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Technologies for Young Femoral Neck Fracture Fixation

Duffin, Matthew MD; Pilson, Holly T. MD

Journal of Orthopaedic Trauma: January 2019 - Volume 33 - Issue - p S20–S26
doi: 10.1097/BOT.0000000000001367
Supplement Article
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Summary: Fixation of young femoral neck fractures represents a challenge in the field of orthopaedic trauma surgery. Conventional methods, including cannulated screw and sliding hip screw constructs, have been studied and found to have similar results with regards to patient outcomes, which has made choosing an optimum fixation strategy difficult. In all of these cases, quality of reduction has been shown to be the most important factor when it comes to creating a favorable environment for fracture healing. Some of these patients, however, continue to have negative sequelae including nonunion, avascular necrosis, femoral head collapse, and poor hip function as a result. In this article, we review the 2 most commonly used constructs and present 2 novel fixation constructs for the fixation of femoral neck fractures in physiologically young patients, including the Smith & Nephew Conquest system and the Aesculap Targon system. We outline techniques for usage of these systems and proposed advantages to these systems compared with conventional fixation methods. We also discuss the results of previously published studies regarding conventional fixation methods and compare with some limited studies that have been published on these newer technologies.

Department of Orthopaedic Surgery, Wake Forest University School of Medicine, Winston-Salem, NC.

Reprints: Holly T. Pilson, MD, Division of Orthopaedic Trauma, Department of Orthopaedic Surgery, 1 Medical Center Boulevard, Winston-Salem, NC 27157 (e-mail: hpilson@wakehealth.edu).

The authors report no conflict of interest.

Accepted October 10, 2018

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INTRODUCTION

For years, the internal fixation of young femoral neck fractures has been an ongoing debate on many fronts, including timing of surgery, open versus closed reduction, surgical approach, and method of fixation. Because of the high-energy nature of these injuries, with differences in bone quality, and physiologic age compared with the elderly femoral neck fracture, treatment of these fractures can be quite challenging. Regardless of choice of treatment, the goal is anatomic reduction and stable internal fixation.

Surgical implants and techniques for fixation of these fractures have evolved throughout the years from the silver screw, the first implant used to treat a femoral neck fracture in 1858 by a German surgeon Von Langenbeck,1 to the use of trifin nails by Smith-Petersen in the 1930s (Fig. 1), followed by the Asnis cannulated screws, which did not appear until 1980 and are still in use in some centers today.1 Variations of these implants and techniques still exist among various vendor systems, with the addition of some newer technologies that have been developed, each of which have been shown to have their own unique advantages and disadvantages.

FIGURE 1

FIGURE 1

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CURRENT TECHNIQUES

The most common implants used for fixation of intracapsular femoral neck fractures in young patients today include cannulated screw and sliding hip screw constructs. Both of these methods have been well described and are designed to provide compression across the fracture site. These constructs have demonstrated varying rates of union, up to 73% after index operation in some studies2; however, complications including nonunion, varus collapse, shortening, and osteonecrosis remain a problem, with rates up to 27%.2 A 2015 meta-analysis of 41 studies regarding young femoral neck fractures found a reoperation rate of 20% after internal fixation of isolated femoral neck fractures, with AVN (14.35%) and nonunion (9.3%) being the most common complications leading to repeat surgeries.3

Cannulated screw fixation of young femoral neck fractures typically involves the placement of 3 screws ranging in diameter from 6.5 to 8.0 mm in an inverted triangle configuration (Figs. 2A, B). Other configurations have been described, such as the addition of a fourth screw transversely into the calcar (Fig. 2C).4 The positioning and placement of these screws has been found to be important with regard to fracture healing and preventing varus collapse. Achieving adequate screw spread within the femoral neck, with the most distal screw along the inferior calcar, and the most superior screw placed along the posterior calcar on the lateral radiograph, has been shown to reduce the risk of nonunion and malunion, implant cutout, and failure.5,6 This method of fixation for femoral neck fractures has a few advantages including insertion over provisional pin fixation, low cost, low amount of bone removal, and can be inserted percutaneously in certain instances.7 Some disadvantages include lack of control over fracture compression and inability to provide fixed angle stability. Another disadvantage attributed to the use of cannulated screws is that a lack of parallelism between the screws can have a detrimental effect on the compressive forces seen across the fracture.8

