Patellar calcar: morphometric analysis by knee magnetic resonance imaging and three-dimensional reconstruction software-assisted

Abstract

Purpose: Patellar calcar corresponds to a greater trabecular bone density area in the patella lateral facet, whose morphometry is uncertain. This study aimed to describe patellar calcar morphometry by knee MRI and develop a 3D reconstruction software-assisted.

Materials and methods: Consecutive adult patients, submitted to knee MRI, between 2014 and 2017, were entered in IMPAX software. Exclusion criteria are history of patellar surgical intervention, trauma, chondromalacia, bone edema or bipartite patella. All MRI images were retrospectively reviewed by three readers. MRI patellar calcar measurements are height, width, thickness and posterior distance. 3D model protocol reconstruction: 3D Slicer software was used to design a preliminary model for each patient, and then all were automatically merged into one, which was finalized using the software segmentation tools. For 3D patellar calcar location, the transpolar axis was designed.

Results: 250 MRI were analyzed, patellar calcar was present in 208 (83.2%); 101 men and 107 women. Mean age was 44.3 ± 15.6 years.

Measurements: height 13.84 ± 2.42 mm (male: 14.50 ± 2.42; female: 13.21 ± 2.26) (p < 0.0001), width 12.21 ± 2.26 mm (male 13.14 ± 2.22; female 11.33 ± 1.93) (p < 0.0001). No statistically significant difference of thickness 0.56 ± 0.22 mm (male: 0.56 ± 0.25; female: 0.56 ± 0.20) and posterior distance 2.37 ± 0.80 mm (male: 2.46 ± 0.89; female: 2.29 ± 0.69) between genders was found. 3D model results: transpolar axis went through the patellar calcar in all the cases.

Conclusions: This study shows in a 3D model reconstruction, what was previously described in the literature, determining for the first time the patellar calcar morphometry in the knee MRI and identifying it as a regular finding in this imaging test.

Keywords: Calcar; Knee; MRI; Magnetic resonance imaging; Patella; Patellar calcar.