Anatomy and Kinesiology
The pelvis is a bony ring formed by the two coxal bones, the sacral bone and the coccyx. The sacrum and the coxal bones articulate together in the articular processes of the sacrum and in the cartilaginous symphysis. The iliac crest extends from the anterior superior iliac spine (ventral) to the posterior superior iliac spine (dorsal). The ischium is raised on the inferoposterior side, known as the ischial tuberosity. In general, the female pelvis is broader and shorter than the male pelvis. The sacral bone and the sacral-iliac joints are further discussed in the “The Examination of the Spine.“
The coxal bone consists of the ilium, ischium and pubic bone, which border each other in the socket of the hip joint (acetabulum). These three bones fuse and in adults these can no longer be regarded as separate bones.
The head of the femur and the acetabulum together form the hip joint (articulatio coxae). The femur consists of a body (shaft) and a proximal and distal end. At the proximal end of the femur, the femoral neck, greater trochanter (lateral) and minor trochanter (medial) can be distinguished, as well as the head of the femur. At the distal end the medial condyle, and its epicondyle, and the lateral condyle, and its epicondyle, can be distinguished.
The collum and head are anteverted with respect to the femoral body (reference points are the anterior sides of both femoral condyles). The anteversion or angle of declination is usually 11° tot 15° [Figure 1].
Figure 1
The size of the angle that the collum makes with the femoral shaft on the frontal plan, the so-called angle of inclination, is about 125° [Figure 2]. In neonates, the angle of inclination is 134° and the angle of declination 40°. The angle of inclination increases until the third year of life (to 144°) and then gradually decreases until the adult situation is reached. After birth, changes take place in the position of the acetabulum that are complementary to the changes in the angle of inclination. The angle of declination gradually decreases from birth onwards, until the adult situation is reached.
Figure 2: The Axes of the Leg
A = Axis of the tibial shaft
B = Axis of the femoral shaft
C = Axis of the collum
The acetabular labrum (the cartilaginous edge of the acetabulum), together with the capsule and the transverse acetabular ligament, surrounds the head of femur. In addition to this, the capsule is further strengthened by the iliofemoral (Bertini) ligament, the pubofemoral ligament and the ischiofemoral ligament [Figure 3].
Figure 3: The Ligaments of the Hip Joint Capsule (Ventral View).
The ischiofemoral ligament is located on the dorsal side
and is therefore, not shown in this figure.
1 = Iliofemoral ligament (medial part)
2 = Iliofemoral ligament (lateral part)
3 = Pubofemoral ligament
The hip joint is a ball and socket joint and can move in the following ways:
In the sagittal plane:
- Flexion (about 120°): Bending of the hip with knee flexed.
- Extension (about 15°): Stretching of the hip.
In the frontal plane:
- Abduction (about 60°): Lifting the laterally extended leg with hip extended.
- Adduction (about 30°): Extension of the leg over the midline with hip extended.
Around a longitudinal axis through the femoral shaft:
- Exorotation: Outwards rotation of the anterior side of the upper leg, realisable in both an extended leg (about 45° is possible) and a flexed hip and knee (about 60° is possible).
- Endorotation: Inwards rotation of the anterior side of the upper leg, realisable in both an extended leg (about 35° is possible) and a flexed hip and knee (about 40° is possible).
For all of these movements, it should be noted that the pelvis will also move in the majority of cases. For example, extension is coupled with a forwards tilt of the pelvis and flexion with a backwards tilt. The associated movement of the pelvis can, to a certain extent, be prevented if the the examiner manually stabilises the patient’s pelvis while the patient is in the supine position on the examination table.
The hip muscles proceed from the pelvis and the trunk to the upper leg and/or lower leg. The following muscles can be distinguished:
- On the ventral side: Iliac muscle, psoas major muscle, sartorius muscle and the rectus femoris muscle.
*The iliac muscle and the psoas major muscle are together referred to as the iliopsoas muscle. - On the buttocks side: The superficial group (gluteus maximus muscle), and the deep group (originates from the pelvis towards the proximal part of the femur). Piriformis muscle, quadratus femoris muscle, external obturator muscle, gluteus minimus and gluteus medius muscles, superior gemellus and inferior gemellus muscle and the internal obturator muscle.
