As a clinical practitioner, when a client presents to you revealing the story of their bodily mishap, the inquirer will weigh all available evidence to come up with a satisfactory answer. The textbook of a career is littered with observations, hunches and discoveries. All you have learned is in there, but it has also built into it healthy suspicion, intuition and a rogues' gallery of bizarre memorable maladies that will be seen once in a lifetime.
Diagnosis is the Sherlock Holmes of clinical experience. It is the sleuth inside let out on one more mystery to solve. You have your Doctor Watson to smooth off the sharp edges of your grandiose ideas, and your Doctors Foreman, Wilson and Chase to bounce rejectable notions at your Gregory House.
Yes, I may have just talked up the everyday task of each clinician in physical medicine, but you don't just come to us for symptom relief. It is all very well to offer treatment, but treatment without justification is just recipe "care". We need to ask ourselves questions about "what else could this be?" This is called differential diagnosis and it pokes and prods at the approach that treats first and asks questions later.
Let us consider the differential diagnosis for something we all will likely experience: knee pain.
Strain - a muscle is injured. Over stretch of muscle tissue tears fibres and causes pain, bruising and limping. This is very common.
Ligament sprain - again a common traumatic cause of knee pain that the patient will clearly recall. The knee joint will have been forced or twisted outside of its natural hinge and rotation directions.
Housemaids knee or bursitis - blunt trauma or long periods spent on the knees point the suspicious inquisitor to this tissue.
The nerves - not a major contributor to knee pain, but sciatic, femoral, tibial and peroneal nerves are some that may make a person think they have a knee problem when they may have a problem elsewhere.
Osteoarthritis - the consequences of time's onslaught. It has characteristic signs of value to the sleuth.
Meniscii - the jelly-like pads that cushion the knee, these can be torn twisting with weight bearing, or in my own experience giving horsey rides to two under-fives at once. As with the other possibilities for diagnosis, these tissues have characteristic problems with pain around the joint line and loss of kneeling ability often unique to their being damaged.
The less frequent problems are detained for questioning, but usually have no part to play in the bulk of "crimes". Infection, malignancy or cancer, rheumatoid arthritis or auto immune disorders are the suspects you should rule out as a habit. Saying this, there is an adage that cautions the clinician not to see the bizarre in the everyday. "When you hear hoofbeats, think horses, not zebras." You won't see much of Charlie the Unicorn either. If you didn't have this in mind, you might see Disseminated Synovial Chromatosis, Fabella Syndrome and Melorheostosis as regular knee troublers - they are not. So a trained diagnoser or diagnostician is looking at all the clues in your story to form a plausible answer.