Osteoporosis and osteoarthritis : similarities and differences

Osteoporosis and osteoarthritis are two different medical conditions, which beside the fi rst part of their name „osteo“, have very little in common. Osteoporosis is a disorder which infl uences bones in terms of reduction of quality and quantity, which can easily result in bone fracture. Clinical signs of osteoporosis show no pain or other symptoms which could point to changes in bone structure, unless a bone fracture is diagnosed. Osteoarthritis is a disease which infl uences joints and its surrounding tissues. Seeing through clinical signs, changes could be verifi ed in terms of pain and limitations of movement and the cause of pain and way of its treatment are numerous. A person can suffer from osteoporosis and osteoarthritis at the same time. Although these medical conditions are more frequent in female than in male population, mechanisms which lead to them may interfere. Osteoporosis and osteoarthritis are muscular-bone disorders with signifi cant morbidity and mortality, but clinical experiences and epidemiological studies have shown their negative correlation. © 2012 All rights reserved


Introduction
Although osteoporosis and osteoarthritis, as medical disorders, have diff erent etiology, pathology as well as clinical signs and symptoms, having similar name oft en leads to a confusion between patients and doctors.Beside the same fi rst part of the name of these two medical disorders, "osteo", osteoporosis and osteoarthritis have very little in common.Osteoporosis is a disease which infl uences bones in terms of reduction of quality and quantity, which can easily result in bone fracture.Clinical signs of osteoporosis show no pain or other symptoms which could point to changes in bone structure, unless a bone fracture is diagnosed.Osteoarthritis is a disease which infl uences joints and surrounding tissues of a body.Seeing through clinical signs, changes could be verifi ed in terms of pain and limitations of movement and the cause of pain and way of its treatment are numerous.Osteoporosis is commonly accepted as a bone disorder while osteoarthritis is generally considered as a joint' cartilage disorder.Th e causes which are included in the pathophysiology of osteoporosis can also be included in the pathophysiology of osteoarthritis of the subchondral bone.Th e treatment is available for both medical disorders and it can help in reduction of medical disorder' symptoms and improve the quality of life (1,2).If the person suff ers from osteoporosis and osteoarthritis at the same time, specifi cally planned program of treatment should be applied in terms of changes' control in both disorders.Th is situation requires management of both disorders in terms of determination of proper and adequate physical activity.Th e recommended program of treatment for osteoporosis includes regular physical activity and the same can be extremely hard to follow if the patient has signifi cant osteoarthritic degenerative changes verifi ed in hip or knee joint.Th erefore the physical activity program should be adapted to one and another degenerative disorder.

What is osteoporosis?
According to the defi nition of the World Health Organization (WHO) osteoporosis is a disease which appears as a consequence of bone mass re-duction and bone morphology disorder.Th erefore bone fractures become more oft en.According to the WHO' data, osteoporosis is the most frequent bone metabolic disorder (3,4).Nowadays, it is even more present than ever and the most frequent cause of it is modern way of living and extended life expectancy.Osteoporosis is a condition of reduced quantity (mass) of the bone below the limits necessary to preserve the integrity of the skeleton.Th e leading symptom is loss of bone mass, which results in brittle bones easily.Th e cells in bones are constantly renewed, but with the bone age it is becoming less valuable mechanically so as to maintain the mechanical quality, it is being remodeled.Osteoporosis is characterized by low bone mass due to an imbalance in favor of bone resorption, leading to changes in bone remodeling.Osteoporosis represents changes in bone density as well as in bone quality, including not only changes in the microarchitecture, but also changes in bone remodeling, remodeling and mineralization of microcracks (5).Th e remodeling process takes 3-4 months, and the same amount of bone that was destroyed is being renewed.Th e complete reconstruction of the bone takes 10 years.In the process of osteoporosis the destroyed bone is not restored completely and bone mass decreases.Th e bones become hollow and crumbling at the least shock (1).Pathogenesis and pathophysiology of osteoporosis is multifactorial: genetics, age, a lack of estrogen, diet and insuffi cient physical activity.Osteoporosis is followed by reduced mobility, pain in bones and joints, cramps and muscle weakness, a decrease in body height, an increased risk of bone fractures, and even spontaneous fractures.More than 90% of hip and spine fractures are caused by osteoporosis, and osteoporotic fractures constitute of 45% of vertebral fractures, 16% of the upper femur (hip), 16% of distal forearm and 20-25% are other fracture localization (pelvis, upper arm, ribs) (1).

What is osteoarthritis?
Osteoarthritis is the most common rheumatic disease that aff ects the joints, although various extra-articular structures can be aff ected.Approximately 10% of the population in general has problems due to osteoarthritis.Th is disease particularly aff ects older people and it is estimated that more than 60% of people aged above 35 years suff er from osteoarthritis.About 55% of people with osteoarthritis have diffi culty in performing activities of daily living, and about 25% of them do not perform these activities.Only osteoarthritis of knee joint causes disability as chronic heart and lung disease combined (5).Pathogenesis and pathophysiology of osteoarthritis is multifactorial: being overweight, the aging process, joint injury or stress, heredity, muscle weakness.Osteoarthritis oft en develops in the joints in which vicinity were fractured bones.It often aff ects cervical or lumbar spine, hip and knee.Cartilage damage in osteoarthritis is the result of an imbalance of enzymes that are released from the cells of articular cartilage (matrix metalloproteinases, aggrecanases and other enzymes).When the enzymes that destroy and build cartilage are produced in equal amounts, cartilage naturally regenerates, and when enzymes of degradation are over-produced, cartilage damage occurs.

