Interfragmentary motion assessment for three different fixation techniques of femoral neck fractures in young adults

Abstract

Background:

Vertical femoral neck fractures in the youth could be happened in high-energy accidents, and because of dominant shearing forces, this fracture is considered as a troublesome injury with a controversy regarding selection of the best fixation method.

Objective:

The long term goal of this quasi-experimental study was to find the more stable fixation method among cannulated screws (CSs), proximal femoral locking plate (PFLP), and dynamic hip screw with derotational screw (DHS+DS) for this kind of fracture.

Methods:

Twelve fresh-frozen cadaveric femurs were assigned to three groups that were matched for mean bone mineral density and stiffness of intact bone. Vertical fractures were artificially mimicked in the specimens and fixed using three different implants, i.e. CSs, PFLP, and DHS+DS. Then, the samples were tested under incremental, cyclic, and failure loading phases.

Results:

The differences in all biomechanical parameters were statistically significant among tested groups ( $p < 0.05$ ). All biomechanical parameters for the DHS+DS method of fixation are significantly different from those corresponding to CSs ( $p < 0.05$ ). There were no significant differences in failure load and failure energy between the PFLP and CSs techniques ( $p > 0.05$ ). Also, there were no significant differences in relative stiffness and femoral head displacement between the PFLP and DHS+DS groups ( $p > 0.05$ ).

Conclusions:

Based on the clinical assumption that restricted weight-bearing regimen is recommended in the postoperative rehabilitation protocol, the results of this study suggest that the priority order of selection for the stable fixation implant of vertical femoral neck fracture in young patients is DHS+DS, then PFLP, and finally CSs.

Keywords

Vertical femoral neck fracture fracture fixation static loading cyclic loading stability interfragmentary movement

1. Introduction

Femoral neck fractures in young patients typically result from a high-energy trauma, such as a motor-vehicle accident. A substantial axial load with the hip in an abducted position is required for the femoral neck fracture in these young individuals. Moreover, the fracture pattern has a tendency to be vertically oriented, and this kind of fracture is subjected to more shear forces than compression forces. Hence, this kind of injury is biomechanically less stable [1–5]. Anatomic reduction and internal fixation with an emphasis on preservation of the blood supply to the femoral head are the treatment goals for these patients. Because of several reported complications such as osteonecrosis (10% to 45%), nonunion (10% to 30%), and loss of fixation (8% to 19%, depending on the method of fixation), surgical care of this fracture is intricate [1,5]. A recent study of patients between fifteen and fifty years old showed that the fracture displacement and the quality of the reduction were the two most important factors which determine the progression of osteonecrosis in young patients with a femoral neck fracture [4]. However, only a few biomechanical studies have evaluated the fixation stability of vertically oriented fractures of the femoral neck (Pauwels’ III femoral neck fracture) to date [5–10].

Due to controversy regarding which method of fixation is the best option, the long term goal of this study was to find the more stable fixation method among selected implants for this kind of fracture. This study consisted of comparing the biomechanical stability of cadaveric bone samples for 3 different fracture fixation techniques, i.e. cannulated screws (CSs), dynamic hip screw with derotational screw (DHS+DS), and proximal femoral locking plate (PFLP). Recent biomechanical studies showed that the construct stiffness of fixed-angle devices to be superior to that of cannulated screws alone for the fixation of Pauwels’ III femoral neck fracture [6–9,11]. Also, previous studies of femoral neck fractures have measured instability of the fracture after fixation through the apparent increase in the fracture gap after osteotomy and reduction [11]. The experimental techniques used in this study applied motion capture analysis to evaluate relative motions between the fractured fragments. By applying this tool, undesirable features of fixation techniques such as toggling and shear displacements that are the signs of instability and inappropriate resistance against shearing forces which results in failure of fracture union can be investigated for vertical femoral neck fracture. Thus, stability of fixed fracture, which is a prerequisite of primary bone healing [10,12,13], was investigated in this study.

