Wellcome at the Julius Wolff Institute

Latest Publications

Dreischarf M, Schmidt H, Putzier M, Zander T
Biomechanics of the L5-S1 motion segment after total disc replacement - Influence of iatrogenic distraction, implant positioning and preoperative disc height on the range of motion and loading of facet joints.
J Biomech. 2015 Jul 2. pii: S0021-9290(15)00361-9. doi: 10.1016/j.jbiomech.2015.06.023. [Epub ahead of print]

Total disc replacement has been introduced to overcome negative side effects of spinal fusion. The amount of iatrogenic distraction, preoperative disc height and implant positioning have been considered important for surgical success. However, their effect on the postoperative range of motion (RoM) and loading of the facets merits further discussion. A validated osteoligamentous finite element model of the lumbosacral spine was employed and extended with four additional models to account for different disc heights. An artificial disc with a fixed center of rotation (CoR) was implemented in L5-S1. In 4000 simulations, the influence of distraction and the CoR's location on the RoM, facet joint forces (FJFs) and facet capsule ligament forces (FCLFs) was investigated. Distraction substantially altered segmental kinematics in the sagittal plane by decreasing range of flexion (0.5° per 1mm of distraction), increasing range of extension (0.7°/mm) and slightly affecting complete sagittal RoM (0.2°/mm). The distraction already strongly increased the FCLFs during surgery (up to 230N) and in flexion (~12N/mm), with higher values in models with larger preoperative disc heights, and increased FJFs in extension. A more anterior implant location decreased the RoM in all planes. In most loading cases, a more posterior location of the implant's CoR increased the FJFs and FCLFs, whereas a more caudal location increased the FCLFs but decreased the FJFs. The results of this study may explain the worse clinical results in patients with overdistraction after TDR. The complete RoM in the sagittal plane appears to be insensitive to detecting surgery-related biomechanical changes.

"The cage geometry substantially influences the predicted fusion outcome. An optimization of long-term behavior of the cage material could improve the fusion outcome, which could not be achieved by optimizing the initial mechanical environment."

Bashkuev M, Checa S, Postigo S, Duda G, Schmidt H.
Computational analyses of different intervertebral cages for lumbar spinal fusion.
J Biomech. 2015 Jun 30. pii: S0021-9290(15)00362-0. doi: 10.1016/j.jbiomech.2015.06.024. [Epub ahead of print]

Lumbar spinal fusion is the most common approach for treating spinal disorders such as degeneration or instability. Although this procedure has been performed for many years, there are still important challenges that must be overcome and questions that need to be addressed regarding the high rates of non-union. The present finite element model study aimed to investigate the influence of different cage designs on the fusion process. An axisymmetric finite element model of a spinal segment with an interbody fusion cage was used. The fusion process was based on an existing mechano-regulation algorithm for tissue formation. With this model, the following principal concepts of cage design were investigated: (1) different cage geometries with constant compressive stiffness and (2) cage designs optimized to provide the ideal mechanical stimulus for bone formation, first at the beginning of fusion and then throughout the entire fusion process. The cage geometry substantially influenced the fusion outcome. A cage that created an optimized initial mechanical stimulus did not necessarily lead to accelerated fusion, but rather resulted in delayed fusion or non-union. In contrast, a cage made of a degradable material produced a significantly higher amount of bone and resulted in higher segmental stiffness. However, different compressive loads (250, 500 and 1000N) substantially affected the amount of newly formed bone tissue. The results of the present study suggest that aiming for an optimal initial mechanical stimulus may be misleading because the initial mechanical environment is not preserved throughout the bone modeling process.

Forien JB, Fleck C, Krywka C, Zolotoyabko E, Zaslansky P.
In situ compressibility of carbonated hydroxyapatite in tooth dentine measured under hydrostatic pressure by high energy X-ray diffraction.
J Mech Behav Biomed Mater. 2015 Jun 12;50:171-179. doi: 10.1016/j.jmbbm.2015.06.005. [Epub ahead of print]

Tooth dentine and other bone-like materials contain carbonated hydroxyapatite nanoparticles within a network of collagen fibrils. It is widely assumed that the elastic properties of biogenic hydroxyapatites are identical to those of geological apatite. By applying hydrostatic pressure and by in situ measurements of the a- and c- lattice parameters using high energy X-ray diffraction, we characterize the anisotropic deformability of the mineral in the crowns and roots of teeth. The collected data allowed us to calculate the bulk modulus and to derive precise estimates of Young's moduli and Poisson's ratios of the biogenic mineral particles. The results show that the dentine apatite particles are about 20% less stiff than geological and synthetic apatites and that the mineral has an average bulk modulus K=82.7GPa. A 5% anisotropy is observed in the derived values of Young's moduli, with E11≈91GPa and E33≈96GPa, indicating that the nanoparticles are only slightly stiffer along their long axis. Poisson's ratio spans v≈0.30-0.35, as expected. Our findings suggest that the carbonated nanoparticles of biogenic apatite are significantly softer than previously thought and that their elastic properties can be considered to be nearly isotropic.

