The most common sequelae of tuberculous spondylitis in an adolescent is-
The usual outcome of healed tuberculosis in the spine is the bony ankylosis, in contrast to any other site in the body, where fibrous ankylosis is the usual outcome.

"Spine is the only site where tuberculosis heals with bony ankylosis". Tuli
Fibrous Ankylosis
Bony-Ankylosis
Pathological dislocation
Chronic osteomyelitis