2. Materials and methods

2.1. Specimens

Twelve fresh-frozen cadaveric femurs including two women and ten men with no known previous history of hip pathology were harvested at autopsy. It should be noted that this investigation, which was approved by the research ethical committee of Tehran University of Medical Sciences, and was conducted in conformity with ethical principles of research. Moreover, the informed consents for extracting required samples from donors’ corpse were officially obtained.

The average age of donors was 36.33 ± 12.64 years (range, 23–56 years), and they had died in accidents or of acute disease without known long periods of immobilization. The bone mineral density and the intact stiffness of each specimen were measured by DEXA scanning and mechanical testing, respectively. Moreover, the specimens were assigned to 3 groups matched for the mean bone mineral density and stiffness of intact bone. In order to maintain the mechanical properties of harvested samples, the specimens were cleaned of soft tissue and stored at −20°C. All samples were thawed at room temperature for 6 hours before testing, and sprayed intermittently with normal saline to keep them hydrated [7,10,14].

2.2. Preparation of samples

Vertical fractures were artificially mimicked in the specimens by an orthopaedic surgeon, and the broken specimens were fixed using 3 different kinds of implants by the same surgeon (Fig. 1). Under fluoroscopic guidance, all specimens were predrilled prior to the osteotomy in order to assist with anatomic reduction and determining the specific size of implant for each specimen. For each sample, a vertical osteotomy was created with a band saw in the transcervical region, simulating a Pauwels’ III femoral neck fracture. The osteotomy extended from the superior femoral neck to the basicervical region to create a fracture oriented at 70 degrees to the horizontal. Partially creation of the osteotomy, inserting guide wires to connect the femoral head and shaft with screws, and after that completing the osteotomy process were steps of modeling vertical femoral neck fractures fixed by different implants. Also, this process was used to maximize the anatomic reduction of the fracture once implants were placed [5,7].

Fig. 1.

(a) Fractured femurs fixed by three internal fixation implants, i.e. proximal femoral locking plate (PFLP), dynamic hip screw with derotational screw (DHS+DS), and cannulated screws (CSs). (b) X-ray images of fixed samples with different fixation methods, i.e. PFLP, DHS+DS, and CSs.

Fig. 1.

(Continued.)

2.3. Fixation methods

In CSs group, three 7.3 mm stainless steel cannulated screws (thread length 32 mm) were inserted parallel into the femoral head in an inverted triangle configuration. The most inferior screw was positioned in the calcar region, above the lesser trochanter. The two cephalad screws were inserted superiorly, 5 mm from the anterior and posterior cortices of the femoral neck, and 5 mm from subchondral bone [7,10]. In DHS+DS group, a 135-degree, 3-hole dynamic hip screw plate, made of stainless steel, was positioned with the central screw directed into the middle of the femoral head. The tip of the screw was seated 5 to 10 mm away from subchondral bone. Three 4.5 mm cortical screws were used to fix the side plate to the femoral shaft. A superior neck 7.3-mm cannulated cancellous derotational lag screw was inserted parallel to the central screw [9,10]. Finally, in PFLP group, a fixed angle proximal femoral locking plate, made of stainless steel, was secured with 2 locking screws in the femoral head: one 7.3-mm cannulated conical screw at 95 degrees to the plate shaft, and one 5.0-mm cannulated conical screw at 110 degrees to the plate shaft. The ends of both screws were positioned 5 mm away from subchondral bone. The side plate was fixed to the proximal femur using four 4.5-mm non locking screws [10]. It is noteworthy that all implants and screws used in this study were made by Pooyandegan Pezeshki Pardis (3P Company).

