Working Diagnosis:
Left lateral patellar dislocation

Treatment:
She was treated with a knee immobilizer in extension for 6 weeks and referred to PT. She was advanced to a patellar stabilization brace once pain free with straight-leg raise, range of motion 0-90 degrees, minimal swelling, and good quad control with weight bearing.

Outcome:
Once patient's quad function returned with PT, she used a patellar stabilization brace for 6 months (with activity only).
She continued to have follow up with her orthopedic surgeon every 6 weeks as she progressed with PT and slowly returned to activities.

Author's Comments:
The patient's risk of recurrent patellar dislocation is about 70%, with the main risk factors being skeletal immaturity and female gender.
Lateral patellar dislocations (LPDs) are common injuries in adolescents (prevalence peak: 14-20 years old). Most LPDs occur via non-contact mechanisms (valgus force with internal rotation of femur on planted foot). Less commonly, direct impact results in LPDs, as in this case. Young patients are at higher risk for recurrence, with rates up to 69% (Lewallen 2013). Repeat dislocations and patellofemoral instability can lead to cartilage damage and patellofemoral arthrosis (Parikh, 2018). The mainstay of treatment for first time dislocations in young patients remains conservative as studies have shown no difference in functional outcomes after surgery for first time dislocators (Nikku,1997) and repair of the medial retinaculum showed no significant benefit in decreased recurrence.

Editor's Comments:
Patellar dislocations in patients under 10 years old are not common. More commonly, acute injury in this age group would result in a fracture. Given the knee effusion and lack of weight bearing, aggressive work up should be completed to rule out a fracture with MRI if radiographs are normal. MRI can detect occult fractures as well as show injury to cartilage and ligaments if fracture is ruled out, as was the case for this patient.

Other risk factors for recurrence include femoral condyle dysplasia, avulsion fracture of the medial patella, and medial retinaculum tear.

References:
Khormaee S, Kramer DE, Yen YM, Heyworth BE. Evaluation and management of patellar instability in pediatric and adolescent athletes. Sports Health. 2015 Mar;7(2):115-23.
Nikku R., Nietosvaara Y, Kallio PE, et al. Operative versus closed treatment of primary dislocation of the patella. Similar 2-year results in 125 randomized patients. Acta Orthop. 1997;68(5):419-423.

Lewallen LW, McIntosh AL, Dahm DL. Predictors of recurrent instability after acute patellofemoral dislocation in pediatric and adolescent patients. Am J Sports Med. 2013;41:575-581.
Parikh SN, Lykissas MG, Gkiatas I. Predicting Risk of Recurrent Patellar Dislocation. Curr Rev Musculoskelet Med. 2018 Jun;11(2):253-260.
Moiz M et al Clinical Outcomes After the Nonoperative Management of Lateral Patellar Dislocations: A Systematic Review Orthop J Sports Med. 2018 Jun 11;6(6):2325967118766275.

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