One of the methods of examination that physical therapists is goniometry. It is an essential course taught as a foundational skill in school where a device (goniometer) is used to measure joint range of motion (ROM). There are additional methods of ROM measurement used as well (some more reliable than others), such as tape measure, double inclinometers, selective functional movement assessment (SFMA), percentages, etc. While there is plenty of debate about the usefulness of goniometry, I want to instead focus on discussing how to perform goniometry.
While there are several ROM texts out there, the majority of them advocate for using a 3-point system when using a goniometer. The method includes picking one point on each axis and centering the fulcrum over the joint. While maintaining those points, the joint is moved to the desired range. In theory this method should work without fail, however, due to the difficulty of maintaining these points, I recommend the 4-point system, which instead you maintain 2 points along each axis without focusing excessively on the fulcrum. That is not to say it should be ignored, but the fulcrum instead should just hover around the joint. The reason why is that when you use a 3-point system, for certain joints it is extremely difficult to maintain those exact 3 points. Inevitably, the fulcrum gets moved somewhere away from its point of origin and if you try and stabilize with one hand, one of the arms of the goniometer deviates from its starting point. By using the 4-point system, you can use one hand on each arm to stabilize the arm against its respective 2 points while moving the joint. In my opinion, it is far easier and far more accurate.
Now I am not saying that the goniometer is the best tool for measurement. It is inaccurate (primarily due to user error) by about +/- 5 degrees each direction. There are certain joints I think that can be better measured with an inclinometer or double inclinometers, like the spine or using a tape measure/ruler for TMJ. Personally, I primarily use the SFMA. I find it is much more accurate to say yes/no by determining whether or not a motion meets certain criteria and it is easier to spot asymmetries. That being said, I still use the goniometer for surgical cases and some other indications, so it is a tool that we need to be as accurate as possible, when used.
-Dr. Chris Fox, PT, DPT, OCS