The subcoracoid distance is correlated with pain and internal rotation after reverse shoulder arthroplasty

Abstract

Background: A proposed etiology of anterior shoulder pain and limited internal rotation after reverse shoulder arthroplasty (RSA) is impingement of the humeral component on the coracoid or conjoint tendon. The primary goal of this study was to investigate radiographic surrogates for potential coracoid or conjoint tendon impingement and their relationship to postoperative pain and internal rotation after RSA.

Methods: A retrospective review of a clinical registry was performed to identify patients with (1) primary RSA, (2) minimum 2-year clinical follow-up, and (3) satisfactory postoperative axillary lateral radiographs. The primary radiographic measurement of interest was the subcoracoid distance (SCD), defined as the distance between the posterior aspect of the coracoid and the anterior glenosphere. Additional measurements were as follows: anterior glenosphere overhang, posterior glenosphere overhang, native glenoid width, lateralization of glenosphere relative to the coracoid tip, lateralization shoulder angle, and distalization shoulder angle. The primary clinical outcome of interest was the 2-year postoperative Visual Analog Scale score. Secondary outcomes were (1) internal rotation (IR) defined by spinal level (IRspine), (2) IR at 90 degrees of abduction, (3) American Shoulder and Elbow Surgeons score, (4) forward flexion, and (5) external rotation at 0 degrees of abduction. Linear regression analyses were used to evaluate the relationship of the various radiographic measures on the clinical outcomes of interest.

Results: Two hundred seventeen patients were included. There was a statistically significant relationship between the SCD and Visual Analog Scale scores: B = -0.497, P = .047. There was a statistically significant relationship between the SCD and IRspine: B = -1.667, P < .001. Metallic lateralization was also positively associated with improving IRspine; increasing body mass index was negatively associated. There was a statistically significant relationship between the SCD and IR at 90 degrees of abduction: B = 5.844, P = .034.

Conclusion: For RSA with a 135° neck shaft angle and lateralized glenoid, the postoperative SCD has a significant association with pain and IR. Decreasing SCD was associated with increased pain and decreased IR, indicating that coracoid or conjoint tendon impingement may be an important and potentially under-recognized etiology of pain and decreased IR following RSA. Further investigations aimed toward identifying a critical SCD to improve pain and IR may allow surgeons to preoperatively plan component position to improve clinical outcomes after RSA.

Keywords: Coracoid impingement; Internal rotation; Reverse shoulder arthroplasty; Reverse shoulder replacement; Subcoracoid distance; Subcoracoid impingement.

Figure 1

Subcoracoid space (SCS), center of rotation to the tip of the coracoid (COR-C), and the center of rotation to the edge of the sphere (COR-S). (A) The purple sphere outlines the glenosphere. The subcoracoid space (SCS; green) is defined as the distance (mm) between the posterior aspect of the coracoid and the anterior glenosphere on the axillary radiograph. (B) The center of rotation to the tip of the coracoid (COR-C; blue) is defined by the distance (mm) from the center of the rotation to the posterior aspect of the coracoid on the axillary radiograph. (C) The center of rotation to the edge of the sphere (COR-S; pink) is defined as the distance (mm) from the center of rotation to the boundary of the glenosphere, or the radius of the glenosphere (purple).

Figure 2

Glenosphere overhand, native glenoid width, and glenoid lateralization. (A) Anterior glenosphere overhang (orange) and posterior glenosphere overhang (blue) were measured on the axillary radiographs as the distance from the most anterior or posterior edge of the native glenoid to the furthest extent of the glenosphere (purple). (B) Native glenoid width (dark green) was measured from the furthest cortical extent but not to include any reactive bone. (C) Glenoid lateralization (yellow) was measured in relation to the coracoid tip by the distance between parallel lines to the native glenoid (dark green) placed at the edge of the glenosphere (red) and coracoid tip (red).

Figure 3

Lateralization shoulder angle (LSA) and distalization shoulder angle (DSA). (A) The lateralization shoulder angle (LSA; lavender) is formed by 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. (B) The distalization shoulder angle (DSA; teal) is formed by a line connecting the most lateral border of the acromion and the superior glenoid tubercle and a line connecting the superior glenoid tubercle and the most superior border of the greater tuberosity.