Hi CarolC, Thanks for the reply.
From what you've described, it doesn't sound like "knuckling". She walks, stands, even runs normally with the exception of rare occasions when she will stand or walk a few steps with the lower portion of the front legs flat on the ground. When eating, she often stands in that position - although she can stand normally to eat as well. If it matters, this is a condition that she's had for several years, but it seems to occur more frequently now.
Viewing the anatomy in the attached link, I see now what I was calling the knee is the actually a "wrist". On our dog, the part of the leg below the wrist joint (?the pastern?) bends back toward the rear legs so it is flat on the ground.http://www.google.com/imgres?imgurl=htt ... CAsQ9QEwAQ
It just occurred to me that she may be feeling pain caused by bruising at the wrist joints. With her very short legs & age, it is difficult for her to jump up over a door stoop. Although we always carry her in & out to go to the yard, she tries to jump the garage door stoop on her own. As a result, she bangs her front leg wrists against it (ouch).