Dorothea Mehler

Number and Locations of Screw Fixation for Volar Fixed-Angle Plating of Distal Radius Fractures: Biomechanical Study

PURPOSE To compare the biomechanical properties of different numbers and locations of screws in a multidirectional volar fixed-angle plate in a distal radius osteotomy cadaver model. METHODS We created an extra-articular fracture in 16 pairs of fresh-frozen human cadaver radiuses. The 32 specimens were randomized into 4 groups. All fractures were fixated with a multidirectional volar fixed-angle plate. We tested 4 different screw-placement options in the distal fragment. The distal fragment was fixed with 4 locking screws in the distal row of the plate in group a, and with 4 locking screws alternately in the distal and proximal rows in group b. In group c, 3 locking screws were used in the proximal row; in group d, 7 locking screws were used, filling all screw holes in the distal and proximal rows of the plate. The proximal fragment was fixed with 3 screws. The specimens were loaded with 80 N under dorsal and volar bending and with 250 N axial loading. Finally, load to failure tests were performed. RESULTS Group d had the highest mean stiffness, 429 N/mm under axial compression, and was statistically significantly stiffer than the other groups. Group b had a mean stiffness of 208 N/mm, followed by group a, with 177 N/mm. Group c showed only a mean stiffness of 83 N/mm under axial compression. There were no statistically significant differences under dorsal and volar bending. CONCLUSIONS In this model of distal radial fractures, there was a difference regarding the stiffness and the placement of screws in the distal rows of a volar fixed-angle plate. Inserting screws in all available holes in the distal fragment offered the highest stability. Using only the proximal row with 3 screws created an unstable situation. Based on these findings, we recommend placing at least 4 screws in the distal fragment and assigning at least 2 screws to the distal row of the multidirectional screw-holes.

Intramedullary Stabilization of Extraarticular Proximal Tibial Fractures : A Biomechanical Comparison of Intramedullary and Extramedullary Implants Including a New Proximal Tibia Nail (PTN)

Objectives: To determine in the laboratory whether there are or are not differences between individual geometrical designs of intramedullary and extramedullary devices used for the fixation of extraarticular proximal tibial fractures. Methods: Five devices were tested: a newly developed Proximal Tibia Nail (PTN), conventional double-plate osteosynthesis (DPO), the Less Invasive Stabilization System (LISS), an augmented Unreamed Tibial Nail with a T-stabilization-plate (UTN + TSP), and an external fixator (ExFix). A 10-mm defect osteotomy was performed on paired human tibiae, and the proximal and distal ends were potted in polymethylmethacrylate cement (PMMA). Each pair of bones was randomly stabilized with the new PTN in 1 tibia (Groups PTN1 through PTN4) and in 1 of the 4 comparative implants in the corresponding contralateral bone. A biomechanical test of the bone implant construct was then performed with a vertical axial force of 350, 600, and 900 N, a bending moment of 6 Nm and a bidirectional rotational strain of 8 Nm. Displacement of bone fragments was measured and depicted as a force-displacement diagram. Results: For axial loading, significant differences were seen between the PTN 2 group compared to the LISS group (P = 0.016) and the PTN 4 group compared to the ExFix group (P = 0.016). No statistically significant differences were seen for the PTN 1 group compared to the DPO group (P = 0.125) and the PTN 3 group compared to the UTN + TSP group (P = 0.453). The bending stiffness of the PTN 1-4 groups was not significantly different from any of the 4 alternative implants. There was comparable torsional stiffness in all implant groups except for the UTN + TSP group, which was less stable and significantly different from the PTN 3 group (P = 0.016). Conclusions: Given the parameters of this investigation, the new PTN would theoretically provide the same mechanical stability as the DPO in axial loading. Higher stability in axial loading may be present when compared to the LISS or the ExFix. Further clinical investigation of this implant will determine its usefulness among proximal tibial fixation devices.

