Comparative Finite Element (FE) Analysis of the Mechanical Behavior in an Innovative Nitinol Staple for Arthrodesis in Distal Interphalangeal Joint.

Objective: Osteoarthritis (OA) is a source of significant limitations for individuals, health systems, and economies. The most common complications of OA are often associated with risk factors related to chronic diseases, cardiovascular disease, and depression. In this article, a new kind of staple is proposed, designed to provide better strength when subjected to bending and torque loads. Methods: This innovative staple has been numerically tested and compared to a MEMOFIX staple by Smith + Nephew, in order to evaluate its mechanical behavior. The radius and ulna were fixed at the lower extremity, while the distal interphalangeal of the little finger was loaded with a bending load of 50 N and a torque moment of 500 N/mm2. Results: For the bending load, a maximum value of stress of 120 MPa in the traditional staple, while 90 MPa are registered in the innovative one. The torsional load produces a value of 107 MPa in the traditional staple and 85 MPa in the innovative one. Conclusion: Computational simulations showed the biomechanical performance of a new type of nitinol staple compared with a traditional one. This staple is designed with an elliptical shape in order to support different kinds of loads. Our results confirm an optimal mechanical behavior, compared to the traditional staple, in terms of the evaluated Equivalent Von Mises stress; also the contact force exerted by the innovative staple was increased.

Numerical investigation of patellar instability during knee flexion due to an unbalanced medial retinaculum loading effect.

Background and aim: Healthy patellofemoral (PF) joint mechanics are critical to optimal knee joint function. Patella plays a vital role in distributing quadriceps load during the knee extension. Patellar tracking, not physiological tracking, causes an increase of strains in PF ligaments, peaks of localized stress of soft tissues and articular cartilage and bony parts, and knee pain; these problems lead to complications such as bone abnormalities and osteoarthritis. This research aimed to develop a Finite Element (FE) model to evaluate patellar instability due to the medial retinaculum asymmetric loading effect. Methods: A numerical model of the knee was obtained by matching nuclear magnetic resonance (MRI) for soft tissues and computerized tomography (CT) for bones, carried on a normal adult. Loading setup was chosen by using literature data. The intensity of the muscle forces was calculated by a static optimization taking into account ground reaction and knee flexion/extension during walking. The effect of patellar instability was obtained by gradually unbalancing this symmetry, one side was unloaded till 90 N, and the other loaded till 110 N. Results: Unbalanced forces of 10 N acting on the retinaculum alone can produce a real difference in displacements of about 7 mm, and an increment of about 44% on patellar contact forces. Conclusion: This research demonstrated how an unbalanced forces acting on the retinaculum can produce significant patellar instability. Patellar instability starts at 25-30° of the knee flexion angle but tends to appear at 15° when the unbalanced muscular loading conditions are acting.

Traumatic and non-traumatic spinal cord injury: Demographic characteristics, neurological and functional outcomes. A 7-year single centre experience.

Objective: The aim of this study is to evaluate demographic and clinical characteristics of a population affected by traumatic and non-traumatic spinal cord injury (SCI) and to analyze functional outcomes after rehabilitation. Methods: This study involved 112 SCI patients (75 male and 37 female) admitted at the Neurorehabilitation Unit of the University Hospital of Messina. The neurological outcomes were evaluated according to the American Spinal Injury Association Impairment Scale (AIS) and by using length of stay, Functional Independence Measure (FIM) and Barthel Index (BI). Results: NT-SCI patients were significantly older, numerous (75,89%) and affected by greater lesions when admitted, than T-SCI ones. Most of lesions were incomplete (93%) and associated with paraplegia (71%). FIM and BI outcomes are similar in both groups, even if T-SCI patients showed greater improvement when discharged. No significant differences were found in the length of stay. The most common complication in non-traumatic SCI group was urinary tract infection and this was observed in 25 patients (29,41%). Linear regression models explained 26% of the variance of LOS and 38% of the variance of functional outcome. Functional status on admission was the strongest determinant of LOS and completeness of the lesion was the strongest determinant of functional outcome. Etiology (traumatic versus non-traumatic) was a weak independent determinant of LOS but was not an independent determinant of functional outcome. Conclusion: SCI patient's rehabilitation should be carried out by taking into account etiology of the injury. It is important to consider this information while developing the targets and planning of the rehabilitation program. In particular, older age negatively influence the degree of disability on admission and the entity of functional recovery in both populations. Non-traumatic lesions could have minor benefits after rehabilitation therapy if compared with traumatic ones.

