"Minimally Invasive Spine Surgery" - This is what every spine surgeon claims to do. Exactly how small is it? Most so called "minimally invasive spine surgery" is actually very traumatic and damaging, from our perspective.
The problem is that "minimally invasive" "has become a trite phrase that has lost its meaning and is used by different authors to describe totally different things" Ref.(1).
Is it bigger than your fingernail, smaller than your fist? There is no specific or standard meaning.
References (1) Decision Making in Spinal Care - 1st Edition Thieme, 2007 - Our Book Chapter