Musculoskeletal strain: This is the most common cause of upper back pain in adolescents, often due to overuse, poor posture, or trauma from sports or daily activities. The age and presentation make this a highly probable diagnosis.

Scheuermann's kyphosis: A condition characterized by an abnormal curvature of the spine, which can cause upper back pain and is more common in adolescents.
Scoliosis: Although often asymptomatic, scoliosis can cause back pain, especially if the curvature is significant. It's a common condition in adolescents and should be considered.
Thoracic outlet syndrome: This condition, involving compression of the nerves and/or blood vessels that pass into the thoracic outlet, can cause pain in the upper back and is possible in adolescents, especially those involved in sports or activities that involve repetitive arm movements.

Spinal tumor or infection (e.g., osteomyelitis, discitis): Although rare, these conditions can be life-threatening or lead to significant morbidity if not promptly diagnosed and treated. Back pain that is persistent, severe, or accompanied by systemic symptoms like fever or weight loss should raise suspicion.
Pulmonary conditions (e.g., pneumonia, pulmonary embolism): These can refer pain to the upper back and are medical emergencies. A thorough history and physical examination are crucial to identify respiratory symptoms or risk factors for these conditions.

Osteogenesis imperfecta: A genetic disorder that affects the production of collagen, leading to fragile bones and potential for fractures or back pain.
Ehlers-Danlos syndrome: A group of disorders that affect connective tissues supporting the skin, bones, blood vessels, and many other organs and tissues, which can lead to musculoskeletal pain, including upper back pain.
Neuromuscular conditions (e.g., muscular dystrophy): Certain conditions can cause muscle weakness and pain, including in the upper back, though these are less common and typically present with other systemic symptoms.