Years ago, when doing scoliosis screening on pre-school children  I noticed that most of the time they had an asymmetric pelvis that tilted the sacrum laterally, unleveling the sacral base, initiating the lateral spinal curves and causing the scoliosis.  This may occur without painful symptoms.  Correcting the asymmetric pelvis with a manual posterior innominate rotation also corrects the scoliosis.

With normal gait in the long straddle position when the pelvis is asymmetrical the sacrum flexes laterally toward the side of loading to drive counter rotation of the trunk, which decreases the loading forces to the femoral head.

This is a commonly overlooked problem associated with low back pain when the line of gravity is shifted forward to the acetabular axis causing an anterior innominate rotation on the sacral axis with asymmetry and fixation. 

Tingren J, Soinila S: Reversible pelvic asymmetry, J of Manipulative and Physiological Therapeutics, September 2006

DonTigny, RL:  A detailed and critical biomechanical analysis of the sacroiliac joints and relevant kinesiology: the implications for lumbopelvic function and dysfunction.  In Vleeming A, Mooney V, Stoeckart R (eds): Movement, Stability & Lumbopelvic Pain: Integration of research and therapy. Churchill Livingstone (Elsevier). Edinburgh, 2007, PP 265-279

 DonTigny RL: Pelvic Dynamics and the Subluxation of the Sacral Axis. CD-ROM. Bozeman, Montana, (c) registered 2001 and continuously revised through 2016

DonTigny RL: Sacroiliac 101: Form and Function - A Biomechanical Study. J of Prolotherapy. 3(1): 561-567, 2011 

DonTigny RL: Sacroiliac 201: Dysfunction and Management A biomechanical solution,  J of Prolotherapy, 3(2): 644-652, 2011

of course, the other possibility of blaming biomechanics is that the physiology is far more complex than having an apparent leg length difference. An overactive gene, called ladybird homeobox 1 (LBX1), is the start of a genetic chain reaction that causes the spine to grow abnormally, but of course, you all knew about that.

If one examines any high level tennis player it will be apparent one arm is more developed.  The stress on the dominant arm prompts the growth of bone and muscle to better " become competent " to perform the high demand duty of hitting the tennis ball.

This growth may happen by intermittent muscle contraction and/or isometric contraction - as is the case with an overactive muscle spindle cell which keeps a muscle in partial contraction (hypertonus) 24/7.

This tendency ( epigenetics ) will also cause muscle to waste away if there is no demand to maintain it's use ( "competence" ).

In the case of spine deformation we can see that :

#1 The hypertonus muscle will get larger often, - because it is getting "exercised" 

#2  An uneven bone length or joint problem causes the body to build up a compensating muscle or muscle group.  This may result in a cascade of problems.

Often it is quite easy to feel the contrast of a muscle group ( side-side ).

I would offer wry neck as an example, - which may be treated using botox to reduce the activate of the over developed muscle tissue.   There is of course some evidence that botox may cause nerve damage in the long term.

please search my article on ' Floor activities and degenerative spines'