Unit VI – The Hip

Objectives:

At the completion of this unit the student will be able to:

  1. Identify the primary bony landmarks of the hip joint and upper leg.
  2. Identify the articulations that form the hip joint.
  3. Identify the key ligamentous and capsular structures of the hip joint.
  4. Discuss the importance of the ligaments and capsule to the stability of the hip joint.
  5. Name the motions of the hip joint and primary muscles that perform these motions and their locations.
  6. Discuss the relationship between the hip joint and the pelvis above, and the knee below.
  7. Apply anatomy knowledge of this area to relevant issues for the dancer.

Bony Structures of the Hip Joint and Upper Leg

 

The bony components of the hip joint include the acetabulum that is part of the pelvis discussed in the previous unit. The lower portion of the pelvis makes up the proximal portion of the hip joint. The distal portion of the hip joint articulation is located on the femur bone. The femur extends to the knee joint as well, so these articulations are intimately related as they form the lower body kinetic chain.

The Acetabulum 

The acetabulum is a deep socket formed by the junction of the ilium, the pubis, and the ischium of the pelvis. It is located on the lateral aspect of the pelvis and forms a bowl-like shape where the head of the femur articulates.  ©
There is a horseshoe shaped articular cartilage that lines the top side of the acetabulum. The lower portion is called the acetabular notch and does not come in direct contact with the femoral head.

 

The Femur Bone

The femur is the longest and heaviest bone in the human body. The femoral head at its superior end is a smooth, spherical surface that articulates with the acetabulum to form the hip joint socket. The femoral head is covered with articular cartilage except at the fovea or tip where a small area for the ligamentum teres attachment is located. The ligamentum teres connects the femoral head to the acetabular notch of the hip bone.

Another important landmark on the femur is the femoral neck. It is the area just distal to the femoral head where the bone constricts in. This is a frequent site of fracture in the elderly. Just distal to the femoral neck is the greater trochanter and the lesser trochanter. These are rough, bony projections that serve as muscle attachment sites that will be discussed below. 

The shaft of the femur is the long middle section and is roughly a triangular shape. At the distal end of the femur are the lateral and medial condyles. These are smooth articular surfaces that make up the proximal portion of the knee joint below. On the posterior portion of the femur shaft is the linea aspera. It is a prominent double ridge to which the adductor and vastus muscles attach. 

 

Variations in Hip Joint Angles Among Individuals
The angle of the pelvis under the spine places the acetabulum of the hip joint in an anterior and inferior position. At the same time, the femoral head is angled obliquely medially, superiorly, and anteriorly in relationship to the shaft of the bone below. Note in the picture to the left that the socket for the femoral head angles forward and down. At the same time the actual head of the femur angles up and forward to fit nicely into the socket of the acetabulum.
The angular relationship of the acetabulum and the femoral head varies among individuals. The average angle between the shaft of the femur and the femoral neck is 135 degrees. A smaller angles brings the femur more the the midline of the body as might be seen in a knocked-kneed individual. A larger angle brings the femur more away from the midline of the body and can produce a more bow-legged posture. 

The anterior orientation of the neck of the femur to the acetabulum is normally 10-30 degrees. This is called anteversion. If the anteversion angle is small, the ball portion of the femur fits well into the acetabulum and the joint will have good hip external rotation.

If, however, the anteversion angle is large, the anterior part of the femoral head is more exposed and can lose contact with the acetabulum and lateral rotation of the hip joint will be reduced. These anatomical variations in bones and joint articulations can determine available range of motion at a joint. This can be an issue for a dancer if anteversion in the hip reduces hip external rotation. This is a bony configuration that cannot be changed or stretched to increase.  

