Symptom Finder - Knee Swelling
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 us see what conditions each of these anatomic structures prompts us to recall.
Skin—Carbuncle, hematoma, and angioneurotic edema may cause swelling.
Subcutaneous tissue—Cellulitis, erythema nodosum, and 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 variouspossibilities. 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 microorganism 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
1. Venereal disease research laboratory test (Charcot joints)
2. Blood cultures (septic arthritis)
3. Tuberculin test (tuberculosis)
4. Electrocardiogram (rheumatic fever)
5. Monospot test (infectious mononucleosis)
6. Coagulation profile (hemophilia)
7. Cervical or urethral smears and cultures (gonorrhea)
8. Lyme disease antibody titer
9. Synovial biopsy
10. Therapeutic trial (gout)
11. Bone scan (osteomyelitis, stress fracture, neoplasm)
12. Febrile agglutinins (brucellosis)
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 us see what conditions each of these anatomic structures prompts us to recall.
Skin—Carbuncle, hematoma, and angioneurotic edema may cause swelling.
Subcutaneous tissue—Cellulitis, erythema nodosum, and 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 variouspossibilities. 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 microorganism 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
1. Venereal disease research laboratory test (Charcot joints)
2. Blood cultures (septic arthritis)
3. Tuberculin test (tuberculosis)
4. Electrocardiogram (rheumatic fever)
5. Monospot test (infectious mononucleosis)
6. Coagulation profile (hemophilia)
7. Cervical or urethral smears and cultures (gonorrhea)
8. Lyme disease antibody titer
9. Synovial biopsy
10. Therapeutic trial (gout)
11. Bone scan (osteomyelitis, stress fracture, neoplasm)
12. Febrile agglutinins (brucellosis)
