A 35-year-old man presents with a one-week history of right knee pain. The injury occurred when he was trying to lift a heavy object and his leg slipped, causing a pull of his quadriceps muscle. The pain is over the patella, and he has been unable to bear weight on the right leg since the injury. He denies history of knee pain. He reports tenderness to palpation of the superolateral patella and significant patellar pain with active extension and flexion of the knee. Radiographic examination of the knee is performed.
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Radiographic examination of the patient’s right knee shows a bipartite patella. MRI was ordered to evaluate for an acute injury to the bipartite patella vs a quadriceps tendon tear. The study revealed edema between the lateral patellar fragment and the native patella, indicating a stress-related response to the pseudarthrosis of the bipartite patella. No quadriceps tear was identified.
Bipartite patella is a normal patellar variant that results from failure of the ossification centers to fuse into a single bone. A separate fragment remains attached via fibrocartilaginous tissue to the main body of the patella. Bipartite patella is most likely to occur in the superolateral region, and approximately 50% of cases are bilateral. The condition is usually asymptomatic (less than 2% become symptomatic) and found incidentally on radiographic examination. A painful bipartite patella can develop from a direct injury that disrupts the fibrocartilaginous zone or from separation forces from the extensor mechanism. Sports activities can cause these injuries, as can occupations requiring repetitive climbing, lifting, or jumping.
Although lateral and sunrise views help make the diagnosis, anteroposterior radiograph is the best diagnostic modality for visualize a bipartite patella. MRI is routinely ordered to rule out other sources of pain in symptomatic patients. Edema noted at or adjacent to the patellar fragment confirms the diagnosis.
Conservative treatment with rest, nonsteroidal anti-inflammatory drugs, and physical therapy with isometric stretching exercises is recommended initially. A brace may be worn with the knee in 30 degrees of flexion or less to reduce traction forces of the quadriceps muscles. Local steroid injection at the fibrocartilaginous junction may be performed as a last resort to potentially avoid surgery in patients with persistent symptoms. A conservative period of treatment for at least 6 months is recommended before surgery is considered.
Surgery is indicated when patients fail to respond to conservative treatment. The most common surgical procedure includes open excision of the accessory fragment. Other procedures include lateral retinacular release, vastus lateralis release, and open reduction and internal fixation.
- Atesok K, Doral MN, Lowe J, Finsterbush A. Symptomatic bipartite patella: treatment alternatives. J Am Acad Orthop Surg. 2008;16(8):455-461.
- Woon C. Bipartite patella. Available at: http://www.orthobullets.com/pediatrics/4049/bipartite-patella. Accessed August 26, 2015.