Profiling Intact Limb Femoral Cartilage Thickness In Those With Lower Limb Amputation Compared To Osteoarthritic And Young Healthy Knees

Individuals with lower-limb amputation (LLA) are at 3 times higher odds of developing knee osteoarthritis (OA) in the intact limb compared to non-amputees. While knee OA is repeatedly identified as a consequence of LLA, a dearth of work has directly profiled cartilage health prior to the onset of OA-related symptoms or radiographic presentation. Data directly evaluating cartilage health in pre- or early-OA stages is crucial to understanding the OA time-course; knowledge necessary to adequately design disease-modifying OA therapies specific to those with LLA. PURPOSE: To compare femoral cartilage thickness via ultrasound (US) in those with LLA compared to OA and healthy knees. METHODS: Femoral cartilage US was acquired in 7 individuals with LLA (Sex:4 M-3F, Age: 51.6 ± 12.9 yrs, BMI: 27.0 ± 6.5), 20 individuals with knee OA (Sex:10 M-10F, Age: 63.9 ± 8.6 yrs, BMI: 30.7 ± 8.5) and 10 young adults (Sex:5 M-5F, Age: 29.6 ± 5.1 yrs, BMI: 24.3 ± 4.1) after a standard 30-minute resting period. The femur was imaged in both transverse (trochlear cartilage) and longitudinal views (medial femoral condyle [MFC]). Cartilage thickness was evaluated as the Euclidean distance between superficial and deep cartilage contours via an open-source MATLAB app. For transverse images, medial:lateral ratios were also computed to compare thickness distributions across groups. Independent t-tests were used to compare cartilage outcomes across all limbs (α = 0.05). RESULTS: Intact knees exhibited thinner medial trochlear cartilage (p = 0.047, Cohen’s d = 1.07) and lesser ML thickness ratios compared to healthy knees (p < 0.01, Cohen’s d = 1.78) and thinner MFC cartilage compared to OA knees (p = 0.01, Cohen’s d = 1.14). OA knees exhibited thinner MFC cartilage compared to healthy knees (p < 0.01, Cohen’s d = 1.48) but no other cartilage outcomes were different (p > 0.05). CONCLUSION: Those with LLA exhibited thinner cartilage and altered cartilage thickness distributions compared to healthy adults. While trochlear cartilage thickness was not different in intact compared to OA knees, effect sizes were moderate and thus, we reason intact limbs in those with LLA show early OA thinning given our smaller sample. Future work is needed to uncover modifiable risk factors linked with cartilage health in those with LLA such as gait mechanics and/or muscle function.