Management of femoral neck fractures in the young patient remains difficult because of high rates of complication. Controversy remains regarding timing of surgery, operative technique, and optimal implant construct because of a lack of prospective clinical trials.
Femoral neck fractures in patients less than 50 years account for less than 5% of all hip fractures.1 Younger high-demand patients are not arthroplasty candidates, and thus preservation of the native hip joint is paramount. Surgeons are often faced with a disadvantaged biological environment with the combination of a displaced, vertical, intracapsular fracture.2
The blood supply to the femoral head is tenuous and easily injured in the setting of displaced fractures. The primary supply to the weight-bearing portion of the femoral head is the lateral epiphyseal branch of the medial femoral circumflex artery. The medial femoral circumflex artery supplies 82% of the femoral head and 67% of the femoral neck. The lateral femoral circumflex artery contributes 18% of the vascularity to the femoral head and 33% to the neck, however, it supplies 48% to the anteroinferior femoral neck.3 Both of these vessels branch into delicate retinacular arteries that course the surface of the femoral neck superiorly into the head. The obturator artery also provides a contribution as it courses through the ligamentum teres.4 In severely displaced fractures, only the contribution from the obturator artery through the ligamentum teres may be preserved. In addition to injury of the blood supply during the index injury, other mechanisms of disruption have been hypothesized including tamponade due to compression from an intracapsular hematoma, traction or malrotation during reduction, or eventual thrombosis due to improper reduction.5,6
Femoral neck fractures are intrasynovial, and the periosteum lacks a cambium layer. In diaphyseal fractures, a hematoma is encapsulated within the periosteum, and the cambium layer of the periosteum supplies pluripotent cells, which promote callus formation.7 In intracapsular fractures, there is a decreased supply of pluripotent cells, and the fracture hematoma is constantly lavaged away by synovial fluid. Thus, secondary fracture healing is not promoted. Rather, only direct fracture healing via osteonal remodeling is possible. This type of bone healing requires an anatomic reduction and compression. Primary healing may occur if there is a small gap in a process known as gap healing. However, the high shear stress environment of femoral neck fractures is minimally forgiving.
These factors contribute to the high reported rates of avascular necrosis (10%–23%), nonunion (8%–19%), malunion (7.1%), implant failure (9.7%), and need for reoperation (20%) (Fig. 1).8–13
TIMING OF SURGERY
Traditionally, efforts are made to treat and stabilize these fractures within 24 hours of injury, with some citing improved outcomes with reduction and fixation in less than 6 hours.14 Patients who are treated within 24 hours have lower inpatient medical and surgical adverse events.15 However, it is important to recognize that patients who are delayed often have higher injury severity scores and concomitant injuries, which naturally predispose them to complication. Emergent reduction and fixation may lessen the vascular insult.16 Although this theoretical benefit is plausible, other studies have shown that a delay of greater than 48 hours did not influence the rate of avascular necrosis12 but did increase the chance of nonunion.17 Level 1 evidence does not exist regarding timing of surgery, though most surgeons managing these fractures prefer operative management in less than 24 hours.18 Timing is likely important, however, reduction plays a larger role in outcomes.
Femoral neck fractures are challenging to reduce, and controversy remains regarding closed versus open reduction. A meta-analysis of closed versus open reduction concluded that there were no significant differences in rates of union and avascular necrosis between these 2 methods. However, there was an increased rate of infection in open reduction.11 It is important to note the possible bias in these studies. The treating surgeon is likely to perform a closed reduction on minimally displaced fractures, which would likely go on to do well regardless of approach. Similarly, fractures with high degrees of displacement, which are more likely to do poorly, are more often treated with an open approach. In children, open reduction yields a higher rate of anatomical reduction and fewer complications, including avascular necrosis.19
Although indirect reduction with intraoperative fluoroscopy is the standard when achieving secondary healing, remember that the intrasynovial environment of femoral neck fractures requires direct fracture healing via osteonal remodeling. An anatomic reduction and compression is required, especially in fractures with a high Pauwel angle.13 In a majority of cases, it is the authors' opinion that an open reduction under direct visualization should be performed.
A Watson-Jones approach can be used to visualize the femoral neck, with the advantage of using the same incision for instrumentation. However, it may be difficult to visualize subcapital fractures via this approach. Alternately, a Smith-Peterson approach may be used to directly visualize the femoral neck. Through this incision, direct manipulation of the fracture fragments can be achieved and a provisional reduction can be obtained. A separate lateral incision, however, is required for instrumentation.
