Biomechanical Comparison of Three Different Intramedullary Nails for Fixation of Unstable Basicervical Intertrochanteric Fractures of the Proximal Femur: Experimental Studies

Finite element analysis of proximal femur bionic nail for treating intertrochanteric fractures in osteoporotic bone

This study compared the biomechanical characteristics of proximal femur bionic nail (PFBN) and proximal femoral nail antirotation (PFNA) in treating osteoporotic femoral intertrochanteric fractures using finite element analysis. Under similar bone density, the PFBN outperforms the PFNA in maximum femoral displacement, internal fixation displacement, stress distribution in the femoral head and internal fixation components, and femoral neck varus angle. As the bone density decreases, the PFBN's biomechanical advantages over PFNA become more pronounced. This finding suggests that the PFBN is superior for treating osteoporotic intertrochanteric femoral fractures.

Intramedullary Impaction of the Basicervical Component Is Determinant of Fixation Failure in a Simple Two-Part Pertrochanteric Fracture

OBJECTIVES

To evaluate initial fracture morphology influences on outcomes in simple 2-part pertrochanteric fracture, with a focus on the basicervical component and its initial impaction.

METHODS

DESIGN

A retrospective cohort series.

SETTING

Single Level I Trauma Center.

PATIENTS SELECTION CRITERIA

Patients older than 60 years with intertrochanteric fractures between 2011 and 2022 were retrospectively reviewed. Inclusion criteria comprised simple 2-part pertrochanteric fractures (Orthopaedic Trauma Association [OTA]/Arbetisgemeinschaftfur Osteosynthesefragen [AO] 31-A1.2) with a basicervical component who underwent cephalomedullary nailing and had a minimum follow-up of 6 months. Patients were divided whether the basicervical component was impacted into the medullary canal (intramedullary impaction [II] group) or displaced beyond the medullary canal (extramedullary [E] group). Exclusion criteria encompassed pathologic fractures, nondisplaced fractures, and basicervical neck fractures (OTA/AO 31-B3).

OUTCOME MEASUREMENTS AND COMPARISONS

Reduction status was assessed as unacceptable if the head and neck (proximal) fragment was positioned intramedullary with respect to the distal fragment in either the anterior posterior or cross-lateral x-ray and acceptable otherwise. In addition, the degree of impaction on x-ray and CT scans (coronal, sagittal, axial) at injury was analyzed as a risk factor for failure. Revision rates and lag screw sliding over 15 mm were compared between the II and E groups.

RESULTS

Hundred fifteen patients (95 female, average age 80 years) were included. The II group (n = 58) compared with E group (n = 57) showed more acceptable postoperative reductions (57% vs. 81%, P = 0.001), but significantly higher fixation failure (16% vs. 3.5%, P = 0.048) and fracture collapse (28% vs. 7%, P = 0.01). II was identified as a significant independent predictor for failure (odds ratio 5.64, 95% confidence interval, 2.14-16.9, P < 0.001) with more than 19.5-mm impaction in sagittal CT scan as the threshold linked to increased failure risk.

CONCLUSIONS

This study highlights the significance of specific intertrochanteric fracture patterns, particularly II of a basicervical component and impaction severity (≥19.5 mm), as drivers of fixation failure.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Meta-analysis of the clinical efficacy of the Gamma3 nail vs Gamma3U-blade system in the treatment of intertrochanteric fractures

BACKGROUND

The traditional Gamma3 nail is a mainstream treatment for femoral intertrochanteric fractures. Literature reports that the Gamma3U-blade system can increase the stability of the Gamma3 nail and reduce complication incidence. However, comparative studies between the Gamma3U-blade and Gamma3 systems are limited; hence, this meta-analysis was performed to explore the clinical efficacy of these two surgical methods.

AIM

To investigate the clinical efficacy of Gamma3 and Gamma3 U-blade for intertrochanteric fractures.

METHODS

A computerized search for Chinese and English literature published from 2010 to 2022 was conducted in PubMed, Cochrane, CNKI, Wanfang, and VIP databases. The search keywords were gamma 3, gamma 3 U blade, and intertrochanteric fracture. Additionally, literature tracking was performed on the references of published literature. The data were analyzed using Revman 5.3 software. Two individuals checked the inputs for accuracy. Continuous variables were described using mean difference and standard deviation, and outcome effect sizes were expressed using ratio OR and 95% confidence interval (CI). High heterogeneity was considered at (P < 0.05, I2 > 50%), moderate heterogeneity at I2 from 25% to 50%, and low heterogeneity at (P ≥ 0.05, I2 < 50%).

RESULTS

Following a comprehensive literature search, review, and analysis, six articles were selected for inclusion in this study. This selection comprised five articles in English and one in Chinese, with publication years spanning from 2016 to 2022. The study with the largest sample size, conducted by Seungbae in 2021, included a total of 304 cases. Statistical analysis: A total of 1063 patients were included in this meta-analysis. The main outcome indicators were: Surgical time: The Gamma3U blade system had a longer surgical time compared to Gamma3 nails (P = 0.006, I2 = 76%). Tip-apex distance: No statistical significance or heterogeneity was observed (P = 0.65, I2 = 0%). Harris Hip score: No statistical significance was found, and low heterogeneity was detected (P = 0.26, I2 = 22%). Union time: No statistical significance was found, and high heterogeneity was detected (P = 0.05, I2 = 75%).

CONCLUSION

Our study indicated that the Gamma3 system reduces operative time compared to the Gamma3 U-blade system in treating intertrochanteric fractures. Both surgical methods proved to be safe and effective for this patient group. These findings may offer valuable insights and guidance for future surgical protocols in hip fracture patients.

Unstable Vancouver B1 periprosthetic femoral fracture fixation: A biomechanical comparison between a novel C-shaped memory alloy implant and cerclage wiring

BACKGROUND

To compare the biomechanical stability of a novel, C-shaped nickel-titanium shape memory alloy (SMA) implant (C-clip) with traditional cerclage wiring in the fixation of a Vancouver B1 (VB1) periprosthetic femoral fracture (PFF).

METHODS

In total, 18 synthetic femoral fracture models were constructed to obtain unstable VB1 fracture with an oblique fracture line 8 cm below the lesser trochanter. For each model, the distal portion was repaired using a 10-hole locking plate and four distal bi-cortical screws. The proximal portion was repaired using either three, threaded cerclage wirings or three, novel C-shaped implants. Specimens underwent biomechanical testing using axial compression, torsional and four-point bending tests. Each test was performed on three specimens.

RESULTS

The C-clip was statistically significantly stronger (i.e., stiffer) than cerclage wiring in the three biomechanical tests. For axial compression, medians (ranges) were 39 (39-41) and 35 (35-35) N/mm, for the C-clip and cerclage wiring, respectively. For torsion, medians (ranges) were, 0.44 (0.44-0.45) and 0.30 (0.30-0.33) N/mm for the C-clip and cerclage wiring, respectively. For the four-point bending test, medians (ranges) were 39 (39-41) and 28 (28-31) N/mm; for the C-clip and cerclage wiring, respectively.

