Bipartite patella revisited: the not so asymptomatic accessory ossicle.

Background: The bipartite patella is a controversial variant, with definitions spanning from normal to stigmata related to patellofemoral dysplasia.

Objective: The purpose of this study is to quantitatively determine if a bipartite patella is in the spectrum of normal versus forme fruste of underlying patellofemoral dysplasia in children using magnetic resonance imaging (MRI) data. A secondary purpose is to assess the MRI findings of the symptomatic bipartite and its implications for patient care.

Materials and methods: A retrospective review of bipartite patellae imaged on knee MRI from 1/2010-3/2024 was conducted. Matched cohorts of control and patellofemoral dysplasia knees were created. Trochlear depth, sulcus angle, CDI, TT-TG, lateral patellar tilt and subluxation, lateral trochlear inclination, and clinical management were evaluated, comparing the bipartite knee MRIs with control and dysplastic knees. Chi-square and Mann-Whitney U tests were used, with P-values for significance set to 0.05.

Results: From 46 patients, 47 bipartite patellae (mean age, 13.3 ± 3.1) were included in the study. In total, 77% (36/47) were male (mean age, 13.6 ± 3.0) while 23% (11/47) were female (mean age, 12.2 ± 3.2). No significant difference in quantitative measurements existed between bipartite patellae and control knees. Significant differences existed for all quantitative measurements defining trochlear dysplasia between bipartite and patellofemoral dysplasia cohorts (P<0.001 for all measurements). Bipartite ossicle edema (39/47, 83%) and Hoffa fat pad edema (17/47, 36%) were frequently present. Six of 47(13%) required surgery for pain management- all had ossicle edema present.

Conclusion: The presence of a bipartite patella does not appear to be associated with underlying patellofemoral dysplasia. The bipartite patella can frequently be a source of a child's pain and should not be treated as a normal ossification variant.