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

Evaluation of the mechanical behaviour of the expandable wedge locked nail fixation in retrograde use: A finite element study

INTRODUCTION

In literature, there have been many studies conducted to research the alternatives of standard interlocking intramedullary nailing. The expandable wedge locked nail fixation, which is thought as a new alternative to the standard interlocking nailing, has been presented in previous numerical studies. The antegrade usage of the wedge locked nail fixation has provided promising results. From this point, the aim of the study is to evaluate mechanical behavior of its retrograde usage on femur models. Additionally, another aim of the study is to investigate the effect of fracture level on mechanical properties of the fixation.

MATERIALS AND METHODS

The mechanical behaviors of the wedge locked nail and standard interlocking nail fixations were compared by finite element methods. Sawbones femurs having osteotomies at five different levels to simulate different fractures were fixed with wedge locked nail or interlocking nail by using retrograde approach. With respect to the fracture level, two different nail lengths were used. Axial compression load was applied to fixations. The mechanical behaviors of the fixations were evaluated with respect to stiffness of the fixations and stresses occurred on both implants and bones.

RESULTS

Any of the wedge locked nail fixation did not slip at canal. The stress and stiffness results were mostly close with each other for both nail types. The maximum stresses at locking elements or bones contacting these elements increased with decreased distance between the fracture and relevant locking elements.

DISCUSSION

The wedge locked nail fixation showed comparable results to the standard interlocking nail fixation with respect to the stiffness and stress. Under axial loading, wedge locked nail provided a secured fixation without any slippage and preserved its position inside the medullary canal. It may be thought as a safe alternative to the standard interlocking nail fixation for retrograde usage. Additionally, according to stress results, it is advised to the surgeons to avoid a close locking to the fracture line.

Screw Stress Distribution in a Clavicle Fracture with Plate Fixation: A Finite Element Analysis

Clavicle midshaft fractures are mostly treated surgically by open internal reduction with a superior or anteroinferior plate and screws or by intramedullary nailing. Screw positioning plays a critical role in determining the stress distribution. There is a lack of data on the screw position and the appropriate number of cortices required for plate fixation. The aim of this study is to evaluate the mechanical behavior of an anterior plate implanted in a fractured bone subjected to 120° of lateral elevation compared to a healthy clavicle using numerical simulations. Contact forces and moments used were obtained from literature data and applied to the healthy and fractured finite element models. Stresses of about 9 MPa were found on the healthy clavicle, while values of about 15 MPa were calculated on the plate of the fractured one; these stress peaks were reached at about 30° and 70° of elevation when the stress shielding on the clavicle sums all the three components of the solicitation: compression, flexion, and torsion. The stress distribution in a clavicle fracture stabilized with plates and screws is influenced by several factors, including the plate's position and design, the type of screw, and the biomechanical forces applied during movements.

Fluoroscopy-free distal screw locking in intramedullary nailing: A retrospective study

Intramedullary nailing is a common orthopedic procedure, but current methods for distal screw locking have several limitations. This study introduces and evaluates a novel technique that aims to overcome these challenges. The findings were statistically significant, with P-values set at .05. Compared to the traditional method, the novel technique demonstrated several advantages. Mean operation times were reduced to 1.2 hours for the new method, in contrast to 1.5 hours for the control group. Hospital stays also favored the new technique, with a mean duration of 2 days, while the control group averaged 3 days. A significant benefit was the marked decrease in radiation exposure, with the new technique eliminating radiation entirely, recording 0.0 mSv compared to the control group's 2.5 mSv. The procedure's success, gauged by the accurate positioning of screws, was higher for the new technique at 92% versus the control's 78%. Furthermore, complication rates were notably lower in the new method, with a 6% incidence compared to 16% in the traditional approach. While the data suggest that the new technique holds promising advantages, such as reduced operation times, decreased radiation exposure, and fewer complications, it is essential to conduct more extensive research for comprehensive validation. Despite the optimistic results, the study acknowledges the need for larger-scale trials to solidify these findings.

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.

Mechanical comparison of standard interlocking, clawed, and expandable wedge locked nail fixations: An experimental and numerical study

INTRODUCTION

Intramedullary nailing has been used as a standard in the treatment of the long bone fractures with its clinical and mechanical advantages. However, using distal locking screws has been associated with longer operative times, higher radiation exposure rates, and complications like breakages of distal screw or nail at the screw hole level. Therefore, attempts to eliminate distal locking screws has been always present for intramedullary nail fixation. With a similar purpose, the present study has been carried out to compare mechanical behaviors of intramedullary nail fixations with different distal locking elements.

