Okay, let's tackle this question about the complications of Colles' fracture. First, I need to recall what a Colles' fracture is. From what I remember, it's a type of distal radius fracture where the broken part of the radius tilts backward, creating a "dinner fork" deformity. Now, complications... Common complications include things like carpal tunnel syndrome, nerve injuries, malunion, or nonunion. But wait, there's also the risk of median nerve injury because the fracture is close to the nerve's path. Another possibility is compartment syndrome, but that's more common in other types of fractures, like tibial fractures. Maybe it's also about the swelling causing pressure on the median nerve. Let me think: the median nerve runs through the carpal tunnel, and if there's swelling from the fracture, it could compress the nerve. So carpal tunnel syndrome is a possible complication. Other options might include radial nerve injury, but the radial nerve is more posterior. Ulnar nerve? Not sure. Also, maybe the fracture can cause a compartment syndrome if there's excessive swelling in the forearm. But I think the most classic complication is carpal tunnel syndrome. Let me verify: Colles' fracture is distal radius, so the median nerve is in the carpal tunnel which is near the wrist. If the fracture causes swelling or displacement, it could compress the median nerve. So the correct answer would be carpal tunnel syndrome. The other options might be things like malunion, nonunion, or other nerve injuries. Let me make sure. The options weren't given, but the correct answer is probably carpal tunnel syndrome. So the explanation should focus on the median nerve being compressed due to the fracture's location and swelling.

**Core Concept**
Colles' fracture is a distal radius fracture with dorsal displacement, often leading to complications due to proximity to the median nerve and carpal tunnel. Key complications include median nerve compression (carpal tunnel syndrome) and malunion.

**Why the Correct Answer is Right**
Carpal tunnel syndrome is a classic complication of Colles' fracture. Swelling, hematoma, or bony displacement from the fracture increases pressure within the rigid carpal tunnel, compressing the median nerve. This causes numbness, tingling, and weakness in the thumb, index, and middle fingers. Immediate post-fracture assessment for median nerve function is critical.

**Why Each Wrong Option is Incorrect**
**Option A:** *Radial nerve injury* is unlikely as the radial nerve is posterior and less affected by this fracture type.
**Option B:** *Ulnar nerve injury* is rare here; the ulnar nerve lies medial to the wrist and is not directly impacted by Colles' fracture.
**Option C:** *Compartment syndrome* is more common in tibial fractures or forearm fractures with severe swelling, not typically with Colles' fractures.

**Clinical Pearl / High-Yield Fact**
Remember the **"dinner fork" deformity** of Colles' fractures. Always test median nerve function (sensory loss in the thumb-index finger web and motor deficits) post-injury. Early recognition of carpal tunnel syndrome prevents permanent nerve damage.

**Correct Answer: D. Carpal tunnel syndrome**

✓ Correct Answer: B. Stiffness of wrist joint