What Bone Is A Femur?

The femur is the thigh bone — the single long bone in the upper leg. It is the longest and strongest bone in the human body, and it is the only bone in the thigh. It runs from the hip joint down to the knee joint, connecting the pelvis to the lower leg.

You have two femurs, one in each leg. They are the main structural support for standing, walking, running, and jumping. Because they carry so much load, they are built differently from most other bones in the body.

What Bone Is A Femur and Where Is It Located?

The femur sits between the hip and the knee. Its top end forms a ball that fits into a socket in the pelvis, creating the hip joint. Its bottom end meets the tibia (shinbone) to form the knee joint. The kneecap, or patella, sits in front of this lower end.

This arrangement makes the femur the central pillar of the leg. Every step you take sends force through it. During walking, the load on each femur is roughly a few times your body weight. During running, the forces are considerably higher. That is why the femur has thick walls of dense outer bone and a unique internal structure that resists bending and twisting.

It is worth clearing up a common point of confusion: the femur is not the same as the hamstring or quadriceps. Those are muscles that surround and move the femur. The femur itself is bone.

What Are the Main Parts of the Femur?

The femur has three main regions — the upper end, the shaft, and the lower end — and each has distinct features that serve a purpose.

The upper end (near the hip)

The top of the femur includes the head, a rounded ball that fits into the hip socket. Just below the head is the neck of the femur, a narrower section that angles the head toward the pelvis. This neck is a common fracture site, especially in older adults.

Two bony bumps called the greater and lesser trochanters sit where the neck meets the shaft. Several powerful hip muscles attach here.

The shaft (the middle)

The shaft is the long, mostly straight middle section. It is roughly cylindrical and built to handle large bending and twisting forces. A ridge called the linea aspera runs down the back of the shaft and serves as an attachment point for muscles.

The lower end (near the knee)

The bottom of the femur widens into two rounded knobs called condyles. These form the top half of the knee joint. The kneecap glides over a groove between them.

Why Is the Femur Considered the Strongest Bone in the Body?

The femur can withstand forces that would break most other bones. Its strength comes from a combination of design features rather than any single property.

First, the outer layer is made of dense cortical bone, which is packed tightly and resists bending. Second, the inner structure is not solid. It contains a lattice of spongy bone arranged along the lines of stress. This layout lets the bone handle force efficiently while keeping weight down.

The shape matters too. The shaft is slightly curved, which helps it absorb impact rather than snapping. The wide upper and lower ends spread load across the joints.

Even so, “strongest” does not mean unbreakable. The femur can fracture under high-impact trauma, such as a car crash or a fall from height. It can also break from weaker forces when bone density is low.

What Does the Femur Do?

The femur does two jobs at once — it supports the body and it makes movement possible.

• Support and load-bearing: It carries your body weight from the pelvis to the lower leg.
• Movement: Muscles attach to it and pull on it to bend the hip and knee.
• Lever for walking and running: Its length gives your leg reach and stride length.
• Blood cell production: Like other large bones, it contains marrow that produces blood cells.
• Mineral storage: It stores calcium and phosphorus, which the body draws on as needed.

The femur also plays a role in how the knee and hip align. Small changes in its angle can affect how force travels through both joints.

How Do Femur Fractures Happen?

Femur fractures fall into two broad groups: those from high-energy trauma in younger people, and those from low-energy falls in older adults.

High-energy breaks usually come from car accidents, motorcycle crashes, or falls from a significant height. These often affect the shaft and can involve serious soft-tissue injury.

In older adults, the more common injury is a hip fracture, which often involves the neck of the femur. These can happen from a simple fall — or even from standing height — when bone strength is reduced. Age-related bone loss and osteoporosis are major reasons this happens.

Symptoms of a femur fracture typically include severe pain, inability to bear weight, swelling, and visible deformity. A hip fracture may cause the leg to look shortened and rotated outward. Anyone with these signs needs emergency medical care.

How Are Femur Problems Diagnosed and Treated?

Diagnosis usually starts with a physical exam and imaging. X-rays can show most femur fractures. When a fracture is suspected but not visible on X-ray, or when the hip is the concern, an MRI or CT scan may be used.

Treatment depends on the type and location of the injury. Many femur fractures need surgery. Common approaches include metal rods placed inside the bone, plates and screws, or, for some hip fractures, partial or total hip replacement. Some stable fractures in children may be treated without surgery, but this is decided case by case.

Recovery takes time and typically involves physical therapy to rebuild strength and movement. Healing timelines vary widely based on age, fracture type, and overall health, so a doctor’s estimate is more reliable than any general figure.

Some clinicians recommend calcium and vitamin D evaluation after a low-trauma fracture, since it can point to underlying bone weakness. This is common practice, though the strength of evidence varies by situation. Anyone concerned about bone health should discuss testing with a doctor rather than self-treating.

How Does the Femur Change With Age?

Bone mass tends to peak in early adulthood and slowly decline afterward. For women, the drop often speeds up after menopause. Over time, this can lower bone density and raise fracture risk.

The femur is affected by this like other bones. A weaker femur is more likely to break from a fall that would once have caused only a bruise. That is why fall prevention and bone health matter more with age.

Regular weight-bearing activity, adequate calcium and vitamin D, and avoiding smoking are generally linked to better bone health. The evidence for these steps is strongest for maintaining general bone density, not for guaranteeing prevention of any specific fracture.

What Else Is Worth Knowing About the Femur?

A few clarifications help avoid common mix-ups.

The femur is sometimes confused with the humerus, the upper arm bone. They look similar in shape, but the humerus is in the arm and is not built for the same load. The femur is much stronger because it carries the body’s weight.

Another point: the femur is not the same as the “funny bone.” That phrase refers to a nerve near the elbow, not a bone in the leg.

Finally, the femur is the only bone in the thigh. If you feel a hard structure in your upper leg, it is the femur — everything else around it is muscle, fat, or connective tissue.