• Loss of knee cartilage volume [ Time Frame: Over 2 years (Cartilage volume will be assessed at baseline and 2 years later) ] [ Designated as safety issue: No ]
  Cartilage volume will be assessed using magnetic resonance imaging (MRI)
  
  

• Progression of knee cartilage defects [ Time Frame: Over 2 years (Cartilahe defects will be measured at baseline and 2 years later) ] [ Designated as safety issue: No ]
  Knee cartilage defects will be measured using MRI.
  
  
• Loss of limb muscle strength [ Time Frame: Over 2 years (limb muscle strength will be assessed at at baseline and 2 years later) ] [ Designated as safety issue: No ]
  
• Enlargement of tibial bone area [ Time Frame: Over 2 years (Tibial bone area will be assessed at baseline and 2 years later) ] [ Designated as safety issue: No ]
  Tibial bone area will be measured using MRI
  
  

Osteoarthritis (OA) is the most common joint disorder in the world. In 2004, OA was estimated to affect over 1.6 million Australians, with total costs of $1.4 billion. OA is the most frequent reason for joint replacement, at a cost of about $1 billion each year. Conventional treatment is palliative and costly, and currently there are no effective medical remedies for OA. These facts have led to 2000-2010 being labelled the Bone and Joint decade, and musculoskeletal disorders being recognised as a National Health Priority. The primary task for OA management should be to identify modifiable risk factors.

Vitamin D deficiency is very common in older people and has been linked with osteoporosis and falls in both older women and men. Emerging data suggests that it also plays an important role in the pathogenesis of knee OA. Firstly, vitamin D may have direct effects on chondrocytes in osteoarthritic cartilage; secondly, chronic vitamin D inadequacy in adults has adverse effects on calcium metabolism, osteoblast activity, matrix ossification and bone density, and thus could impair the ability of bone to respond optimally to pathophysiological processes in OA; and thirdly, low vitamin D levels are associated with loss of muscle strength and muscle mass in older men and women, which may be associated with an increased risk of knee OA. Some observational studies have shown that vitamin D insufficiency is associated with the progression and development of radiographic knee or hip OA. Recently we have demonstrated that baseline serum levels of 25-hydroxy-vitamin D(25-(OH)D) predicts change in cartilage volume in older adults over 2 years, and increases in vitamin D levels are associated with a further protective association. This suggests that vitamin D supplementation may enhance cartilage and bone health, and thus prevent disease progression in patients with knee OA.

The aim of this study is to compare the effects of vitamin D supplementation versus placebo on knee structural changes and lower limb muscle strength in patients with symptomatic knee osteoarthritis over a 2- year period.

The proposed study design is a randomised, placebo-controlled, double-blind clinical trial. We will recruit 400 subjects (50-79 years old, having relatively good health and serum vitamin D level of <60 and >12.5 nmol/L) with symptomatic knee OA for at least 6 months using a combined strategy in Southern Tasmania and Melbourne. Participants in the intervention arm (n=200) will receive 50,000 IU (1.25 mg) cholecalciferol tablets given once monthly, whilst those in the control arm (n=200) will receive an identical inert placebo. All participants will be provided recommended standard of care. Knee structural changes including knee cartilage volume, cartilage defects, tibial bone area, bone marrow lesions, and meniscal pathology (assessed by MRI), and lower limb muscle strength at baseline and 2 years later will be determined as outcome measures. Other explanatory factors, such as serum vitamin D levels, knee pain, height, weight, physical activity, and smoking will also be determined through study period.

Significance:

Observational evidence suggests that vitamin D deficiency may have a role in the progression of OA and there are biologically plausible mechanisms to explain this. However, randomized controlled trials using a sensitive method are required to determine whether intervening with vitamin D supplementation can in fact slow the progression of this disease. In this study, the randomized, placebo-controlled, double-blind design, and the use of MRI to provide sensitive and precise measures of knee structural change will ensure a rigorous evaluation of the impact of vitamin D supplementation on knee OA. It will be the first long term clinical trial to determine comprehensively the effects on knee structural changes (cartilage, bone, and meniscus) utilizing the pioneering MRI techniques and limb muscle strength assessment. This study builds upon previous clinical and epidemiological studies that supports the objectives of the Bone and Joint Decade organization and addresses a National Health Priority Area.