Final answer:
Syndesmoses transforms into synostoses during endochondral ossification, where cartilage is replaced with bone as a person matures, changing a flexible joint into a rigid, immovable one.
Step-by-step explanation:
Syndesmoses are replaced by synostoses as a result of the process known as endochondral ossification, where cartilage is gradually replaced by bone. This typically happens as a person ages or when the growing bones in children reach maturity. In syndesmosis joints, bones are connected by bands of connective tissue, allowing for movement and flexibility. However, when the bones fully develop, and the cartilage ossifies, this flexible connection is replaced by a more stable and rigid joint, known as a synostosis, which is characterized by bones being directly fused with no movement allowed.
An example of this process can be observed in the distal tibiofibular joint. Early in life, it acts as a syndesmosis comprised of fibrous connective tissue, promoting strength and stability needed for weight bearing. As one reaches skeletal maturity, this joint may ossify, becoming a synostosis that fuses the tibia and fibula together, thus eliminating the gap and the movement between them.