The influence of foot geometry on the calcaneal osteotomy angle based on two-dimensional static force analyses

Background: Malalignment of the hindfoot can be corrected with a calcaneal osteotomy (CO). A well-selected osteotomy angle in the sagittal plane will reduce the shear force in the osteotomy plane while walking. The purpose was to determine the presence of a relationship between the foot geometry and loading of the calcaneus, which influences the choice of the preferred CO angle. Methods A static free body force analysis was made of the posterior calcaneal fragment in the second half of the stance phase to determine the main loads: the plantar apeunorosis (PA) and Achilles tendon (AT). The third load is on the osteotomy surface which should be oriented such that the shear component of the force is zero. The force direction of the PA and AT was measured on 58 MRIs of the foot, and the force ratio between both structures was taken from the literature. In addition the PA-to-AT force ratio was estimated for different foot geometries to identify the relationship. Results: Based on the wish to minimize the shear force during walking, a mean CO angle was determined to be 33º (SD8) relative to the foot sole. In pes planus foot geometry, the angle should be higher than the mean. In pes cavus foot geometry, the angle should be smaller. Conclusion: Foot geometry, in particular the relative foot heights is a determinant for the individual angle in performing the sliding calcaneal osteotomy. It is recommended to take into account the foot geometry (arch) when deciding on the CO angle for hindfoot correction.Biomechanical EngineeringMechanical, Maritime and Materials Engineerin

Postoperative stability following a triple pelvic osteotomy is affected by implant configuration: a finite element analysis

BackgroundThe triple pelvic osteotomy is an established surgical method with multiple modifications regarding surgical technique and choice of implant. The stability of the osteotomy is affected by numerous factors, and among these, the three-dimensional implant configuration is a scientifically less explored aspect.MethodsWe used a finite element model of a hemi-pelvis with a standardized triple osteotomy to calculate relative flexibility for loads in all translational degrees of freedom for five different implant configurations. Two of the configurations used entry points only feasible when implant removal was not necessary.ResultsThe stability of the osteotomy improved with an increased distance between the implants in the plane of the osteotomy as well as for a more perpendicular angle relative to the osteotomy plane. The implant configurations with more entry points available made this easier to adhere to.ConclusionThe use of bioabsorbable implants may provide better opportunities for optimal implant constructs which can, to a certain degree, compensate for the lesser mechanical stiffness of bioabsorbable polymers as compared to metal implants

Имитационное компьютерное моделирование нестабильности наколенника, которое сопровождается дисплазией отростков бедренной кости

Створено динамічну модель пателофеморального суглоба. Проведено визначення кутових та лінійних переміщень наколінка, а також еквівалентних за Мізесом напружень в хрящі наколінка при згинанні колінного суглоба від 0° до 30° в нормі та при нестабільності наколінка, що супроводжується дисплазією виростків стегнової кістки тип А та В. Встановлено, що при нестабільності наколінка концентратори напружень розташовуються лише на латеральній фасетці незалежно від типу дисплазії. Тип дисплазії впливає на кутові та лінійні переміщення наколінка, а також розподіл еквівалентних за Мізесом напружень в хрящі наколінка в нормі та при нестабільності.Constructed a dynamic model of patelofemoral joint on human-based simulation computer model of a complex system of movement connected elastic and rigid bodies. Options patella biomechanical movement of bodies connected by joints defined by vector given angular velocity of rotation of the tibia. Patella speed depends on patellar spring-equivalents tension forces in connection, providing interaction force between the bodies of the simulation model. In this article, using of information technologies and application software a dynamic simulation model of patellofemoral joint is created. By calculation and theoretical determination of the angular, linear displacements of the patella, and the equivalent of von Mises stress in the patellar cartilage at knee flexion from 0° to 30° in normal and patellar instability, which is accompanied by trochlear dysplasia type A and B established that the concentrators at patellar instability are placed only on the lateral facet, regardless of the type of trochlear dysplasia. Type of dysplasia affects patellar displacement and distribution of von Mises equivalent stress in the patellar cartilage in normal and at instability. The adequacy of the results of the numerical experiment tested by convergence controlled parameters values of stresses in the zones of maximum gradient.В данной работе на современном уровне развития информационных технологий и прикладного программного обеспечения создана динамическая имитационная модель пателофеморального сустава. Проведено расчетно-теоретическое определение угловых, линейных смещений надколенника, а также эквивалентных за Мизесом напряжений в хряще надколенника при сгибании коленного сустава от 0° до 30° в норме и при нестабильности, что сопровождается дисплазией мыщелков бедра тип А и В. Установлено, что при нестабильности надколенника концентраторы напряжений размещаются только на латеральной фасетке независимо от типа дисплазии. Тип дисплазии влияет на смещение надколенника и распределение эквивалентных за Мизесом напряжений в хряще надколенника в норме и при нестабильности

Computer aided intertrochanteric osteotomy planning and surgery simulation

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1994.Includes bibliographical references (p. 135-144).by Patrick J. Lord.Ph.D

Use of embedded strain gages for the in-vitro study of proximal tibial cancellous bone deformation during knee flexion-extension movement: development, reproducibility and preliminary results of feasibility after frontal low femoral osteotomy

