The line of pull in a static progressive orthosis with an outrigger should be at what degree to avoid shearing?

• A. 90 degrees
• B. 60 degrees
• C. 135 degrees
• D. 0 degrees

Answer: (A)

To gain controlled ROM with a static progressive orthosis and an outrigger, the force should create a pure bending moment about the joint while minimizing shear on the soft tissues and joint surfaces. Positioning the line of pull roughly perpendicular to the segment (about ninety degrees) maximizes the rotational moment about the joint, making extension or flexion gains more efficient and reducing shear forces. If the pull is more aligned with the bone (closer to zero degrees) or at odd angles, more of the force translates into shear or translation at the joint, which can irritate tissues and be less effective for ROM. Angles like sixty or one hundred thirty-five degrees mix torque with shear and are not as ideal. Therefore, aim for a line of pull at about ninety degrees.