- Classification of Osteoarthritis
- Functions of Articular Cartilage
- Pathophysiology – How Does Osteoarthritis Develop
- Why does Pain Occur in Osteoarthritis?
- Risk Factors of Osteoarthritis
- Differential Diagnoses
- Imaging in Osteoarthritis
- Lab Studies
- Treatment of Osteoarthritis
- Subsets of Primary Osteoarthritis
- Radiologic Classification of Osteoarthritis
- Prognosis of Osteoarthritis
Osteoarthritis, the most common joint disease is a heterogeneous group of conditions resulting in common tissue and radiological changes. Conventionally labeled as degenerative disorder due to excessive wear and tear, currently, osteoarthritis is thought to involve not only cartilage but also the entire joint organ, including the subchondral bone and synovium. Abnormal mechanics and inflammation is thought to contribute as well. So, the term degenerative joint disease may not be appropriate.
The prevalence of the disease increases dramatically among persons older than 50 years.
The prevalence of osteoarthritis is higher among women than among men in age group >55 years.
Osteoarthritis can be divided into primary and secondary forms.
Primary osteoarthritis is said to be idiopathic, occurring in previously intact joints without any having no apparent initiating factor. It is related to the aging process and typically occurs in older individuals. But some researchers have shown this to be due to subtle or even unrecognizable congenital or developmental defects.
Primary generalized osteoarthritis, erosive osteoarthritis, and chondromalacia patellae are considered as a subset of primary osteoarthritis.
Secondary osteoarthritis occurs due to some predisposing condition that affects the joint. For example – trauma. It can occur in young individuals.
Primary osteoarthritis to the joints of the hands, the knees, hips, and spine. The secondary OA can affect any joint.
Classification of Osteoarthritis
- Peripheral joints
- Apophyseal joints
- Intervertebral joints
- Chronic (occupational, sports)
- Underlying joint disorders
- Local (fracture, infection)
- Diffuse (rheumatoid arthritis)
- Systemic metabolic or endocrine disorders
- Ochronosis (alkaptonuria)
- Wilson disease
- Kashin-Bek disease
- Crystal deposition disease
- Calcium pyrophosphate dihydrate (pseudogout)
- Basic calcium phosphate (hydroxyapatite-octacalcium phosphate-tricalcium phosphate)
- Monosodium urate monohydrate (gout)
- Neuropathic disorders (Charcot’s joints)
- Tabes dorsalis
- Diabetes mellitus
- Intra-articular corticosteroid overuse
- Bone Dysplasias
Functions of Articular Cartilage
[Read more about of Synovial Joint]
Osteoarthritis is a disease of joints, particularly the cartilage of the joints. The main load on articular cartilage is produced by contraction of the muscles that stabilize or move the joint.
Although cartilage is an excellent shock absorber, at most sites it is only 1 to 2 mm thick too thin to serve as the sole shock absorbing structure in the joint. However, additional protective mechanisms are provided by subchondral bone and muscles around the joint.
Articular cartilage serves two essential functions in the joint
It provides a remarkably smooth bearing surface, so that, with joint movement, the bones glide effortlessly over each other.
Articular cartilage prevents the concentration of stresses, so the bones do not shatter when the joint is loaded.
Pathophysiology – How Does Osteoarthritis Develop
Osteoarthritis may develop when
- The bio-material properties of the articular cartilage and subchondral bone are normal, but excessive loading of the joint causes the tissues to fail or
- The applied load is reasonable, but the material properties of the cartilage or bone are inferior.
Repetitive impact loading soon leads to joint failure.
This fact accounts for the high prevalence of OA at specific sites related to vocational or avocational overloading. In general, the earliest changes occur at the sites in the joint that are subject to the greatest compressive loads.
More than 80 percent of all cases of idiopathic OA of the hip may be due to subtle congenital or developmental defects, such as congenital subluxation or dislocation, acetabular dysplasia, Legg-Calve-Perthes disease and slipped capital femoral epiphysis.
In spite of being classified as noninflammatory arthritis, increasing evidence has shown that inflammation occurs as cytokines [such as interleukin-17] and metalloproteinases have been found involved in matrix degradation.
In early osteoarthritis, cartilage swelling occurs due to increased synthesis of proteoglycans as an effort to repair cartilage damage.
As osteoarthritis progresses, [which may take years], the level of proteoglycans decreases leading to cartilage softening and loss of elasticity. Flaking and fibrillations develop along the articular cartilage.
