Assessment of the infraspinatus spinal stretch reflex in the normal, athletic, and multidirectionally unstable shoulder

To examine neural aspects of motor control in the glenohumeral joint, this study evaluates utilization of an innate spinal segmental pathway, the spin al stretch reflex, as an investigational tool that reflects neural circuitr y. The purpose of this study was to determine if this reflex could be evoke d from the infraspinatus muscle, if the testing apparatus and protocol for elicitation were reliable, and it the reflex response varies between groups of subjects and therefore could be useful clinically. These reflex charact eristics were evaluated in the infraspinatus muscle, since rotator cuff mus cle activity in subjects with glenohumeral instability exhibits differences in electromyographic activity and coordination patterns, implicating its r ole in dynamic stability. Normal shoulders were compared with athletic shou lders and shoulders with multidirectional instability. The spinal stretch r eflex was elicited in a controlled and reliable manner. Shoulders with mult idirectional instability exhibited a more-prominent spinal stretch reflex r esponse than normal shoulders, whereas athletic shoulders exhibited a more- quiescent spinal stretch reflex response. As the spinal stretch reflex prob ably plays a role in motor control, variation in this reflex profile may re flect some differences in development that contribute to the variable expre ssion of dynamic glenohumeral stability. This study suggests that the spina l stretch reflex profile may be a useful clinical tool to assist in discrim inating between the normal and pathologic state. This information may also be useful in the evaluation of new treatment approaches exploiting spinal c ord plasticity and spinal stretch reflex mutability through neuromuscular t raining.