**Core Concept**
A transverse fracture of the patella with separation of fragments is a type of patellar fracture that requires precise treatment to restore patellar function and prevent long-term complications. This condition often occurs due to high-energy trauma, such as a fall from a height or a direct blow to the patella.

**Why the Correct Answer is Right**
The best treatment for a transverse fracture of the patella with separation of fragments is open reduction and internal fixation (ORIF). This involves surgically reducing the fracture fragments and stabilizing them with screws, wires, or plates to allow for early mobilization and rehabilitation. The goal of ORIF is to restore the normal anatomy of the patella, alleviate pain, and prevent complications such as patellar malalignment, arthritis, or quadriceps weakness.

**Why Each Wrong Option is Incorrect**
**Option A:** Closed reduction and percutaneous pinning is often used for non-displaced or minimally displaced patellar fractures, but it may not be sufficient for a transverse fracture with separation of fragments.

**Option B:** Patellectomy, or removal of the patella, is a last-resort option for severe patellar fractures or those with poor bone quality, but it can lead to long-term complications such as quadriceps weakness and patellar tendonitis.

**Option C:** Casting and immobilization may be used for non-displaced patellar fractures, but it is generally not effective for transverse fractures with separation of fragments, which require more aggressive treatment to restore patellar function.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the timing of surgical intervention is critical in the treatment of patellar fractures. Early ORIF, typically within 7-10 days of injury, can lead to better outcomes and reduced complications.

**Correct Answer: A. Open reduction and internal fixation.**