chapter 4 - general principles of dislocations

Question 1

what is a dislocation

Answer 1

there is no contact between the articular surfaces that normally constitute the joint

Question 2

what is subluxation?

Answer 2

joint surfaces are abnormally opposed but there is some contact

Question 3

what is joint congruity?>

Answer 3

it means that in a normal joint the opposing articular surfaces are shaped to fit against each other - ie they are congruent. Alteration or displacement will result in the joint being incongruent.

Question 4

what is the joint space?

Answer 4

it is a radiological entity- what we see is the radiolucent articular cartilage which appears to be a black space on xray

Question 5

why is the joint space black, eventhought it is not actually a space?

Answer 5

it is the radiolucent articular cartilage which is not calcified and therefore appears to be black

Question 6

what does a decreased joint space indicate?

Answer 6

worn or thin cartilage

Question 7

what is the synovial space?

Answer 7

a space which has the potential to distend to accomodate fluid

Question 8

why do joints dislocate? give 3 factors responsible for the stability of a joint.

Answer 8

1. bone congruity
2. joint capsule and surrounding ligaments
3. muscles acting across the joint

Question 9

list 3 striking features of a dislocation

Answer 9

deformity and loss of normal bony landmarks
painful loss of function
distal neurovascular complications

Question 10

which special investigation is NB for a dislocated joint

Answer 10

standard xray - AP and lateral views

Question 11

which 6 specific dislocations are often missed by the inexperienced doctor?

Answer 11

cervical spine ( uni-facet dislocation)
posterior sternoclavicular dislocation
posterior shoulder dislocation
radial head
carpal and tarsal bones
tarso metatarsal  (lisfranc)

Question 12

2 reasons why dislocations have to be treated more urgently than most fractures

Answer 12

1. the articular ends are larger than the shaft and therefore there is a high risk of compression of nerves and vessels
2. large displacements will cause traction injuries to the neurovascular structures

Question 13

why is an angiogram always indicated in a knee joint dislocation despite normal pulses?

Answer 13

there is a risk of intimal tears or flaps whcih may result in the occlusion of a vessel

Question 14

how to manage a dislocation

Answer 14

open or closed reduction

Question 15

when is an open reduction indicated

Answer 15

fracture/dislocations ie both occur together
occasionally irreducible dislocation
old un reduced dislocations

Question 16

what is the management of a dislocation post reduction?

Answer 16

• splinting and rest for a few days till swelling subsides

- bracing and controlled exercise programme for 6 wks to 3m

Question 17

who is likley to present with an unreduced dislocation?

Answer 17

elderly pt
alcoholic
mentally challenged
epileptic after convulsion
multiply injured pt

Question 18

what is the approach to the management of an unreduced dislocation? outline the 3 scenarios

Answer 18

1. stable pain free joint with adequate function = accept the dislocation
2. unstable or painful joint with impaired function = attempt to manipulate gently under anaesthesia with full muscle relaxation and if this fails –> open reduction
3. joint which remains painful or unstable despite reduction= arthroplasty or athrodesis

Question 19

which 2 joints are prone to recurrent dislocation and why?

Answer 19

shoulder
patella femoral joint
= both have a small area of bony contact on one side of the joint and no bony containment

Question 20

how do you treat a joint that is prone to dislocation

Answer 20

soft tissue reconstruction

osteotomy