FIGURE 2

FIGURE 2

Sliding hip screw systems, with or without the use of an antirotation screw, have also been used to provide stable fixation of femoral neck fractures, allowing for compression across the fracture site to encourage bony healing (Fig. 3). Although there are options of constructs with holes in the side plate ranging from 2 to 20, studies have shown that 2-hole plates are as strong as 4-hole plates in cycles of simulated physiologic loading, as well as load to failure.9 The importance of screw placement has also been well described in regards to the recommended tip–apex distance of less than 25 mm to decrease the incidence of screw cutout.10 Because the sliding hip screw systems only have 1 screw across the fracture site, if applied in isolation, one reported advantage is eliminating the need for parallelism, which may be more important in cannulated screw fixation.

FIGURE 3

FIGURE 3

The Synthes dynamic helical hip system is a variant of the sliding hip screw construct, which provides a locking compression plate affixed to the shaft of the femur with a helical blade for fixation into the femoral head, as opposed to a threaded screw (Fig. 4). The concept of guided collapse of the fracture for compression at the fracture site to facilitate healing remains the same with both implants. The helical blade in this system is designed to improve cutout resistance and increase rotational stability when compared with traditional cannulated lag screw constructs.11,12 This and other sliding hip screw systems are implanted using the same surgical techniques with careful consideration of quality of reduction, whether open or closed. The main advantage of the Synthes dynamic helical hip system in the treatment of young femoral neck fractures over cannulated screw and sliding hip screw constructs is the ability to reduce and stabilize the fracture without the risk of creating additional rotational deformity that can arise from the clockwise circular torque of traditional screw insertion.

FIGURE 4

FIGURE 4

Cannulated screws constructs have been compared with sliding hip screw systems for treatment of femoral neck fractures in young patients without a clear consensus regarding the superior option. One prospective randomized study of 85 patients compared outcomes between groups treated with sliding hip screws (40 patients) and cannulated screws (45 patients).13 In this particular study, patients requiring open reduction were excluded. Outcomes measured were pain relief, Harris Hip Score, and radiographic union. No significant results were found between the 2 groups with regard to time to union, functional outcome scores, and union rate. The sliding hip screw group, however, was found to have statistically higher operative time, incision size, and intraoperative blood loss.13 This study had similar results to a large meta-analysis comparing study results of similarly designed studies between 1974 and 2017, showing no significant differences in Harris Hip Scores between the SHS and cannulated screw groups.14 However, the pooled data from this meta-analysis did show significantly fewer postoperative complications and faster time to union among the SHS group.14

One study suggests that the decision for choice of implant should be primarily dictated by the fracture pattern, location within the neck, and Pauwels angle, with the fracture pattern being the most important determinant of the ideal implant choice.15 In this publication, data from multiple previous studies were compared with regard to ultimate strength, load cycles to failure, and displacement of the femoral head for various fracture types. Conclusions drawn from these comparisons showed that unstable basicervical patterns fixed with cannulated screws demonstrated a lower ultimate load to failure, whereas in the subcapital or transcervical patterns, there was no compromise in fixation strength.15 Other conclusions drawn from these data were that for Pauwels type III fracture patterns, cephalomedullary nail fixation was significantly stronger in axial loading when compared with cannulated screws and sliding hip screw systems.15

The FAITH trial, a large multicenter randomized controlled study, examined the reoperation rates between sliding hip screw and cancellous screw constructs, as well as other outcomes such as medically related adverse events and avascular necrosis.16 Patients from this study were randomized to either sliding hip screw (557 patients) or cancellous screw constructs (551 patients).16 Although the primary outcome of reoperation rates did not show a significant difference between the 2 groups, avascular necrosis rates were found to be higher in the sliding hip screw cohort when compared with the cancellous screw cohort (9% vs. 5% respectively, P = 0.0319).16 One theory behind this difference is that the sliding hip screw construct does not control rotational deformity, as well as the cancellous screw construct, and may in fact introduce a rotational malreduction during insertion and final tightening/seating.

