**Core Concept**
Tuberculous spondylitis, also known as Pott's disease, is a form of osteoarticular tuberculosis that primarily affects the spine. It is characterized by the destruction of the intervertebral disc and adjacent vertebral bodies, leading to instability and potential deformity. In adolescents, the disease can cause significant morbidity and long-term sequelae.

**Why the Correct Answer is Right**
Bony ankylosis is the most common sequelae of tuberculous spondylitis in adolescents due to the body's attempt to stabilize the affected spine. This occurs as a result of the fusion of adjacent vertebrae, which is a natural response to the destruction of the intervertebral disc and adjacent vertebral bodies. The fusion process is often accompanied by the formation of a bony bridge, which can lead to a loss of spinal mobility. The pathophysiology of tuberculous spondylitis involves the invasion of Mycobacterium tuberculosis into the vertebral bodies, leading to caseous necrosis and destruction of the surrounding tissue.

* **Option A:** Fibrous ankylosis is incorrect because it is a rare sequelae of tuberculous spondylitis. Fibrous ankylosis is a type of ankylosis that occurs due to the formation of fibrous tissue, whereas bony ankylosis is the more common and characteristic outcome of tuberculous spondylitis.
* **Option C:** Pathological dislocation is incorrect because it is a potential complication of tuberculous spondylitis, but not the most common sequelae. Pathological dislocation can occur due to the destruction of the surrounding tissue and the loss of spinal stability.
* **Option D:** Chronic osteomyelitis is incorrect because it is a separate condition that can occur in conjunction with tuberculous spondylitis, but it is not the most common sequelae of the disease.

**Clinical Pearl / High-Yield Fact**
It is essential for physicians to recognize the potential long-term sequelae of tuberculous spondylitis, including bony ankylosis, and to implement appropriate management strategies to prevent deformity and maintain spinal stability.

**✓ Correct Answer: B. Bony-ankylosis**