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Femoral Neck Fractures in Young Patients: State of the Art

Chan, Daniel S. MD

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Journal of Orthopaedic Trauma: January 2019 - Volume 33 - Issue - p S7-S11
doi: 10.1097/BOT.0000000000001366
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Abstract

INTRODUCTION

Most intracapsular femoral neck fractures occur in the elderly population.1 Femoral neck fractures in young patients are much less common and typically a result of a high-energy mechanism.2 The fracture pattern is more vertical (Pauwels III, >50 degrees) and usually involves significant varus displacement.3 This injury is associated with complications such as osteonecrosis and nonunion, with reported rates of 11%–86% and 16%–59%, respectively.4–7

These complications require a salvage procedure, such as total hip arthroplasty, which in a young patient is not ideal. Therefore, achieving an anatomic reduction and stable fixation is critical to a successful union and a good functional outcome. This review will discuss the treatment of high-energy femoral neck fractures in young patients.

Relevant Anatomy, Fracture Classification, and Surgical Approaches

The 3 main blood supply sources are the medial and lateral femoral circumflex artery and the obturator artery.8–11 The majority of the blood supply to the femoral head comes from the medial femoral circumflex artery.11 The terminal branches of the medial femoral circumflex are intracapsular and are at risk of being disrupted (kinked or torn) by the displacement of femoral neck fractures and may be significant factor in the development of osteonecrosis.12–15 Other variables that may contribute are the quality of reduction or fixation7,16–20 and elevated intracapsular pressure.15,21–26

Young patients generally have better bone quality, and a high-energy mechanism can cause a femoral neck fracture pattern that is vertically oriented with a shear component making it biomechanically more unstable.27–31 The most descriptive classification used for femoral neck fractures in young patients is the Pauwels classification. As the degree of the femoral neck fracture line relative to the horizontal plane increases, the types differ (<30 degrees type I, between 30 degrees and 50 degrees type II, >50 degrees type III), and the instability of the fracture.27 Type III fractures are associated with increased risks of fixation failure, osteonecrosis, and malunion or nonunions.27–31

Goal for surgical treatment of femoral neck fractures in young patients is achieving union through an anatomic reduction and stable fixation while avoiding osteonecrosis. Time to surgery remains controversial. Advantages of early surgery include unkinking vessels via urgent reduction and an intracapsular decompression,8,16,32 both intended to improve perfusion of the femoral head and reduce the risk of osteonecrosis. There are studies that support this approach, concluding that delayed treatment was associated with an increased risk of osteonecrosis.17,33,34 However, conversely, there are several studies that show no difference in the osteonecrosis rate after surgical treatment delayed more than 24 hours.18,35 Until further studies are performed to provide more conclusive data regarding timing, surgery should be delayed until there is a medically stable patient and a surgical team able to best maximize the chances of anatomic reduction.

Pauwels type III femoral neck fractures in young patients are typically displaced and unstable, an acceptable alignment through a closed reduction can be difficult to obtain, and an open reduction is required.36 Patient positioned supine with the leg draped free on a radiolucent table seems to allow for the most freedom to best achieve an anatomic reduction; however, there are surgeons who prefer the leg in traction on a fracture table.

Two surgical approaches are most often used: the Watson-Jones37 and modified Smith-Peterson approaches. The Watson-Jones uses the interval between the tensor fasciae latae and gluteus medius. A T-capsulotomy allows for direct visualization of the fracture. The lateral exposure also provides for application of fixation through the same incision. In contrast, the modified Smith-Peterson approach is a commonly used anterior approach to the hip, using the interval between the sartorius and tensor fasciae latae superficially and the rectus femoris and gluteus medius deep. Again, a capsulotomy provides direct visualization of the fracture; however, with this approach only provisional or accessory fixation after reduction can be placed and the primary fixation requires a second lateral approach to the proximal femur and vastus ridge/subvastus lateralis for implantation.

Common reduction techniques with the leg free include using a 5-mm Schanz pin in the femoral shaft to manipulate the distal fracture segment. The Schanz pin is an excellent aid to apply lateral traction to disimpact the fracture and more precisely control the rotation of the distal segment to help obtain an anatomic reduction. K-wires (2.0 mm) can also be used as “joy-sticks” to more finely manipulate the proximal segment. This technique tends to be easier to perform from the anterior modified Smith-Peterson approach. When reducing a Pauwels type III fracture, there is often a fracture spike that can be “keyed in” to guide the reduction, and the orientation of the fracture allows for a point-to-point clamp be placed to hold the reduction. Another powerful tool is the jungbluth clamp when exposure is adequate and the inferomedial spike on the proximal fragment has room and purchase for a 3.5-mm screw. This clamp allows the surgeon to apply a few reduction maneuvers: create length, translate the fragments in the AP plane, and apply fracture compression.

Provisional or accessory fixation applied to the inferomedial femoral neck region in type III fractures have been reported to buttress this spike.38 One of the advantages of this plate may be to provide better provisional reduction while placing fixation implant from the lateral approach, especially to counteract the significant rotational forces that are applied when placing a sliding hip screw implant and risking loss of reduction. Additionally, an inferomedial plate more directly addresses the shear instability of a type III fracture pattern and augments the stability to most common fixation constructs applied.39

Fixation Options

A 2014 report of a survey of the Orthopaedic Trauma Association's Membership revealed that a consensus on the treatment of femoral neck fractures in young patients “remains elusive.”40 Cannulated screws were used 43% versus a sliding hip screw with or without an anti-rotation screw (47%). Three parallel cancellous lag screws placed in an inverted triangle perpendicular to the fracture is the primary goal in treating most femoral neck fractures41; however, type III fractures are difficult because of the shear instability and resultant varus malalignment.42 An alternative construct has been described using cannulated screws: 1 perpendicular to the fracture line engaging the inferior femoral head and neck and 1 or 2 screws parallel in the axis of the femoral neck43 (Fig. 1).

