Do Ahlbäck scores identify subgroups with different magnitudes of cartilage thickness loss in patients with moderate to severe radiographic osteoarthritis? One-year follow-up data from the Osteoarthritis Initiative

Kellgren-Lawrence grades (KLG) are frequently used for patient selection in clinical trials. The Ahlback radiographic grading system has been developed for moderate and severe knee OA. KLG 3 is comparable to Ahlback 1 and KLG 4 is subdivided into Ahlback 2–5. The objective of this study was to investigate if the Ahlback scoring system is able to subdivide patients with moderate to severe knee OA (KLG 3/4) into groups with different sensitivity to change in cartilage thickness. This study was based on 108 Osteoarthritis Initiative (OAI) participants with KLG 3/4. Baseline KLG scores were available from the OAI database; Ahlback scores were performed using the same x-rays. Cartilage thickness change in the weight-bearing femorotibial cartilage was analysed from baseline and year 1 3D FLASH MRI for the entire femorotibial joint (FTJ), the medial (MFTC) and the lateral compartment (LFTC) and for the location-independent ordered values 1 and 16 (OV 1/OV 16) representing the subregions with largest loss (OV 1) and gain (OV 16) within each knee. Of the 108 patients, n = 30/78 had KLG 3/4. The corresponding Ahlback scores (1–5) were n = 30/33/36/9/10. Cartilage thickness changes between Ahlback groups showed no statistically significant difference for FTJ, MFTC, LFTC and OV 1, but change in OV 16 was significantly higher in Ahlback 4 knees (p = 0.03) compared to Ahlback 1–3 knees. Radiographic knee OA grading with Ahlback scores was not superior to KLG for prediction of cartilage thickness loss over 1 year, in patients with moderate and severe knee OA supporting the continuous use of the easier and more widely used KLG.