Mitchell's osteotomy augmented with bio-absorbable pins for the treatment of hallux valgus: A comparative finite element study.

BACKGROUND: There is an inadequacy of conventional means to assess the surgical outcomes of a bunion surgery. We used the Finite Element Analysis for evaluating the typical Mitchell's procedure outcomes with or without bio-absorbable pins. METHODS: We developed a 3D FE model based on the CT images of a female volunteer with hallux valgus. A typical procedure was simulated on the foot model and two pins were virtually inserted for enhancing the fixation. We validated our model by comparing the predicted pressure results with the plantar pressure measured by a specific platform. RESULTS: The comparison of the plantar pressure distribution revealed similar patterns. A greater displacement was observed on the medial side of the osteotomy, but it was decreased after using pins. The maximum average pressure under the 1st metatarsal head was decreased after the osteotomy. The respective pressure under the 3rd and 5th metatarsal head was decreased more after using pins, while, under the 2nd and 4th metatarsal head, an increase was developed. CONCLUSION: The use of pins had no significant influence on the healing process but gave additional stability inside the osteotomy and could be used in cases where enhancement is needed. The surgeon should be familiar with the expected stress rising to the other metatarsal, considering the concomitant pathology or the additional interventions that should be performed.

Effects of foot posture on fifth metatarsal fracture healing: a finite element study.

The goal of this study was to evaluate the effects of maintaining different foot postures during healing of proximal fifth metatarsal fractures for each of 3 common fracture types. A 3-dimensional (3D) finite element model of a human foot was developed and 3 loading situations were evaluated, including the following: (1) normal weightbearing, (2) standing with the affected foot in dorsiflexion at the ankle, and (3) standing with the affected foot in eversion. Three different stages of the fracture-healing process were studied, including: stage 1, wherein the material interposed between the fractured edges was the initial connective tissue; stage 2, wherein connective tissue had been replaced by soft callus; and stage 3, wherein soft callus was replaced by mature bone. Thus, 30 3D finite element models were analyzed that took into account fracture type, foot posture, and healing stage. Different foot postures did not statistically significantly affect the peak-developed strains on the fracture site. When the fractured foot was everted or dorsiflexed, it developed a slightly higher strain within the fracture than when it was in the normal weightbearing position. In Jones fractures, eversion of the foot caused further torsional strain and we believe that this position should be avoided during foot immobilization during the treatment of fifth metatarsal base fractures. Tuberosity avulsion fractures and Jones fractures seem to be biomechanically stable fractures, as compared with shaft fractures. Our understanding of the literature and experience indicate that current clinical observations and standard therapeutic options are in accordance with the results that we observed in this investigation, with the exception of Jones fractures.

Modeling signaling pathways in articular cartilage.

Chondrocytes, the only cell type in articular cartilage, are responsible for maintaining the composition of cartilage extracellular matrix (ECM) through a complex interplay of anabolic and catabolic stimuli. Although understanding the way chondrocytes respond to stimuli is of utmost importance for shedding light into the etiology of joint diseases, an integrative approach to studying their signaling transduction mechanisms is yet to be introduced. Herein, we propose an approach that combines high throughput proteomic measurements and state of the art optimization algorithms to construct a predictive model of chondrocyte signaling network, downstream of 78 receptors of interest.

Investigation on the distal screw of a trochanteric intramedullary implant (Fi-nail) using a simplified finite element model.

Numerous studies have been published concerning the characteristics and the behaviour of the intramedullary devices in the treatment of the intertrochanteric hip fractures. However, there is still room for further exploration and exploitation concerning the implant behaviour with respect to the parts of the implant assembly (nail, lag screw and distal screw). Towards this direction, the present paper aimed at revealing the effect of the position of the distal screw on the mechanical behaviour of the fixation device. For this purpose, a simplified model was developed and analysed with the finite element method. In total, five different locations for the distal screw were examined. In all cases, the bone was fixed at its distal end while the external load was applied at the tip of the lag screw towards the hip and in the form of orthonormal force components applied individually. The results of the FE analyses were illustrated in appropriately formed plots revealing the sensitivity of the behaviour of the implant with respect to the location of the distal screw. The main conclusion derived from the present investigation was that moving the distal screw apically decreases the stresses on the distal screw but increases the stresses on the lag screw. In turn, this indicates the existence of a location for the distal screw that compromises these two effects in an optimum way.

