A novel glenoid classification for pre-operative planning in reverse shoulder arthroplasty: “Chandigarh Classification”

Objectives Reverse shoulder arthroplasty has seen tremendous uptake over the past two decades with better implant designs, higher usage, and expanding indications. One of the major limitations of the traditional Walch classification for glenoid morphology is that it does not factor in the overall size of the glenoid and, hence, baseplate fit. The aim of the present retrospective cohort study was to develop a new classification system for glenoid morphology and undertake its frequency mapping in our patient population. Materials and Methods Institutional ethics approval was obtained from the Institutional Review Board before the initiation of the study. Data from a previously conducted computed tomography (CT)-based study at our institute of 600 normal shoulders were used to develop a new classification system for glenoid morphology. 2D and 3D CT scans of shoulders being operated for reverse shoulder arthroplasty from January 2022 to March 2023 were retrospectively included in the frequency mapping analysis. Inter-observer reliability of the new classification was also assessed. Results The new classification combines the circle concept (to assess baseplate fit) with the traditional Walch Classification (to assess glenoid wear and version). Glenoids are divided into two types: Type O (<25 mm maximum anteroposterior [AP] diameter) and Type N (≥25 mm maximum AP diameter). Each type is subdivided into 3 subtypes according to Walch A, B, and C. A total of 120 patients were included in the retrospective analysis, with the vast majority being either walch A with overhang of base plate (AO) (42%) or Walch A with normal fit baseplate (AN) variants (36%). The new classification has a high degree of inter-observer reliability (kappa value = 0.878). Conclusion Our proposed new glenoid classification (the “Chandigarh classification”) incorporates both glenoid size and wear pattern. The single highest frequency population was AO glenoids, suggesting that a large proportion of patients have baseplate overhang (with a 25 mm baseplate) on a relatively symmetrical glenoid.