BASELINE C-SCORE ON WEIGHT-BEARING CT PREDICTS 2-YEAR WORSENING OF KNEE PAIN IN WOMEN

Abstract

INTRODUCTION

The B-score is a statistical score derived from non-weight-bearing MRI to assess femoral bone shape and its relationship with knee OA. However, CT scans may offer a more reliable and robust evaluations of bone shape, as they not only provide clearer differentiation between bone and soft tissue but also eliminate distortion artefact that can occur with MRI.

OBJECTIVE

To investigate a new “C-score” for femoral bone shape derived from CT as a predictive imaging biomarker for worsening knee pain in men and women with or at risk for knee osteoarthritis.

METHODS

This study included 649 knees from 389 participants (219 women) with a mean±SD age of 63.8±9.6 years and BMI of 28.5±5.0 kg/m². C-scores were calculated from baseline weight-bearing CT (WBCT) imaging of the knee joint: 0.37 mm voxels, FOV 30 × 20 cm, 120 kVp, 5.0 mA on a LineUp scanner, Curvebeam LLC, Warrington, PA. All distal femurs were segmented using Stradview to produce a surface mesh. A canonical distal femur mesh was registered using wxRegSurf to each individual femur to build the study population shape model. Each knee's C-score was derived from the distance along the vector for femur shape between the average KL0/1 and KL2/3/4 shapes from the study population using a custom script in MATLAB. A single unit of the C-score was standardized as 1SD along this vector for the KL0/1 population (Figure 1). Generalized estimating equations adjusted for age, sex, BMI and presence of up to 2 knees per participant were used to assess associations between baseline C-score and 2-year minimally clinically important worsening (MCIW) of the Western Ontario McMaster’s University Osteoarthritis Scale (WOMAC) pain subscore (2 points). MCIW is defined as the smallest difference on a pain scale that either patients perceive as worsening or requires change in treatment.

RESULTS

186 knees demonstrated pain worsening (32.71% women and 23.2% men). 98 knees had MCIW of pain (19.0% women and 9.8% men). C-scores ranged from -2.64 to +3.34 in women and -3.96 to +2.83 in men, with mean±SD values of 0.16±1.06 and -0.52±1.01 respectively (p-value for difference between sexes p=0.0003). Women without MCIW pain had a mean C-score of +0.31, while those with worsening pain had a mean C-score of +0.72. Men had mean C-scores of -0.03 and -0.01, respectively. In fully adjusted models, baseline C-score predicted 2-year MCIW pain (OR: 1.27, 95% CI: 1.00–1.62, p=0.047). In sex-stratified models, the odds ratios for 2-year MCIW pain in women and men were 1.49 (95% CI: 1.10–2.01, p=0.0159) and 1.01 (95% CI: 0.70–1.47, p=0.95), respectively.

CONCLUSION

Higher C-scores in women were significantly associated with worsening knee pain over 2 years, suggesting the C-score as a potential predictive biomarker for knee pain progression.