Statistical investigation about spinal clinical asymmetry in a school population.

BACKGROUND: Spinal disorders and obesity are increasing and are an important cause for concern among healthcare and educational bodies. There is a wide variability in the literature of clinical positivity for scoliosis in the examination of the spine. AIM: Our study aims to investigate a relationship between scoliosis hump in schoolchildren and obesity, evaluating different kind of variables. METHODS: The sample was comprised by 478 schoolchildren from Italy, with a mean age of 12.6 years (SD: 1.861). They were classified by using ATR test, body mass index (BMI), the Edinburgh Inventory, the deep flexion test. RESULTS: Results of ATR test evidence 26 subjects (5,4%) positive for ATR ≥ 7; 102 subjects (21,3%) positive for ATR ≥ 6; and finally 191 subjects (40,0%) positive for ATR ≥ 5. There were 191 (40%) subjects with scoliosis; obesity was present in 62 (13%) cases and, after the regression, associations were found between scoliotic posture and gender, presence of obesity, and flexibility. CONCLUSIONS: Our study confirms a relationship between obesity and scoliosis, which increases with the age. Female subjects have higher risks to develop humps and spinal disorders. It is advisable to use a combination of several parameters to achieve a more sensitive evaluation.

Stress shielding FE analysis on the temporomandibular joint.

AIMS: The purpose of this study is to develop a FE model of the temporomandibular joint (TMJ) to investigate a musculoskeletal System of forces able to taking into account the effect of all the muscles on the TMJ in terms of stress evaluated on the bone. METHODS: A 3-dimensional finite element model of the mandible was constructed from the images generated by cone-beam computed tomography of a patient undergoing fixed orthodontic treatment. In order to define the loading force system an exustive study was developed to investigated the entity of the Lateral pterygoid, Masseter, medial pterygoid, Temporalis, and Geniohoid digastric, muscles. RESULTS: Stresses in the TMJ components (disc, mandible condyle and the fossa eminence on the skull) were obtained. The results have shown stress distribution during normal occlusion. CONCLUSION: An appreciation of the anatomical and mechanical features associated with the TMJ can serve as a foundation for understanding a patient's clinical presentation. Performance of a thorough patient history and clinical examination can guide the clinician toward an improved diagnostic process.

Stress distribution in the humerus during elevation of the arm and external abduction.

OBJECTIVE: The purpose of this study is to estimate stress distribution occurring in the humerus during elevation and external rotation of the arm.Methods: contact forces and moments were estimated using telemeterized shoulder implants. An accurate three-dimensional (3D) finite element (FE) model of the natural scapula was developed, and loaded by data obtained by instrumented prosthesis. RESULTS: Stresses of about 40 MPa were found on the homerus during the elevation phase acting at 30° and 80°, while a peak of 60 MPa was found during the external rotation phase at 20°. The stress aging on scapula was of about 45 MPa, while the acromion was subjected at about 30 MPa. Stresses aging on ligaments were of about 15 MPa. CONCLUSION: These results indicated that the transfer of major muscle and joint reaction take place predominantly through the thick bony ridges, and stresses induced can be dangerous especially for patients with shoulder problems or during the first post-operative weeks after shoulder fractures or joint replacements.

Stress shielding analysis on easy step staple prosthesis for calcaneus fractures.

OBJECTIVE: The calcaneus is the most frequently injured tarsal bone, with calcaneal fractures meaning that 60% of the fractures affect the foot and about 1%-2% of all fractures. METHODS: Two 3D FE model of the foot were realized in order to compare the stress shielding occurring in a health foot and in a fractured one implanted with an easy step prosthesis by Stryker. This dispositive is indicated for calcaneus fractures. RESULTS: Results evidence the efficacy of this kind of prosthesis as the Eq. Von mises stresses are comparable in the two model. Higher concentration of stress are concentered on the Easy step. CONCLUSION: In conclusion, the easy step staple prosthesis allows obtaining excellent results in terms of calcaneus fracture treatments. The correct implant size for a given patient can be determined by evaluating the patient's height, weight, functional demands and anatomy.

