What is the most likely diagnosis for a 15-year-old basketball player with painful lumps on the knees and light growth on the upper tibia midline below the kneecap, with full range of motion and no joint tenderness?

Osgood-Schlatter Disease

This 15-year-old basketball player most likely has Osgood-Schlatter disease (OSD), a self-limiting traction apophysitis of the tibial tubercle that is the most common cause of anterior knee pain in adolescent athletes. 1, 2

Clinical Presentation Matches Classic OSD

The clinical picture is pathognomonic for Osgood-Schlatter disease:

• Painful lumps on both knees at the tibial tuberosity (the "light growth on the upper tibia midline below the kneecap") is the hallmark finding of OSD 1, 3
• Age 15 years falls within the peak incidence range of 12-15 years for males 1
• Basketball player - OSD occurs in adolescent athletes participating in high-impact sports involving jumping and running 1, 4
• Full range of motion with no joint tenderness - this distinguishes OSD from intra-articular pathology, as OSD is an extra-articular apophysitis that does not affect joint mobility 3
• Bilateral involvement is common in OSD 4

Why This Is NOT Other Conditions

The presentation excludes other serious pathology that must be considered in adolescents with bone pain:

• Not osteosarcoma or Ewing sarcoma: While bone sarcomas occur in adolescents (peak age 15 years for Ewing sarcoma, 15-19 for osteosarcoma), they present with persistent non-mechanical pain, often with night pain, and would show progressive swelling if the tumor extends through the cortex 5
• Not Blount disease (tibia vara): This presents as tibial bowing and is associated with severe obesity (mean BMI ~35-41 kg/m²), not localized tibial tuberosity prominence 5
• Not slipped capital femoral epiphysis: This affects the hip, not the knee, and would present with limited hip range of motion 5

Diagnostic Approach

The diagnosis of OSD is primarily clinical and does not require imaging in typical presentations: 1, 2

• Pain localized to the tibial tuberosity is the most agreed-upon diagnostic criterion (97% of healthcare professionals consider this essential) 2
• Pain exacerbated by jumping, running, or stair climbing is characteristic 3, 4
• Palpable prominence or swelling at the tibial tuberosity on examination 1, 3

If imaging is obtained, radiographs may show superficial ossicles in the patellar tendon, but this is not necessary for diagnosis 3. Ultrasound findings in OSD include increased tendon thickness and Doppler signal at the tendon and tuberosity, but these are research findings rather than clinical requirements 4.

Management Strategy

Conservative management is successful in over 90% of patients and should be the initial approach: 1, 3

• Patient education (99% of clinicians use this) explaining the self-limiting nature of the condition 2
• Exercise therapy focusing on quadriceps and hamstring stretching (92% of clinicians recommend this) - particularly addressing rectus femoris shortening which alters knee biomechanics 6, 1, 2
• Activity modification based on pain intensity - managing training load is considered critical by 97% of clinicians 2
• Symptoms typically resolve with skeletal maturity (physeal closure) 1, 3

Critical Pitfall to Avoid

Do not assume all anterior knee pain in adolescents is benign OSD. If the patient has persistent non-mechanical pain lasting more than a few weeks, night pain, systemic symptoms, or progressive swelling without the characteristic tibial tuberosity localization, consider bone sarcoma and obtain plain radiographs in two planes as the first investigation 5. However, this patient's presentation with bilateral tibial tuberosity prominence, activity-related pain, preserved range of motion, and no joint tenderness is classic for OSD rather than malignancy.