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Bersini S.,Laboratory of Biological Structure Mechanics | Bersini S.,Polytechnic of Milan | Sansone V.,University of Milan | Frigo C.A.,Polytechnic of Milan
Computer Methods in Biomechanics and Biomedical Engineering | Year: 2015

Obtaining tibio-femoral (TF) contact forces, ligament deformations and loads during daily life motor tasks would be useful to better understand the aetiopathogenesis of knee joint diseases or the effects of ligament reconstruction and knee arthroplasty. However, methods to obtain this information are either too simplified or too computationally demanding to be used for clinical application. A multibody dynamic model of the lower limb reproducing knee joint contact surfaces and ligaments was developed on the basis of magnetic resonance imaging. Several clinically relevant conditions were simulated, including resistance to hyperextension, varus–valgus stability, anterior–posterior drawer, loaded squat movement. Quadriceps force, ligament deformations and loads, and TF contact forces were computed. During anterior drawer test the anterior cruciate ligament (ACL) was maximally loaded when the knee was extended (392 N) while the posterior cruciate ligament (PCL) was much more stressed during posterior drawer when the knee was flexed (319 N). The simulated loaded squat revealed that the anterior fibres of ACL become inactive after 60° of flexion in conjunction with PCL anterior bundle activation, while most components of the collateral ligaments exhibit limited length changes. Maximum quadriceps and TF forces achieved 3.2 and 4.2 body weight, respectively. The possibility to easily manage model parameters and the low computational cost of each simulation represent key points of the present project. The obtained results are consistent with in vivo measurements, suggesting that the model can be used to simulate complex and clinically relevant exercises. © 2015 Taylor & Francis Source

Luca A.,Istituto Ortopedico | Lovi A.,Istituto Ortopedico | Brayda-Bruno M.,Istituto Ortopedico | Galbusera F.,Laboratory of Biological Structure Mechanics
European Spine Journal | Year: 2014

Conclusion The efficacy of PSO should be balanced with the high risk of the procedure reported in the literature. Management of revision surgery after PSO may require the addition of anterior column support to maintain correction and reduce complications.Summary of background data The complication rate of pedicle subtraction osteotomy is substantially higher than other corrective procedures available for the treatment of spinal sagittal imbalance: in particular, hardware failures and mechanical complications affect this technique and their biomechanical explanation is still purely speculative.Study design Author experience and literature review. Objectives To compare different revision techniques in the treatment of implant failure after pedicle subtraction osteotomy (PSO).Methods The author’s experience and the literature regarding the revision techniques for PSO failures are discussed.Results In this paper, eight consecutive revision cases due to rod breakage after PSO surgery are reported. In our experience, the main goals are to restore the spinal balance, through a posterior approach (correction and hardware revision and implementation) and to get a solid anterior fusion (both through a traditional anterior approach or minimally invasive transpsoas approach). ©Springer-Verlag Berlin Heidelberg 2014. Source

Costa F.,Humanitas Clinical and Cancer Research Center | Villa T.,Polytechnic of Milan | Anasetti F.,Laboratory of Biological Structure Mechanics | Tomei M.,Humanitas Clinical and Cancer Research Center | And 5 more authors.
Spine Journal | Year: 2013

Background context: There is no universal consensus regarding the biomechanical aspects and relevance on the primary stability of misplaced pedicle screws. Purpose: The study is aimed to the determination of the correlation between axial pullout forces of pedicle screws with the possible screw misplacement, including mild and severe cortical violations. Methods: Eighty-eight monoaxial pedicle screws were implanted into 44 porcine lumbar vertebral bodies, paying attention on trying to obtain a wide range of placement accuracy. After screw implantation, all specimens underwent a spiral computed tomography scan, and the screw placements were graded following the scales of Laine et al. and Abul Kasim et al. Axial pullout tests were then performed on a servohydraulic material testing system. Results: Decreasing pullout forces were determined for screws implanted with increasing cortical violation. A smaller influence of cortical violations in the medial direction with respect to the lateral direction was observed. Screws implanted with a large cortical violation and misplacement in the craniocaudal direction were found to be significantly less stable than screws having comparable cortical violation but in a centered sagittal position. Conclusions: These results provide adjunctive criteria to evaluate more accurately the fate of a spine instrumentation. Particular care should be placed in the screw evaluation regarding the craniocaudal positioning and alignment. Source

Soleimani S.,Laboratory of Biological Structure Mechanics | Pennati G.,Laboratory of Biological Structure Mechanics | Dubini G.,Laboratory of Biological Structure Mechanics
International Journal of Engineering, Transactions B: Applications | Year: 2014

In this study, the rheology of blood clot is measured with the help of rotational rheometer. Several shear strains (0.5, 1 and 2%) are applied with two frequencies (5 and 10 Hz) from the incipient time of clot formation and the response of the sample is measured in the form of shear stress and the phase lag which is interpreted with storage and loss moduli. In this study the ratio of loss to storage modulus is studied and the blood clot gel-point as the transition from viscoelastic fluid to viscoelastic solid is investigated. By increasing the frequency, "tan delta" decreases before the gel-point and increases after the gel-point which indicates the viscoelastic fluid and viscoelastic solid behaviour,respectively. Moreover, by increasing the shear strain, "tan delta" varies with lower rate at luidic stage (Ra1 and Ra3) and with higher rate at solid stage (Ra2 and Ra4). It is also shown that increasing the shear strain causes a delay on gel-point formation. Source

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