Comprehensive Osteopathic Medical Licensing Examination (COMLEX USA) Practice

What does Fryette's third law state about joints and motion?

1. Motion one plane does not affect other planes

2. Motion in one plane alters motion in other planes

3. All planes of motion are independent

4. Only the transverse plane is affected by movement

The correct answer is: Motion in one plane alters motion in other planes

Fryette's third law states that motion in one plane alters motion in other planes, which is fundamental in understanding the biomechanics of spinal motion. This concept highlights the interdependence of movements; when a joint is moved in one direction, it can influence the range and quality of motion in other directions. This is particularly relevant in osteopathic manipulative treatment and assessment of spinal mechanics. While joint movement might appear to be isolated within a single plane, Fryette’s third law illustrates that the anatomical and physiological relationships among different planes of motion are interconnected. For example, if the spine is flexed (a motion in the sagittal plane), this can lead to restrictions or changes in rotation or side-bending (transverse and coronal planes, respectively). This principle aids in the understanding of conditions such as spinal restrictions, where multiple planes of motion may be compromised due to dysfunction or pathology. The other options suggest alternatives that do not align with the known effects of joint mechanics as described by Fryette’s laws. Specifically, they incorrectly imply that movements in different planes are either completely independent or only affected under limited circumstances, which is contrary to the observed interaction between joint movements across different planes.