Human motion occurs in three planes or axes. Functional activities of daily living rarely occur in one plane; therefore, motion can be described as triplanar or occurring in all three planes simultaneously
The sagittal plane is a vertical plane that divides the body into right and left halves. Motion occurs from front to back. We call this motion flexion and extension. Flexion can be described as two bony levers coming closer together. Extension is the opposite.
The frontal or coronal plane is a vertical plane that divides the body into front and back halves. Motion occurs from side to side. We call this motion abduction and adduction. Abduction is away from the body or outward while adduction is towards the body or inward.
The transverse plane is a horizontal plane that divides the body into upper and lower halves. Rotation is the motion that occurs in this plane. Medial or internal rotation refers to rotation towards the center of the body. Lateral or external rotation refers to rotation away from the center of the body.
Walking is an example of multiple triplanar movement patterns involving the whole body. The legs and feet support the body's weight providing for balance and forward progression. Bones act as lever arms to form joints or pivot points. Muscles work with gravity and momentum to create the source of power for walking.
The ability to walk efficiently is based upon the proper alignment of the bones of the feet, which in turn affect the alignment of the ankles, knees and hips. Muscle strength from above is also a factor. Weak or missing muscles create abnormal rotational patterns causing mal-alignment of the joints below. An effective brace must provide for triplanar control of the foot and ankle while providing triplanar support for weak muscles. It must work from the ground up and the top down simultaneously. Triplanar control in an orthotic support system is dependent upon the design and materials used.