Osteoarthritis and osteoporosis: Clinical and research evidence of inverse relationship

Abstract

The etiology of osteoporosis (OP) and osteoarthritis (OA) is multifactorial: both constitutional and environmental factors, ranging from genetic susceptibility, endocrine and metabolic status, to mechanical and traumatic injury, are thought to be involved. When interpreting research data, one must bear in mind that pathophysiologic factors, especially in disorders associated with aging, must be regarded as either primary or secondary. Therefore, findings in end-stage pathology are not necessarily the evidence or explanation of the primary cause or event in the diseased tissue. Both aspects of research are important for potentially curative or preventive measures. These considerations, in the case of our topic--the inverse relationship of OP and OA--are of particular importance. Although the inverse relationship between two frequent diseases associated with aging, OA and OP, has been observed and studied for more than 30 years, the topic remains controversial for some and stimulating for many. The anthropometric differences of patients suffering from OA compared with OP are well established. OA cases have stronger body build and are more obese. There is overwhelming evidence that OA cases have increased BMD or BMC at all sites. This increased BMD is related to high peak bone mass, as shown in mother-daughter and twin studies. With aging, the bone loss in OA is lower, except when measured near an affected joint (hand, hip, knee). The lower degree of bone loss with aging is explained by lower bone turnover as measured by bone resorption-formation parameters. OA cases not only have higher apparent and real bone density, but also wider geometrical measures of the skeleton, diameters of long bones and trabeculae, both contributing positively to better strength and fewer fragility fractures. Not only is bone quantity in OA different but also bone quality, compared with controls and OP cases, with increased content of growth factors such as IGF and TGFbeta, factors required for bone repair. Furthermore, in vitro studies of osteoblasts recruited from OA bone have different differentiation patterns and phenotypes. These general bone characteristics of OA bone may explain the inverse relationship OA-OP and why OA cases have fewer fragility fractures. The role of bone, in particular subchondral bone, in the pathophysiology, initiation and progression of OA is not fully elucidated and is still controversial. In 1970, it was hypothesized that an increased number of microfractures lead to an increase in subchondral bone stiffness, which impairs its ability to act as a shock absorber, so that cartilage suffers more. Although subchondral bone is slightly hypomineralized because of local increased turnover, the increase in trabecular number and volume compensates for this, resulting in a stiffer structure. There is also some experimental evidence that osteoblasts themselves release factors such as metalloproteinases directly or indirectly from the matrix, which predispose cartilage to deterioration. Instead, the osteoblast regener...

Osteoarthritis and bone mineral density: are strong bones bad for joints?

“…1 In 1972, Foss and Byers 2 studied a series of femoral heads excised either in the surgical treatment of hip fracture or total hip replacement for OA; they observed very few pathological changes of OA in the fracture specimens, whereas bone density appeared to be increased in the OA patients, as assessed on radiographs of the second metacarpal. Since then, numerous studies have been published examining the relationship between systemic BMD and OA, and several authors have reviewed this topic.…”

“…Since then, numerous studies have been published examining the relationship between systemic BMD and OA, and several authors have reviewed this topic. 1,3,4 OA is recognised to be a heterogeneous disease that can be defined in different ways (for example, in terms of clinical symptoms, radiographic change or a combination of these features). 5 Despite this, epidemiological studies of the relationship between BMD and OA have almost exclusively defined OA radiographically, usually using a summary grading system such as the Kellgren-Lawrence grade.…”

Patients With Hip Osteoarthritis Have a Phenotype With High Bone Mass and Low Lean Body Mass

“…However, there also are studies inferring that patients with OA have a general high bone mineral density (BMD) [4,9,12,13,17,24,29,30] and high BMI [17,29]. If this phenotype could be found in all patients with OA, independent of the affected joint, is unclear.…”

Osteogenic potential and responsiveness to leptin of mesenchymal stem cells between postmenopausal women with osteoarthritis and osteoporosis

“…Conversely, most women with OP look thinner and smaller. 14,15 Therefore, obesity is thought to participate in the regulation of bone metabolism. 13,16,17 Leptin, known as the protein product of the obesity gene, is naturally drawn into bone metabolism research.…”