3D-printed anatomic models of the knee for evaluation of patellofemoral dysplasia in comparison to standard radiographs and computed tomography

Abstract

Purpose: To evaluate 3D-printed anatomic models of the distal femur and patella for diagnosis and classification of patellofemoral dysplasia in comparison to conventional radiographs (CR) and CT.

Method: Following local ethics committee approval, CT-datasets of 50 patients were segmented and 3D-anatomic models of the distal femur and patella were printed. An expert panel reviewed CR, CT, 3D-models and patient history and classified the femoral trochleas into normal or Dejour type A-D and the patellas into Wiberg type A-C, which served as the standard of reference. The same classifications were performed by two readers independently, first based on 3D-models and after 3 weeks based on CR and CT. Descriptive statistics, ROC-analysis and inter-reader reliability were performed.

Results: Trochlear dysplasia was present in 28/50 patients. Evaluations of 3D-models vs. CR/CT for trochlear dysplasia showed a sensitivity/specificity of 89.3 %/100 % vs. 96.4 %/68.2 % for reader 1 and 96.4 %/100 % vs. 96.4 %/90.9 % for reader 2, and an area under the curve of 0.946 vs. 0.823 for reader 1 (p = 0.029) and 0.982 vs. 0.937 for reader 2 (p = 0.147). Evaluations of 3D-models vs. CR/CT for the Dejour classification showed a sensitivity/specificity of 32.1 %/100 % vs. 57.1 %/68.2 % for reader 1 and 46.4 %/100 % vs. 50 %/90.9 % for reader 2 without significant differences. No significant differences existed for Wiberg-classification (50-66 % exact matches) or inter-reader reliabilities between 3D-models and CR/CT for all assessments (Kappa 0.428-0.92).

Conclusion: In comparison to radiographs and CT, 3D-models achieve similar diagnostic accuracy for detection of patellofemoral dysplasia and have the potential to improve diagnosis for less experienced physicians.

Keywords: 3D printing; Joint instability; Multidetector computed tomography; Patellofemoral joint; Radiography.