Over time, the loss of cartilage results in loss of joint space which is greater in areas of loading in weight-bearing joints. [ In contrast, inflammatory arthritides lead to uniform joint space narrowing.]
Cartilage erosion with time leads to denuding of the underlying bone. Increased stresses lead to increased vascularity and cellularity in the bone which becomes thickened and dense at areas of pressure.
Cystic degeneration also occurs in subchondral bone [due to bone necrosis secondary to chronic impaction or to the intrusion of synovial fluid. ]
Osteophytes are formed at margins of joints by increased vascularization of subchondral bone, bone metaplasia of synovial connective tissue, and ossification of cartilaginous protrusions. Fragmentation of cartilage or breakage of osteophyte can lead to loose bodies in joint [joint mice].
The daily stresses like loading accelerate the catabolic effects of the chondrocytes and further disrupt the cartilaginous matrix.
Why does Pain Occur in Osteoarthritis?
Articular cartilage is an aneural structure. That means it cannot cause the pain. Therefore other structures are responsible for joint pain. Pain in osteoarthritis is thought to be because of various mechanisms
- Periosteal elevation due to osteophytes
- Increased intraosseous pressure due to the increased blood supply of subchondral bone
- Muscle fatigue/spasm
- Overall joint contracture
- Joint effusion and stretching of the joint capsule
- Meniscal Tear
- Psychological factors
- Foraminal narrowing leading to compression of the nerve roots in the spine
Risk Factors of Osteoarthritis
Risk factors for osteoarthritis include the following
Age is the biggest risk factor. Osteoarthritis is more common in older individuals. It is rarely seen in persons younger than 40 years of age.
Women are more likely to develop osteoarthritis.
Higher weight has been associated with a higher risk of getting osteoarthritis and this risk is more pronounced in case of knee OA.
Defective cartilage and other congenital joint problems may predispose to joint degeneration. e.g.congenital hip dislocation, slipped femoral capital epiphysis.
Diseases like rheumatoid arthritis, gout, and others that affect joints can cause the degenerative changes to occur.
A major injury to a joint may alter the joint anatomy and thus result in early degeneration. An infection may result in cartilage damage.
Repetitive Stress Injury
Repetitive stress injury occurs when the joint is subjected to repetitive forces regularly. It generally occurs in occupations that require repetitive use of the joints. For example typing or vibrational tools.
Significant Family History
Osteoarthritis is thought to have a genetic component, as well as significant family history, hastens the risk. Heritable metabolic causes like alkaptonuria, Wilson disease also make osteoarthritis more likely.
Sickle cell disease and thalassemia are associated with osteoarthritis occurrence.
Diabetes, tabes dorsalis, and syringomyelia take away sensation and proprioception making it vulnerable to increased wear and tear.
- Paget disease
- Avascular necrosis of bone e.g. femoral head
- Meniscectomy of knee
- Reduced levels of sex hormones
- Endocrinal disorders – Diabetes, acromegaly, hypothyroidism, hyperparathyroidism.
Older age, higher BMI, varus deformity and multiple involved joints are associated with rapid progression of knee osteoarthritis
Presentation – Signs and Symptoms of Osteoarthritis
Early in the disease process, the joints may be normal and without symptoms.
Pain is the most frequent clinical feature of osteoarthritis. Difficulty in walking may be present in case of weight-bearing joints.
The pain of osteoarthritis is often felt as a deep ache and is localized to the involved joint. The pain is aggravated by joint use and relieved by rest initially. As the disease progresses, it may become persistent. Night pain, interfering with sleep, is seen particularly in advanced osteoarthritis of the hip.
Initially, pain can be relieved by rest and may respond to simple analgesics. However, with the progression of the disease, joint instability may occur and pain may not respond to medications.
Stiffness, especially during rest and morning stiffness lasting for less than 30 minutes may be present. Stiffness usually comes in osteoarthritis when the disease has progressed. This is in contrast to rheumatoid arthritis where the stiffness is a prominent feature in the early stage too. The stiffness is more pronounced after a period of inactivity.
Systemic manifestations i.e symptoms involving the whole body are not a feature of primary osteoarthritis..
Palpation may reveal some warmth over the joint. Periarticular muscle atrophy may be due to disuse or to reflex inhibition of muscle contraction.
In the advanced stages of osteoarthritis, there may be a gross deformity, bony hypertrophy, subluxation, and marked loss of joint motion.
Physical examination may reveal a decreased range of motion and crepitus, especially in advanced disease.
Palpable osteophytes may be present. For example Heberden and Bouschard’s nodes in hands
Inflammatory changes are typically absent or minimum.
