KNEE SWELLING
Think of the anatomy of the knee in developing a differential
diagnosis. Starting from the surface and penetrating deep in the knee, you
have skin, subcutaneous tissue, Bursa, ligaments, synovium, cartilage, and
bone. We should not forget the arteries and veins. Let’s see what conditions
each of these anatomic structures prompts us to recall.
Skin—Carbuncle, hematoma, angioneurotic edema may cause swelling.
Subcutaneous tissue—Cellulitis, erythema nodosum,
lipoma may cause swelling.
Bursa—Inflammation of numerous bursa about the knee
may cause swelling.
Ligaments—Torn or strained collateral ligaments and anterior or
posterior cruciate ligaments may lead to instability of the joint and
associated swelling.
Synovium—This is the site of infections such as streptococcus,
gonorrhea, tuberculosis, and brucellosis. It is also the site of autoimmune
disorders such as rheumatoid arthritis, lupus erythematosus, and rheumatic
fever. Gout and pseudogout affect the synovium of the knee. Hemorrhage into
the synovium is common in hemophilia and other coagulation disorders.
Cartilage—Trauma to the meniscus causes rupture and swelling.
Degeneration of the cartilage in osteoarthritis produces significant
swelling. Repeated trauma to the cartilage occurs in Charcot joints.
Bone—Osteomyelitis, bone tumors, aseptic bone
necrosis (Osgood-Schlatter disease), and ochronosis are considered here.
Arteries—A popliteal aneurysm is brought to mind by remembering this
structure.
Veins—Varices and thrombophlebitis may produce swelling around the
knee.
Approach to the Diagnosis
The history and physical are very important in ruling out some of the
various possibilities. If the swelling is painless, Charcot joints should be
considered. A history of fever suggests septic arthritis but is also common
in rheumatic fever and rheumatoid arthritis. Unilateral swelling is most
likely the result of trauma, gout, pseudogout, torn meniscus, or septic
arthritis, whereas bilateral swelling is seen more commonly in rheumatoid
arthritis, osteoarthritis, lupus erythematosus, and Reiter disease. The age
of the patient will suggest the most likely possibilities. Knee swelling in
a young individual would most likely be due to rheumatoid arthritis,
rheumatic fever, gonorrhea, or lupus erythematosus, whereas knee swelling
in elderly persons is more likely to be due to osteoarthritis, gout, or
pseudogout.
The workup should begin with a CBC, urinalysis, sedimentation rate,
arthritis panel, chemistry panel, and x-ray of the knees. If it can be
determined that the swelling is due to synovial fluid, arthrocentesis should
be done and the fluid analyzed for crystals, mucin clot, leukocyte count,
and micro-organism by smear and culture. An MRI or arthroscopy may be
necessary, but an orthopedic surgeon or rheumatologist should be consulted
before ordering these expensive tests.
Other Useful Tests
-
Venereal disease research laboratory (VDRL) test (Charcot joints)
- Blood cultures (septic arthritis)
- Tuberculin test (tuberculosis)
- Electrocardiogram (EKG) (rheumatic
fever)
- Monospot test (infectious mononucleosis)
- Coagulation profile (hemophilia)
- Cervical or urethral smears and cultures (gonorrhea)
- Lyme disease antibody titer
- Synovial biopsy
- Therapeutic trial (gout)
- Bone scan (osteomyelitis, neoplasm)
- Febrile agglutinins (brucellosis)
Book Source Details
- Book Title: Differential Diagnosis in Primary Care
- Author(s): R. Douglas Collins MD, FACP
- Year of Publication: 2007
- Copyright Details: Differential Diagnosis in Primary Care, Copyright © 2007 Lippincott Williams & Wilkins.
Other Book Chapters Related to Knee swelling
Read excerpts from these other book chapters related to Knee swelling:
Medical Books Excerpts
- KNEE PAIN
- "Algorithmic Diagnosis of Symptoms and Signs" (2003)
- [ read ]
- Knee Pain
- "In A Page: Pediatric Signs and Symptoms" (2007)
- [ read ]
- Knee Pain
- "The 10-Minute Diagnosis Manual: Symptoms and Signs in the Time-Limited Encounter" (2000)
- [ read ]
Copyright Details: Differential Diagnosis in Primary Care, Copyright © 2008 Williams & Wilkins.
More About Causes of Knee swelling
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