Osteoarthritis

Definition

Osteoarthritis is the most common form of arthritis (inflammation of the joints). It is a degenerative joint disease involving erosion of joint linings and narrowed joint space and characteristic "bumps" of the bone areas around it called osteophytes.

Pathophysiology

Cellular inflammation is not present in osteoarthritis. Instead, the disease is a joint inflammation driven by macrophages (instead of T/B cells like in rheumatoid arthritis), which will release proinflammatory chemicals. These chemicals mediate production of enzymes that break down linings of the joints, leading to tissue destruction at the joint.

Risks:

Aging
Joint Injury
Obesity
Family history of osteoarthritis - genetic form that leads to collagen mutations can manifest as early as adolescence.
Joint shape and structure

Symptoms & Signs

Sharp pain in the involved joint. In the morning, the pain lasts ~30 minutes, but worsens with use of that joint. Pain improves with rest.
Tenderness in joints
Decrease in range of movement (due to osteophytes and pain).
Heberden nodes: DIP joint swelling - characteristic of systemic osteoarthritis.
Instability; for example, knee buckles when bearing weight.
Advanced disease: Joint deformity (subluxation, malposition)
Osteoarthritis usually affects the following joints:

Distal interphalangeal (DIP) joints
First metatarsophalangeal joint
Low neck joints
Lumbar spine
Knees and Hips

Best Imaging Modality

Gold Standard: Radiography of the symtpomatic joint

The 4 characteristic signs of osteoarthritis are: joint space narrowing, osteophyte formation, subchondral sclerosis, and subchondral cysts. Radiography can measure the joint space as well as display these signs. There is a grading scale for osteoarthritis that can be evaluated on the x-ray:

Grade 0: Normal joint
Grade 1: Subjective joint space narrowing, possible osteophytes
Grade 2: Definitely osteophyte formation, subjective joint space narrowing
Grade 3: Moderate osteophytes, definite joint space narrowing, some sclerosis.
Grade 4: Large osteophytes, Marked joint space narrowing, severe sclerosis (appears as pale white), definite bone deformity.

In most cases not for osteoarthritis. However, it can identify the disease before radiographs. Look for:

Bone marrow lesions
Cartilage defects

Cons: it has lower sensitivity than x-ray.

Ultrasound

U/S can identify structural changes. Specifically it can look for:

Synovial inflammation
Joint effusion

Cons: Operator-dependent, cannot assess bone itself.

Treatment

Lifestyle Modifications: Exercises (aerobic and strengthening combination), Weight loss (10%), Walking aids and braces.
Medicine: as needed for pain: NSAIDs, capsaicin (apply to skin over joint), duloxetine (for multiple joints and contraindications to NSAIDs), injections of glucocorticoids (steroids; every 3 months).
Surgery: Total joint replacement (ex: knee replacement).

References

Deveza LA. Overview of the management of osteoarthritis. UpToDate. 2022. (Accessed on July 2022)