"1)Ruptured fibers can no longer sustain a load; thus increased loads are placed on neighboring fibers, making them more susceptible to rupture.
2) Disruption of the tendon fibers also disrupts local blood supply within the tendon, thus inducing ischemia.
3) Disrupted tendon fibers are exposed to joint fluid, which has a lytic effect on tendons that impairs the healing process.
4) When tendons heal, the scar tissue that replaces the ruptured tendon fibers does not have the same tensile strength as the original tissue; thus it is a increased risk of failure.
5) Once a tear becomes full thickness, loads that normally are distributed through the entire intact tendon often are transmitted at the torn margins of the rotator cuff tendon. This process produces a "zipper effect" and extends or unzips the tendon from the tuberosity. "
From the information above, it is evident that in many instances, partial thickness rotator cuff tears progress to full thickness tears. The physiologic tissue structure following an injury has changed. The blood flow and tensile strength of that tissue has been permanently altered. It does appear that partial tears do progress. So where does this leave us?
Fortunately, the physical therapy paradigm is shifting from a pathoanatomic to a pathokinesiologic model. Despite having a partial rotator cuff tear, patients can respond positively with conservative management. By addressing capsular mobility deficits, scapulohumeral strength and flexibility problems, and the presenting movement dysfunction, surgery is not always indicated following a rotator cuff tear. The Secrets book also states that variable amounts (33-90%) of individuals demonstrate improvements in pain and overall function despite having a full thickness rotator cuff tear.
Not all patients will succeed with conservative management, but address your primary impairments and movement dysfunction and you will be able to decrease patient's pain and improve their function.
Placzek, Jeffrey D., and David A. Boyce. Orthopaedic Physical Therapy Secrets. St. Louis, MO: Mosby Elsevier, 2006. Print.