3. Axial plane
Neck is anteverted (10-15)
At birth 35-40,
As child develops its get reduced
due to power of muscles, gravity
Excessive anteverison seen in CP
5. It is established that static force on the femoral
head is greater than the weight of the body.
Force acting on femoral head influenced by
pelvic angle and position of trunk and limbs
6. JOINT REACTION FORCE
Newton’s Third Law Of Motion
Depends on abductor pull and body weight pull
8. JRF DURING DYNAMIC PHASE
2W during SLR
3W in single leg stance
5W in walking
10W while running
9. These forces must be kept in mind when recommending exercise for a
patient who is not yet ready for weigh bearing.
Joint reaction force increases during climbing and descending stair
Mainly during descending
11. To lean towards the affected hip
Increasing the weight bearing surface by osteotomy
By weight loss(per kg , gets reduced by about 3 kg)
By using a cane in the opposite hand(30 % decrease)
Decrease the speed of walking
15. Johnston study conclusions
The loads on the hip were significantly reduced
placing centre of acetabulum as far medially, inferiorly, anteriorly
Prosthesis with a short neck and reduced neck shaft angle(130)
Lateral transfer of GT has less desirable effect
17. Offset Of Femur And Prosthesis
Offset - perpendicular line drawn from center of femur head to axis of
head
Short offset head gives greater strength
Disadvantages
Short abductor lever arm
Joint force become more vertical thus increasing the abductor pull
Increased offet
Disadvantages
Increased stress on medial neck ,medial femoral cement leading to loosening and
failure
18.
19. Lateralization Of Abductors
By using a short offset prosthesis , lateralization of GT
To maintain abductor lever arm
To maintain angle of inclination of abductor muscle pull
Lateral and distal displacement of 1cm is enough- Charnley
20.
21. Deepening Of Socket.
Not practiced now
0.5 cm lateralization of GT = 1-1.5 cm deepening
To keep angle of abductors normal lateral projection of GT to be
maintained
22. CHARNLEY’s STUDY
Compared various variables like
45mm , 40mm , 35mm offset
Normal socket and deepening of socket
Normal Trochanter and 0.5cm lateralization of trochanter
Findings
Optimal use of 45mm offset is with 0.5cm lateral displacement of trochanter and no deepening of
socket
40 mm offset- lateral transfer of trochanter without deepening of socket
35mm offset-
0.5cm lateral troch displacement- bending moment decreased by 47% and joint reactive force increased
by 3.8%
1cm lat displacement- bending mom- reduced by 23.7% and Jrf reduced by 6.6%
23. In nutshell
For long offset prosthesis
No deepening of acetabulum needed excessively
For short offset prosthesis
Medialisation of acetabulum needed
Lateralization of GT needed
24. FRICTIONAL FORCES
Friction at acetabular cap depends on
Magnitude of compressive force
Direction of force- 15 inclined medially from vertically
Frictional moment and axis around which they act
Radius of the ball
Coefficient of friction between mating surfaces
Hinweis der Redaktion
Add equation from book. Initial statement. Add fig, jrf.
NOW PRESERVING OF SUBCHONDRAL BONE ABDUCTOR LEVER ARM IS ALTERED ONLY RELATIVE TO THE OFFSET OF HEAD OF STEM.