2.4. Testing protocol

After simulating fixed vertical fracture of femoral neck, all samples were positioned in 25 degrees of adduction, and loaded using a quasi-acetabulum fixture in an incremental; cyclic; and failure phases (Fig. 2) [10,14]. To simulate partial weight-bearing in the immediate postoperative period, the loading steps included [7,10,14–17]: (I) Incremental loading: each specimen was loaded to a maximum of 700 N at a rate of 1 mm/min displacement before and after fixation; (II) Cyclic Loading: each fixed sample was tested under sinusoidal cyclic loading by applying 100–700 N force at a frequency of 3 Hz for 10,000 cycles in which the number of cycles approximates the expected interval for fracture consolidation [10,15]; and (III) Failure loading: survived specimens were loaded at a rate of 1 mm/min to reach failure criterion, defined as downward femoral head displacement or fracture displacement greater than 5 mm, observation of instability in load-displacement curve, fracture extension beyond the plane of the osteotomy, penetration of the femoral head by the fixation device, or permanent implant deformation [10,15]. It should be noted that failure criterion used in this study was based on the fracture displacement of 5 mm or more.

Fig. 2.

Test setup, red arrow shows downward femoral head displacement.

2.5. Motion capture analysis

In regard to measuring interfragmentary movement, position of makers, video recording, and post-processing steps are elaborated on as follow. Five pairs of markers (three on the anterior surface and two on the posterior side) were placed around the osteotomy, 10 mm apart from each other, as well as with one marker on the femoral shaft, and the corresponding marker on the adjacent femoral head (Fig. 3) [10,12,13]. Digital Casio EX-FH100 camcorders (10.1 MP High Speed Digital Camera, 10x Ultra Wide Angle Zoom, CMOS Shift Image Stabilization, and 3.0 inch LCD) were used to trace relative movement of each pair of markers during the loading phases. To measure two-dimensional movements of fracture fragments in the posterior and anterior aspects of the human femur, anterior and posterior camcorders were positioned at a distance of 35 cm and perpendicular to the plane of movement (Fig. 3). Before loading, for each aspect, a calibration frame consisting of a graph paper was placed on the plane of motion, and the camcorder was focused on the markers and zoomed in until the calibration object represented 1280 pixels × 720 pixels. As a result, each pixel equals to 0.1 mm in distance. Hence, the relative positions of the fractured fragments were traced during loading by using HD movie recordings (30 fps) [10]. For two-dimensional motion capture analyses of fracture fragments, each videotape of static loading phase was converted to the frames with the rate of 1 fps, and 160 frames were extracted from recorded movies for the cyclic loading. Then, the obtained frames were converted to the appropriate videos and imported into the SkillSpector program, V.1.3.2 (Video4-coach, Denmark) for future analyses [10].

Fig. 3.

(a) Femoral neck viewed from: (I) anterior side, and (II) posterior side, showing the osteotomy with visible markers. Locations of markers are identified: 1) ant-inf, 2) ant-mid, 3) ant-sup, 4) pos-inf, and 5) post-sup. (b) Test setup that shows (I) position of calibration frame and (II) position of camcorders.

Using Eq. (1), see below, the pixel locations can be transformed into relative interfragmentary motion in order to assess the movement of the fracture gap. In this equation, $RM$ is the femoral head motion relative to the shaft; $X_{H}$ and $X_{S}$ are the locations of the markers on the head and shaft, respectively, in X direction; $Y_{S}$ and $Y_{H}$ are the locations of the markers on the shaft and head, respectively, in Y direction [10,12]. $\begin{matrix} (1) & RM = \sqrt{{(X_{H} - X_{S})}^{2} + {(Y_{H} - Y_{S})}^{2}} . \end{matrix}$

Considering the orientation of the fracture plane relative to the global X axis (θ), transferring the marker location to the local coordinate system was possible by using Eqs (2)–(4), where ( $x_{L}$ , $y_{L}$ ) is the local coordinate location of the marker, θ is the orientation of the fracture plane with respect to the global x axis, ( $X_{1}, Y_{1}$ ) is the position of the lower marker on the fracture plane, ( $X_{2}, Y_{2}$ ) is the position of the upper marker on the fracture plane, and ( $X_{G}, Y_{G}$ ) is the global coordinate location of the marker (see Fig. 4). It is worth mentioning that changes in relative position of each pair of markers on the x axis of the local coordinate system, parallel to the fracture line, show shear movement of fractured fragments. Also, changes in relative position of each pair of markers on the y axis of the local coordinate system (perpendicular to the fracture line) correspond to axial motion of the fractured fragments [10,12] $\begin{array}{l} (2) & θ = {tan}^{- 1} ((Y_{2} - Y_{1}) / (X_{2} - X_{1})), \\ (3) & x_{L} = (X_{G} - X_{1}) cos θ - (Y_{G} - Y_{1}) sin θ, \\ (4) & y_{L} = (X_{G} - X_{1}) sin θ + (Y_{G} - Y_{1}) cos θ . \end{array}$

Fig. 4.

