Submitted to: American College of Rheumatology
Publication Type: Abstract Only
Publication Acceptance Date: 8/10/2008
Publication Date: 10/24/2008
Citation: Lo, G.H., Smith, M., Mcadams, E., Carr, K.A., Nuite, M., Dawson-Hughes, B., Palermo, N., Mcalindon, T.E. 2008. Baseline Vitamin D Status is Predictive of Longitudinal Change in Tibial BMD in Knee Osteoarthritis (OA). American College of Rheumatology. Paper No. 193.
Technical Abstract: With its lack of effective treatment and high prevalence, the public health impact of OA is substantial. Peri-articular bone in OA can be evaluated with the medial:lateral tibial BMD ratio (M:L BMD) obtained from dual x-ray absorptiometry (DXA). Higher M:L BMD is associated with medial OA features on MRI and x-ray. However, there are no longitudinal data on tibial BMD change, or its relationship with pertinent exposures such as vitamin D. This is a longitudinal study of participants in a randomized controlled trial (RCT) of vitamin D for symptomatic knee OA. The parent study is ongoing so investigators are still blinded to treatment allocation. Baseline vitamin D levels were measured. DXA and 1.5 T MRIs of the study knee were obtained at baseline and at 1 year follow-up. We calculated the M:L BMD with a region of interest (ROI) depth of 2cm from knee DXAs. We also used 2 other ratio assessments, the PROXIMAL M:L BMD measuring the proximal 1cm of the aforementioned ROI and the DISTAL M:L BMD the distal 1cm. Those in the highest quartile of change in M:L BMD over 1 year were defined as increase in M:L BMD, the middle two as stable M:L BMD, and the lowest as decrease in M:L BMD. The median vitamin D level defined high v. low vitamin D status. To focus on medial disease, those with lateral cartilage damage on MRI were excluded. We performed logistic regression with increase in M:L BMD as the outcome and baseline vitamin D as the predictor. We then looked at decrease in M:L BMD as the outcome. We also performed an ordinal logistic regression with increase, stable, and decrease in M:L BMD as the outcome. We repeated all analyses evaluating the PROXIMAL M:L BMD and the DISTAL M:L BMD. At the end of the study, participants (N=80) (age 65.7 (+/-8.6), BMI 30.0 (+/-5.0), 63.8% female) had a mean vitamin D level of 31.5 (+/-13.3). In those with symptomatic knee OA, a high baseline vitamin D level was associated with a lower odds of increase in M:L BMD and higher odds of decrease in M:L BMD over 1 year. Sufficient change occurred in M:L BMD to detect a difference over 1 year. Results were similar when evaluating the DISTAL M:L BMD but not PROXIMAL M:L BMD. Vitamin D status seems to beneficially influence local changes in bone in knee OA, even in bone somewhat distal from the joint. Results from the parent study RCT will help clarify this relationship. M:L BMD may be useful as a simple inexpensive outcome measure of bone in OA that changes over 1 year.