Summary

This study aims to demonstrate a novel technique using undersized Grammont design humeral prosthesis in an onlay fashion with metaphyseal bone grafting to avoid stress shielding including radiological and clinical outcomes of this technique.

Abstract

Introduction

Reverse shoulder arthroplasty (RSA) has been increasingly utilised for degenerative conditions around the shoulder with good results. Press-fit fixation of the humeral stem is becoming more popular in RSA. However, humeral bone stress shielding can be noted in some cases as early as one year after RSA using press-fit humeral stem, subsequently affecting the survivorship of the implant. The Australian Joint Registry reveals that 54% of the revision cases in the RSA are because of the humeral side. The aim of this study is to demonstrate a novel technique using undersized Grammont design humeral prosthesis in an onlay fashion with metaphyseal bone grafting to avoid stress shielding and to present the radiographic and clinical outcomes of patients who underwent RSA following this technique.

Methods

Consecutive patients who underwent RSA for degenerative changes of the shoulder following the onlay Grammont technique from 2018 to 2022 were included in the study. The key steps of this technique involve the use of undersized Grammont-style stem, metaphyseal impaction bone grafting, and adjustment of the height and offset of the stem depending on patient stature, desired lateralisation and distalisation, and joint and soft tissue tension. Radiographic assessments were compared using plain radiographs obtained immediately after surgery, and at one and two years postoperatively. These assessments included the metaphyseal fill ratio (metFR), diaphyseal fill ratio (diaFR), stress shielding, scapular notching, and stem alignment. Preoperative and two-year postoperative range of motion, VAS for pain, Constant Murley Score, ASES score, and UCLA scores were also obtained.

Results

A total of 61 patients were evaluated with at least 2 years follow-up. The average metFR and diaFR were maintained from 0.66 and 0.54 immediately after surgery, to 0.67 and 0.54 at 2 years, respectively. None or mild stress-shielding was observed in 96% of the cases (40.7% none, 55.9% mild). No stem had a change in position of more than 5 and no humeral implant loosening was noted. No scapular notching was observed in 66% of patients, whereas 23.7% had mild and 10.2% had moderate signs of notching. All clinical assessments significantly improved at 2 years (p<0.001).

Conclusion

The onlay Grammont technique with metaphyseal impaction bone grafting and low fill ratio stem showed significantly low stress shielding and excellent clinical results without compromising the initial press-fit stability and avoiding notching in primary RSA. This technique also allows flexibility to adjust the humeral stem offset depending on the desired lateralisation, patient stature, and joint and soft tissue tension, which may help mitigate the possible complications of overlateralisation. This technique also allows conversion of an inlay stem to an onlay design by keeping the stem slightly proud, with the aim of avoiding the complications associated with Grammont-style stem while avoiding the possibility of overdistalisation when using an onlay stem. This technique presents a promising solution for reducing humeral complications in RSA.