Schematic picture of the proximal femur showing global and local coordinate systems. The local coordinate system is oriented such that the x-axis is along and the y-axis is perpendicular to the fracture line.

In each loading step, maximum interfragmentary movement of each pair of markers was compared among three fixation methods.

2.6. Statistical analysis

Due to the small number of samples (4 samples in each group), nonparametric Kruskal–Wallis and Mann–Whitney U tests were performed, and the level of significance was determined to be $p < 0.05$ . The software package SPSS (V.19) was also used for the statistical evaluations.

3. Results

3.1. Properties of intact samples

There were no differences in age, bone mineral density (BMD), and stiffness of intact bones between the tested groups ( $p > 0.05$ ). The average age of donors was 36.33 ± 12.64 years (range, 23–56 years). Also, the average bone mineral densities for the groups were between 0.75 ± 0.15 g/cm² and 0.79 ± 0.25 g/cm²; and the range of the mean intact stiffness of the tested groups was 1.04 ± 0.097 KN/mm to 1.11 ± 0.086 KN/mm.

3.2. Biomechanical parameters

The average biomechanical properties of different fixation methods (CSs, DHS+Ds, and PFLP) can be found in Table 1. The differences in all biomechanical parameters were statistically significant among tested groups ( $p < 0.05$ ). Relative stiffness (stiffness of bone-implant structure after fixation divided by stiffness of the same intact bone before fixation), downward femoral head displacement, failure load, and failure energy for the DHS+DS method of fixation are significantly different from those corresponding to the CSs ( $p < 0.05$ ). There were no significant differences in failure load and failure energy between the PFLP and CSs techniques ( $p > 0.05$ ). Also, there were no significant differences in relative stiffness and femoral head displacement between the PFLP and DHS+DS groups ( $p > 0.05$ ). Hence, the most stable construct was the DHS+DS, and the PFLP structure seems more stable than CSs construct.

Table 1
The average biomechanical properties of three different fixation methods (CSs, DHS+DS, and PFLP). Four fresh-frozen cadaveric samples were used in each group to compare biomechanical stability of internal implants for fixation of vertival femoral neck fracture

Fixation method Relative stiffness Downward femoral head displacement (mm) Failure load (kN) Failure energy (J)

CSs $0.27 \pm 0.07$ $4.71 \pm 0.96$ $2.01 \pm 0.46$ 3.17±0.69

DHS+DS $0.58 \pm 0.06$ $2.06 \pm 1.06$ $4.61 \pm 0.73$ 11.04±2.95

PFLP $0.51 \pm 0.11$ $2.43 \pm 0.56$ $2.54 \pm 0.86$ 5.06±2.35

Fixation method	Relative stiffness	Downward femoral head displacement (mm)	Failure load (kN)	Failure energy (J)
CSs	$0.27 \pm 0.07$	$4.71 \pm 0.96$	$2.01 \pm 0.46$	3.17±0.69
DHS+DS	$0.58 \pm 0.06$	$2.06 \pm 1.06$	$4.61 \pm 0.73$	11.04±2.95
PFLP	$0.51 \pm 0.11$	$2.43 \pm 0.56$	$2.54 \pm 0.86$	5.06±2.35

