Finite element comparative analysis of three different internal fixation methods in the treatment of Pauwels type III femoral neck fractures.

BACKGROUND: Comparison of 4 cannulated lag screws (3 inverted triangular cannulated screws + anti-rotating screws;4 CLS), dynamic hip screws + derotational screws (DHS + DS), and femoral neck fixation system (FNS) in the treatment of Biomechanical properties of middle-aged Pauwels type III femoral neck fractures. METHODS: The femur CT data of a healthy young volunteer was selected and imported into Mimics software to construct a three-dimensional model of a normal femur. Pauwels type III femoral neck fractures were simulated according to the 70° fracture line. Use Geomagic and SolidWorks software to optimize and build CLS, DHS + DS, and FNS fracture internal fixation models. Finally, Ansys software was used to analyze the stress distribution, peak value, and maximum displacement of the proximal fracture fragment and internal fixation; the displacement distribution, and peak value of the fracture surface at the fracture end. RESULTS: ① The stress peaks of the proximal fracture fragments in the three groups were concentrated near the femoral calcar. The peak stress of the FNS group was the largest, and the DHS + DS group was the smallest. ②The displacement of the fracture fragments was all located at the top of the femur. The peak displacement of the FNS group was the largest, and the DHS + DS group was the smallest. ③ The internal fixation stress of the three groups is concentrated in the middle part of the device. The stress distribution of the first two groups of models is more uniform than that of FNS. The peak stress of FNS is the largest and the CLS is the smallest. ④ The internal fixed displacements are all located at the top of the model. The peak displacement of the CLS is the largest, and the DHS + DS is the smallest. ⑤ The displacement of the fracture surface is in the upper part of the fractured end. The peak displacement of the FNS group was the largest, and the DHS + DS group was the smallest. CONCLUSION: Compared with the other two internal fixation methods, dynamic hip screw + derotational screw (DHS + DS) showed good biomechanical stability. When Pauwels type III femoral neck fracture occurs in young adults, DHS + DS can be given priority as the preferred treatment for this type of fracture.

Finite element analysis of new headless compression supporting screw for the treatment of unstable femoral neck fracture.

BACKGROUND: Femoral neck fracture is an unsolved challenge in orthopedics. The complication rate in particular is high. There remains a lack of consensus on the optimal choice of internal fixation for unstable femoral neck fracture. OBJECTIVE: The study aimed to develop a new headless compression supporting screw (HCSS) for the treatment of unstable foemoral neck fracture. METHODS: We designed a new HCSS and used a femoral neck fracture (Pauwels III fracture) model (left, fourth-generation composite, Sawbones) and three-dimensional finite element analysis to compare the biomechanical performance of HCSSs with that of cannulated compression screws (CCSs) for treatment of unstable femoral neck fracture. RESULTS: Maximum displacement, peak von Mises stress, peak strain, and rotation for the HCSS were smaller than those for the CCS. The stress was more widely distributed for the HCSS, whereas the stress was concentrated for the CCS. CONCLUSIONS: The HCSS resulted in better biomechanical stability than that from the CCS. For Pauwels III fractures the HCSS exhibits better resistance to shear forces and better support, providing a new clinical treatment.

Biomechanical analysis of two medial buttress plate fixation methods to treat Pauwels type III femoral neck fractures.

BACKGROUND: Femoral neck fractures in young people are usually Pauwels Type III fractures. The common treatment method are multiple parallel cannulated screws or dynamic hip screw sliding compression fixation. Due to the huge shear stress, the rate of complications such as femoral head necrosis and nonunion is still high after treatment. The aim of our study was to compare the stabilities of two fixation methods in fixating pauwels type III femoral neck fractures. METHODS: All biomimetic fracture samples are fixed with three cannulated screws combined with a medial buttress plate. There were two fixation groups for the buttress plate and proximal fracture fragment: Group A, long screw (40 mm); Group B, short screw (6 mm). Samples were subjected to electrical strain measurement under a load of 500 N, axial stiffness was measured, and then the samples were axially loaded until failure. More than 5 mm of displacement or synthetic bone fracture was considered as construct failure. RESULTS: There were no significant differences in failure load (P = 0.669), stiffness (P = 0.842), or strain distribution (P > 0.05) between the two groups. CONCLUSIONS: Unicortical short screws can provide the same stability as long screws for Pauwels Type III Femoral Neck Fractures.