Complications with modern fixation techniques and technologies, as well as unclear results of superior fixation methods, demonstrate the continued need to study these fracture patterns, surgical fixation techniques, and implants, as well as strive to develop new methods and technologies to improve outcomes.

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NEW TECHNOLOGIES

Novel technologies developed in recent years aimed at improving and combining concepts used in classic treatments of femoral neck fractures. These new systems are just beginning to be used in the United States and in Europe. The Smith & Nephew Conquest system is currently being used at some centers in the United States, whereas the Aesculap Targon system, developed in 2007, is currently only approved for use in Europe. Both systems aimed at combining features of traditional methods while improving angular stability and providing more controlled collapse. These systems both tout laterally based plates with proximal telescoping locking compression screws and locking and/or nonlocking options in the shaft of the plate. Although the concepts behind these systems are similar, there are some differences between the 2.

The Smith & Nephew Conquest system (Fig. 5) consists of a stainless steel plate designed with consideration of proximal femur anatomy. The proximal screw geometry is configured in the traditional inverted triangle orientation, with trajectories along the inferior calcar and the superior anterior and superior posterior calcars. The inferior calcar screw has an 8.5-mm core diameter, whereas the superior screws have an option for 7.5-mm or 8.5-mm core diameter. These screws are cannulated, can telescope up to 10 mm for guided compression intraoperatively, and have an integrated internal spring that allows for continued controlled compression postoperatively (Fig. 6). They have variable pitch for improved fixation in the lateral cortex and lock into the proximal plate to resist screw back out. The Conquest plating system comes in a 1- or 3-hole, left and right specific orientation for the distal plate geometry (Fig. 7). The plates are designed for 4.5-mm locking or nonlocking screws in the shaft. This system also provides provisional fixation holes at the proximal and distal ends for insertion of 2.0-mm K-wires.17

FIGURE 5

FIGURE 5

FIGURE 6

FIGURE 6

FIGURE 7

FIGURE 7

The Aesculap Targon system (Fig. 8)18 is a similar system used in Europe for treatment of femoral neck fractures with a few notable differences when compared with the Smith & Nephew Conquest system. The Targon plate is made of titanium alloy with 4 proximal locking telescoping screw options and 2 distal locking shaft screw options. The proximal screws are 6.5 mm in core diameter, cannulated, and allow for up to 20 mm of sliding compression. They are angled at 130 degrees with respect to the plate. The plate is nonspecific with respect to laterality and contours to the average lateral proximal femoral anatomy. The distal locking holes accept 4.5-mm diameter screws. This system uses an alignment jig that all guide pins and drills can be placed through.19

FIGURE 8

FIGURE 8

Both the Smith & Nephew Conquest and Aesculap Targon systems aimed at providing a comprehensive system for the provision of a fixed angle compression screw construct to allow for more controlled compression across the fracture while eliminating issues with screw back out, femoral neck shortening, and varus collapse that can be seen with traditional implants.

The Smith & Nephew Conquest system is FDA approved in the United States for the treatment of displaced and nondisplaced intracapsular femoral neck fractures and just began a limited market release in 2017. As such, there are no studies to date pertaining to this system. The Aesculap Targon system, on the other hand, has been in use in Europe since 2007.