CONCLUSION

Results from this small study show that the novel, C-shaped SMA appears to be biomechanically superior to traditional cerclage wiring in terms of stiffness, axial compression, torsion and four-point bending, and may be a valuable alternative in the repair of VB1 PFF. Further research is necessary to support these results.

Lessons learned from biomechanical studies on cephalomedullary nails for the management of intertrochanteric fractures. A scoping review

INTRODUCTION

The increasing socioeconomic need for optimal treatment of hip fractures in combination with the high diversity of available implants has raised numerous biomechanical questions. This study aims to provide a comprehensive overview of biomechanical research on the treatment of intertrochanteric fractures using cephalomedullary devices.

METHODS

Following the PRISMA-P guidelines, a systematic literature search was performed on 31.12.2022. The databases PubMed/MEDLINE and Web of Science were searched. Scientific papers published between 01.01.2000 - 31.12.2022 were included when they reported data on implant properties related to the biomechanical stability for intertrochanteric fractures. Data extraction was undertaken using a synthesis approach, gathering data on criteria of implants, sample size, fracture type, bone material, and study results.

RESULTS

The initial search identified a total of 1459 research papers, out of which forty-three papers were considered for final analysis. Due to the heterogeneous methods and parameters used in the included studies, meta-analysis was not feasible. A comprehensive assessment of implant characteristics and outcome parameters was conducted through biomechanical analysis. Various factors such as proximal and distal locking, nail diameter and length, fracture model, and bone material were thoroughly evaluated.

CONCLUSION

This scoping review highlights the need for standardization in biomechanical studies on intertrochanteric fractures to ensure reliable and comparable results. Strategies such as avoiding varus, maintaining a sufficient tip-apex-distance, cement augmentation, and optimizing lesser trochanteric osteosynthesis enhance construct stability. Synthetic alternatives may offer advantages over cadaveric bone. Further research and meta-analyses are required to establish standardized protocols and enhance reliability.

A novel intramedullary nail design of intertrochanteric fracture fixation improved by proximal femoral nail antirotation

A proper and reliable fracture fixation is important for fracture healing. The proximal femoral intramedullary nail (IN), such as proximal femoral nail anti-rotation (PFNA) or Gamma nail, is widely used for intertrochanteric fracture fixation. However, it still suffers considerable stress concentrations, especially at the junction between the nail and the blade or lag screw. In this study, we propose a novel intramedullary nail design to enhance the intramedullary nail integrity by introducing a bolt screw to form a stable triangular structure composed of the nail, the lag screw, and the bolt screw (PFTN, Proximal femoral triangle nail). Systematic finite element numerical simulations were carried out to compare the biomechanical performances of PFTN and PFNA under both static and dynamic loads during the postures of ascending and descending stairs. The simulation results highlight the advantages of the proposed PFTN design with lower stresses, less stress concentration, and higher structure stability.

Structure-mechanical analysis of various fixation constructs for basicervical fractures of the proximal femur and clinical implications; finite element analysis

OBJECTIVE

This present study was conducted to determine the structural-mechanical stability of various fixation constructs through finite element (FE) analysis following simulation of a basicervical fracture and to introduce the clinical implications.

MATERIALS AND METHODS

We simulated fracture models by using a right synthetic femur (SAWBONES®). We imported the implant models into ANSYS® for placement in an optimal position. Five assembly models were constructed: (1) multiple cancellous screws (MCS), (2) FNS (femoral neck system®), (3) dynamic hip screw (DHS), (4) DHS with anti-rotation 7.0 screw (DHS + screw), and PFNA-II (Proximal Femoral Nail Antirotation-II®). The femur model's distal end was completely fixed and 7° abducted. We set the force vector at a 3° angle laterally and 15° posteriorly from the vertical ground. Analysis was done using Ansys® software with von Mises stress (VMS) in megapascals (MPa) and displacement (mm) RESULTS: The displacements of the proximal femur were 10.25 mm for MCS, 9.66 mm for DHS, 9.44 mm for DHS + screw, 9.86 mm for FNS, and 9.31 mm for PFNA-II. The maximum implant VMS was 148.94 MPa for MCS, 414.66 MPa for DHS, 385.59 MPa for DSH + screw, 464.07 MPa for FNS, and 505.07 MPa for PFNA-II. The maximum VMS at the fracture site was 621.13 MPa for MCS, 464.14 MPa for DHS, 64.51 MPa for DHS + screw, 344.54 MPa for FNS, and 647.49 MPa for PFNA-II. The maximum VMS at the fracture site was in the superior area with the high point around the posterior screw in the MCS, anterosuperior corner in the DHS, the posteroinferior site of the FNS, and posterosuperior site around the entry point in the PFNA-II. In the DHS + screw, the stresses were distributed evenly and disappeared at the maximum VMS fracture site.

CONCLUSION

Based on the fracture site and implant's stress distribution, the model receiving the optimal load was a DHS + screw construct, and the FNS implant could be applied to anatomically reduced fractures without comminution. Considering the high-stress concentration around the entry point, a PFNA-II fixation has a high probability of head-neck fragment rotational instability.

U-blade gamma 3 vs. gamma 3 nails for intertrochanteric hip fracture: Meta-analysis

Background and Objective

Intertrochanteric fracture is a growing problem in the traumatology department. The use of intramedullary devices has increased, representing the first treatment option in intertrochanteric fractures. U-Blade devices appeared to avoid rotation of the femoral head over the femoral neck. The aim of this study was to conduct a meta-analysis of the surgical treatment of intertrochanteric fractures comparing in terms of safety and efficacy the U-Blade Gamma 3 nail vs. the conventional Gamma 3 nail.

Methods

A literature search for intertrochanteric fracture 31A1-31A3 according to the AO foundation/orthopaedic trauma association (AO/OTA) classification was performed. Baseline characteristics of each article were obtained; radiological outcomes were tip apex distance (TAD), sliding distance (mm), cut-out rate, and lateralization rate. Surgery time (min) was also recorded. A meta-analysis was performed with ReviewManager 5.4.

Results

Five retrospective studies (n = 993 patients) were included. With respect to TAD and sliding distance, there were no differences between two groups [mean difference (MD) 0.47, 95% confidence interval (CI), -0.46 to 1.40] and (MD 0.39, 95% CI, 0.13-0.66). The cut-out rate and lateralization rate did not show differences between two groups (p > 0.05). Finally, surgery time was significantly higher in the U-Blade Gamma 3 group (MD -4.84, 95% CI, -7.22 to -2.46).

Conclusions

The use of U-Blade Gamma 3 did not show significant differences in the radiological results compared with the conventional Gamma 3 nail.

