss at the screws further away from the fracture line occurred. This study found that the two screws nearest to the fracture line are more vulnerable to loosening. The radial stress of the screw plays a larger role in screw loosening than the axial stress. Bone resorption triggered by the high radial stress of screws is indicated as the mechanism of screw loosening in the diaphyseal plate fixation. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1498-1507, 2019.

Reducing Fracture Risk Adjacent to a Plate With an Angulated Locked End Screw.

Locking screws often are used in the treatment of osteoporotic fractures. Studies show that locking screws can increase bone stresses at the plate end, which increases the possibility of peri-implant fracture. This study evaluates whether the technique used to insert the end screw is related to the fracture tolerance adjacent to the plate. Twelve groups of plate constructs were evaluated using a fibular diaphyseal surrogate with mechanical properties similar to osteoporotic bone. All inboard screws were nonlocked with only the end screw fixation differing among groups. The end screws were inserted either perpendicularly to the plate or at an angle of 30 degrees for 6- and 12-hole plates. For both orientations, the end screws were inserted nonlocked, locked, or by a locked overdrilling technique, resulting in 6 groups per plate length. The perpendicular nonlocked screws represented a control group. The constructs were tested to failure in 4-point bending to determine peak load, failure energy, and stiffness. All constructs failed by peri-implant fracture along a plane through the 2 cortical holes of the end screw. Compared with the control group, an angulated locked screw at the plate end significantly increased the peak bending moment and energy required to produce a fracture for both plate lengths (6-hole, P = 0.008, P < 0.001; 12-hole, P = 0.006, P < 0.001). The use of an angulated locked end screw may enhance the resistance of osteoporotic bone to peri-implant fractures caused by bending forces.

Biomechanical Evaluation of Locking Plate Radial Shaft Fixation: Unicortical Locking Fixation Versus Mixed Bicortical and Unicortical Fixation in a Sawbone Model

Compression plating is a commonly accepted technique for treating diaphyseal forearm fractures. The purpose of this study was to evaluate the stabilizing effects of two hybrid fixations that replace the end screws of a locked unicortical fixation with bicortical (locked or unlocked) screws and to compare these hybrid fixations to an unlocked bicortical fixation. Sixteen composite radius sawbones were equally divided into 4 groups. We performed a midshaft osteotomy and plate fixation on the volar surface with 1 of 4 different constructs: 3 unlocked bicortical screws on each side (unlocked bicortical), 3 locked unicortical screws on each side (locked unicortical), or with 2 unicortical locked screws near the fracture and 1 bicortical unlocked (unlocked hybrid) or locked (locked hybrid) screw distant from the fracture on each end (LCP system, Synthes USA, Paoli, PA). Specimens were tested in nondestructive 4-point bending and torsion on a servo-hydraulic material testing system. The construct stiffness was obtained from the linear portion of the load-displacement curves after 3 cycles of preconditioning. The results from all groups were compared using analysis of variance and post hoc Bonferroni tests. Under torsional loads, replacing the end screws of a locked unicortical configuration with bicortical screws significantly improved the construct stiffness: 57.6% increase for the locked screws and 51.6% increase for the unlocked. In anteroposterior (AP) bending, the highest improvement over the locked unicortical configuration came from the locked hybrid constructs (42.9% increase). When compared with the unlocked bicortical configuration, both hybrid constructs provide equivalent stability in torsion but superior stability in AP bending. Replacing a single set of unicortical locked screws with locked or unlocked bicortical screws distant from the fracture site improves torsional stability of the construct by more than 50%, giving stability equal to standard unlocked plating. The hybrid fixation, however, with locked bicortical end screws has the best stability in AP bending.

Actuation and Control of a Micro Electrohydraulic Digital Servo Valve

Structure of the micro digital servo valve is given. A micro stepper motor is used as electrical-to-mechanical interface of the valve. A special mechanical device is designed to convert the rotation of the stepper motor into the linear motion of the spool. This moving conversion device functions through an eccentric ball head rigidly connected to the axis of the stepper motor and plugged into a slot at the central spool land. While the stepper motor rotates, the eccentric ball head will actuate the spool to make a linear motion. Unlike conventional servo or proportional valves, in which the spool is forced to central position by a spring force, when the current supply is switched off, the digital valve has a program to control the spool to its central position each time the electrical power supply is switched on or off. The two end screws are used to adjust the position of the sleeve to sustain a mechanical central position coincided with electrical central position given by the stepper motor after initialization. The adjustment has to be carried once before the first time the servo valve is put into service. This paper presents theoretical analysis and experimental study of dynamic characteristics of the proposed micro digital servo valve. Experimental results demonstrated that the valve takes the advantage of high accuracy and fast response.

