What is the difference between a "type I" lunate and a "type II" lunate?
The "type I" lunate articulate only with one distal carpal bone -- the capitate. The "type II" lunate articulates with two distal carpal bones -- the capitate and hamate.
What may develop from a type II lunate configuration? Why is there bone marrow edema in the hamate?
The type II lunate leads to altered mechanics in the wrist, resulting in accelerated cartilage loss at the hamate-lunate articulation and impingement with bone marrow edema (the abnormal signal).
There is a small facet between the lunate and the tip of the hamate, with abnormally decreased T1 and increased T2 signal in the proximal hamate.