Diagnostic tests of ankle pain consist of the following. A thorough history taking and physical examination can tell the physician in 90 to 95% what the most probable diagnosis is for a particular ankle pain. The diagnostic tests will rule out the other possibilities and will also confirm the diagnosis. Hopefully this way the physician will have a 100% accuracy with the diagnosis. A bone scan can be very helpful in the diagnostic armamentarium of the physician in a CRPS case. A bone scan is more sensitive than X-rays in detecting occult fractures, showing acute arthritis and in many cases of CRPS show some abnormalities in the bone scan, which measures changes in the circulatory distribution pattern.
X-rays are very useful for ruling out most fractures except for early stress or hairline fractures.
Degenerative arthritis has typical X-ray changes with bony spurs, narrowing of the ankle joint, and possibly a soft tissue shadow from an effusion. With rheumatoid arthritis the X-rays have a different appearance with erosions, cysts and osteoporotic bone appearance in the bones adjacent to the ankle joint. However, similar appearances can also be found in some cases of gout and degenerative arthritis.
A CT scan or MRI scan can sometimes be very useful when more details have to be seen. A CT scan for instance may be useful if there is a bone cyst and the details of this need to be seen or in the case of further delineation of a bone lesion near the ankle, which looks suspicious for cancer. On the other hand an MRI scan would be useful to check for a subtalar fracture, a nerve entrapment or a ligamentous tear as these soft tissue details would show up very well.
An “ankle strain”– or is it?
Here is an example where things did not quite work out that way: A physician treated a painful ankle condition of a 58-year old woman as an ankle strain because she had slipped and the ankle got stressed sideways putting pressure onto the ligaments. X-rays were done to rule out a fracture, but they were negative for a fracture thus confirming that the proper diagnosis was that of an ankle strain. The patient was also instructed to return after two weeks, should her symptoms not improve. This woman was in the postmenopausal age group and her physician fortunately ordered a further test, namely a nuclear medicine bone scan, which picked up a hairline fracture. The original plain X-rays had missed this. However, now that two further weeks had elapsed repeat X-rays at that time could possibly (but not always) have shown callus formation, which means there would be new bone formation in the area of the stress fracture. The reason such detail is important is that the management is quite different: this woman needed a cast put in place so that the stress fracture would heal properly. However, because she was postmenopausal, she also had to be checked for osteoporosis with further appropriate testing and if this was found to be positive, she would have needed proper therapy for the osteoporosis so that this stress fracture would heal properly and future fractures in ankles, hips and wrists would be avoided.
Blood tests are useful to rule out metabolic conditions such as diabetes mellitus, hypothyroidism or hyperparathyroidism. Such tests as the ESR and C-reactive protein have been mentioned in other chapters and would be indicative of inflammatory disease such as polymyalgia rheumatica and rheumatoid arthritis. RA titer for rheumatoid arthritis, and ANA titer for lupus are also useful blood tests, mostly to rule out these diseases in a more chronic ankle problem. More general tests are also useful to check out the patient’s general health. Sometimes the patient may have other diseases such as an infection, liver disease, a blood cancer, all of which would be readily visible by certain screening tests.
Synovial fluid sampling: If there is an effusion in the ankle joint, then the physician or specialist (orthopedic surgeon, rheumatologist) can obtain a fluid sample and send it to the laboratory for analysis. Depending on what the test shows the result would then be normal, inflammatory, non-inflammatory or septic (Ref. 1). This in turn can then lead to a list of several possible diagnoses as follows.
Some of the possibilities when an effusion is present (modified from Ref.1, p.415 )
|trauma||metabolic disease causing osteoarthritis||rheumatoid arthritis||gonococcal|
|low platelet count||amyloidosis||Reiter’s syndrome||tubercular|
|tumor||osteochondritis dissecans||gout and pseudogout||fungal|
|vitamin C deficiency (scurvy)||sickle cell disease||ulcerative colitis and Crohn’s disease||Pseudomonas aeruginosa|
|neuropathic joint||trauma||psoriatic arthritis||Lyme disease|
There are at times some overlaps as trauma can cause an effusion that is bloody or that is not. Similarly a neuropathic joint in a person who lost feeling in the ankle and therefore traumatizes it a lot, can also be in more than one category.
1.The Merck Manual, 7th edition, by M. H. Beers et al., Whitehouse Station, N.J., 1999. Chapter 49.
2. Goldman: Cecil Textbook of Medicine, 21st ed.(©2000)W.B.Saunders
3. Ferri: Ferri’s Clinical Advisor: Instant Diagnosis and Treatment, 2004 ed., Copyright © 2004 Mosby, Inc.
4. Rakel: Conn’s Current Therapy 2004, 56th ed., Copyright © 2004 Elsevier