Rocking the straight leg of a supine recipient primarily affects the ____ joint.

Rocking the straight leg of a supine recipient primarily affects the hip joint due to the mechanics of leg movement and the anatomical structure of the hip. When performing the rocking technique, the hip joint acts as the primary pivot point, allowing for flexion and extension at the joint. This motion engages the hip muscles and can enhance circulation, promote relaxation, and increase the range of motion in that area.

While the knee and ankle joints are involved in the overall movement of the leg, the hip is the main joint that experiences the most significant impact during the rocking motion. The shoulder is not directly engaged in this technique, as it pertains to the movement of the lower body rather than the upper body. Thus, the hip joint is correctly identified as the primary joint affected.