title: High rate of recurrent patellar dislocation in skeletally immature patients: a long-term population-based study.
abstract: OBJECTIVE
  Patellar dislocation can occur in isolation or be associated with chronic instability. The goals of this study are to describe the rate and factors associated with additional patellar instability events (ipsilateral recurrence and contralateral dislocation), as well as the development of patellofemoral arthritis in patients who are skeletally immature at the time of first patellar dislocation.
  
  
  METHODS
  The study included a population-based cohort of 232 skeletally immature patients who experienced a first-time lateral patellar dislocation between 1990 and 2010. A chart review was performed to collect information related to the initial injury, treatment, and outcomes. Subjects were followed for a mean of 12.1 years to determine the rate of subsequent patellar dislocation (ipsilateral recurrence or contralateral dislocation) as well as clinically significant patellofemoral arthritis.
  
  
  RESULTS
  104 patients had ipsilateral recurrent patellar dislocation. The cumulative incidence of recurrent dislocation was 11% at 1 year, 21.1% at 2 years, 37.0% at 5 years, 45.1% at 10 years, 54.0% at 15 years, and 54.0% at 20 years. Patella alta (HR 10.6, 95% CI 3.6, 36.1), TT-TG ≥ 20 mm (HR 18.7, 95% CI 1.7, 228.2), and trochlear dysplasia (HR 23.7, 95% CI 1.0, 105.2) were associated with recurrence. Similarly, 18 patients (7.8%) had contralateral patellar dislocation. The cumulative incidence of patellofemoral arthritis was 0% at 2 years, 1.0% at 5 years, 2.0% at 10 years, 10.1% at 15 years, 17% at 20 years, and 39.0% at 25 years. Osteochondral injury was associated with arthritis (HR 25.7, 95% CI 6.2, 143.8). There was no association with trochler dysplasia (HR 1.2, 95% CI 0.2, 5.0), recurrent patellar instability (HR 1.2, 95% CI 0.2, 7.2), gender (HR 1.3, 95% CI 0.3, 5.6), or patellar-stabilizing surgery (HR 0.7, 95% CI 0.2, 3.5) and arthritis.
  
  
  CONCLUSIONS
  Skeletally immature patients had a high rate of recurrent patellar instability that was associated with structural abnormalities such as patella alta,TT-TG ≥ 20 mm, and trochlear dysplasia. Approximately 10% of patients experienced a contralateral dislocation and 20% of patients developed arthritis by 20 years following initial dislocation. Osteochondral injury was associated with arthritis.
  
  
  METHODS
  Retrospective case series, Level IV.
authors.affiliation: Departments of Orthopedic Surgery, Mayo Clinic, 200 First Street SW, Rochester, MN, 55905, USA. sanders.thomas@mayo.edu.
authors.forename: Thomas L
authors.identifier: http://orcid.org/0000-0001-7741-9692
authors.initials: TL
authors.lastname: Sanders
authors.affiliation: Departments of Orthopedic Surgery, Mayo Clinic, 200 First Street SW, Rochester, MN, 55905, USA.
authors.forename: Ayoosh
authors.initials: A
authors.lastname: Pareek
authors.affiliation: Departments of Orthopedic Surgery, Mayo Clinic, 200 First Street SW, Rochester, MN, 55905, USA.
authors.forename: Timothy E
authors.initials: TE
authors.lastname: Hewett
authors.affiliation: Departments of Orthopedic Surgery, Mayo Clinic, 200 First Street SW, Rochester, MN, 55905, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Stuart
authors.affiliation: Departments of Orthopedic Surgery, Mayo Clinic, 200 First Street SW, Rochester, MN, 55905, USA.
authors.forename: Diane L
authors.initials: DL
authors.lastname: Dahm
authors.affiliation: Departments of Orthopedic Surgery, Mayo Clinic, 200 First Street SW, Rochester, MN, 55905, USA.
authors.forename: Aaron J
authors.initials: AJ
authors.lastname: Krych
mesh_terms: D000293:Adolescent; D001168:Arthritis / Q000145:classification / Q000453:epidemiology / Q000503:physiopathology; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D008297:Male; D008910:Minnesota / Q000453:epidemiology; D010329:Patella / Q000002:abnormalities; D031222:Patellar Dislocation / Q000453:epidemiology*; D057071:Patellofemoral Joint / Q000503:physiopathology; D012008:Recurrence; D012189:Retrospective Studies; D012307:Risk Factors
keywords: Arthritis; Contralateral; Patellar dislocation; Patellofemoral; Recurrent; Skeletally immature