The effects of implant length and diameter prior to and after osseointegration: a 2-D finite element analysis.

A two-dimensional finite element analysis was used to evaluate the effects of implant length and diameter on the stress distribution of a single-implant supported crown and the strain distribution of its surrounding bone prior to and after the phase of osseointegration. The effect of length was investigated using implants with a diameter of 3.75 mm and lengths of 8 mm, 10 mm, 12 mm, and 14 mm. The effect of diameter was investigated using implants with a length of 10 mm and diameters of 3 mm, 3.75 mm, 4.5 mm, and 5mm. The phase prior to osseointegration was simulated by assuming a coefficient of friction for the interface between the implant and the surrounding bone, while the phase after osseointegration was simulated by assuming a fixed bond on the interface between the implant and the surrounding bone. The FEA results indicated a tendency towards stress reduction on the implant, both prior to and after osseointegration, when the length was increased. However, the calculated stresses on the implant were lower after the phase of osseointegration. Although no specific correlation could be seen regarding the influence of implant diameter, the calculated stresses on the implant were again lower after the phase of osseointegration. For all these cases, the maximum stress concentration occurred at the abutment-implant interface. As far as bone tissue was concerned, there was a tendency towards strain reduction, before and after osseointegration, when the length of the implant was increased from 10 mm up to 14 mm. This tendency was not manifested for the range of 8 to 10 mm. The effect of implant diameter on bone tissue was not clear. It appears that implants of a diameter more than 5 mm are not preferable for immediate loading. Finally, it seems that cortical bone is not influenced by the phase of osseointegration, while trabecular bone is highly affected.

A bone-remodelling scheme based on principal strains applied to a tooth during translation.

This paper investigates the role of principal strains within the periodontal ligament (PDL) during bone remodelling in orthodontics and particularly in the case of bodily motion (pure translation). Using analytical formulas of stress and strains within the PDL for the particular case of a paraboloidal central incisor during translation, the strains are directly related to the motion of the interface between the alveolar bone and the PDL, called bone surface. It is shown that both normal and shear strains within the PDL are of the same importance for bone surface motion. Moreover, both "mean average" and "geometrical average" of principal strains within the PDL play a significant role in the bone remodelling process, as they contribute with the same proportionality. In summary, the proposed formulas differ than previous ones that had been successfully applied to describe remodelling within long bones. The proposed theory is also sustained by a linear finite element analysis.

Parametric finite element analysis and closed-form solutions in orthodontics.

The goal and clinical relevance of this work was the development of closed formulas that are correct and simple enough for a fast decision making by the orthodontist in the daily praxis. This paper performs a parametric three-dimensional finite element linear analysis on a maxillary central incisor with a root of paraboloidal shape, which is subjected to typical orthodontic force-systems. Parameters of most importance, such as the tooth mobility in translation and in pure moment rotation including orthodontic centers, as well as the stresses inside the periodontal ligament are calculated for a large variety of over four hundred different couples of root lengths and root diameters around a nominal value. Regression analysis is afterwards performed and establishes closed-form solutions, which are also explained in terms of analytical strain energy and hydrostatic stress considerations within the periodontal ligament characterised by a small compressibility. The obtained expressions include both the root length as well as the root diameter.

Numerical Estimation of the Centres of Rotation and Resistance in Orthodontic Tooth Movement.

The position of the centre of resistance (Cre) as well as the centre of rotation (Cro) of a tooth under a force-system is still an open question. This paper presents a reliable and efficient three-dimensional rigid-body finite element technique to accurately estimate these centres. The influence of not only the root length but also the root diameter, the thickness of the periodontal ligament, as well as its material properties on the position of the Cre and Cro is investigated. Additionally, an explanation is given for the meaning of the coefficient (0.068 h(2) ) involved in Burstone's theoretical formula which is generalised and is expressed as the ratio of the flexibilities of tooth support in translation and pure moment rotation, respectively. The former ratio determines the position of the centres of rotation as a function of the applied moment-to-force ratio (M/F) and the relevant curve remains an isosceles hyperbola for any arbitrary-shaped tooth. The present study focuses on single-rooted teeth, such as maxillary canines and maxillary incisors, but the proposed methodology is generally applicable to any tooth.