Anatomical zones and blood supply features
The proximal femur includes the head (caput femoris), neck, greater and lesser trochanters (trochanter major et minor). The key criterion for classifying these injuries is the attachment of the hip joint capsule to the base of the femoral neck. Based on this, fractures are divided into intracapsular (injuries to the head and neck) and extracapsular (trochanteric and subtrochanteric regions).
Bone healing potential directly depends on the angioarchitecture. The primary blood supply to the proximal region is provided by the medial and lateral circumflex femoral arteries (a. circumflexa femoris medialis et lateralis). They form an extracapsular arterial ring, from which the ascending cervical arteries arise.
In femoral neck injuries, these vessels are damaged. Subcapital fractures completely deprive the femoral head of blood supply, creating avascular conditions. Transcervical fractures partially preserve the blood supply. Unlike the neck, the intertrochanteric region is covered by a well-developed periosteum and is abundantly vascularized, ensuring a high healing potential provided adequate reduction is achieved.
Classification of intracapsular fractures
Femoral neck injuries are classified according to several criteria. Based on changes in the neck-shaft angle, fractures are divided into valgus (impacted, angle increases) and varus (non-impacted, angle decreases).
Pauwels' classification, based on the angle between the fracture line and the horizontal plane, has special prognostic significance:
- Group I (<30°): the fracture line is close to horizontal. Converging (compressive) forces occur, creating optimal conditions for bone union.
- Group II (30–50°): an intermediate variant of instability.
- Group III (50–90°): the plane is close to vertical. "Shearing" forces predominate, tending to displace the fragments apart. This is the most unfavorable variant, frequently leading to secondary displacement and pseudoarthrosis.
Displacement biomechanics and clinical presentation
The clinical presentation of a fracture includes groin pain, limb shortening, and external rotation. Displacement of bone fragments is driven by gravity and the powerful pull of attached muscles:
- Abduction of the proximal fragment: caused by the gluteus medius and minimus muscles (m. gluteus medius et minimus).
- External rotation: the result of contraction of the short external rotators—the piriformis (m. piriformis), gemelli (mm. gemelli), obturator internus (m. obturatorius internus), and quadratus femoris (m. quadratus femoris) muscles.
- Flexion: driven by the pull of the iliopsoas muscle (m. iliopsoas), which attaches to the lesser trochanter (particularly pronounced in subtrochanteric fractures).
In simple trochanteric injuries, muscle tension often promotes the approximation of fragments, whereas in intertrochanteric injuries, muscle contraction conversely causes fragment separation, making reduction more difficult.
Diagnostics and occult injuries
The mainstay of diagnosis is anteroposterior and lateral radiography of the pelvis. These images are used to assess bone integrity and the Singh Index, an indicator of cancellous bone density. Normally (grade 6), all trabecular groups are visualized (principal and secondary compressive, and tensile groups). In osteoporosis, trabeculae disappear, and Ward's triangle (a radiolucent area in the neck) expands, forming a "weak spot".
Occult fractures—injuries without displacement that are invisible on standard radiographs—present a particular challenge. The patient experiences groin pain and is unable to bear weight on the leg.
The following methods are used to confirm the pathology:
- Log-roll test: gentle internal and external rotation of the straightened leg. The onset of joint pain indicates an occult fracture.
- MRI: the gold standard for diagnosis when radiographic findings are equivocal.
- CT: an alternative when MRI is contraindicated.
- Bone scintigraphy: assesses bone metabolism, but changes may not be visible within the first 72 hours after injury.
For Pauwels' classification: the "steeper" (more vertical) the fracture line, the faster the fragments will "slip" downward (Group III has the worst prognosis).
Class and exam questions
Why do intracapsular fractures frequently get complicated by nonunion?
Due to the meager blood supply of the femoral head (damage to the ascending cervical arteries) and the absence of periosteum on the femoral neck, which prevents the formation of a robust bone callus.
What to do if a patient has groin pain after a fall, but X-rays show no fracture?
A log-roll test must be performed, and if positive, an MRI should be ordered to rule out an occult femoral neck fracture.
How to distinguish an impacted fracture from a non-impacted one based on the angle?
In an impacted fracture, the neck-shaft angle typically increases (valgus fracture), while in a non-impacted fracture, it decreases (varus fracture).
What is the specific feature of intertrochanteric fractures compared to femoral neck fractures?
The intertrochanteric region has an abundant blood supply and dense cancellous bone, which is why such fractures have a high healing potential and unite well with stable fixation.
What else to study on this topic
- Radiographic assessment of bone density: The Singh Index
- Biomechanics of muscle traction in subtrochanteric fractures
- Management algorithm for elderly patients: ruling out syncope and myocardial infarction
- Log-roll test in clinical practice
- Avascular necrosis of the femoral head: pathogenesis
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