Finite Element Analysis of Proximal Femur Bionic Nail (PFBN) Compared with Proximal Femoral Nail Antirotation and InterTan in Treatment of Intertrochanteric Fractures

Objective

To compare the biomechanical properties of proximal femur bionic nail (PFBN), proximal femoral nail antirotation (PFNA) and InterTan in the treatment of elderly intertrochanteric fractures AO/OTA 31‐A1.3 by finite element analysis.

Methods

We used Mimics, Unigraphics and other software to establish normal femur and AO/OTA 31‐A1.3 fracture models, and reconstructed PFBN, PFNA and InterTan intramedullary nail models, and assembled them on the fracture model. The ANSYS software was used to compare the femoral von Mises stress distribution, deformation distribution, and internal fixation stress distribution of each group under a load of 2100 N.

Results

It could be seen that the femoral maximum stress, femoral maximum displacement, and maximum stress of internal fixation of the PFBN group were lower than those in the PFNA group and the InterTan group. The maximum femoral stress of the PFBN was 190.25 MPa, while the maximum stress of the femur of the PFNA and InterTan groups were 238.41 Mpa and 226.97 Mpa. The maximum femoral displacement of each group were located at the top of the femoral head, and the maximum displacement of the PFBN group was 14.373 mm, and the maximum displacement values of the PFNA and InterTan groups were 19.49 and 15.225 mm. For the stress distribution of intramedullary nail, the maximum stress of the three kinds of internal fixation was located on the main nail. The maximum stress of PFBN was 1191.8 MPa, compared with 2142.8 MPa for PFNA and 1702.3 MPa for InterTan. And the maximum stress on the PFBN pressure nail was 345.35 MPa, compared with 868.6 MPa for the PFNA spiral blade and 545.5 MPa for InterTan interlocking twin nails.

Conclusion

Compared with PFNA and InterTan, PFBN has better mechanical properties. The biomechanical characteristics of PFBN are more advantageous than PFNA and InterTan internal fixation system in the treatment of femoral intertrochanteric fractures.

Biomechanical comparison of the femoral neck system and the dynamic hip screw in basicervical femoral neck fractures

The purpose of this study was to compare the fixation stability of proximal fragments and the mechanical characteristics in proximal femur models of basicervical femoral neck fracture fixed by the femoral neck system (FNS) versus the dynamic hip screw. The mean axial stiffness was 234 ± 35 N/mm in the FNS group and 253 ± 42 N/mm in the DHS group, showing no significant difference (p = 0.654). Mean values for x-axis rotation, y-axis rotation, and z-axis rotation after cycle load were 2.2 ± 0.5°, 6.5 ± 1.5°, and 2.5 ± 0.6°, respectively, in the FNS group and 2.5 ± 0.7°, 5.8 ± 2.1°, and 2.2 ± 0.9°, respectively, in the DHS group, showing no significant differences (p = 0.324, p = 0.245, and p = 0.312, respectively). The mean values of cranial and axial migration of screws within the femoral head were 1.5 ± 0.3 and 2.1 ± 0.2 mm, respectively, in the FNS group and 1.2 ± 0.3 and 2.4 ± 0.3 mm, respectively, in the DHS group, showing no significant differences (p = 0.425 and p = 0.625, respectively). The average failure load at vertical load was 1342 ± 201 N in the FNS group and 1450 ± 196 N in the DHS group, showing no significant difference (p = 0.452). FNS fixation might provide biomechanical stability comparable to that of DHS for treating displaced basicervical femoral neck fractures in young adults.

The lateral femoral wall thickness on the risk of post-operative lateral wall fracture in intertrochanteric fracture after DHS fixation: A finite element analysis

BACKGROUND

Patients with a lateral femoral wall (LFW) fracture were reported to have high rates of re-operation and complication. Although the LFW thickness was a reliable predictor of post-operative or intra-operative LFW fracture, there was a paucity of literature evaluating the critical stress distributions on the femur and screws of intertrochanteric fractures treated with dynamic hip screw (DHS). This study aimed to investigate the biomechanical performance of intertrochanteric fractures with different LFW thickness treated with DHS device.

METHODS

A three-dimensional model of the proximal femur was established by computed tomography images. The intertrochanteric fracture model with three different LFW thickness (10 mm, 20.5 mm and 30 mm, respectively) was created, which was fixed by DHS. The von Mises stress on the proximal femur, lateral femoral wall, DHS and the total displacement of the device components were evaluated and compared for three different LFW thickness model.

RESULTS

The maximum von Mises stress in the proximal fragment of the 10 and 20.5 mm model increased by 80.56% and 57.97% when compared with the 30 mm model. The peek von Mises stress around the blade entry point of the 10 mm and 20.5 mm model increased by 89.26% and 66.39% when compared with the 30 mm model. The peek von Mises in the DHS located near the junction of the barrel and side plate of each model and the 30 mm model had the smallest von Mises stress compared with the other two models. Furthermore, the maximum displacement in the 30 mm model was much smaller than that in the10mm model and 20 mm model.

CONCLUSIONS

The intertrochanteric fracture with a thinner LFW tended to have a higher risk of LFW fracture stabilized by a DHS device. Thus, the intertrochanteric fractures with a thinner LFW should not be treated by DHS alone and the intramedullary nail or an addition of trochanteric stabilization plate(TSP) was recommended.

Biomechanical performance of short and long cephalomedullary nail constructs for stabilizing different levels of subtrochanteric fracture

INTRODUCTION

The aim of this study was to assess biomechanical performance of short and long Cephalomedullary nail constructs consisting of different number of distal screw for stabilizing different levels of subtrochanteric fracture.

MATERIALS AND METHODS

The femur obtained from computed tomography scanner was used to create a transverse fracture at 15 mm (level A), 35 mm (level B), and 55 mm (level C) below the lesser trochanter. Short and long Cephalomedullary nails were virtually inserted to the fractured femur. Four-node tetrahedral element was used to build up finite element (FE) models for biomechanical analysis. The analysis focused on post-operative stage of partial weight-bearing.

RESULTS

Stress on the implant localized at the surface between lag screw/nail and distal screw/nail. Short Cephalomedullary nail exhibited higher stress than long Cephalomedullary nail. The stress in short Cephalomedullary nail could be reduced by using two distal screws fixation and the fracture at level A produced less stress than that of level B and C. Either short or long nail with two distal screws is sufficient to withstand the stress magnitude produced from the physiologic load. When single dynamic distal screw was used, stress on implant, elastic strain at fracture gap, and bone stress reached the high values. Elastic strain of the fracture gap at level C were less than that of level A and B, but no statistically significant difference. There was no proximal cancellous bone damage observed from the FE analysis.

CONCLUSIONS

Long Cephalomedullary nail with at least two distal locking screws remains a proper implant for subtrochanteric fracture fixation in overall locations. However, short Cephalomedullary nail with two distal screws may be a candidate for a high subtrochanteric fracture. Single dynamic screw insertion is strongly not recommended with either short or long nail regarding implant failure.

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.