Biomechanical analysis for five fixation techniques of Pauwels-III fracture by finite element modeling.

BACKGROUND AND OBJECTIVES: There are many fixation methods for Pauwels- III fracture, the most common implants are Locking Plate (LP), Dynamic Hip Screw (DHS), Multiple Lag Screw (MLS), and mixed fixture (DHS+MLS) implants, the common procedure is HemiArthroplasty (HA). However, how these fixtures biomechanically function is not clear. The aims of this study are to compare the mechanical behaviors of these five implants by finite element modeling and determinate the most suitable procedure for individuals with Pauwels- III fractures. METHODS: We gathered 20 sets of femur images from CT scans in the *.dicom format first, and then processed them by using reverse engineering software programs, such as Mimics, Geomagic Studio, UG-8, Pro-Engineer and HyperMesh. Finally, we assembled and analyzed the five types of fixture models, the LP, DHS, MLS, DHS+LS and HA models, by AnSys. RESULTS: These numerical models of Pauwels III fractures, including fixators and a simulative HA, were validated by a previous study and a cadaver test. Our analytical findings include the following: the displacements of all fixtures were between 0.3801 and 1.0834 mm, and the differences were not statistically significantly different; the resulting average peaks in stress were e(Ha) = 43.859 ≤ d(LP) = 60.435 ≤ b(MLS) = 68.678 < c(LS+DHS) = 98.478 < a(DHS) = 248.595 in Mpa, indicating that the stress of DHS and DHS+LS are greater than those of LP, HA and MLS, while the last 3 models were not significantly different. CONCLUSIONS: To optimize the treatment for Pauwels III factures clinically, HA and LP should be proposed.

Hybrid triad provides fracture plane stability in a computational model of a Pauwels Type III hip fracture.

The study utilized finite element method to determine displacements and stresses in a set of Pauwels Type III femoral neck fractures repaired using 3 techniques (cannulated screws (Triad), sliding hip screw (SHS), and a Hybrid (SHS + cannulated screws). The research found that shear displacement doubled between the 65° and 75° fracture angles regardless of fixation construct. The SHS alone was the least stable construct, with highest construct stresses and shear displacement along the fracture plane. The stability of the Hybrid and Triad constructs were similar, but stress in the Hybrid was lower suggesting it would provide a higher load to failure than the Triad.

Abordaje de Smith Petersen modificado para fracturas de cuello femoral Pauwels III - Garden IV / Modified Smith Petersen approach to femoral neck fracture Pauwels III - Garden IV

El abordaje de Smith Petersen modificado (SPM), permite la reducción de fracturas del cuello femoral desde anterior, manteniendo la fijación a través de un abordaje lateral. Realizar la reducción bajo visión directa mejoraría la calidad de la reducción y los resultados en fracturas complejas de cuello femoral. MÉTODOS: Estudio retrospectivo de ocho pacientes con fracturas de cuello femoral Pauwels III/Garden IV secundarias a un accidente de alta energía operadas con abordaje SPM. Registramos el tiempo de evolución desde el accidente hasta la cirugía. Se realizó radiografía y tomografía axial computada postoperatoria. Seguimos los pacientes con radiografías mensuales hasta evidenciar consolidación de la fractura y casos de necrosis avascular. RESULTADOS: En promedio, los pacientes fueron operados 2,1 días tras el accidente y fueron seguidos con una mediana de 24,5 meses tras su cirugía. Siete de los ocho pacientes consolidaron. Sólo un caso presentó una no-unión que requirió de una prótesis total de cadera. No hubo casos de necrosis avascular. CONCLUSIÓN: Las fracturas de cuello femoral de alta energía en pacientes jóvenes son lesiones poco frecuentes. Aunque esta serie es pequeña, llama la atención que tratándose de lesiones desplazadas y con rasgos verticales no observamos casos de necrosis avascular, a pesar de algunos casos con prolongado tiempo de evolución desde el accidente hasta la cirugía. Creemos que esas fracturas deben operarse lo antes posible, pero que es más importante lograr una reducción anatómica en vez de retrasar algunas horas la cirugía. En nuestra experiencia, el abordaje de SPM facilita la reducción adecuada en fracturas complejas de cuello femoral.

