Joint contact forces and soft-tissue tension in the Depuy Delta XTEND reverse shoulder prosthesis

Abstract

The glenohumeral joint is able to precisely stabilize the humeral head in the middle of the glenoid cavity and at the same time allows a large range of motion. Thisis mostly accomplished by the active muscles and passive structures of the joint,the rotator cuff. Large defects in the tendons of the rotator cuff can lead to a cufftear arthropathy with a loss of the natural joint mechanics. Reverse total shoulderarthroplasty offers promising results in pain relief, overhead elevation and increasing external rotation. Despite well-established surgical methods in the utilization ofreverse shoulder prostheses, complications such as instability due to insufficient softtissue tension and the resulting dislocation of the joint still occur. Due to the lack of available measuring equipment, the surgeon’s experience is currently solely responsible for sufficient pretensioning of the tendons and muscles of the shoulder joint,leading to a substantial variability in surgery outcomes. The intraoperative determination of soft-tissue tension can be identified by the acquisition of intra articularloads in the glenohumeral joint during the surgery. To determine joint reactive forcesin an Depuy Delta XTEND reverse prosthesis system the glenosphere component has been equipped with strain gauge technology to utilize spatial load measurement.Furthermore, a custom load sensor has been developed to identify loads related to soft-tissue tension in the humeral component of the prosthesis. The respective measurementelectronics for the acquisition of the sensor signals have been preparedand used successfully during ex-vivo calibration measurements. The instrumented glenosphere component showed a good sensitivity to loads in all spatial directionsand the custom humeral load sensor provided a good overall performance. Relativeload measurement errors have been identified as approximately 10% for the glenospheresensor, the relative errors of the humeral sensor was below 2%. Thus, the created prototypes provide a good basis for the quantitative measurement of the intra-articular forces of the glenohumeral joint as well as the strongly correlating tension of the musculo-tendinous complex associated with joint stability. The two sensors provide an overall good foundation for further improvements in the intraoperative assessment of soft-tissue tension and demonstrate the complexity of the instrumentation of prosthesis components.