Biomechanical study on the stability and strain conduction of intertrochanteric fracture fixed with proximal femoral nail antirotation versus triangular supporting intramedullary nail

OBJECTIVES

Based on the features of the three-dimensional spatial structure of the proximal femoral trabeculae, we developed a bionic triangular supporting intramedullary nail (TSIN) for the treatment of the femoral intertrochanteric fracture. The current study aimed to compare the mechanical stability and restoration of mechanical conduction between proximal femoral nail antirotation (PFNA) and TSIN to fix the intertrochanteric fractures.

METHODS

Firstly, five sets of PFNA and TSIN with the same size were selected and fixed on a biomechanical testing machine, and strain gauges were pasted on the main nail, lag screw, and supporting screw to load to the vertical load to 600 N, and the displacement and strain values were recorded. Secondly, formalin-preserved femurs were selected, and the left and right femurs of the same cadaver were randomly divided into two groups to prepare intertrochanteric femur fractures (AO classification 31-A1), which were fixed with PFNA (n = 15) and TSIN (n = 15), respectively. Sixteen sites around the fracture line were chosen to paste strain gauges and loaded vertically to 600 N, and then, the fracture fragment displacement and strain values were recorded. Finally, a 10,000-cycle test ranging from 10 to 600 N was conducted, and the cycle number and displacement value were recorded.

RESULTS

The overall displacement of PFNA was 2.17 ± 0.18 mm, which was significantly greater than the displacement of the TSIN group (1.66 ± 0.05 mm, P < 0.05) under a vertical load of 600 N. The strain below the PFNA lag screw was 868.29 ± 147.85, which was significantly greater than that of the TSIN (456.02 ± 35.06, P < 0.05); the strain value at the medial side of the PFNA nail was 444.00 ± 34.23, which was significantly less than that of the TSIN (613.57 ± 108.00, P < 0.05). Under the vertical load of 600 N, the displacement of the fracture fragments of the PFNA group was 0.95 ± 0.25 mm, which was significantly greater than that of the TSIN group (0.41 ± 0.09 mm, P < 0.05). The femoral specimens in the PFNA group showed significantly greater strains at the anterior (1, 2, and 4), lateral (7, 9, and 10), posterior (11), and medial (15 and 16) sites than those in the TSIN group (all P < 0.05). In the cyclic compression experiment, the displacements of the PFNA group at 2000, 4000, 6000, 8000, and 10,000 cycles were 1.38 mm, 1.81 mm, 2.07 mm, 2.64 mm, and 3.58 mm, respectively, which were greater than the corresponding displacements of the TSIN group: 1.01 mm, 1.48 mm, 1.82 mm, 2.05 mm, and 2.66 mm (P₈₀₀₀ = 0.012, P₁₀₀₀₀ = 0.006).

CONCLUSIONS

The current study showed that TSIN had apparent advantages in stability and stress conduction. TSIN enhanced the stability of intertrochanteric fractures, particularly in superior fracture fragments, improved stress conduction, reduced the stress in the anterior and medial femur, and restored the biomechanical properties of the femur.

Additional use of anti-rotation U-blade (RC) decreases lag screw sliding and limb length inequality in the treatment of intertrochanteric fractures

The purpose of this study is to compare the cut-out rate and sliding distance associated with limb length inequality between operations using a standard non-sliding lag screw versus those using a non-sliding lag screw with U-blade (RC) in the Gamma3 nail. This is a retrospective review of two case series involving different lag screws for the Gamma3 nail. Propensity score matching analysis was used to adjust the confounding factors. A comparative analysis of 304 patients who treated with Gamma3 nail with either a standard non-sliding lag screw or a U-Blade (RC) lag screw was performed. Between 2014 and 2018, 152 patients were treated with U-blade (RC) lag screws, and these patients were matched with those treated with standard lag screws. There was no significant difference in cut-out rate between groups. However, additional use of anti-rotation U-blade (RC) could significantly decrease lag screw sliding, with the group treated with U-Blade (RC) lag screws exhibiting shorter sliding, especially in AO/OTA31 A2 and A3 fractures. Also, in A2 and A3 fractures, the mean lag screw sliding distance was greater than that seen in A1 fractures in both groups. These findings can help trauma surgeons choose the proper implant to reduce leg length inequality.

The safety and accuracy of the fluoroscopic imaging during proximal femoral fixation: A computerized 3D reappraisal of the joint penetration risk

BACKGROUND

To assess the success of proximal cephalomedullary nailing operations for treating trochanteric fractures, surgeons utilize 2D fluoroscopy to observe the relative positions of the femoral head and the implant. One distance-based risk parameter, observed from the AP and Lateral projections, is the Tip-Surface Distance(TSD) that dictates how close to the outer cortex should the implant tip be residing to avoid post-surgical complications such as cut-out or joint penetration. In this study, the safety and the accuracy of the orthogonal fluoroscopic imaging were evaluated.

METHODS

A femoral head model was created and the risk zone was defined as a hemispherical shell of 5 mm thickness beneath the subchondral cortex, which should not be violated during screw insertion. The remaining hemisphere beneath the risk zone was designated as the safe zone. To assess the effect of head size, each simulation was conducted for 34, 47, and 60 mm diameter(D_femur) femoral heads. The rate of safe zone violation was calculated for all possible screw endpoints with a TSD of at least 5 mm on fluoroscopic orthogonal views (TSD_AP and TSD_Lat).

RESULTS

The minimum risk of joint penetration was achieved when the TSD_AP/TSD_Lat ratio was 1. For D_femur of 34 mm there was a risk of 91.7% of the safe zone violation when each TSD_AP and TSD_Lat were 5 mm and 0% for 9 mm. For D_femur of 47 mm, the risk was 92.2% for 5 mm and 0% for 11 mm. For D_femur of 60 mm, the risk was 92.3% for 5 mm and 0% for 13 mm. Safety maps were constructed for all possible TSD combinations for 34, 47, and 60 mm femoral heads.

CONCLUSIONS

Depending solely on the orthogonal fluoroscopic images is not a safe and accurate technique for assessing joint penetration risk during proximal femoral fixation due to the spherical geometry of the femoral head. The screw tip can lie completely outside of the femoral head even when it appears inside, in both orthogonal fluoroscopic views. Evidently, when using TSD, more stringent distance limits should be chosen, contrary to the recommended 5 mm limit. Our safety maps for TSD combinations may be used to check the security of the implantation.

Benefit of lag screw placement by a single- or two-screw nailing system in elderly patients with AO/OTA 31-A2 trochanteric fractures

Objective

To retrospectively analyze the clinical outcomes of two intramedullary fixation devices, the INTERTAN nail and Gamma3 nail, for treatment of AO/OTA 31-A2 trochanteric fractures in elderly patients.

