Impact of scapular notching on glenoid fixation in reverse total shoulder arthroplasty: an in vitro and finite element study

Abstract

Background: The high incidence of scapular notching in reverse total shoulder arthroplasty (RTSA) has spurred several methods to minimize the bone loss. However, up to 93 % of RTSA with accompanying scapular notching have been reported to maintain good implant stability for over 10 years. The purpose of this study is to investigate the correlation between scapular notching and glenoid fixation in RTSA.Methods: An in-vitro setup was used to measure the notch-induced variations of the strain on the scapular surface and the micromotion at the bone-prosthesis interface during arm abductions of 30°, 60° and 90°. Finite element analysis (FEA) was used to study the bone and screw stresses as well as the bone-prosthesis micromotion in cases of a grade 4 notch during complicated arm motions.Results: The notch resulted in an apparent increase of inferior screw stress in the root of the screw cap and the notch-screw conjunction. However, the maximal stress (172 MPa) along the screw after notch is still much less than the fatigue strength of the titanium screw (600 MPa) under cyclic loading. The bone-prosthesis micromotion results did not present significant notch-induced variations.Conclusions: Scapular notching will not lead to significant effects on the initial stability of glenoid component in RTSA. This finding may explain the long-term longevity of RTSA in cases of severe scapular notching. The relationship between scapular notching and weak regions along the inferior screw may explain why fractures of the inferior screw are sometimes reported in patients with RTSA clinically.

Cause analysis of the liner dissociation of a customized reverse shoulder prosthesis based on finite element analysis

“…Most FEA studies of reverse shoulder prosthesis used the static analysis method, so the role of inertia was not essential and could be ignored (Denard et al, 2017;Ingrassia et al, 2018;Zhang et al, 2020). However, the impingement is a high-speed and dynamic process, and a fully dynamic finite element model is necessary (Cooper et al, 2019).…”

Effect of stress‐shielding‐induced bone resorption on glenoid loosening in reverse total shoulder arthroplasty

“…Except for the inferior strain gauges, which were parallel to the lateral border, the strain gauges at the other locations were all approximately vertical to the articular surface of the glenoid. A method previously reported by the authors was used for fixing the strain gauges in position 21 . The bone surface at the target location was cleaned and abraded with 400 grit silicon‐carbide paper.…”

“…A method previously reported by the authors was used for fixing the strain gauges in position. 21 The bone surface at the target location was cleaned and abraded with 400 grit siliconcarbide paper. The strain gauges were then bonded in position using M-Bond 200 adhesive (Vishay Measurements Group UK Ltd, Hants, UK).…”

Treating posteriorly eroded glenoids with augmented baseplate or bony increased-offset reverse shoulder arthroplasty: a finite element comparison

“…Use of two to four compression screws for RSA fixation is common practice; however, to date, it has not been replicated in FEA studies of RSA 4,8,42 31,36 . Due to the glenoid erosion in the present study, the screw engagement length for the anterior and posterior compression screws was shorter than that studied by Terrier or Pitocchi; therefore, the preload force used here was estimated as 150 N by extrapolating Pitocchi et al's results for a shorter screw scenario.…”

“…Primary to the success of both AUG-RSA and BIO-RSA is the ability to overcome the challenges presented by the patient's limited bone stock to achieve high quality initial fixation that limits micro-motion between the baseplate/graft and reamed glenoid bone. Numerous biomechanical studies using experimental and computational methods have been undertaken to investigate the fixation of non-augmented implants for cases both with and without posterior glenoid erosion 4,7,11,14,15,17,38,41,42 . However, very few biomechanical studies exist that investigate augmented RSA to treat glenoid erosion 10,28,35 .…”