Thread by @Retlouping

Another episode in “old man shouting at clouds” Twitorials

Today’s episode is on “the myth of coupling” illustrated using the cervical spine.

The term coupling is a common used term especially in descriptions of spinal motion and manual therapy. It is a common biomechanical..

Term often used in the description of osteokinematics and arthrokinematics. I will propose that coupling is a myth and does not occur in reality. Coupling is a product of using stylised planes and axes to describe biomechanics. I will post pictures at the end

As you can not add picture in a thread.
A nice simple example of true coupling is a simple screw, it is not hard to understand that if you turn a screw clockwise it will translate anteriorly into a surface, the reverse occurs if you turn the screw anticlockwise (counter in US)

This is where the concept of coupling is revealed, you can not create rotation by pushing on a screw, as anyone knows if they have tried hitting a screw with a hammer. So coupling is dependant on specific movement initiation. I have tweeted about this in the past here

“coupling is simply disproved by the fact the language used is wrong & if something is “coupled” it will always occur together ,example a screw, rotation & translation always occur. You can not uncouple a screw. Gliding a screw does not create rotation, flawed model of manual PT”

It is common to learn that in the cervical spine (as discussed in my earlier post this week below C2) side flexion and Rotation are coupled. This is referring to the biomechanics of the Cx spine. There is a problem with this oft taught concept, it is WRONG for two reasons. I

Reason one, it uses the wrong language (even Bogduk falls foul of this) and reason two side ending and rotation are not coupled. Think about the screw, you can’t uncouple a movement, coupling means they occur together. Hence if you now rotate you neck, and then side bend...

They are unique and different motions that DO NOT occur together. The issue is two fold, side bending and rotation are the language of grooms anatomical functional motion, the language of biomechanics, specifically osteokinematics can only be described in terms of “rotation”...

Around and axis, and translation along a plane. These are the classic six degrees of freedom. A more true statement for the neck may be that formal plane rotation and transverse plane rotation around the sagittal and vertical axes always occur together and hence are coupled.

The problem is that this is also NOT true.
The big problem with osteokinematics is that it tries to describe the motion of a vertebrae suing the stylized planes and axes, these planes and axes do not occur in reality (only actually found in the semicircular canal as of the ear)

Osteokinematics is thus like a map reference it is not reality it is just a position on a map.

Penning published on this over 24 years ago, and it appears to have gone much unnoticed.

Simple proposal the true planes of motion of any joint are the joint surfaces.

We know that axes are perpendicular to the planes of motion , hence the axis of road action will occur 90 degrees to the joint plane.
In the cervical spine the true axis of rotation is 90 degrees to the Z- joint surface and is illustrated from Pennington work below.

Once this is appreciated you can now understand why coupling is no longer necessary to describe cervical osteokinematics.

As I proposed in my earlier tweetorial , if you functionally side bend, or if you functionall rotate your dad and neck, these motions below C2 are the same

Biomechanically, the difference is loading on the joints due to head weight. So how are the the same? Simple if you use an axis 90 degrees to the z-joint and rotate around this axis and glide along the z-joint plane you get the illusion of coupled motion ie rotation in frontal..

And transverse plane. When infact it is just rotatio around the Z-joint axis. You can build a simple model using a box and a knitting needle and play with this at home. It takes some mental gymnastics to visualize without a model.

A previous tweet”
“The term “coupling” is a motion illusion due to having to describe motion in terms of the stylized planes & axes. Coupling does not exist, ie in cervical spine side bending & rotation are the same osteokinematics below C2 the coupling myth is due to the model.

So simply put if you turn your head fully ot the left, or if you tip your and neck fully to the left, these biomechanical move nets of the cervical spine are identical osteokinematics, the load on the joints is different due ot the head weight. The obvious visual difference

Of the two functional movements comes from what the head joints do, as previously described in my post on the head joints.

Remember the hea can move independently on the neck and this is the key difference in the two movements, in functional rotation the head moves with the neck

In functional side bending the head side flexes and roadsters the opposite direction to the neck. Try it and see. In sid elfexion left the head is almost at end range right rotation, this is the classic gym rat self manipulation position for the AA joint.

I know this can seem complex and confusing, but knowing th facts will help reason through typical clinical presentations, that’s for another day.

Thanks for reading, pics and illustrations below.

I know that the rotation is the wrong way as this is an anterior view but it illustrates the loading point

Coupling

https://twitter.com/retlouping/status/982003442330857474?s=21

https://twitter.com/retlouping/status/982003442330857474

https://twitter.com/retlouping/status/981995656230338560?s=21

https://twitter.com/retlouping/status/981995656230338560

@threadreaderapp unroll please

Here is a video I just made demonstrating the illusion of coupled motion in the cervical spine. The true motion is around the axis perpendicular to the zygapohyseal joint plane per Pennines work.

The language differences of biomechanics and anatomical functional movement.

The myth that is coupled motion