Patellofemoral joint biomechanics

1. Biomechanics of
Patello-femoral Joint (PFJ)
• Articular components
• Patellofemoral motion
• Forces acting around
patella
• Pathomechanics
Lecture 3

2. Patella
 Largest sesamoid bone in the body
 Triangular shaped bone embedded within
quadriceps tendon
 Primarily acts as an anatomical pulley for
quadriceps muscle
2

3. Articular surface
3

4. Patellar articular surface
4

5. Patellar Rotation
5

6. Patellar Tilt and Shift
6

7. Patellar flexion/ extension
7

8. PFJ Contact (On Patella)
8

9. 9
PFJ Contact (On Patella)

10. 10
PFJ Contact (On Patella)

11. 11
PFJ Contact (On Patella)

12. 12
PFJ Contact (On Patella)

13. 13
PFJ Contact (On Patella)

14. 14
PFJ Contact (On Patella)

15.  One of the most incongruent joints in the body
Stability depends on:
 Static structures
 Dynamic structures
 Length of patellar tendon
 Lateral lip of femoral condyle
Stability of Patella
15

16. Forces acting on Patella
16

17. Activities Patellofemoral Joint
Forces
Walking 0.5 X Body Weight
Ascending or
descending stairs
3.3 X Body Weight
Squatting 6-7 X Body Weight
Activities Quadriceps Forces
5 flexion 30% of Body Weight
30 flexion 2 X Body Weight
45 flexion 3 X Body Weight
75 flexion 6 X Body Weight
Forces in and around patella
17

18. 18
Fig: Neumann DA
Biomechanics of PFJ
Neumann, 2010

19. Vertical position of patella:
Insall Salvati index
 Normally : the ratio of patellar tendon to the
length of patella is 1:1
Variations:
 Patella alta- high position of patella
 Patellar baja- lower position of patella
19

20. Q- angle
 Normal Q-angle: 10o - 15o
 >20o Pathological
20

21. Causes for Increased Q-angle
 Tight IT band
 Genu valgum
 Femoral Anteversion
 Imbalance between VM and VL muscle
 Lateral tibial torsion
 Laxity of medial retinaculum
 Tight lateral retinaculum
 Prolonged pronation of foot
21

22. External (flexion) torque in
Open kinetic chain
22 Neumann, 2010

23. External (flexion) torque in
Closed kinetic chain
23 Neumann, 2010

24. Causes of Knee Pain
24
 Osteoarthritis
 Ligament injuries
 Meniscal tear
 Bursitis
 Plica syndrome
 Fat pad syndrome
 Patellar tendinitis
 Hamstring strain
 IT band frictional
syndrome
 Patellofemoral Pain
syndrome etc

25. Summary
25

26. References:
 Norkin C, Levengie P. Joint structure and
function. 4th Edition
 Neumann DA. Kinesology of musculoskeletal
system, Foundation for Physical Rehabilitation,
2nd Edition
 Kapandji IA. The Physiology of Joints. Volume 2,
Lower Limb. 5th Edition
26