What are Fryette's three laws?
Fryette’s Laws describe how spinal segments interact biomechanically under different postural conditions and loading states, particularly in the thoracic and lumbar spine. These principles are essential for healthcare professionals in osteopathy, physical therapy, and manual medicine, offering a systematic approach to assess and treat spinal dysfunctions.
Developed by Dr. Harrison Fryette, these three laws form the basis for understanding coupled motion, vertebral misalignments, and somatic dysfunctions in clinical practice.
First law: Neutral mechanics
Fryette's first law states that when the spine is in a neutral position (neither flexed nor extended), side bending to one side will be accompanied by rotation to the opposite side. This principle sums up how the facet joints and vertebral bodies interact in the thoracic and lumbar spine, ensuring that the vertebrae rotate to the left when your side bends to the right. This law applies particularly well to the thoracic spine and lumbar spine but does not apply to the cervical spine.
Second law: Non-neutral mechanics
The second law of Fryette's Laws explains that when the spine is flexed or extended (non-neutral), side bending to one side will be accompanied by rotation to the same direction. This type of motion, known as type II motion or type II somatic dysfunction, is common in the thoracic and lumbar regions of the spine when it is not in a neutral position.
For instance, if the lumbar spine is flexed or extended, side bending to the right will also cause the vertebrae to rotate to the right, demonstrating how vertebral motion changes based on spinal positioning.
Third law: Motion modification
Fryette's third law states that if motion is introduced in one plane, it will negatively affect motion in the other planes. In other words, moving the spine in one direction, such as flexion or extension, will limit your ability to move in other directions, like lateral flexion or rotation. This law is essential for understanding how bending forces in one plane can restrict vertebral motion in other planes, affecting the overall flexibility and movement of the spine.
By grasping these three laws about spinal motion, healthcare professionals can better diagnose and treat spinal issues, ensuring optimal patient care and improved outcomes in manual medicine.