Die proximale extraartikuläre Tibiafraktur

ZusammenfassungDie Stabilisierung proximaler extraartikulärer Tibiafrakturen stellt unter Verwendung der gebräuchlichen Osteosyntheseverfahren unverändert ein Problem dar. Die Wahl des Operationsverfahrens hängt unter anderem von der Situation der oftmals erheblich kompromittierten frakturumgebenden Weichteile ab. An der proximalen Tibia besteht zusätzlich das Problem von Fehlstellungen der Fraktur. Neben der Gefahr einer intraoperativen Frakturdislokation durch Muskelzug und den operativen Zugang kommt es gehäuft zu sekundären Fehlstellungen durch relative Implantatinstabilität.Es wurden verschiedene Verfahren zur Versorgung dieser Frakturen entwickelt; sie zeichnen sich durch differierende biomechanische Eigenschaften aus, erfordern unterschiedliche Operationstechniken und werfen ihrerseits spezifische Probleme auf.Insbesondere die neueren winkelstabilen Implantate (z. B. LISS = “less invasive stabilization system”) bieten entscheidende Vorteile gegenüber den instabileren konventionellen Plattenosteosynthesen und externen Fixationssystemen. Die Verbesserung der bisher üblichen Geometrie intramedullärer Kraftträger sowie die Einführung von Winkelstabilität im Bereich der proximalen Verriegelungsschrauben (PTN = “proximaler Tibianagel”) lassen dieses Verfahren theoretisch als biomechanisch optimale Lösung erscheinen. Vor dem Hintergrund eigener klinischer Erfahrungen und biomechanischer Untersuchungen werden Lösungsmöglichkeiten für diese spezielle Problematik aufgezeigt und bewertet.AbstractOperative stabilization of proximal tibial fractures by use of conventional osteosynthesis is still problematic. The choice of the osteosynthetic treatment is strongly influenced by the situation of the surrounding soft tissue. Additional problems in this particular location may occur with malalignment in the fracture site after operation. Primary intraoperative malalignment may occur due to dislocating muscle forces or to the operative approach itself. Secondary dislocation is mainly due to the unstable fixation of the proximal fragment by the implant.Today many different implants with specific biomechanical properties are available. Each system requires a particular operative technique and can lead to individual implant-related problems.The new angle stable implant systems (e. g. LISS = “less invasive stabilization system”), offer significant advantages over conventional plate osteosyntheses and external fixation systems.Improvement of the geometry of standard intramedullary osteosyntheses and introduction of angle stability in the proximal interlocking screws (PTN = “proximal tibial nail”) seemingly make this system the optimal solution, concerning biomechanics.On the background of our own clinical experiences and biomechanical investigations, the article discusses solutions for this particular problem.

Intramedullary nailing vs. palmar locked plating for unstable dorsally comminuted distal radius fractures: A biomechanical study

BACKGROUND The purpose of this study was to compare the stability of a 2.4mm palmar locking compression plate and a new intramedullary nail-plate-hybrid Targon DR for dorsally comminuted distal radius fractures. METHODS An extraarticular 10mm dorsally open wedge osteotomy was created in 8 pairs of fresh frozen human radii to simulate an AO-A3-fracture. The fractures were stabilized using one of the fixation methods. The specimens were loaded axially with 200 N and dorsal-excentrically with 80 N. 2000cycles of dynamic loading and axial loading-to-failure were performed. FINDINGS Axial loading revealed that intramedullary osteosynthesis (Targon DR: 369 N/mm) was significantly (p=0.017) stiffer than plate osteosynthesis (Locking compression plate: 131 N/mm). With 214 N/mm the intramedullary nail also showed higher stability during dorsal excentric loading than the Locking compression plate with 51 N/mm (p=0.012). After 2000 cycles of axial loading with 80 N the Targon DR-group was significantly stiffer than the Locking compression plate-group under both loading patterns. Neither group showed significant changes in stiffness after 2000 cycles. Under dorsal excentric loading the Targon DR-group was still significantly stiffer with 212 N/mm than the Locking compression plate-group with 45 N/mm (p=0.012). The load to failure tests demonstrated higher stability of intramedullary nailing (625 N) when compared to plate osteosynthesis (403 N) (p<0.025). INTERPRETATION The study shows that intramedullary fixation of a distal AO-A3 radial fracture is biomechanically more stable than volar fixed-angle plating under axial and dorsal-excentric loading in an experimental setup.

Locking Plates for Corrective Osteotomy of Malunited Dorsally Tilted Distal Radial Fractures: A Biomechanical Study

The purpose of the study was to compare the biomechanical properties of five different palmar fixation plate designs in a distal radius osteotomy cadaver model. A 1 cm metaphyseal osteotomy gap was made to simulate a corrective osteotomy and the osteotomy plated. Axial load was applied to the distal end of each construct by a material testing machine under control of a motion analysis video system. The specimens were arranged into five implant groups of eight specimens each. No test group developed deformity and movement of the fracture gap greater than 2 mm with a load of 100 N. Increasing the load to 250 N revealed statistically significant differences in stiffness and failure load between the different plates. Axial failure strength and stiffness were greater for the radial correction plates than for the other implants. The former may provide enough stability for corrective osteotomy of dorsally angulated distal radial malunions, even when the osteotomy gap is only filled with cancellous bone graft instead of cortical bone graft.

