What is Osteoarthritis?
Osteoarthritis (OA) is a chronic arthropathy that is characterized by a disruption and potential loss of joint cartilage, resulting in pain and locomotive disability. Osteoarthritis is also known as Degenerative Joint Disease, or Hypertrophic Osteoarthritis.
Based on various studies, it is believed to be one of the most common forms of arthritis and joint disorders worldwide, which often becomes symptomatic (although not always symptomatic) in the early 40s and 50s, but almost universal by the age of 80. Self-reported estimates from the Australian Bureau of Statistics between the periods of 2014 to 2015 suggest that over 3.5 million people in Australia (15.3% of the population) have some form of arthritis, with prevalence higher amongst women than men (18.3% compared with 12.3%). From these statistics, it has been reported that more than half of these people (58.9%) had osteoarthritis. A further increase is yet to be expected due to the increasing prevalence of ascending life expectancy, obesity and injury.
Classification: Primary and Secondary Osteoarthritis
Historically, Osteoarthritis has been classified in two ways: primary (idiopathic) or secondary.
Primary Osteoarthritis (PO) – PO is an idiopathic phenomenon occurring in previously intact joints (that have not been impaired in any form or manner). It can be localized in certain joints of the hands (i.e. proximal and distal interphalangeal joints, as well as joints at the base of the thumb), knees, hips and spine (apophyseal articulations).
Secondary Osteoarthritis (SO) – Generally speaking, this form of Osteoarthritis results from conditions that alter the microenvironment of cartilage. The conditions that follow usually include: congenital joint abnormalities, metabolic defects (e.g. hemochromatosis), significant trauma, endocrine and neuropathic diseases, disorders that change the structure and function of hyaline cartilage (for example, gout, chondrocalcinosis), as well as other infections causing post-infectious arthritis.
The Underlying Causes of Osteoarthritis
When it comes to the cause of Osteoarthritis, many epidemiological studies of the last decades have tried to define the risk factors associated with the disorder, including:
- genetic predisposition;
- increased mechanical stress or injury (e.g. torn meniscus);
- a consequence of an antecedent incidence, such as intra-articular fractures and ligament lesions;
- transmission of inflammatory mediators from the synovium into the cartilage;
- joint congruency, defects in cartilage metabolism and greater bone density;
- a consequence of systemic diseases such as rheumatoid arthritis, hemochromatosis, haemophilia, post-infectious arthritis, osteochondrosis dissecans, or obesity;
- a result of a congenital or developmental anatomic abnormalities.
Osteoarthritis Symptoms and Signs
Not all radiological Osteoarthritis is associated with clinical symptoms, nor are all variations of symptomatic Osteoarthritis associated with disability. Although it is almost impossible to establish the onset of the disease in degenerative Osteoarthritis as it is often gradual, in Secondary Osteoarthritis patients usually recall to have experienced a precedent injury, which therefore becomes the prime source for disease initiation. Egloff uses the example of an intra-articular fracture, which implicates incongruence or breakage of the joint line, followed by deviation of the axis as well as an altered load distribution of the joint. These fractures usually result in some degree of cartilage damage, which according to Higgins triggers an inflammatory response that can stimulate cytokines to perform cartilage degradation.
One of the earliest symptoms of Osteoarthritis is pain, which some patients often describe as a deep ache. The pain tends to worsen by bearing weight or physical activity, but is usually relieved with rest. Stiffness follows long periods of inactivity, particularly in the morning after awakening, but lessens with movement.
However, as Osteoarthritis progresses, joint motion becomes restricted limiting the ability to perform activities of daily living. Furthermore, patients begin to develop tenderness and other crepitus or grating sensations at the affected joints. Other contributing factors include: flexion contractures, proliferation of cartilage, bone, ligament, tendon, capsules and synovium, in addition to various amounts of joint diffusion that ultimately cause joint swelling and enlargement.
Later symptoms include: locking or catching (due to abnormally placed meniscus or mechanical block by intra-articular loose bodies), deformity and subluxations, as well as muscle spasms or tenderness on palpation.
Which joints are most commonly affected in generalised Osteoarthritis?
The joints that are most commonly affected in generalised Osteoarthritis include:
- Thumb carpometacarpal joint and First metatarsophalangeal joint.
- Erosive Osteoarthritis – often affects the distal interphalangeal (DIP) and proximal interphalangeal (PIP) joints, causing synovitis or Heberden and Bouchard nodes (cysts in the hand) to occur.
- Cervical and Limbal Spinal Osteoarthritis – occurs in the intervertebral disks and zygapophyseal joints in the cervical and lumbar vertebrae, which may lead to myelopathy and radiculopathy.
- Hip Osteoarthritis – causing a gradual loss of the range of motion in the hip joints and is usually symptomatic when the patient conducts weight bearing activities.
- Knee Osteoarthritis - causes cartilage to be lost (in 70% of cases medial loss occurs), in addition to the ligaments becoming lax and loss of stability in the joints.