Assessment of Shoulder Mobility and Stability in Reverse Total Shoulder Arthroplasty: a Sensor Perspective

In reverse total shoulder arthroplasty stability is primarily controlled by the soft-tissue constraints rather than the congruency of the articulating surfaces. However, assessing the tension in these stabilizing structures currently remains highly subjective intraoperatively. In an attempt to quantify this feel during surgery, an intra-articular load sensor is introduced in this paper. In an in-vitro setting, the load sensor was used in eight reverse total shoulder arthroplasties on full torso specimens. The specimens were mounted on an inclined chair, such that the scapula could freely move to mimic surgical conditions. The resulting load vectors were captured through the range of motion under three different conditions, subjectively categorized by the surgeon as having a low, normal and high tightness. In neutral rotation and under a subjectively optimal condition assessed as neither too tight nor too loose, glenohumeral loads in the range of 10-20lbs were observed. For the same subjectively assessed optimal shoulder, loads up to 30lbs were observed under maximum internal/external humeral rotation. This contrasts the subjectively assessed loose and tight conditions, where lower resp. higher loads were observed that additionally affected the range of motion. On the other hand, stability was potentially missing under loose conditions as no increase in load was observed near the limits of the range of motion, indicating the lack of soft tissue restraint. In conclusion, this series of invitro experiments has shown the relevance and potential clinical value of assessing a Health Sciences EPiC Series in Health Sciences Volume 3, 2019, Pages 398–401 CAOS 2019. The 19th Annual Meeting of the International Society for Computer Assisted Orthopaedic Surgery P. Meere and F. Rodriguez Y Baena (eds.), CAOS 2019 (EPiC Series in Health Sciences, vol. 3), pp. 398–401 shoulder’s stability and mobility using intra-articular load measurements during the trialing phase.