 

Ligament and Capsular Structures of the Hip

There are several important structures that provide additional stability to the hip joint. The labrum is the fibrocartilaginous ring that attaches to the rim of the acetabulum. It is like a rubber washer ring that encircles the opening of the acetabulum and helps to increase the depth of the hip socket and hold the femoral head in place.
The capsule of the hip attaches all the way around the rim of the acetabulum and down to the base of the neck of the femur. It is thick and reinforced by ligaments. The primary ligaments on the anterior of the hip joint are the iliofemoral ligament and the pubofemoral ligament.
The iliofemoral ligament is shaped like a V and is the stronger of the two ligaments. It passes from the anterior inferior iliac spine down onto the line separating the femoral neck from the lesser and greater trochanters. The pubofemoral ligament runs from the pubic region of the pelvis toan area just above the lesser trochanter on the femur.
When viewed schematically these ligaments make a “Z” across the front of the hip capsule. These ligaments serve as “check rings” for the motions at the hip. A portion of the “Z” ligament is taut with flexion or extension of the hip, while other portions are taut during abduction and abduction. All portions of the “Z” ligament are taut with external rotation of the hip. These ligaments serve to increase joint stability and help protect the joint from injury when moving in extreme motion positions. The capsule helps deepen the hip joint space, as well as forming a fibrous ring around the hip joint area. 
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The additional ligament structures further protect the stability of the joint. Because of the depth of the hip joint socket, the strong ligamentous support around the joint, and the angulation of the bones to form the hip joint, it is a very stable joint. The hip joint is rarely dislocated. 

 

Movements of the Hip  

There are many motion options at the hip joint. Motion can occur with the pelvis fixed and the femur below moving, or the femur can be fixed and the pelvis can move from above. When the pelvis is fixed the femur motion includes:
Hip Flexion – this occurs when the angle between the anterior surface of the thigh and the trunk decreases; bringing the knee to the chest is hip flexion.

 There is greater range of motion for hip flexion when the knee is bent. If the knee is straight the flexibility of the hamstring limits the motion of the leg toward the chest. Notice the difference in range of motion for hip flexion from the top left picture where the knee is straight, and the top right picture where the knee is bent.  

Hip Extension - this occurs when the angle between the posterior surface of the thigh and the trunk decreases. This is taking the leg to the back.  There is much less available range of motion into hip extension compared to hip flexion.

 A dancer can appear to have more hip extension by increasing lumbar lordosis in the trunk. Rocking the  pelvis forward over the femur can also give the illusion of hip extension. When the knee is bent hip extension is reduced due to muscle length limitations for the quadriceps muscle in the front of the upper leg. This is visible in the pictures top left and top right. The dancer on the left has the knee straight and thus has 20 degrees of hip extension, while the dancer on the right has the knee bent and only 10 degrees of hip flexion.  

Hip Adductionthis occurs when the thigh moves toward midline of the body or past midline to cross in front of the other leg
Hip Abduction – this occurs when the thigh moves away from the middle of the body. When the femur is in neutral rotation there is only about 40 degrees of hip abduction because the leg makes contact between the femoral neck and the upper edge of the acetabulum. More abduction can be achieved by externally rotating the hip to clear this bony landmark.

In the picture top left the dancer has the hip in neutral and only 30 degrees of hip abduction. The dancers in the other positions have rotated the hip to clear the femur from under the lip of the acetabulum and allow more abduction to occur.

Hip External or Lateral Rotation – this occurs when the femur rotates on its own long axis and the toes of the foot move away from the middle of the body.

Hip Internal or Medial Rotation - this occurs when the femur rotates on its own long axis and the toes of the foot move toward the middle of the body. The entire lower leg moves as a unit.

 

 

There are additional movements at the hip that can occur when the femur is fixed below and the pelvis moves from above. The pelvis can tip forward from its superior aspect into anteversion. This motion increases the arch or lumbar lordosis in the spine. The pelvis can tip backward from its superior aspect into retroversion which decreases the arch in the back or decreases lumbar lordosis. There is also some rotation or tipping of the pelvic ring over the legs as the body propels itself forward in space or shifts weight from leg to leg. 
Figure to the far right depicts lumbar lordosis which is caused by the pelvis tilting into anteversion. ©

 

Muscles around the Hip Joint

There are many muscles that act around the hip joint. These will be discussed as they relate to the motion they produce about the hip. Muscles that cross the hip and pass down to the knee will be mentioned, but dealt with in more detail in Unit VII on the knee.