Schwachmeyer V, Kutzner I, Bornschein J, Bender A, Dymke J, Bergmann G
Medial and lateral foot loading and its effect on knee joint loading.
Clin Biomech (Bristol, Avon). 2015 Jun 12. pii: S0268-0033(15)00165-5. doi: 10.1016/j.clinbiomech.2015.06.002. [Epub ahead of print]

BACKGROUND: The medial knee contact force may be lowered by modified foot loading to prevent the progression of unilateral gonarthrosis but the real effects of such gait modifications are unknown. This study investigates how walking with a more medial or lateral rollover of the foot influences the in vivo measured knee contact forces.

METHODS: Five subjects with telemeterized knee implants walked on a treadmill with pronounced lateral or medial foot loading. Acoustic feedback of peak foot pressure was used to facilitate the weight bearing shift. The resultant contact force, Fres, the medial contact force, Fmed, and the force distribution Fmed/Fres across the tibial plateau were computed from the measured joint contact loads.

FINDINGS: During lateral foot loading, the two maxima of Fres during the stance phase, Peak 1 and Peak 2, increased by an average of 20% and 12%, respectively. The force distribution was changed by only -3%/+2%. As a result, Fmed increased by +16%/+17%. Medial foot loading, on the other hand, changed Fres only slightly, but decreased the distribution by -18%/-11%. This led to average reductions of Fmed by -18%/-18%. The reductions were realized by kinematic adaptations, such as increases of ankle eversion, step width and foot progression angle.

INTERPRETATION: Medial foot loading consistently reduced the medial knee compartment, and may be a helpful gait modification for patients with pronounced medial gonarthrosis. The increase of Fmed during lateral foot loading was most likely caused by muscular co-contractions. Long-term training may lead to more efficient gait and reduce co-contractions.

Märdian S, Schmölz W, Schaser KD, Duda GN, Heyland M.
Interfragmentary lag screw fixation in locking plate constructs increases stiffness in simple fracture patterns.
Clin Biomech (Bristol, Avon). 2015 Jun 12. pii: S0268-0033(15)00172-2. doi: 10.1016/j.clinbiomech.2015.06.008. [Epub ahead of print]

The aim of the current biomechanical cadaver study was to quantify the influence of an additional plate-independent lag screw on construct stiffness in simple fracture models at the distal femur stabilised with a locking plate. Plate constructs with interfragmentary lag screw reveal similar axial and torsional stiffness values compared to intact bone as opposed to bridging plate constructs that showed significantly lower stiffness for both loading conditions.

Figure: Throughout all tests all distal screw options of the plate were used (a). In order to avoid embedding of the plate at the distal and proximal end modelling clay was used as shown (b). The prepared specimen was then tested according to the test protocol. The picture (c) shows the set-up of the biomechanical testing (*: insertion point of the lag screw at the anterior cortex). A schematic illustration of the different test configurations is additionally shown (d).

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Upcoming Event at Berlin-Brandenburg School for Regenerative Therapies

Research Unit "Regeneration in Aged Individuals"

Unter der Projektleitung von Prof. Georg Duda hat die Deutsche Forschungsgemeinschaft e.V. den Antrag einer Forschergruppe mit dem Arbeitstitel "Regeneration in Aged Individuals: Using bone healing as a model system to characterize regeneration under compromised conditions" für eine Laufzeit von drei Jahren bewilligt.

Die Forschergruppe bezeichnet sich dabei als ein enges Arbeitsbündnis mehrerer Wissenschaftler, die gemeinsam eine Forschungsaufgabe bearbeiten. Neben dem Julius Wolff Institut sind innerhalb der CharitéUniversitätsmedizin Berlin auch die Institute der Medizinischen Genetik und Humangenetik sowie der Medizinischen Immunologie und das Centrum für Muskuloskeletale Chirurgie und das Berlin-Brandenburger Centrum für Regenerative Therapien beteiligt. Weitere Einrichtungen sind das Institut für Biochemie der Freien Universität Berlin und das Deutsches Rheuma-Forschungszentrum Berlin.  Lesen Sie mehr