Dimensional accuracy analysis of implant framework castings from 2 casting systems

<h3>Purpose</h3> To compare the dimensional accuracy of implant framework castings from an argon vacuum casting machine with those from a centrifugal casting machine. <h3>Materials and Methods</h3> Three 4 × 10-mm external hex-type implants (3i/Implant Innovations) were embedded in an acrylic resin block 7 mm apart, with a 2 mm offset of the middle implant. Eight reference points were marked on the implant collars. Twenty implant bar frameworks were waxed with UCLA abutments, invested with a ringless system, and subjected to the same thermal cycle. Ten wax patterns were cast in gold alloy using an oxygen-propane torch and centrifugal casting system; 10 were cast using an argon vacuum casting machine (KDF; Denken). The White 1-screw technique was applied after sequentially tightening the mesial and distal abutment screws to 10 Ncm. Fit of the implant framework castings was evaluated by measuring the marginal opening between the casting and implant at the reference points. These measurements were averaged and statistically compared for differences. <h3>Results</h3> The mean marginal openings at the most distant measuring locations from the tightened retaining screw at location 1 was between 44 and 48 μm for the centrifugal system compared to between 28 and 32 mm for KDF (<i>P</i><.01). For screws tightened at location 3, the mean marginal openings at the most distant measuring locations were between 40 and 51 mm for the centrifugal system compared to between 27 and 29 μm for KDF (<i>P</i><.01). <h3>Discussion</h3> In comparison with the centrifugal casting and oxygen-propane system, the argon vacuum system was more accurate and user friendly and less technique-sensitive. <h3>Conclusion</h3> The argon vacuum casting machine tested produced more accurate, better-fitting implant-supported prosthesis frameworks than a conventional centrifugal casting system. The "1-screw" method of evaluating casting fit was most effective when either of the prostheses' end screws were tightened.—<i>Reprinted with permission of Quintessence Publishing.</i>

Internal Fixation of Diaphyseal Fractures of the Forearm by Interlocking Intramedullary Nail

This study was designed to evaluate the efficacy of the treatment of diaphyseal fractures of the forearm using the ForeSight forearm interlocking intramedullary nail. Retrospective study. University-affiliated teaching hospital. Eighteen patients with 32 displaced diaphyseal forearm fractures were identified. All fractures were treated with the ForeSight forearm interlocking intramedullary nail. Eighteen fractures were stabilized with static interlocking technique. The assessment of patients was based on the time to union, the functional recovery, and the incidence of complications. Physical capability was evaluated by using the rating system of Grace and Eversmann. Patient-rated outcome was assessed by completion of the Disability of Arm Shoulder Hand questionnaire (DASH). All fractures healed with the index procedure. The average time to union for fractures utilizing a closed technique was 10 weeks; for fractures using an open reduction technique, 15 weeks. The mean pronation was 62 (range, 0-96) degrees, and the mean supination was 80 (range, 0-105) degrees. Compared with the normal arm, the mean loss of rotation of the forearm was 32 (range, 5-162) degrees. Using the rating system of Grace and Eversmann, 13 patients had an excellent or good result, 3 had an acceptable result, and 2 had an unacceptable result. Using the patient-rated functional questionnaire, the mean DASH of 19 (range, 4-72) points at the time of the most recent follow-up indicated a mild-to-moderate impairment. There were 7 postoperative complications. The incidence of complications was 22% (7/32). One cross-union between forearm bones occurred in a patient with a closed head injury and high-energy trauma. Two nondriving end screws of the ulna nail backed out causing wrist pain and had to be removed. There were 4 superficial infections occurring all in the fractures that necessitated an open reduction technique. The overall rate of infection was 12.5% (4/32). Three patients who presented with an open fracture needed a skin graft to cover the open wound. Forearm interlocking intramedullary nailing is an acceptable method to stabilize displaced diaphyseal forearm fractures in adult.