The history and physical examination findings are usually sufficient to diagnose and differentiate osteoarthritis from other arthritides. Confirmation can be done by typical radiological features and laboratory values are typically within the reference range.
Following differential diagnoses may be considered
- Rheumatoid arthritis
- Metabolic bone disorders
- Hypermobility syndromes
- Neuropathic joints
- Crystalline arthropathies (ie, gout and pseudogout)
- Inflammatory arthritis (eg, rheumatoid arthritis)
- Seronegative spondyloarthropathies
- Septic arthritis or postinfectious arthropathy
- Lyme Disease
- Patellofemoral Arthritis
Imaging in Osteoarthritis
In the early stages, the radiograph may be normal, but joint space narrowing becomes evident as articular cartilage is lost. Other characteristic radiographic findings include subchondral bone sclerosis, subchondral cysts, and osteophytosis.
A change in the contour of the joint due to bony remodeling and subluxation may be seen.
Following investigations are not routinely needed or done in most of the cases of osteoarthritis. MRI shows joint narrowing, subchondral osseous changes, osteophytes and can visualize cartilage. Computed tomography may be used in the diagnosis of malalignment of joint.
Bone scans yield a symmetrically patterned, very mildly increased uptake and can help to differentiate osteoarthritis from osteomyelitis and bone metastases. Though the diagnosis of OA is often straightforward, it is important to ensure that joint pain in a patient with radiographic evidence of OA is not due to some other cause, such as.
Because primary OA is not systemic, the erythrocyte sedimentation rate, serum chemistry determinations, blood counts, and urinalysis are normal.
Analysis of synovial fluid reveals mild leukocytosis.
The synovial fluid analysis is of particular value in excluding other conditions, such as calcium pyrophosphate dihydrate deposition disease, gout or septic arthritis.
Fluid analysis after arthrocentesis can differentiate osteoarthritis from other causes of joint pain and infection.
Treatment of Osteoarthritis
Till date, no pharmacologic agent has been shown to prevent, delay the progression or, or reverse the pathologic changes of Osteoarthritis in humans. Therefore the treatment is palliative only.
It is being increasingly recognized that nonpharmacologic management is as important and often more important than drug treatment.
The treatment of osteoarthritis aims at alleviation of pain and improvement of function.
The treatment includes drugs and nonpharmacological measures like heat and cold, lifestyle changes, weight loss, physical therapy and reducing the load on weight-bearing joints.
Paracetamol is effective for mild or moderate osteoarthritis pain without apparent inflammation. If the response is poor, other NSAIDs can be used.
Topical NSAID preparations, particularly diclofenac and capsaicin, are useful in patients with symptomatic disease that is limited to a few sites.
Tramadol, an opioid drug, can be used in a patient with highly resistant pain or GI toxicity from NSAIDs. Oxycodone and fentanyl patch can also be used in severe cases.
The selective serotonin-norepinephrine reuptake inhibitor duloxetine has been found to be effective in treating osteoarthritis pain but needs more studies.
Muscle relaxants Carisoprodol and baclofen may benefit patients with evidence of muscle spasm.
Glucosamine and chondroitin sulfate have been used and are popular but with limited benefit.
Intra-articular pharmacologic therapy includes injection of a corticosteroid or sodium hyaluronate (ie, hyaluronic acid [HA] or hyaluronan), which may provide pain relief and have an anti-inflammatory effect on the affected joint.
Steroid injections generally result in clinically and statistically significant pain reduction as soon as 1 week after injection but the benefit lasts only for 4-6 weeks.
A patient should not receive more than three injections per year.
Intra-articular injection of sodium hyaluronate is also called viscosupplementation is said to be effective but the mechanism of action is not understood.
Recently prolotherapy has been found to be effective in a trial in knee osteoarthritis.
- Exercise and weight reduction
- Cardiovascular or resistance exercises
- Aquatic exercises
- Weight loss, for overweight patients
- Walking aids/Orthoses
- Neck braces and knee braces, walkers, crutches or canes, and orthopedic footwear
- Improve function of moveable parts of the body
- Support, align, prevent, or correct deformities.
- Local heat or ice
- Finger Splints
Exercises in Osteoarthritis
Exercise leads to an improvement in pain, physical function, and walking distance.
Quadriceps strengthening helps to protect the articular cartilage from further stress. Stretch exercises increase the range of motion.
Swimming is considered a good exercise in osteoarthritis
Tai chi is a potentially effective treatment for pain associated with osteoarthritis of the knee.
