Knee Anatomy

The hip is one of the body’s largest and most stable joints, connecting the thigh to the pelvis. The hip joint allows for a wide range of movements including flexion (bending), extension (straightening), abduction (moving the leg outward), adduction (moving the leg inward), and rotation. The hip joint is composed of several structures:

Femur: The thigh bone, whose rounded upper end (the femoral head) forms the ball of the hip joint.

Pelvis: The large bony structure that forms the socket of the hip joint. The relevant part of the pelvis is the acetabulum — a cup-shaped cavity that receives the femoral head to form the ball-and-socket joint.

Femoral Neck: The narrow region of bone that connects the femoral head to the shaft of the femur. Its angle and length are important factors in hip function and stability.

Muscles are structures that move the joint. For a muscle to move a joint it must cross the respective joint. The hip muscles form several major groups:

Hip Flexors: A group of muscles, including the iliopsoas, located at the front of the hip that work together to bring the thigh toward the body.

Gluteal Muscles: Located at the back and side of the hip, these muscles — gluteus maximus, medius, and minimus — drive hip extension, abduction, and rotation.

Adductors: A group of muscles on the inner thigh that pull the leg toward the midline

External Rotators: A deep group of six muscles, including the piriformis, that rotate the femur outward and contribute to hip stability.

Iliopsoas Tendon: Connects the iliopsoas muscle to the lesser trochanter of the femur. It is the primary hip flexor tendon and can be a source of snapping or pain in the groin.

Gluteal Tendons: Connect the gluteal muscles to the greater trochanter of the femur. Degeneration of these tendons is a common cause of lateral hip pain.

Hamstring Tendons: Connect the hamstring muscles to the ischial tuberosity (sitting bone) of the pelvis, contributing to hip extension.

Like all joints in the body, the hip joint is covered by articular cartilage.

Articular Cartilage: Covers the surface of the femoral head and the inner lining of the acetabulum. It provides a smooth, low-friction surface allowing the bones to glide against each other. Wear of this articular cartilage is defined as arthritis.

In addition to articular cartilage, the knee joint contains two structures called meniscii

Labrum: A ring of fibrocartilage attached to the rim of the acetabulum. Like the meniscus in the knee, it deepens the socket, acts as a seal to maintain joint fluid pressure, distributes load across the joint surface, and enhances stability. Tears of the labrum are a common source of hip pain, particularly in younger and active patients.

Ligaments are tissue structures that connect one bone to another. Their main function is to provide stability to a joint. There are three main ligaments that reinforce the hip joint capsule:

Iliofemoral Ligament: The strongest ligament in the body, running from the pelvis to the front of the femur. It limits extension and prevents the hip from bending too far backward.

Pubofemoral Ligament: Runs from the pubic part of the pelvis to the femur, limiting abduction and extensionMedial Collateral Ligament (MCL): Runs along the inner side of the knee, providing stability and preventing excessive inward movement (valgus stress)

Ischiofemoral Ligament: Located at the back of the joint, it runs from the ischium to the femur and limits internal rotationThe anterolateral ligament (ALL) runs along the outside of the knee and is ofen injured at the same time as the ACL

Ligamentum Teres: A small internal ligament connecting the femoral head directly to the acetabulum. It carries a small blood vessel that contributes to femoral head blood supply and may play a role in joint stability.

Understanding the anatomy of the hip is essential for diagnosing and treating injuries and conditions affecting this joint.