Femur

Introduction

Introduction to the Femur

The femur is the longest, heaviest, and strongest bone in the human body. It extends from the hip joint proximally to the knee joint distally, transmitting the body's weight from the pelvis to the tibia. The femur is a classic long bone with a proximal epiphysis (head, neck, greater and lesser trochanters), a diaphysis (shaft), and a distal epiphysis (medial and lateral condyles). Its complex architecture—including the angle of inclination (neck‑shaft angle) and the angle of torsion—reflects the biomechanical demands of bipedal gait. The bone provides extensive surfaces for the attachment of powerful muscles acting on the hip and knee. A thorough understanding of femoral osteology is essential for the diagnosis and management of fractures, for hip and knee arthroplasty, and for understanding muscular function and neurovascular relationships.

Study

1. General Features and Orientation

The femur is oriented so that its proximal end is directed medially and slightly anteriorly to articulate with the acetabulum, while its distal end expands to form the weight‑bearing condyles of the knee. In the anatomical position, the shaft slopes obliquely from lateral (above) to medial (below), contributing to the tibiofemoral valgus angle. The femoral head faces medially, upwards, and slightly forwards. The neck joins the shaft at an angle of approximately 125° (range 115–140°) in adults. A second important angle is the angle of femoral torsion (anteversion), normally about 12–15°, measured between the axis of the femoral neck and the coronal plane of the femoral condyles. The linea aspera runs along the posterior shaft and serves as a major aponeurotic attachment site.

2. Proximal End: Head, Neck, Trochanters

The femoral head forms approximately two‑thirds of a sphere and is covered by hyaline cartilage, except at the fovea capitis (a small central depression for the ligamentum teres). The head articulates with the acetabulum. The neck connects the head to the shaft and is trapezoidal in cross‑section. Its anterior surface is entirely intracapsular, while the posterior surface is only partially intracapsular; this has critical implications for intracapsular femoral neck fractures and the blood supply to the head.

The greater trochanter is a large, quadrilateral bony prominence at the junction of the neck and shaft, projecting superiorly and posteriorly. It gives attachment to the gluteus medius, gluteus minimus, piriformis, obturator internus and externus, and gemelli muscles. The trochanteric fossa lies on its medial surface and receives the obturator externus tendon. The lesser trochanter is a conical posteromedial projection below the neck, receiving the iliopsoas tendon. The two trochanters are united by the intertrochanteric line anteriorly (a roughened line marking the attachment of the iliofemoral ligament) and the intertrochanteric crest posteriorly (bearing the quadrate tubercle for the quadratus femoris muscle).

3. Shaft (Diaphysis)

The femoral shaft is almost cylindrical but is convex anteriorly. Its middle third is triangular in cross‑section with three surfaces (anterior, medial, lateral) and three borders (medial, lateral, and the prominent posterior linea aspera). The linea aspera is a roughened double‑lipped ridge that receives the attachments of the vastus medialis, vastus lateralis, adductor muscles, and the short head of biceps femoris. Proximally, the linea aspera divides into the medial lip (continuing as the spiral line toward the lesser trochanter) and the lateral lip (blending into the gluteal tuberosity, for the gluteus maximus). Distally, it diverges into the medial and lateral supracondylar lines, which bound the popliteal surface of the femur. The nutrient foramen, directed proximally, is usually found on the medial lip of the linea aspera.

4. Distal End: Condyles and Intercondylar Fossa

The distal femur expands into the large medial and lateral condyles, which are covered by hyaline cartilage and articulate with the tibial plateau and patella. The condyles are separated posteriorly and inferiorly by the deep intercondylar (notch) fossa, which houses the cruciate ligaments. The medial condyle is larger and extends more distally, compensating for the oblique shaft. Anteriorly, the patellar surface (trochlea) is a grooved articular area for the patella, with the lateral lip being more prominent to prevent lateral patellar dislocation. Epicondyles project from the non‑articular sides of each condyle: the medial epicondyle bears the adductor tubercle for the adductor magnus tendon, and the lateral epicondyle gives attachment to the lateral collateral ligament and popliteus tendon. The gastrocnemius heads originate from the posterior surfaces of the condyles just above the articular margins.

5. Ossification and Development

The femur ossifies from one primary centre (diaphysis, appearing at the 7th week intrauterine) and four secondary centres: the distal epiphysis (end of 9th fetal month), the femoral head (6–12 months), the greater trochanter (4 years), and the lesser trochanter (12–14 years). The distal femoral epiphysis is the first secondary centre to ossify and is an important marker of fetal maturity. The growth plate between the head and neck fuses at 14–19 years. The greater and lesser trochanters fuse at 16–18 years. The distal epiphysis fuses at 16–20 years. Knowledge of these times is important in the assessment of fractures involving the growth plates and in forensic age estimation.

6. Clinical Considerations

Femoral neck fractures are common in osteoporotic elderly patients and can be intracapsular (high risk of avascular necrosis of the femoral head due to disruption of the retinacular vessels) or extracapsular (intertrochanteric). The Garden classification is used for subcapital fractures. Femoral shaft fractures are usually high‑energy injuries. Distal femoral fractures, including supracondylar and intercondylar patterns, can involve the articular surface and require anatomical reduction. The angle of inclination and anteversion are important in congenital and acquired hip disorders (e.g., coxa vara, coxa valga, increased femoral anteversion). The linea aspera serves as a surgical landmark for rotational alignment during intramedullary nailing. The femoral head's blood supply—primarily from the medial femoral circumflex artery—enters via the capsular vessels along the neck; disruption leads to avascular necrosis.

Summary

Summary of the Femur

The femur is the longest bone, composed of a head, neck, shaft, and distal condyles. Proximally, the head articulates with the acetabulum; the trochanters and intertrochanteric lines serve as major muscle attachments. The shaft bears the linea aspera and nutrient foramen. Distally, the condyles form the knee joint with the tibia and patella. The neck‑shaft angle and torsion are important for bipedal gait. Ossification follows a predictable pattern, and the rich but vulnerable blood supply of the femoral head is a critical clinical consideration. Fractures of the femur are classified by location and have significant morbidity.