Epidemiology of Patellar Instability :
- Most commonly occurs in 2nd-3rd decades of life
- Risk factors include
- Ligamentous laxity (Ehlers-Danlos syndrome)
- Dysplastic vastus medialis oblique (VMO) muscle
- Lateral displacement of patella
- Patella alta
- causes patella to not articulate with sulcus, losing its constraint effects
- Trochlear dysplasia
- Excessive lateral patellar tilt (measured in extension)
- Lateral femoral condyle hypoplasia
- Increased quadriceps angle (Q angle)
- average for women 15 degrees
- average for men 10 degrees
- Previous patellar instability event
- “Miserable malalignment syndrome”
- A term named for the 3 anatomic characteristics that lead to an increased Q angle :
- femoral anteversion
- genu valgum
- external tibial torsion / pronated feet
- A term named for the 3 anatomic characteristics that lead to an increased Q angle :
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