An 8-year-old girl injures her knee. Her mother asks why the kneecap looks small on the radiograph compared with an adult. The patella differs from most other large sesamoid bones in that it:
- A Ossifies from a centre present at birth
- B Ossifies between 3 and 6 years of age, earlier than other sesamoids ✓
- C Never completes ossification
- D Ossifies only after skeletal maturity is reached
Correct answer: B. Ossifies between 3 and 6 years of age, earlier than other sesamoids
Explanation
The patella, the largest sesamoid bone in the body, ossifies from multiple centres appearing between 3 and 6 years of age and fusing rapidly thereafter. All other sesamoid bones, such as those beneath the first metatarsal head, characteristically ossify at puberty. It forms within the quadriceps tendon and articulates exclusively with the femur. This timing difference explains the small patella seen on a child's radiograph and separates it from the general pubertal rule for accessory sesamoids.
Reference: Gray's Anatomy for Students, 4th ed.
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Written and medically reviewed by the StethoPrep medical team.