Locking Head Screws Research Articles

Analysis of Efficacy and Failure in Proximal Humerus Fractures Treated With Locking Plates

The purpose of this study was to determine the efficacy of proximal humerus locking plates (PHLP) and to clarify predictors of loss of fixation. Retrospective review of patients with proximal humerus fractures fixed with a PHLP. Five Level 1 trauma centers. One hundred fifty-three patients (111 female, 42 male) 18 years or older with a displaced fracture or fracture-dislocation of the proximal humerus treated with a PHLP between January 1, 2001 and July 31, 2005. Demographic data, trauma mechanism, surgical approach, and perioperative complications were collected from the medical records. Fracture classification according to the AO/OTA, radiographic head-shaft angle, and screw tip-articular surface distance in true anteroposterior (AP) and axillary lateral radiographs of the shoulder were measured postoperatively. Varus malreduction was defined as a head-shaft angle of <120 degrees. Statistical analysis was done to establish correlations between loss of fixation and postoperative head-shaft angle in the true AP radiograph, patient age, fracture type, trauma mechanism, number of locking head screws, and type of plate. The mean age was 62.3 +/- 15.4 years (22-92) and the mean injury severity score (ISS) was 9.5 +/- 10.16 (4-57; n = 73). The surgical approach was deltopectoral (90.2%) or transdeltoid (9.8%). No intraoperative complications were reported. The mean postoperative head-shaft angle was 130 degrees (95 degrees to 160 degrees; SD = 13). The overall incidence of loss of fixation was 13.7%. There was a statistically significant association between varus reduction (<120 degrees) and loss of fixation (30.4% when the head-shaft angle was <120 degrees versus 11% when the head-shaft angle was > or =120 degrees; P = 0.02). This series presents the experience using PHLP in 5 Level 1 trauma centers. There were no intraoperative complications related to the locking plate systems. Despite the use of fixed-angle devices, loss of fixation occurred, primarily in the presence of varus malreduction. Our findings suggest that avoiding varus should substantially decrease the risk of postoperative failures.

Minimally Invasive Plate Osteosynthesis (MIPO): concepts and cases presented by AO East Asia

The Journal of Bone and Joint Surgery. British volumeVol. 89-B, No. 10 Book ReviewsFree AccessMinimally Invasive Plate Osteosynthesis (MIPO): concepts and cases presented by AO East Asia Edited by G. O. Tong and S. Bavonratanavech Pp. 370. New York: Thieme, 2006. ISBN: 3-13-143391-4. Euro 199.95.N. GearyN. GearySearch for more papers by this authorPublished Online:1 Oct 2007https://doi.org/10.1302/0301-620X.89B10.0891412aAboutSectionsPDF/EPUB ToolsDownload CitationsTrack CitationsPermissionsAdd to Favourites ShareShare onFacebookTwitterLinked InRedditEmail This AO instructional manual is a comendium of experience of the South-East Asian AO group. This book is well produced, eminently readable and the illustrations are clear and appropriate to the text. It should be a standard reference text in theatres and hospital libraries. The first third of the book deals with principles of minimally invasive fracture surgery and integrates this into updated AO principles. The latter two thirds cover specific techniques in relation to humeral, femoral, tibial and clavicular fractures. Icons at the top right corner of the page aid quick refernce by indicating the anatomical zone covered. It would have been helpful to differentiate more clearly the background basic science content of the first third.Purchase includes a DVD containing all the illustrations from the text which can be saved to your computer to illustrate your educational material. Illustrative animation on the DVD is referenced in the text by an icon but not to indicate when there is a video to illustrate a surgical approach. The videos are clear and well produced, but when run from the DVD menu, Quicktime runs in small form factor and does not have a full screen option. The reader would do better to run the videos directly from < Drive> :Applikation\Material\video in any MPEG player.It is never stated but slowly dawns on the viewer that this is a cadaveric workshop, not a surgical theatre. I can fault the content of the publication only in two minor areas. Having pointed out the proximity of the vessels to the middle third of the clavicle, and recommending general anaesthetic, the authors do not point out that as there is a risk of perforation of the subclavian vein, positive pressure ventilation should be recommended to avoid air embolism resulting from negative intra-thoracic pressure. Whilst the authors say that these plates seldom hav to be removed, it is necessary when an injured joint subsequently required prosthetic replacement. They point out that there are particular difficulties in removing the Locking Head Screws but specific techniques of removal are not described, (readers have to refer to AO Dialogue 4/06).This book is well produced, eminently readable and the illustrations are clear and appropriate to the text. It should be a standard reference text in theatres and hospital libraries.FiguresReferencesRelatedDetails Vol. 89-B, No. 10 Metrics Downloaded 222 times History Published online 1 October 2007 Published in print 1 October 2007 InformationCopyright © 2007, The British Editorial Society of Bone and Joint Surgery: All rights reservedPDF download