After the approach is complete, different techniques may be used for reduction. Schanz pins may be inserted into the head segment for manipulation. Traditional instruments including pointed reduction clamps may also be useful. The authors have found a modified point-to-point reduction clamp, particularly useful in reducing these fractures (Fig. 2). Pilot holes for each tine are drilled on either side of the fracture and the clamp is seated, delivering compression after length alignment and rotation are restored.
Adjunctive small or mini-fragment plates can be helpful.20,21 Much has been written about the mini-fragment plate placed along the calcar of the femoral neck.22,23 Plates in this position can serve a buttress function and help neutralize shear. In the authors experience, application of this plate requires hip flexion and external rotation, which can be difficult with a tenuous provisional fixation. However, a mini-fragment plate along the anterior-inferior neck is easily placed without significant manipulation of the leg. This anterior-inferior plate can be helpful as an adjunctive reduction plate before definitive stabilization (Fig. 3). A calcar plate can then be placed as a final step in augmenting the mechanical construct (Fig. 4).
Implants widely available today include fully and partially threaded cannulated screws, fixed-angle sliding hip screws, and fixed-angle locking plates. Screws are non–fixed-angle constructs. Partially threaded screws allow for compression across the fracture, whereas fully threaded screws do not. A sliding hip screw is a fixed-angle device that allows for compression. A fixed-angle locking plate does not allow compression.
The use of fixed-angle locking plates is not recommended for femoral neck fractures because of catastrophic failure.24 Although fixing these fractures anatomically and at length is the ideal scenario, the biologic bridge connecting union to fixing femoral neck fractures at length has yet to be established.
Of the remaining methods of fixation, sliding hip screws have been shown to have a lower short-term failure rate than cannulated screws.25,26 However, there is not enough evidence to recommend an optimal method of internal fixation in regards to long-term outcome.27
Screws are advantageous in terms of reduction. At worst, screws do not disrupt a good provisional reduction, and at best, they fine tune or improve a provisional reduction. A compression screw may be used in the superior neck to decrease varus alignment. However, screws lack in maintaining the neck–shaft angle and preventing varus collapse and retroversion. They are not effective in combating shear forces.
Fixed-angle sliding hip screws resist shear and varus collapse; however, they have a higher propensity to disrupt a provisional reduction. This is especially true in the rotational plane because the sliding screw is advanced in transcervical or subcapital fracture patterns. It is the authors experience that despite abundant provisional fixation, sliding hip screws exert a strong rotational force on the head segment, often causing inadvertent rotational malreduction. Even in cases where this malreduction is realized and corrected, irreversible damage to the femoral head blood supply may have occurred. Although the fixed-angle sliding screw has been shown to be biomechanically superior,28–30 this advantage is not realized in clinical studies.13,26 This may be due to disruption of a provisional anatomic reduction, which mitigates the biomechanical advantage. This rotational disruption of reduction may also lead to increased rates of avascular necrosis.31
A new generation of implants is emerging, which may leverage the mechanical strengths of fixed-angle devices and reductive advantages of cannulated screws. The Smith and Nephew Conquest device uses cannulated screws that are made fixed angle by threading into a lateral locking plate. These screws have an indwelling spring mechanism, which delivers continued compression to the fracture. This continued compression may decrease postoperative pain and have biological advantages in terms of fracture resorption. These advantages are currently theoretical and need to be studied. The Conquest combines the mechanical advantages of a fixed-angle construct to resist shear and varus collapse with the reductive and biologic advantages of screws with continued compression (Fig. 5).
The DePuy Synthes Femoral Neck System has an articulated blade and screw construct that exerts no rotational moment on the head segment and is protective of an anatomic provisional reduction. It may optimize the mechanical advantage of a sliding hip screw by mitigating the negative effects of rotational displacement (Fig. 6). Both the Conquest and Femoral Neck System allow for dynamic compression of the fracture with weight-bearing.
Femoral neck fractures in young patients remain extremely challenging to treat because of a tenuous blood supply and disadvantageous fracture healing environment. Although the ideal window for fixation has not been established, reduction is more important than timing alone, and the patient should be taken to the operating room in a scenario that allows for optimal reduction and fixation in regards to surgeon, staff, and patient stability. The new generation of hybrid fixed-angle constructs build on the strengths and diminish the shortcomings of traditional treatment options and may decrease rates of nonunion and avascular necrosis.
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Keywords:Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.
femoral neck fracture; nonunion; young