Principles of internal fixation: intramedullary fixation (Lewis)

Question 1

What are the implants used for IM fixing in small animals

Answer 1

Steinmann pins
K wires
Rush pins
interlocking nails

Question 2

Diameter of steinmann pins

Answer 2

Large

Question 3

Diameter of K wires

Answer 3

small

Question 4

3 points of 3 point fixation

Answer 4

1. Proximal epiphyseal/metaphyseal cancellous bone
2. Endosteal surface of diaphysis
3. Distal epiphyseal/metaphyseal cancellous bone

Question 5

What forces are counteracted by IM fixation devices

Answer 5

Resistant to bending
Little resistance to shear
Unsuitable for sole method of stabilizing communted fx

Question 6

What is the resistance to bending of IM fixation devices

Answer 6

Diameter of the pin ^4th power

Question 7

Trocar tip

Answer 7

3 sided point

sharp

Question 8

Threaded tip

Answer 8

Do NOT use as IM pin

easy to pull out

Question 9

Chisel tip

Answer 9

2 sided with bevel

use when trying to make pin bend and reflect

Question 10

Normograde pin placement

Answer 10

pin is inserted at one end of the bone, then driven across the fx site

Question 11

Retrograde pin placement

Answer 11

pin is inserted through the fx site, driven out one end of the bone, reduced, and driven across the fx site

Question 12

Cutting the pin flush with the bone

Answer 12

less irritation but difficult to retrieve

Question 13

Countersink cutting the pin

Answer 13

no irritation but difficult to retrieve

Question 14

Tie in cutting the pin

Answer 14

contributes to stability, prevents migration, easily retrieved, increased morbidity

Question 15

Placing pins or wires in a manner of rush pins

Answer 15

dynamic 3 point fixation
Salter harris Fx
Chisel tip
stress pinning- metaphyseal or physeal fx

Question 16

Advantages of interlocking nails

Answer 16

controls bending, rotational, and axial forces

Question 17

Process of nail application

Answer 17

Nail positioned within medullary cavity
Screw penetrates (hehe) cortex-nail-cortex
at least one screw prox. and distal to fx

Question 18

IM pinning of femur

Answer 18

Normograde in trochanteric fossa

Question 19

IM pinning of tibia

Answer 19

normograde
Craniomedial aspect of tibial plateau
do NOT enter hock distally

Question 20

IM pinning radius

Answer 20

do not pin radial fractures

Question 21

IM pinning ulna

Answer 21

tension band technique

normograde or retrograde

Question 22

IM pinning of humerus

Answer 22

Retrograde
Exits through greater tubercle
Seated distally in or proximal to the medial portion of the condyle