Methods

In total, 165 elderly patients underwent treatment for AO/OTA 31-A2 trochanteric fractures in our hospital from June 2017 to June 2018 (INTERTAN group, n = 79; Gamma3 group, n = 86). All patients underwent radiological and clinical investigations and were followed up for an average of 12 months. Age, sex, fracture type, surgical time, intraoperative blood loss, fracture healing time, and complications were compared between the two groups.

Results

The surgical time was significantly shorter and the intraoperative blood loss volume was significantly lower in the Gamma3 than INTERTAN group (58.2 ± 2.5 vs. 81.7 ± 14.2 minutes and 170 ± 29 vs. 220 ± 16 mL, respectively). However, there were no significant differences in the reduction quality, hospital stay, fracture healing time, Harris hip score, postoperative complications, or 1-year postoperative mortality.

Conclusion

Both INTERTAN and Gamma3 nails may be effective for surgical treatment of AO/OTA 31-A2 trochanteric fractures in elderly patients. However, the Gamma3 nail was superior to the INTERTAN nail in terms of surgical time and intraoperative blood loss.

Design and biomechanical study of slide-poking external fixator for hip fracture

Background

Femoral head collapse and coxa vara lead to internal fixator failure in elderly patients with hip fracture. External fixator application is an optimal choice; however, the existing methods have many disadvantages.

Methods

Type 31-A1.3 hip fracture models were developed in nine pairs of 1-year-old fresh bovine corpse femur specimens. Each left femur specimen was fixed by a dynamic hip screw (control group), and each right femur specimen was fixed by the slide-poking external fixator (experimental group). Vertical loading and torsion tests were then performed in both groups.

Results

In the vertical loading experiment, a 1000-N load was implemented. The mean vertical downward displacement of the femoral head in the experimental and control groups was 1.49322 ± 0.116280 and 2.13656 ± 0.166374 mm, respectively. In the torsion experiment, when the torsion was increased to 10.0 Nm, the mean torsion angle in the experimental and control groups was 7.9733° ± 1.65704° and 15.4889° ± 0.73228°, respectively. The slide-poking external fixator was significantly more resistant to compression and rotation than the dynamic hip screw.

Conclusion

The slide-poking external fixator for hip fractures that was designed and developed in this study can provide sufficient stability to resist compression and rotation in hip fractures.

The effect of medullary fill on varus collapse in AO 31A3 intertrochanteric (reverse obliquity) fracture treated with cephalomedullary nails

OBJECTIVE

Cephalomedullary nails are tools commonly used for surgical fixation in proximal femoral fractures. The most common complications in their use are varus collapse and screw cutout of the femoral head. The objective of this study is to examine the effects of intramedullary nail movement on varus collapse and screw cutout.

MATERIALS AND METHODS

The study was conducted on 70 composite femur models treated with PFNA. We divided the femurs into 4 groups based on the differences in nail diameter, fracture type and filling of the distal intramedullary area. All femurs were exposed to axial cyclic loading. Each femur was examined in terms of intramedullary nail movement and amount of erosions in femoral medulla [amount of erosion in femoral head (FT distance), amount of erosion in femoral neck (FB distance), amount of erosion in trochanteric major (TB distance) and expansion of trochanter tip (TT distance)].

RESULTS

We found that degree of nail movement in the intramedullary region was inversely correlated with nail diameter and directly correlated with instability of fracture. One of the parameters used to evaluate varus development, FB distance, was affected by the degree of intramedullary nail movement and fracture type. TB distance was affected by nail diameter.

CONCLUSIONS

Nail diameter and fracture type are effective in intramedullary nail movement. Varus collapse progress is accelerated by the increase in nail movement in the intramedullary region. Thus, we conclude that it is important to strengthen diaphyseal adherence, which decreases intramedullary movement of the nail.

LEVEL OF EVIDENCE

III; well-design case control study.

Three-dimensional finite element analysis of intramedullary nail with different materials in the treatment of intertrochanteric fractures

Intramedullary nails are the common treatment options for femoral intertrochanteric fractures. However, aseptic loosening is considered to be one of the primary forms of failure that can be caused by the stress shielding between the bone and implants. The matching in mechanical properties of implant and bone is a key issue to prevent this failure. Polyetheretherketone (PEEK) and Function-graded (FG) materials are widely used in clinical because of their excellent mechanical properties. In this study, to investigate the biomechanical behaviors of intramedullary nails made of Ti-6Al-4V alloy, Stainless Steel (SS), PEEK and two FG materials, three-dimensional finite element models of intertrochanteric fracture femur with intramedullary nail were constructed with ABAQUS. The maximum von Mises stress on the femoral fracture surface fixed by PEEK intramedullary nail was the largest, followed by FG intramedullary nail, which help stimulate bone growth and subsequently reduce fracture healing time. Compared with traditional metal intramedullary nails, PEEK and FG implants might increase von Mises stress along the same path in the proximal femur. The results showed that PEEK and FG intramedullary nails obviously changed the stress distributions in the bone and reduced stress shielding. This finding indicated that PEEK and FG intramedullary nails have the potential to become alternatives to the conventional metal intramedullary nails.

Biodegradable cement augmentation of gamma nail osteosynthesis reduces migration in pertrochanteric fractures, a biomechanical in vitro study

BACKGROUND

Cut-out of gamma nail often results from poor primary bone stability, suboptimal reduction (varus) and excentric placement of the head element which may lead to "instability" and frequently requires revision. Various studies have shown that augmentation with polymethylmethacrylate cement increases the primary stability of osteosynthesis. However, it has not yet been widely used in fracture treatment due to certain disadvantages, e.g., the lack of osteointegration, the formation of an interface membrane or the presence of toxic monomers. Few studies show that biodegradable bone cements increase the stability of osteosynthesis in different anatomical regions and therefore could be an alternative to polymethylmethacrylate cement in the treatment of pertrochanteric fractures.

METHODS

Two biomechanical situations were simulated using 24 Sawbones (simple and multifragmentary pertrochanteric fractures; AO-classification 31-A1 and 31-A2. Both groups were stabilized using the Gamma3® nailing system with and without biodegradable bone cement. Sawbones underwent the same cyclic loading test, simulating 10.000 gait cycles loading the bones with three times body weight. Migration was determined by comparing computed tomography scans recorded before and after the mechanical testing. The three-dimensional migration of the lag screw was calculated, and the rotation of the head around the longitudinal axis was determined.

FINDINGS

Biodegradable cement reduced migration by approximately 35% in 31-A1 fractures (25.4% in 31-A2 fractures) and the rotation of the head around the lag screw by approximately 37% in 31-A1 fractures (17.8%, 31-A2).

INTERPRETATION

Use of biodegradable bone cement improved the primary stability of gamma nail osteosynthesis in the biomechanical model.

[Effectiveness of proximal femoral nail anti-rotation for high plane intertrochanteric femur fractures]

Objective

To evaluate the effectiveness of proximal femoral nail anti-rotation (PFNA) in treatment of high plane intertrochanteric femur fractures.

