Anatomic magnetic resonance imaging measurements in first-time patellar dislocators by sex and age

Context: Anatomic differences of the knee in first-time patellar dislocators have not been clearly elucidated. Objective: To compare structural differences of the knee in those who have sustained an acute first-time patellar dislocation resulting in a medial patellofemoral ligament (MPFL) tear by sex and age (≤17 years old, ≥18 years old). Design: Case series. Setting: Retrospective magnetic resonance imaging analysis. Patients or Other Participants: Thirty-five acute first-time patellar dislocators with an associated MPFL tear. Main Outcome Measure(s): Patellar height using 3 methods, patellar alignment using congruency angles, and trochlear morphology using the sulcus angle. We compared the means of these variables by sex and age. The intraclass correlation coefficient was then calculated to assess the agreement of the independent reviewers. Results: A total of 21 left and 14 right knees were analyzed. The MPFL tear location did not differ by sex (P ¼ .34) or age (P ¼ .43). Patellar height did not differ as measured by the Caton-Deschamps ratio (P ¼ .29 for sex, P ¼ .49 for age), Insall-Salvati index (P ¼ .15 for sex, P ¼ .33 for age), or patellotrochlear index (P ¼ .67 for sex, P ¼ .49 for age). The congruence angle (P ¼ .81 for sex, P ¼ .06 for age) and trochlear morphology as measured by the sulcus angle (P ¼ .64 for sex, P ¼ .45 for age) were similar between groups. Conclusions: Patellar height and trochlear morphology did not differ by sex or age among patients whose first-time patellar dislocations resulted in an MPFL tear. In addition, the location of the tear did not appear to vary by sex or age.