I was talking to a friend of mine recently who is looking at movement analysis techniques using various gizmos that I don’t understand. This resulted in me thinking through various movements, considering how we analyse movement, and how we determine what we think a joint is feeling. Anyone who has done a FASTER course will know that there are 5 ways of achieving any one joint motion, for example, 5 ways of achieving hip flexion, hip internal rotation etc.
So how do we decide? Well, if you’ve been with us for a while you will have seen the Diploma develop over the last few years. In particular there has been a shift in thinking towards the bones move, joints feel, muscles react concept. This allows you to more easily see what is going on, even in planes that are not easy to see at some joints.
Someone smart also once said that force can neither be created nor destroyed, which means that you are looking at what is driving the motion and, therefore, where the force is coming from. This allows us to understand movement even if we can’t see what is happening in a particular joint or plane of movement.
If we stick to gait for now, we know that as a front leg it is the ground reaction force that is the primary driver for the lower limb and up to the lumbar spine. As a result we can use this information to decide which motion is occurring in each of the three planes.
As a general rule you are looking at the bone that is closer to the driver moving faster. However, as with all rules there are exceptions, and in particular in the foot you have to be careful as the shape of some of the joint surfaces allow this rule to be broken.
Let’s look at an example: we’ll use the front leg load in the right knee for this.
We know that as a result of the motions at the foot that the tibia is anteriorly rotating, tilting left, and rotating left.
It’s easy to see from this that in the sagittal plane the knee will be flexing as both bones are moving in opposite directions to create flexion. Again in the frontal plane both bones are moving in opposite directions to create abduction. Things get a little more tricky in the transverse plane. It’s hard to see from the outside if there is internal or external rotation, and because the bones are both rotating to the left there’s no obvious explanation there. So we have to look at where the movement is being driven. The force is coming from the ground up. This means we can assume the tibia is rotating faster than the femur, giving us internal rotation in the transverse plane.
Hopefully, that’s easy to see but let’s go through the back leg in gait, just to be thorough.
The tibia is anteriorly rotating, tilting right and rotating right. The femur is anteriorly rotating, tilting left and rotating right.
Now in the sagittal plane the tibia and the femur are both anteriorly rotating. However, the driver now is not the ground reaction force, but comes from the opposite leg swinging through and the forward momentum of walking. As a result, the femur will be rotating faster, resulting in knee extension. In the frontal plane they are moving in opposite directions so it is easy to see the knee is going through adduction. Again, in the transverse plane they are both rotating in the same direction. This time they are both rotating to the right, however with the driver coming from the top down we can assume that the femur will be rotating faster. This will result in the knee feeling internal rotation in the transverse plane.
This simple example shows both how the driver change influences the bone movements and how we determine what the joint feels. If you go through that thought process at each joint and each plane of motion you will have a very powerful assessment and treatment tool.