The relationship of distal femoral cartilage thickness with disease activity and quadriceps muscle strength in patients with ankylosing spondylitis

The Relationship of Distal Femoral Cartilage Thickness with Disease Activity and Quadriceps Muscle Strength in Patients with Ankylosing Spondylitis Objective: Ankylosing Spondylitis (AS) is a chronic inflammatory disease that can affect the axial skeleton and large peripheral joints such as the knee. One of the two important structures in the knee that carries the body weight is the distal femoral cartilage and the other is the quadriceps muscle. The aim of our study was to investigate the relationship of distal femoral cartilage thickness (DFCT) with disease activity and quadriceps muscle strength in patients with AS. Methods: A total of 30 patients between the ages of 18-65 who were diagnosed with AS according to the 1984 Modified New York criteria were included in our study. The demographic information of the patients, as well as the medications used, the delay in diagnosis, and smoking habits were recorded. In order to determine AS disease activity, the BASDAI questionnaire was applied to the patients and the score was recorded. DFCT measurements were made from 3 different points of the knee (medial condyle, intercondylar area and lateral condyle) in maximum flexion using an ultrasonography device (Esaote MyLab 70) and a 6-18 MHz linear probe. Biodex System 3 isokinetic test and exercise device was used to determine quadriceps muscle strength. Quadriceps muscle strength values such as peak torque (PT), peak torque/body weight (PT/BW), and average power (AP) obtained at angular velocities of 60˚/s and 180˚/s were recorded. Results: In our study, which included 19 male and 11 female patients, the mean age of the patients was 41.13±5.46 (min=29-max=50) years, the mean duration of AS disease was 11.3±6.19 (min=0-max=26) determined as the year. The mean delay in diagnosis of AS was 3.50 (min=0-max=16) years. All quadriceps muscle strength values of male patients were found to be significantly higher than female patients (p<0.05). In male patients, DFCT values of all 3 condyles of the knee (medial condyle, intercondylar area and lateral condyle) were found to be significantly higher than in female patients (p<0.05). The DFCT value of the patients who received TNFi as medical treatment was found to be significantly higher than those who used cDMARDs and NSAIDs (p<0.05). There was a significant negative correlation between BASDAI score and all quadriceps muscle strength values (p<0.05). There was no significant relationship between BASDAI score and DFCT values (p>0.05). A significant positive correlation was found between the PT/BW force value at 180˚/s angular velocity and the DFCT values of all three condyles of the knee (p<0.05). A significant positive correlation was found between PT and AP force values at 180˚/s angular velocity and DFCT values of the medial condyle of the knee (p<0.05). There was no statistically significant correlation between the quadriceps muscle strength values at 60˚/s angular velocity and the DFCT values (p>0.05). Conclusion: We found that quadriceps muscle strength decreased as disease activity increased in patients with AS. We found a positive correlation between quadriceps muscle strength and DFCT. There was no significant relationship between disease activity and DFCT. Considering the effect of the knee joint on mobilization and functionality in daily life, we think that targeting low disease activity in patients with AS and performing strength exercises for the quadriceps muscle should be considered in AS rehabilitation programs. Future studies will make it possible to better understand the relationship of DFCT with disease activity and quadriceps muscle strength in patients with AS.