Femoral neck fractures

Introduction

Femoral neck fractures are an unhappily common adverse event associated with [osteoporosis]. Although the surgical treatment for these fractures is refined and well practiced, poor outcomes are the norm: many patients die soon after they fracture their hip, and many of those who do not die fail to regain their pre-injury level of function.

Femoral neck fractures are often the results of falls, and Grisso et al ¹ have shown that the risk of falling is an independent risk for fracture, apart from the bone density.
The typical femoral neck fracture patient is frail and elderly. By contrast, the typical patient with a Stress fracture of the femoral neck (which at times progresses to a full fracture) is a young and vigorous athlete. As such, it is best to consider the [stress fracture of the femoral neck ] a distinct entity, as we do.

Anatomy

Conceptually, the neck of the femur is the part of the bone spanning the head proximally and the intertrochanteric region distally. The true intracapsular aspect of the neck, however, excludes the posterior aspect of the distal 1/3rd of the neck, and the functional transition from neck to intertrochanteric bone is not 100% abrupt.

The importance of the neck is not only for its structural contribution to the hip but its position as the conduit of blood vessels (branches of the medial and lateral circumflex femoral arteries) to the head. As such, a neck fracture may disrupt this blood supply and a "healed fracture" may still lead to osteonecrosis of the head with a poor outcome.

The ligamentum teres attaches the head to the acetabulum. This offers no benefit to the patient with a fracture (the blood supply coming from the ligamentum is present only in children) and indeed may hinder removal of the head during surgery.

Patient History and Physical Findings

The typical patient with a femoral neck fracture is an elderly slightly built Caucasian lady with at least 2 medical co-morbidities who presents with a painful hip and a shortened and externally rotated lower extremity after a fall.

Beware of an acute medical condition (seizure, syncope, MI) that was the cause of the fall.

Imaging and Diagnostic Studies

The diagnosis of femoral neck fracture is often obvious on the basis of plain xrays. If a typical patient (ie, an elderly slightly built Caucasian lady who presents with a painful hip after a fall) has no obvious fracture on xray, MRI must be used to exclude the diagnosis and allow discharge from the hospital; without that confirmation, the tentative diagnosis of an occult non-displaced fracture must be made and the patient should be admitted. (The treatment of a displaced fracture is more intense and the outcomes presumably inferior - so don't let a missed non-displaced fracture become something worse on your watch.)

Note that a bone scan is not immediately reliable, so unless you are willing to house the patient for 3 days or so until is becomes reliable, MRI is the test of choice.

Classification

Anatomic:

The standard categorization of femoral neck fractures is into two groups: the subcapital fracture and the basi-cervical (which are extracapsular and may behave a bit more like an intertrochanteric fracture). Transcervical fractures have also been described, however this group is controversial. Many argue that: a) the exact location of the fracture cannot be idendified by radiography, b) transcervical and basicervical fractures are functionally equal, and c) that subcapital and transcervical fractures are essentially the same and that any visible difference is artifactual and a result of x-ray parallax¹.

Fracture Displacement:

For subcapital fractures, the Garden Classification is the most used:

• I: incomplete or impacted
• II: complete but nondisplaced
• III: complete, partially displaced
• IV: complete and fully displaced

A BMSD modification, linking treatment to classification, would be to group types I and II into a unified "type A", representing the stable fractures (probably) amenable to fixation and III and IV into "type B", the unstable fractures (probably) more in need of prosthetic replacement.

Fracture Angle: Pauwels Classification

Garden reported the consistent finding of fracture lines 50 degrees from horizontal and argued that any change in obliquity was a misinterpretation of the x-ray ² . No consistent relationship has been shown between Pauwels Type and incidence of nonunion or osteonecrosis¹. For these reasons, the Pauwels classification is currently used to describe femoral neck delayed unions and nonunions¹.

• Type I: < 30 degrees from horizontal
• Type II: 30 - 50 degrees from horizontal
• Type II: >70 degrees from horizontal

Treatment

Nonoperative management is reserved only for those with extremely high surgical risk or demented nonambulators with minimal hip pain¹

Stable fractures are probably amenable to fixation whereas unstable fractures and probably more in need of prosthetic replacement. The hedge word "probably" is included because the truth of the matter is that good outcomes could result from even "mismatched" treatment, and the right choice is based not only on outcomes data (ie, rates of osteonecrosis and non-union for a given presentation), which we are only beginning to collect, but also patient preferences for the various possible intermediate and final outcomes and the patients' tolerance for risk factors we have not even begun to assess. About 8-33% of impacted fractures will displace without internal fixation. This number decreases to 5% with internal fixation¹.