FIGURE 1.
FIGURE 1.:
Cannulated screw fixation construct for minimally displaced Pauwels type III femoral neck fracture.

The use of a sliding hip screw with an anti-rotation screw has been found to be very effective in treating type III femoral neck fractures (Fig. 2). When compared with 3 cannulated screws, this construct resulted in less loss of reduction and greater loads to failure.29 Biomechanical results support these findings where a sliding hip screw with anti-rotation screw construct was superior in type III fractures compared with cannulated screws in either the inverted triangle or the modified off-axis pattern described above.30,44

FIGURE 2.
FIGURE 2.:
Fixed-angle sliding hip screw with anti-rotation screw fixation construct for displaced Pauwels type III femoral neck fracture.

The addition of the anti-rotation screw to the sliding hip screw construct was shown to significantly strengthen the fixation for these high-energy fracture patterns.30 Similarly, the addition of an inferior medial plate to a sliding hip screw or cannulate screw construct was shown to increase load to failure 183% and construct stiffness 35%.39

The success of the sliding hip screw construct is directly related to the placement of the implant and addition of the anti-rotation screw.36,45 Another concern with the sliding hip screw is the amount of bone that is removed with its implantation and the difficulty of achieving a successful reconstruction if a nonunion repair is required.

Regardless of fixation construct used for femoral neck fractures, preserving femoral neck length can be difficult. In particular, fractures treated with partially threaded cannulated screws, while progressing toward union, often settle and heal with a shortened femoral neck disrupting neck–shaft offset and functional hip abductors and is associated with lower quality of life and increased revision rates.46–49 In one report of femoral neck fractures in young patients, 54% of patients had >5 mm of shortening, and 32% resulted in >1 cm of shortening.50 One approach to this problem was to create a length-stable construct by replacing the partially threaded screws with fully threaded screws after an anatomic reduction was obtained and the fracture was compressed.51,52 This approach was applied with a proximal femoral locking plate, attempting to achieve a fixed-angle and length-stable construct for femoral neck fractures.53 A 37% failure rate led to the product being pulled from the market, and the proposed explanations include a lack of fracture compression, and too stiff a construct inhibiting fracture micromotion that led to nonunion and hardware failure.

In Pauwels type III fractures, varus malalignment and shear instability are significant concerns; therefore, a fixed-angle device (sliding hip screw with anti-rotation screw) has been effective in addressing these issues. However, although union is achieved with dynamic compression, resulting femoral neck shortening is undesirable. Locking, femoral neck length-stable implants are associated with high failure rates likely due to excessive stiffness and a lack of fracture compression. Newer implants have been introduced to offer fixed-angle alternatives to potentially minimize bone removal with placement and decrease femoral neck shortening.

One femoral neck system that has been introduced offers fixed angle fixation using a screw-locked-in-a-bolt construct through a side plate.54 This fixation complex slides together to allow for controlled collapse and compression. A biomechanical investigation in Pauwels type III femoral neck fractures showed that it was not significantly different in stiffness or cyclic loading when compared with a sliding hip screw with anti-rotation screw and DHS blade.

Another locking plate system offering a fixed-angle construct with sliding cancellous screws has been used in Europe with positive reported results.55–57 The locking screws provide more rotational stability and less toggling of screws within the femoral neck. The sliding cancellous screws allow for controlled compression and collapse toward union. The results include lower nonunion and revision rates compared with cancellous screws and decreased femoral neck shortening.

Recently, a similar locked plating system for femoral neck fractures has been introduced in the United States. Three parallel cancellous screws, in an inverted triangle pattern, also provides rotational stability and minimizes toggling. The unique element to this system is that the cancellous screws are barreled and spring-loaded such that when inserted in the extended position, when the capture is released, it provides constant compression across the fracture (Fig. 3). Constant compression is proposed to not just increase union rates but also decrease femoral neck shortening by minimizing micromotion and bone resorption. Additionally, anecdotal reports indicate that patients seem to have less postoperative pain and advance weight-bearing more quickly possibly due to the enhanced stability. Further investigation is needed to elucidate the advantages and short-comings of this new femoral neck fixation system.

FIGURE 3.
FIGURE 3.:
Fixed-angle locking plate with 3 parallel spring loaded cancellous screws providing constant compression across displaced Pauwels type III femoral neck fracture.

CONCLUSIONS

There are still several controversies surrounding the treatment of high-energy femoral neck fractures in young patients, namely, time to surgery, surgical approach, and optimal fixation. Until more conclusive data are available, an urgent open reduction and internal fixation, with the most appropriate surgical approach, best enables obtaining an anatomic reduction and optimizes femoral head perfusion. Regarding optimal fixation, surgeon experience and purposeful implant selection toward desired fixation goals as dictated by the fracture pattern and patient characteristics are critical to achieving successful union and outcomes.

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Keywords:

femoral neck; fracture; Pauwels; vertical shear; osteonecrosis

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