 

The Hip Flexors 

Iliopsoas

The primary hip flexor is the iliopsoas, which has already been discussed. Remember it is two muscles that work in harmony, one primarily in the trunk and passing to attach on the lesser trochanter of the femur, while the iliacus arises on the internal iliac fossa and also passes across the hip to attach to the lesser trochanter. This muscle has an intimate connection to the spine, the pelvis, and the lower extremity. If the iliacus portion is shortened it can pull the leg into a flexed position or pull the spine forward into a forward bent position. In a society in which individuals do a lot of sitting this is a concern, since the hip flexor remains in a shortened position for extended periods of time. If that muscle is chronically shortened it can cause movement restrictions and pain syndromes. When the muscle performs a shortening or isotonic contraction it will bring the femur or leg bone toward the trunk – i.e. hip flexion.

 

Rectus Femoris
Rectus Femoris  arises from the anterior inferior iliac spine and passes across the hip joint, down the shaft of the femur superficially and attaches to the patellar tendon at the knee. Because of its attachments it crosses two major joints in the lower extremity so it has muscle actions at both joints. If the pelvis is fixed it flexes the hip and extends the knee (important in walking). If the femur is fixed it can rotate the pelvis forward from its superior aspect (anteversion).

Tensor Fascia Latae

© The tensor fascia latae (in red), arises from the anterior part of the external lip of the iliac crest and the outer surface of the anterior superior iliac spine. It inserts into the iliotibial tract. The iliotibial tract is a heavy fibrous area of the deep fascia of the upper leg (shown in silver to left).
Fascial tissue is found throughout the body and is a thin covering over the muscles. If you have every skinned or cleaned raw chicken and wiped away the thin whitish layer over the meat you have seen fascia. In the leg, this fascia becomes thickened and dense as it passes down the lateral aspect of the femur. The area between the gluteus maximus, posteriorly, and the tensor fascia latae, anteriorly, is this fibrous band called the iliotibial tract. It resembles the density of the packing tape used to hold boxes shut. The iliotibial tract, along with the tensor fascia latae and the gluteus muscles, assists in stabilizing the hip and knee joints during standing and walking.(visible right as the long, thick white band)   ©

 

The Hip Extensors

Gluteus Maximus
The antagonist or opposite muscle to the hip flexor is the large and powerful gluteus maximus. It is the large buttock muscle located posterior to the sacrum. It arises from the posterior aspect of the ilium, the lower and posterior portion of the sacrum, and the side of the coccyx. It attaches at the iliotibial tract along the posterior aspect. It produces hip extension when activated.
 If the gluteus muscle is weak, the posterior support from below the pelvis can be compromised allowing more stress on the pelvis and lumbar spine. Other less powerful muscles may need to perform the hip extension motions and can result in problems in the pelvis and lower leg. Shortening of the gluteus can change the alignment of the pelvis and produce a slight anterior tip to the pelvis.

 

Secondary Muscles that Produce Hip Extension

The gluteus maximus is the primary hip extensor muscle. It can also provide some lateral or external rotation of the hip. It is the largest muscle in the body and along with fatty tissue, makes up the bulk of the buttock. 

Other smaller muscles can assist the gluteus maximus in producing hip extension. They include all 3 portions of the hamstring muscle that arise from the ischial tuberosity and pass down to attach at the knee. The posterior aspect of the gluteus medius along the lateral aspect of the leg, and a portion of the adductor magnus muscle, can also contribute to hip extension. These are secondary muscles that can produce hip extension.

 

Abduction and Adduction of the Hip

The lower leg moves in several directions under the trunk and pelvis. Flexion and extension were mentioned above. Several important muscles contribute to abduction (moving the leg away from the midline of the body) and adduction (moving the leg toward the midline of the body).

Hip Abduction:

Gluteus Medius

 The gluteus medius is a fan-shaped muscle with a broad origin on the external surface of the ilium. The fibers converge and insert on the greater trochanter of the femur. Its primary function is abduction of the hip. It may also assist with medial or internal hip rotation and serve as a flexor or extensor of the hip. It is important for stabilizing the pelvis when walking or standing on one foot.

 

Gluteus Minimus

 The gluteus minimus is a small muscle located deep and somewhat anterior to the gluteus medius muscle. It arises from the external aspect of the ilium, but slightly more inferior and anterior than gluteus medius. It serves to abduct the hip also.

