We report the case of a young boy who presented a dorsal defect of the patella (DDP) with fracture after a small sport trauma. The patient's parents (professional of health care) had been warned on a possible tumoral disease in a previous consultation and claimed for an accurate diagnosis. Although fracture is rarely reported in DDP, the radiographic image strongly suggested this condition; nevertheless, the diagnosis accuracy requested by the parents lead to indicate a biopsy that showed irregular fragments of laminar bone and hyaline cartilage islands similar to articular cartilage compatible with a non-specific developmental ossification defect. The lytic defect was filled with morselized cancellous bone graft, the fracture having a normal consolidation. With a follow-up of 4 years, the patient is asymptomatic, and the radiological morphology of the patella is normal. Although DDP is accepted to be a radiologically well-defined condition, images may perhaps not get accuracy enough for diagnosis and biopsy may be indicated by clinical and radiological features different than the typical ones. Although fracture is rarely reported in case of DDP, it has not to be considered as indicative of tumor or malignancy.