Introduction
The femur, or the thigh bone, is the longest bone in the body and is responsible for weight bearing and gait stability. The proximal end of the femur comprises the pyramid-shaped femoral neck and two rough bony prominences; the greater trochanter (major trochanter) and the lesser trochanter (minor trochanter), serve as an attachment to the muscles and facilitate movement of the hip and the knee. The subtrochanteric region is the area within five centimeters distal of the lesser trochanter. The femoral calcar is a vertical plate lying deep to the lesser trochanter and is composed of a multilayer compact bone with a thickness of less than one millimeter. It provides significant structural integrity to the proximal femur bone; and can withstand great forces (more than 1000 Newtons) upon standing and during gait, and secondary forces from various muscle attachments, such as abductors, adductors, external rotators, etc., which increase the stress around the hip and the proximal femur bone.
What Is a Subtrochanteric Fracture?
A break or discontinuity in the proximal femur bone within five centimeters of the lesser trochanter is called a subtrochanteric fracture. These fractures are less common, account for approximately 7 to 34 percent of femoral fractures, and have a bimodal distribution. These fractures are seen in young adults less than 40 years due to high-energy trauma and elderly individuals above 50 years due to low-energy trauma. The incidence of these fractures is almost equal in males and females at a young age; however, the incidence among females increases with age.
What Are the Types of Subtrochanteric Fractures?
1. Subtrochanteric fractures are classified based extension of the fracture into the piriformis fossa (Russell - Taylor classification):
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Type I: No extension into the piriformis fossa.
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Type II: Extension into the greater trochanter with the involvement of the piriformis fossa.
2. Based on the fracture morphology and mechanism, subtrochanteric fractures are classified into [AO/Orthopedic Trauma Association(OTA) classification]; where (A, B, and C represent the energy of the trauma) and (1, 2 or 3 represent the mechanism of fracture)
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Simple fractures (A), Transverse (3).
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Wedge fractures (B), Fragmented (3).
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Complex fractures (C), Spiral (1).
3. Atypical subtrochanteric fractures are associated with bisphosphonates therapy and identifying the underlying primary risk factor. These types of fractures are divided into major and minor criteria by the American Society for Bone and Mineral Research (ASBMR). To determine a fracture as atypical, four of the five major criteria are required, while the minor criteria may or may not be present. The major criteria include; minimal comminution, lateral cortical thickening, low-impact trauma, the origin of fractures at the lateral cortex, and medial spike associated with complete fractures. Minor criteria include dull or aching pain, delayed fracture healing, bilateral complete or incomplete femoral diaphysis fracture, and primary or metastatic bone tumors.
What Are the Causes of Subtrochanteric Fractures?
Some of the causes of subtrochanteric fractures include:
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High-energy trauma, such as motor vehicle accidents, and collisions, or falls from heights, is mainly seen in young individuals.
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Low-energy trauma, such as ground-level falls or falls from standing height, is usually seen in elderly individuals.
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Pathologic or atypical subtrochanteric fractures are seen in old patients under bisphosphonate therapy due to cortical weakness.
What Are the Signs and Symptoms of Subtrochanteric Fractures?
Some of the signs and symptoms of subtrochanteric fractures include:
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Serious multiple injuries in case of high-energy trauma.
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Skin abrasions, bleeding, and bruises with extensive soft tissue damage.
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Severe hip or thigh pain which increases movement.
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Significant swelling, which is tender on palpation.
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Inability to bear weight and unable to flex the hip.
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Shortened or externally rotated lower extremity.
What Are the Risk Factors Associated With Subtrochanteric Fractures?
Some risk factors associated with subtrochanteric fractures include:
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Patients undergoing treatment for osteoporosis with bisphosphonates.
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Chronic diseases such as diabetes mellitus.
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People with low bone density.
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Infection at the fracture site is a potential risk, as it interferes with bone healing. Superficial infections can be treated by antibiotics, but deep infections may require surgical irrigation, debridement, and implant removal. It is replaced with an antibiotic intramedullary implant followed by oral or intravenous (IV) antibiotics.
How Are Subtrochanteric Fractures Diagnosed?
Subtrochanteric fractures due to high-energy trauma may be associated with multiple injuries, bleeding, bruises, and damage to the soft tissues. These fractures are usually closed injuries; however, a skin examination must be performed due to the high degree of flexion of the proximal segment. Patients present with hip or thigh pain associated with an inability to bear weight. Physical examination includes a complete assessment of the surrounding neurovascular structures. Radiological investigations include orthogonal femur and knee (full-length views) radiographs, anteroposterior and lateral views of the hip, and anteroposterior pelvis radiographs. Optional radiographs, such as traction views, may be recommended in some cases to determine the fragments in comminuted patterns. Computed tomography (CT scan) may be performed as a part of the initial evaluation and may not always be preferred. Radiographic findings represent external rotation, abduction, and flexion of the proximal and adducted distal segments. Bisphosphonate-related fractures reveal an increase in the lateral and diaphyseal thickness of the cortical bone, lack of comminution, and a medial spike in case of a complete fracture.
How Are Subtrochanteric Fractures Managed?
Management of subtrochanteric fractures is challenging, and may encounter certain difficulties during the treatment. The goal is to determine the appropriate treatment strategy and prevent potential complications. Non-operative treatment is usually not recommended in subtrochanteric fractures due to the risk of malunion or nonunion. It is considered only in the case of patients with a high mortality risk from anesthesia or those severely ill patients with minimal hip discomfort. Anatomic reduction techniques include the application of clamps, joysticks, blocking wires or screws, etc. Positioning the patient before reduction is of utmost importance as it allows for an easier reduction of the distal fragment.
Surgical management is the treatment of choice for subtrochanteric fractures and can be divided into two major categories; intramedullary (IM) nailing and extramedullary plating.
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Intramedullary nailing is considered the gold standard treatment due to minimal blood loss, decreased hospital stay, and reduced operative time. This treatment facilitates immediate weight-bearing and improved functional outcomes. Intramedullary nails are metal rods (implants) that are inserted into the medullary cavity of the bone to provide stable support, increase stiffness and rigidity and decrease the strain on the implant. The entry point of the intramedullary nail and design determines the fracture reduction and stability.
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Extramedullary plating refers to the use of fixed-angle blades or locking metal plates for the fixation of subtrochanteric fractures. It presents technical difficulties, especially the fixed angle compared to IM nailing, as it increases the operative time, high infection rates, and cases of nonunion. However, when an open reduction is required, a provision fixation using a small fragment plate can be done, which helps reduce malunion rates.
What Are the Complications of Subtrochanteric Fractures?
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Treatment of bisphosphonate fractures has an increased risk of nonunion or iatrogenic fracture due to brittle bone and thickening of the cortical bone. It can be treated by revision surgery or discontinuation of bisphosphonate therapy.
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Non-union of the fractured segments following treatment may be due to improper anatomical reduction; it can be managed by exchanging implants, with or without bone grafting.
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Malunion or abnormal union of the fracture segments, especially in comminuted fractures, can be due to rotational errors and may result in hip pain and gait abnormalities. It can be managed by corrective osteotomy (making cuts in the bone to relieve the symptoms and facilitate normal alignment).
Conclusion
A subtrochanteric fracture is a break or discontinuity in the proximal femur bone within five centimeters of the lesser trochanter. These are rare fractures that possess a challenge to treat due to complex and powerful forces which cause the injury creating difficulty in the reduction and implant fixation. It is associated with severe thigh or hip pain, inability to weight bearing, significant swelling, and deformity. Operative management is the treatment of choice for subtrochanteric fractures to achieve appropriate alignment and stability and to promote healing.