A review of locking compression plate biomechanics and their advantages as internal fixators in fracture healing

Metallic implants are often involved in the open reduction and internal fixation of fractures. Open reduction and internal fixation is commonly used in cases of trauma when the bone cannot be healed using external methods such as casting. The locking compression plate combines the conventional screw hole, which uses non-locking screws, with a locking screw hole, which uses locking head screws. This allows for more versatility in the application of the plate. There are many factors which affect the functionality of the plate (e.g., screw placement, screw choice, length of plate, distance from bone, etc.). This paper presents a review of the literature related to the biomechanics of locking compression plates and their use as internal fixators in fracture healing. Furthermore, this paper also addresses the materials used for locking compression plates and their mechanical behavior, parameters that control the overall success, as well as inherent bone quality results.

Vergleichende biomechanische Untersuchung zur internen Stabilisierung der transforaminalen Sakrumfraktur

Reliable osteosynthesis for fractures in the different regions of the human pelvis are described in the literature while there is no common and satisfying treatment for unstable sacral fractures. Because of the posterior pelvic rings special anatomic conditions a local plate osteosynthesis seems to be advantageous. In many fields of modern fracture treatment locking implants show superior results. The prototype of a local locking plate osteosynthesis was compared to a common local plate and two sacroiliac screws. The implants were tested using six plastic models of the pelvis and three embalmed human specimens. A Tile C1 fracture was created by disruption of the pubic symphysis and a transforaminal osteotomy. The specimens were exposed to axial loading in an upright single-leg stance with a maximum of 800 N for the plastic models and 200 N for the human specimens. An ultrasonic-based measuring system recorded translations (X, Y, Z) and rotations (alpha, beta, gamma). Parameters such as pattern of motion, translation/rotation, load to failure and remaining dislocation were evaluated. Concerning most of the evaluated parameters the local plate osteosynthesis was inferior compared with two sacroiliac screws. There were no significant differences between the locking implant and the local plate osteosynthesis. Compared with the two sacroiliac screws the locking implant shows biomechanically equal results but allows greater anterior rotation and remaining dislocation. Because of the lower bone quality, the results from the anatomic specimen tested were not utilisable. The locking implant is biomechanically an alternative compared with two sacroiliac screws. Problems occurred due to the preset direction of the locking head screws.

Biomechanical testing of the locking compression plate: When does the distance between bone and implant significantly reduce construct stability?

To investigate in vitro the mechanical stability of a locking compression plate (LCP) construct in a simulated diaphyseal fracture of the humerus at increasing distances between the plate and bone. A series of biomechanical in vitro experiments were performed using composite humerus sawbone as the bone model. Osteotomy created in the mid-diaphyseal region. A 10mm osteotomy gap was bridged with a seven-hole 4.5 stainless steel plate with one of four methods: a control group consisted of a dynamic compression plate applied flush to the bone and three study groups which comprised of a LCP applied flush to the bone, at 2mm and at 5mm from the bone. Standard AO technique used with locking head screws used for LCP fixation. Static and dynamic loading tests performed in a custom made jig in which the bone model was fixed both proximally and distally. Samples were subjected to cyclical compression, compression load to failure, cyclical torque and torque to failure. Plastic deformation and failure was assessed using three-dimensional measurements. Scanning electron microscopy of the plate and screw surface allowed detailed inspection of micro-fracture in areas of fatigue. Comparable results were achieved in both the DCP and LCP constructs in which the plate was applied at or less than 2mm from the bone. When applied 5mm from the bone the LCP demonstrated significantly increased plastic deformation during cyclical compression and required lower loads to induce construct failure. At a distance 5 mm we observe an inferior performance in the mechanical properties of the LCP construct with decrease in axial stiffness and torsional rigidity. If it is desirable for an LCP to be used the distance between plate and bone should be <or=2 mm.

