Aetiology
Traumatic theory: micro-avulsion at the insertion of the patellar tendon (apophysis) caused by repeated traction injury.[1][5]
Circulation theory: disturbance in the circulation of the apophysis due to rapid bone growth during adolescence, leading to the inability of the apophysis to withstand traction forces from the patellar tendon.[5]
Pathophysiology
As the tibial apophysis matures, its secondary ossification centre undergoes 4 stages:
Stage 1: cartilaginous (age 0 to 11 years)
Stage 2: apophyseal (age 12 to 14 years)
Stage 3: epiphyseal (age 15 to 18 years, tubercle apophysis coalesces with the tibial epiphysis)
Stage 4: bony (age >18 years, tibial epiphyses fuses).
It is hypothesised that the disease process occurs predominantly during the apophyseal stage: the secondary ossification centre is unable to withstand forces from the patellar tendon, which leads to avulsion or fragmentation of bone or cartilage. The separated piece or pieces continue to grow and ossify, while the intervening area may become filled with fibrous tissue, resulting in a persistent non-union and formation of a separate ossicle. Alternatively, the area may heal and fuse with the rest of the apophysis, resulting in a prominent tibial tubercle.[1]
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