MSK 7a: the hip Flashcards
Describe the articulations of the hip joint
- 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
What is the non-articulating part of the acetabulum called?
The acetabular fossa
Central, deep, thin, formed mainly by the ischium
Function of the acetabular labrum
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
When are the hip joint articulations most in contact with one another?
Flexed 90 deg
Abducted 5 deg
Laterally rotated 10 deg
Describe the joint capsule of the hip
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
What are the accessory ligaments of the hip?
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
What are the main ligaments of the hip joint?
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
What does line of pull mean?
Muscles will produce different movements depending on where they act in relation to a line of axis (anterior-posterior, medial-lateral or ventral)
How does position of the knee affect the movement of the hip?
Knee flexed=relaxed hamstrings, so hip can be flexed until thigh almost anterior to abdomen
Extension limited due to iliofemoral ligament
How is the hip flexed?
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
How is the hip adducted?
Muscles that cross joint and act medial to the A/P axis: Pectineus Adductor longus, brevis and magnus Obturator externus Gracilis
Lateral (external) hip rotators
Obturator externus and internus
Piriformis
Superior and inferior gemelli
Extensors of the hip
Gluteus maximus Adductor magnus Semitendinosus Semimembranosus Long head of biceps femoris
Abductors of the hip
Gluteus medius
Gluteus minimus
Tensor fasciae latae
Medial (internal) rotators of hip
Gluteus medius and minimus: anterior parts
Tensor fasciae latae
Describe the blood supply to the hip
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)
Describe the nerve supply of the hip
Anteriorly: femoral nerve (L2-L4)
Posteriorly: nerve to quadratus femoris (L4-S1)
Superiorly: superior gluteal nerve (L4-S1)
Inferiorly: obturator nerve (L2-L4)
Hip dysplasia
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
Acquired hip dislocation
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
Describe some common hip fractures and which structures they might damage
Easiest to draw out with arteries/nerves on then mark fracture sites and possible complications :)
Slipped upper femoral epiphysis (dislocation)
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
Neck of femur fracture
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
Trochanteric femoral fracture
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
Describe the bursae around the hip and why they might develop bursitis
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
What is arthritis?
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
