Aperson breaks a bone and has it set and put in a cast, but it does not heal. what would be the best thing for the doctor to investigate as a possible cause?

the bone marrow, which should have supplied the growing bone with blood
the ligaments, which should have held the ends of the bone together while it mended
the synovial fluid in the bone, which should have carried nutrients to the growing bone
the osteoblasts, which should have been building the new bone

The osteoblasts, which should have been building the new bone

Explanation:

Bones are the one of the types of connective tissues and have hard extracellular matrix. Osteoblasts are the cells that serve in formation of extracellular matrix of bones as these cells secrete collagen fibers and inorganic salts present in the matrix of bone. Hence, if a bone is not able to heal after fracture, osteoblast cells should be checked for their activity.

that scientist would be robert hooke