Provisional fixation of unstable femoral neck basicervical fractures: A web-based survey and biomechanical assessment using a sliding hip screw construct

INTRODUCTION

The number of hip fracture cases, including femoral neck fractures, is expected to increase significantly by mid-century, and it is estimated that the global incidence will reach more than 2 million in 2050.^[1] Managing these fractures safely and cost-effectively will be of uttermost importance. Many surgeons have considered basicervical femoral neck fractures to be a difficult subtype to treat due to the inherent rotational instability of the fracture.^[2,3]

While an adequate reduction can be commonly achieved, displacement of the fracture typically occurs during insertion of the fixation device, commonly a sliding hip screw (SHS) or cephalomedullary nail (CMN).

Multiple provisional fixation techniques have been described to counteract this instability, including a superior derotational screw, one or two superior Kirschner wires (K-wires), and different types of clamps and bone hooks.^[4,5] Typically, the surgeon applies one or a number of these methods depending on personal preference or training received without any concrete evidence to support the choice of method. The addition of a superior derotational screw to the SHS in the unstable femoral neck and hip fractures has been shown to offer superior rotational stability,^[3,6] but unfortunately, there is a lack of studies exploring other provisional fixation methods. In addition, the majority of biomechanical studies have assessed the stability of the fracture after the final fixation construct is applied. However, fracture displacement can commonly occur intraoperatively during insertion of the lag screw for an SHS or CMN.

Therefore, we designed our study in two parts. The first part was a web-based survey of practicing orthopedic surgeons to explore commonly used methods of provisional fixation in unstable basicervical femoral neck fractures. The survey results were then used to guide our biomechanical testing, which assessed the rotational stability of four of the most commonly applied provisional fixation methods in a basicervical femoral neck fracture synthetic bone model. We hypothesized that the derotational screw and the transcervical-transacetabular (TC-TA) K-wire constructs would provide superior rotational stability compared to one or two superior K-wires.

MATERIALS AND METHODS

Web-based survey

A web-based anonymous survey was sent, through e-mail, to all surgeon members of the Canadian Orthopaedic Association (COA), Orthopaedic Trauma Association (OTA), and Saudi Orthopedic Association (SOA) between January 2019 and October 2019. Reminders were sent on a monthly or bimonthly basis and the survey was closed in November 2019, at which time, the data were collected and evaluated.

The web-based survey consisted of questions concerning the type and length of the surgeon’s practice, in addition to questions related to the management of unstable basicervical hip fractures (type of preferred fixation construct, a preferred technique of provisional fixation if any, and order of fixation) [Supplemental - Figure 1]. The survey was initially piloted on 10 volunteers to assess the time required to complete the survey and the clarity of the questions before sending it to the member surgeons. In addition, data were collected and descriptive statistics were analyzed. For data analysis, the Chi-square test was performed to compare the variables and P < 0.05 was considered statistically significant.

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Figure 1:

Osteotomized femoral neck in the basicervical region.

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Biomechanical study

Rotational stability was assessed using twenty, fourth-generation composite left proximal femurs (model number: SKU-3403, SawBones®) which were vertically osteotomized in the basicervical region (at an angle of 70°) to simulate an unstable basicervical femoral neck fracture [Figure 1]. All fractures were osteotomized and fixed using a mold to standardize fracture location and SHS placement. These fractures were anatomically reduced and held within a prefabricated mold to maintain the reduction and fracture compression. One of the four provisional fixation constructs was applied; Group 1: Single 7.3 mm derotation screw, Group 2: Two superior 2.0 mm K-wires, Group 3: One superior 2.0 mm K-wire, and Group 4: A TC-TA 2.0 mm K-wire transfixing into pelvic SawBone model potted in a stationary position [Figure 2]. An SHS guidewire was then inserted centrally in the femoral head and reamed and tapped to a tip apex distance of <20 mm. The SHS was then inserted with a torque limiter to the appropriate depth to maintain a uniform torque force during insertion for all specimens. All trials were performed by a single, fellowship-trained orthopedic trauma surgeon (MMZ). Rotational stability was assessed using an open-source software package developed by Jackson et al. to perform multi-camera 3D data acquisition using consumer-grade cameras (GoPro Hero 5, Medium FOV, 48 fps, 2.7 k).^[7] This method was chosen over conventional systems such as Northern Digital Inc. This method was chosen over conventional optical tracking systems such as Polaris (Northern Digital Inc.) because it does not require heavy physical markers which were found to affect rotational stability during pilot testing. Using this technique, markers could be painted on the surface of the femur and tracked during SHS insertion.

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Figure 2:

(a) One 2.0 mm K-wire and transcervical-transacetabular K-wire constructs. (b) Two superior 2.0 mm K-wire construct. (c) Single derotation screw construct.

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Total rotation was determined by the final maximal angular rotation about the neck axis during insertion. For the femurs used, the total rotation was converted to a displacement based on the diameter of the basicervical region to approximate the total displacement seen at the fracture site. A sample size analysis determined that to achieve a power of 0.80 to detect a 1.9 mm difference in rotational stability, four samples were required per group. For data analysis, the one-way analysis of variance was performed to compare the variables, and P < 0.05 was considered statistically significant.

RESULTS

Web-based survey

One hundred and forty-two surgeons completed the survey. The mean years in the practice of respondents were 13.3 years. More than half of the surgeons (52.8%) described their practice as academic, while 38% had a community practice and 9.2% were in private practice. A trauma fellowship was completed by 58.5% of the respondents.