MATERIALS AND METHODS

In this study, mechanical behaviors of standard interlocking and clawed nail fixations were compared experimentally in the first part. Six fourth generation Sawbones femurs, which have a simulated subtrochanteric fracture, were divided equally and were fixed with standard interlocking and clawed nails. During axial compression tests, experimental strain measurements were taken from all fixations. After validation of numerical models with using experimental strains and stiffnesses, mechanical behaviors of standard interlocking, clawed, and wedge locked nail fixations were compared numerically under axial compression loads. In numerical comparison, the stress-strain distributions were evaluated.

RESULTS

Experimental results showed that although that there was no significant difference in stiffnesses, standard nail fixation bore two times higher loads than clawed nail fixations. Under loading, decrease in the distance between fracture surfaces was approximately seven times higher in the clawed nail fixation when compared to standard nail fixations. Numerical results showed that wedge locked nail fixation provided equivalent mechanical behavior to standard interlocking nail.

DISCUSSION

In experiments of clawed nail fixation, the high decrease in the distance between fracture surfaces was evidence of the slippage of nail in the medullary canal. For a safe fixation, claws should be deployed when they are completely in contact with the cortical bone, they should be stuck into the bone in a fair amount, and the deployment in the distal third of the femur should be avoided. According to experimentally validated numerical analyses, wedge locked nail fixation may be an alternative for standard interlocking nail fixation if experimental studies support the present results.

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.

Numerical evaluation of the mechanical properties of a novel expandable intramedullary nailing: A new alternative to standard interlocking nailing

INTRODUCTION

There has been a great effort in preventing the disadvantages of distal locking in intramedullary nailing to date. From this scope, a novel expandable nail fixation eliminating distal locking screws has been designed. The primary aim of this numerical parametric study is to investigate mechanical behavior of expandable nail fixation on the fractured femur model under different contact parameters which are effective in maintaining the nail position and to specify the appropriate values of these contact parameters for a safe fixation. The second aim is to compare mechanical behavior of the expandable nail fixation with the standard interlocking nail fixation.

MATERIALS AND METHODS

The expandable nail has three wedges which are responsible for distal fixation by compressing the medullary canal in the radial direction. 4th generation Sawbones femur model was used as bone model. A transverse osteotomy with 20 mm gap was created to simulate a subtrochanteric fracture. The fixations have been examined under axial compression with 1200 N and torsion with 7 Nm. In the parametric study, the tightening torque and static friction coefficient in wedge-canal contact were selected as contact parameters. The outputs were stiffnesses of the fixations, equivalent von-Mises stress distribution on the models, and load sharing between the canal and distal locking elements.

RESULTS

The results of the parametric study showed that the model with the tightening torque of 3 Nm and friction coefficient of 0.7 was the safest. The load borne by wedges is generally prone to increase with increased tightening torque and friction coefficient. The both fixations showed close stiffness and stress values.

CONCLUSION

The tightening torque of the wedge locking mechanism is directly effective in maintaining the nail position constant in canal, and the safety of the fixation is better ensured with increased tightening torque but stress states on bone must be carefully evaluated. The expandable nail provided comparable results to standard interlocking nails with respect to the fixation stiffness, stress, and contact forces. The expandable nailing may be evaluated as an alternative in the fractures of long bones in the case that the numerical results are supported by future experimental studies.

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.

Femoral trochanteric fracture: PFNA spiral blade placement with the aid of an angler

Objective

To investigate the effect of angler-assisted proximal femoral nail antirotation (PFNA) spiral blade fixation in treating femoral trochanteric fractures.

Methods

Patients who underwent angler-assisted PFNA screw blade fixation (angler-assisted group), or conventional internal fixation-intramedullary nailing (traditional surgery group) were included. Intraoperative indicators and treatment effects data were retrospectively analysed.

Results

Statistically significant differences were observed between the angler-assisted group (n = 27) and traditional surgery group (n = 28) regarding surgery duration (71.24 ± 8.01 min versus 81.50 ± 11.56 min), number of intraoperative fluoroscopy images (7.28 ± 0.91 versus 12.83 ± 1.55), and surgical bleeding volume (88.80 ± 7.98 ml versus 121.11 ± 27.21 ml). Rates of one-time intramedullary pin puncture for internal fixation in the angler-assisted and traditional surgery groups were 92.59% (25/27) and 32.14% (9/28), respectively. At 1 year following surgery, fractures in both groups had healed without internal fixation failure or fracture displacement failure. Harris hip function scores were 90.68 ± 4.23 (angler-assisted group) versus 81.69 ± 5.85 (traditional surgery group).

Conclusions

Angler-assisted intramedullary nailing with PFNA spiral blade provides good spiral blade positioning, low internal fixation failure rate, low fluoroscopy, short surgery time, and low bleeding volume. Hip function was well restored.

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.

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.