Influence of Screw Positioning in a New Anterior Spine Fixator on Implant Loosening in Osteoporotic Vertebrae

A biomechanical study was designed to assess implant cut-out of three different angular stable anterior spinal implants. Subsidence of the implant relative to the vertebral body was measured during an in vitro cyclic loading test. The objective of the study was to evaluate two prototypes (Synthes) of a new anterior spine fixator with different screw angulations in comparison to the established MACSTL(R) Twin Screw Concept (Aesculap). The influence of factors like load-bearing cross-sectional area, screw angulation and bone mineral density upon implant stability should be investigated. Epidemiologic data predict a growing demand for appropriate anterior spinal fixation devices especially in patients with inferior structural and mechanical bone properties. Although different concepts for anterior spinal instrumentation systems have been tried out, implant stability is still a problem. Three angular stable, anterior spinal implants were tested using 24 human lumbar osteoporotic vertebrae (L1-L5; age 84 (73-92)): MASC TL system (Aesculap); prototype 1 (MP1) with 18 degrees and prototype 2 (MP2) with 40 degrees screw angulation (both Synthes). All implants consisted of two screws with different outer screw diameters: 7-mm polyaxial screw with 6.5-mm stabilization screw (MASC TL), two 5-mm locking-head screws each (MP1 and MP2). Bone mineral density (BMD) and vertebral body width of the three specimen groups were evenly distributed. The specimens were loaded in craniocaudal direction (1Hz) for 1000 cycles each at three consecutive load steps; 10-100 N, 10-200 N and 10-400 N. During cyclic loading subsidence of the implant relative to the vertebral body was measured in the unloaded condition. Cycle number at failure (defined as a subsidence of 2 mm) was determined for each specimen. A survival analysis (Cox Regression) was performed to detect differences between implant groups at a probability level of 95%. High correlations were found between BMD and number of cycles until failure (MP1; r = 0.905, P = 0.013; MP2: r = 0.640, P = 0.121; MACS TL: r = 0.904, P = 0.013) and between load bearing cross sectional area and number of cycles until failure (MP1: r = 0.849, P = 0.032;MP2: r = 0.692, P = 0.085; MACS TL: r = 0.902, P = 0.014). Both Prototypes survived significantly longer than the MACS TL implant (MP1: P = 0.012, MP2: P = 0.014). The survival behaviour of MP1 and MP2 was not significantly different (P = 0.354). Implant stability within each implant group was influenced by BMD and load bearing cross-sectional area. The angulation of the two screws did not have a significant influence on cut-out. As conclusion from this study, promising approaches for further implant development are: 1) increase of load-bearing cross-sectional area (e.g., larger outer diameter of the anchorage device), 2) screw positioning in areas of higher BMD (e.g., opposite cortex, proximity to pedicles or the endplates).

Locked internal fixator: sensitivity of screw/plate stability to the correct insertion angle of the screw.

Internal fixators with angular stability have been developed to provide high stability without compression of the plate on to the bone. Angular and axial stability of a plate-screw construct can be achieved using a conically threaded screw head undersurface and a corresponding conically threaded plate hole. Furthermore, the insertion angle of the screw must correspond precisely to the axis of the screw hole. This is not always achieved in clinical practice and may result in screw loosening. The objective of this study was to examine the relationship between the stability of the locked screw-plate on the insertion angle of the screw. Locking screws were inserted in an isolated (Point Contact Fixator, PC-Fix) or combined (Locking Compression Plate, LCP 4.5) locking hole with the use of an aiming device. The optimal insertion angle for these plates is perpendicular to the plate surface. The screws were inserted with an axis deviation of 0 degrees (optimal condition), 5 degrees , and 10 degrees respective to the optimal angle (variance +/- 1 degrees ). The samples were tested under shear or axial (push out) loading conditions until failure occurred. An Instron materials testing machine was used. Locking screws inserted in the isolated locking hole (PC-Fix) showed a significant decrease of failure load if inserted at 5 degrees and 10 degrees angle. Using an optimal insertion angle (0 degrees ), failure load was 1480 +/- 390 N, with 5 degrees axis deviation 780 +/- 160 N, P = 0.0001, and with 10 degrees axis deviation 550 +/- 110 N, P = 0.0001. Screws inserted in the combined locking hole (LCP) also showed a significant decrease of push-out force of 77% (4960 +/- 1000 N versus 1120 +/- 400 N) with 10 degrees axis deviation. Compared to optimal insertion angle (0 degrees ), bending load to failure did decrease up to 69% (1240 +/- 210 N vs. 390 +/- 100 N) with 10 degrees axis deviation. A locking head screw exhibits high stability with a moderate axis deviation in the angle of insertion of up to 5 degrees . However, there is a significant decrease in stability with increasing axis deviation (>5 degrees ). An aiming device is recommended to provide optimal fixation with angular stability.

