The healing stages of an intramedullary implanted tibia: A stress strain comparative analysis of the calcification process

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.

Combined Medial Plate and Intramedullary Nailing for the Fixation of Extra-Articular Proximal Tibial Fractures: a Biomechanics Study

Purpose: The extra-articular proximal tibial fractures continue to have high malunion rates despite development in intramedullary nailing (IMN) technology. Combined plate and IMN fixation can increase mechanical stability. The purpose of this study was to investigate combined plate and IMN for the treatment of extra-articular proximal tibial fracture using a biomechanical model.

Methods: A 10-mm defective osteotomy was created in the fourth-generation composite tibia to simulate extra-articular proximal tibial fractures (AO/OTA 41A2). The fractures were stabilized with IMN alone (IMN group), IMN with supplementary medial plate (M-IMN group), and IMN with supplementary lateral plate (L-IMN group). The biomechanical properties of each specimen were tested under axial compression loading, bending stress, and cyclic loading. The maximum displacement of the fragments and implant-bone construct failure was recorded.

Results: The maximum displacement of the M-IMN group was significantly less than either the L-IMN or IMN group in both axial compression loading and bending stress (p < 0.05 for both comparisons). All specimens in the three groups survived in 10,000 cyclic loading without hardware deformation. The maximum stiffness of failure was similar between the M-IMN and L-IMN groups, but the IMN group was statistically lower than either the L-IMN or the IMN group (p < 0.05).

Conclusion: The results indicated that combined medial plate and IMN fixation could effectively increase the mechanical stability of proximal tibial fractures.

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.

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.

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.

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.

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.

Comparison of intramedullary nailing and plate fixation in distal tibial fractures with metaphyseal damage: a meta-analysis of randomized controlled trials

Background

Distal metadiaphyseal tibial fractures are commonly seen lower limb fractures. Intramedullary nail fixation (IMN) and plate internal fixation (PL) are the two mainstay treatments for tibial fractures, but agreement on the best internal fixation for distal tibial fractures is still controversial. This meta-analysis was designed to compare the success of IMN and PL fixations in the treatment of distal metadiaphyseal tibial fractures, in terms of complications and functional recovery.

Methods

A systematic research of the literature was conducted to identify relevant articles that were published in PubMed, MEDLINE, Embase, the Cochrane Library, SpringerLink, Clinical Trials.gov, and OVID from the database inception to August 2018. All studies comparing the complication rate and functional improvement of I2MN and PL were included. Data on the 12 main outcomes were collected and analyzed using the Review Manager 5.3.

Results

Eleven studies were included in the current meta-analysis. A significant difference in malunion (RR = 1.76, 95%CI 1.21–2.57, P = 0.003), superficial infection (RR = 0.29, 95%CI 0.13–0.63, P = 0.002), FFI (MD = 0.09, 95%CI 0.01–0.17, P = 0.02), and knee pain (RR = 3.85, 95%CI 2.07–7.16, P < 0.0001) was noted between the IMN group and PL group. No significant difference was seen in the operation time (MD = − 10.46, 95%CI − 21.69–0.77, P = 0.07), radiation time (MD = 7.95, 95%CI − 6.65–22.55, P = 0.29), union time (MD = − 0.21, 95%Cl − 0.82–0.40, P = 0.49.), nonunion (RR = 2.17,95%CI 0.79–5.99, P = 0.15), deep infection (RR = 0.85, 95%CI 0.35–2.06, P = 0.72), delay union (RR = 0.92, 95%CI 0.45–1.87, P = 0.82), AOFAS (MD 1.26, 95%Cl − 1.19–3.70, P = 0.31), and Disability Rating Index in 6 or 12 months (MD = − 3.75, 95%CI − 9.32–1.81, P = 0.19, MD = − 17.11, 95%CI − 59.37–25.16, P = 0.43, respectively).

Conclusions

Although no significant difference was seen between IMN and PL fixation with regards to the operation time, radiation time, nonunion, deep infection delay union, union time, AOFAS, and Disability Rating Index, significant differences were seen in occurrence of malunion, superficial infection, FFI, and knee pain. Based on this evidence, IMN appears to be a superior choice for functional improvement of the ankle and reduction of postoperative wound superficial infection. PL internal fixation seems to be more advantageous in achieving anatomical reduction and decreasing knee pain.

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.