Hans Hely

RheinMain University of Applied Sciences

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Pol Maria Rommens

Johannes Gutenberg University Mainz

Dorothea Mehler

Johannes Gutenberg University Mainz

Erol Gercek

University Medical Center of the Johannes Gutenberg University Mainz

Frank Hartmann

Klinikum Lippe

J. Degreif

Johannes Gutenberg University Mainz

Daniela Klitscher

Johannes Gutenberg University Mainz

Sven-Oliver Dietz

Johannes Gutenberg University Mainz

M. Otto

Zentrum für Pathologie und Zytodiagnostik

L. P. M�ller

Johannes Gutenberg University Mainz

Sebastian Kühn

Universitätsklinikum Gießen und Marburg

Cooperative Institutions

Johannes Gutenberg University Mainz

University Medical Center of the Johannes Gutenberg University Mainz

Klinik und Poliklinik für Psychosomatische Medizin und Psychotherapie

University of Cologne

University Hospital Cologne

Klinik und Poliklinik für Psychosomatik und Psychotherapie

Centrum für Integrierte Onkologie

Martin Luther University Halle-Wittenberg

Klinik und Poliklinik für Orthopädie, Physikalische Medizin und Rehabilitation

Luther University

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Friction of ceramic and metal hip hemi-endoprostheses against cadaveric acetabula

Archives of Orthopaedic and Trauma Surgery (2004)

L. P. M�ller J. Degreif L. Rudig Dorothea Mehler Hans Hely

Cadaveric spasm

10.1007/s00402-004-0734-x

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Citations (29)

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

Biomedical Engineering / Biomedizinische Technik (2013)

Isabella Mehling Rebekka Scheifl Dorothea Mehler Daniela Klitscher Hans Hely

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.

Breakage

Bend radius

10.1515/bmt-2012-0105

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Citations (15)

Friction in Hip Hemiendoprostheses. Review of Literature and Own Model Using Cadaveric Acetabula

Hip International (2002)

L. P. Müller J. Degreif Hans Hely Dorothea Mehler M. Otto

The science of tribology concerning hip arthroplasty has mainly dealt with total endoprosthesis, whereas measurement values of hemiendoprosthetic implants are rare. The small amount of experimental tribologic data concerning hemiendoprosthetic implants in the form of pendulum trials, animal experiments, in vivo measurements on human hip joints and pin on disc studies will be reviewed in the following work. The reported frictional coefficients in these studies were between 0.014-0.57. In order to test the friction coefficients of different femur head hemiendoprostheses (unipolar ceramic- and metal heads) against fresh cadaveric acetabula, the HEPFlEx-hip simulator (Hemi-EndoProsthesis Flexion Extension) was developed. In the simulator, the various hemiendoprosthetic heads are placed on a special cone and tested against a cadaver acetabulum cast in MCP 47 woodmetal. The plane of movement of the apparatus is uniaxial with a flexion-extension movement of 35 degrees. The force is produced pneumatically with amounts of up to 5 kN. Newborn calf serum serves as a lubricant. A PC collects the data from torque-, force-, and angle-sensors on-line and allows the simultaneous processing and visualization of the data. The frictional coefficients produced by the different head materials and the relevance of the play between the hemiendoprothesis head size and acetabulum can be determined. Preliminary results showed that the mean friction coefficient at 1 kN loading was =0.024-0.063 for ceramic against cartilage and =0.033-0.075 for metal against cartilage. (Hip International 2002; 2: 126-34).

Cadaveric spasm

Biomechanics

10.1177/112070000201200219

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Citations (0)

How does spinal canal decompression and dorsal stabilization affect segmental mobility? A biomechanical study

Archives of Orthopaedic and Trauma Surgery (2009)

Karl-Stefan Delank Erol Gercek Sebastian Kühn Frank Hartmann Hans Hely

Facetectomy

Facet (psychology)

Biomechanics

10.1007/s00402-009-1002-x

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Citations (42)

Biomechanical effect of graded minimal-invasive decompression procedures on lumbar spinal stability

Archives of Orthopaedic and Trauma Surgery (2012)

Frank Hartmann Claudia Janßen Susanne Böhm Hans Hely Pol Maria Rommens

Facetectomy

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Laminotomy

10.1007/s00402-012-1543-2

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Citations (26)

Impact of Different Screw Designs on Durability of Fracture Fixation: In Vitro Study with Cyclic Loading of Scaphoid Bones

PLoS ONE (2016)

Dominik Gruszka Robert D Herr Hans Hely Peer Hofmann Daniela Klitscher

Purpose The use of new headless compression screws (HCSs) for scaphoid fixation is growing, but the nonunion rate has remained constant. The aim of this study was to compare the stability of fixation resulting from four modern HCSs using a simulated fracture model to determine the optimal screw design(s). Methods We tested 40 fresh-frozen cadaver scaphoids treated with the Acumed Acutrak 2 mini (AA), the KLS Martin HBS2 midi (MH), the Stryker TwinFix (ST) and the Synthes HCS 3.0 with a long thread (SH). The bones with simulated fractures and implanted screws were loaded uniaxially into flexion for 2000 cycles with a constant bending moment of 800 Nmm. The angulation of the fracture fragments was measured continuously. Data were assessed statistically using the univariate ANOVA test and linear regression analysis, and the significance level was set at p < 0.05. Results The median angulation of bone fragments φ allowed by each screw was 0.89° for AA, 1.12° for ST, 1.44° for SH and 2.36° for MH. With regards to linear regression, the most reliable curve was achieved by MH, with a coefficient of determination of R2 = 0.827. This was followed by AA (R2 = 0.354), SH (R2 = 0.247) and ST (R2 = 0.019). Data assessed using an adapted ANOVA model showed no statistically significant difference (p = 0.291) between the screws. Conclusions The continuous development of HCSs has resulted in very comparable implants, and thus, at this time, other factors, such as surgeons' experience, ease of handling and price, should be taken into consideration.

