Acetabulofemoral Joint (Hip)

Bones: The acetebulum is the cup like depression of the joint that is formed at the junction of the ilium, ischium, and pubis. The head of the femur then fits in the acetebulum. The top of the ilium is what most people know as the bone side of their hip by their waist.

Cartilage: For the large amount of movement of this joint there is a layer of highly lubricated hyaline cartilage that covers the surface of the bones in the ball and socket joint. Between the joint is a synovial sac which is a thin fluid filled membrane adding additional lubrication to the joint, its degradation can lead to arthritis. Overlaying the connection around the bones is a fibrous capsule enclosing the joint.

Ligament: The ilofemoral ligament connects from the ilium to the femur and when standing prevents your core and upper body from alling backwards. This is the strongest ligament in the body (keeping the body upright with hardly any strain) but when seated and relaxed it allows you to lean backwards. The ischiofemoral ligament is situated that it prevents excess internal rotation of the joint. Lastly the pubofemoral ligament which restricts excess abduction (moving the leg away from the body to the side) and excess rotation. All of which named after the bones they join (the bones of the acetebulum and the femur).

Tendon: There are a number of muscular tendons that come together by the joint and connect to the pubic bone and what most people know as their groin muscles.

Muscles/Mechanics:

• Flexion: This is lifting the leg (bringing the femur closer to the body) which is done by a combination of nine muscles. The two most important (most influential in flexion) of which being the Psoas major which run from the lumbar vertebrae to the top of the femur and the Iliacus which runs from the top of the ilium to the top of the femur.
• Extension: This is stretching the leg back behind you which is done by four muscles. These muscles being the Gluteus maximus and the hamstrings, the most influential being the Biceps femoris. The glute muscle has a long tendon that runs from the bottom side of the buttocks down to the end of the femur.
• Abduction: This is moving the limb away from the body (to the side) and is done by six muscles, two of which are of little importance to the motion. All three Gluteus muscles are involved (minimus, medius, maximus) and the Tensor fasciae latae, which are positioned on the outside of the leg, therefore when contracted pull the femur outwards. On a side note one of the minor muscles, the Sartorius muscle, is the longest muscle in the body, running the entire length of the femur.
• Adduction: This is pulling the leg back towards the center line of the body, of which there are seven that originate in the pelvic region and attach along the length of the femur.
• Medial Rotation: This is turning the leg inwards. This is done by a combination of the Extensor Glutial medius, minimus, the tensor fachiae latae and the Adductors longus, brevis, and magnus.
• Lateral Rotation: This is turning the leg outwards. There are arguably six main muscles that contribute to this motion the most influential usually being the Piriformis muscle connecting from the sacrum to the head of the femur.

Mechanics:

• There are 22 muscles that originate or attach to the femur, different combinations of contractions of which perform different actions.
• The Glutes arguably being the most important as they stabilize the hip and keep it from "swaying" thus keeping the body in place.
• Also due to the large number of muscles people are often still able to walk (with maybe a painful limp) even after a decent amount of trauma to the leg.
• This a a ball and socket joint with the largest range of motion in the body (as the shoulder joint is several joints together), however its maximum potential is rarely reached in most people (requiring a large amount of stretching to get there).

Range of motion: Due to the shape of the head and neck of the femur the angles of the motion would be different when compared to the direction of the body of the femur, for this we will use the position of the body of the femur and using only the muscles of the leg to orient the femur. From standing the leg can flex (especially with the knee bent) so that the femur moves roughly 160 degrees. The leg can extend backwards (without bending forward) close to 60 degrees. The leg can be abducted away from the body to about 110 degrees from standing. The leg can be adducted towards the body (crossing the other leg) about 30 degrees from standing. The leg is able to outwards and inwards from a natural standing position at least 90 degrees.

• These numbers can be increased with insane amounts of stretching, using both hips or bending the back, or during the act of stretching and using other limbs to push the hip joint.

Manipulation:

• Striking the leg, such as a muay thai shin kick to the side of the leg will damage muscles and tendons that will make hip/leg movements very painful.
• A scoop kick to the center of the femur is and easy way to jam the walking mechanics of the leg, stopping the opponent from getting close to you.
• A side or scoop kick by the head of the femur could possible dislocate or break the the joint (even more so against an older opponent).
• Otherwise there are few direct manipulations of the hip, many of the leg locks or sweeps only affect the hip along with the ankle and knee.

Stretching: This is arguably the most desired stretched joint especially for martial artists. Stretching regularly and holding the uncomfortable pose for about 20 seconds will improve the range of motion of the joint to the numbers stated above. Stretching should be gradual and feel substantially uncomfortable without immense pain.

Conditioning: It can be very useful to condition the muscles of the leg to sustain impact, by starting with lightly having a partner kick the thigh such as a muay thai shin kick.

Injury: It is common (during much physical activity) to over flex the flexors which stretches the extensors, this is when your hamstrings hurt. In older people as previously stated the head of the femur is weaker and more likely to be damaged, otherwise the femur is the strongest bone in the body.

For information on additional joints please refer back to the Joints page.