What causes severe medial ankle pain in teens?

Ankle pain: Most common causes of ankle pain are injuries to ankle (resulting in sprains, stress fracture), achilles tendonitis other un common causes are arthritis, gout most ankle pain reponds to rest, ice, elevating foot and immobilization if pain persists needs to see your physician.

Medial ankle pain: It depends. Did they sprain their ankle ? Also do they have flat feet? Cause a teen with flat feet can develop posterior tibial tendonitis.

Shin splints.: It could be shin splints, a condition of soft tissue irritation against the lower leg bone. Particularly if they're still growing.

Depends: There are too many sources of ankle to pain list here. The treatment and the ability to control it would depend on an accurate diagnosis and workup. See a foot and ankle specialist for the right plan.