In general, we try to avoid joint replacement in younger patients, and thus we 'push the envelope' in terms of which fractures in young people are pinned. Older age, greater displacement, greater time from injury to treatment and underlying hip pain are factors predictive of arthroplasty.  In the the older but active patient with displaced femoral neck fractures, several randomized controlled trials have show better functional outcomes with total hip arthroplasty versus hemiarthroplasty or internal fixation. However, we we do not have good prospective data to show what patient or injury characteristics are more amenable to fixation versus replacement.

Note that because (most of) the neck is intracapsular, the fracture hematoma could theoretically lead to increased intracapuslar pressure, tamponade of the femoral head blood supply and ultimately osteonecrosis). Indeed, increased intraarticular pressures after femoral neck fractures relieved with aspiration or capsulotomy has been reported in numerous studies. For that reason, some surgeons have historically advocated performance of a capsulotomy to decompress that pressure build-up if urgent pinning is attempted, especially in a young patient.  However, the literature does not show improved outcome associated with this practice and it's use has become relatively uncommon ^{3 4}
(Author's note: I was told that by my teachers and I repeat it to my students, yet I have never had occasion to do this. Can somebody find a reference?)
The fundamental guiding principle in operative fixation of femoral neck fractures involves accurate reduction and timely and stable fixation. Studies have show that the greatest risk to failure of these fractures is a malreduction. Although timing of surgery has been much discussed in the literature, these is no consensus on a threshold at which time outcomes become unacceptably poor or when arthroplasty result become better. Increased displacement and time to surgery likely increase likelihood of osteonecrosis of the femoral head. However, whether either independently affects malunion or nonunion rates is uncertain.  Furthermore, osteonecrosis in the setting of these fractures often does not lead to hip pain or arthritis. In general and if internal fixation is chosen, closed reduction is attempted for displaced fractures. If reduction cannot be achieved, open reduction through an anterolateral Watson-Jones approach or an anterior Smith-Peterson approach should be used to achieve open manual reduction. If there is good cortical apposition, 3 cancellous screws (with juxtacortical placement posteriorly and inferiorly) will provide adequate fixation. In the setting of cortical comminution, a fixed angle device provides more rigid support. More vertically oriented fractures may also benefit from a fixed angle device or the use of a 4th cancellous screw.

Postoperative Care

Include immediate postoperative care and rehabilitation

Outcomes

The typical triad of outcomes after severe injuries is seen: not so bad, bad and very bad. It usually is some variation on the theme of 'bad': this fracture is a severe and substantial physiological insult to most patients.

Complications

• Surgery was a success but patient still does poorly
• Dislocation if replacement performed (if you are demented, following hip precautions will be hard!)
• Nonunion: up to 5% of nondisplaced fractures and up to 25% of displaced fractures¹
• Osteonecrosis: Up to 10% of nondisplaced fractures and up to 27% of displaced fractures¹
• Fixation faiulure
• Prominent hardware

Red Flags and Controversies

• How quickly must we operate ? Long gaps between admission and surgery are typically associated with poor outcomes but maybe that is because sicker patients are those subject to delay
• Because demented patients will find following hip precautions difficult, should we simply avoid the posterior approach and use only the anterior-lateral ?
• Should we fix or replace?
• If we replace, is it a hemi or a total?
• If we replace with a hemi, is it unipolar or bipolar?
• Is it ethical to use low demand stems, or is it unfair bedside rationing ?
• Do we even know what we are doing? (Garden classification seems hard to apply)
• Should we admit the patient to the medicine service or to orthopedics?
• Does body mass protect against fracture because of a diminution of osteoporosis or because of a soft tissue padding effect?

Selected References

1. Bucholz RW, Heckman JD, Court-Brown CM, Tornetta P, Koval KJ. Rockwood and Green's Fractures in Adults: Rockwood, Green, and Wilkins' Fractures, 2 Volume Set. Sixth Edition. Lippincott Williams & Wilkins; 2005

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