A retrospective study from Queen Elizabeth Hospital in London (one of the flagship institutions for Aesculap Targon system) reviewed case notes and x-rays of patients treated with the Targon system for intracapsular femoral neck fractures between 2008 and 2011 with a minimum of 24-month follow-up.20 Forty-three patients were included for the final review. Thirty-one (72%) had undisplaced and 12 (28%) had displaced femoral neck fractures. An overall nonunion rate of 2% was observed, with only 1 case occurring in the displaced group and 0 in the undisplaced group.20 The authors compared their results with a previous study by Madsen et al,21 which reported an overall union rate of 64% for sliding hip screw and 84% for multiple cannulated screws over 2 years in a randomized controlled trial. A separate study from Peterborough District Hospital used prospective data gathered from 83 patients with intracapsular hip fractures between August 2006 and December 2007 treated with the Targon system and showed an overall nonunion rate of 9.6% (3% and 15% in undisplaced and displaced fracture groups, respectively).22 This study found their results to be similar to nonunion rates previously reported with the use of cannulated screws and sliding hip screws at rates of 6% for undisplaced and 33% for displaced fractures.23 Takigawa et al24 also published a study comparing fixation results of undisplaced and displaced intracapsular femoral neck fractures using the Targon system with previously published data on other implants, including sliding hip screws and 3 cannulated screw techniques and again found lower rates of nonunion compared with previously published data on conventional implants. This study had a cohort of 84 patients, 55 having nondisplaced femoral neck fractures and 29 having displaced femoral neck fractures. Average follow-up in this study was 16.4 months, with a range of 6–45 months. The nonunion rate in the study by Takigawa et al24 was 0 in undisplaced fractures and 2.4% in displaced fractures. These results compared favorably with previous published data from the study by Parker and Blundell,25 which showed cumulative nonunion rates as high as 27% in patients with both displaced and undisplaced fractures treated with cannulated screws or sliding hip screws. Thein et al26 compared the Targon system with multiple cancellous screws for displaced fractures and reported a nonunion rate of 3.2% with the Targon system and 46.8% in the multiple cancellous screw group. Eschler et al27 published a comparison between the Targon system (27 patients) and sliding hip screw (25 patients) and found 0% nonunion using the Targon and 12% in the sliding hip screw group.

In the same study from Queen Elizabeth Hospital, 3 cases of AVN were reported using the Targon system, resulting in an overall rate of 7% (6% and 8% in undisplaced and displaced fracture groups, respectively).20 These results compare favorably with previously published literature on femoral neck fractures treated with the Targon system including the literature by Parker and Stedtfeld22 (AVN rate of 3% for undisplaced and 7% for displaced fractures). The AVN rate in the previously mentioned study by Takigawa et al24 was reported to be 5.5% in undisplaced fractures and 13.8% in displaced fractures. Previously published literature by Parker and Stedtfeld22 reported an AVN rate of 4.5% in undisplaced and 11.1% in displaced fractures treated with the Targon system. Thein et al26 reported 8.5% AVN rate after multiple cancellous screws in unstable fracture patterns. Eschler et al27 reported 4% AVN rate using the Targon and 0% after sliding hip screw. Takigawa et al24 also concluded that overall, 88.5% of patients achieved the preinjury level of mobility, which was similar to data published on other conventional fixation systems. Although the study from Queen Elizabeth Hospital did not compare the Targon system with traditional fixation methods, it does show reproducible results with the use of the Targon design system at nonspecialized institutions.

Another study from the University of Rostock in Germany compared the Targon system with traditional sliding hip screw fixation. This prospective randomized study treated 52 patients with femoral neck fractures with either the Targon (27 patients) or sliding hip screw (25 patients) systems.27 Patients were randomized based on date of admission with even dates being treated with a sliding hip screw and odd dates treated with the Targon system. At the final follow-up, all patients were examined by the same independent observer, who was not involved in treatment. Outcomes were measured based on the Harris Hip Score, a visual analog pain scale, and radiographs. Results of this study showed less subsidence of the implant with an average of 5.0 mm in the Targon system group compared with 9.8 mm in the sliding hip screw group. Functional assessment with the Harris Hip Score showed slightly better results for sliding hip screw with an average score of 87.7 compared with 69.5 for the Targon system. Pain as rated by the visual analog score, however, revealed better results with the Targon system with average scores of 1.6 compared with 2.6 in the sliding hip screw group.27

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SUMMARY

Femoral neck fractures in young patients continue to present a challenge in the field of orthopaedic surgery. Continued advancements in technology and an understanding of these fractures are necessary to improve patient outcomes. The Smith & Nephew Conquest system and the Aesculap Targon system offer a solution that combines the benefits of cannulated screw and sliding hip screw fixation strategies. These systems provide the fixed angle advantage of the sliding hip screw with multiple points of fixation afforded by cannulated screw fixation, in addition to adding spring-assisted guided compression at the fracture site with a fixed angle locking construct. Early studies of the Targon system have shown promising results in rates of nonunion, AVN, and patient-reported outcome. More studies with these systems are needed to continue to improve outcomes and drive further innovations in this challenging area of orthopaedic surgery.

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Keywords:

femoral neck fracture; young; cannulated screw; sliding hip screw

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