Femoral Neck Fractures

Introduction

The femoral neck fracture is among the most common and most consequential of orthopedic injuries, with a lifetime risk in women of approximately 17 percent and in men of approximately 6 percent in industrialized populations. The annual incidence is approximately 700 per 100,000 in women over 80 years and is projected to grow substantially as populations age, with global hip fracture numbers approaching 6 million annually by 2050 in some projections. The one-year mortality following hip fracture in the elderly approaches 20 to 30 percent — a figure that has not changed substantially over decades of orthopedic intervention, reflecting the marker that hip fracture provides for general frailty and decline. The orthopedic management of the femoral neck fracture combines the urgency of restoring weight-bearing function (to permit mobilization and avoid the cascade of immobilization-related complications) with the central management question of fixation versus replacement that depends on patient age, displacement, time from injury, and bone quality. This chapter, drawing principally on Rockwood and Green’s Fractures in Adults, AO Principles of Fracture Management, Apley & Solomon’s, and Miller’s Review of Orthopaedics, addresses the contemporary management of femoral neck fractures.

Surgical Anatomy and Blood Supply

The femoral neck extends from the femoral head to the intertrochanteric line, with a typical length of 4 to 5 cm and an angulation relative to the femoral shaft (neck-shaft angle) of approximately 130 degrees in adults. The anteversion of the femoral neck (the angle between the neck and the transcondylar axis of the distal femur) is typically 10 to 15 degrees of anterior rotation in adults. The blood supply to the femoral head is critical to the understanding of femoral neck fractures. The principal supply is through the medial femoral circumflex artery, a branch of the deep femoral artery. The medial femoral circumflex courses posteriorly around the femoral neck and gives off retinacular branches that ascend along the posterior aspect of the femoral neck within the synovial reflection to enter the femoral head near the cartilage-bone junction. These lateral epiphyseal arteries supply approximately 70 to 80 percent of the femoral head. Smaller contributions come from the lateral femoral circumflex artery (anteriorly) and the artery of the ligamentum teres (a branch of the medial femoral circumflex or, less commonly, of the obturator artery — supplying the head through the foveal vessels, of variable contribution in adults and more important in children). The clinical implication is that the displaced femoral neck fracture disrupts the retinacular vessels as they cross the fracture line, producing immediate and severe ischemia of the femoral head fragment. The duration of ischemia correlates with the subsequent risk of avascular necrosis: prompt reduction may restore circulation through the disrupted but not transected vessels, while prolonged displacement or repeated manipulation may produce irreversible ischemia.

The neck-shaft angle and Singh index of trabecular pattern on AP radiographs of the hip provide secondary information about bone quality. The calcar femorale is the dense vertical plate of bone deep within the proximal femur, providing structural support for the inferior medial neck region; its integrity is important in fixation construct stability.

Classification

Two classification systems are predominant: the Garden classification (focused on radiographic displacement) and the Pauwels classification (focused on shear angle).

Garden Classification (1961) The Garden classification divides femoral neck fractures into four types by displacement on the AP radiograph: Garden I: Incomplete or impacted valgus fracture. The trabecular pattern of the inferior femoral head appears slightly valgus relative to the trabeculae of the neck. Garden II: Complete fracture without displacement. The fracture line is complete but the head and neck remain in anatomical alignment. Garden III: Complete fracture with partial displacement. The fragments are displaced but maintain some contact. Garden IV: Complete fracture with full displacement. The fragments are completely separated, with the head fragment typically rotated. The inter-observer reliability of the Garden classification has been criticized — multiple studies have demonstrated only moderate agreement on the four-type system. The practical simplification to non-displaced (Garden I and II) versus displaced (Garden III and IV) is widely used and has better inter-observer agreement. The most important clinical distinction is the displaced versus non-displaced dichotomy, as it predicts both AVN risk and treatment approach. Pauwels Classification (1935) The Pauwels classification divides femoral neck fractures by the angle of the fracture line relative to the horizontal: Pauwels I: Fracture angle less than 30 degrees from horizontal. The fracture line is more transverse; compressive forces predominate at the fracture site. Pauwels II: Fracture angle 30 to 50 degrees from horizontal. Intermediate forces. Pauwels III: Fracture angle greater than 50 degrees from horizontal. The fracture line is more vertical; shear forces predominate, with a higher failure rate of fixation. The Pauwels classification was originally derived to predict biomechanical fixation challenges; the modern application is in selecting fixation constructs that resist shear

forces in Pauwels III patterns (often a sliding hip screw with anti-rotation screw, or fixed- angle plate fixation). Anatomic Location Femoral neck fractures are further classified by location: subcapital (just below the femoral head), transcervical (mid-neck), and basicervical (at the junction of the neck and the intertrochanteric region — sometimes grouped with extracapsular fractures because of the different blood supply and more reliable healing).