Biomechanische Studie zu vier winkelstabilen distalen palmaren Radiusplatten und einer nichtwinkelstabilen Radiusplatte: Steifigkeit und Versagenstests am Kadavermodell / Biomechanical study of four palmar locking plates and one non-locking palmar plate for distal radius fractures: stiffness and load to failure tests in a cadaver model

Zusammenfassung Fünf unterschiedliche Plattensysteme zur Versorgung von distalen Radiusfrakturen über einen palmaren Zugang wurden im biomechanischen Kadavermodell untersucht. Dazu wurde eine 1 cm breite metaphysäre Osteotomie unmittelbar proximal zum Gelenkspalt durchgeführt und die jeweilige Platte entsprechend den Anweisungen des Herstellers fixiert. Unter axialer Belastung wurde das Konstrukt dann in einer pneumatisch angetriebenen Testmaschine (Sincotec) geprüft. Jedes Implantatsystem wurde an jeweils 8 Leichenknochen bezüglich der Steifigkeit gemessen. Keines der Konstrukte zeigte Deformitäten im Osteotomiespalt von über 2 mm unter Lasten bis zu 100 N. Bei Lasten bis zu 250 N stellten sich signifikante Differenzen bezüglich der Steifigkeit und der Versagenscharakteristika der unterschiedlichen Plattensysteme dar. Die mittlere Steifigkeit unter axialer Belastung (MW±SD) betrug 356,4±138,6 N/mm für die Radiuskorrekturplatte ohne lateralen Ausläufer, 299,7±86,3 N/mm für die Radiuskorrekturplatte mit lateralem Ausläufer, 132,8±41,5 N/mm für die distale volare Radiusplatte, 112,5±40,2 N/mm für die 3,5 mm Titan Locking-Compression-Platte und 91,9±29,2 N/mm für die 3,5 mm Standard T-Platte. Dabei zeigte das nichtwinkelstabile Implantat (STP-Platte) die geringste Steifigkeit. Unerwartet gab es Differenzen von über 100% bezüglich der Steifigkeit zwischen den auf den ersten Blick weitgehend ähnlich erscheinenden winkelstabilen Implantaten. Zusätzlich erfolgte die Auswertung der in der Literatur beschriebenen Ergebnisse von biomechanischen Untersuchungen bei der distalen Radiusfraktur. Abstract Five different palmar fixation plate designs were compared in a distal radial osteotomy cadaver model with regard to their biomechanical properties. A metaphyseal osteotomy gap of 1 cm was performed and the osteosynthesis was plated according to the manufacturers instructions. Axial load was applied to the construct by a pneumatic material testing machine. Five implant groups with eight cadavers each were tested concerning stiffness. None of the constructs developed deformity and movement of the fracture gap larger than 2 mm with a load of 100 N. Increasing the load to 250 N revealed significant differences in stiffness and failure load between the different plates. The mean stiffness under axial load (mean±standard deviation) was 356.4± 138.6 N/mm for the radius correction plate without lateral tongue, 299.7±86.3 N/mm for the radius correction plate with lateral tongue, 132.8±41.5 N/mm for the distal volar radius plate, 112.5±40.2 N/mm for the 3.5 mm titanium locking compression plate and 91.9±29.2 N/mm for the standard stainless steel 3.5 mm T-Plate. The non-angular stable implant (STP plate) had the lowest stiffness. Unexpectedly, there were differences over 100% concerning the stiffness between the at first glance nearly similar angular stable implants. Additionally, a review of the literature concerning biomechanical investigations of the distal radial fracture was performed.

Are there any differences in various polyaxial locking systems? A mechanical study of different locking screws in multidirectional angular stable distal radius plates.

Abstract Numerous angular stable plates for the distal radius exist, and technically based comparisons of the polyaxial locking interfaces are lacking. The aim of this mechanical study was to investigate three different locking interfaces of angular stable volar plates by cantilever bending: VA-LCP Two-Column Distal Radius Plates 2.4 mm (Synthes® GmbH, Oberdorf, Switzerland), IXOS® P4 (Martin, Tuttlingen, Germany) and VariAX™ (Stryker®, Duisburg, Germany). We assessed the strength of 0°, 5°, 10° and 15° screw locking angles and tested the bending strength from 10° to 5° angles by cyclic loading until breakage. The final setup repeated the above assessments by inclusion of four locking screws. The single screw-plate interfaces of the VA-LCP showed the highest bending moment at an angle of 0° and 5°, the IXOS® P4 at an angle of 10° and 15° and the VariAX™ when changing the insertion angle from 10° into 5°. The strength of polyaxial locking interfaces and mechanism of failure proved to be different among the examined plates.

Treatment of distal intraarticular tibial fractures: A biomechanical evaluation of intramedullary nailing vs. angle-stable plate osteosynthesis.