 

Tensor Fascia Latae

The tensor fascia latae, as mentioned above in the hip flexor group, originates on the anterior part of the external lip of the iliac crease, (near the ASIS). It attaches into the iliotibial tract on the anterior aspect. It is a primary abductor of the hip, but also functions to internally rotate the hip joint. It may also assist with knee extension.

 

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Other Secondary Muscles that Abduct the Hip Joint

 The superficial portion of the gluteus maximus, discussed above, can provide some hip abduction. The deep external hip rotators, discussed below, can also contribute to hip abduction, but the gluteus medius/minimus and the tensor fascia latae are the primary hip abduction muscles.

 

Hip Adduction:
The primary adductor at the hip is the large adductor muscle group located on the inside of the leg. They are a group of five muscles with insertions located on the medial femur.
Adductor Brevis 

 The adductor brevis arises from the inferior aspect of the pubic ramus and attaches to the distal two thirds of the pectineal line and the upper half of the linea aspera on the femur.

Adductor Longus

 The adductor longus originates on the anterior surface of the pubis and over the pubic symphysis region, medial to the adductor brevis. It passes anteriorly to the adductor brevis and attaches on the lower aspect of the aspera of the femur.

 

Gracilis

 The gracilis arises from the inferior half of the symphysis pubis and along the inferior ramus of the pubic bone. It attaches to the tibial shaft just below the medial condyle. It is a long, thin, superficial muscle that is relatively weak, but crosses the hip and the knee areas.

Pectineus

 The pectineus arises from the superior aspect of the pubis to the pectineal line on the femur that connects the lesser trochanter to the linea aspera.

 

Adductor Magnus 

 The adductor magnus is the largest and strongest of the adductor muscle group. It has two parts. The origin of the anterior fibers is the inferior pubic ramus and the ramus of the ischium. The origin of the posterior fibers is the ischial tuberosity. The anterior portion has a broad insertion on the linea aspera of the femur, while the posterior portion runs straight down and inserts must above the medial femoral condyle on the adductor tubercle at the distal end of the femur.

 

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All of the 5 muscles above adduct the hip joint. These muscles can act in a small way for other actions around the hip. The gracilis also flexes and medially rotates the knee since it also crosses that joint. The adductor muscle group is frequently strained and is called a “pulled groin” when this occurs.

 

Other Secondary Hip Adductors:

Several other muscles may contribute to hip adduction. These include the iliopsoas and the biceps femoris of the hamstring, and  the deep portion of the gluteus maximus.

 

Internal or Medial Rotation of the Hip

The gluteus medius, gluteus minimus, and the tensor fascia latae which have been discussed above for hip abduction are the primary internal rotators of the hip joint. They work together to turn the big toe inward toward the midline of the body. Remember this motion originates in the proximal hip area, though the entire leg rolls inward.

 

External or Lateral Rotation of the Hip

 There are 6 deep, short muscles that make up the muscles that rotate the hip externally. They are all located deep to the muscles discussed above that perform the other motions of the hip.  

Piriformis

 The most familiar external hip rotator is the piriformis. It originates on the anterior surface of the sacrum along its upper 4 sacral foramina. It attaches to the superior border of the greater trochanter of the femur. The piriformis passes through the sciatic notch. The sciatic nerve passes deep to the piriformis muscle. If there is tightness or guarding in the piriformis, or inflammation in the sciatic nerve, pain in the buttock and into the posterior leg can result. If the piriformis is tight it can cause leg pain or numbness, as well as local pain in the center of  the buttock,  made worse with sitting. This is called “piriformis syndrome” and is relatively common. 

