The genealogy site MooseRoots tallied the top ten middle names from 1900 until 2015 using data from the SSA. The tally is by decade. The website closed down in 2015 that's why the last tally is five years and not a full decade.
Each of the 11 and a half decades - Elizabeth, Marie, and Ann. Anne was in the top 4 times.
10 times -Lee
7 times - Louise, Lynn, and Mae. May made two appearances.
6 times - Jean
5 times - Jane, and Renee
4 times - Rose
3 times - Ruth, Nicole, Kay, Mary, Michelle, and Sue
2 times - Faith, Irene, Grace
Once - Lou, Margaret, and Dawn
I was surprised that Lee was so popular as a middle name for so long. I also thought Denice would be in there for the 1960's and 70's.