<p>Abstract</p> <p>Background</p> <p>This paper reports the development of an in-vitro technique allowing quantification of relative (not absolute) deformations measured at the level of the cancellous bone of the tibial proximal epiphysis (CB_TPE) during knee flexion-extension. This method has been developed to allow a future study of the effects of low femoral osteotomies consequence on the CB_TPE.</p> <p>Methods</p> <p>Six strain gages were encapsulated in an epoxy resin solution to form, after resin polymerisation, six measurement elements (ME). The latter were inserted into the CB_TPEof six unembalmed specimens, just below the tibial plateau. Knee motion data were collected by three-dimensional (3D) electrogoniometry during several cycles of knee flexion-extension. Intra- and inter-observer reproducibility was estimated on one specimen for all MEs. Intra-specimen repeatability was calculated to determine specimen's variability and the error of measurement. A varum and valgum chirurgical procedure was realised on another specimen to observed CB_TPEdeformation after these kind of procedure.</p> <p>Results</p> <p>Average intra-observer variation of the deformation ranged from 8% to 9% (mean coefficient of variation, MCV) respectively for extension and flexion movement. The coefficient of multiple correlations (CMC) ranged from 0.93 to 0.96 for flexion and extension. No phase shift of maximum strain peaks was observed. Inter-observer MCV averaged 23% and 28% for flexion and extension. The CMC were 0.82 and 0.87 respectively for extension and flexion. For the intra-specimen repeatability, the average of mean RMS difference and the mean ICC were calculated only for flexion movement. The mean RMS variability ranged from 7 to 10% and the mean ICC was 0.98 (0.95 - 0.99). A Pearson's correlation coefficient was calculated showing that RMS was independent of signal intensity. For the chirurgical procedure, valgum and varum deviation seems be in agree with the frontal misalignment theory.</p> <p>Conclusions</p> <p>Results show that the methodology is reproducible within a range of 10%. This method has been developed to allow analysis the indirect reflect of deformation variations in CB_TPEbefore and after distal femoral osteotomies. The first results of the valgum and varum deformation show that our methodology allows this kind of measurement and are encourageant for latter studies. It will therefore allow quantification and enhance the understanding of the effects of this kind of surgery on the CB_TPEloading.</p

Planning the Surgical Correction of Spinal Deformities: Toward the Identification of the Biomechanical Principles by Means of Numerical Simulation

The set of surgical devices and techniques to perform spine deformity correction has widened dramatically. Nevertheless, the rate of complications due to mechanical failure remains rather high. Indeed, basic research about the principles of deformity correction and the optimal surgical strategies (i.e. the choice of the fusion length, the most appropriate instrumentation, the degree of tolerable correction) did not progress as much as the techniques. In this work, a software approach for the biomechanical simulation of the correction of patient-specific spinal deformities aimed to the identification of its biomechanical principles is presented. The method is based on three dimensional reconstructions of the spinal anatomy obtained from biplanar radiographic images. A user-friendly graphical interface allows for the planning of the deformity correction and to simulate the instrumentation. Robust meshing of the instrumented spine is provided by using consolidated computational geometry and meshing libraries. Based on finite element simulation, the program predicts the loads acting in the instrumentation as well as in the biological tissues. A simple test case (reduction of a low grade spondylolisthesis at L3-L4) was simulated as a proof-of-concept. Despite the limitations of this approach, the preliminary outcome is promising and encourages a wide effort towards its refinement

Effect of Lesser Tuberosity Osteotomy Size and Repair Construct During Total Shoulder Arthroplasty

Background. Lesser tuberosity osteotomy has been shown to decrease post-operative subscapularis dysfunction. The purpose of this study was to determine the effect of osteotomy thickness and suture configuration on repair integrity. Methods. One side of twelve matched-pair cadaveric shoulders was randomly assigned either a thick osteotomy (100% lesser tuberosity height) or a thin (50% height) osteotomy. Both sides of the matched-pairs were given the same repair, either 1) compression-sutures or 2) compression-sutures plus one tension-suture. This created four groups of six paired specimens. CT imaging measured tuberosity dimensions pre- and post-osteotomy to validate fragment height and area. The repairs were loaded cyclically and then loaded to failure. A video system measured fragment displacement. Percent area of osteotomy contact was calculated from the CT and displacement data. Results. The average initial displacement was less in the thin osteotomy groups (p=0.011). Adding a tension-suture negated this difference. A significant number of thin compared to thick repair sites remained intact during load to failure (p=0.001). No difference occurred due to maximal load between the repair groups (p=0.40) and construct stiffness was greater when a tension-suture was used (p=0.032). Percent area of osteotomy contact revealed no differences between the osteotomy (p=0.431) and repair (p=0.25) groups. Conclusion. The study showed that thin osteotomies displaced less than thick osteotomies. Adding a tension band improved construct stability and eliminated some failure modes. The ideal repair was a thin wafer with both tension and compression sutures. This construct had smaller total displacement, a reasonable osteotomy percent contact area, and acceptable maximum load