Osgood-Schlatter Disease: This condition is characterized by knee pain, swelling, and tenderness over the proximal aspect of the tibia, which matches the patient's symptoms. It is a common overuse injury in adolescent athletes, particularly during growth spurts.

Patellofemoral Pain Syndrome: This condition is also common in adolescent athletes and can cause knee pain, especially with activities that put stress on the knee. The absence of specific symptoms like anemia, erythema, or warmth does not rule out this diagnosis.
Medial Tibial Stress Syndrome (Shin Splints): Although more commonly associated with pain in the lower two-thirds of the tibia, some cases can present with pain more proximally, and it's an overuse injury that could be considered in an athlete.
Sinding-Larsen-Johansson Syndrome: This condition affects the distal pole of the patella and can cause knee pain in adolescents, similar to Osgood-Schlatter disease but in a different location.

Osteosarcoma: Although rare, osteosarcoma is a malignant bone tumor that can present with pain and swelling in the affected bone, which in this case could be the proximal tibia. It's crucial to consider this diagnosis to ensure timely treatment if present.
Ewing's Sarcoma: Another rare but serious condition, Ewing's sarcoma can cause bone pain, swelling, and sometimes systemic symptoms like fever. Early diagnosis is critical for effective treatment.
Infection (Osteomyelitis or Septic Arthritis): While the absence of erythema, warmth, or systemic symptoms makes infection less likely, it's a critical diagnosis not to miss due to its potential for serious complications if not promptly treated.

Chronic Recurrent Multifocal Osteomyelitis (CRMO): A rare condition characterized by recurring episodes of bone pain and inflammation, often without clear signs of infection. It can affect various bones, including the tibia.
Hypertrophic Pulmonary Osteoarthropathy: A rare condition associated with lung diseases, characterized by clubbing of the fingers, joint pain, and swelling, which could potentially cause knee pain, although it's less likely in this scenario.