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Objectives

After completing this material the reader shall be able to:

1) List the radiographic criteria for systematically evaluating joints and joint disease.

2) Define: joint effusion, arthritis mutilans, and enthesopathy.

3) List common joint disorders that are associated with arthritis.

4) Explain the importance of a lesion (erosion, for example) having either a well-defined or ill-defined margin.

5) List target areas in the foot and calcaneus for common arthritic disorders.

6) Distinguish between the joint disorders (based on radiographic findings).

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Welcome to Podiatry Management's CME Instructional program. Our journal has been approved as a sponsor of Continuing Medical Education by the Council on Podiatric Medical Education.

You may enroll: 1) on a per issue basis (at $17.50 per topic) or 2) per year, for the special introductory rate of $109 (you save $66). You may submit the answer sheet, along with the other information requested, via mail, fax, or phone. In the near future, you may be able to submit via the Internet.

If you correctly answer seventy (70%) of the questions correctly, you will receive a certificate attesting to your earned credits. You will also receive a record of any incorrectly answered questions. If you score less than 70%, you can retake the test at no additional cost. A list of states currently honoring CPME approved credits is listed on pg. 246. Other than those entities currently accepting CPME-approved credit, Podiatry Management cannot guarantee that these CME credits will be acceptable by any state licensing agency, hospital, managed care organization or other entity. PM will, however, use its best efforts to ensure the widest acceptance of this program possible.

This instructional CME program is designed to supplement, NOT replace, existing CME seminars. The goal of this program is to advance the knowledge of practicing podiatrists. We will endeavor to publish high quality manuscripts by noted authors and researchers. If you have any questions or comments about this program, you can write or call us at: Podiatry Management, P.O. Box 490, East Islip, NY 11730, (631) 563-1604 or e-mail us at bblock@prodigy.net.

An answer sheet and full set of instructions are provided on pages 246-248.--Editor

Several arthritides (types of arthritis) have a predilection for the foot (Table 1). Without question, osteoarthritis is the most common, primarily because of the mechanical wear and tear that weight-bearing activities place on cartilage. However, it is not unusual for the inflammatory rheumatic diseases (rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis, and Reiter's syndrome) to first appear or be diagnosed in the feet. Furthermore, gouty arthritis and diabetic neuropathic osteoarthropathy target have a predilection for the foot.

The archetypal radiographic presentations of joint disorders that have been described in the literature are not necessarily what the clinician encounters in everyday practice. The classic picture is typically the patient who was diagnosed with the joint disease many years or even decades ago. In contrast, the patient with acute symptomatology may initially come for help at the onset of disease or soon thereafter. In such a case, the radiographic findings are frequently subtle and nonspecific, the clinical findings are vague, and the diagnosis is often elusive. Furthermore, atypical cases are common. The challenge, therefore, is to identify the subtle, early radiographic findings, because the classic features of a particular joint disorder do not manifest until many years later. To maximize the detection of early arthritis, you "must know how to look, where to look, and what to look for." (1) Then, along with the clinical and other laboratory findings, you must list and consider the probable differential diagnoses.

Systematic Approach to Differentiating Joint Disorders

A detailed, systematic approach for evaluating pedal joints entails three considerations (2) (Table 2). For obvious reasons, the symptomatic joint or joints are assessed first. The asymptomatic joints of both extremities should also be evaluated, for two reasons: Most joint disorders target both extremities, and joints may be affected that are clinically asymptomatic. (Joint disease is one of the few conditions that warrants performing a bilateral radiographic study.) The examination doesn't stop here, however. Sites distant from involved joints, osseous and soft tissue are also considered. Abnormal findings at the calcaneal entheses and heel pain, for example, can be associated with joint disease. Finally, the distribution of radiographic findings must be assessed for specific patterns. (3) Many articular disorders demonstrate characteristic patterns of joint involvement that help distinguish one disease from another.

Articular disorders affecting the foot may involve one or multiple joints. Monoarticular joint disease is generally attributed to either trauma, infection, or acute gouty arthritis (Table 3). Less common causes of pedal monoarticular disease include rheumatoid monoarthritis and pigmented villonodular synovitis. Examples of polyarticular joint disorders affecting the foot include osteoarthritis, rheumatoid arthritis, seronegative arthritis (psoriatic arthritis, ankylosing spondylitis, and Reiter's syndrome), neuropathic osteoarthropathy, and chronic tophaceous gout.

Differentiation of joint disorders can be simplified by applying a general classification system to the presenting features. One categorization of arthritis has been based on underlying pathologic processes: degenerative, inflammatory, and metabolic (4) (Table 4). This classification, unfortunately, does not include neuropathic osteoarthropathy. In 1904, Goldthwaite used radiographic criteria to distinguish between osteoarthritis and rheumatoid arthritis. (5) These criteria can be expanded to include the remaining forms of pedal arthritis.

Joint disorders affecting the foot can be divided into two radiographic categories, based on the predominant radiographic feature: hypertrophic and atrophic (Table 5). Hypertrophic joint disease features bone over-growth and enlargement. The characteristic findings are subchondral sclerosis and osteophyte formation at the margin of a joint. Detritus arthritis, a subcategory of hypertrophic arthritis, includes those disorders that exhibit fragmentation in addition to exaggerated hypertrophic features. The loss of bone substance, primarily through erosion, and joint space narrowing, with or without periarticular osteoporosis, characterize the atrophic joint disorders. A subdivision of this group is commonly associated with an adjacent soft tissue mass clinically and the preservation of joint space. Forrester and Brown have used the term "lumpy-bumpy" joint disease to characterize this latter group. (4)

Neuropathic osteoarthropathy is divided into two subtypes: forefoot, and the combined midfoot and tarsus. Its radiographic features vary depending on location: Forefoot sites exhibit findings characteristic of atrophic joint disease; the midfoot and tarsal sites display features of detritus (hypertrophic) arthritis.

Each of the roentgen features associated with joint disease is discussed individually in the following sections. Remember the radio-graphic categories of joint disorders; you can recognize associations between certain roentgen findings and arthritis categories, improving your diagnostic acumen.

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Roentgen Features at Involved Joints: Primary Findings

Osseous Erosion

Bone erosion is a primary feature of all joint disorders except hypertrophic joint disease. Generally speaking, erosion associated with active atrophic joint disease appears small, ill defined, and irregular (Figure 1). This characterization contrasts with the larger, well-defined C-shaped erosion classically seen in the disorders associated with an adjacent soft tissue mass (Figure 2). Erosion associated with gouty arthritis, however, is indistinguishable early in the disease process, but preservation of joint space and target involvement of the first metatarsophalangeal joint differentiate gouty arthritis from the other inflammatory rheumatic disease in the proper clinical setting. The presence of an erosion excludes osteoarthritis as a primary diagnosis; however, both a trauma-induced subchondral bone defect and a subchondral bone cyst can mimic the appearance of an erosion (Figure 3).

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