The answer: “Not Always”.
Yesterday we helped a young lady from western NC who had Harrington Rod fusion done years ago for idiopathic scoliosis.
She developed back pain and flat back syndrome, and had a surgeon in Tennessee  try to help her with a Dynesys motion-sparing stabilization posteriorly.
She really did not improve after that surgery, and her pain actually got worse and worse along with her kyphotic posture.
Yesterday I performed an anterior/posterior revision reconstruction for her.  
Step 1:  ANTERIOR: removing the 2 lowest discs anteriorly, and “jacking them up” using ALIF titanium cages with bone graft.
Step 2: POSTERIOR:  removed the Dynesys hardware which had actually loosened, and then did 2 posterior osteotomies, so more lordosis could be created.  I then did instrumentation connecting Harrington rod down to the iliac wings bilaterally and then placed bone graft.

This was all performed on one day, under one anesthetic.
Estimated blood loss : 1200 cc.
Blood transfused: 1 unit PRBC.
Total Surgical time:  6 hours.
Postop Location: PACU and then to Orthopaedic Spine Unit / Private Room with family.

Lordosis Correction:  from 20 degrees preop to 56 degrees intra-operatively.

We have developed some special instrumentation techniques which have improved the lordosis correction while creating stronger constructs to improve fusion rates.
Additional research is being performed in cooperation with NC State Dept Mechanical Engineering to develop better constructs and insertion technniques for complex scoliosis and revision surgery.

While there is a lot of enthusiasm right now for motion-sparing spine surgery, its use in spinal deformity and flatback deformity is probably fairly limited, since it is not necessarily fixing the deformity, nor the pain generators.

Lloyd A Hey, MD MS
https://www.heyclinic.com
Hey Clinic for Scoliosis and Spine Surgery.