Computational comparison of tibial diaphyseal fractures fixed with various degrees of prebending of titanium elastic nails and with and without end caps

Mechanical behaviors of titanium, nickel-titanium, and stainless elastic intramedullary nail in fixation of tibial diaphyseal fractures

INTRODUCTION

Elastic nails have been widely used in the diaphyseal fracture fixation of long bones in adolescents. However, high complication rates have been reported in cases involving weights exceeding 55 kg. The existing nails are fabricated with different metals in clinical settings; however, the effect of the materials on the mechanical responses of the fractured bone remains unclear. Hence, the present study is conducted to compare the mechanical responses of typically used metals, namely titanium, stainless, and nickel-titanium, for elastic nails in the fixation of tibial diaphyseal fractures.

MATERIAL AND METHODS

A sawbone tube is used to determine the contact force, which is developed after constraining the nail inside the narrow canal using different nail materials. Furthermore, a finite element (FE) model of the tibial diaphyseal fracture is developed to predict the fracture gap deformation based on different nail materials under axial compression and bending loads. The push-out force in the FE simulation is compared with that of a case without an end cap.

RESULTS

In the sawbone tube, the results indicate that the contact force developed by the titanium nail is significantly higher than those developed by stainless and nickel-titanium nails. The contact forces developed by the titanium, stainless steel, and nickel- titanium nails are 385 (SD 34), 358 (SD 49), and 258 (SD 42) N, respectively. In the FE simulation, the titanium nail yields the highest push-out force when an end cap is not used, and the push-out forces in axial compression are 201, 183, and 87 N in the titanium, stainless, and nickel-titanium nails under axial compression, respectively. By contrast, the stainless nail yields the smallest gap deformation when an end cap is used.

CONCLUSION

Results of the present study show that the end cap is an important factor affecting the mechanical responses of nails fabricated using different materials. Titanium nails are preferred when an end cap is not used, whereas stainless nails are preferred when an end cap is used.

Tibial shaft fractures in children: flexible intramedullary nailing in growing children especially weighing 50 kg (110 lbs) or more

Currently the gold standard in surgical treatment of displaced tibial shaft fractures in children with open growth cartilage is elastic stable intramedullary nailing (ESIN). The purpose of this study is the analysis of indications, complications, and duration of treatment using intramedullary flexible nails in children who are still growing but especially weighing 50 kg or more. Hospital records from 2017 to 2020 were retrospectively reviewed to identify the children from 4 to 17 years of age with displaced tibial shaft fractures admitted to the hospital. Only children with open growth cartilage, with a minimum of 6 months of follow-up and complete clinical data, were included. Studies of 91 children xwere analyzed. The average patient age at the time of the injury was 10.88 ± 2.82 years. In the entire group, 31.9% children weighed 50 kg or more, and 68.1% of the children were below this weight. All children were treated using ESIN. The mean time to nail removal was 8.4 ± 4.09 months in the whole group of children stabilized with ESIN. There were no differences in the two groups depending on the weight ( P = 0.637). Only two adverse events were observed. This study demonstrates that the use of ESIN in displaced tibial shaft fractures in growing children weighing 50 kg or more is acceptable and safe. The discussion to be made is whether it is still an acceptable method of treatment for this type of fracture due to the progressive obesity epidemic in children and adolescents.

Finite element study of the effects of fragment shape and screw configuration on the mechanical behavior of tibial tubercle osteotomy

PURPOSE

Tibial tubercle osteotomy (TTO) is a surgical technique used in the management of severe fractures of the knee joint and revision total knee arthroplasty. Limited research discusses the performance of the osteotomy and fixation of the TTO with screws. Therefore, this study investigated the effects of fragment shape and screw configuration on the mechanical behavior in the fixation of the TTO using the finite element (FE) method.

METHODS

FE TTO models with three fragment shapes and three screw configurations were developed. The three fragment shapes were a step cut, bevel cut, and straight cut. The screw configurations were two parallel horizontal and downward screws and two trapezoidal screws. A 1654-N upward tension force was applied on the tibia tubercle, and the distal end of the tibia was completely fixed.

