Relationship between Feline Knee Joint Osteoarthritis and Bone Mineral Density Quantified Using Computed Tomography and Computed Digital Absorptiometry.

Simple Summary: Osteoarthritis (OA) is a common and painful condition affecting 91% of cats, with knee joint OA present in 50% of cases. Diagnosing feline knee joint OA typically involves clinical examination and radiographic imaging, which also provides information about bone health, including bone mineral density (BMD). While the link between knee joint OA and BMD is well-established in humans, it has not been studied in cats. Understanding this relationship could shed light on how bone changes contribute to OA. This study aims to measure the BMD of cat knee joints, compare different BMD measurement methods, and explore how BMD changes with various severities of OA. For this purpose, 46 cat knee joints were analyzed using two techniques: computed tomography (CT) for the volumetric BMD (vBMD) and conventional radiography with a method called computed digital absorptiometry (CDA) for relative BMD (rBMD). This study found a positive correlation between vBMD and rBMD in key areas of the knee, such as the distal femur, patella, and proximal tibia. Additionally, this study adjusted rBMD for bone size differences (corrected rBMD) because variations in bone width were observed. All measures—vBMD, rBMD, and corrected rBMD—differed between normal knee joint and knee joint with mild to severe OA. Furthermore, all measures showed a linear increase as OA severity worsened. This suggests that there is a relationship between OA and BMD in the feline knee joint, which can be preliminarily confirmed by this study. Osteoarthritis (OA), including knee joint OA, is a common chronic condition in cats. In both cats and humans, knee joint OA is characterized radiographically by the presence of osteophytes, enthesiophytes, subchondral sclerosis, and joint space narrowing. However, only in humans have these radiographic signs been reported to increase bone mineral density (BMD). Therefore, this study aims to quantify the volumetric (vBMD) and relative (rBMD) BMD measures of the feline knee joint and compare BMD measures between various severities of OA to test the hypothesized OA–BMD relationship in the knee joint in cats. The 46 feline knee joints were imaged using computed tomography (CT) and conventional radiography supported by the computed digital absorptiometry (CDA) method to obtain vBMD and rBMD, respectively. Both BMD measures were assessed in three regions of interest (ROIs): the distal femur (ROI 1), patella (ROI 2), and proximal tibia (ROI 3). In all locations, vBMD and rBMD showed moderate (ROI 2: r = 0.67, p < 0.0001) to strong (ROI 1: ρ = 0.96, p < 0.0001; ROI 3: r = 0.89, p < 0.0001) positive correlations. Due to differences (p < 0.0001) in the width of the distal femur (17.9 ± 1.21 mm), patella (8.2 ± 0.82 mm), and proximal tibia (19.3 ± 1.16 mm), the rBMD was corrected (corr rBMD) using the thickness coefficient of 0.46 ± 0.04 for ROI 2 and 1.08 ± 0.03 for ROI 3. Regardless of the quantification method used, BMD measures increased linearly from a normal knee joint to severe OA, with differences in BMD between normal and mild to severe knee joint OA. The OA–BMD relationship in the feline knee joint can be preliminarily confirmed. [ABSTRACT FROM AUTHOR]