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. 2025 May 14;9(5):1585-1593.
doi: 10.1016/j.jseint.2025.04.017. eCollection 2025 Sep.

Variability in ultimate humeral height of an inlay humeral stem does not impact outcomes following reverse shoulder arthroplasty

Max A Saráchaga Mendoza  1   2 , Brian C Werner  3 , Patrick J Denard  4 ; Shoulder Arthroplasty Research Committee (ShARC) Group; Philipp Moroder  5 , Patric Raiss  6
Collaborators, Affiliations

Variability in ultimate humeral height of an inlay humeral stem does not impact outcomes following reverse shoulder arthroplasty

Max A Saráchaga Mendoza et al. JSES Int. .

Abstract

Background: In reverse shoulder arthroplasty, humeral components can be classified as either inlay or onlay implants. However, factors like the depth of seating and use of spacers can cause an inlay component to vary in height, functioning as an onlay component. It is unclear whether the positioning of an inlay humeral component as inlay or onlay position influences clinical outcomes. The aim of this study was to analyze the impact of humeral component position on clinical outcomes following reverse total shoulder arthroplasty.

Methods: This was a multicenter retrospective study analyzing radiographic and clinical data from reverse shoulder arthroplasties performed with the same 135° humeral component. Postoperative radiographs were examined to quantify the lateralization and distalization of the humeral component. The distance from the anatomical neck of the humerus to the glenosphere was measured to categorize the implantation as either inlay or onlay. Clinical data, including patient-reported outcomes and range of motion, were compared between groups. Linear regression was used to assess the association of angular measures and clinical outcomes during follow-up.

Results: A total of 194 patients with a mean age of 69.3 years (42-90) were included. Postoperative humeral position was classified as a true inlay in 25.3% and some degree of onlay in 74.7%. The modified distalization shoulder angle was greater in the inlay group, whereas the distance to the glenosphere was greater in the onlay group. Baseline patient-reported outcomes were similar, apart from a higher internal rotation at 90° in the onlay group. At 2-year follow-up, only the Western Ontario Osteoarthritis of the Shoulder index showed a statistically significant difference, with a higher score for the inlay group (88.9 ± 17 vs. 82.8 ± 18.1; P = .04). Linear regression analysis showed an association between the distance to the glenosphere and 0° and 90° external rotation, as well as the spinal level internal rotation. The complication rate was similar between groups.

Conclusion: Clinical outcomes following reverse shoulder arthroplasty with a 135° neck shaft angle designed inlay humeral implant are favorable, with either inlay or onlay implantation. Clinical outcomes were excellent, with minimal differences based on final humeral positioning. The inlay stem offers the advantage to be placed as either inlay or onlay, based on the surgeon's preference or the patient's needs. Patients' characteristics and surgeon preference should be considered when deciding which configuration to use.

Keywords: Clinical outcomes; Humerus; Inlay; Onlay; Reverse shoulder arthroplasty; Shoulder.

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Figures

Figure 1
Figure 1
Radiographic assessment of lateralization. (A) GLSA. (B) gLSA. (C) hLSA. The GLSA is an angle measured between a line connecting the superior glenoid tubercle and the most lateral border of the acromion and a line connecting the most lateral border of the acromion and the most lateral border of the greater tuberosity. The gLSA is the angle between a line connecting the superior glenoid tubercle and the most lateral border of the acromion and a line connecting the most lateral border of the acromion and the GPP. The GPP is defined as the most lateral point of the glenosphere. The hLSA angle is measured with a line connecting the most lateral border of the acromion and the GPP and a line connecting the most lateral border of the acromion and the most lateral border of the greater tuberosity. GLSA, global lateralization shoulder angle; gLSA, glenoid lateralization shoulder angle; hLSA, humeral lateralization shoulder angle; GPP, glenoid pivot point.
Figure 2
Figure 2
Radiographic assessment of distalization. (A) DSA. (B) mDSA. The DSA is an angle formed between a line from the most lateral border of the acromion to the superior glenoid tubercle and a line that goes from the superior glenoid tubercle to the most superior border of the greater tuberosity. The mDSA is measured with a line connecting the most lateral border of the acromion and the superior glenoid tubercle and a line from the superior glenoid tubercle to the calcar. DSA, distalization shoulder angle; mDSA, modified distalization shoulder angle.
Figure 3
Figure 3
Radiographic assessment of distalization. (A) GDA. (B) HDA. The GDA is measured with a line from the most lateral border of the acromion to the superior glenoid tubercle and a line from the superior glenoid tubercle to the GPP. The HDA is an angle formed of a line from the superior glenoid tubercle to the GPP and a line from the superior glenoid tubercle to the calcar. The mDSA is the sum of the HDA and the GDA. GDA, glenoid distalization angle; HDA, humeral distalization angle; GPP, glenoid pivot point; mDSA, modified distalization shoulder angle.
Figure 4
Figure 4
Measurement of distance to the glenosphere.
See this image and copyright information in PMC

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