Final answer:
Most synovial joints are diarthroses, allowing for free movement. These joints have a synovial cavity and are categorized into uniaxial, biaxial, or multiaxial, based on their axes of motion.
Step-by-step explanation:
The correct completion for the given statement is: Most synovial joints are diarthroses. Synovial joints are characterized by the presence of a synovial cavity, which allows the articulating bones within to move freely. As mentioned, synovial joints represent the category known as diarthroses in the functional classification, which are joints allowing for free movement. These joints are further categorized based on the number of movement axes they provide: uniaxial (movement in one plane), biaxial (movement in two planes), or multiaxial (movement in all three anatomical planes). Synovial joints are capable of a wide range of motions, which are essential for the mobility of the appendicular skeleton. Examples of such joints include the knees, elbows, and shoulders.