The Effect of Unloading on Bilateral Femoral Cartilage Thickness in Active Females

Research investigating the effect of femoral cartilage thickness frequently includes an unloading period prior to any loading intervention. The duration of this period varies between studies, ranging from 0 to 60 minutes with most studies using 30 or 45 minutes. Niehoff et al. (2011) reported either no changes or increases in cartilage thickness after 30 minutes using MRI. PURPOSE: To investigate the effect of unloading time on femoral cartilage thickness in active females for both knees. METHODS: 18 college aged (18-23 years old) physically active injury-free females laid supine on a padded plinth. Ultrasound images were collected for both knees prior to and every 15 minutes for 45 minutes. Mindray M7 ultrasound machine was used to measure thickness in three regions: medial condyle (MC), lateral condyle (LC), and intercondylar notch (IC). One way ANOVA was performed to determine the effect of time on each region’s cartilage thickness for each leg. Post hoc testing was utilized to identify which pairs of times differed. Additionally, dependent t-tests were run to compare each region’s cartilage thickness prior to unloading. RESULTS: There was a significant effect of time on MC cartilage thickness for both the right and left knees (p = 0.004 and p = 0.031, respectively). The right knee MC thickness increased significantly after 15, 30, and 45 minutes of unloading (p=0.007, p=0.004, and p=0.008, respectively) while the left knee MC thickness significantly increased only after 45 minutes of unloading (p=0.036). Time only had a significant effect on right knee IC thickness (p = 0.026) with the thickness being larger after 15 minutes and after 45 minutes when compared to the initial thickness (p = 0.019 and p = 0.027, respectively). There was no effect of time on LC thickness for either knee. Prior to unloading, there was a significant difference in IC and LC cartilage thickness with the left knee values being larger than the right knee values. CONCLUSION: The unloading affects the medial condyle thickness more consistently than in intercondylar notch and lateral condyle. Prior activities or status may alter how unloading affects each knee. It appears that 45 minutes of unloading is most desirable. Research funded by the Swenson Summer Research Fellowship Program.