**Core Concept**
The reimplantation of an amputated digit involves a series of precise and timely surgical steps to restore blood flow and function to the affected limb. One critical aspect of this process is the stabilization and fixation of the amputated digit to prevent complications and promote optimal healing.

**Why the Correct Answer is Right**
The first structure to be fixed during reimplantation is the **flexor tendon**. This is because the flexor tendons provide the necessary blood supply to the digit through the **nutrient vessels** that run within the tendon sheath. By fixing the flexor tendon first, the surgeon ensures that the digit receives a reliable blood supply, which is essential for healing and preventing tissue necrosis. The flexor tendon is typically fixed using a **Kirschner wire**, which provides stable fixation and allows for gentle tensioning of the tendon.

**Why Each Wrong Option is Incorrect**
* **Option A**: The metacarpal bone is not fixed first during reimplantation, as it is not directly related to the blood supply of the digit.
* **Option B**: The extensor tendon is not fixed first, as it is not as critical to the blood supply of the digit as the flexor tendon.
* **Option D**: The skin is not fixed first, as it is not a critical structure for blood supply and can be safely delayed until later in the procedure.

**Clinical Pearl / High-Yield Fact**
When reimplanting an amputated digit, it is essential to prioritize the fixation of the flexor tendon to ensure a reliable blood supply to the digit. This is a critical step that can make or break the success of the reimplantation.

**Correct Answer:** C.