Hallux valgus (HV): A multi-approach investigation analysis.

OBJECTIVE: this study aims to develop a 3D FE model of the foot suffering from valgus hallux in order to investigate the plantar pressure distributions between bony structures. METHODS: in a first phase a baropodometric analysis was performed, successively a FE analysis was performed comparing results and obtaining information on the stress shielding. RESULTS: the valgus hallux deforms the correct spreading of the stress inside the bony structures causing an overloading of pressure located on the hallux and downloading the other toes. CONCLUSION: This comparative study can furnish important indications about the distribution of the stress patterns on the foot.

Tibio talar contact stress: An experimental and numerical study.

AIMS: Tibio-talar contact stress has been evaluated and successively compared by performing an ankle contact finite element (FE) analysis and an experimental test carried on an assembled simple synthetic model of ankle equipped with a high-resolution (Tekscan) pressure sensor. METHODS: A numerical FEM analysis was carried out by simulating the ankle joint (foot, and tibia) in order to investigating the stress shielding on the contact surfaces. The foot was constrained at the base while a load of 980 N was applied on the top of the tibia. The same setup was experimentally reproduced by introducing a high-resolution (Tekscan) pressure sensor between tibia and foot. RESULTS: Results evidenced a good agreement between numerical and experimental data, a percentage difference of 15% was evaluated on the equivalent Von Mises contact stress. CONCLUSION: The obtained results reveal interesting consequences deriving by taking into account how the stress shielding can influence the integrity and resistance of bones. The methods used for this validation enable formal comparison of computational and experimental results, and open the way for objective statistical measures of regional correlation between FE-computed contact stress distributions from comparison articular joint surfaces.

Healing of tibial comminuted fractures by the meaning of an innovative intramedullary nail.

In this paper, an innovative design of prosthesis, conceived to heal the comminuted fractures of long bones has been investigated. The proposed prosthesis consists of two shell valves hinged to each other by a central pin and bearing slits along the surface in such a way as to guarantee the exchange of body fluids and at the same time ensure the structural stability of the bone. Two screws then hold the two valves together. The operative technique for the introduction of this type of prosthesis for the decomposed fracture of long bones consists in the incision of the fracture site, introduction of the open shell prosthesis with reduction of the fracture and composition of the bone fragments, closure by means of fixing screws of the prosthesis shell, stitching open wound flaps. A complete numerical FE model of an implanted femur was analyzed, by considering a vertical load of 980 N. Analyses confirmed results, in terms of mechanical performances, comparable with the others traditional systems of prosthesis.

Finite element analysis of the foot: Stress and displacement shielding.

The foot is at the base of the antigravity control system (postural or equilibrium system) that allows the man to assume the upright posture and to move in the space. This podalic cohesion is achieved by the capsulo-ligamentous and aponeurotic formations to which are added the muscular formations with functions of "active ligaments" and postural. A three-dimensional (3D) finite element model of human foot was developed using the real foot skeleton and soft tissue geometry, obtained from the 3D reconstruction of MR images. The plantar fascia and the other main ligaments were simulated using truss elements connected with the bony surfaces. Bony parts and ligaments were encapsulated into a skin of soft tissues, imposing a linear elastic behavior of material in the first case and the hyperelastic law in the second. The model was tested by applying a load of 350 N on the top of the talus and the reaction force applied on the Achilles tendon equal to 175 N acting, and putting it in contact with a rigid wall. The results evidence that the most stressed areas, localized around the calcaneus following a trajectory that includes the cuboid and spreading into metatarsals and first phalanges. The foot is a "spatial" structure perfectly designed to absorb and displace the forces, brought back to the infinite planes of the space.

Flatfoot and normal foot a comparative analysis of the stress shielding.