RESULTS

The results indicated that the step cut resulted in higher stability than the bevel and straight cut, but the stress was higher as well. Among the screw configurations, two parallel downward screws resulted in the highest stability, given the same fragment shape. In the horizontal configuration, the step cut tibia developed the largest contact force to achieve stability of the bone fragment under loading.

CONCLUSION

The fragment shape with a step cut and fixation with two parallel horizontal or downward screws are suggested for TTO, while the trapezoidal screw configuration is not suggested. Furthermore, the downward screw configuration is a suitable strategy to reduce bone stress.

Computational comparison of bone cement and poly aryl-ether-ether-ketone spacer in single-segment posterior lumbar interbody fusion: a pilot study

Posterior lumbar interbody fusion (PLIF) with a spacer and posterior instrument (PI) via minimally invasive surgery (MIS) restores intervertebral height in degenerated disks. To align with MIS, the spacer has to be shaped with a slim geometry. However, the thin spacer increases the subsidence and migration after PLIF. This study aimed to propose a new lumbar fusion approach using bone cement to achieve a larger supporting area than that achieved by the currently used poly aryl-ether-ether-ketone (PEEK) spacer and assess the feasibility of this approach using a sawbone model. Furthermore, the mechanical responses, including the range of motion (ROM) and bone stress with the bone cement spacer were compared to those noted with the PEEK spacer by finite element (FE) simulation. An FE lumbar L3-L4 model with PEEK and bone cement spacers and PI was developed. Four fixing conditions were considered: intact lumbar L3-L4 segment, lumbar L3-L4 segment with PI, PEEK spacer plus PI, and bone cement spacer plus PI. Four kinds of 10-NM moments (flexion, extension, lateral bending, and rotation) and two different bone qualities (normal and osteoporotic) were considered. The bone cement spacer yielded smaller ROMs in extension and rotation than the PEEK spacer, while the ROMs of the bone cement spacer in flexion and lateral bending were slightly greater than with the PEEK spacer. Compared with the PEEK spacer, peak contact pressure on the superior surface of L4 with the bone cement spacer in rotation decreased by 74% (from 8.68 to 2.25 MPa) and 69.1% (from 9.1 to 2.82 MPa), respectively, in the normal and osteoporotic bone. Use of bone cement as a spacer with PI is a potential approach to decrease the bone stress in lumbar fusion and warrants further research.

Role of screw proximity in the fixation of transverse patellar fractures with screws and a wire

PURPOSE

Clinical and biomechanical studies have reported that using supportive screws and a wire instead of the common Kirschner wires for modified tension band wiring improves the stability of fractured patellae. However, the effect of screw proximity on the fixation of a fractured patella remains unclear. Therefore a numerical study was conducted to examine the effects of screw proximity on biomechanical responses in a simulated patellar fracture fixed using two parallel cannulated screws and anterior tension band wiring.

METHODS

A patellar model with a transverse fracture and loads simulating patellar tendon forces applied on the patella were used in the present simulation. The surgical fixation consisted of two 4.0-mm parallel partially threaded cannulated screws with a figure-of-eight tension band made using a 1.25-mm stainless steel wire. Biomechanical responses at two screw proximities, 5 and 10 mm from the leading edge of the patella, were investigated.

RESULTS

Superficial screw placement (5 mm) yielded higher stability, lower wire loads, and lower bone contact pressures than the deep placement (10 mm). The deep placement of screws exerted a higher load on the wire but a lower force on the screw than superficial placement did.

CONCLUSION

This is the first numerical study to examine the effects of screw location on the fixation of a fractured patella using cannulated screws and tension band wiring. Considering the favorable biomechanical responses, superficial placement (5 mm below the leading edge of the patella) is recommended for screw insertion when treating a transverse fractured patella.

