Figure 1. Anteroposterior radiograph of the left knee.
Figure 2. Lateral view of the left knee.
Figure 3. Merchant view.
A 28-year-old man presents with left knee pain after a fall 5 days prior. He was stepping off his truck and his knee hit a steel railing. He reports “a fair amount of pain” after the fall but since then has been able to walk and the pain is improving. On physical examination, the patient has no pain over the patella and is able to do straight leg raises without discomfort. He initially visited an urgent care center and was diagnosed with a patella fracture (Figures 1-3). He was placed in a knee immobilizer with crutches.
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The patient has a classic bipartite patella on radiographs, which was misdiagnosed as a patella fracture at the urgent care clinic. A bipartite patella is a congenital abnormality caused by failure of the patella growth plate to fuse. The abnormality is usually asymptomatic and found incidentally on imaging.1
The radiograph of a bipartite patella classically shows a bony island at the superolateral pole of the patella. The majority of abnormalities are located at the superolateral portion (75%) of the patella, 20% are located on the lateral margin, and 5% are on the inferior pole.1 A bipartite patella has smooth edges in between the bony island and main patella, which helps differentiate it from a fracture.1,2
A painful bipartite patella is rare and may be caused by a traumatic injury to the knee that disrupts the fibrocartilaginous connection between the main patella and accessory fragment.2 The presence of edema on magnetic resonance imaging (MRI) along the fibrocartilaginous connection can confirm an acute injury.1 Surgical excision of the accessory bone is only considered in patients with persistent pain beyond 6 months.2 Initially, patients should be treated with ice, oral nonsteroidal anti-inflammatory drugs, and activities to tolerance.1,2
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor in chief of the Journal of Orthopedics for Physician Assistants.
1. Berger RJ, Yen YM. Bipartite patella. OrthoBullets. Accessed September 12, 2022.
2. Iossifidis A, Brueton RN. Painful bipartite patella following injury. Injury. 1995;26(3):175-176. doi:10.1016/0020-1383(95)93496-5