answered Dec 07, 2009 at 12:01PM
I do not know of any direct reason for a tight lumbar spine to cause a rotator cuff tear.
Rotator cuff injury can occur with overuse- a single severe incident or chronic multiple injuries.
A tight lumbar spine may prevent full motion in that area- which could cause poor mechanics from the lumbar area up the skeletal system, including the shoulders- a severe motion (throwing, etc.) without proper coordinated & compensatory motions elsewhere, may direct extreme forces to the shoulder area & may contribute to the possibility of rotator cuff stress & injury.
Normal,Total body mechanics are necessary, for proper function- especially at the extremes of activity.