Bipartite Patella: A Rare Anatomical Variant Mimicking Patellar Fracture

INTRODUCTION–OBJECTIVE:

The patella is the largest sesamoid bone in the human body and typically develops from a single ossification center

at approximately 2–3 years of age. The presence of two or more ossification centers is observed in about 15% of

cases. A secondary ossification center usually appears between the ages of 10 and 12 and fuses with the patella

during adolescence. Failure of this secondary ossification center to fuse results in a condition known as bipartite

patella(accessory patella). The prevalence reported in the literature ranges between 0.8% and 2%, and it is

observed three times more frequently in males than in females. Radiological diagnosis can be established using

radiography, computed tomography(CT), or magnetic resonance imaging(MRI). Although numerous radiological

and orthopedic studies on bipartite patella exist in the literature, studies evaluating this anatomical variant from a

forensic medical perspective are limited. The aim of this study is to present the forensic medical evaluation of a

case initially diagnosed as a patellar fracture following a fall from the open door of a moving city bus, but later

identified as bipartite patella.

CASE:

A 13-year-old male patient presented to the Emergency Department with complaints of pain and mild swelling in

the left knee after falling from the open door of a moving city bus. Physical examination revealed a 2 cm laceration

under the chin, a 1 cm abrasion on the left knee, tenderness, and minimal edema. Based on left knee radiography

and CT performed in the Emergency Department, a diagnosis of patellar fracture was made and the patient was

discharged after immobilization with a splint. Seven days after the incident, the patient was referred for a definitive

forensic report. During the evaluation, bilateral knee radiographs and left knee CT demonstrated bipartite patella

in both patellae, with no evidence of traumatic findings or fracture lines.

DISCUSSION–CONCLUSION:

Bipartite patella is considered an anatomical variant and is usually detected incidentally. It is bilateral in

approximately 30–40% of cases and is more frequently observed in males. According to the location of the

accessory fragment, bipartite patella is classified as Type I(5%) when located inferiorly, Type II(20%) when

located laterally, and Type III(75%) when located superolaterally. In the present case, the accessory fragment was

located superolaterally and was therefore classified as Type III. According to the Turkish Penal Code, if an injury

results in a bone fracture, the penalty imposed on the offender may be increased; therefore, accurate identification

of fractures is of critical importance in forensic evaluations. Consequently, in cases of knee trauma, detailed

clinical examination, evaluation of bilateral radiographs, and, when necessary, further assessment with CT or MRI

through a multidisciplinary approach are essential to avoid misinterpretation of anatomical variants such as

bipartite patella as fractures. This approach may prevent misdiagnosis and potential errors in forensic medical

assessments.

Keywords: Bipartite patella, fracture, forensic radiology