Hip – Bones, Ligaments, Muscles & Conditions
The hip joint is one of the largest joints in the body. It is composed of one osseous joint. The hip is built for weight bearing and movement in several different planes. Most of the stability of the hip is derived from the capsule, ligaments, muscle and a cartilaginous tissue called the labrum.
Bone and Joint
The hip, like the shoulder, is a ball and socket joint. It is formed by the head of the femur (thigh bone), which sits in the acetabulum, a part of pelvis. The head of the femur is large (ball) and the acetabulum (socket) is shallow. This makes the joint unstable but simultaneously allows for greater mobility.
The bony joint surfaces of the head of the femur and acetabulum are covered with articular cartilage. The articular cartilage has a smooth and shiny surface that allows the ends of the bones to slide freely over each other.
Common conditions of the hip joint are hip osteoarthritis, hip rheumatoid arthritis, hip fractures, aseptic necrosis of the hip, and hip dislocation, slipped femoral epiphysis and degenerative hip disease.
The muscles and tendons in the hip provide stability and active movement. . The anterior muscles (iliopsoas, rectus fermoris) move the hip forward. The posterior muscles, hamstrings and luteus maximus, move the hip backward. The lateral muscles, gluteus minimus, gluteus medius, and tensor fascia latae, move the hip out to the side or abduct the leg. These muscles also stabilize the hip and pelvis when walking and running.
The muscles of the inner thigh, or adductors, function to bring the hip and leg toward the opposite leg. They are called the adductor magnus and adductor longus. The deeper muscles of the hip, or rotators, function to rotate the hip in and out. The hip rotators include the piriformis, gemellus superior, gemellus inferior, obturator internus, obturator externus, and quadratus femoris.
Common conditions of the hip muscles include hamstring strain, hamstring tear, psoas strain, adductor strain, muscle tear and piriformis syndrome.
Ligaments and Labrum
The hip joint is protected and surrounded by a soft tissue sleeve called the hip joint capsule. Ligaments, soft tissue structures that connect bone to bone, reinforce the capsule. The capsule and ligaments provide passive stability to the hip joint, but allow movements in different planes. The labrum of the hip is a fibrocartilagenous structure that is located at the level of the acetabulum. It provides added depth and stability to the joint.
Common conditions of the ligaments and labrum include labral tear, hip dislocation and capsulitis.
A burse is a fluid filled sac that decreases friction between two tissues. The primary burse of the hip is the greater trochanter burse. It is located on the outside of the hip between the gluteus mininmus and gluteus medius muscles, into the greater trochanter of the femur. It can become inflamed as a result of direct trauma or overuse.
This condition is referred to as hip bursitis or trochanteric bursitis.