Clinical Assessment

The classical presentation is the elderly patient with a low-energy fall who presents with hip pain and inability to bear weight, with the affected leg held in slight external rotation and shortening. Active straight-leg raise is markedly limited with severe pain. Greater trochanter tenderness and pain with hip log-rolling are present. The pain is typically in the groin or anterior thigh, sometimes referred to the knee. The patient should be assessed for the mechanism of fall (mechanical fall versus syncope or cardiac event, with implications for medical workup), comorbidities that affect operative risk, functional baseline (independent ambulation versus assisted, with implications for treatment choice), and cognitive status (with implications for adherence to postoperative protocols and rehabilitation). The non-displaced or impacted femoral neck fracture in the high-functioning elderly patient may present with surprisingly mild symptoms and the ability to bear weight — these patients may walk in on a fractured hip if it is impacted in valgus. A high index of suspicion is required in elderly patients with low-energy fall and hip pain, even with apparent ability to bear weight. The imaging is typically a standard AP pelvis radiograph (showing both hips for comparison) and a cross-table lateral or frog-leg lateral of the affected hip. MRI is the imaging study of choice when radiographs are negative or equivocal but clinical suspicion remains; MRI demonstrates the fracture line, the bone marrow edema, and any associated injury (occult intertrochanteric or pubic ramus fracture, sacral insufficiency fracture). MRI is sensitive within 24 hours of injury. CT is an alternative for those who cannot tolerate MRI but is less sensitive for occult fractures.

Treatment Principles — The Central Algorithm

The treatment algorithm depends on the interaction of age, fracture displacement, and functional status. The principal options are: Non-operative management: Reserved for non-displaced or impacted fractures in patients who are non-ambulatory or in whom surgery is contraindicated. The pain control allows mobilization to chair and tolerance of nursing care; the fracture heals in malposition or fails to heal. The mortality in this group is very high but operative intervention may not improve it.

Internal fixation: For non-displaced fractures (Garden I and II) in any age group, and for displaced fractures (Garden III and IV) in young patients where preservation of the native head is the goal despite AVN risk. Hemiarthroplasty: For displaced fractures in elderly patients with limited functional demand and intact acetabular cartilage. Total hip arthroplasty (THA): For displaced fractures in elderly patients with high functional demand, in patients with pre-existing acetabular pathology (osteoarthritis, rheumatoid arthritis), and in active patients with reasonable life expectancy. The choice between hemiarthroplasty and THA in the elderly displaced femoral neck fracture has been the subject of considerable investigation, with growing evidence favoring THA in the relatively younger, healthier, more active elderly patient. The HEALTH trial (Bhandari et al., 2019), a large multicenter randomized trial, demonstrated no significant difference in re-operation rate at 24 months between THA and hemiarthroplasty for displaced femoral neck fractures in patients aged 50 or older who were ambulatory before fracture. Subsequent secondary analyses and other trials have shown that THA offers better functional outcomes in the high-functioning elderly patient at the cost of slightly higher early complication rates (dislocation in particular).

Internal Fixation

Indications Internal fixation is indicated for non-displaced fractures (Garden I and II) in patients of all ages, and for displaced fractures (Garden III and IV) in younger patients (typically under 60 to 65 years) where the native femoral head is preferable to arthroplasty. Techniques The standard fixation technique is three or four cancellous screws (typically 6.5 or 7.3 mm partially threaded cannulated screws) in a triangular or inverted triangular configuration. The inferior screw is placed just above the inferior cortex (the calcar), providing inferior buttress; the two superior screws are spaced symmetrically above. The screws should engage the subchondral bone of the femoral head without penetrating the joint. The sliding hip screw (SHS, dynamic hip screw, DHS) with an additional cephalad anti- rotation screw is an alternative, particularly for basicervical fractures and Pauwels III patterns with more vertical fracture lines. The sliding mechanism allows controlled fracture site compression as the patient bears weight, although this may produce excessive shortening in severely comminuted patterns. The FAITH trial (Femoral Neck Fracture Trial Investigators, 2017), a large multicenter randomized trial comparing cancellous screws versus sliding hip screw fixation for femoral neck fractures, demonstrated broadly similar outcomes between the two with a slight trend toward less reoperation in the sliding hip screw cohort. The choice between the two techniques remains a matter of surgeon preference and fracture characteristics.