Gap between the fragment and the tibia affects the stability of tibial tubercle osteotomy: A finite element study

Tibial tubercle osteotomy (TTO) is commonly performed in cases of complicated juxta-articular trauma or revision total knee arthroplasty. However, strategies for firmly fixing the resulting osteotomy bone fragment are not sufficiently understood. This study aims to investigate the effect of the location of the gap between the fragment and the tibia and with various fixed screw configurations on TTO stability, contact force on the fragment, and bone stress by using the finite element method. A TTO model with a 1-mm gap, either above or below the fragment, was developed. Furthermore, five screw configurations, including two parallel horizontal screws placed at 20- and 30-mm intervals, two parallel downward screws, two trapezoid screws, and two divergent screws, were used. A vertically upward 1600-N force was applied on the tibial tubercle to mimic a worst-case condition. Placing the fragment close to the superior cutting plane (above the gap) yielded greater stability and less stress on the bone than did placing it close to the inferior cutting plane. The superior cutting plane of the tibia generated the largest contact force on the superior plane of the fragment for static balance under loading. Additionally, among all screw configurations, the configuration involving two parallel downward screws resulted in the highest stability but also the greatest stress on the cortical bone. The fragment obtains a solid barrier and support from the tibia immediately after surgery to against the patellar tension force when the fragment is close to the superior cutting plane of the tibia.

Roles of the screw types, proximity and anterior band wiring in the surgical fixation of transverse patellar fractures: a finite element investigation

BACKGROUND

Cannulated screws with an anterior wire are currently used for managing transverse patellar fracture. However, the addition of anterior wiring with various types of screws via open surgery to increase the mechanical stability is yet to be determined. Hence, this study aimed to compare the mechanical behaviors of a fractured patella fixed with various screws types and at various screw locations with and without the anterior wire. The present study hypothesized that using the anterior wire reduces the fracture gap formation.

METHODS

A finite element (FE) model containing a fractured patella fixed with various types of cannulated screws and anterior wiring was created in this study. Three types of screws, namely partial thread, full thread, and headless compression screws, and two screw depths, namely 5 and 10 mm away from the anterior surface of the patella, were included. The effect of the anterior wire was clarified by comparing the results of surgical fixation with and without the wire. Two magnitudes and two loading directions were used to simulate and examine the mechanical responses of the fractured patella with various fixation conditions during knee flexion/extension.

RESULTS

Compared with partial thread and headless compression screws, the full thread screw increased the stability of the fractured patella by reducing fragment displacement, fracture gap formation, and contact pressure while increasing the contact area at the fracture site. Under 400-N in the direction 45°, the full thread screw with 5-mm placement reduced the gap formation by 86.7% (from 2.71 to 0.36 mm) and 55.6% (from 0. 81 to 0. 36 mm) compared with the partial thread screw with 10-mm placement, respectively without and with the anterior wire.

CONCLUSION

The anterior wire along with the full thread screw is preferentially recommended for maintaining the surgical fixation of the fractured patella. Without the use of anterior wiring, the full thread screw with 5-mm placement may be considered as a less invasive alternative; however, simple screw fixation at a deeper placement (10 mm) is least recommended for the fixation of transverse patellar fracture.

Biomechanical investigation of tibial tubercle osteotomy fixed with various screw configurations

INTRODUCTION

To date, the effects of various screw configurations on the stability of tibial tubercle osteotomy (TTO) are not completely understood. Hence, the first aim of this study is to evaluate the stability of TTO under various screw configurations. The second aim is to evaluate the internal stresses in the bone and the contact forces on the bone fragment that are developed by the tibia and screws in response to the applied load after the equilibrant is revealed.

METHODS

To calculate the biomechanical responses of the bone and screw under loading, finite element (FE) method was used in this study. Six types of screw configurations were studied in the simulation: two parallel horizontal screws placed at a 20 mm interval, two parallel horizontal screws placed at a 30 mm interval, two parallel upward screws, two parallel downward screws, two trapezoid screws, and two divergent screws. The displacement of the bone fragment, contact forces on the fragment, and the internal stress in the bone were used as indices for comparison.

