Interestingly, while having a high bone density affords a greater degree of protection against osteoporosis--the bone disease associated with aging that causes bones to become progressively more porous and brittle--and more likely to fracture--high bone density actually increases the risk of osteoarthritis.1 Thus patients with osteoporosis have a lower incidence of degenerative joint disorders such as finger osteoarthritis.2

At the same time, certain clinical markers for bone resorption can assess both the likelihood of developing osteoporosis as well as the extent of bone damage occurring after osteoarthritis has developed. Specifically, two collagen cross links measured in urine, pyridinium and d-pyridinium, provide information both on the pathogenesis of osteoarthritis as well as the rate of bone turnover crucial for osteoporosis (see Osteoporosis links).

Because pyridinium is found extensively in bone cartilage, it is excreted in the urine in higher amounts when cartilage breaks down. For this reason, research indicates that it may serve as an important biomarker for assessing joint destruction in osteoarthritis and rheumatoid arthritis.3 Indeed, a study by researchers at the Center for Rheumatic Diseases in Glasgow, Scotland found that elevated urinary pyridinium cross links (pyridinium and deoxypyridinium) correlated with osteoarthritis of the knee. They concluded that these cross link markers could serve as useful indicators of disease activity in osteoarthritis.4

Other research findings have tied collagen cross links to even more specific clinical factors associated with arthritis. For example, investigators from the Royal London Hospital found that levels of cross links correlated with X-ray examinations in women with osteoarthritis--even in cases where the disease was as yet mild and asymptomatic.5 Another controlled study examining cross link levels in patients with rheumatoid arthritis and osteoarthritis found clinical parameters of both diseases associated with high levels of these urinary markers. They concluded that "both pyridinium cross links in urine may therefore provide information on the stage, activity, level of bone involvement and efficacy of drug therapy in arthritic diseases."6