Overhead Perturbation Training for Glenohumeral Joint Instability

Overview

The purpose of the trial is investigate the benefits of a novel, newly invented exercise technique protocol relative to physiological changes in upper limb proprioception (primary) and subjective readiness for return to sport (secondary). The intervention (Overhead perturbation training) will be compared with a control intervention (non-perturbed stimulus) in a population of type II anterior glenohumeral joint instability patients (according to the Stanmore classification of instability). Each group will be assessed at baseline for glenohumeral joint proprioception (via lazer-pointer active relocation test), as well as perceived functional level (via Western Ontario Shoulder Instability index) and Shoulder Instability-Return to Sport after Injury (SIRSI) score. They will then undertake a 6 week exercise regime which is exactly the same- except the intervention used perturbated stimulus and the control uses non-perturbed stimulus. Outcome measures are re-assessed at the end of the intervention period. Results will be assessed statistically for statistical significance.

Overhead athletic performance requires both static and dynamic mechanisms to coordinate glenohumeral and scapulothoracic stability to induce the appropriate motor response. Active function is predicated on a sufficient balance of muscular strength, endurance, flexibility and neuromuscular response to proprioceptive input. Coordinating, planning and synthesising complex multi-joint information is a process within the central nervous system, from the periphery to the higher centres of the brain, in a synergy of afferent and efferent feedback. Joint position sense plays an important role for the shoulder joint in two key components of athletic performance: conscious limb placement and unconscious motor patterning in response to external force during movement. Such motor patterns can be characterised as the motor responsiveness to perturbations of joint position. This assists efficiency of muscular coordination when the shoulder is placed in the long lever position during overhead activities, where the desired motor pattern reaction is essential alongside contractile strength for successful performance and attenuation of injury risk. It is suggested that efficiency in neuromuscular control to provide responsive stabilization is necessary to sustain high levels of overhead performance and to avoid injury. The neuromuscular control response of the shoulder musculature on glenohumeral and scapulothoracic joint positions becomes deficient in the presence of structural injury. For example, rotator cuff injury specifically leads to deficiencies in neuromuscular control timing, patterning and strength compared with asymptomatic clients. Perturbation of upper limb position during overhead activities causes unpredicted change in tissue length, resulting in a responsive pattern of muscular contractions. The OPT exercise series ensures that the deficient client is exposed to positions of vulnerability against displacement of the limb by external force. It is postulated that neural adaptations are induced through introduction of both rhythmic and sudden alterations to these positions A training stimulus (such as OPT) which facilitates neuromuscular control and speed of response to perturbation has potential to enhance overhead function. This signifies the role of neuromuscular control training in both rehabilitation and prevention of shoulder joint injury. The inclusion of this type of exercise training during rehabilitation and as part of injury risk minimisation strategies is an important component to sustain synchronization of muscular movement patterns. Population in Focus The subjects recruited for this study will be explained in greater depth further in the proposal, however are characterised by having a degree of functional glenohumeral joint instability. The physiotherapy class setting which will be utilised as the source of referrals is a heterogenous group of upper limb disorder patients, with a distinct sub group of individuals with functional instability who achieve sufficient recovery to meet the criteria for return to sport. According to the Stanmore classification of shoulder instability this group would correspond to Polar type II-III- that is placed on a continuum between atraumatic structural instability and non-structural, muscle patterning instability. Current treatment versus OPT The optimal management of anterior shoulder instability in those who undertake sport continues to be a challenge. Exercise therapy rehabilitation in a structured protocol shows statistically significant changes in validated outcome measures (Oxford Instability Shoulder Scores and Western Ontario Shoulder Index scores) but fails to incorporate exercise at the point of most instability through range of motion, particularly with sufficient challenge to the neuromuscular system to promote adaptation against perturbation at this point. Of course OPT is not suggested to replace traditional measures of exercise therapy, but instead is designed to complement and optimise rehabilitation. By influencing both the physical and psychometric obstructions to return to activity, the OPT aims to improve patient care and enhance quality of life in its users. This has the additional benefit of streamlining the care pathway of this patient population, and in preparing them to return to higher levels of function, will potentially reduce recurrence of future injury. The pathway for these patients is optimised and made more efficient by providing the same amount of therapist contact, in a class setting to incorporate multiple users at once, but should enhance post intervention clinical scores. The application of similar programmes as a component of rehabilitation is already considered elsewhere; however the specific nature of OPT is suggested to enhance even these currently used protocols.