First clinical results of the Locking Compression Plate (LCP)

The Locking Compression Plate (LCP) is a new screw-plate system that offers the possibility of inserting conventional and locking head screws into the specially designed combination holes. It represents a further development of the PC-Fix and the LISS and was released for clinical application in March 2000. In a prospective multicentre study, the new system was used to treat 144 patients (f: 67, m: 77; average age: 51.4 years) with 169 fractures: of these, 57 were tibial fractures, 45 humerus, 19 radius and 18 femoral. After one year, clinical and radiological follow-up assessment was carried out on 127 patients with 151 fractures (88%). In 130 fractures (86%), healing took place within the expected period and without complication or secondary dislocation ("uneventful healing"). In 19 patients, a total of 27 unexpected complications occurred ("adverse events"), in which 18 revision operations were necessary in 13 patients: five for implant loosening/pull-out, four for plate failure, one for non-union, five for secondary fractures immediately adjacent to the implant after a subsequent injury and two for infection. Analysis by a committee of experts indicated that mechanical complications arose entirely from technical errors of application (incorrect fixation technique, incorrect choice of plate). No purely implant-related complications were observed. The new system can be regarded as technically mature. It offers numerous fixation possibilities and has proven its worth in complex fractures situations and in revision operations after the failure of other implants. A good knowledge of biomechanics is essential as well as precise preoperative planning.

Angular Stability Plate System (LCP) - the new AO standard for plate osteosynthesis

Locking Compression Plate (LCP) represents the latest development of AO plates, combining the features of conventional plates and internal fixators. This is achieved by a so-called combi-hole merging the Dynamic Compression Unit (DCU) of the DCP and the threaded hole of locked plates. Therefore all kinds of conventional screws as well as threaded locking head screws (LHS) can be inserted through the plate depending on the specific local requirements. However, LCP represents not a new plate per se, but rather a plate/screw system to enrich the well known АО-plate designs with the option of interlocking. As the mechanical characteristics have not changed by adding a combi-hole the complete set of small (3,5 mm) and broad (4,5/5,0 mm) АО-plates is available. Additionally LCP-systems adapted to certain anatomic regions, like the proximal humerus and distal radius as well as Tomofix2 plates for osteotomies have been developed. We report about our first experience in clinical use of LCP. Prom April 2000 till December 2002,310 LCP systems have been implanted in 274 patients. 303 plates (97,7%) were implanted for fixation of 285 fractures with different localization in 267 patients, including 17 pediatric fractures (5,9%),9 periprosthetic fractures (3,2%),5 delayed-unions (1,8%) and 4 pathologic fractures (1,4%). Seven plates (2,3%) were implanted to fix osteotomies. Of all plates 111 (35,8%)) implants were fixed with locking head screws,194 (62,6%) with both types of screws and only in 5 plates (l,6%o) conventional screws were used. 73 (23,5%o) of all plates were inserted using a minimal-invasive approach and 237 (76,5%) via an open procedure. Postoperative complications occurred in 14/267 patients (5,2%) exclusively treated for fractures, representing a complication rate of 5,2%o in 15/285 fractures. Loosening of implants were seen in 1,4%), deep wound infection in 1,05%), osteomyelitis, refracture and postoperative hematoma in 0,7%o, respectively. Secondary malalignment and problems with implant removal occurred in 1 patient (0,35%), respectively. No delayed or non-unions were observed. In LCP all options of plate osteosynthesis are included, so fixation can be adapted more accurately to the local situation and operative procedure is facilitated.

Comparison of fixation strengths of locking head and conventional screws, in fracture and reconstruction models

Claimed clinical advantages of the locking-head mandibular reconstruction plating system include the ability to achieve stability with fewer numbers of screws per bony segment as compared with conventional screws. The purpose of this study was to test the hypothesis that increased resistance to displacement will be obtained when using locking-head as compared with the same number of conventional screws per segment in both fracture and reconstruction models. Eight groups were tested based on the screw number (two or four), screw type (locking-head or conventional), and fracture (bony apposition) or reconstruction model (1-cm defect). Two-dimensional beam mechanics using adult bovine ribs and the Instron machine were used to develop a load-displacement curve up to 150 N for each specimen. An osteotomy was then created and the segments were reduced, with preload (fracture model) or with a 1-cm defect (reconstruction model), and plated using the Synthes locking-head plate with either two or four bicortical locking-head (4.0-mm) or conventional (2.7-mm) screws per segment. The fixed ribs were loaded to 150 N, and the displacement was recorded. Locking-head screws provided superior resistance when using two screws per segment in the reconstruction model as compared with conventional screws. Minimal difference was seen between other screw types within a model. The fracture model offered significantly greater (3.1 to 3.7X) resistance to displacement than did the reconstruction model. Locking-head screws provided significantly increased resistance to displacement when only two screws per segment were used in the reconstruction model. When four screws per segment were used, there was no significant difference between locking-head and conventional screw types in either model. The effect of bony buttressing is significant and may explain why miniplates often fail in the atrophic mandible but are successful in the fully dentate patient.