Epidemiology
Rare
- ? dislocates in utero or post-natal period
Usually bilateral
Aetiology
Familial
Associated with Down's / Larsen's & Arthrogryposis
Pathology
Persistent lateral patella dislocation
- hypoplastic flat LFC
- aberrant lateral insertion quadriceps
- hypoplastic flat patella
Examination
FFD knee
Valgus knee
Plus
- laterally rotated patella
- absent active extension
- difficult to palpate high & lat patella
Common diagnosis as toddler after started walking
Xray
Unrewarding till > 3 years
- doesn't usually ossify til 2 - 3 year
- can be delayed until the 6th year
- ossification complete about puberty
US / MRI
Demonstrate dislocated patella
Management
Timing
Operate when diagnosis made
- gives chance for PFJ to remodel
Operation
Technique
1. Large lateral release
2. Medial plication / VMO advancement
3. Roux Goldthwaite
+/- Galeazzi - Semitendinosis transfer
+/- Hamstring release for FFD
Later problems with PFJ incongruity common as have two flat surfaces & hence early location better
Roux-Goldthwait procedure
- lateral 1/2 patella tendon detached
- transferred beneath intact medial 1/2
- sutured to medial tibia (to insertion of sartorius)
- modification is transfer medial 1/2 patella tendon to MCL