The Hip

Question 1

Describe the composition of the hip bone

Answer 1

Formed by the fusion of 3 bones (ilium, ischium and pubis). Separated by triradiate cartilage

Question 2

Describe the articulating components of the hip joint

Answer 2

The acetabulum is a cup-like depression located on the inferolateral aspect of the pelvis. Its cavity is deepened by the presence of a fibrocartilaginous collar – the acetabular labrum. The head of femur is hemispherical, and fits completely into the concavity of the acetabulum.

Both the acetabulum and head of femur are covered in articular cartilage, which is thicker at the places of weight bearing.

Question 3

Describe the key features of the hip joint.

Answer 3

The hip joint is a ball and socket synovial joint, formed by an articulation between the pelvic acetabulum and the head of the femur.

It forms a connection from the lower limb to the pelvic girdle, and thus is designed for stability and weight-bearing – rather than a large range of movement.

The hip joint consists of an articulation between the head of femur and acetabulum of the pelvis.

Question 4

Describe the intracapsular ligaments of the hip joint.

Answer 4

The only intracapsular ligament is the ligament of head of femur. It is a relatively small structure, which runs from the acetabular fossa to the fovea of the femur.

It encloses a branch of the obturator artery (artery to head of femur), a minor source of arterial supply to the hip joint.

Question 5

What are the three main extra capsular ligaments of the hip joint?

Answer 5

There are three main extracapsular ligaments, continuous with the outer surface of the hip joint capsule. Iliofemoral, pubofemoral and ischiofemoral.

Question 6

Iliofemoral ligament

Answer 6

Iliofemoral ligament – spans between the anterior inferior iliac spine and the intertrochanteric line of the femur.

It has a ‘Y’ shaped appearance, and prevents hyperextension of the hip joint

Question 7

Pubofemoral ligament

Answer 7

Pubofemoral – spans between the superior pubic rami and the intertrochanteric line of the femur.
It has a triangular shape, and prevents excessive abduction and extension.

Question 8

Ischiofemoral ligament

Answer 8

Ischiofemoral – spans between the body of the ischium and the greater trochanter of the femur.
It has a spiral orientation, and prevents excessive extension.

Question 9

Describe the arterial supply of the hip joint.

Answer 9

The arterial supply to the hip joint is largely via the medial and lateral circumflex femoral arteries – branches of the profunda femoris artery (deep femoral artery). They anastomose at the base of the femoral neck to form a ring, from which smaller arteries arise to supply the hip joint itself.

Question 10

Describe and explain that factors that act to increase stability of the hip joint.

Answer 10

• The first structure is the acetabulum. It is deep, and encompasses nearly all of the head of the femur. This decreases the probability of the head slipping out of the acetabulum (dislocation).
• There is a fibrocartilaginous collar around the acetabulum which increases its depth, known as the acetabular labrum. The increase in depth provides a larger articular surface, further improving the stability of the joint.
• The iliofemoral, pubofemoral and ischiofemoral ligaments are very strong, and along with the thickened joint capsule, provide a large degree of stability. These ligaments have a unique spiral orientation; this causes them to become tighter when the joint is extended.

In addition, the muscles and ligaments work in a reciprocal fashion at the hip joint:

• Anteriorly, where the ligaments are strongest, the medial flexors (located anteriorly) are fewer and weaker.
• Posteriorly, where the ligaments are weakest, the medial rotators are greater in number and stronger – they effectively ‘pull’ the head of the femur into the acetabulum.

Question 11

Which movements can be carried out at the hip joint?

Answer 11

Flexion, extension, abduction, adduction, medial and lateral rotation.

Question 12

Which muscles allow for flexion at the hip?

Answer 12

Flexion – iliopsoas, rectus femoris, sartorius

The degree to which flexion at the hip can occur depends on whether the knee is flexed – this relaxes the hamstring muscles, and increases the range of flexion.

Question 13

Which muscles allow for extension at the hip?

Answer 13

Extension – gluteus maximus, semimembranosus, semitendinosus and biceps femoris

Extension at the hip joint is limited by the joint capsule and the iliofemoral ligament. These structures become taut during extension to limit further movement.

Question 14

Which muscles allow for abduction at the hip?

Answer 14

Abduction – gluteus medius, gluteus minimus and the deep gluteals (piriformis, gemelli etc.)

Question 15

Which muscles allow for adduction at the hip?

Answer 15

Adduction – adductors longus, brevis and magnus, pectineus and gracillis

Question 16

Which muscles allow for lateral rotation at the hip?

Answer 16

Lateral rotation – biceps femoris, gluteus maximus, and the deep gluteals (piriformis, gemelli etc.)

Question 17

Which muscles allow for medial rotation at the hip?

Answer 17

Medial rotation – gluteus medius and minimus, semitendinosus and semimembranosus

Question 18

What are the external rotators of the hip?

Answer 18

Priformis 
Superior gemellus
Obturator Internus 
Inferior gemellus 
Quadrates femoris

Question 19

What causes avascular necrosis of the femur?

Answer 19

Disruption of blood supply to head of femur
Childhood = artery of ligamentum teres (circumflex not developed enough to compensate)
Adulthood = Circumflex arteries (minimal supply from artery of ligamentum teres)

Question 20

How can you differentiate between a hip dislocation and a hip fracture?

Answer 20

Fracture - leg is shortened and externally rotated

Dislocation - shortened and internally rotated

Question 21

Describe the key features of OA of the hip joint

Answer 21

• More common in males over 40
• Joint stiffness
• Pain in hip, gluteal and groin areas radiating to the knee
• Mechanical pain
• Limited walking function

Question 22

Describe a posterior dislocation of the femur

Answer 22

Posterior dislocation – the femoral head is forced posteriorly, and tears through the inferior and posterior part of the joint capsule, where it is at its weakest.

The affected limb becomes shortened and medially rotated.

The sciatic nerve runs posteriorly to the hip joint, and is at risk of injury (occurs in 10-20% of cases).

Question 23

Describe an anterior dislocation of the femur

Answer 23

Anterior dislocation (rare) – occurs as a consequence of traumatic extension, abduction and lateral rotation. The femoral head is displaced anteriorly and (usually) inferiorly in relation to the acetabulum.

It is often associated with fractures of the femoral head.

Question 24

What is an intracapsular fracture of the hip joint?

Answer 24

• More common in elderly women
• Result of minor trip or stumble
• This fracture occurs within the capsule of the hip joint
• It can damage the medial femoral circumflex artery and cause avascular necrosis of the femoral head
• The distal fragment is pulled upwards and rotated laterally

Question 25

What is an extra capsular fracture of the hip joint?

Answer 25

• More common in young and middle aged people
• Blood supply to femur is intact
• Leg is shorter and laterally rotated

Question 26

What causes femoral shaft fractures?

Answer 26

Require a lot of force, usually the result of traumatic injury.

Question 27

How do femoral fractures present?

Answer 27

• Often occur as a spiral fracture, which causes leg shortening. The loss of leg length is due to the bony fragments overriding, pulled by their attached muscles.
• Surrounding tissues may also be damaged, must assess neuromuscular supply.

Question 28

How do you manage an extra capsular fracture of the hip joint?

Answer 28

Pin if possible, using screws or nails

Question 29

How do you manage intracapsular fractures of the hip joint?

Answer 29

Replace (due to risk of avascular necrosis) - partial or total hip replacement

Question 30

What is a hemiarthroplasty?

Answer 30

A hemiarthroplasty is a surgical procedure which replaces one half of the hip joint (the head of femur) whilst leaving the other half intact. It is usually performed to replace the head of the femur when the blood supply has been disrupted by a fracture.