OBJECTIVE:Knee cartilage damage is often linked to mechanical overloading. However, cartilage requires mechanical load to remain healthy, suggesting that underloading may be detrimental. We examined knee overloading and underloading by defining cumulative load as the joint effects of body mass index (BMI) and daily walking, and examined the relation of cumulative load to worsening cartilage damage over two years.
METHODS:We used data from the Multicenter Osteoarthritis Study. BMI and steps/day via accelerometry were measured at the 60-month visit. Cartilage damage on magnetic resonance imaging (MRI) was semi-quantitatively scored using WORMS at the 60-month and 84-month visits; worsening damage was defined as increased WORMS between visits. Risk ratios and 95% confidence intervals (RR[95%CI]) were calculated using binomial regression, adjusting for potential confounders.
RESULTS:We included 964 participants (66.9 ± 7.5 years, 62% female, BMI: 29.7 ± 4.8 kg/m2 , 7153 ± 2591 steps/day). Participants with moderate (6000-7900) or high (>7900) steps/day and high BMI (>31 kg/m2 ) had 2.83[1.46-5.48] and 2.61[1.50-4.54] times the risk for worsening medial tibiofemoral damage, respectively, compared with those with similar steps/day and low BMI (18-27 kg/m2 ). Participants with low (<6000) steps/day and low BMI had 2.03[1.06-3.92] and 2.28[1.06-4.85] times the risk for worsening medial tibiofemoral and lateral patellofemoral damage, respectively, compared with those with high steps/day and low BMI. Effect estimates for other compartments did not reach statistical significance.
CONCLUSIONS:This study provides preliminary evidence that both overloading and underloading may be detrimental to medial tibiofemoral cartilage, and underloading may be detrimental for lateral patellofemoral cartilage.
Arthritis Rheumatol. 2019 Nov 29. doi: 10.1002/art.41181. [Epub ahead of print]