Proximal Epiphysis of the Femur
The upper end of the femur has a complex structure designed to withstand major weight-bearing loads. It features the femoral head (caput femoris), which articulates with the acetabulum of the pelvis. The head bears a small depression known as the fovea of the head (fovea capitis femoris).
Connecting the head to the shaft is a narrowed region called the femoral neck (collum femoris). At the base of the neck are two massive bony prominences called trochanters (trochanteres):
- Greater trochanter (trochanter major) — located laterally. Adjacent to its medial side is the trochanteric fossa (fossa trochanterica).
- Lesser trochanter (trochanter minor) — located medially and posteriorly.
Anteriorly, the trochanters are connected by the intertrochanteric line (linea intertrochanterica), while posteriorly they are connected by the much more prominent intertrochanteric crest (crista intertrochanterica). Some individuals may exhibit an additional third trochanter (trochanter tertius).
Femoral Shaft (Diaphysis)
The shaft of the femur (corpus femoris) is nearly cylindrical in cross-section. Its anterior surface is entirely smooth, whereas the posterior surface prominently features the linea aspera (linea aspera).
The linea aspera divides into two lips proximally:
- Medial lip (labium mediale).
- Lateral lip (labium laterale), which extends superiorly into the gluteal tuberosity (tuberositas glutea).
Additional lines diverge from these lips. Superiorly, the pectineal line (linea pectinea) extends toward the lesser trochanter. Inferiorly, the medial and lateral supracondylar lines (linea supracondylaris medialis et lateralis) diverge toward the respective epicondyles, enclosing a flat, triangular area on the posterior surface called the popliteal surface (facies poplitea).
Distal Epiphysis
The lower end of the femur widens to form two large articular prominences—the condyles (condyli). The medial condyle (condylus medialis) and lateral condyle (condylus lateralis) articulate with the tibia. Directly above the condyles are the medial and lateral epicondyles (epicondylus medialis et lateralis).
The distal epiphysis also features several key surfaces and fossae:
- Patellar surface (facies patellaris) — located anteriorly to articulate with the patella.
- Intercondylar fossa (fossa intercondylaris) — located posteriorly between the condyles.
- Intercondylar line (linea intercondylaris) — separates the intercondylar fossa from the popliteal surface above.
Anatomy of the Patella
The patella (patella) is a key sesamoid bone crucial for knee joint biomechanics. It features a broad base (basis patellae) directed superiorly and a pointed apex (apex patellae) directed inferiorly.
Its anterior surface (facies anterior) is convex and rough for tendon attachments. The posterior articular surface (facies articularis) articulates with the femoral patellar surface and bears distinct facets corresponding to the femoral condyles.
Determining Femoral Side (Side Determination)
To determine whether an isolated femur is from the left or right side, follow three simple steps:
- Position the bone vertically: the proximal end (with the head and neck) must point superiorly, and the distal end (with the condyles) inferiorly.
- Identify anterior vs. posterior: the anterior surface of the shaft is smooth, while the posterior surface features the rough linea aspera and the deep intercondylar fossa inferiorly.
- Orient the trochanters: the greater trochanter always projects laterally, and the lesser trochanter points medially.