Maintaining good flexibility of the piriformis can reduce the chances of this problem occurring. If there is sacral dysfunction the piriformis may also become irritable or tight. Since it originates on the anterior portion of the sacrum, any alignment problems with the sacrum can cause tenderness in the piriformis muscle.
Obturator  Internus

 The obturator internus arises from the obturator membrane and portions of the ischium and ilium in that internal bowl of  the pelvis. The muscle forms a broad band in this area and then passes posterior through the lesser sciatic notch. The lesser sciatic notch is the smaller indentation of the ischium located distal to the greater sciatic notch. The obturator internus makes a sharp bend around the body of the ischium once it passes through the notch and then inserts on the medical aspect of the greater trochanter, just  medial to the piriformis insertion. This muscle externally rotates the hip, but also provides some stability to the hip joint because of its broad origin.(In the picture above it is the middle red muscle)

Obturator Externus

 The obturator externus arises from the rami of the pubis and ischium on the external surface and the external surface of the obturator membrane. It passes posterior to the femoral neck  and inserts on a fossa on the medical surface of the greater trochanter just distal to the insertion of the obturator internus. (In the picture above left it is the most inferior red muscle shown).

 

Gemellus Superior and Inferior

 The gemellus muscles are two small muscles that are located above and below the obturator internus. The gemellus superior originates from the external surface of the spine of the ischium and the gemellus inferior originates from the proximal part of the tuberosity of the ischium. They pass on either side of the obturator internus and attach with its tendon to the medical surface of the greater trochanter of the femur. These two muscles reinforce the action of the obturator internus. The gemellus muscles have been compared to a hammock supporting the pelvis.

Quadratus Femoris

 The quadratus femoris runs from the lateral aspect of the ischium to the posterior aspect of the greater trochanter distal to the attachment of the piriformis. It is a more rectangular shaped muscle, but also perform external rotation of the hip.

Secondary Muscles That Externally Rotate the Hip

 The small, deep muscles in the buttock are the primary muscles that produce hip lateral or external rotation. Several other muscle groups can contribute to external hip rotation. These include the gluteus maximus and the biceps femoris of the hamstring (long head), and the adductor muscles.

 

The Relationship of the Trunk to the Lower Extremity  

From previous discussions it is clear that there is an intimate relationship between the pelvis, the hip, and the lower extremity. The pelvis forms the central keystone for balance and stability. The hip joint is the intermediate joint that produces the primary motions for the leg moving under the pelvis. Motion can occur with the pelvis fixed and the leg moving, or with the leg fixed and the pelvis moving above. Many of the muscles discussed traverse from bony attachments on the pelvis and cross the hip to attach on the femur. Several muscles cross the hip and traverse to cross the knee. For this reason there is integration that takes place between all of these body areas for any pelvic and lower extremity motions. We will explore the anatomy of the knee and the foot/ankle in the next two units. Then we will discuss more fully the integration of the pelvis, the hip, and the lower extremity in the context of walking and moving.
Application to the Dancer:

Most dance techniques emphasize the positions of the hip. Some modern techniques focus more on parallel hip positions, while ballet strongly emphasizes the “turn out“ or external rotation position of the hips. It is important for the dancer to understand how the deep lateral hip rotators provide the key external rotation at the hip. Some of the overlying larger muscle groups may contribute, but dance training should emphasize proper function of the external rotator muscles. 

It is also important to remember that a dancer’s external hip motion is limited primarily by the amount of bony motion at the hip joint. As you recall, we discussed earlier the bony angle of the head of the femur and its neck to its position in the acetabulum. This angle is determined and solidly set by puberty. In early dance years some slight increases in this bony angle may occur with training, but only a small amount. Once puberty takes place and the bony angles are established, a dancer cannot alter this bony alignment. For this reason, dance instructors in elite ballet companies screen dancers to determine whose natural bony angles lend themselves to maximum external rotation of the hip. Stretching exercises can maximize the muscle flexibility around the hip and perhaps provide some slight additional hip rotation, but it will not alter the bony structure of the dancer.

 

 Dance teachers will emphasize proper alignment of the lower extremity to minimize the risk of injury. It is important to maintain good alignment and ensure that the rotation at the hip is within the dancer’s normal motion. It is also important not to try to increase the appearance of rotation by increasing torsion to the joints below (the knee and ankle) so the dancer appears to have more external rotation of the leg. This is dangerous and can predispose the dancer to injury. Further discussion about lower extremity alignment will follow the units on the knee and foot/ankle.

 

This concludes Unit VI. Return to Blackboard to proceed to Unit VII.