Femur (Os femoris) is the long bone of the thigh, lying between the hip and knee. Its upper end joins the hip bone, and its lower end joins the tibia and patella. It supports body weight and provides attachment sites and leverage for muscles that move the lower limb.
Where is the femur located?
The left femur and right femur each lie within the muscles of the corresponding thigh. The head sits in the acetabulum, the cup-shaped socket on the outer side of the hip bone. Below, the femur meets the tibia, the main weight-bearing bone of the leg, and the patella, the kneecap.
The shaft slopes towards the body's midline as it descends from the hip to the knee. The fibula, the slender bone on the outer side of the leg, does not articulate with the femur: their surfaces do not form a joint.
The main regions can be summarised as follows. Proximal means nearer the trunk, and distal means farther from it.
| Region | Main features | Anatomical role |
|---|---|---|
| Proximal end | Head, neck, greater and lesser trochanters | Forms the hip joint and provides muscle attachments |
| Shaft | Body of the bone and linea aspera | Transmits load and provides muscle attachments |
| Distal end | Condyles, epicondyles and patellar surface | Forms the femoral part of the knee joint |
What are the landmarks at the upper end?
The head is the rounded proximal part of the femur. Most of its surface is covered by articular cartilage, the smooth tissue covering bone surfaces within joints. A small depression, the fovea of the head, provides attachment for the ligament of the head of the femur; a ligament is a band of connective tissue joining skeletal structures.
The neck connects the head to the shaft. It projects upwards and medially, meaning towards the body's midline, and positions the head within the acetabulum while keeping the shaft clear of the pelvis.
The greater trochanter is a large bony projection on the lateral, or outer, side. It receives attachments from several hip muscles, including gluteus medius and gluteus minimus. The lesser trochanter projects from the posterior and medial aspect, meaning the back and inner side, and receives the iliopsoas tendon, the connective tissue attaching that muscle to bone.
The intertrochanteric line connects the trochanters anteriorly, on the front, while the intertrochanteric crest connects them posteriorly. These landmarks help distinguish the front from the back of the proximal femur.
What are the features of the femoral shaft?
The shaft, also called the body, is the elongated middle portion of the bone. It has a slight forward curve, and its anterior surface is relatively smooth. Its posterior surface bears the linea aspera, a prominent longitudinal ridge.
The linea aspera has medial and lateral lips that provide attachment for muscles and connective tissue partitions between muscle groups. Several adductor muscles, which draw the thigh towards the body's midline, attach along this region. Parts of the quadriceps femoris, the muscle group that straightens the knee, also arise from the femur.
A dense outer layer of compact bone surrounds the shaft's medullary cavity, the internal space containing bone marrow. Nutrient vessels enter through openings in the bone to supply its internal tissues.
What are the landmarks at the lower end?
The distal femur broadens into medial and lateral condyles, rounded projections with joint surfaces. They articulate with the superior articular surfaces of the tibial condyles, with the menisci partly interposed between the joint surfaces. Posteriorly, a deep intercondylar fossa, or depression between the condyles, separates them.
Anteriorly, the condyles are connected by the patellar surface, a grooved joint surface along which the patella moves as the knee bends and straightens. Above the condyles lie the epicondyles, non-articular projections that provide ligament attachment sites.
The adductor tubercle is a small prominence above the medial epicondyle. It receives the tendon of the hamstring part of adductor magnus, a portion of that muscle which helps extend the hip.
Which joints does the femur form?
The femur participates in the hip and knee joints, both belonging to the articular system, the body's joints. Both are synovial joints: their opposing joint surfaces are separated by a fluid-containing cavity enclosed by a capsule.
At the hip, the femoral head articulates with the acetabulum to form a ball-and-socket joint. This arrangement permits bending, straightening, movement towards and away from the midline, and rotation of the thigh.
At the knee, the femoral condyles articulate with the tibia, while the patellar surface articulates with the patella. The knee mainly bends and straightens, with some rotation when bent. The cruciate ligaments, which cross within the knee, attach to the femur in the intercondylar region.
What does the femur do?
As part of the skeletal system, the framework of bones, the femur transmits weight from the pelvis towards the tibia. Its shape and joint surfaces support the lower limb while allowing movement at the hip and knee.
Its projections and ridges provide attachment sites for the muscular system, the body's muscles. Muscle pull uses the femur as a lever to move the thigh or leg. Muscles attached near the upper end also help stabilise the pelvis during standing and walking.
How can you identify the femur in the 3D model?
In the 3D model next to the article, rotate and zoom to locate the thigh bone, then select and isolate it. Hide surrounding structures or fade them to keep attention on the selected bone while changing the viewing angle.
Rotate the selected bone to compare different viewing angles, and zoom to adjust the view. Switch layers or pull parts apart to change how the selected bone is viewed relative to surrounding structures.