Methods

A retrospective analysis was performed on 33 patients who underwent closed reduction and PFNA fixation for high plane intertrochanteric femur fracture between January 2016 and June 2019. There were 12 males and 21 females with an average age of 75.1 years (mean, 47-89 years). The fractures were caused by falling from height in 21 cases, by traffic accident in 7 cases, and by other injuries in 5 cases. Fractures were classified as type A in 14 cases and type B in 19 cases according to self-defined fracture classification criteria; and as type 31-A1.2 in 14 cases and as type 31-A2.2 in 19 cases according to AO/Orthopedic Trauma Association (AO/OTA) classification criteria. The time from injury to operation was 2-5 days (mean, 2.7 days). The operation time, intraoperative blood loss, hospital stay, fracture reduction quality, fracture healing time, internal fixation failure, and Parker-Palmer score were recorded.

Results

The operation time was 40-75 minutes (mean, 55 minutes). The intraoperative blood loss was 50-150 mL (mean, 64 mL). The hospital stay was 5-15 days (mean, 8.7 days). All incisions healed by first intention. Twenty-eight patients were followed up 12-18 months with an average of 13.6 months. The fracture reduction quality was rated as excellent in 9 cases (32.1%), good in 17 cases (60.7%), and poor in 2 cases (7.1%) by Chang's criteria. Parker-Palmer score was 6-9 (mean, 7.9) at last follow-up.

Conclusion

High plane intertrochanteric femur fracture is a special type of intertrochanteric fracture, which can be diagnosed by imaging examination. PFNA fixation can achieve satisfactory results and prevent the occurrence of internal fixation failure effectively.

The cement-bone bond is weaker than cement-cement bond in cement-in-cement revision arthroplasty. A comparative biomechanical study

This study compares the strength of the native bone-cement bond and the old-new cement bond under cyclic loading, using third generation cementing technique, rasping and contamination of the surface of the old cement with biological tissue. The possible advantages of additional drilling of the cement surface is also taken into account. Femoral heads from 21 patients who underwent a total hip arthroplasty performed for hip arthritis were used to prepare bone-cement samples. The following groups of samples were prepared. A bone—cement sample and a composite sample of a 6 weeks old cement part attached to new cement were tested 24 hours after preparation to avoid bone decay. Additionally, a uniform cement sample was prepared as control (6 weeks polymerization time) and 2 groups of cement-cement samples with and without anchoring drill hole on its surface, where the old cement polymerized for 6 weeks before preparing composite samples and then another 6 weeks after preparation. The uniaxial cyclic tension-compression tests were carried out using the Zwick-Roell Z020 testing machine. The uniform cement sample had the highest ultimate force of all specimens (n = 15; R_m = 3149 N). The composite cement sample (n = 15; R_m = 902 N) had higher ultimate force as the bone-cement sample (n = 31; R_m = 284 N; p <0.001). There were no significant differences between composite samples with 24 hours (n = 15; R_m = 902 N) and 6 weeks polymerization periods (n = 22; R_m = 890 N; p = 0.93). The composite cement samples with drill hole (n = 16; R_m = 607 N) were weaker than those without it (n = 22; R_m = 890 N; p < 0.001). This study shows that the bond between the old and new cement was stronger than the bond between cement and bone. This suggests that it is better to leave the cement that is not loosened from the bone and perform cement in cement revision, than compromising bone stock by removal of the old cement with the resulting weaker cement-bone interface. The results support performing cement-in-cement revision arthroplasty The drill holes in the old cement mantle decrease cement binding strength and are not recommended in this type of surgery.

Cyclic Damage Accumulation in the Femoral Constructs Made With Cephalomedullary Nails

Background: The purpose of this study was to evaluate the risk of peri-prosthetic fracture of constructs made with cephalomedullary (CM) long and short nails. The nails were made with titanium alloy (Ti-6Al-4V) and stainless steel (SS 316L).

Methods: Biomechanical evaluation of CM nail constructs was carried out with regard to post-primary healing to determine the risk of peri-implant/peri-prosthetic fractures. Therefore, this research comprised of, non-fractured, twenty-eight pairs of cadaveric femora that were randomized and implanted with four types of fixation CM nails resulting in four groups. These constructs were cyclically tested in bi-axial mode for up to 30,000 cycles. All the samples were then loaded to failure to measure failure loads. Three frameworks were carried out through this investigation, Michaelis–Menten, phenomenological, and probabilistic Monte Carlo simulation to model and predict damage accumulation.

Findings: Damage accumulation resulting from bi-axial cyclic loading in terms of construct stiffness was represented by Michaelis–Menten equation, and the statistical analysis demonstrated that one model can explain the damage accumulation during cyclic load for all four groups of constructs (P > 0.05). A two-stage stiffness drop was observed. The short stainless steel had a significantly higher average damage (0.94) than the short titanium nails (0.90, P < 0.05). Long titanium nail group did not differ substantially from the short stainless steel nails (P > 0.05). Results showed gender had a significant effect on load to failure in both torsional and bending tests (P < 0.05 and P < 0.001, respectively).

Interpretation: Kaplan–Meier survival analysis supports the use of short titanium CM nail. We recommend that clinical decisions should take age and gender into consideration in the selection of implants.

Outcomes of U-Blade Lag Screw for Cephalomedullary Fixation of Unstable Trochanteric Femur Fractures: A Case Control Study

Background:

Unstable trochanteric femur fractures in elderly patients with osteoporosis are still challenging. Gamma3 nail with the U-blade lag screw (U-blade gamma nail) has been developed to improve mechanical stability of proximal femoral fragment. This study aimed to compare the clinical and radiologic outcomes of U-blade gamma nail to proximal femoral nail antirotation (PFNA), and standard Gamma3 nail (gamma nail) for unstable trochanteric femur fractures.

Methods:

A retrospective matched-pair case study was performed with U-blade gamma nail, PFNA, and gamma nail. During 2012-2018, 970 patients with unstable trochanteric femur fractures were reviewed. Matching criteria were set as follows: 1) sex; 2) age (± 3 years); 3) body mass index (± 2 kg/m²); 4) bone mineral density (± 1 T-score in femur neck). Finally, a total of 159 patients were enrolled. We assessed the tip-apex distance (TAD), neck shaft angle, and hip screw sliding distance using plain radiographs. Also, we evaluated the clinical outcomes with Koval’s grade and fixation failure during 2 years.

Results:

The mean postoperative TAD was not significantly different among the 3 groups (p = 0.519). However, the change in the TAD at 1 year (p = 0.027) and 2 years (p = 0.008) after surgery was significantly smaller in U-blade gamma nail group compared with PFNA and gamma nail group. The hip screw sliding distance at 1 year (p = 0.004) and 2 years (p = 0.001) after surgery was significantly smaller in U-blade gamma nail group compared with PFNA and gamma nail group. However, there was no significant difference of Koval’s grade and fixation failure among the 3 groups (p = 0.535).

