MSK 7a: the hip

Question 1

Describe the articulations of the hip joint

Answer 1

• Hip bone: fusion of the ilium, ischium and pubis by tri-radiate cartilage
• acetabulum: “socket” of joint, margin is incomplete inferiorly (acetabular notch; supported by ligament)
• acetabular rim: heavy and prominent. Semi-lunar articular part covered with cartilage (lunate surface)
• acetabular labrum: fibrocartilage rim on margin of acetabulum

Question 2

What is the non-articulating part of the acetabulum called?

Answer 2

The acetabular fossa

Central, deep, thin, formed mainly by the ischium

Question 3

Function of the acetabular labrum

Answer 3

Increases articular contact area by 10%, so more than 50% of head of femur fits in
Transverse acetabular ligament: strengthens inferior portion; continuation of the labrum where the acetabular notch is

Question 4

When are the hip joint articulations most in contact with one another?

Answer 4

Flexed 90 deg
Abducted 5 deg
Laterally rotated 10 deg

Question 5

Describe the joint capsule of the hip

Answer 5

Loose external fibrous capsule + internal synovial membrane
Attachments:
-proximal: acetabulum and transverse acetabular ligament
-distal: intertrochanteric line of femur and root of greater trochanter
-anterior: intertrochanteric line
-posterior: lateral part of neck of femur (this is extracapsular)

Stability achieved by the tightened fibrous layer and the ligaments

Question 6

What are the accessory ligaments of the hip?

Answer 6

TRANSVERSE ACETABULAR: reinforces missing inferior part of acetabulum

LIGAMENT OF HEAD OF FEMUR: triangular synovial fold, very weak, contains small arterial blood from obturator artery to head of femur

Question 7

What are the main ligaments of the hip joint?

Answer 7

ILIOFEMORAL: the body’s strongest ligament

• protects anteriorly and superiorly in a Y-shape
• attaches to the ASIS and acetabular rim proximally, and the intertrochanteric line distally
• prevents hyperextension (draws femoral head more tightly into acetabulum)

PUBOFEMORAL:

• protects anteriorly and inferiorly
• attaches to obturator crest of pubis, passes laterally and inferiorly to merge with the fibrous layer of joint capsule
• tightens in extension and abduction so prevents overabduction

ISCHIOFEMORAL: weakest of the three

• from ischial part of acetabular rim; posterior then spirals superolaterally to neck of femur
• limits extension

Question 8

What does line of pull mean?

Answer 8

Muscles will produce different movements depending on where they act in relation to a line of axis (anterior-posterior, medial-lateral or ventral)

Question 9

How does position of the knee affect the movement of the hip?

Answer 9

Knee flexed=relaxed hamstrings, so hip can be flexed until thigh almost anterior to abdomen
Extension limited due to iliofemoral ligament

Question 10

How is the hip flexed?

Answer 10

Muscles that cross joint and act anterior to the M/L line of axis:

Iliopsoas
Sartorius
Rectus femoris

Synergistic:
Pectineus
Adductor longus, brevis and magnus
Gracilis

Question 11

How is the hip adducted?

Answer 11

Muscles that cross joint and act medial to the A/P axis:
Pectineus
Adductor longus, brevis and magnus
Obturator externus
Gracilis

Question 12

Lateral (external) hip rotators

Answer 12

Obturator externus and internus
Piriformis
Superior and inferior gemelli

Question 13

Extensors of the hip

Answer 13

Gluteus maximus
Adductor magnus
Semitendinosus
Semimembranosus
Long head of biceps femoris

Question 14

Abductors of the hip

Answer 14

Gluteus medius
Gluteus minimus
Tensor fasciae latae

Question 15

Medial (internal) rotators of hip

Answer 15

Gluteus medius and minimus: anterior parts

Tensor fasciae latae

Question 16

Describe the blood supply to the hip

Answer 16

Main source: profunda femoris branches; occasionally direct branches of femoral artery:
-medical circumflex femoral
-lateral circumflex femoral
These give rise to the retinacular arteries, main source from medial