When asked about the type of fixation construct preferred for unstable basicervical femoral neck fractures, 50% preferred an SHS, 43.7% preferred a CMN, and 6.3% preferred other constructs (including cannulated screws, blade plate, and arthroplasty) [Figure 3]. A form of provisional fixation was applied to counteract the unstable pattern of these fractures by 79.6% of the responding surgeons. Interestingly, 35.5% of surgeons using a CMN do not routinely use any form of provisional fixation versus only 7% of surgeons applying an SHS construct (P < 0.001). Derotational screw (43.4%) and one superior K-wire (39.8%) were the most commonly used forms of provisional fixation [Figure 4]. More surgeons (47.8%) preferred to apply the provisional fixation before the final construct guidewire, while 41.6% preferred to start with the final construct guidewire before applying the provisional fixation and 9.7% had no specific preference [Figure 5].

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Figure 3:

Respondents type of preferred fixation for unstable basicervical femoral neck fractures.

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Figure 4:

Respondents preferred method of provisional fixation for unstable basicervical femoral neck fractures.

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Figure 5:

Respondents preferred order of fixation for unstable basicervical femoral neck fractures.

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The number of years in practice, type of practice, and completion of an orthopedic trauma fellowship were not significantly associated with the preferred fixation construct. On the other hand, we observed that surgeons in academic practice were more likely to apply a form of provisional fixation compared to other practices (P < 0.05).

DISCUSSION

More orthopedic surgeons in our survey preferred an SHS (50%) construct for the management of unstable basicervical femoral neck fractures, while a large number preferred a CMN (43.7%) construct for these fractures. In addition, a significantly larger number of participant surgeons that applied a CMN construct did not apply any form of provisional fixation compared to surgeons using an SHS construct. This can be attributed to the difficulty of applying a form of provisional fixation with a CMN (especially a derotational screw) unless a “Miss a nail” technique is applied. When a form of provisional fixation was applied, a derotational screw or a single superior K-wire was the most commonly used method.

Slobogean et al. showed in a survey of orthopedic surgeons, which included members of the OTA and COA, that for displaced young femoral neck fractures, a similar number of respondents preferred an SHS construct (49%) or a multiple screws construct (46%).^[8] They also found that of the surgeons that preferred an SHS, 46.1% preferred to supplement it with a derotational screw. A similar study by Sciacca et al. explored the preferred fixation method of displaced femoral neck fractures in the young and old age groups by 52 surgeons at an international AO course.^[9] They found that the majority of surgeons preferred screw fixation for the young patients and a form of arthroplasty for the older age groups. Luttrell et al. surveyed active OTA members regarding preferred constructs for vertically oriented femoral neck fractures.^[10] Of the 272 respondents, 47% preferred an SHS with or without a derotational screw. We are not aware of any study that explored different types of preferred provisional fixation methods for unstable basicervical femoral neck fractures.

Biomechanically, we have shown that the derotational screw group offered significantly superior rotational stability at the time of SHS insertion compared to the single superior K-wire group. In addition, although the two superior K-wires and TC-TA K-wire groups had less rotational displacement compared to the single superior K-wire group, this did not reach statistical significance.

Multiple studies in the literature biomechanically compared different types of constructs used for the management of unstable basicervical femoral neck fractures. However, we are not aware of any study that explored the amount of displacement seen with different types of provisional fixations at the time of SHS insertion.^[11-14]

Blair et al. biomechanically compared three fixation techniques (three parallel cannulated cancellous screws, SHS, and SHS with a derotational screw) in an osteoporotic cadaveric basicervical hip fracture model.^[3] They found that the SHS construct outperformed the three cannulated screws construct in axial load, while there was no significant difference between the tested constructs in torsional and lateral bend testing. These results were reproduced in a biomechanical cadaveric study by Deneka et al., where SHS with a derotational screw demonstrated a higher average peak force and load to failure when compared to three cancellous screws when axial and torsional forces were applied.^[15]

In a biomechanical synthetic femora model of Pauwels type III femoral neck fractures by Johnson et al., the SHS with a derotational screw was superior to both an inverted triangle and modified crossed cannulated screw construct when axially loaded.^[16] In addition, Bonnaire et al. highlighted the significance of a derotational screw for the management of femoral neck fractures.^[6] Their biomechanical cadaveric study showed less fracture gap formation when a derotational screw was added to the SHS construct compared to an SHS alone.

While we found that the derotational screw constructs supplied improved rotational stability during the SHS insertion, Blair et al. highlighted in their study that it does not provide any increased fixation after SHS insertion.^[3] We tested the constructs using synthetic SawBone models, which eliminate the soft-tissue constrain, which may have a role in fracture stabilization. Unfortunately, we found no studies in the literature that compared K-wire provisional fixation to derotational screw fixation in a cadaveric model. This would be an excellent aspect to explore in future research directives.

This study has limitations, as is with any biomechanical study. The use of synthetic bone in our biomechanical testing may be considered a weakness, but we believe that cadaveric bone may introduce interspecimen variability, which is reduced with synthetic bone. In addition, the web-based survey was based on a questionnaire whose validity and reliability have not been established.

One strength of the study is that the biomechanical test methods were designed from the survey results and feedback. An additional strength of the study is that the amount of displacement was measured during the SHS insertion, which simulates the rotational force applied intraoperatively in these cases. Furthermore, the amount of torque applied to the specimens was kept from exceeding a maximum torque by applying a torque limiter to the SHS.

CONCLUSION

Our present study highlights that multiple provisional fixation methods are currently used to counteract the rotational instability of unstable basicervical femoral neck fractures. Biomechanically, we have shown that a single 7.3 mm derotational screw construct outperforms the single superior K-wire in rotational stability at the time of SHS screw insertions, which were the most commonly used methods by surgeons participating in our survey. However, more studies are required to assess these findings in different bone models and the amount of clinically relevant rotational displacement in these unstable fracture patterns.