Conclusion:

U-blade gamma nail showed favorable radiologic results in terms of the change in the hip screw position. However, U-blade gamma nail was not superior to PFNA and gamma nail in clinical outcomes.

Biomechanical comparison of medial sustainable nail and proximal femoral nail antirotation in the treatment of an unstable intertrochanteric fracture

AIMS

Restoration of proximal medial femoral support is the keystone in the treatment of intertrochanteric fractures. None of the available implants are effective in constructing the medial femoral support. Medial sustainable nail (MSN-II) is a novel cephalomedullary nail designed for this. In this study, biomechanical difference between MSN-II and proximal femoral nail anti-rotation (PFNA-II) was compared to determine whether or not MSN-II can effectively reconstruct the medial femoral support.

METHODS

A total of 36 synthetic femur models with simulated intertrochanteric fractures without medial support (AO/OTA 31-A2.3) were assigned to two groups with 18 specimens each for stabilization with MSN-II or PFNA-II. Each group was further divided into three subgroups of six specimens according to different experimental conditions respectively as follows: axial loading test; static torsional test; and cyclic loading test.

RESULTS

The mean axial stiffness, vertical displacement, and maximum failure load of MSN-II were 258.47 N/mm (SD 42.27), 2.99 mm (SD 0.56), and 4,886 N (SD 525.31), respectively, while those of PFNA-II were 170.28 N/mm (SD 64.63), 4.86 mm (SD 1.66), and 3,870.87 N (SD 552.21), respectively. The mean torsional stiffness and failure torque of MSN-II were 1.72 N m/° (SD 0.61) and 16.54 N m (SD 7.06), respectively, while those of PFNA-II were 0.61 N m/° (SD 0.39) and 6.6 N m (SD 6.65), respectively. The displacement of MSN-II in each cycle point was less than that of PFNA-II in cyclic loading test. Significantly higher stiffness and less displacement were detected in the MSN-II group (p < 0.05).

CONCLUSION

The biomechanical performance of MSN-II was better than that of PFNA-II, suggesting that MSN-II may provide more effective mechanical support in the treatment of unstable intertrochanteric fractures. Cite this article: Bone Joint Res 2020;9(12):840-847.

Management of Low-Energy Basicervical Proximal Femoral Fractures by Proximal Femoral Nail Anti-Rotation

Objective

To evaluate clinical and radiological outcomes of proximal femoral nail anti‐rotation (PFNA‐II) devices and demonstrate the effectiveness of PFNA‐II for the treatment of basicervical fractures in elderly patients.

Methods

A retrospective review of all patients treated with PFNA‐II for a proximal femoral fracture between January 2013 and February 2017 at three different institutions (Shanghai General Hospital, Shanghai Punan Hospital and Shanghai Seventh People's Hospital) was conducted. The X‐ray films were strictly reviewed by three trauma surgeons and a professional radiology doctor. Patients over 60 years of age who met the following criteria were included: (i) sustained low‐energy trauma; (ii) a two‐part fracture; (iii) fracture line located at the base of the femoral neck and that was medial to the intertrochanteric line and exited above the lesser trochanter but was more lateral than a classic transcervical fracture. Follow‐up time should be longer than 6 months. A total of 52 patients who met the inclusion criteria were selected. The average age at diagnosis was 75.1 years (range, 63–91 years); 13 patients were men and 39 were women. The same proximal femoral nail anti‐rotation devices and the same surgical procedures were applied to all patients. Postoperative radiographic union time and modified Harris hip scores were used as major indicators for evaluating the effectiveness of surgery.

Results

The average follow‐up period was 22.5 months (18.5, 23.9, and 21.2 months, respectively) and radiographic unions were observed at an average of 19.6 weeks (range, 12–28 weeks). The patients were evaluated immediately after surgery, as well as 6 weeks, 3 months, 6 months, 1 year, and 2 years postoperatively. Of the 49 patients, 38 had good reduction qualities (75.5%), 9 acceptable (18.3%), and 3 poor (6.1%). Radiographic union was confirmed in all fractures at an average of 19.6 weeks (range, 12–28 weeks). The mean Harris hip score was 84.9 (range, 65–99): excellent in 9 patients (18.36%), good in 30 (61.22%), medium in 8 (16.32%), and poor in 2 (4.08%). Slight persistent pain occurred in 3 patients, but these patients could still walk with the help of a cane. Two patients had symptoms of excessive telescoping. Eight patients experienced postoperative medical complications, mainly pneumonia and urinary tract infection.

Conclusion

Based on the clinical and radiological outcomes, the PFNA‐II devices provide strong rotational stability and excellent clinical prognosis, and are an appropriate treatment option for basicervical proximal femoral fracture in elderly patients.

Procedure for Femoral Intertrochanteric Fractures using the "Three-Finger Method" Assisted by Proximal Femoral Nail Antirotation

Objective

To assess long‐term follow‐up evaluations for the treatment of femoral intertrochanteric fractures with the “three‐finger method” assisted by proximal femoral nail antirotation (PFNA).

Methods

From January 2010 to January 2017, 123 patients were selected and followed for the treatment of femoral intertrochanteric fractures with PFNA assisted by the “three‐finger method” (application of the index finger, middle finger, and ring finger in the process of surgery to assist PFNA). There were 56 male patients and 67 female patients aged 52–93 years with an average age of 75.6 years, and 88 cases were due to a fall and 35 due to a traffic accident injury. The femoral necks were fixed with PFNA assisted by the “three‐finger method” applying the following procedure: traction reduction, determining the incision, inserting the needle, and placing screw. The Harris hip score, postoperative complications, hip pain and function status were statistically analyzed to evaluate the surgical efficacy and to discuss the surgical technique of the “three‐finger method” assisted by PFNA.

Results

According to the Harris scoring criteria, patients were followed for 1, 2, 4, 6, and 8 years, and the good outcomes of patients were recorded. The excellent and good rate of 87% was the highest in the second year of follow‐up. Then, the rate decreased following the eighth year of follow‐up. The excellent and good rate of 82.7% was the lowest. The patients with incisions healed well, there were no instances of fat liquefaction or infection. There were three cases of effusion, the rate was 2.4%. The secretions were cultured, and no bacterial growth was found. After treatment of the wound, it healed, and the spiral blade used for the femoral head did not wear out. There was one case of femoral head necrosis. There was no significant correlation between hip pain and sex and age (P > 0.05), and the function of the hip joint was significantly correlated with the age of the patients (P < 0.05).

Conclusion

The “three‐finger method” in the process of surgery to assist PFNA for the treatment of patients with intertrochanteric fractures of the femur simplified the operation steps, reduced the operation difficulty, shortened the operation time, improved the operation efficiency, and reduced the incidence of postoperative complications.

