2025 ISAKOS Congress in Munich, Germany

2025 ISAKOS Biennial Congress Paper


Effect of Glenosphere Lateralization or Inferiorization and Humeral Offset on Range of Motion after Reverse Total Shoulder Arthroplasty: A Robotic Assessment

Maximilian Hinz, MD, Munich GERMANY
Alex Brady, MSc, Vail, CO UNITED STATES
Wyatt Buchalter, BS, Vail UNITED STATES
Natalie Cortes, M.S., Vail, Colorado UNITED STATES
Rony-Orijit Dey Hazra, MD, Dr.med. UNITED STATES
Marco-Christopher Rupp, MD, Munich, Bavaria GERMANY
Matthew T. Provencher, MD, Vail, CO UNITED STATES
Peter J. Millett, MD, MSc, Vail, CO UNITED STATES

Steadman Philippon Research Institute, Vail, Colorado, UNITED STATES

FDA Status Cleared

Summary

The reverse total shoulder arthroplasty implant configuration that was associated with the most favorable postoperative range of motion was a +4-mm lateralized glenosphere, which led to significant improvements in all three motions, and a +3-mm humeral liner, which was associated with improved abduction and flexion range of motion.

Abstract

Objective

The use of preoperative three-dimensional (3D) planning and patient-specific instrumentation for reverse total shoulder arthroplasty (rTSA) has gained in popularity. There exists a paucity of data on the influence of component selection on postoperative range of motion (ROM). The purpose of the present study was to evaluate the effect of glenosphere lateralization or inferiorization and humeral offset on postoperative ROM using a 6-degrees-of-freedom (6-DOF) robotic arm.

Methods

Twelve cadaveric shoulders underwent computed tomography. Reverse total shoulder arthroplasty implantation was planned using 3D software. Each shoulder was dissected of all soft tissue and rTSA (Univers ReversTM, Arthrex Inc.) implantation was performed by a fellowship-trained orthopaedic surgeon using patient-specific instrumentation. Each specimen was mounted to a 6-DOF robotic arm and tested with 3 different glenospheres (standard, + 4 mm lateralized or +2.5 mm inferiorized) and non-constrained humeral liners (+3, +6 or +9 mm) for a total of 9 configurations. Robotic assessment consisted of ROM testing in abduction, flexion and adduction under 5 Nm torque. To match the repeated measures design, a 2-factor linear mixed effect model was created for each test whereby the choice of the glenosphere was a categorical factor and humeral offset was a continuous factor.

Results

The statistical model showed no interaction between the choice of the glenosphere and humeral liner, so their effects were analyzed separately. Lateralizing the glenosphere by 4.0 mm or inferiorizing it by 2.5 mm significantly improved abduction ROM (+ 3.6° and + 3.5°, P < 0.001, respectively) and adduction ROM (+ 4.0° and + 4.9°, P < 0.001, respectively) when compared with the standard glenosphere. Glenosphere lateralization also improved flexion ROM significantly (+ 4.0°, P < 0.001) whereas glenosphere inferiorization led to no significant change. Increasing humeral offset significantly reduced abduction ROM (- 0.5°/mm, P < 0.001) and flexion ROM (- 0.9°/mm, P < 0.001), but did not significantly affect adduction ROM.

Conclusion

The rTSA implant configuration that was associated with the most favorable postoperative ROM was a +4-mm lateralized glenosphere, which led to significant improvements in all three motions, and a +3-mm humeral liner, which was associated with improved abduction and flexion ROM. A +2.5-mm inferiorized glenosphere also led to significant improvements in abduction and adduction ROM, but not did improve flexion ROM. The use of a +6-mm or +9-mm humeral liner negatively affected abduction and flexion ROM.