Modified Smith Petersen Approach (MSP) allows an anterior reduction for femoral neck fractures, keeping the fixation through a lateral approach to the hip. Performing the reduction under direct visualization would improve the quality of the reduction and the outcomes in complex fractures of femoral neck. METHODS: Retrospective study including eight patients with femoral neck fracture classified as Pauwels III / Garden IV, in which MSP was performed. We kept record of the time from the accident until the final surgery. Post-operative studies included plain radiograph and CT scan. Monthly radiographic controls were obtained until fracture healing was achieved or radiological signs of avascular necrosis were found. RESULTS: Surgery was performed in an average of 2.1 days after the accident. Postoperative follow-up was an average of 24.5 month. Consolidation was achieved in seven of the eight patients, only one patient evolved into a nonunion of femoral neck which required a total hip arthroplasty. CONCLUSION: High energy femoral neck fractures in young patients are infrequent injuries. Even though this is a small series of patients it comes to our attention that being displaced fractures with vertical fracture lines we didn't find any case of avascular necrosis despite some of the cases the prolonged timing since the accident to surgery. We believe that this type of fracture should be treated as soon as possible but is more important to achieve an anatomical reduction than pass over the 12 hours threshold. In our experience MSP approach facilitates the achievement of an adequate reduction and complex femoral neck fractures.

A meta-analysis of different internal fixation strategies of Pauwels III femoral neck fractures / 上海交通大学学报（医学版）

Objective • To compare the clinical and functional outcomes of cannulated screw (CS) with sliding hip screw (SHS) in the fixation of Pauwels III femoral neck fractures systematically. Methods • In the meta-analysis, articles were searched from Pubmed database, Embase database, Cochrane library, CNKI database, and Sinomed database. The selected articles were analyzed by Revman 5.26 software. Results • Six clinical studies met the inclusion criteria. A total of 350 patients including 213 with CS fixations and 137 with SHS fixations were pooled in the meta-analysis. The results showed that the non-union rate in SHS group was significantly lower than that in CS group. However, the surgery time was significantly shorter in CS group. Conclusion • SHS fixation has the advantage of reducing postoperative non-union rate in Pauwels III femoral neck fractures, but the operative process is relatively complicated, which seemingly causes more blood loss during surgery, and may lead to a less satisfactory functional recovery.

Augmentation by cerclage wire improves fixation of vertical shear femoral neck fractures-A biomechanical analysis.

BACKGROUND: Femoral neck fractures in young individuals are typically vertical shear fractures. These injuries are difficult to stabilize due to a significant varus displacement force across the hip with weight bearing. The purpose of this study was to evaluate the biomechanical stability offered by the addition of an augmented wire to conventional inverted triangle triple screw fixation for stabilizing vertical shear femoral neck fracture. METHODS: Sixteen medium 4th-generation synthetic composite femurs (Sawbones Pacific Research Laboratories, Vashon, WA) were divided into two groups. Vertical osteotomy was performed to mimic Pauwels III femoral neck fracture. Group A (n=8) was fixed with three parallel 6.5-mm cannulated screws (Stryker) with washer in inverted triangle configuration. In group B (n=8), all the screws were set using methods identical to group A, with the addition of the cerclage wire. Both groups were tested with nondestructive axial compression test at 7 and 25° of valgus stress, respectively. Then axial cyclic loading test with 1000N was applied for 1000 cycles, and interfragmentary displacement was measured with Fastrak magnetic tracking system (Polhemus, Colchester, VT, USA). Finally, destructive axial compression test was conducted at 7°of valgus stress. RESULTS: Axial stiffness showed that group B had a 66% increase (879N/mm vs. 1461N/mm, P<0.01) at 7° valgus and a 46% increase (1611N/mm vs. 2349N/mm, P<0.01) at 25° valgus in comparison with group A. Interfragmentary fracture displacement after cyclic loading was significantly less for group B compared with group A (0.34 vs 0.13mm, P=0.0016). For axial failure load, there was 42% increase in group B compared with group A (2602N/mm vs. 3686N/mm, P=0.0023). CONCLUSIONS: Our study demonstrates that the addition of a cerclage wire to inverted triangle triple screws provides substantial improvement in mechanical performance regarding fixation of vertically oriented femoral neck fractures when compared with the conventional construct. Our study provides support from a mechanical analysis perspective for the reported clinical usefulness of the cerclage wire.