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C h e c k o u t A B M P 's l a t e s t n e w s a n d b l o g p o s t s . Av a i l a b l e a t w w w. a b m p . c o m . 47 FUNCTIONAL ANATOMY education Accessory Motions By Christy Cael When evaluating joint range of motion and performing various techniques, practitioners should be aware of the different movement components that make full range of motion possible. Most practitioners are familiar with large, observable movements like shoulder flexion or ankle plantarflexion. These gross movements are called physiological movements. In contrast, the term accessory motion describes the subtle and less visually observable movement of a joint's articulating surfaces relative to each other. The amount of give in the joint capsule and ligaments that surround that joint determines the magnitude and direction of accessory motion and is called joint play. Different types of accessory motion include roll, glide, and spin. These terms describe what happens between the joint surfaces as the joint is taken through specific physiological movements. Each of these accessory motions helps maintain joint position during physiological movements, and reduces compression, decreases friction, and maintains optimal contact between the articulating surfaces of the joint. ROLL Rolling occurs when a series of points on one bony surface comes in contact with a corresponding series of points on the other (Image 1A). This is similar to various points on a car tire contacting various points on the ground as a car rolls forward, leaving a tread mark on the ground. For example, the rounded condyles of the femur roll on the depressed tibial plateau as the knee is flexed and extended. Roll occurs when the articulating surfaces are incongruent. GLIDE Gliding occurs when a point on one bony surface comes in contact with a series of points on another (Image 1B). This is similar to a skidding motion: the tire isn't rolling, but the car still moves forward, thus a set point on the tire contacts various points on the ground. Gliding is sometimes referred to as translation. Often, gliding and rolling occur together, maintaining optimal joint position. Gliding occurs in isolation (without roll) when the two articulating surfaces are congruent and flat or congruent and curved. 1A 1B