Patellar Instability

Question 1

What are general risk factors for patellar instability?

Answer 1

1) Previous patellar instability event
2) Ligamentous laxity
3) “Miserable Malalignment Syndrome” (increased Q angle); femoral anteversion, genu valgum, external tibial torsion

Question 2

What are anatomical characteristics that can lead to patellar instability?

Answer 2

1) Trochlear dysplasia
2) Lateral patellar tilt
3) LFC hypoplasia
4) patella alta

Question 3

What is the origin of the medial patellofemoral ligament?

Answer 3

Between the medical femoral epicondyle and adductor tubercle; usually the site of rupture

Question 4

What is the J sign a/w patellar instability?

Answer 4

excessive lateral translation in extension which “pops” into groove as the patella engages the trochlea early in flexion

Question 5

What is TT-TG distance?

Answer 5

measures the distance between 2 perpendicular lines from the posterior cortex to the tibial tubercle and the trochlear groove; >20mm is abnormal

Question 6

What non-operative treatments are available for patellar instability?

Answer 6

NSAIDs, PT with quad/core/hip strengthening, J-brace

Redislocation rates with nonoperative treatment may be high (15-50%) at 2-5 years

Question 7

What surgical options are available for patellar instability?

Answer 7

1) MPFL reconstruction (gracilis graft, Galeazzi procedure)
2) Fulkerson (TT-TG >20mm; reduce by 10-15mm)
3) Distalization of tubercle
4) Elmsie-Trellat (medial slide osteotomy of tubercle)

Question 8

Which of the following best describes the radiographic landmarks on a lateral radiograph for locating the femoral attachment of the medial patellofemoral ligament (MPFL) during reconstruction?

Answer 8

Anterior to a line extended from the posterior cortex of the shaft and proximal to Blumensaat’s line