In a previous blog on REAL and RELATIVE motion, the importance of understanding the difference between bone and joint motion was described. In extremity joints, the relative joint motion is labeled as if the distal bone moved on a stationary proximal bone. In the spinal joints, motion is described in a very different way. The reference bone is the top bone. In order to minimize confusion, in the spine the top bone is referred to as the superior bone (instead of proximal). The bottom bone of a joint is called the inferior bone (instead of distal).
When the head moves in any of the three planes it will create spinal joint motion in a “top-down” sequence. The driving force is moving down into the spine. In contrast, when the pelvis moves in response to the legs, that pelvis movement will create lumbar spinal joint motion from the “bottom-up”. The driving force is coming up into the spine. When the shoulders rotate in the transverse plane, motion will be driven “top-down” into the thoracic and lumbar spine. At the same time the cervical spine will experience “bottom-up” motion in the opposite direction. Simultaneously the driving force is down into the thoracic and lumbar while up into the cervical.
Let’s use left cervical joint rotation to appreciate the 5 different real bone motion combinations that can produce the “same” left cervical rotation.
Relative left rotation of the cervical spine is produced by these 5 real bone motion combinations:
- Head rotates to the left, shoulders stationary
- Superior bone motion and relative joint motion are the same. This joint motion results from a “top-down” driver.
- Head is stationary, shoulders rotate to the right
- The inferior bone rotates to the right, which results in the opposite (left) relative cervical joint motion. The left cervical joint rotation is being driven “bottom-up”.
- Head and shoulders rotate to the left, but the head rotates faster
- Both bones are moving in the same direction, and if they move at the same rate, there will be no relative joint motion. With the superior bone moving faster, the real head motion and the relative cervical joint motion are the same. This is called “top-down” because the superior bone is moving faster.
- Head and shoulders rotate to the right, but the shoulders rotate faster
- The bones are moving in the same direction. The inferior bone (shoulders) is moving faster than the superior bone. Although the head is rotating to the right, the relative cervical joint motion is left rotation. This is called “bottom-up” because the inferior bone is moving faster.
- Head rotates to the left, shoulders rotate to the right
- The bones are rotating in opposite directions. The real bone motion of the head and the relative cervical joint motion are the same, but the amount of left cervical rotation is increased by the shoulder rotation to the right. The relative cervical joint left rotation is being driven both “top-down” and bottom-up”.
In summary, the rules for naming spinal motion are different (superior on inferior) than in the extremity joints (distal on proximal). Motion can be driven top-down, bottom-up, or both. This will happen in each of the three planes. As movement practitioners, this knowledge must be applied to whatever activities our clients choose to engage in. The challenge for us all is to utilize examination movements (and training programs) that can create the appropriate real bone motion combinations that will result in the desired relative joint motion.