Patellofemoral Instability

Question 1

Objective instability

Answer 1

True atraumatic dislocation with an anatomical abnormality

Question 2

Potential instability

Answer 2

Patella pain, a feeling of the knee giving way or locking, with an associated underlying anatomical abnormality

Question 3

Factors that predispose the patellofemoral joint to instability
(morphological, static and dynamic)

Answer 3

1. Trochlear dysplasia
2. Patella alta
3. Lateral condylar hypoplasia
4. Torsional abnormality

Question 4

% of patients that will experience subsequent instability following a first event

Answer 4

17%

Question 5

Goals of realignment surgery

Answer 5

1. Stabilise patellar tracking

2. Optimise load transmission within the joint

Question 6

Trochlear dysplasia

Answer 6

Flattening or elevation of the central area of the trochlear groove, rather than deficiency of the lateral facet of the groove

Question 7

Primary static restraint preventing lateral subluxation or dislocation of the patella

Answer 7

MPFL

extra-synovial ligament

Question 8

3 Layers of the lateral fascial system contributing to a lateral soft-tissue constraint

Answer 8

1. Superficial layer is confluent with the iliotibial band
2. Intermediate layer extends from the deep layer of the iliotibial band to the midlateral aspect of the patella
3. Deep layer is confluent with the knee capsule

Question 9

Vastus medialis obliquus (VMO)

= lower part of the Vastus medialis

Answer 9

First part of the quadriceps to weaken and the last to strengthen when function is inhibited

Question 10

Q angle in females and males

Answer 10

Female 15°

Male 10°

Question 11

Q angle greatest when

Answer 11

Greatest in full extension as the tibia rotates externally (screw home mechanism)

Question 12

When is the patella at greatest risk from dislocation?

Answer 12

In full extension

No bony congruity

The compressive forces pushing the patella onto the trochlear are least

Quadriceps tension pulls the patella in a proximo-lateral direction

Question 13

Anatomical variations that increase the Q angle

Answer 13

1. Torsional deformities at the femoral neck or shaft
2. Laterally positioned tibial tubercle
3. External tibial torsion
4. Genu valgum

Question 14

Positive J-sign

Answer 14

When the patella displaces laterally on the terminal part of extension

Frequently in slim females with ligamentous hyperlaxity

Question 15

Patella glide test for instability

Answer 15

Patient supine with the knee extended, asked to relax the knee

Pressure is applied to the patella in a medial and lateral direction

Greater than 1cm of glide is regarded as abnormal

Question 16

Patella apprehension test

Answer 16

For instability

Lower limb is abducted over the side of the bed

Gentle laterally directed pressure is applied to the patella

The knee is then passively flexed and the patient observed

A patient suffering from patella subluxation or dislocation will exhibit apprehension