The timing of fixation for displaced femoral neck fractures has historically been considered an emergency, with the classical teaching that operative intervention within 6 to 12 hours of injury reduces AVN risk. The contemporary evidence is more mixed — most studies show no clear benefit from very early surgery beyond what comes from prompt and adequate reduction, with patient stabilization and adequate operative resources being more important than emergency surgery. The general consensus is that surgery should be performed within 24 to 48 hours of injury for the medically stable patient. Outcomes and Complications The complications of internal fixation include nonunion (5 to 30 percent depending on displacement and patient factors), avascular necrosis (10 to 45 percent in displaced fractures), and fixation failure with cut-out or back-out of screws. The combined rate of “treatment failure” requiring conversion to arthroplasty in displaced femoral neck fractures treated with internal fixation in the elderly is approximately 30 percent at 5 years — a substantial figure that supports the move toward primary arthroplasty in this population. In the younger patient with displaced femoral neck fracture, the AVN rate of approximately 30 percent and the nonunion rate of 10 to 15 percent must be accepted because the alternatives (primary arthroplasty in a young patient) have their own substantial long- term concerns. The patient must be counseled about these risks and about the possibility of late conversion to arthroplasty.

Hemiarthroplasty

Indications Hemiarthroplasty is appropriate for displaced femoral neck fractures in the elderly patient with limited functional demands and intact acetabular cartilage. The classical indication has been the household ambulator — the patient who walks within the home but not extensively outside — where the limitations of hemiarthroplasty match the patient’s functional level. Techniques The classical unipolar hemiarthroplasty replaces the femoral head with a single-piece stemmed prosthesis. The bipolar hemiarthroplasty uses a smaller inner ball that articulates within an outer cup that itself articulates with the acetabular cartilage — theoretically reducing wear on the acetabular cartilage by allowing motion at the inner articulation. The clinical evidence has not consistently demonstrated long-term advantages of bipolar over unipolar designs, although bipolar designs may be useful in selected patients where conversion to THA may be needed. The choice between cemented and uncemented stem fixation is informed by patient age, bone quality, and the literature. The AAOS guideline and the NICE guidance recommend cemented stems for hip fracture in the elderly, reflecting evidence of lower pain, lower revision rates, and lower thigh pain compared with uncemented stems. The risk of bone

cement implantation syndrome (sudden hemodynamic collapse during cementation, related to fat and marrow embolization — see Topic Trauma-7) is the principal concern with cemented stems and requires careful technique and anesthetic management. Outcomes Hemiarthroplasty produces a reliable functional outcome in the appropriate population, with most patients returning to their pre-fracture functional level. The principal long-term concern is acetabular cartilage wear (acetabular protrusio) in active patients, which can be 10 to 15 percent at 10 years in active patients but is much less of an issue in the typical low-demand population. Dislocation rates of hemiarthroplasty are typically 1 to 3 percent, similar to or slightly lower than THA in this population.

Total Hip Arthroplasty

Indications THA is increasingly favored for displaced femoral neck fractures in higher-demand elderly patients, in those with pre-existing acetabular pathology, and in patients with reasonable life expectancy where the long-term advantages of better function will be realized. The threshold for choosing THA over hemiarthroplasty has progressively lowered, with many centers now offering THA to most ambulatory, cognitively intact patients with reasonable comorbidities. Technique The technical considerations include the choice of approach (the posterolateral approach is most common but has the highest dislocation rate; the direct anterior approach has gained popularity with lower dislocation rates but requires specialized table or experience; the anterolateral approach is intermediate), the choice of acetabular component (cementless cup with high-friction surface and screws for additional fixation, with options including ceramic-on-ceramic, ceramic-on-poly, or metal-on-poly bearings), and the choice of femoral component (cemented or uncemented stem). The dual-mobility cup, with a polyethylene head that articulates within a larger metal cup, has gained substantial popularity for hip fracture THA because of its very low dislocation rates. Outcomes THA in the fracture context produces excellent functional outcomes in the appropriate patient, with most patients returning to community ambulation and previously enjoyed activities. The principal concern is dislocation (3 to 10 percent depending on approach and patient factors — substantially higher than in elective THA), reflecting the soft-tissue laxity in the fractured hip and the patient population’s tendency to cognitive limitations affecting compliance with hip precautions. Dual-mobility designs have substantially reduced dislocation rates and are increasingly the standard for hip fracture THA.

