Valutazioni strumentali e outcome di pazienti operati di protesi inversa di spalla: nuovi approcci e nuove prospettive.

The study conducted on the reverse shoulder arthroplasty has been divided into two related research branches: STUDY N. 1 Aim: In case of massive and irreparable rotators cuff damage, with shoulder joint pseudoparalysis, a therapeutic option is represented by the implant of a reverse shoulder arthroplasty (RSA). It consists in the alteration of the normal anatomy of the shoulder and, in particular, it implies the application of a sphere, called Gleno-sphere, which replaces the normal glenoid concavity, and the realization of a concavity at the level of the convex surface of the humeral head, thus creating an anatomical overturning. Hence, with respect to a standard anatomic prosthesis, the innovative design of the Grammont prosthesis changes the anatomical profiles of the humeral and glenoid joint surface. Due to this new anatomic structure, and without the support of the supraspinous muscle (that is one of the rotators cuff), the glenoid humeral movement is completely managed by the deltoid (by exploiting the action of the deltoid in the elevation and abduction of the shoulder), with the eventual support of the teres minor. It is therefore necessary to acquire new motor patterns for the execution of the scapular-humeral movements. This study aims at measuring the length of their acquisition by the central nervous system, in presence of a prosthesis that modifies the standard shoulder joint anatomy, through different rehabilitative approaches: neuro-motor personalised rehabilitation vs rehabilitation through a standard rehabilitative protocol. The experimental hypothesis that stands behind this goal is that a neuro-motor rehabilitative procedure that uses “biofeedback” is more suitable and effective in the acquisition of new motor patterns by patients who have to acquire ex novo a motor scheme. Comparing the two functional recovery paths of the shoulder, it emerges that a rehabilitation centered on the usage of “biofeedback” (that implement motor acquisition with visual and proprioceptive afferents), can partly compensate for the lack of proprioceptive afferents from the supraspinous muscle and from the the capsular and periprosthetic structures damaged by the basic pathology or sacrificed for the RSA implant, thus guaranteeing a better outcome. The analysis of the results deriving from the evaluations effectuated during the two functional recovery paths, with respect to the arc of motion and to muscle activation, as foreseen in the research protocol, shows statistical relevant differences about the proprioceptive skill. STUDY N. 2 Aim: This study aims at detecting central nervous system (CNS) activation patterns related to the execution of voluntary shoulder movements in subjects undergone reverse shoulder arthroplasty (RSA). RSA determines innovative changes in shoulder mechanics, muscle contraction effect, and sensory information, requiring sensory recalibration and new muscle synergies for shoulder control. Functional recovery, therefore, results from motor learning processes expected to be related to new specific CNS activation patterns, detectable with functional Magnetic Resonance Imaging (fMRI). Diseases and injuries, determining persistent alterations of the musculoskeletal system, are very frequent in the course of life and require rapid adaptations to recovery and maintain maximal motor function. Understanding both central processes, that constitute the background of these adaptations, and the changes in motor strategies and muscle synergies, could be helpful in improving therapeutic measures in terms of patient eligibility criteria, prosthesis design, surgical technique, and rehabilitative intervention. Hopefully, this research will blaze a new trail to an increased comprehension of the adaptations occurring after analogue changes in other musculoskeletal districts. In addition, the analysis of CNS activation after RSA represents a novel approach to the fMRI study of motor learning, since in our study, unlike the most diffused paradigms in which central plasticity is elicited by the execution of new motor tasks or as an adaptation to CNS lesions, central modifications are elicited as an adaptation to permanent peripheral changes in the musculoskeletal system. This original point of view has the potential to discover aspects of central adaptation not yet evidenced. The CNS activation patterns elicited during the repetitions of standardized shoulder movements have been analysed by means of BOLD (Blood Oxygenation Level Dependent) fMRI. The patients underwent RSA 6 months before the test. Activation was assumed when “Z score” exceeded the value of 4 relative to BOLD signal recorded in patients at rest. Activation patterns elicited during a RSA shoulder voluntary movement were compared (within the subject) with those elicited during the same movement with the contralateral healthy limb and with those from the controls, in order to highlight the pecularities ascribable to the RSA intervention. In cortical contralateral activation during voluntary test movements involving both S1 and M1, the intensity and extent of BOLD enhancement during a RSA shoulder movement was comparable with that observed in control conditions. Only minor non systematic differences have been appreciated in single cases, consisting in a small contralateral prevalence of cortical activation during RSA limb activity. The most evident effect consisted in an enhanced activation of the cerebellum during RSA shoulder movements, wich resulted more intense and extended, than in control conditions. The enhancement of the BOLD signal has been observed mainly in the ipsilateral cerebellar hemisphere, even if, in some cases, it included the contralateral one too. The inferior lateral aspect of the posterior cerebellar lobe showed the most extensive and intense signal enhancement, but, frequently (%), the activation pattern also included the superior aspect of the same lobe. The large recruitment of cerebellar structures, evidenced during RSA shoulder movements, suggests a fundamental role of the cerebellum in the control of RSA shoulder, necessary to recalibrate sensory-motor processing for an efficacious programming and control of the movement. These results are in line with previous studies evidencing a significant cerebellar activation in motor tasks, requiring continuous feedback and adaptation for their correct kinematics, due to the continuous presence of unexpected perturbing conditions following RSA and joint pathology. RSA, indeed, is characterized by deep structural and sensory-motor changes of the shoulder, determining completely new execution conditions, whose challenge is worsened by concomitant degenerative and inflammatory processes of varying intensity. These characteristics represent a permanent perturbative factor requiring continuous adaptation of the motor command. Indeed, even six months after surgery some parameters of important ADL movements, such as the achievement of muscle flexion and abduction, still evidence limitations (target-approaching speed, humeral elevation angular speed and fluidity of movement) (Postacchini 2015) suggesting the persistence of perturbating factors, that the control system tries to neutralize. The increased control, demanded during movement execution, results in the large recruitment of cerebellar networks and in the enhancement of the BOLD cerebellar signal. Considering the key role of the cerebellum in RSA shoulder control, its structural and functional integrity may represent an eligibility criterion for RSA, which otherwise is likely to fail. A pre-surgery clinical evaluation of the cerebellar function, including a possible functional imaging study, could be then recommended, in order to select eligible subjects for RSA.