Patellofemoral joint

Question 1

Patellofemoral joint - about / info

Answer 1

• Multiaxial plane joint – therefore mobile in multiple directions
• Sesamoid bone – tracking of patella movts very affected by quadriceps muscle action + position of patella against femur
• In the extended position, w/ the quadriceps muscle relaxed, the patella is free in its mobility
• Anatomy reflects functional roles as a knee extensor + decelerator, optimising weight-bearing capacity
• primary function of the patella is to act as a fulcrum or pivot surface, effectively increasing the lever arm of the quadriceps.
• patella is well adapted to bearing high compressive loads while minimising friction forces

Question 2

Patellofemoral joint stability

Answer 2

The patella is stabilized in its position by:
1. ligaments:
- medial & lateral retinaculum
- patellar ligament (tendon)
- medial patellofemoral ligament
2. quadriceps muscle component forces

Question 3

Patella tracking and alignment

Answer 3

• The Q-angle – the angle formed b/w a line connecting the ASIS to the midpoint of the patella + a line connecting the tibial tuberosity + the midpoint of the patella
• Normal Q-angle = 10° to 15° (measured with the knee either in full extension or slightly flexed)
• Q-angle >20° in knee extension may be associated with increased lateral displacement forces + patellar tilt (e.g. can happen as a result of hip anteversion)
• Patella mal-tracking can also occur w/ uneven quadriceps muscle forces – e.g VL&raquo_space; VM

Question 4

Patellofemoral joint motions during knee flexion

Answer 4

From 20° of knee flexion + further flexion range, patella mobility is reduced due to static constraints of:
- intercondylar groove (patella surface) of the distal femur – the lateral facet is more prominent anteriorly + steeper than the medial facet to help stabilize the patella against excessive lateral pull
- Patellar ligament (limits superior translation)
- Quad tendon & retinaculum (limits inferior translation)
- Lateral retinaculum & ITB (limits medial movements)
- Medial retinaculum + Medial Patellofemoral ligament (MPFL) (limits lateral movts)

Question 5

Patellofemoral OKC and CKC motion during knee joint flexion

Answer 5

• Tibia on femur (OKC) – relaxed quadriceps allows the patella lig to pull the patella inferiorly on femur
• Femur on tibia (CKC) increased strain on patellar ligament

Question 6

Patellofemoral contact during knee joint flexion

Answer 6

• the least contact occurs in full extension of the knee
• the contact surface area on the posterior patella shifts superiorly as the knee flexes, as the patella sits relatively lower on the femur

Question 7

Patellofemoral motion related to forces

Answer 7

• Max contact force + contact area b/w the patella = occurs b/w 60-90° knee flexion, w/ increased loading seen during weight bearing
• At end-of-range knee flexion (135 degrees) the patella rests largely below the intercondylar groove of the femur

Question 8

Patella forces during knee extension

Answer 8

• The difference b/w quadriceps force + patella tendon insertion creates a slight lateral muscular force on the patella
• Vastus medialis oblique fibres are the only dynamic control to prevent lateral tracking of the patella

Question 9

Patellofemoral joint OKC + CKC extension

Answer 9

• CKC exercises have been shown to increase functional ability + activity of VM muscles compared to the vastus lateralis muscle,
• This may be desirable w/ lateral tracking patella problems to bring the patellar alignment more medial, + reducing the Q angle

Question 10

patellofemoral joint ligaments - Patellar tendon/ligament

Answer 10

• Superior attachment from the apex of the patella, continuous w/ fibres of the quadriceps tendon, extending inferiorly to the tibial tuberosity
• Limits superior displacement of the patella
• During knee flexion, responsible for maintaining patella position hence lowering the contact area on the femur

Question 11

patellofemoral joint ligaments - Medial patellofemoral ligament (MPFL)

Answer 11

• Directly connected with vastus intermedius + patella
• Thick band within the medial retinaculum
• Most taut in full extension
• Limits lateral displacement of the patella

Question 12

Medial and lateral retinaculum

Answer 12

• Provide patellofemoral joint stability throughout knee range of motion
• Deep + superficial fibres
• Various medial + lateral knee structures contribute to these retinacula