RESULTS

Among all configurations, the configuration of two parallel downward screws yielded the highest stability with the lowest fragment displacement and gap opening. Although the maximum displacement of the TTO with the configuration of two parallel horizontal screws was slightly higher than that of the downward configuration, the difference was only 0.2 mm. The configuration of two upward screws resulted in the highest fragment displacement and gap deformation between the fragment and tibia. The stress of the osteotomized bone fragment was highest with the configuration of two upward screws.

CONCLUSION

Based on the present model, the current configuration of two parallel horizontal screws is recommended for TTO. If this is inappropriate in a specific clinical scenario, then the downward screw configuration may be used as an alternative. By contrast, the configuration of two parallel upward screws is least suggested for the fixation of TTO.

Biomechanical investigation of the type and configuration of screws used in high tibial osteotomy with titanium locking plate and screw fixation

Background

To maintain the corrected alignment after high tibial osteotomy (HTO), fixation with titanium locking plate and screws is widely used in current practice; however, screw breakage is a common complication. Thus, this study was to investigate the mechanical stability of HTO with locking plate and various screw fixations, including the length as well as the type.

Methods

A finite element (FE) model involving a distal femur, meniscus, and a proximal tibia with HTO fixed with a titanium locking plate and screws was created. The angle of the medial open wedge was 12°, and bone graft was not used. Two types of screws, namely conventional locking and far-cortical locking screws, with various lengths and configurations were used. At the proximal tibia, conventional locking screws with different lengths, 30 and 55 mm, were used; at the tibia shaft, different screw fixations including one-cortical, two-cortical, and far-cortical locking screws were used.

Results

The use of far-cortical locking screw generated the highest equivalent stress on the screws, which was four times (from 137.3 to 541 MPa) higher than that of the one-cortical screw. Also, it led to the maximum deformation of the tibia and a greater gap deformation at the osteotomy site, which was twice (from 0.222 to 0.442 mm) larger than that of the one-cortical screw. The effect of different locking screw length on tibia deformation and implant stress was minor.

Conclusion

Thus, far-cortical locking screws and plates increase interfragmentary movement but the screw stress is relatively high. Increasing the protection time (partial weight duration) is suggested to decrease the risk of screw breakage in HTO through fixation with titanium far-cortical locking screws and plates.

Comparison of Mechanical Stability of Elastic Titanium, Nickel-Titanium, and Stainless Steel Nails Used in the Fixation of Diaphyseal Long Bone Fractures

Elastic nails made of the nickel-titanium shape memory alloy (Nitinol) have been reported to control bone modeling in animal studies. However, the mechanical stability of the Nitinol nail in the fixation of long bone fractures remains unclear. This study compared mechanical stability among nails made of three materials, namely Nitinol, titanium, and stainless steel, in the fixation of long bone fractures. These three materials had identical shapes (arc length: π/2 and radius: 260 mm). A cylindrical sawbone with a 10-mm gap and fixed with two C-shaped elastic nails was used to examine the stability of the nails. A finite element (FE) model was developed based on the sawbone model. The end cap for elastic nails was not used in the sawbone test but was considered based on a constraint equation in FE simulation. The results of stability tests appeared to depend on the presence or absence of the end cap. In the sawbone test, the titanium nail yielded a higher ultimate force against the applied load than did the stainless steel and Nitinol nails before the gap completely closed; the difference in linear stiffness between the nails was nonsignificant. In FE simulation, the titanium nail produced smaller gap shortening than did stainless steel and Nitinol nails without the end cap; the difference in gap shortening between the nails was minor with the end cap. The titanium elastic nail should be a better choice in managing diaphyseal long bone fractures when the end cap is not used. For Nitinol and stainless steel nails, the end cap should be used to stop the nail from dropping out and to stabilize the fractured bone.