Step 1: Understanding Kienbock disease.
Kienbock disease is a disorder of the wrist characterized by avascular necrosis of the lunate bone.
This means that the blood supply to the lunate is compromised, leading to death of the bone tissue.
Step 2: Why lunate is most affected.
The lunate bone has a vulnerable blood supply, primarily from small branches of the radial and ulnar arteries.
When these vessels are insufficient or get damaged, the lunate undergoes necrosis, while other carpal bones usually remain unaffected.
Step 3: Clinical presentation.
Patients present with chronic wrist pain, stiffness, and decreased grip strength.
On X-ray, sclerosis, collapse, and fragmentation of the lunate bone may be observed.
Step 4: Analysis of options.
- (A) Lunate: Correct, as this is the bone affected in Kienbock disease.
- (B) Scaphoid: Commonly fractured and may undergo avascular necrosis, but that is not called Kienbock disease.
- (C) Trapezoid: Rarely involved in avascular necrosis.
- (D) Trapezium: Associated with thumb carpometacarpal arthritis, not Kienbock disease.
Step 5: Conclusion.
Thus, the lunate bone is specifically affected in Kienbock disease.