For years I thought that I could actually mobilize or manipulate the thoracic spine by literally moving the facets/zygapophyseal (Z) joints into specifically desired directions… I believed that I was able to cranially or caudally glide the T4-5 Z joints. The reason I believed it was that it made theoretical sense and certainly all the guru manual therapists could not be wrong.
Based on the laws of physics, friction is required at the skin-fascia interface for applied forces to be directly transmitted to the underlying Z joints.
This study involved chiropractors who performed thoracic manipulations to determine if they could maintain their location of contacts over the underlying vertebra.
Using an ingenious device, this study measured the friction at the thoracic skin-fascia interface and determined the reaction force vectors during various thoracic manual therapies.
To no surprise, the subjects exhibited negligible friction between the thoracic skin and underlying fascia, concluding during thoracic spinal mobilizations or manipulations, one cannot glide a Z joint at a given angle by simply directing a thrust in that direction.
Try this simple experiment. Press your finger hard on you TMJ and slide it up and down. Will your TMJ move or does your skin simply move up and down?
Now put your thumb on the skin over your T10 transverse process and ask yourself the same question.
Reference: Bereznick DE, Ross JK, McGill SM. The frictional properties at the thoracic skin-fascia interface: implications in spine manipulation. Clin Biomech (Bristol, Avon). 2002 May;17(4):297-303.
View Greg Lehman video: https://youtu.be/QxKy9QXvd-I