In factures of the distal tibia with simple articular extension, the optimal surgical treatment remains debatable. In clinical practice, minimally invasive plate osteosynthesis and intramedullary nailing are both routinely performed. Comparative biomechanical studies of different types of osteosynthesis of intraarticular distal tibial fractures are missing due to the lack of an established model. The goal of this study was first to establish a biomechanical model and second to investigate, which are the biomechanical advantages of angle-stable plate osteosynthesis and intramedullary nailing of distal intraarticular tibial fractures. Seven 4(th) generation biomechanical composite tibiae featuring an AO 43-C2 type fracture were implanted with either osteosynthesis technique. After primary lag screw fixation, 4-hole Medial Distal Tibial Plate (MDTP) with triple proximal and quadruple distal screws or intramedullary nailing with double proximal and triple 4.0mm distal interlocking were implanted. The stiffness of the implant-bone constructs and interfragmentary movement were measured under non-destructive axial compression (350 and 600 N) and torsion (1.5 and 3Nm). Destructive axial compression testing was conducted with a maximal load of up to 1,200 N. No overall superior biomechanical results can be proclaimed for either implant type. Intramedullary nailing displays statistically superior results for axial loading in comparison to the MDTP. Torsional loading resulted in non-statistically significant differences for the two-implant types with higher stability in the MDTP group. From a biomechanical view, the load sharing intramedullary nail might be more forgiving and allow for earlier weight bearing in patients with limited compliance.

The Retrograde Tibial Nail: Presentation and biomechanical evaluation of a new concept in the treatment of distal tibia fractures

Displaced distal tibia fractures require stable fixation while minimizing secondary damage to the soft tissues by the surgical approach and implants. Antegrade intramedullary nailing has become an alternative to plate osteosynthesis for the treatment of distal metaphyseal fractures over the past two decades. While retrograde intramedullary nailing is a standard procedure in other long bone fractures, only few attempts have been made on retrograde nailing of tibial fractures. The main reasons are difficulties of finding an ideal entry portal and the lack of an ideal implant for retrograde insertion. The Retrograde Tibial Nail (RTN) is a prototype intramedullary implant developed by our group. The implant offers double proximal and triple distal interlocking with an end cap leading to an angle-stable screw-nail construct of the most distal interlocking screw. Its design meets the requirements of a minimally invasive surgical approach, with a stable fracture fixation by multiple locking options. The 8mm diameter curved nail, with a length of 120 mm, is introduced through an entry portal at the medial malleolus. We see possible indications for the RTN in far distal tibial shaft fractures, distal extraarticular metaphyseal tibial fractures and in distal tibia fractures with simple extension into the ankle joint when the nail is combined lag screw fixation. A biomechanical comparison of the current RTN prototype against antegrade nailing (Expert Tibial Nail, Synthes(®), ETN) was performed. Both implants were fixed with double proximal and triple distal interlocking. Seven biomechanical composite tibiae were treated with either osteosynthesis techniques. A 10mm defect osteotomy 40 mm proximal to the joint line served as an AO 43-A3 type distal tibial fracture model. The stiffness of the implant-bone constructs was measured under low and high extra-axial compression (350 and 600 N) and under torsional load (8 Nm). Results show a comparable stability during axial loading for the two implant types with slightly higher stability in the RTN group. Rotational stability was superior for the RTN. Statistical analysis proved a significant difference (p<0.05) between the ETN and RTN for rotational stability. This study suggests that retrograde tibia nailing with the RTN is a promising new concept for the treatment of distal tibia fractures.

A new angle stable nailing concept for the treatment of distal tibia fractures.

PurposeSurgical treatment of distal tibial fractures demands a stable fracture fixation while minimizing the irritation to the soft tissues by approach and implant. Biomechanical studies have demonstrated superior performance for angular-stable locked nails over standard locked nails in distal tibial fractures. The experimental Retrograde Tibial Nail (RTN) is a minimally invasive local intramedullary osteosynthesis, which has been under design by our group. We conducted a biomechanical comparison in composite tibiae of the Retrograde Tibial Nail against the Expert Tibial Nail (Synthes®). Our hypothesis was that the RTN would provide equivalent biomechanical stability with respect to extra-axial compression, torsion and load to failure testing, in an extra-articular distal tibia fracture model.MethodsBiomechanical composite bone testing was conducted in 14 biomechanical composite tibiae in an AO 43 A3 fracture model. In both groups, triple angle stable interlocking was performed in the distal fragment.ResultsResults show a statistically non-significant higher stability of the ETN during the axial loading tests. Torsional stability testing resulted in a statistically superior performance for the RTN (p = 0.018).Destructive extra-axial compression resulted in failure of six ETN constructs, while all RTN specimens survived the maximal load.ConclusionsThe experimental Retrograde Tibial Nail provides the key features for the treatment of distal tibial fractures. It combines a minimally invasive local intramedullary osteosynthesis with the ability to securely fix the fracture by multiple angle stable locking options.