Recognizing Joint Disease

Chapter 23 Recognizing Joint Disease

An Approach to Arthritis

Imaging studies play a key role in the diagnosis and management of arthritis and are the method by which many arthritides are first diagnosed. Other arthritides are initially diagnosed on clinical and laboratory grounds and imaging is used to document the severity, extent, and course of the disease (Table 23-1).

Conventional radiographs demonstrate osseous abnormalities but provide only indirect and usually delayed evidence of abnormalities involving the soft tissues, such as the synovial lining of the joint, the articular cartilage, muscles, ligaments, and tendons surrounding the joint. MRI is used to demonstrate those soft tissue abnormalities.

TABLE 23-1 ARTHRITIS: WHO MAKES THE DIAGNOSIS?

Usually Diagnosed Clinically	Frequently Diagnosed Radiologically
Septic (pyogenic) arthritis	Osteoarthritis
Psoriatic arthritis	Early rheumatoid arthritis
Gout	Calcium pyrophosphate deposition disease
Gout	Ankylosing spondylitis
Hemophilia	Septic (TB)
Hemophilia	Charcot (neuropathic) joint—late

Anatomy of A Joint

Figure 23-1 contains a diagram of a typical synovial joint and compares the structures visualized on conventional radiographs and MRI.

The articular cortex is the thin, white line as seen on conventional radiographs that lies within the joint capsule and is usually capped by hyaline cartilage, called the articular cartilage. The bone immediately beneath the articular cortex is called subchondral bone.

Lining the joint capsule is the synovial membrane containing synovial fluid. The synovial membrane is frequently the earliest structure involved by an arthritis.

Conventional radiographs will demonstrate abnormalities of the articular cortex and the subchondral bone and will provide late, indirect evidence of the integrity of the articular cartilage.

On conventional radiographs, the synovial membrane, synovial fluid, and the articular cartilage are usually not directly visible. All, however, are visible using MRI.

While MRI is more sensitive in directly visualizing the soft tissues in and around a joint, conventional radiographs remain the study of first choice in evaluating for the presence of an arthritis.

Figure 23-1 Diagram, radiograph, and MRI image of a true joint.

A, A representation of a synovial joint shows the articular cortex, which corresponds to the thin, white line within the joint capsule that is usually capped by articular cartilage. The bone immediately beneath the articular cortex is called subchondral bone. Within the joint capsule is the synovial membrane and synovial fluid. B, On conventional radiographs, the articular cortex (solid white arrow) and subchondral bone (solid black arrows) are visible but the cartilage and synovial fluid are not (dotted white arrow). C, A T1-weighted coronal MRI of the knee shows the medial (MM) and lateral (LM) menisci, anterior (ACL) and posterior (PCL) cruciate ligaments, articular cartilage (dotted black arrow), joint capsule (dotted white arrow), synovial fluid (solid white arrow), and marrow in the subchondral bone (SC). The cortex of the bone (solid black arrow) produces little signal and is dark.

Classification of Arthritis

First, let’s define what an arthritis is and then we’ll outline a classification of arthritides. An arthritis is a disease that affects a joint and usually the bones on either side of the joint, almost always accompanied by joint space narrowing (Fig. 23-2).

We will divide arthritides into three main categories: (Table 23-2)

• Hypertrophic arthritis is characterized, in general, by bone formation at the site of the involved joint(s). The bone formation may occur within the confines of the parent bone (subchondral sclerosis) or protrude from the parent bone (osteophyte) (Fig. 23-3A).

• Erosive arthritis indicates underlying inflammation and is characterized by tiny, marginal, irregularly shaped lytic lesions in or around the joint surfaces called erosions (Fig. 23-3B).

• Infectious arthritis is characterized by joint swelling, osteopenia, and destruction of long, contiguous segments of the articular cortex (Fig. 23-3C).

Within each of these three main categories, we’ll look at a few of the more common types of arthritis that also have characteristic imaging findings.

Figure 23-2 Arthritis or not?

An arthritis is a disease that affects a joint and usually the bones on either side of the joint, almost always accompanied by joint space narrowing. A, This disease meets those specifications. There is narrowing of the hip joint, and both the femoral head and the acetabulum are abnormal (solid white arrow). This is osteoarthritis of the hip. B, There is an abnormality of the femoral head (sclerosis) but the joint space is normal as is the acetabulum (solid black arrow). This is avascular necrosis of the femoral head.

TABLE 23-2 CLASSIFICATION OF ARTHRITIS

Figure 23-3 The imaging hallmarks of the three major categories of arthritis.

A, Hypertrophic arthritis features subchondral sclerosis (solid black arrow) and marginal osteophyte production (solid white arrow). B, Erosive (inflammatory) arthritis features characteristic marginal lytic erosions (solid white and black arrows). C, Infectious arthritis features destruction of the articular cortex (dotted white arrow).

