**Core Concept**
Bennett's fracture is a type of intra-articular fracture of the base of the first metacarpal bone, which involves the joint surface. The fracture occurs due to a combination of axial load and rotation forces, often resulting from a fall onto a flexed wrist. The fixation of Bennett's fracture requires precise reduction and immobilization to restore the joint surface and allow for proper healing.

**Why the Correct Answer is Right**
The muscle that hinders the fixation of Bennett's fracture is the **abductor pollicis longus (APL)**. This muscle is responsible for abducting the thumb and is closely attached to the base of the first metacarpal bone. During fixation, the tension in the APL muscle can pull the fracture fragments apart, making it challenging to achieve and maintain proper reduction. The APL muscle's action is particularly problematic in Bennett's fracture because it can cause the fracture fragments to rotate and displace, compromising the joint surface.

**Why Each Wrong Option is Incorrect**
**Option A:** **Extensor pollicis brevis (EPB)** - While the EPB muscle is also attached to the base of the first metacarpal bone, it is not as directly involved in the fixation of Bennett's fracture as the APL muscle. The EPB muscle does not have as significant a role in the rotation and displacement of the fracture fragments.

**Option B:** **Flexor pollicis longus (FPL)** - The FPL muscle is not directly involved in the fixation of Bennett's fracture. Its action is more related to flexion of the thumb, which is not a primary concern during the fixation of this fracture.

**Option C:** **Opponens pollicis (OP)** - The OP muscle is not directly involved in the fixation of Bennett's fracture. Its action is more related to opposition of the thumb, which is not a primary concern during the fixation of this fracture.

**Option D:** **Extensor pollicis longus (EPL)** - The EPL muscle is not directly involved in the fixation of Bennett's fracture. Its action is more related to extension of the thumb, which is not a primary concern during the fixation of this fracture.

**Clinical Pearl / High-Yield Fact**
When fixing Bennett's fracture, it is essential to take into account the tension in the APL muscle and to carefully reduce and immobilize the fracture to prevent rotation and displacement of the fracture fragments.

**Correct Answer:** .