Differential characteristics of reduction of muscle fi bers in osteoporosis and osteoarthritis
Osteoporosis is associated with the presence of type II muscle fi bers in the stage of decrease in muscle mass, bone mineral density and with reduced levels of AKT (protein kinase B -PKB), as the main regulator of muscle mass.Osteoarthritis is connected with the muscle reduction which is expressed to a lesser extent, but in direct relation with disease duration and severity.Osteoarthritis and osteoporosis are associated with reduced muscle mass and muscle strength, but still there are no morphological studies on the reduction of muscle tissue, so the basic mechanisms of reduction of muscle mass are not yet known.Th e aim of the study Terracciano C. et al. was to assess the relationship osteoporosis -osteoarthritis with a reduction in muscle mass and correlation with disease severity.Muscle protein levels of AKT, specifically a component IGF-1/PI3K/Akt pathway is a major regulator of muscle mass.AKT is known as protein kinase B (PKB); it is the serine / threoninespecifi c protein kinase that plays a key role in several cellular processes such as glucose metabolism, apoptosis, cell proliferation, transcription and cell migration.Muscle biopsy was performed in 15 women with osteoporosis and in 15 women with osteoarthritis (age range, 60-85 years).According to statistical analysis, type II fi bers are decreased in muscle mass which correlates with bone mineral density (BMD) in the group of women with osteoporosis and Harris Hip Score (HHS), and duration of illness in a group of women with osteoarthritis.HHS is a tool for assessing the functionality aft er hip arthroplasty.Th e results showed that in women with osteoporosis, type II muscular fi ber atrophy correlates inversely with BMD.In the group of women with osteoarthritis, muscle atrophy was noticed to a lesser extent, and there was homogeneity among the types of fi ber related to duration of disease and HHS.Within a group of women with osteoporosis, the level of AKT was signifi cantly reduced compared to the muscles in the group of women with osteoarthritis.Th is study shows that osteoporosis is connected with frequent diff use type II muscle fi ber atrophy, in proportion to the degree of bone loss, whereas in osteoarthritis, muscle atrophy is associated with functional impairment caused by disease (7).Osteoarthritis and osteoporosis clinical and research evidence of inverse relationship Osteoporosis and osteoarthritis, as serious medical conditions, have two characteristics in common; both are associated with aging and multifactorial.Although the relationship between osteoporosis and osteoarthritis is especially important, as the inverse relationship, the two diseases are studied for the last 30 years, and yet their relationship is controversial and stimulating for further study.Regarding the anthropometric characteristics of patients with osteoarthritis compared to people with osteoporosis, following are well established.People who have osteoarthritis have a stronger body structure and more obesity, and increased BMD.Th is increase in BMD was also linked to higher values of bone mass.With aging, bone loss in osteoarthritis is lower unless when measured in the vicinity of the aff ected joints (hand, hip, knee).A small degree of bone loss with aging is explained by lower degree of bone resorption.People with osteoarthritis in eff ective have higher bone density, but wider measures of skeletal geometry, the diameter of long bones and trabeculae, which positively contributes to better strength and lower bone fragility.Osteoarthritis is characterized with an increased content of growth factors such as IGF and TGF beta, which are required for the regeneration of bone.Experimental evidence show that osteoclasts have metalloproteinase that directly or indirectly from the matrix creates a precondition for a deterioration of a medical fi nding of cartilage.Th e capacity of osteoblastic bone regeneration in osteoporosis is compromised in comparison with osteoarthritis.Th e claim that drugs which suppress bone transport in osteoporosis may be useful for osteoarthritis, such as bisphosphonates, is incorrect (8).Adaptive mechanisms that are present on the wrist, which is aff ected by osteoarthritis, lead to a reduction in fracture risk, despite the presence of osteoporosis, low bone density and bone mass.It was found that the cortical bone volume and trabecular thickness is signifi cantly (p <0.05) higher in the group of women with osteoarthritis than in the group with fractures.Th is study confi rms the presence of compensatory mechanisms in osteoarthritis in the preservation of the mechanical ability of bone structure, regardless of low bone density, bone mass and lower fracture risk (9).

Conclusion
Osteoporosis and osteoarthritis are two major health problems of modern society, and can aff ect the quality of life in diff erent ways.Since both diseases are part of the aging process, one should take all preventive measures and identify any joint pain, and bone density test should be done in particular age in order to check whether there are changes that would indicate to osteoporosis.Both diseases are complex disorders of the musculoskeletal system, although they show eff ect on diff erent tissues, both are aff ecting the bones.A person may have osteoporosis and osteoarthritis at the same time.Although these disorders are more present in women than men, the mechanisms that lead to them may overlap.Osteoarthritis and osteoporosis are senile musculoskeletal disorders with signifi cant morbidity and mortality, and clinical ex-perience and epidemiological studies have shown that there is a negative correlation between them.

Confl ict of interest
None to declare.
of adaptive mechanisms of femoral neck in osteoarthritis and osteoporotic fracture Study of Rubinacci A. et al. refers to diversity of adaptive mechanisms in the distribution of femoral neck in osteoarthritis and osteoporotic fracture.It was done by comparative analysis of peripheral quantitative computed tomography (pQCT) of femoral bone in 32 postmenopausal women which were undertaken the hip arthroplasty due to osteoarthritis or osteoporotic femoral fracture.