Radiographic findings involved in knee osteoarthritis progression are associated with pain symptom frequency and baseline disease severity: a population‐level analysis using deep learning

Abstract Purpose To (1) develop a deep‐learning (DL) algorithm capable of producing limb‐length and knee‐alignment measurements, and (2) determine the association between limb‐length discrepancy (LLD), coronal‐plane alignment, osteoarthritis (OA) severity, and patient‐reported knee pain. Methods A multicenter, prospective patient cohort from the Osteoarthritis Initiative between 2004 and 2015 with full‐limb standing radiographs at 12 month follow‐up was included. A convolutional neural network was developed to automate measurements of the hip–knee–ankle (HKA) angle, femur, and tibia lengths, and LLD. At 12 month follow‐up, patients reported their frequency of knee pain since enrollment and current level of knee pain. Results A total of 1011 patients (2022 knees, 52.3% female) with an average age of 61.2 ± 9.0 years were included. The algorithm performed 12,312 measurements in 5.4 h. ICC values of HKA and LLD ranged between 0.87 and 1.00 when compared against trained radiologist measurements. Knees producing pain most days of the month were significantly more varus (mean HKA:− 3.9° ± 2.8°) or valgus (mean HKA:2.8° ± 2.3°) compared to knees that did not produce any pain ( p < 0.05). In varus knees, those producing pain on most days were part of the shorter limb compared to nonpainful knees ( p < 0.05). Baseline Kellgren–Lawrence grade was significantly associated with HKA magnitude, LLD, and pain frequency at 12 month follow‐up ( p < 0.05 all). Conclusion A higher frequency of knee pain was associated with more severe coronal plane deformity, with valgus deviation being one degree less than varus on average, suggesting that the knee tolerates less valgus deformation before symptoms become more consistent. Knee pain frequency was also associated with greater LLD and baseline KL grade, suggesting an association between radiographically apparent joint degeneration and pain frequency. Level of evidence IV case series.