Femur
Long Bone; Appendicular Skeleton · Located in the thigh (femoral region). It sits between the hip and the knee, angled medially (the 'Q' angle) to bring the knees closer to the body's center of gravity.
Also known as: Thigh Bone
Classification
Long Bone; Appendicular Skeleton
Location
Located in the thigh (femoral region). It sits between the hip and the knee, angled medially (the 'Q' angle) to bring the knees closer to the body's center of gravity.
Origin
Endochondral ossification. It features one primary center for the shaft (8th week fetal) and four secondary centers: one for the head, one for each trochanter, and one for the distal epiphysis.
Dimensions
The femur is the longest and heaviest bone in the human body. In an average adult male, it measures approximately 48 cm (19 in) in length and 2.34 cm in diameter. It accounts for roughly 25% of an individual's total stature.
Description
The femur is the foundational pillar of the lower limb. Its design maximizes strength while maintaining a range of motion at the hip, acting as a crucial lever for the powerful muscles of the thigh.
Key Features
Spherical head, distinct neck-shaft angle, greater and lesser trochanters, and large distal condyles. The linea aspera on the posterior side is a definitive identification marker.
Anatomical Description
The femur consists of a proximal end with a spherical head (caput femoris), a neck (collum), and two prominent bony projections known as the greater and lesser trochanters. The shaft (corpus) is cylindrical and bows anteriorly. The distal end expands into medial and lateral condyles for articulation with the tibia.
Dimensions & Proportions
The femur is the longest and heaviest bone in the human body. In an average adult male, it measures approximately 48 cm (19 in) in length and 2.34 cm in diameter. It accounts for roughly 25% of an individual's total stature.
Surface Features
Distinguished by the linea aspera on the posterior shaft, the gluteal tuberosity, and the fovea capitis (a pit on the head). The cortical surface is generally smooth except at muscle attachment sites where it becomes rugose.
Articulations
Proximally, it articulates with the acetabulum of the pelvis (hip joint). Distally, it articulates with the tibia and patella (knee joint). These are synovial joints (ball-and-socket and hinge, respectively).
Muscle Attachments
The greater trochanter serves as the insertion for the gluteus medius/minimus. The lesser trochanter receives the iliopsoas. The shaft provides origin for the vastus muscles, and the linea aspera serves as an insertion for the adductor group.
Blood Supply
Primary supply comes from the profunda femoris artery via the nutrient artery (entering the shaft) and the medial and lateral circumflex femoral arteries which supply the head and neck.
Developmental Origin
Endochondral ossification. It features one primary center for the shaft (8th week fetal) and four secondary centers: one for the head, one for each trochanter, and one for the distal epiphysis.
Clinical Significance
Commonly prone to neck fractures (often called 'broken hips' in elderly) and mid-shaft fractures due to high-energy trauma. It is a major site forosteoporosis-related morbidity.
Age & Sex Determination
Sex is estimated using the femoral head diameter (usually >47mm in males) and the subtrochanteric shape. Age is estimated via the closure of the distal epiphysis (approx. 16-20 years) and the proximal epiphysis (approx. 14-19 years).
Forensic Importance
Crucial for stature estimation using Trotter and Gleser formulas. Its durability makes it one of the most likely bones to survive taphonomic processes for DNA extraction.
Comparative Anatomy
In quadrupeds, the femur is typically shorter and broader. The femoral neck is generally shorter than in humans, reflecting different mechanical loads associated with bipedalism.
Evolutionary History
The femur evolved in early tetrapods to support weight on land. The specific elongation and angulation of the human femur are adaptations for efficient bipedal locomotion.
Imaging Characteristics
On X-ray, the Ward's triangle is a radiolucent area in the neck used to assess bone density. CT is used to view complex intra-articular distal fractures.
Pathological Conditions
Osteoarthritis of the hip/knee, Avascular Necrosis (AVN) of the head, Osteosarcoma (often found in the distal femur), and Paget's disease.
Surgical Relevance
Site of Total Hip Arthroplasty (THA) and intramedullary (IM) nailing for shaft fractures. The femoral artery lies anteriorly in the femoral triangle, a critical area for surgeons.
Similar Bones
The humerus is most similar; distinguish the femur by its spherical head on a long neck, the presence of trochanters (vs. tubercles), and the massive size of the distal condyles.
Interesting Facts
The femur is theoretically stronger than steel of equivalent weight and can support up to 30 times the body's weight in compressive forces.
Photography Tips
Photograph the posterior view to show the linea aspera. Capture the proximal end at a 45-degree angle to clearly demonstrate the neck-shaft angle and trochanters.