Patellofemoral joint stress

Question 1

PFJ stress

Answer 1

incr. magnitude of PFJ > incr PFJ stress > dec. contact area

Even small decreases in body weight can substantially reduce PFJ load during functional activities

Question 2

PFJ reaction force:

Answer 2

Quadriceps torque during functional activities:
Level walking = 0.5 x BW Stair climbing = 3-4 x BW
Squat = 7-8 x BW
May be magnified by patellar malalignment
PRESSURE = FORCE (BW) / AREA

Question 3

Local Imparements

- quadriceps atrophy

Answer 3

• Unilateral PFP (between-limb comparison):
• meta-analysis: atrophy in PFP limb (thickness, CSA, volume)
• VMO = VL
• PFP vs. control participants:
  meta-analysis: atrophy in PFP
• no difference in PFP vs. controls

Quadriceps atrophy may decrease VMO pennation angle and medial stabilising force

Question 4

lower quadriceps strength in older adolescents & adults

Answer 4

• age 12-15 years - no difference in isometric knee extension strength (males & females)
• age 15-19 years - lower peak isometric quadriceps torque
  (females)
• adults: lower quadriceps peak torque in PFP vs. unaffected limb (females) and compared to controls (males)
• meta-analysis: lower knee extension peak torque is a risk factor for PFP
• Quadriceps strength deficits may be present before PFP onset, and persist

Question 5

altered quadriceps neuromuscular control

Answer 5

Vastus lateralis 12-15˚
Vastus medialis obliquus 5- 55˚
- Delayed onset of VMO vs VL was a risk factor for PFP
-Quadriceps dysfunction may be present before PFP onset, and persist

Question 6

altered quadriceps neuromuscular control 2

Answer 6

Why is this important?
- significant increase in lateral PFJ load with 5ms VMO delay
- load more concentrated on lateral PFJ
- lateral patellar stress is associated with lateral patellar lesions,
and can be reduced by increased VMO activity
however A delay in VMO onset timing is not present in all people with PFP

Question 7

local impairments - shorter hamstring length

Answer 7

• people with PFP have shorter hamstrings compared to controls
• people with reduced hamstring length have greater total and lateral PFJ stress during squat descent and ascent

Question 8

local impairments - altered hamstring neuromuscular control

Answer 8

• delayed onset of medial vs. lateral hamstrings during isometric hamstring contraction in
  PFP vs. controls
  mean difference 53.8ms
• increased lateral hamstring and quadriceps activity during hop test in PFP vs controls
• May increase pressure on the lateral patellar facet

Question 9

local impairments

Answer 9

• altered hamstring neuromuscular control
• shorter hamstring length
• altered quadriceps neuromuscular
• quadriceps atrophy

Question 10

Proximal Impairments - altered hip kinematics

Answer 10

greater hip adduction and IR during functional activities in PFP vs controls

(e. g. SL squat, stairs, hopping, running)
- Hip adductions and IR are predictors of pain and function
- hip IR and dynamic knee valgus during drop landing is a risk factor for PFP
- greater hip add. during running is a risk factor for PFP in female runner
* altered hip movement patterns may be present before PFP onset, and persist

Question 11

altered hip kinematics

Why is this important?

Answer 11

in weight bearing, the femur IR under the patella

• Non weight-bearing:
  Patellar tilt results from patellar rotation
• Weight-bearing:
  Patellar tilt results from Internal femoral rotation
• increased femoral IR (5-10°) during walking increases PFJ cartilage stress by ~30%

Question 12

proximal impairments

- lower hip strength

Answer 12

• moderate evidence of lower isometric strength in PFP vs controls (males & females)
• moderate to strong evidence of no association between isometric hip strength & risk of PFP development
• Deficits in isometric hip muscle strength may be a result of PFP, rather than a cause

Question 13

proximal impairments

- altered gluteal neuromuscular control

Answer 13

Gmed delayed and shorter in duration during stair ascent, descent and running in PFP vs controls
- delayed GMed correlated with greater hip add. during running

Question 14

proximal impairment

- lower isometric trunk strength

Answer 14

lower trunk isometric strength in PFP vs. controls

• ext.
• flx with rotation
• side bridge
• delayed onset of transversus abdominus and internal oblique in PFP vs controls

Question 15

proximal impairments

Answer 15

• lower hip strength
• altered gluteal neuromuscular control
• lower isometric trunk strength

Question 16

distal impairments

greater foot pronation

Answer 16

• people with PFP (vs. controls) have significantly greater: ankle dorsiflexion
• calcaneal angle
• navicular drop, navicular drift
• Foot Posture Index
• arch height mobility, foot mobility magnitude
• greater navicular drop is a risk factor for PFP development
• Greater foot pronation may be present before PFP onset, and persist

Question 17

greater rearfoot eversion during functional tasks

Answer 17

• people with PFP (vs. controls) have significantly greater:
• peak RF eversion during SL squat and stair ascent
• peak RF eversion during SL triple hop
• runners with PFP use a greater percentage of their available pronation ROM during running
• peak RF eversion has a positive correlation with peak hip adduction in PFP and controls
• Greater foot pronation may have implications for proximal control