Patellofemoral evaluation with magnetic resonance imaging in 51 knees of asymptomatic subjects

PURPOSE: The objective of this study is to evaluate patellofemoral joint imaging on magnetic resonance imaging (MRI) in asymptomatic subjects to assess normal values and to test statistical correlation and reliability of MRI scan. METHODS: An analysis of 51 standard MRI examinations was performed. Sulcus angle (SA), patellar axis (PA), lateral patellofemoral angle (LPFA), and lateral patellofemoral length (LPL) were measured. None of the patients suffered from patellofemoral complaints. Patients with patella alta and significant hydrops were excluded. The measurements were assessed with a 2-week interval by two raters under blinded conditions. Statistical analysis was applied by an independent analyst. RESULTS: The mean SA referenced 142.4 ± 6.9°, PA 5.3 ± 3.8°, LPFA 13 ± 4.4°, and LPL 0.8 ± 2.9 mm. Inter-observer variability showed high correlation for LPL and PA, as the repeatability coefficient was high (LPL; 1.49 (LN), 5.7 (ST) and PA; 4.1 (LN), 5.8 (ST). Also, intra-observer variability showed good correlation for LPL and PA. CONCLUSION: The results represent patellofemoral values in the normal population. They indicate that MRI is a reliable imaging technique to determine lateral patellofemoral length and patellar axis. Lateral patellofemoral angle and sulcus angle showed a poor correlation and should not be used for decision making. LEVEL OF EVIDENCE: Development of diagnostic criteria in a consecutive series of patients and a universally applied “gold” standard, Level II.