Gamma3 nail with U-Blade (RC) lag screw is effective with better surgical outcomes in trochanteric hip fractures

The objective of this retrospective study was to investigate the surgical outcomes of AO/OTA 31 A1-3 trochanteric fractures treated with the new-generation Gamma3 nail with U-Blade (RC) lag screw and to analyze the risk factors related to fixation failure. A total of 318 consecutive patients who underwent cephalomedullary nailing using Gamma3 nail with U-Blade lag screw for trochanteric hip fractures between September 2015 and June 2018 were enrolled. The average age was 80 years and most patients (69%) were women. The mean follow-up was 12.2 months with a minimum of 6 months. 309 (97.2%) showed bony union with a mean time to union of 13.5 ± 8.7 weeks. Cut-out occurred in 2 patients (0.6%) and 7 patients showed excessive collapse (≥15 mm) of the proximal fragment. These 9 patients were assigned to the failure group. The presence of a basicervical fracture component and comminution of the anterior cortex on preoperative 3-D CT showed a significant association with fixation failure, including cut-out, although comminution of the anterior cortex was the only independent risk factor for fixation failure on multivariate logistic regression analysis. Gamma3 nail with U-Blade lag screw showed favorable results for trochanteric hip fractures, with low cut-out rate (0.6%). However, more caution is required in treating trochanteric fractures with a basicervical fracture component and anterior cortex comminution even with this nail.

Mechanical Assessment of Fatigue Characteristics between Single- and Multi-Directional Cyclic Loading Modes on a Dental Implant System

Mechanical testing based on ISO 14801 standard is generally used to evaluate the performance of the dental implant system according to material and design changes. However, the test method is difficult to reflect on the clinical environment because the ISO 14801 standard does not take into account the various loads from different directions during chewing motion. In addition, the fracture pattern of the implant system can occur both in the horizontal and the vertical directions. Therefore, the purpose of this study was to compare fatigue characteristics and fracture patterns between single directional loading conditions based on the ISO 14801 standard and multi-directional loading condition. Firstly, the static test was performed on five specimens to derive the fatigue load, and the fatigue load was chosen as 40% of the maximum load measured in the static test. Subsequently, the fatigue test was performed considering the single axial/occlusal (AO), AO with facial/lingual (AOFL) and AO with mesial/distal (AOMD) directions, and five specimens were used for each fatigue loading modes. In order to analyze the fatigue characteristics, the fatigue cycle at the time of specimen fracture and displacement change of the specimen every 500 cycles were measured. Field emission scanning electron microscopy (FE-SEM) was used to analyze the fracture patterns and the fracture surface. Compared to the AO group, the fatigue cycle of the AOFL and AOMD groups showed lower about five times, while the displacement gradually increased with every 500 cycles. From FE-SEM results, there were no different surface morphology characteristics among three groups. However, the AOMD group showed a vertical slip band. Therefore, our results suggest that the multi-directional loading mode under the worst-case environment can reproduce the vertical fracture pattern in the clinical situation and may be essential to reflect on the dental implant design including connection types and surface treatments.

The early failure of the gamma nail and the dynamic hip screw in femurs with a wide medullary canal. A biomechanical study of intertrochanteric fractures

BACKGROUND

Intertrochanteric fractures may occur in a bone with a wide medullary canal that may lead to significant mobility of a intramedullary nail, contrary to an extramedullary device. This study evaluates the Dynamic Hip Screw and the gamma nail in AO 31.A2.1 fractures in these circumstances.

METHODS

Synthetic femora with canals drilled to 18 mm were used. Five fixation types were examined: a 2 - hole and a 4 - hole Dynamic Hip Screw with a 2 - hole plate, a standard gamma nail with dynamic and static distal locking and a long gamma nail. The specimens were tested with cyclic axial loading, from 500 N increasing of 50 N increments in each cycle. Force at failure, overall stiffness, stiffness at the fracture site, location and mode of failure were recorded.

FINDINGS

The short gamma nails dislocated into varus under preload because the nail migrated laterally. The Dynamic Hip Screw was initially stable, but some specimens rotated around the lag screw. The gamma nail was rotationally stable. Both implants failed through femur fracture. The long gamma nailed failed by screw cut - out at forces lower than the ultimate force of the short gamma nail.

INTERPRETATION

This study shows that the gamma nail is unstable in a large medullary canal but offers better rotational stability of the proximal fragment. A modification of the nail design or the operative technique may be considered.

Finite element analysis of two cephalomedullary nails in treatment of elderly reverse obliquity intertrochanteric fractures: zimmer natural nail and proximal femoral nail antirotation-ΙΙ

Background

More elderly patients are suffering from intertrochanteric fractures. However, the choice of internal fixation is still controversial, especially in the treatment of unstable intertrochanteric fracture; thus, previous implants continue to be improved, and new ones are being developed. The purpose of our study was to compare the biomechanical advantages between the zimmer natural nail (ZNN) and proximal femoral nail antirotation-II (PFNA-II) in the treatment of elderly reverse obliquity intertrochanteric fractures.

Methods

A three-dimensional finite element was applied for reverse obliquity intertrochanteric fracture models (AO31-A3.1) fixed with the ZNN or PFNA-II. The distribution, peak value and position of the von Mises stress and the displacement were the criteria for comparison between the two groups.

Results

The stresses of the internal fixation and femur in the ZNN model were smaller than those in the PFNA-II model, and the peak values of the two groups were 364.8 MPa and 171.8 MPa (ZNN) and 832.3 MPa and 1795.0 MPa (PFNA-II). The maximum amount of displacement of the two groups was similar, and their locations were the same, i.e., in the femoral head vertex (3.768 mm in the ZNN model and 3.713 mm in the PFNA-II model).

Conclusions

The displacement in the two models was similar, but the stresses in the implant and bone were reduced with the ZNN. Therefore, the ZNN implant may provide biomechanical advantages over PFNA-II in reverse obliquity intertrochanteric fractures, as shown through the finite element analysis. These findings from our study may provide a reference for the perioperative selection of internal fixations.

Optimized Dental Implant Fixture Design for the Desirable Stress Distribution in the Surrounding Bone Region: A Biomechanical Analysis

The initial stability of a dental implant is known to be an indicator of osseointegration at immediate loading upon insertion. Implant designs have a fundamental role in the initial stability. Although new designs with advanced surface technology have been suggested for the initial stability of implant systems, verification is not simple because of various assessment factors. Our study focused on comparing the initial stability between two different implant systems via design aspects. A simulated model corresponding to the first molar derived from the mandibular bone was constructed. Biomechanical characteristics between the two models were compared by finite element analysis (FEA). Mechanical testing was also performed to derive the maximum loads for the two implant systems. CMI IS-III active (IS-III) had a more desirable stress distribution than CMI IS-II active (IS-II) in the surrounding bone region. Moreover, IS-III decreased the stress transfer to the nerve under the axial loading direction more than IS-II. Changes of implant design did not affect the maximum load. Our analyses suggest that the optimized design (IS-III), which has a bigger bone volume without loss of initial fixation, may minimize the bone damage during fixture insertion and we expect greater effectiveness in older patients.