The acetabulofemoral joint, commonly called the hip joint, scientifically termed is located in between the pelvis and the femur of the legs. The hip is a joint responsible for supporting the body’s weight during both movement and rest periods. The hip helps the body maintain balance and assists in ambulation.
The bones of the hip include the femur, the ilium, the ischium, and the pubis. The pubis, ischium, and ilium together constitute the pelvis while the thigh bone is the femur. The bones together make up the hip. The hip itself is a ball and socket joint, much like the shoulder. The structures necessary to create this joint are the socket, the joint capsule, muscle, ligaments, and the neck/trochanter of the femur.
Those are the joints and bones which make up the hip, but to understand the role these joints/bones play in the body, a closer look at these structures is necessary.
General Hip Anatomy
The hip is a ball-and-socket joint, similar to the joint in the shoulder. Part of the reason for the hip’s stability is that there is a very deep socket, called the acetabulum, in the hip joint. A strong capsule joint supported by ligaments and muscles also provides extra stability to the hip. The hip has different layers to it, with the deepest layer being the bones that comprise it. On top of these bones are the ligaments which surround the joint capsule. The muscles and tendons in the hip are linked with the ligaments. Finally, on the top layer is the blood vessels and nerves. The hip joint is made out of fibrous, dense tissue – and these tissue groups include the ischiofemoral, pubofemoral, iliofemoral ligaments.
Bones Of The Hip
The skeleton of the human body is made out of bones and the cartilage supporting those bones. Cartilage and bones are both connective tissues, and cartilage can be made out of different ratios of elastin or collagen. Cartilage is an extremely flexible type of tissue, which is why it is located around joints. Unfortunately, because cartilage has no blood cells it can’t repair itself very easily. By contrast, bones are good at self-repair.
The bones found in the hip include the three bones of the pelvis and the thigh bone or femur. The three bones which form the pelvis are the pubis, the ilium, and the ischium. The ilium is the bone at the top of the waist, while the pubis bones are found just below the ilium. The pubis curves downward and forwards from the ileum. The ischium is located just behind the pubis bone. These bones join together to make up a socket on the outer rim of the pelvis, the acetabulum.
The hip joins the trunk of the body to the leg. The ball of the hip joint is made out the head of the femur, and the femoral head slots into the acetabulum. This femoral head lies and rotates within the acetabulum. The acetabulum is a semi-circle/half-sphere, while the head of the femoral is spherical as well, though about two-thirds of a sphere.
The longest bone in the body is the femur. The femoral head is connected to the shaft by the femur’s neck. The hip joint is attached to the posterior surface of the femoral neck via the capsular ligament. The neck of the femur terminates at the lesser and greater trochanter prominences. The abductor muscles attach to the greater trochanter while the lesser trochanter is the site of attachment for the iliopsoas tendon.
The greater trochanter is a large, prominent section of the femur, located on the outside of the thigh. The greater trochanter is where the tendons of several different muscles attach to the hip. These muscles include piriformis, the Gemelli, the obturator and the gluteus. The greater trochanter is also the widest part of the lower legs.
Ligaments Of The Hip
There are a variety of ligaments which encircle the hip and give it support. These ligaments found within the hip include the pubofemoral ligaments, the ischiofemoral ligaments, and the iliofemoral ligaments. These three ligaments together make up the extracapsular ligaments. These ligaments form the joint capsule and encircle the entire hip joint. The strongest out of the three ligaments is the iliofemoral ligament. A condition known as avascular necrosis results from the damaging of the ligamentum teres. The condition results when the small artery that supplies blood to the femur is damaged.
There is another ligament found near the hip, the intracapsular ligament. This ligament is responsible for holding the hip in place, only being moved when the hip is dislocated. The intracapsular ligament frequently helps link a small artery, the foveal artery, to the femur’s head.
Muscles Of The Hip
The muscles in the hip are responsible for the movement of the hip and, by proxy, the leg. The muscles work together to enable movement and keep the hip in alignment. The hip muscles work together to carry out 4 different types of movement: extension, flexion, adduction, and abduction. The muscles of the hip can be divided into three different groups. The anterior muscles are located on the front of the hip while the posterior muscles are located on the back of the hip.
The medial muscles are located on the outside of the hip. The quadricep group of muscles is the muscles dound on the anterior portion of the thigh and they are the rectus femoris, the lateralis, the vastus medialis, and the intermedius. The quads of the body compose about three-quarters of the muscle mass of the thigh. The quads are responsible for the bending/flexion of the hip, as well as the extension/straightening of the knee.
The piriformis, hamstring and gluteal muscles are found on the buttocks, and the main extensor of the hip is the gluteus maximus. This muscle group also functions to keep the femur head trapped within the hip socket. The sartorius muscles and the gluteal muscles assist in the abduction of the hip, pulling/pushing the leg away from the middle portion of the body. The abduction of the leg is what enables sideways movement.
The hip can also rotate medially, move internally, to turn the foot inwards towards the spine. The foot can also be turned laterally or outwards. The piriformis muscle is what lets the hip rotate laterally, which is necessary in order for the legs to cross.
Nerves And Blood Vessels
The different muscles in the hip are supplied and innervated by the nerves in the hip. The nerves in the hip include the obturator nerve, the lateral femoral cutaneous nerve, the femoral nerve, and the sciatic nerve. The obturator nerve, in addition to supplying the hip, is responsible for thigh sensation. The most recognized/notable nerve in the thigh and hip is probably the sciatic nerve. The sciatic nerve is about the size of the thumb, quite large as nerves go. The sciatic nerve runs along the gluteus maximus and down the rear portion of the leg. The sciatic nerve splits into several branches past this point and continues traveling down into the foot.
The nerves in the foot are responsible for carrying information about the muscles in the foot, as well as general pressure, pain, and temperature to the brain. The brain receives this information and processes it, and then makes decisions about movement which is carried down to the feet via the nerves. If the hip is dislocated, the sciatic nerve can be injured.
Blood vessels and arteries that supply the hip include the external and internal iliac artery, the obturator artery, the inferior and superior gluteal arteries and the femoral artery. The femoral artery is involved in the cardiac cath, and it runs to the knee from the hip. The femoral head is supplied mainly by vessels which are dispersed from the main femoral artery.
Bursae are found near the joints of the hip. They are sacks filled with synovial fluid encasing a membrane referred to as the synovial membrane. The synovial fluid is similar to raw egg whites in its consistency. The function of the bursae and the synovial fluid is to reduce the friction that occurs as ligament and bones, ligaments and tendons, or tendons and bones rub together. Joints have bursae around them, and because the hip joint is so large it has many bursae, around 20 total. If the bursae are infected or inflamed, this condition is referred to as bursitis.
One of the most prominent bursae in the hip region is the greater trochanteric bursa, and it is located in between the muscles and tendons of the greater trochanter and the greater trochanter itself. Inflammation of this bursa can occur if the iliotibial band isn’t flexible enough. Two other bursae that are commonly inflamed include the bursa found near the ischial tuberosity and the iliopsoas bursa.