Causes and mechanisms of development (Pathogenesis)
The primary cause of osteoarthritis development is chronic mechanical overload. The disease is divided into:
- Primary osteoarthritis: when excessive load (e.g., sports or heavy labor) damages a previously healthy joint.
- Secondary osteoarthritis: when normal physiological load damages a joint already compromised by trauma, dysplasia, or another disease.
The pathogenesis is based on proteoglycan deficiency. The cartilage loses hydrophilicity (moisture) due to the breakdown and leaching of protein-polysaccharide complexes. Simultaneously, the synovial fluid loses hyaluronan, and its cushioning and lubricating properties deteriorate. Consequently, the articular cartilage thins, cracks, and its fragments form "joint mice".
Pathomorphology and bone changes
The loss of the cartilage layer sharply increases pressure on the underlying bone. The following changes develop:
- Subchondral osteosclerosis: compaction of bone tissue due to loss of shock absorption.
- Bone cysts: oval defects form in the spongy bone due to venous stasis and local ischemia. Their rupture into the joint cavity leads to erosive osteoarthritis.
- Osteophytes: bone-cartilage growths along the edges of the articular cartilage (in the areas of joint capsule and ligament attachment). They cause deformation, hence the term "deforming arthrosis".
- Secondary synovitis: inflammation of the synovial membrane due to phagocytosis of cartilage debris (which is why the disease is also called osteoarthritis).
Clinical presentation
The disease begins gradually, without an acute onset.
Features of pain syndrome:
- Pain with load: subsides at rest early in the disease, and later occurs with minimal pressure (even in a standing position).
- "Starting" pain: occurs after rest (in the morning), but unlike rheumatoid arthritis, it quickly resolves after a few movements. It is associated with the friction of cartilage debris, which is displaced from the contact zone during movement.
- Night pain: dull and constant, associated with venous stasis and increased intraosseous pressure. Characteristically, it subsides with walking.
Later, crepitus (persistent crunching during movement), secondary synovitis, joint deformations (due to osteophytes), and contractures join the clinical picture.
Hand joint involvement
In the hands, osteoarthritis manifests as specific nodules (osteophytes):
- Heberden's nodes (Heberden's nodes): localized on the distal interphalangeal joints (dorsal-lateral surface). Erosive osteoarthritis is characteristic.
- Bouchard's nodes (Bouchard's nodes): located on the proximal interphalangeal joints (lateral surface). They give the fingers a spindle-like shape.
- Rhizarthritis: isolated involvement of the first carpometacarpal joint of the hand (often in postmenopausal women).
Diagnostics
The main method is radiography in two standard projections. The earliest and primary radiological sign is joint space narrowing. In the early stages of monoarthritis, it can only be detected by comparison with an image of a healthy, symmetrical joint. In later stages, osteophytosis, osteosclerosis, bone cysts, and discongruency (subluxations) are revealed.
Briefly: answers to topical questions
What stages of osteoarthritis are distinguished according to the Kellgren–Lawrence radiological classification?
According to the Kellgren–Lawrence radiological classification, 5 stages of osteoarthritis are distinguished:
- Stage 0 — no radiographic changes.
- Stage I — doubtful changes: joint space narrowing is absent or barely noticeable, small marginal osteophytes appear.
- Stage II — minimal changes: slight joint space narrowing.
- Stages III and IV — late stages; stages III–IV are an indication for surgical treatment.
Which groups of drugs belong to symptomatic slow-acting drugs for osteoarthritis (SYSADOA)?
Symptomatic slow-acting drugs (SYSADOA) for the treatment of osteoarthritis include medications from several pharmacological groups. According to the Anatomical Therapeutic Chemical Classification, this category includes:
- M01AX — other non-steroidal anti-inflammatory and antirheumatic drugs.
- M01BX — other anti-inflammatory and antirheumatic agents in combination with other drugs.
- M09AX — other drugs for disorders of the musculoskeletal system.
This group of drugs includes, in particular, diacerein.
What are the indications for total joint arthroplasty in osteoarthritis?
Indications for total hip replacement in primary or secondary coxarthrosis:
- Stage III according to the Kosinskaya classification;
- Stages III and IV according to the Kellgren and Lawrence classification;
- in rare cases, earlier stages if other treatment options have proven ineffective.
The choice of treatment method is individual and depends on complaints, symptom severity, and functional limitations.
What clinical forms of osteoarthritis are distinguished depending on the affected joint (eponyms and terms)?
Depending on the localization of the lesion, the following forms and terms of osteoarthritis are distinguished:
- Coxarthrosis — osteoarthritis of the hip joint.
- Gonarthrosis — osteoarthritis of the knee joint.
- Rhizarthritis — osteoarthritis of the first carpometacarpal joint of the hand.
- Heberden's nodes — hard nodules on the dorsal-lateral surfaces of the distal interphalangeal joints of the hand.
- Bouchard's nodes — nodules on the lateral surface of the proximal interphalangeal joints, giving the finger a spindle-like shape.
When multiple joints are involved, polyosteoarthritis develops.
Class and exam questions
What is the difference between starting pain in osteoarthritis and morning stiffness in rheumatoid arthritis?
Starting pain in osteoarthritis subsides after a few movements when cartilage debris is displaced from the friction zone. Morning stiffness in rheumatoid arthritis lasts for hours.
Why do night pains occur in osteoarthritis?
They are caused by increased intraosseous pressure due to venous stasis in the cancellous bone. A feature of such pain is that it subsides with walking.
Does osteoarthritis lead to bony ankylosis?
No, despite severe deformations and almost complete disappearance of the joint space, primary osteoarthritis never results in bony fusion (ankylosis).
What is a joint mouse?
This is a free fragment of exfoliated cartilage within the joint cavity. When it becomes trapped, joint blockade syndrome occurs (acute pain and sharp restriction of movement).
What else to study on this topic
- Biochemical changes in synovial fluid (sulfated polysaccharides)
- Pathogenesis of tendobursitis in osteoarthritis
- Mechanism of formation of myogenic and arthrogenic contractures
- Symptoms of secondary reactive synovitis
- Differential diagnosis of crepitus and the "click" sign
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