summary Congenital Dislocation of Patella is a rare congenital knee condition that presents with an irreducible, lateral dislocation of the patella. Diagnosis is confirmed clinically with genu valgum, knee contractures and presence of a patella that is dislocated posterolaterally. Treatment is surgical reduction and stabilization in majority of cases. Epidemiology Incidence rare Demographics usually dislocated at birth often missed or misdiagnosed can be reduced at birth with subluxation and later fixed dislocation in childhood Etiology Pathophysiology pathoanatomy osseous abnormalities small or absent patella hypoplastic trochlea external tibial torsion soft tissues abnormalities thickened, tight lateral structures including iliotibial band retinaculum tight quadriceps causing superiorly subluxed patella Associated conditions Larson syndrome arthrogryposis diastrophic dysplasia nail-patella syndrome Down syndrome Ellis-van Creveld syndrome Anatomy Osteology the patella is the largest sesamoid bone ossification males at 4-5 yrs. old females at 3 yrs. old accessory ossification center appears between 8-12 years separate fragment attached to patella by fibrocartilaginous tissue Function fulcrum for the quadriceps protects the knee joint articular cartilage of patella is thickest in body (up to 1cm) enhances lubrication of the knee see complete knee biomechanics Blood supply blood supply to patella is predominantly from distal to proximal 6 arteries contribute from popliteal artery superior lateral geniculate artery superior medial geniculate artery inferior lateral geniculate artery inferior medial geniculate artery from superficial femoral artery supreme geniculate artery from anterior tibial artery recurrent anterior tibial artery Presentation History associated syndromes present Symptoms delayed walking can mimic cerebral palsy Physical exam inspection genu valgum knee flexion contractures "smiley face" appearance of knee caps femoral condyles abnormally prominent small patella which is difficult to palpate laterally motion limited active flexion as genu valgum worsens, patella subluxes posterolaterally causing quadriceps to act as knee flexor Imaging Radiographs recommended views not helpful in children younger than 3 years old because patella is not ossified in children > 3 years of age AP lateral and sunrise findings dislocated patella hypoplastic trochlea Ultrasound or MRI indications children <3 years of age can help diagnose non-ossified, dislocated patella Treatment Nonoperative observation indications for most part not recommended as the condition impairs long term function if left untreated Operative surgical reduction (Andrish technique) indications perform early to allow for trochlear intervention technique (below) Techniques Surgical reduction (Andrish technique) soft tissue reduction steps divide and lengthen lateral retinaculum between oblique and transverse layers dissect vastus lateralis from intermuscular septum and advance proximally on quadriceps tendon release distal patellomeniscal ligaments lengthen quadriceps tendon, shorten patellar tendon to correct patellar alta tighten medial structures via medial patellofemoral reconstruction reroute semitendinosus through medial collateral ligament and attach to patella osseous realignment distal realignment usually not needed with adequate release if needed, realignment limited due to tibial tubercle apophysis Roux-Goldthwait is preferred Complications Recurrence