Femoral Shaft

The femoral shaft, or body of the femur, is the long, cylindrical portion of the femur extending from the lesser trochanter proximally to the supracondylar ridges distally. It is the primary weight-bearing structure of the femur and plays a vital biomechanical role in locomotion, force transmission, and muscle attachment. As the strongest and longest bone segment in the human body, the femoral shaft endures immense mechanical loads and serves as a major anatomical landmark for orthopedic interventions.

Structure

The femoral shaft is a slightly curved, tubular structure composed of compact cortical bone that surrounds a central medullary cavity. The shaft has a gentle anterior convexity and gradually flattens distally. It is triangular in cross-section, with distinct borders and surfaces that provide anchorage for multiple muscles and intermuscular septa.

Borders

• Linea aspera: A prominent longitudinal ridge on the posterior surface, serving as a major site for muscle attachment.
• Medial border: Runs from the lesser trochanter to the medial supracondylar ridge.
• Lateral border: Extends from the greater trochanter region to the lateral supracondylar ridge.

Surfaces

• Anterolateral surface: Located between the lateral and anterior borders, gives origin to part of the vastus intermedius muscle.
• Anteromedial surface: Found between the anterior and medial borders; also serves as an attachment for vastus medialis.
• Posterior surface: Bordered by the linea aspera, it supports the insertion of adductor muscles and origin of vastus medialis and lateralis.

Location

The femoral shaft is located in the central thigh region, extending from just below the lesser trochanter to the point where the bone flares out into the medial and lateral supracondylar ridges above the knee. It lies deep to the quadriceps anteriorly and adductors medially, and is closely associated with the femoral neurovascular bundle proximally.

• Proximal limit: Just below the lesser trochanter
• Distal limit: Superior borders of the medial and lateral condyles

Function

• Weight-bearing: Transmits body weight from the pelvis to the knee and supports upright posture and locomotion.
• Muscle attachment: Serves as a site for origin and insertion of numerous thigh muscles that control hip and knee motion.
• Force distribution: Absorbs compressive, tensile, and torsional forces during movement and transfers them to the lower leg.

Muscle Attachments

The femoral shaft provides anchorage for several muscles of the anterior, medial, and posterior compartments of the thigh.

Muscle	Attachment Site	Function
Vastus lateralis	Lateral lip of linea aspera and lateral surface	Knee extension
Vastus medialis	Medial lip of linea aspera	Knee extension
Vastus intermedius	Anterior and lateral surfaces of shaft	Knee extension
Adductor longus	Middle third of linea aspera	Hip adduction
Adductor brevis	Proximal part of linea aspera	Hip adduction
Adductor magnus	Length of linea aspera and medial supracondylar line	Hip adduction and extension
Short head of biceps femoris	Lateral lip of linea aspera	Knee flexion and lateral rotation

Blood Supply

The femoral shaft receives a robust blood supply from branches of the profunda femoris (deep femoral) artery. These include:

• Nutrient artery: Enters the shaft through the nutrient foramen located along the linea aspera, supplying the medullary cavity and inner two-thirds of cortical bone.
• Perforating arteries: Three to four branches from the profunda femoris artery that pierce the adductor magnus and supply the posterior and lateral aspects of the shaft.
• Periosteal arteries: Small vessels from surrounding muscular branches that supply the outer third of cortical bone.

Nerve Supply

While the femoral shaft itself has limited sensory innervation, the periosteum and surrounding musculature are innervated by branches of the:

• Femoral nerve: Supplies anterior thigh muscles and periosteum.
• Obturator nerve: Supplies medial compartment muscles and periosteum near the linea aspera.
• Sciatic nerve: Supplies posterior compartment muscles attached to the femur.

Ossification

The femoral shaft ossifies from a primary center that appears during the 7th week of intrauterine life. Secondary ossification centers appear later at the proximal and distal ends (femoral head, greater trochanter, and condyles), but the shaft continues to elongate via endochondral growth at the metaphyses until the growth plates close in late adolescence.

• Primary ossification: 7th fetal week
• Growth plate closure: Around age 18–20 years

Fracture Classification

Fractures of the femoral shaft are typically high-energy injuries and classified based on location and pattern:

Type	Description
Transverse	Straight break across the shaft
Oblique	Angled fracture line
Spiral	Twisting force results in helical break
Comminuted	Multiple fracture fragments
Segmental	Two or more fractures separating a segment of bone

Clinical Significance

• Femoral shaft fractures: Common in high-impact trauma (e.g., road traffic accidents), often require intramedullary nailing or external fixation. Blood loss can be significant.
• Compartment syndrome: Rare but potentially limb-threatening complication of femoral shaft fracture due to bleeding or swelling in the thigh.
• Malalignment: Improper healing can result in rotational or angular deformities affecting gait.
• Stress fractures: Seen in athletes and military recruits from repetitive overuse, particularly in the mid-diaphysis.

Surgical Relevance

• Intramedullary nailing: Standard treatment for shaft fractures; the nail is inserted through the piriformis fossa or greater trochanter and passed down the shaft.
• External fixation: Used in polytrauma patients or open fractures to stabilize the limb temporarily or definitively.
• Osteotomies: Performed in deformity correction, sometimes involving deliberate break and realignment of the shaft.

Imaging

The femoral shaft is assessed using:

• Plain radiographs: AP and lateral femur views to identify fractures, bone alignment, and pathology.
• CT scan: Useful for evaluating complex or comminuted fractures, rotational deformities, and pre-surgical planning.
• MRI: Ideal for early detection of stress fractures or tumors affecting the diaphysis.