Hypertrophic Arthritis

Hypertrophic arthritis is characterized by bone formation, either within the confines of preexisting bone (subchondral sclerosis) or by bony protrusions extending from the normal bone (osteophytes).

Primary Osteoarthritis (Also Known as Primary Degenerative Arthritis, Degenerative Joint Disease)

This is the most common form of arthritis, estimated to affect over 20 million Americans. It results from intrinsic degeneration of the articular cartilage, mostly from the mechanical stress of excessive wear and tear in weight-bearing joints.

It mostly involves the hips, knees, and hands and increases in prevalence with increasing age.

The imaging findings in osteoarthritis:

Marginal osteophyte formation. A hallmark of hypertrophic arthritis, osseous transformation of cartilaginous excrescences and metaplasia of synovial lining cells lead to the production of these bony protrusions at or near the joint (Fig. 23-4).

Subchondral sclerosis. This is a reaction of the bone to the mechanical stress to which it is subjected when its protective cartilage has been destroyed.

Subchondral cysts. As a result of chronic impaction, necrosis of bone and imposition of synovial fluid into the subchondral bone, cysts of varying sizes form in the subchondral bone.

Narrowing of the joint space. This is seen in all forms of arthritis.

What joints are involved?

• In osteoarthritis, destruction of the cartilaginous buffer between the apposing bones of a joint leads to narrowing of the joint space most often on the weight-bearing side of the joint: hip (superior and lateral) and knee (medial) (Fig. 23-5).

• In most patients with osteoarthritis of the interphalangeal joints of the hands, the first carpometacarpal joint (base of thumb) is also affected (Fig. 23-6). It is also common for osteoarthritis to affect the distal interphalangeal joints, especially in older females.

Figure 23-4 Osteoarthritis.

The hallmarks of osteoarthritis are demonstrated in this patient’s right hip. There is marginal osteophyte formation (solid white arrow), a process by which osseous transformation of cartilaginous excrescences and metaplasia of synovial lining cells leads to the production of bony protrusions at or near the joint. There is also subchondral sclerosis (solid black arrows), representing reaction of the bone to the mechanical stress to which it is subjected when its protective cartilage has been destroyed. Subchondral cyst formation is also present(dotted black arrow).

Figure 23-5 Osteoarthritis of hip (A) and knee (B).

In osteoarthritis, destruction of the cartilaginous buffer between the apposing bones of a joint leads to narrowing of the joint space most often on the weight-bearing side of the joint. In the hip (A), the superior and lateral surface is most affected (solid white arrow) while in the knee (B), the medial compartment is more affected (solid black arrow).

Figure 23-6 Osteoarthritis of the hands (A and B).

In the hands, osteoarthritis affects primarily the distal and then proximal interphalangeal joints. There are osteophytes at the distal and proximal phalangeal joints (solid white arrows) and the joint spaces are narrowed. There is also subchondral sclerosis present at the carpal-metacarpal joint of the thumb (solid black arrow). Osteoarthritis of the hands occurs most often in older women.

Secondary Osteoarthritis (Secondary Degenerative Arthritis)

Secondary osteoarthritis is a form of degenerative arthritis of synovial joints that occurs because of an underlying, predisposing condition, most frequently trauma, that damages or leads to damage of the articular cartilage.

The radiographic findings of secondary osteoarthritis are the same as those for the primary form with several special clues to help suggest secondary osteoarthritis:

• It occurs at an atypical age for primary osteoarthritis (e.g., a 20-year-old with osteoarthritis) (Box 23-1).

• It has an atypical appearance for primary osteoarthritis (e.g., primary osteoarthritis is usually bilateral and often symmetrical; severe osteoarthritic changes of one hip while the opposite appears perfectly normal should alert you to the possibility of secondary osteoarthritis).

• It may appear in an unusual location for primary arthritis, (e.g., the elbow joint) (Fig. 23-7).

Box 23-1 Some Causes of Secondary Osteoarthritis

Avascular necrosis

Calcium pyrophosphate deposition disease

Rheumatoid arthritis

Figure 23-7 Secondary osteoarthritis, right hip.

Notice the marked discrepancy between the two hips with severe and advanced osteoarthritis of the right hip (solid black arrow) and a normal left hip (solid white arrow). The radiographic findings of secondary osteoarthritis are the same as those for the primary form except it occurs at an atypical age for primary osteoarthritis, it has an atypical appearance for primary osteoarthritis, and it may appear in an unusual location for primary osteoarthritis. This patient had a slipped capital femoral epiphysis on the right, and it was never attended to medically.

Eventually any arthritis that affects the articular cartilage, no matter what the etiology, can lead to changes of secondary osteoarthritis.

Tags: Learning Radiology Recognizing the Basics

Mar 2, 2016 | Posted by admin in GENERAL RADIOLOGY | Comments Off

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