OBJECTIVE: this study aims to develop a comprehensive 3D FE model of the foot to investigate the effect of soft tissue stiffness on the plantar pressure distributions and the internal load transfer between bony structures. METHODS: the stress shielding occurring on the plantar surface of a flatfoot was investigated and compared with the mechanical behavior of a healthy foot, trough baropodometric analyses and the FE models. RESULTS: the flatfoot evidences a more intensive stress-shielding map with significant values of pressure acting on the medial plantar fascia. CONCLUSION: Clinically and radiographically, symptomatic adult flatfoot is a complex abnormality involving all three dimensions and multiple joints within the foot.

Healing of femoral fractures by the meaning of an innovative intramedullary nail.

In this paper, an innovative design of nail, conceived to heal fractures of long bones has been investigated. Its functioning is based essentially on sliding of conical surfaces located in a spindle and in a series of holding pins radially disposed around it. Spindle and holding pins are connected together by means of a sleeve. Medial and distal screws are not necessary. Rotational and longitudinal motions of the spindle are transformed in a radial expansion of the holding pins by the sliding of conical surfaces. A complete numerical FE model of an implanted femur was realized and analyzed by the mean of two loading configurations: LC1 by imposing a vertical load of 980 N, and LC2 by considering resultants of the muscle actions. Analyses confirmed results, in terms of mechanical performances, comparable with the others traditional systems of prosthesis.

Characterization of an innovative intramedullary nail for diaphyseal fractures of long bones.

In this paper, an innovative design of nail for fractures occurring on long bones has been investigated. Its functioning is based essentially on sliding of conical surfaces, located in a spindle and in holding pins. Spindle and holding pins are connected together by a sleeve. The sliding transforms the rotational and translational motion of the spindle to a radial expansion of the holding pins, protruding inside the intramedullary canal. In order to evaluate mechanical behavior of the prosthesis different benchmarks and tests were numerically performed by an FE code. Results confirm good performances in terms of strength, under compression, bending and torque loading. Moreover, a complete model of the nail implanted on a tibia, has been developed and tested evaluating two loading configurations. Results confirmed a satisfactory behavior of the nail in terms of stress and strain shielding, comparable to the others traditional systems of prosthesis. In conclusion, this kind of nail appears to offer a good solution for elderly patients, which could not endure complications due to a complex surgery, as distal or medial screws are not necessary.

Experimental strain analysis on the entire bony leg compared with FE analysis.

The present study addresses the question of evaluating, by combining both experimental and numerical approaches, the stress/strain distribution within a complete model of the entire lower bony chain. With this purpose an experimental model and a complete 3D finite element one were realised. A load of 700 N has been applied at the top of pelvis and the feet were rigidly fixed. Obtained results reveal interesting consequences deriving by taking into account the complete bony chain; it is possible to get information on load sharing between bones, location of high strain concentrations, and bone relative motion.

Carotid artery stenosis near a bifurcation investigated by fluid dynamic analyses.

Haemodynamic physical parameters play a role in determining endothelial cell phenotype and influence vascular remodelling. Accurate measurement of total pressure, velocity magnitude, and wall shear stress is vital for studies on the pathogenesis of atherosclerosis. This paper investigated a lesion-based computational fluid dynamic (CFD-Fluent) pilot analysis to understand the complex haemodynamic changes prevailing in patients with high-grade carotid artery stenosis (CS) 90%. All subjects were examined with colour-flow Doppler, power Doppler, and digital subtraction angiography to enable visualization of carotid stenosis and plaque surface morphology, and used to generate computational meshes. Two models were devised: the first without any stenosis and the second with an 82% grade of stenosis localized in the external carotid artery. The distribution of the principal parameters can be obtained by computational fluid dynamics (CFD-Fluent) using patient-specific geometries and flow analytical measurements. The total pressure distribution ranged between 16,000 and 8,000 Pa in the case of normal carotid artery and 16,000 and 5,500 Pa in the case of the stenosed artery. The velocity registered a peak in the stenosis region of 5 m/s. The mean wall shear stress within the stenosis region was 360 Pa. In conclusion, patient-based CFD-Fluent analysis of CS predicts a complex haemodynamic environment with large spatial haemodynamic parameter variations that occur very rapidly over short distances. Our results improve estimates of the flow changes and forces at the vessel wall in CS and the link between haemodynamic changes and stenosis pathophysiology.