Haven't seen the above links but a few issues to note.

1. I am not Mackenzie trained. However there are more than just extension exercises in his classifcation and treatment system.

2. A study has shown that in 30% of "normals", the disc actually moves POSTERIORLY with extension of the L/S as shown on Wikipedia reference-linkMRI (Edmondston SJ et al 2000 MRI evaluation of L/S flexion and extension in asymptomatic individuals - Manual Therapy 5(3):158-164. They postulated that this may be due to the state of the disc. Peter Fazey is currently investigating how the Nucleus Pulposus (NP)moves in rotation as well.

3. C/S discs have no fluid. it is more like fibrocartilage. Mercer and Bogduk 1999 The ligaments and annulus fibrosus of human adult cerical IVD - Spine 24(7):619-626. So it is unlikely that the fragment that "bulges" in the C/S is a fluid filled NP pushing on the AF (annulus fibrosus).

Hope that helps! Abstracts for the above articles can be found at PubMed (Medline) - the free Medline