Functional assessment? Range of motion, strength, etc.

You need devices which can objectively measure the strength of something like an ankle in multiple vectors of motion. And then algorithms which can combine the data into a meaningful index.

That doesn't sound very difficult. You could measure the angle that someone could extend before feeling pain, or ensure the ankle could apply a certain amount of pressure before the patient feels pain, etc.

It would be very difficult to bring that to market as an FDA certified medical device. And then repeat the process for every other joint.

I doubt you would need to get the FDA involved at all.

There is basically no risk of harm from such a thing. If all you are doing is using it verify whether a surgery worked or not, then it's not actually a treatment is it? Surgeons make their own tools, jigs and tests all the time.

And if for some reason you had to, there are different grades of hard with a medical regulating body. For instance, it is super easy to develop medical tools. Harder again to do implants, harder again to do medicines.

So I want to reiterate. Not hard at all.

- source. Worked for a medical device company that did implants, wound care and medical tools. Surgeons would often ask for custom tooling or jigs through us that we would get made up for them.

I'm not sure if that was sarcastic or not, but you mean devices like hanging scales and string, and a protractor?

Ah, but it's a medically certified protractor! Disposable (for safety of course) and $500 a pop.

It seems to me that squat, deadlift, and an agility test would probably cover that.

well....get to work?

Speaking from an orthopedic perspective (though most fields are similar), there are literally thousands of ways to measure this, they are called (not surprisingly) outcome measures and they are basically the foundation of almost every medical study. Many are a collection of questions or items that add up to a given score which is how they are able to be statistically analyzed.

Some are subjective like pain (VAS or visual analog pain scale, “rate your pain 1-10”), ability to do daily activities, “would you have this procedure again?”, return to pre-injury activity level, etc.

Others are objective like range of motion, strength, bone healing noted on Xray or ct, tendon / ligament healing observed on mri, histiologic healing observed from follow up biopsy, rehospitilzation rates, revision surgery rates, infection rates, or mortality rates (the ultimate objective outcome measure).

There is hardly a shortage of outcome measures out there, and researchers propose new ones all the time, but they need to be validated as relevant and accurate by other studies before they are widely adopted.

http://www.orthopaedicscores.com

In some studies, they used things like positions and angles between bones (before and after surgery).

Unfortunately questionnaires might be only thing sometimes. My message is that, we should be more sceptical about them

Technologies exist that give quantitative biomechanical analysis and "before" and "after" comparison, for example when fitting an orthesis or prosthesis.