What is a subcapital femoral neck fracture in an older adult with osteoporosis?

What is a Subcapital Femoral Neck Fracture?

A subcapital femoral neck fracture is a break in the femoral neck immediately below the femoral head at the junction with the articular cartilage, representing an intracapsular hip fracture that occurs most commonly in elderly patients with osteoporosis and carries high risk for avascular necrosis due to disruption of the femoral head blood supply. 1, 2

Anatomic Location and Classification

• The subcapital region is the narrow zone of the femoral neck directly beneath the femoral head, where the bone transitions from the spherical head to the cylindrical neck 3
• This fracture occurs within the hip joint capsule (intracapsular), which has critical implications for blood supply to the femoral head 4
• Subcapital fractures are classified by displacement using the Garden staging system (stages I-IV), with stages III and IV representing displaced fractures that require different treatment approaches 3, 5

Clinical Presentation in Older Adults with Osteoporosis

• Patients typically present with a shortened and externally rotated limb, the classic deformity of displaced intracapsular fractures 2
• Severe groin pain radiating to the knee with tenderness over the anterior hip capsule is characteristic 2
• Critically, some patients with minimally displaced subcapital fractures may retain limited ambulation ability, so the ability to walk does not exclude a serious fracture 6
• Limited range of motion in all planes, particularly internal rotation and flexion, is typically observed 2
• Leg length discrepancy with the affected limb appearing shorter is common 2

Pathophysiology in Osteoporotic Bone

• Subcapital fractures occur in patients with abnormal bone from osteoporosis, representing insufficiency fractures where normal stress is applied to weakened bone 5
• The fracture disrupts the precarious blood supply to the femoral head, which relies on retinacular vessels that course along the femoral neck within the joint capsule 4
• External rotation of the distal fracture fragment creates a characteristic radiographic appearance that can sometimes mimic pathologic fracture, showing a radiolucency in the superolateral subcapital region 3
• This appearance occurs in 17% of subcapital fractures and is caused primarily by rotation and displacement of fracture fragments 3

High-Risk Nature and Complications

• Subcapital fractures are inherently high-risk injuries with increased rates of delayed union, nonunion, displacement, and avascular necrosis if not recognized and treated promptly 5
• The intracapsular location means that hematoma formation can tamponade the already compromised blood supply to the femoral head 4
• In elderly patients with osteoporosis, these fractures are associated with 7-10% mortality at one month and 30% mortality at one year 5
• The vulnerability of this patient population is apparent in prolonged hospital stays, complex care needs, and high morbidity 5

Diagnostic Approach

• AP pelvis and lateral hip radiographs are required to confirm fracture displacement and assess chronicity 2
• Radiographs may occasionally show findings that mimic pathologic fracture due to fragment rotation and displacement, but this appearance occurs in non-pathologic osteoporotic fractures 3
• Complete blood count and basic metabolic panel are necessary to assess for anemia, infection, and metabolic derangements 2

Treatment Principles for Displaced Fractures

• For elderly patients with displaced subcapital femoral neck fractures, arthroplasty is strongly recommended over internal fixation 5, 1
• Hemiarthroplasty is preferred for frail patients with multiple comorbidities, cognitive dysfunction, or limited pre-injury mobility 1, 2
• Total hip arthroplasty is preferred for healthy, active, independent patients without cognitive dysfunction who have higher functional demands 1, 2
• Cemented femoral stems are strongly recommended to improve function, reduce pain, and decrease periprosthetic fracture risk in osteoporotic bone 5, 1, 2
• Surgery within 24-48 hours of admission significantly improves outcomes and reduces mortality 2, 6

Critical Pitfall

• Subcapital fractures can occur as a catastrophic complication after treatment of intertrochanteric fractures with dynamic hip screws, particularly when the lag screw is not placed deep enough (within 5-8 mm of subchondral bone) in osteoporotic patients 7, 8, 9