Figure 1. Potential sites for sensory and motor impairments associated with supraspinatus tendon tear.

Tendon tear, soft tissue and/or joints damage, and local inflammatory environment sensitize peripheral nociceptors (mechanical or chemical high-threshold peripheral nociceptors (e.g. Free endings) that cause pain and increase the sensitivity of central pain centers (peripheral and central sensitization, respectively). They may also induce impairments in proprioceptive outputs (Muscle spindles; Golgi tendon organ, Ruffini endings; Pacinian corpuscles) and in the central processing of proprioceptive information (proprioceptive pathways; primary sensory cortex. Motoneurons innervating both extrafusal and intrafusal muscle fibers (α- and γ– motoneurons, respectively) may equally undergo remodeling and impairments. Neuromuscular junction may also be altered as a result of reduced neural activity, muscle impairments, and central alterations within the motor nervous system. At the nerve level, stretch and/or compression caused by muscle retraction, mass compression, and manipulation of the previously retracted muscle or direct nerve manipulation during surgery can result in injury of both sensory and motor axons. The suprascapular nerve may be damaged at any point of its path but the suprascapular notch and the cervical roots are identified as the most common sites for injury. Nerve(s) damage can further increase pain, limit the afferent transduction of proprioceptive information, and aggravate muscle changes.