Final answer:
The considered a locked position in the sacroiliac joint is Nutation of sacrum. The correct answer is options A.
Step-by-step explanation:
Joints are classified based on their structures and functions. Based on structures, joints are classified into three, these are fibrous, cartilaginous and synovial joints. The fibrous joints is made up of connective tissues which can not move, for instance, sutures.
Based on fuctions, the joints are divided into three, which are: synarthroses, amphiarthroses and diarthrosis. The synarthroses joint is made up of fibrous joints.
Nutation and counternutation refer to the subtle movements of the sacrum, which is the triangular bone at the base of the spine. Nutation occurs when the sacrum tilts forward and downward. In contrast, counternutation is the opposite motion when the sacrum tilts backward and upward.