Glad I found this post and I'm not the only one.  I was out at the driving range a couple days ago and suddenly my middle knuckle on my right hand started killing me and I had to stop.  As far as I know I don't have any arthritis.  The knuckle just got swollen and very painful to bend.  It could be my grip because I interlock my pinkies.  I noticed that it puts more pressure on my middle finger to grip that way.  Once my knuckle gets better I'm going to try not locking...