Scaphoid fracture

10.1371/journal.pone.0145949

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Development of a multisegmental test body to calibrate and validate studies with spinal testing devices with follower load

Biomedical Engineering / Biomedizinische Technik (2011)

Frank Hartmann Erol Gercek Sven-Oliver Dietz Hans Hely Pol Maria Rommens

Spinal testing devices need a tool for calibration and comparison of accomplished studies. The objective of this study was the development of a polysegmental test body, which simulates several functional spinal motion units and provides a standard calibration.The test body consists of aluminum moldings simulating the vertebral bodies, rubber discs simulating the intervertebral discs and cylindrical guide elements with ball joints simulating the vertebral joints. The test body was tested multidirectional with a moment of 7.5 Nm and follower loads up to 800 N.The results showed sigmoid load-deformation curves of the test body similar to a human lumbar cadaver spine, but with a higher range of motion (ROM). The follower load had no influence during extension-flexion, but an increasing follower load during lateral bending and rotation caused increased friction and restoring forces with a decrea-sed ROM.The polysegmental test body does not show the same mechanical behavior like a polysegmental human cadaver spine in all directions of motion, but it provides reproducible values without requiring preconditioning as proposed for human specimen.This test body could improve the comparability of cadaver studies performed with different spinal testing devices by standardization of the test set-ups.

Biomechanics

10.1515/bmt.2011.004

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Citations (3)

Biomechanical Comparison of an Interspinous Device and a Rigid Stabilization on Lumbar Adjacent Segment Range of Motion

Acta chirurgiae orthopaedicae et traumatologiae Cechoslovaca (2011)

Frank Hartmann S. Dietz Sebastian Kühn Hans Hely Pol Maria Rommens

PURPOSE OF THE STUDYDecompression surgery with or without fusion is the gold standard treatment of lumbar spinal stenosis, but adjacent segment degeneration has been reported as a long-term complication after fusion.This led to the development of dynamic implants like the interspinous devices.They are supposed to limit extension and expand the spinal canal at the symptomatic level, but with reduced effect on the range of motion of the adjacent segments.The aim of the present study is the evaluation of the biomechanical effects on the range of motion (ROM) of adjacent lumbar segments after decompression and instrumentation with an interspinous device compared to a rigid posterior stabilization device. MATERIALS AND METHODSEight fresh frozen human cadaver lumbar spines (L2-L5) were tested in a spinal testing device with a moment of 7.5 Nm in flexion/extension, lateral bending and rotation with and without a preload.The preload was applied as a follower load of 400N along the curvature of the spine.The range of motion (ROM) of the adjacent segments L2/L3 and L4/L5 was measured with the intact segment L3/L4, after decompression, consisting of resection of the interspinous ligament, flavectomy and bilateral medial facetecomy, and insertion of the Coflex ® (Paradigm Spine, Wurmlingen) and after instrumentation with Click X ® (Synthes, Umkirch) as well. RESULTSThe interspinous and the rigid device caused a significant increase of ROM at both adjacent segments during all directions of motion and under follower load, without significant difference between these devices.The ROM of L2/L3 tends to increase more than the ROM of L4/L5 after instrumentation without statistical significance. DISCUSSIONThe "dynamic" Coflex device caused a significant increase of ROM at both adjacent lumbar segments comparable to the increase of ROM after instrumentation with the rigid Click X device.Other in vitro studies observed comparable biomechanical effects on the adjacent segments after fusion, but biomechanical spacer studies concentrated on the "noncompressible" X-Stop ® and could not demonstrate a significant adjacent segment effect of this device. CONCLUSIONSThe hypothesis, that an interspinous device would reduce the stress on adjacent segments compared to a rigid posterior stabilization device, could not be demonstrated with this biomechanical in vitro study.Therefore, the protection of adjacent segments after instrumentation with dynamic devices is still not completely achieved.

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Biomechanics

10.55095/achot2011/062

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Citations (18)

Der HEPFIEx-Simulator, eine Apparatur zur Bestimmung der Reibzahlen zwischen Hüftkopf-Prothesen und Knorpel / The HEPFlEx Simulator, a Device for Measuring the Friction between Femoral Head Prostheses and Cartilage

Biomedical Engineering / Biomedizinische Technik (2002)

Dorothea Mehler L. P. Müller Hans Hely J. Degreif Pol Maria Rommens

We describe a device designed to investigate friction between various femoral head prostheses and human acetabula. It enables not only the determination of friction and the relevance of the play between the femoral head and acetabulum, but also the evaluation of the kinematic behaviour of bipolar prostheses. In the simulator, the various femoral head prostheses are placed on a special cone and tested against a human cadaveric acetabulum. The swiveling range of the device is uniaxial, and the swiveling angle is +/- 35 degrees. The maximum force produced pneumatically is 5kN. Testing of the simulator with a TEP was successful and friction-coefficients of < 0.1 were measured, as are reported in the literature.

Cadaveric spasm

Biomechanics

10.1515/bmte.2002.47.3.63

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Citations (1)

Biomechanical effect of different interspinous devices on lumbar spinal range of motion under preload conditions

Archives of Orthopaedic and Trauma Surgery (2010)

Frank Hartmann Sven-Oliver Dietz Hans Hely Pol Maria Rommens Erol Gercek

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Biomechanics

10.1007/s00402-010-1235-8

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Citations (28)