The main causes of knee pain can best be recalled by utilizing an etiologic mnemonic such as VINDICATE.
· V—Vascular. This brings to mind Aseptic bone necrosis, (Osgood-Schlatter disease) thrombophlebitis, hemophilia, scurvy, and sickle cell anemia.
· I—Inflammatory suggests septic arthritis of gonorrhea, streptococcus, Lyme disease, and rat bite fever, as well as tuberculosis and syphilis. Cellulitis may involve the subcutaneous tissue around the joint.
· N—Neoplasm raises the possibility of osteogenic sarcoma and giant cell tumors.
· D—Degenerative disorders prompt the recall of osteoarthritis.
· I—Intoxication suggests gout, pseudogout, and drugs such as hydralazine that initiate a lupus syndrome and diuretics that induce gout.
· C—Congenital disorders bring to mind alkaptonuria as a cause of joint pathology.
· A—Autoimmune disorders include lupus erythematosus, rheumatic fever, rheumatoid arthritis, serum sickness, Reiter syndrome, and the arthritis associated with gastrointestinal disease such as granulomatous colitis.
· T—Trauma brings to mind sprains, fractures, dislocations, torn collateral or cruciate ligaments, laceration of the meniscus, and hematomas.
· E—Endocrine disorders causing joint pain include diabetes mellitus (pseudogout), hyperparathyroidism, and acromegaly.
Approach to the Diagnosis
Many causes of joint pain can be isolated by a careful history and physical examination. A history of trauma would suggest a sprain, torn meniscus, or fracture. If there is fever, look for septic arthritis. Bilateral involvement of the knee joint is typical of osteoarthritis or rheumatoid arthritis, whereas unilateral involvement would suggest gout, pseudogout, septic arthritis, and hemophilia. Younger patients are more prone to a traumatic lesion such as sprain or torn meniscus and Osgood-Schlatter disease. Older patients are more likely to have osteoarthritis or gout.
With the history of trauma, the first thing to do is anterior, posterior, lateral, and oblique x-rays of the joint. A magnetic resonance imaging (MRI) or arthroscopy may be necessary, but consult an orthopedic surgeon first.
Without a history of trauma, add a laboratory workup including complete blood count (CBC), sedimentation rate, anti-streptolysin O (ASO) titer, chemistry panel, arthritis panel, and blood cultures (if there is fever). Synovial fluid analysis and cultures may need to be done if there is sufficient joint fluid. A therapeutic trial of colchicine may be diagnostic of gout.
Other Useful Tests
1. Antinuclear antibody (ANA) (lupus erythematosus)
2. Coagulation profile (hemophilia)
3. Serologic test for Lyme disease
4. Bone scan (osteomyelitis)
5. Rheumatology consult
6. Orthopedic consult