Lengthening of long bones ceases when the epiphyseal plate undergoes closure; typical ages: females around 18 years, males around 21 years.

• A. Epiphyseal plate closure
• B. Periosteal thickening
• C. Medullary cavity expansion
• D. Cartilage calcification

Answer: (A)

Growth in length for long bones happens at the epiphyseal growth plate, where cartilage is continually produced and gradually ossified to add bone length. When the plate closes, the cartilage is fully replaced by bone and a bony line remains, signaling that no more growth in height is possible. This closure is what ends lengthening, which is why the typical ages differ by sex—earlier in females (around 18) and a bit later in males (around 21) due to hormonal puberty timing.

Other processes don’t halt length growth in the same way. Periosteal thickening adds bone to the outside and increases bone diameter rather than length. Medullary cavity expansion relates to changes inside the shaft during remodeling, not to stopping growth in height. Cartilage calcification is a normal part of turning cartilage into bone, but it’s the completion of that process and the formation of the epiphyseal line that ends lengthening.