Special Considerations

Femoral Neck Fractures in Young Patients The femoral neck fracture in a young patient (under 50, typically 20 to 50 years) is a distinct clinical entity — high-energy mechanism, attempt at head preservation despite AVN risk, and the central concept that primary arthroplasty in this age group has substantial long-term concerns. The treatment is urgent reduction and rigid internal fixation, typically with cannulated screws or a sliding hip screw construct, with the patient counseled about the substantial AVN risk (typically 25 to 35 percent) and the possibility of late conversion to arthroplasty. The timing of surgery in the young patient has been the subject of more focused investigation, with some evidence supporting urgent surgery (within 6 to 12 hours) to maximize the chance of preserving the head’s blood supply, although the evidence is not entirely consistent. Capsular decompression (drainage of the intracapsular hematoma) has been proposed as a means of reducing the intracapsular pressure that may compromise the residual blood supply through the retinacular vessels. Some authors recommend this routinely; others reserve it for selected cases or do not perform it at all. Pediatric Femoral Neck Fractures The pediatric femoral neck fracture is uncommon but has substantially worse outcomes than the adult equivalent, with AVN rates of 30 to 50 percent reported in many series despite optimal management. The classical Delbet classification divides pediatric femoral neck fractures into four types: type I transepiphyseal, type II transcervical, type III cervicotrochanteric, and type IV intertrochanteric. Type I and II have the highest AVN risk. Treatment is anatomical reduction and rigid internal fixation with smooth K-wires or cannulated screws (avoiding the physis when possible), with prompt operative intervention. Bilateral Femoral Neck Fractures Bilateral fractures are uncommon but described, typically in osteoporotic patients with very low-energy mechanism or in patients with seizure disorders. Bilateral fixation or arthroplasty proceeds in the same operation when the patient’s physiological state allows; otherwise the most symptomatic side is addressed first. Atypical Femoral Fractures and Bisphosphonate-Associated Fractures Patients on long-term bisphosphonate therapy are at risk of atypical femoral fractures — transverse subtrochanteric or femoral shaft fractures with characteristic radiographic features (lateral cortical thickening, transverse fracture line, medial spike), often preceded by prodromal pain. These are addressed in the femoral shaft chapter (Topic Trauma-23) but warrant mention here because of their association with osteoporosis treatment.

Postoperative Management The cornerstone of postoperative management is early mobilization — ideally on the day of surgery or the first postoperative day — with weight bearing as tolerated. Multiple trials have demonstrated that early mobilization reduces complications and improves outcomes. VTE prophylaxis is universal (see Topic Trauma-7). Multimodal pain management including peripheral nerve blocks (fascia iliaca block, lumbar plexus block) reduces opioid use and facilitates mobilization. Comprehensive geriatric care with input from medical, nursing, physiotherapy, and social work teams improves outcomes in the hip fracture population. The Frailty Hip Fracture Service model with co-management between orthopedics and geriatrics has been shown to reduce mortality and complications. The secondary fracture prevention with bone-protection medication (bisphosphonates, denosumab, teriparatide), calcium and vitamin D supplementation, fall-prevention assessment, and outpatient follow-up is essential — the patient who has sustained a hip fracture has approximately 4 to 5 times the risk of a second fragility fracture within a year if these measures are not addressed.

Summary and Take-Home Points

The femoral neck fracture combines the urgency of restoring function in the elderly with the central management algorithm built around displacement (Garden I-II versus III-IV), age, and functional status. The blood supply to the femoral head through the retinacular vessels of the medial femoral circumflex artery is disrupted by displacement, producing the high AVN risk of displaced fractures. The central algorithm is: non-displaced fractures (Garden I-II) in any age receive internal fixation with cancellous screws; displaced fractures (Garden III-IV) in younger patients (under 60-65) receive urgent anatomical reduction and rigid internal fixation despite the substantial AVN and nonunion risks; displaced fractures in elderly patients with reasonable functional status and pre-fracture ambulation increasingly receive primary total hip arthroplasty (with dual-mobility designs gaining popularity to reduce dislocation); displaced fractures in low-demand elderly patients receive hemiarthroplasty (with cemented stems preferred in osteoporotic bone). The HEALTH and FAITH trials provide the evidence base for these choices. The complications of fixation include AVN, nonunion, and fixation failure with substantial combined treatment failure rates approaching 30 percent in displaced fractures in the elderly. The complications of arthroplasty include dislocation (particularly with posterolateral approach), bone cement implantation syndrome (with cemented stems), and the longer-term concerns of wear and revision. The systemic management — prompt surgery (within 24-48 hours), early mobilization, multidisciplinary geriatric co- management, and secondary fracture prevention — is at least as important as the orthopedic technique in determining the long-term outcome. The chapter that follows turns to the pertrochanteric (intertrochanteric) fracture — extracapsular and with a substantially different blood supply situation — where the principles of construct selection

(sliding hip screw versus cephalomedullary nail) provide a parallel decision-making framework.