THE RELATIONSHIP BETWEEN PATELLAR MORPHOLOGY AND LATERAL PATELLAR INSTABILITY

Abstract

Background: Lateral patellar instability (LPI) is a substantial cause of morbidity in the pediatric population. Previously identified risk factors for LPI include trochlear dysplasia, a lateralized tibial tubercle, genu valgum, femoral anteversion, and external tibial torsion. Less is known regarding the relationship between patellar morphology and LPI. Purpose: The goal of this study is to determine whether there exists a relationship between patellar morphology and LPI. Methods: Magnetic resonance imaging (MRI) evaluation was performed for patients under 18 years of age with LPI and compared to a control group of MRIs of patients with anterior cruciate ligament (ACL) rupture. Using T2 axial MRI images, the lateral and medial facet angle of both the bone and cartilage of the patella was measured at three locations: the most proximal and distal aspects of the patella where the cartilage of the facets could be identified and the widest point of the patella. The width of the patella at each point was also recorded, resulting in 15 total data points per subject (5 at each of the three locations on the patella). Results were analyzed and compared between the instability group and the control group to determine any relationship between facet angle and LPI. Results: 196 MRIs were reviewed, 97 in the instability group and 96 in the control group. The LPI group was noted to have a less steep angle at the proximal medial patellar facet of both the bone (LPI 27.2° ± 9.3° ; control 32.7° ± 8.8°, p < 0.001) and cartilage (LPI 26.5° ± 8.8°, control 32.7° ± 8.4°, p < 0.001) as well as a less steep angle of the cartilage at the distal lateral facet (LPI 23.4° ± 7.2°, control 25.6° ± 6.6°, p = 0.033). No other differences were noted for the remaining 12 data points. Conclusion: The are very few differences in patellar morphology between patients with and without LPI. Patients were LPI have a less steep angle of the bone of the proximal medial facet, the cartilage of the proximal medial facet, and the cartilage of the distal lateral facet when compared to a control group. [Figure: see text]