CT

Anatomy

Pelvis is a true ring

- any anterior fracture must have a posterior injury as well

- integrity of the posterior sacroiliac complex is key

Bony Anatomy

2 innominate bones + sacrum

Symphysis pubis < 5mm

SI joint 2-4 mm

Principle

Irradiate a slice of tissue from multiple angles

Measure the output from different sides

Tissues have different densities

- with denser tissue fewer x-rays reach the detectors

Hounsfield scale

Bone    2000

ST        40

Water   0

Fat       -100

Air       -1000

Ossification

Patella may develop from one or multiple ossification centres at 3 years

Failure of centres to fuse may produce bipartite or tripartite patella

- usually bilateral and painless

Classically superolateral

Classification Saupe

I   Inferior Pole 5%

II  Lateral 20%

AP / Long Leg Views

Quantify Valgus Malalignment

Lateral Xray

1.  Assess Patella Alta

30^o flexion

Definition

Non-traumatic or traumatic condition of femoral head with bone death

Epidemiology

20 - 50 yo (average 38)

- M: F 4:1

NHx  

70-80% with AVN will progress within 1 year

Epidemiology

Young men

Aetiology

FOOSH

- axial load, dorsiflexion and radial deviation

DISI occurs in ulna deviation

Herbert Classification

Type A    Stable acute fracture

A1 Tubercle

NHx

Convincing association with development of osteoarthritis

- arthritic changes beginning at radial styloid

- progress to scaphocapitate & capitolunate 

Epidemiology

Extremely uncommon

Stability provided by joint capsule /costoclavicular & interclavicular ligaments 

Recurrent instability uncommon

Many apparent dislocations in adolescents may be growth plate injuries 

-will remodel without treatment

If OA from chronic dislocation may resect SCJ

Definition

Patients usually complain of subluxation rather than dislocation

- rarely requires reduction

Different entity to acute posterior dislocation usually

Epidemiology

Rare

Aetiology

1.  Ligamentous laxity > 50%

- commonly associated with MDI

- posterior only 20%

- posterior & inferior 20%

Epidemiology

Rare 

- 2% of acute dislocations

Often missed

- < 1/ 52 25%

- < 6/52 25%

- < 6/12 25%

- > 6/12 25%

Aetiology