Minor source in adults: artery to head of femur (branch of obturator artery)

Question 17

Describe the nerve supply of the hip

Answer 17

Anteriorly: femoral nerve (L2-L4)
Posteriorly: nerve to quadratus femoris (L4-S1)
Superiorly: superior gluteal nerve (L4-S1)
Inferiorly: obturator nerve (L2-L4)

Question 18

Hip dysplasia

Answer 18

A common defect that affects girls more than boys, causing congenital hip displacement that is bilateral in 50% of cases.

Anatomy: femoral head not properly located in the acetabulum, so is dislocated at birth or soon after. Incorrect angle between femur and head of femur, shallow acetabulum with damaged cartilage

Signs: inability to abduct thigh, shortened apparent leg length, positive Trendelenberg, often leads to arthritis if residual defects remain

Question 19

Acquired hip dislocation

Answer 19

RARE, due to very strong articulation
May occur during car crash when hip is flexed, adducted and medially-rotated, causing a posterior dislocation. Anterior dislocation can be caused by an injury forcing hip extension, abduction and lateral rotation.

Anatomy:

• Capsule and acetabulum disrupted, possibility of sciatic nerve damage
• extensors and adductors pull femur up the external ilium surface, causing shortened apparent leg length
• gluteus medius and minimus attached to greater tubercle, in dislocation anterior fibres pull the greater trochanter medially causing internal rotation

Question 20

Describe some common hip fractures and which structures they might damage

Answer 20

Easiest to draw out with arteries/nerves on then mark fracture sites and possible complications :)

Question 21

Slipped upper femoral epiphysis (dislocation)

Answer 21

Epiphysis and diaphysis “slip” out of their normal position to each other; femur rides up and forward in relation to epiphysis.

Symptoms: hip pain then limp

Most common in adolescent males. Due to acute trauma or repetitive microtraumas

Complications: predisposes to arthritis, some risk of avascular necrosis of HoF. Treated with surgical pinning

Question 22

Neck of femur fracture

Answer 22

Mainly affects elderly people due to osteoporosis, as this is the weakest part of the femur and lies at a marked angle to the line of weight-bearing. Fracture is often intracapsular

Causes shortening and lateral rotation of the leg

Often disrupts blood supply by tearing retinacular arteries and medial circumflex femoral artery, so can cause avascular necrosis. Would need hip replacement

Treatment:

• healthy patients can be ‘fixed’ following reduction of fracture
• unhealthy patients need replacement

Question 23

Trochanteric femoral fracture

Answer 23

Extracapsular
Due to direct trauma, so more common in younger patients
Less risk of osteonecrosis as better blood supply
Usually treated with a dynamic hip screw

Question 24

Describe the bursae around the hip and why they might develop bursitis

Answer 24

TROCHANTERIC BURSA: largest bursa, between gluteus maximus and greater trochanter. Bursistis may develop from repetitive actions such as running on a steepy-elevated treadmill. Point tenderness over and just posterior to the greater trochanter, pain radiates over iliotibial tract. Pain elicited by manually resisting abduction and lateral rotation of thigh while lying on unaffected side

ILIOPSOAS BURSA: deep to iliopsoas. May present as swelling below the inguinal ligament

ISCHIOGLUTEAL BURSA: near ischial tuberosity. Sitting down can inflame e.g. cycling, as overwhelms the ability of the bursa to dissipate friction. Causes localised pain over the bursa that increases with movement of gluteus maximus

Question 25

What is arthritis?

Answer 25

Inflamed synovium and damage to cartilage

OSTEOARTHRITIS: mainly cartilaginous damage, pain from mechanical grinding, predisposal due to previous joint injuries

RHEUMATOID ARTHRITIS: problem begins in synovium inflammatory, joint cartilage destroyed, sytemic, then becomes more of a mechanical problem