Force transfer between the plate and the bone: relative importance of the bending stiffness of the screws and the friction between plate and bone

Stability in plate fixation of fractures relates to the motionless fastening between plate and bone. When the plate is affixed to the bone, high shear force may appear between plate and bone, particularly near the end screws, which can lead to motion under weight-bearing. Two mechanisms might be involved in the prevention of motion: the bending stiffness of the screws or the friction between the screw and the plate. Experiments performed in vivo and in vitro show that with conventional plates, motion is prevented by friction and depends upon the axial force of the screw, pressing the plate onto the bone. The torque applied to the screws is crucial. Motion appears under smooth plates under relatively low physiological loads. With newly developed internal fixators, the motion is prevented by the structural stiffness of the plate-screw system.

Screw Omission and the Stability of Posterior Pedicle Screw Constructs for Short-Segment Stabilization

To determine the net contribution of a spinal construct to stability, and whether extending the construct to another level in situations in which a defective pedicle cannot have a screw inserted, we performed biomechanical tests in which we evaluated three-, four-, and five-level synthetic spinal constructs in which the location and number of pedicle screws were varied above and below a vertebrectomy defect. We subjected all constructs to axial, compression, lateral bending, flexion, extension, and torsional forces with the use of an Instron biaxial machine. Left-right symmetrical constructs were more stable than asymmetrical ones. Three-level constructs were statistically stiffer than the longer ones in compression, left bending, and flexion. Torsional stability, however, was greater in the longer constructs. Five-level constructs with both end screws in place had greater torsional stiffness than when they were missing a screw. In vertebrectomy defects, if four screws cannot be placed across it, then the engagement of two screws is indicated. The stability provided by a single screw at a spinal level is minimal. Additional screws augment the purchase of the construct in the bone; however, they do not afford further protection to the defect.

Flexion failure of posterior cervical lateral mass screws. Influence of insertion technique and position.

The strength of posterior cervical lateral mass fixation was evaluated in a cadaver model for two techniques of screw insertion. To compare the flexion failure strengths of posterior cervical plate fixation for two techniques of screw placement at the superior and inferior screw hole positions, and to evaluate the effect of bone mineral density on fixation strength. Biomechanical analyses of various screw insertion techniques for posterior cervical lateral mass fixation have never evaluated the effect of screw position along the plate. Individual C3-C6 segments of 24 human cadaveric cervical spines were used. The spinous process and lamina were removed to simulate a postlaminectomy situation. Vertebral body bone mineral density for each specimen was determined by dual-energy radiograph absorption scanning. In each lateral mass, a bicortical 3.5-mm screw was placed using either the Magerl or Roy-Camille insertion technique through an end hole of a titanium bone plate. For "superior" screws, the plate was directed caudally; for "inferior" screws, the plate was directed cranially. Screw violation of the surrounding facet joint was noted. An increasing flexion moment was applied by loading the plate 4 cm from the screw head at a rate of 10 cm/min using a servohydraulic testing machine until screw failure. For the superior screw hole position, the Magerl screw sustained a significantly higher average moment to failure (190.2 Ncm) than the Roy-Camille screw (138.7 Ncm; P < 0.05). For the inferior screw hole position, there was no significant difference in flexion failure strength between the two techniques (Magerl screws, 287.7 Ncm; Roy-Camille screws, 308.2 Ncm). For each insertion technique, inferior screws were nearly twice as strong as superior screws (P < 0.01). Violation of the inferior articular process occurred with 53% of Roy-Camille screws and with none of the Magerl screws. Lateral mass fracture on screw insertion occurred with 6% of the Roy-Camille screws and with 7% of the Magerl screws. Significant correlation between screw path length and load to failure was found only at the superior screw hole position. Correlation with vertebral body bone mineral density was significant at both positions. The Magerl technique has advantages over the Roy-Camille technique for placing the end screws when performing posterior cervical lateral mass plate fixation, providing greater strength superiorly and not violating unfused facet joints inferiorly. Evaluation of bone mineral density by dual-energy radiographic absorption scanning is predictive of failure strength for both test modes.

A Comparison of Unicortical and Bicortical End Screw Attachment of Fracture Fixation Plates

Plate fixation is considered by many clinicians to be the treatment of choice for displaced diaphyseal fractures of the forearm. One possible complication associated with plate fixation is refracture with the plate in situ or after plate removal. With the plate in situ, refracture typically occurs through the last screw hole near the end of the plate. Some clinicians have advocated the use of unicortical end screws to minimize the risk of such refractures. In this study, we performed a series of in vitro tests to compare the breaking strength of plated bone analogues that used either unicortical or bicortical end screws. The plated constructs that used unicortical end screws were significantly weaker in the two most important physiologic loading modes. Based on these results, we conclude that the use of unicortical end screws may result in a greater risk of refracture with the plate in situ.