Download Unit VI – The Hip

Unit VI – The Hip
Objectives:
At the completion of this unit the student will be able to:
1.
2.
3.
4.
Identify the primary bony landmarks of the hip joint and upper leg.
Identify the articulations that form the hip joint.
Identify the key ligamentous and capsular structures of the hip joint.
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 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.
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 less 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 medical 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. Between the two distal condyles, on the posterior
aspect of the distal femur is a large opening called the intercondylar fossa.
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. 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.
The anterior orientation of the neck of the femur to the acetabulum is normally 10-30
degrees. This is called anteversion and 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 the lateral rotation of the hip joint
will be reduced. These anatomical variations in bones and in 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 to 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. The additional ligament structures further protect the stability of the joint.
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.
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.
Hip Adduction – this 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.
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.
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.
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.
Muscles Around the Hip Joint
The Hip Flexors and Extensors
Iliopsoas
The primary hip flexor is the psoas, which has already been discussed. It has an intimate
connection to the spine, the pelvis, and the lower extremity. If the iliacus 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 – ie hip flexion.
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 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.
Adduction and Abduction of the Hip
The lower leg moves in several direction under the trunk and pelvis. Flexion and
extension was mentioned