Arthritis

Question 1

Contrast osteoarthritis with rheumatoid arthritis.

Answer 1

OSTEOARTHRITIS
Cause: Deterioration of cartilage and overgrowth of bone often due to “wear and tear”.

Joints: More often affects the larger weight-bearing joints, such as the hips and knees.

Complaints: Worse pain at the end of the day, when wear and tear builds up.

Systemic?: NO

Gender?: NONE

Labs?: Lab tests normal

X-rays: Bone spurs, sclerosis common. Asymmetric joint space narrowing (where the wearing and tearing took place)

Exam: Effusion, tenderness

RHEUMATOID ARTHRITIS:
Cause: Autoimmune inflammation of the synovial membranes, which leads to the destruction of the articular cartilage.

Joints: More often affects the smaller joints of the hands, wrists and feet.

Complaints: The stiffness is worse after rest, such as the first thing in the morning, and often lasts at least 30 minutes or more.

Systemic?: Can be a systemic disease.

Gender?: Rheumatoid arthritis is three times more common in females versus males

Labs?: 80% of patients are sero-positive (ie positive rheumatoid factor)

X-rays: Osteopenia more common. Symmetric joint space loss

Exam: Effusion, tenderness but redness/warmth more common. Synovitis

Question 2

If both rheumatoid arthritis and osteoarthritis can lead to end-stage destruction of the joint -and both can-why is it important to differentiate between the two?

Answer 2

RA/OA difference holds three important distinctions:

Because RA is a systemic disorder than can affect many organs of the body; therefore, it is important to check for, manage, and prevent other manifestations of the disease---ie, DIAGNOSE EXTRA-ARTICULAR disease
RA has a different prognosis, in terms of overall health as well as joint specific.
The diagnosis affects treatment: treatment for RA is not just symptomatic, and it also targets the root cause of the disease: immune abnormalities. This is accomplished with biologics and disease-modifying anti-rheumatic drugs (DMARDs) and Biologics. The goal is not just palliation but to STOP DISEASE PROGRESSION!

Question 3

Given the typical (degenerative) etiology of osteoarthritis, how then might a 20 year old person have this condition?

Answer 3

The most likely cause of osteoarthritis in a young person is trauma.

Trauma, in turn, can cause arthritis in 3 ways (at least)

1. DIRECT DAMAGE Damage to the articular surface directly can of course lead to breakdown.
2. Chronic damage inflicted from loose ligaments. In the figure below, you see that (on the left) if the tire is not secured, there will be focal loading on parts of the tire (and tire damage accordingly). Similarly, a loose joint can have eccentric loading on small areas, and in those areas there will be increased pressure (again, recalling P=F/A). This pressure leads to breakdown
3. Trauma can disrupt the blood supply, and the arthritis may be from AVN

As shown here, dead bone can collapse leading to deformity of the joint surface

Question 4

What is the role of body mass vis a vis osteoarthritis? Why might we think that this not be a pure mechanical phenomenon? (hint: Framingham)

Answer 4

Intuitively, excess load should cause excess wear:
Excess body mass increases the load placed on joints which increases stress and accelerates the breakdown of cartilage.

However, OA may not be a pure mechanical phenomenon because being overweight has also been associated with higher rates of hand OA –this suggests that a circulating systemic factor may also play a role.

Basal thumb (C-MC) arthritis is more common among the obese; yet unless these people are doing a lot of handstands, this joint should not be excessively loaded by body mass

Question 5

What are the cardinal signs of Osteoarthritis of the knee on plain radiographs? How (mechanistically) do they appear?

Answer 5

1. osteophytes (circled),
2. asymmetric joint space narrowing (short arrow)
3. subchondral sclerosis (long arrow), and
4. subchondral cysts (hard to see here).

Asymmetric joint space narrowing occurs as articular cartilage is lost is areas of abnormal load. Notice above that the lateral space is wide (though not necessarily disease-free; it may be wide because the joint is tilted to the medial side. That is, if the bones are touching, there is no cartilage; if they are not touching, maybe there is cartilage, maybe there isn’t.)

Osteophytes typically develop. Why? Maybe as a (futile/foolish) reparative response. Maybe because of abnormal loads stimulating bone. “Peaking of the tibial spines”, ie higher than expected, may be considered a form of osteophytosis.

Subchondral sclerosis is simply the deposition of bone in area under areas of stress—Wolff’s law. This makes the bone stiff and less compliant, and more prone to further damage.

Cysts form when joint fluid seeps through the cracks in the cartilage and get into bone. When the fluid escapes into the soft tissue, a BAKERS CYST may develop.

Question 6

Why is Osteoarthritis painful?

Answer 6

This is not known with certainty. The key point to recall is that for a given objective presentation, the subjective presentation can be quite variable.

In osteoarthritis, the cartilage may wear away in some areas, greatly decreasing its ability to act as a shock absorber. As the cartilage deteriorates, the joint tips (collapses where cartilage is lost) and soft tissue may stretch (on the tensile side), perhaps causing pain.

Fluid in the knee could be under pressure and also painful by simple distension.

Also, bone edema (seen frequently in DJD) can cause pain, as we know in the cases of “kissing contusions”.

The short answer is: we are not sure. Cartilage does not have the receptors to feel pain. Hence, it must be the bone or the synovium that transmits the pain—but not all “ugly” joints hurt. You cannot look at an xray and predict necessarily if somebody has pain; more to the point, you cannot look at an xray showing DJD and predict necessarily if the pain is necessarily caused by the DJD (and not, say, bursitis, radiculopathy or vascular disease).

Recall: a dog can have lice and fleas. In the case of arthritis, you can certainly have a second disease present concurrently (after all, it is typically a condition of aging, so other systems may be winding down too!) and you cannot even be sure that the arthritis you see literally in black and white is symptomatic.

(Note: there is certainly a relationship between objective presentation and subjective presentation. It’s just not perfectly correlated. Just as hoof beats suggest horses, not zebras, pain right where there is joint space narrowing with osteophytes suggests that DJD is the cause.)