3.3. Interfragmentry movement curves

Figures 5–7 show typical curves of the maximum change in relative position of the fractured fragments and their components (axial and shear relative position, respectively parallel and perpendicular to the fracture line) at each loading phase for different fixation methods. In the case of employing DHS+DS, interfragmentary movement curves show oscillatory trends for all locations around the fracture site, and axial interfragmentary movement curves show descending trends. Also, shear interfragmentary movement curves of this kind of fixation display either oscillatory or descending trends (Fig. 5). In the case of using PFLP, interfragmentary movement curves show oscillatory trends for some locations around the fracture site while trends of other curves were descending. Moreover, axial interfragmentary motion-load curves of PFLP group display either descending or oscillatory trends, and anterior curves show a change in the sign from positive to negative during loading. In addition, shear interfragmentary movement versus load curves of this method of fixation exhibit either oscillatory or ascending trends (Fig. 6). For the CSs group, interfragmentary movement curves were distinct for different locations around the fracture site, and represents greater changes in relative position of the fractured fragments compared to PFLP group. Besides, axial interfragmentary motion-load curves exhibit either descending or ascending trends, and most of them show a change in the sign from positive to negative during loading. Furthermore, shear interfargmentary movement-load curves of this method of fixation display either ascending or descending trends (Fig. 7).

Fig. 5.

Typical curves of interfragmentary movement for DHS+Ds group. Figures (a), (b) and (c) show respectively total, axial, and shear relative position of the fracture fragments versus different loading steps for various locations around the fracture site (step 1: initial position, step 2: incremental loading (at max load), steps 3–6: cyclic loading).

Fig. 6.

Typical curves of interfragmentary movement for PFLP group. Figures (a), (b) and (c) show respectively total, axial, and shear relative position of the fracture fragments versus different loading steps for various locations around the fracture sit (step 1: initial position, step 2: incremental loading (at max load), steps 3–6: cyclic loading).

Fig. 7.

Typical curves of interfragmentary movement for CSs group. Figures (a), (b) and (c) show respectively total, axial, and shear relative position of the fracture fragments versus different loading steps for various locations around the fracture site (step 1: initial position, step 2: incremental loading (at max load), steps 3–6: cyclic loading).

Fig. 8.

Mean curves of average relative position of the fractured fragments in anterior and posterior aspects versus different loading steps for different fixation methods: (a) DHS+DS group, (b) PFLP group, and (c) CSs group (step 1: initial position, step 2: incremental loading (at max load), steps 3–6: cyclic loading).

Figure 8 shows mean curves of the average relative position of the fractured fragments in anterior and posterior aspects for different fixation methods. In the case of using DHS+DS, the average relative position of the fractured fragments in anterior aspect is very much similar to that of posterior aspect during loading. For the PFLP group and CSs group, the average relative position of the fractured fragments in anterior aspect is different from that of the posterior aspect. In PFLP group, the trend of average relative position curve in anterior aspect is nearly similar to that of posterior aspect, but for CSs group, they are completely different. Moreover, in the case of employing CSs, the difference in the average relative position of the fractured fragments between anterior and posterior aspects increases during loading.

Fig. 9.

Typical pictures from anterior (right and middle) and posterior (left) views of cadaveric bone samples fixed by three different implants after 10,000 cycles of loading: (a) DHS+DS group, (b) PFLP group, (c) CSs group.

Figure 9 shows typical pictures of cadaveric bone samples fixed by DHS+DS, CSs, and PFLP at the end of 10,000 cycles of loading. It should be noted that all samples survived during both incremental and cyclical loading. Besides, the failure mode of the DHS+DS group was sliding and a slight tilting; while it was sliding, tilting, and rotation for PFLP and CSs.

4. Discussion

Vertical femoral neck fractures may be exposed to high shear forces in daily normal activities, and thus may be predisposed to nonunion or loss of fixation. The dominance of shear forces in vertical femoral neck fractures causes femoral head displacement, and sliding of the upper segment with respect to the lower part; which this can ultimately disrupt the bone healing process in the fractured area [1,3,18]. In order to have a normal healing process, a stable fixation method should resist undesirable displacements at the fracture site during the bone healing process [7].

