JOINT STRUCTURE AND OSTEOARTHRITIS

Joints are responsible for movement and stability of the skeleton: in a healthy joint the cartilage is a cushion, permitting the bones to rotate, glide, and roll upon each other smoothly and easily during activities like walking.

Articular cartilage tissue varies in thickness, cell density, matrix composition, and mechanical properties within the same joint, among joints and among species. Nonetheless, it consists of the same components and has the same general structure.

ARTICULAR CARTILAGE IS COMPOSED OF:

  1. specialized cells called chondrocytes
  2. dense extracellular matrix (ECM) principally composed of water, collagen, and proteoglycans, with other noncollagenous proteins and glycoproteins present in lesser amounts

To form articular cartilage, chondrocytes organize collagen, proteoglycans and other components into a unique, highly ordered structure, they generate extracellular matrix during growth and maintain tissue homeostasis during adult life.

Chondrocytes control the maintenance of the articular surface with the right turnover of the matrix macromolecules thanks to the ability to synthesize and secrete proteinases and the other matrix components.

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AGEING AND OSTEOARTHRITIS

The correct definition of osteoarthritis (OA) is a chronic (long-term) condition characterized by focal areas of loss of articular cartilage within the synovial joints, associated with hypertrophy of the bone and thickening of the capsule. In this sense it is a reaction of the synovial joints to injury.
During the normal biological process of ageing, multiple factors may impact on joint structure, determining an imbalance between the normal coupling of degradation of joint and the synthesis of articular cartilage and extracellular matrix with development of a classic age-related disorder, the Degenerative Joint Disease (DJD) also known as Osteoarthritis (OA).

In osteoarthritis the gradual loss of matrix proteoglycans and subsequent loss of mechanical integrity result in a degeneration and gradual loss of articular cartilage.

Pro-inflammatory cytokine networks with a considerable degree of complexity influence the metabolic state of chondrocytes and are important in the pathogenesis of OA.

OA is the most common form of arthritis associated with risk factors such as age, gender, prior joint injury, obesity, genetic predisposition, and mechanical factors, including malalignment and abnormal joint shape.

OA is believed to be caused by a combination of factors. Due to the long period of painless progression, the disease is rarely diagnosed at an early time point. This makes diagnosing the exact cause in specific patients extremely difficult. Injury due to mechanical stress, although poorly understood, is considered to play a predominant role during initial stages of the disease.

Biochemical and genetic factors are likely to contribute to the further progression.

The role of genetics in the onset of OA is becoming increasingly playing a larger role than first thought. These studies indicate that some forms of OA may have a genetic component of up to 65%.

Systemic factors Intrinsic factors
(anatomically or physiologically pertain to a joint)
Extrinsic factors
(somehow acting on a joint)
  • Higher age
  • Female gender
  • Race
  • Inheritance
  • Possibly nutritional factors
  • Deformities
  • Injuries / damages
  • Malalignment
  • Laxity
  • Proprioceptive deficiencies
  • Obesity
  • Muscle weakness
  • Repetitive overuse (occupational or sports)

Osteoarthritis can affect all joints of the body but not all localizations have the same consequences for the individual or society. Some joints are more prone to be affected by osteoarthritis than others. Exact conditions for the individual joints are sparse, mostly non-representative and differ considerably depending on definition (radiographic vs. symptomatic), age group, sample size, ethnicity and region.

Severe osteoarthritis of the large joints like the hip or the knee will lead to more dramatic effects such as immobility of the individual and loss of working resources to society.

Osteoarthritis is most common among adults over 65 years old, but people of any age can develop it. Prevalence rises significantly after age 50 in men and after age 40 in women.

    The main symptoms of osteoarthritis are:
  • Pain and stiffness in a joint after getting out of bed or sitting for long.
  • Swelling in one or more joints, especially those at the ends of the fingers (closest to the nail), thumbs, neck, lower back, knees, and hips.
  • Crunching feeling or the sound of bone rubbing on bone.
  • Not being able to use your joint normally – Your joint may not move as freely or as far as normal.
  • Deformed joints. Joints can start to look like they are the wrong shape, especially as arthritis gets worse.