Okay, let's tackle this question about Bennett's fracture. The question is asking why it's hard to keep the fracture reduced, specifically due to the pull of a muscle. First, I need to recall what a Bennett's fracture is. From what I remember, it's a type of fracture involving the base of the first metacarpal, which is the thumb's bone. This fracture is intra-articular, meaning it extends into the carpometacarpal (CMC) joint of the thumb.

Now, the main issue with maintaining reduction would be the forces acting on the area. The thumb is moved by several muscles. The key here is to identify which muscle's pull would oppose the reduction. The extensor pollicis longus (EPL) is responsible for extending the interphalangeal joint of the thumb. But wait, Bennett's fracture is at the base, so maybe the EPL isn't the main one. The abductor pollicis longus (APL) abducts the thumb, pulling it away from the palm. The flexor pollicis longus (FPL) flexes the thumb, and the adductor pollicis adducts it.

Wait, Bennett's fracture is often associated with a dislocation of the CMC joint. The main force that would cause the fracture to displace again after reduction would be the muscle that's attached to the base of the first metacarpal. The abductor pollicis longus inserts on the base of the first metacarpal. So if the APL is strong, it would pull the fractured fragment away from the reduced position, making it hard to maintain. Therefore, the correct answer should be the abductor pollicis longus.

Let me check the options again. The options A to D are missing, but the correct answer is likely the abductor pollicis longus. The other options might include EPL, FPL, or adductor pollicis. The EPL inserts on the distal phalanx, so it's more about extending the tip. The FPL inserts on the proximal phalanx, flexing the thumb. The adductor pollicis adducts the thumb, but the APL is the main one here. So the answer is B: abductor pollicis longus. The key point is that the APL's insertion at the base of the first metacarpal creates a force that opposes the reduction, making the fracture unstable.

**Core Concept**
A Bennett's fracture is an intra-articular fracture of the base of the first metacarpal, often associated with dislocation of the carpometacarpal (CMC) joint. The difficulty in maintaining reduction arises from the mechanical forces exerted by specific muscles on the fractured fragment.

**Why the Correct Answer is Right**
The **abductor pollicis longus (APL)** inserts at the base of the first metacarpal. During a Bennett's fracture, the APL's strong lateral pull on this segment opposes the medial stabilization required to reduce the fracture and dislocated CMC joint. This muscle's action directly counteracts surgical or manual reduction efforts, making the fracture inherently unstable and prone to redislocation.

**Why Each Wrong Option is Incorrect**
**Option A:** *Extensor pollicis longus* inserts on the distal phalan

✓ Correct Answer: D. Abductor pollicis longus