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.
The convex-concave rule determines the direction of glide and roll. This rule states that the shape of the joint surfaces will determine how they move. Most joint surfaces are either convex (rounded outward or arched) or concave (rounded inward or hollowed) (Image 2). If a concave joint surface (e.g., the proximal tibia) is moving on a fixed convex surface (e.g., the distal femur), gliding will occur in the same direction as rolling (Image 3A). Conversely, if a convex surface (e.g., the distal femur) is moving on a fixed concave surface (e.g., the proximal tibia), gliding and rolling will occur in opposite directions (Image 3B). According to this rule, the type of accessory motion at the tibiofemoral joint is dependent on whether the subject is weight-bearing (standing on a fixed tibia) or non-weight-bearing (sitting or lying down with a fixed femur).

Spin
Spinning occurs when one surface rotates clockwise or counterclockwise around a stationary longitudinal axis. This motion is similar to that of a tire rotating around its axle. Because the tibiofemoral joint is a modified hinge joint, it is able to rotate slightly. At the end of knee extension, the tibia spins laterally relative to the femur (Image 4). This movement allows the tibiofemoral joint to turn and lock, creating greater joint stability when fully extended. The spinning movement is reversed (the tibia rotates medially) to unlock the joint at the beginning of knee flexion.
Direct manual treatment of joint play and accessory motion is described as joint mobilization and is specifically excluded from the scope of practice of massage therapists in many states. However, there is still value in understanding the purpose and mechanics of accessory motion when assessing and treating issues related to range of motion. Hypomobility is often the result of reduced joint play compounded by adhesions, hypertonicity, and even neuromuscular dysfunction in the structures around a given joint. Effectively assessing the presence (or lack of) joint play and directing clients to appropriate treatment in conjunction with addressing these other issues is critical in restoring or maintaining full, normal range of motion.

Christy Cael is a licensed massage therapist and certified strength and conditioning specialist. Her private practice focuses on injury treatment, biomechanical analysis, craniosacral therapy, and massage for clients with neurological issues. She is the author of Functional Anatomy: Musculoskeletal Anatomy, Kinesiology, and Palpation for Manual Therapists (Lippincott Williams & Wilkins, 2009). Contact her at christy_cael@hotmail.com.