INTRODUCTION

Reverse total shoulder arthroplasty represents a helpful solution in restoring function and relieving pain for patients with several shoulder pathologies. However, the recovery of function for activities of daily living can be prolonged or incomplete. The reasons can be different. The aim of this work is to evaluate the causative relationship between the range of lateralization and the load distribution in movements simulating the daily life joint activities. We also collected data about the primary and final implant's lengthening and glenoid components (inclination, version, rotation and lateralization) and we compared them with load values measured during flexion-extension, internal-external rotation and during static positions: "over-the-head", "behind-back" and "cross-the-body".

MATERIALS AND METHODS

22 patients underwent reverse total shoulder arthroplasty implantation assisted by GPS navigation system (Exactech Inc, Gainesville, FL, USA). Preoperative data were collected by planning software. Intraoperative data were recorded using computer-assisted surgery; a wireless joint load sensor placed into the humeral trial insert was used to record joint load in real time while the RTSA was taken through passive motion.

RESULTS

Mean and the Standard Deviation of the force data for each movement and position have been evaluated. It has emerged that, preserving a final lateralisation from 18 to 22 mm, the average of force recorded, considering each movement and position, resulted between 11.8 and 22.5 lbf; the force on the glenoid's surface is influenced by the final lateralisation, the lengthening of the implant and the grade of abduction of the arm during the movement.

CONCLUSION

The data spread is consistent and narrow, especially for internal-external rotation and "behind-back" position. The limited number of patients did not allow the simultaneous analysis of multiple parameters and that limits our statistic results. Future trials should examine a broader range of patient-reported outcome measures and outcome variables including active range of motion kinematic data. This join load sensor could improve the understanding of how intraoperative joint load measurement may influence postoperative patient function and satisfaction. Future studies should integrate the post-operative follow-up in order to increase the knowledge about the causative relationship between intra-operative data and outcomes. This could improve the surgeon experience and his choices before and during the surgical act. This preliminary study evidenced a clear trend that can be statistically reinforced by enlarging the dataset.