Issue link: https://www.massageandbodyworkdigital.com/i/841282
48 m a s s a g e & b o d y w o r k j u l y / a u g u s t 2 0 1 7 FUNCTIONAL ANATOMY 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. 2 Convex surface Concave surface 3A Femur Tibia 3B 4 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.