Since there is controversy regarding the ideal fixation method for a vertical femoral neck fracture [3,10], the main scope of this research was to make comparisons among three commonly used fixation techniques by applying an in-vitro quasi-experimental cadaveric approach. Also, to the best of our knowledge, this is the first experimental study employing motion capture analysis to compare the biomechanical stability of these internal implants (CSs, DHS+DS, and PFLP) for vertical femoral neck fracture in the young.

Results of this study showed that stiffness, downward femoral head displacement, failure load, and failure energy resulted with the DHS+DS method of fixation provides the most stable structure, compared to two other methods, i.e. CSs and PFLP. This study also showed that there were no significant differences in stiffness and downward femoral head displacement between the PFLP and DHS+DS methods. Moreover, failure load and failure energy in the PFLP and CSs were statically equivalent (see Table 1). Comparing trends of interfragmentary movement-load curves among different groups demonstrated that the DHS+DS method of fixation can keep the proximal and distal segments well connected together, but PFLP and CSs techniques could not do so properly (see Figs 5–8). Also, PFLP group represented fewer changes in relative position of the fractured fragments compared to CSs group (Figs 6–8). In addition, trends of axial interfragmentary movement-load curves showed axial compression in DHS+DS technique for all locations around the fracture site (Fig. 5). On the other hand, PFLP and CSs groups showed the femoral head non-uniform separation and rotation, which were less intense for PFLP method of fixation than that of CSs (Figs 6 and 7). Finally, trends of shear interfragmentary movement-load curves demonstrated maximum shear and rotation resistance for the DHS+DS group followed in a descending order by PFLP and CSs techniques (Figs 5–7). Figure 9 shows typical pictures of cadaveric bone samples fixed by DHS+DS, CSs, and PFLP at the end of 10,000 cycles of loading, which indicates that the femoral head fixed by DHS+Ds has the greatest resistance against the intrinsic instability of this kind of fracture (i.e. destructive shear and rotation forces), followed in a descending order by PFLP and CSs techniques. To sum up, according to the biomechanical parameters and interfragmentary-load curves, the specimens fixed with DHS+DS provided the greatest resistance against femoral head sliding, tilting, and rotation compared to two other fixation methods, i.e. PFLP and CSs (see Table 1 and Figs 5–8). Also, it is worth mentioning that the union of this kind of fracture occurs during the primary bone healing process which necessitates absolute stability at the fracture site. Hence, it could be deduced that DHS+DS may require shorter healing time than that of PFLP, which needs less time for healing than CSs. Although there were no significant difference in failure load and failure energy between the PFLP and CSs methods of fixation, but stiffness, downward femoral head displacement, and interfragmentary movements of the PFLP construct showed that sliding, tilting, and rotation resistance of the fractured femurs fixed by the PFLP is greater than those fixed by the CSs (see Table 1 and Figs 6–8).

Similar to previous studies [6–9,11], results of this research showed that fixed angle devices are stronger than CSs technique for the fixation of vertical femoral neck fracture. In recent studies by Aminian et al. [7] and Nowotarski et al. [9] femoral neck locking plates were reported as the strongest fixation method for vertical femoral neck fracture. It should be noted that the locking plates used in those studies [7,9] were different from PFLP employed in this research. In this study, PFLP with two locking screws was compared with DHS+DS and CSs. But, in Aminian et al.’s study [7], the Synthes PFLP (Synthes, Paoli, PA, USA) with three locking screws was compared to DHS, DCS and CSs, and in Nowotarski et al.’s 2012 [9], a newly designed PFLP with two locking screws and a transfer lag screw was compared with DHS+DS and CSs. Considering our results, PFLP with its two locking screws could not provide sufficient compression at the fracture site; therefore, it was less stable than DHS+DS, which provided a stronger support at inferior location around the fracture site. For CSs and DHS+DS, a wide range of stiffness and failure load were reported by previous studies [5–9,11,19–21]. The discrepancy observed among various studies might be due to the differences in the assumptions made on loading and boundary conditions (loading regimes and load application devices), femur orientations, fracture orientation, femur types (e.g., cadaveric vs. synthetic), and properties of tested implants used in various studies.