- On the lateral side: Tensor fascia latae muscle.
- On the medial side: Adductors.
- On the dorsal side of the upper leg: Hamstrings (biceps femoris muscle, semimembranosus muscle and semitendinosus muscle).
The most relevant muscles from a clinical viewpoint (including the upper leg muscles) that exert force on the hip are:
- The iliopsoas muscle and the rectus femoris muscle (in particular during flexion).
- The gluteus maximus muscle and the hamstrings (in particular during extension).
- The tensor fascia latae muscle and the gluteus medius and gluteus minimus muscles (in particular during abduction and endorotation by the foremost fibres of the tensor fascia latae muscle and the gluteus medius muscle).
- The piriformis muscle (in particular during exorotation).
- The sartorius muscle (flexion, exorotation).
- The gracilis muscle, pectineus muscle and the adductor longus, adductor brevis and adductor magnus muscles (in particular during adduction and exorotation).
*While walking and while playing football, the adductors can act as flexors.
Terminology
Torsion
A rotation along the longitudinal axis of a long bone.
Ischiocrural Muscles or Hamstrings
Collective name for the long head of the biceps femoris muscle, the semitendinosus muscle and the semimembranosus muscle.
*The short head (caput brevis) of the biceps femoris muscle is also considered to be one of the ischiocrural muscles by some, despite the fact that the caput brevis originates on the femur (lateral lip of linea aspera).
Triceps Coxae Muscle
Collective term for the inferior gemellus and superior gemellus muscles and the internal obturator muscle.
Valleix Points
These points are projections of the sciatic nerve on the skin, namely L5 paravertebrally, on the middle of the gluteus maximus muscle and the middle of the gluteal fold.
Coxa Vara
Abnormality characterised by a small angle of inclination. The usual consequence of this is a higher than normal position of the greater trochanter with respect to the femoral head. The abnormality may be congenital or secondary.
Coxa Valga
Abnormality characterised by a large angle of inclination. This abnormality is mostly associated with an enlarged angle of declination. The abnormality may be congenital or secondary.
Coxa Anteverta
Abnormality that is characterised by an enlargement of the angle of declination. People who suffer from this condition tend to turn their feet inwards when walking (‘toeing-in’). The person walks with legs positioned in endorotation. The cause is not usually known.
Flexion Contracture
A shortening of the hip flexors (mostly of the iliopsoas muscle), usually as a consequence of the homolateral hip being kept in the flexion for a prolonged period due to pain. Lumbar lordosis is often exaggerated as a compensatory measure.
Adduction Contracture
A shortening of the adductors, which can be seen as a phenomenon accompanying osteoarthritis of the hips. The distance between the anterior superior iliac spine and the greater trochanter is greater on the homolateral side, which may lead to pelvic asymmetry to the detriment of the contralateral side.
Abduction Contracture
Shortening of the abductors. The distance between the anterior superior iliac spine and the greater trochanter is reduced on the homolateral side, which may lead to pelvic asymmetry to the detriment of the homolateral side.
‘Snapping Hip’
This phenomenon arises when the iliotibial band ‘shoots’ over the greater trochanter during walking (‘lateral snapping hip’); or if the iliopsoas muscle slides over the trochanter minor (‘anterior snapping hip’).
Duchenne Sign
This phenomenon is frequently seen in patients with a hip disorder or paresis of the abductors. The walking or standing patient leans over, considerably displacing the torso over the affected hip joint so that the body’s centre of gravity is located above the hip joint of the weight bearing leg. This reduces the force that the abductors must exert and the ultimate pressure load on the hip.
*A mild displacement of the torso on the weight bearing leg during walking is a physiological phenomenon.
Trendelenburg Sign
This phenomenon can be seen in patients with severe paresis or paralysis of the hip abductors. The abductors of the affected side are consequently unable to prevent adduction in the hip joint of the affected side. If the patient is asked to stand on the affected leg, the pelvis on the contralateral side will drop. Normally, the pelvis should remain more or less horizontal or even be displaced cranially on the contralateral side. This phenomenon may also be clearly present during walking.