A cane can be used in the contralateral hand for hip or knee osteoarthritis.
Occupational adjustments may be necessary for some patients with osteoarthritis.
Pulsed electromagnetic field stimulation, TENS and acupuncture have been found to be effective in recent researches.
Osteotomy is used in active patients younger than 60 years. These are most commonly done in a hip or knee. Osteotomies provide reasonable physical activity. The principle underlying this procedure is to shift weight from the damaged cartilage to healthy or alter the load on the joint.
Osteotomy is most beneficial for significant genu varum, or bowleg deformity.
Osteotomy can lessen pain, but it can also lead to more challenging surgery if the patient later requires arthroplasty.
Contraindications for osteotomy are as follows.
Patients undergoing osteotomy require partial weight-bearing until bony healing occurs. Afterward, exercise is indicated.
Arthroplasty or joint replacement alleviates pain and may improve function. At least, 10-15 years of viability are expected from joint replacement in the absence of complications.
Fusion consists of the union of bones on either side of the joint. This procedure relieves pain but prevents motion and puts more stress on surrounding joints.
Subsets of Primary Osteoarthritis
These include primary generalized osteoarthritis (PGOA), erosive osteoarthritis, and chondromalacia patellae.
Primary generalized osteoarthritis
It is characterized by the familial and often premature development of Heberden and Bouchard nodes. There is often early degeneration of joint cartilage of multiple joints like the first carpometacarpal joints, knee joints, hip joints, and spine. The disease typically progresses rapidly and has a severe appearance on images.
An erosive osteoarthritis is a form of primary osteoarthritis marked by a greater degree of inflammation, with erosive abnormalities and, in some cases, ankylosis. The disease most commonly occurs in postmenopausal women, and it may be hereditary. Laboratory findings are generally uninformative.
It is typically bilateral and symmetrical, and it occurs in the interphalangeal joints of the hands or rarely base of the first metacarpal or even in the feet.
Erosions are centrally located and osteophytes are present, giving the appearance of central erosions flanked by raised lips of bone (called gull wing appearance). Fusion eventually may occur.
Chondromalacia patellae is associated with cartilaginous changes along the undersurface of the patella and is characterized by crepitus and pain at the anterior knee that most commonly occurs in young adults. Xrays are mostly normal and MRI is imaging study of choice.
Radiologic Classification of Osteoarthritis
In a simple way, the extent of disease can be described as
- Surface irregularity
- Partial-thickness irregularity
- Full-thickness irregularity with or without underlying subchondral bone change
This method is generally sufficient
The Kellgren-Lawrence grading system is the most universally accepted method of classifying radiographic osteoarthritis and uses the following 4 radiographic features:
- Joint space narrowing
- Subchondral sclerosis
- Subchondral cysts
- No radiographic features of osteoarthritis are present.
- There is a doubtful narrowing of joint space narrowing [ A normal joint, therefore, appears to have a space between the bones. Any decrease in space implies a reduction in cartilage cover.] and possible osteophytes[small bony projections that from around joint margins. They are responsible for limiting the range of motion and can cause pain.]
- There is the presence of osteophytes and possible joint space narrowing on the anteroposterior weight-bearing radiograph.
- [weight bearing radiographs imply x-rays taken while the person stands on both the feet. A nonweight bearing x-ray is taken when a person is lying down and thus not bearing weight on knees]
- Grade III Kellgren Lawrence is characterized by multiple osteophytes, definite joint space narrowing, sclerosis [seen as increased white areas in the bone at the joint margin] and possible bony deformity.
- It is characterized by large osteophytes, marked joint space narrowing, severe sclerosis, and definitely bony deformity.
It is based on arthroscopic findings in patients affected with osteoarthritis. These are –
- Grade I – Softening and swelling
- Grade II – Fragmentation and fissuring of less than 0.5 inches
- Grade III – Fragmentation and fissuring of greater than 0.5 inches
- Grade IV – Erosion down to the subchondral bone
Prognosis of Osteoarthritis
The progression of osteoarthritis is characteristically slow, occurring over several years or decades.
One of the peculiar things about osteoarthritis is that severity on x-rays may not correlate with symptoms. Some people experience a great deal of pain with only mild osteoarthritis on X-ray, and some people experience only mild pain while their X-rays show severe osteoarthritis.
Patients with osteoarthritis who have undergone joint replacement have a good prognosis, with success rates for hip and knee arthroplasty generally exceeding 90%. However, a joint prosthesis may have to be revised 10-15 years after its placement.
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