There were several limitations in this research. Firstly, the osteotomy was created by a smooth saw cut, which makes it different from the real bone fracture surface. Secondly, because of the limitations in the number of cadavers, the number of specimens was limited. This limitation was the reason to make a quasi-experimental investigation here. Thirdly, although interfragmentetary motions are three-dimensional kinematic phenomena, these movements were evaluated in two-dimensional space. Finally, for the sake of simplicity, some physiologic force components acting across the hip joint, such as muscle forces, were neglected in this research, which deserve more care in the future work.

5. Conclusions

It is noteworthy that the results of this study are in agreement with the experimental section of our previous research [10] which only was done on three samples. In addition, although they confirm repeatability of reported outcomes regarding DHS+DS and CSs methods, using more samples shows that some biomechanical parameters of PFLP implant (i.e. stiffness and femoral head displacement) are closer to that of DHS+DS technique, and others (i.e. failure load and failure energy) are closer to that of CSs method. Hence, it could be concluded that while PFLP system is a fixed angle device, it could not resist enough against shearing forces during the healing process of this kind of fracture.

In conclusion, the ultimate goal of this study was to find the more stable method of fixation among CSs, DHS+DS, and PFLP for the vertical femoral neck fracture in young adults. Assuming that restricted weight-bearing regimen will be applied in the postoperative rehabilitation protocol, results of this research suggested that the priority order of selection for internal fixation implants of vertical femoral neck fracture in young patients, with the goal of having a faster bone healing process, is: DHS+DS, then PFLP, and finally CSs. In addition, since surgeons’ skills as well as method of surgery, e.g. the position and number of screws, are influential factors in stability of bone-implant constructs, these factors should be also controlled and taken into account.

Footnotes

Acknowledgements

Amirkabir University of Technology, Tehran University of Medical Sciences, and Iranian Tissue Bank and Research Center.

Conflict of interest

The authors have no conflict of interest to report.

References

Liporace

Gaines

Collinge

and Haidukewych

G.J.

, Results of internal fixation of Pauwels type-3 vertical femoral neck fractures, J. Bone Joint Surg. Am. 90(8) (2008), 1654–1659. doi:10.2106/JBJS.G.01353.

C.C.

, Using biomechanics to improve the surgical technique for internal fixation of intracapsular femoral neck fractures, Chang Gung Med. J. 33(3) (2009), 241–251.

Keating

and Aderinto

, The management of intracapsular fracture of the femoral neck, Orthop. Trauma 24(1) (2010), 42–52. doi:10.1016/j.mporth.2009.11.001.

Haidukewych

G.J.

Rothwell

W.S.

Jacofsky

D.J.

Torchia

M.E.

and Berry

D.J.

, Operative treatment of femoral neck fractures in patients between the ages of fifteen and fifty years, J. Bone Joint Surg. Am. 86(8) (2010), 1711–1716.

Hawks

M.A.

Kim

Strauss

J.E.

Oliphant

B.W.

Golden

R.D.

Hsieh

A.H.

et al., Does a trochanteric lag screw improve fixation of vertically oriented femoral neck fractures? A biomechanical analysis in cadaveric bone, Clin. Biomech. 28(8) (2013), 886–891. doi:10.1016/j.clinbiomech.2013.08.007.

Baitner

A.C.

Maurer

S.G.

Hickey

D.G.

Jazrawi

L.M.

Kummer

F.J.

Jamal

et al., Vertical shear fractures of the femoral neck: A biomechanical study, Clin. Orthop. Relat. Res. 367(1) (1999), 300–305.

Aminian

Gao

Fedoriw

W.W.

Zhang

L.Q.

Kalainov

D.M.

and Merk

B.R.

, Vertically oriented femoral neck fractures: Mechanical analysis of four fixation techniques, J. Orthop. Trauma 21(8) (2007), 544–548. doi:10.1097/BOT.0b013e31814b822e.

Lepine

M.S.

Barfield

W.R.

Desjardins

J.D.

and Hartsock

L.A.

, The effect of moment arm length on high angled femoral neck fractures (Pauwels’ III), J. Biomed. Sci. Eng. 3(5) (2010), 448–453. doi:10.4236/jbise.2010.35062.

Nowotarski

P.J.

Ervin

Weatherby

Pettit

Goulet

and Norris

, Biomechanical analysis of a novel femoral neck locking plate for treatment of vertical shear Pauwel’s type C femoral neck fractures, Injury 43(6) (2012), 802–806. doi:10.1016/j.injury.2011.09.012.

10.

Samsami

Saberi

Sadighi

and Rouhi

, Comparison of three fixation methods for femoral neck fracture in young adults: Experimental and numerical investigations, J. Med. Biol. Eng. 35(5) (2015), 566–579. doi:10.1007/s40846-015-0085-9.

11.

Bonnaire

F.A.

and Weber

A.T.

, Analysis of fracture gap change: Dynamic and static stability of different stability of different osteosynthetic procedures in the femoral neck, Injury 33(1) (2002), 24–32. doi:10.1016/S0020-1383(02)00328-5.

12.

Bradley

E.J.

Nabhani

and Spears

I.R.

, The effect of the degree of screw tension on interfragmentary displacement in stabilized fractures of the femoral neck, Curr. Orthop. Prac. 20(3) (2009), 291–299. doi:10.1097/BCO.0b013e3181972894.

13.

Nabhani

Bradley

E.J.

and Hodgson

, Comparison of two tools for the measurement of interfragmentary movement in femoral neck fractures stabilised by cannulated screws, Robot Comput. Integr. Manuf. 26(6) (2010), 610–615. doi:10.1016/j.rcim.2010.06.014.

14.

Jazrawi

L.M.

DeWal

Kummer

F.J.

and Koval

K.J.

, Laboratory evaluation of hip fracture fixation devices, Bull. Hosp. Jt. Dis. 60(4) (2002), 114–123.

15.

Yang

Chen

Zhang

Wang

et al., Biomechanical evaluation of a new device for internal fixation of femoral neck fractures, Artif. Cells Blood Substit. Immobil. Biotechnol. 39(4) (2011), 252–258.

16.

Koval

K.J.

Sala

D.A.

Kummer

F.J.

and Zuckerman

J.D.

, Postoperative weight-bearing after a fracture of the femoral neck or an intertrochanteric fracture, J. Bone Joint Surg. Am. 80(3) (1998), 352–356.

17.

Bergmann

Deuretzbacher

Heller

Graichen

Rohlmann

Strauss

et al., Hip contact forces and gait patterns from routine activities, J. Biomech. 34(7) (2001), 859–871. doi:10.1016/S0021-9290(01)00040-9.

18.

T.V.

and Swiontkowski

M.F.

, Treatment of femoral neck fractures in young adults, J. Bone Joint Surg. Am. 90(10) (2008), 2254–2266.

19.

Zdero

Keast-Butler

and Schemitsch

E.H.

, A biomechanical comparison of two triple-screw methods for femoral neck fracture fixation in a synthetic bone model, J. Trauma 69(9) (2010), 1537–1544. doi:10.1097/TA.0b013e3181efb1d1.

20.

Rupprecht

Grossterlinden

Ruecker

A.H.

Oliveira

A.N.

Sellenschloh

Nüchtern

et al., A comparative biomechanical analysis of fixation devices for unstable femoral neck fractures: The intertan versus cannulated screws or a dynamic hip screw, J. Trauma 71(3) (2011), 625–634. doi:10.1097/TA.0b013e31820e86e6.

21.

Selvan

V.T.

Oakley

M.J.

Rangan

and Al-Lami

M.K.

, Optimum configuration of cannulated hip screws for the fixation of intracapsular hip fractures: A biomechanical study, Injury 35(2) (2004), 136–141. doi:10.1016/S0020-1383(03)00059-7.