Radiographic assessment of reverse shoulder arthroplasty: a narrative review of post-operative parameters and measurements

Abstract

Background

Reverse total shoulder arthroplasty (rTSA) has become an established treatment for degenerative and traumatic shoulder conditions. Accurate post-operative radiographic evaluation is essential for assessing implant positioning and alignment. However, considerable variability exists in how post-operative radiographs are interpreted and reported in the literature. This narrative review aimed to synthesize the current evidence on post-operative radiographic evaluation after rTSA and to summarize the most commonly reported radiographic parameters used to assess implant positioning, alignment, and shoulder reconstruction.

Methods

This narrative review included studies that provided clear and comprehensive descriptions of post-operative radiographic parameters, resulting in 9 eligible studies. Radiographic measurements including the lateralization shoulder angle, distalization shoulder angle, neck–shaft angle, humeral offset, inferior glenosphere overhang, rTSA angle, filling ratio, acromiohumeral distance, and screw orientation were analyzed in relation to implant positioning and radiographic assessment.

Results

The reviewed studies consistently described a range of radiographic parameters used to evaluate rTSA reconstruction on standard radiographs. Lateralization shoulder angle and distalization shoulder angle were used to quantify humeral lateralization and distalization, whereas acromiohumeral distance reflected humeral lengthening and deltoid tension. Neck–shaft angle and humeral offset described humeral reconstruction, while inferior glenosphere overhang and rTSA angle assessed glenoid component positioning. Overall, substantial heterogeneity was observed in measurement techniques and definitions across studies, limiting direct comparison and reproducibility.

Conclusion

Post-operative radiographic evaluation remains a fundamental component of rTSA follow-up. Standardized interpretation of routine anteroposterior, axillary, and scapular Y radiographs may improve consistency in reporting and clinical decision-making. The development of validated and standardized radiographic parameters is essential to improve reproducibility and optimize post-operative assessment after rTSA.

Reverse total shoulder arthroplasty (rTSA), first developed by Paul Grammont in 1987.² It has evolved from a procedure reserved for patients with rotator cuff arthropathy to one widely applied across a spectrum of shoulder pathologies, including complex fractures, massive irreparable cuff tears, and glenohumeral arthritis both with and without glenoid bone loss.^{10,14,16,32,36} Advances in implant design and surgical technique have enabled rTSA to address challenging cases of glenoid deficiency using augmented baseplates, bone grafting, and even patient-specific customized components, achieving stable fixation and favorable clinical outcomes.

Despite these advances, post-operative complications such as dislocation, scapular notching, periprosthetic fractures, and component loosening remain clinically relevant.¹³,^15,24,28 Radiographic evaluation plays a critical role in identifying these issues, guiding post-operative management, and assessing implant performance over time. Standard post-operative imaging typically including anteroposterior (AP), axillary, and scapular Y views is routinely used to evaluate implant alignment, fixation, and potential complications.^9,12,17,30 However, there is no consensus regarding which radiographic parameters should be systematically assessed or how these findings should be correlated with functional outcomes.

Several parameters have been proposed to quantify component position and shoulder biomechanics following rTSA. These include the lateralization shoulder angle (LSA) and distalization shoulder angle (DSA), which describe humeral–glenoid alignment⁴; the neck–shaft angle (NSA), indicating humeral stem orientation¹; humeral offset (HO), reflecting medialization or lateralization of the humerus⁵; and inferior glenosphere overhang (IGO), used to predict notching risk.⁸ Proper interpretation of these measurements provides valuable insight into implant performance, deltoid tension, and potential sources of mechanical failure. However, variability in measurement techniques and reporting across studies limits comparability and clinical applicability.

A standardized, evidence-based approach to post-operative radiographic assessment could enhance consistency among surgeons and radiologists, improve early complication detection, and guide design optimization in future implants. The purpose of this narrative review is to summarize the current evidence on post-operative radiographic evaluation after rTSA and to provide a comprehensive overview of the key radiographic parameters used to assess implant positioning, alignment, and overall shoulder reconstruction.

Materials and methods

This narrative review was conducted to summarize the radiographic parameters used in the post-operative evaluation of rTSA and their clinical relevance. A review of the literature was performed using the PubMed/MEDLINE database to identify studies addressing post-operative radiographic assessment following rTSA. Studies were included if they provided a clear description of a post-operative radiographic parameter, including its definition, measurement technique, interpretation, or clinical application. Articles focused on implant positioning, component alignment, radiographic assessment methods, and radiographic findings associated with clinical outcomes or complications were considered. Studies lacking sufficient detail regarding radiographic measurements or not directly related to post-operative rTSA imaging were excluded.

As the objective of this article was to provide a descriptive overview of currently reported radiographic assessment methods, a formal systematic review methodology, meta-analysis, and risk-of-bias assessment were not performed. The selected studies were reviewed narratively, with emphasis on commonly reported radiographic parameters, their measurement techniques, and their reported association with implant positioning, functional outcomes, and post-operative complications. Nine studies met the inclusion criteria and were included in the final review.

Radiographic evaluation based on X-rays

The lateralization shoulder angle and the distalization shoulder angle

In the AP view, several studies focused on the alignment between the humeral and glenoid components. Boutsiadis et al, assessed this using 2 angular measurements. The LSA 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. The DSA 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. Moreover, LSA values between 75° and 95° were correlated with better active external rotation while DSA between 40° and 65° resulted in better active anterior elevation and abduction⁴ (Fig. 1).

Figure 1.

True anteroposterior (Grashey) radiograph of a left reverse shoulder arthroplasty demonstrating measurement of the lateralization shoulder angle (LSA) and distalization shoulder angle (DSA). (A) The LSA is defined as the angle between a line connecting the superior glenoid tubercle to the most lateral border of the acromion and a line connecting the most lateral border of the acromion to the most lateral border of the greater tuberosity. (B) The DSA is defined as the angle between a line connecting the most lateral border of the acromion to the superior glenoid tubercle and a line connecting the superior glenoid tubercle to the most superior border of the greater tuberosity. Radiographs courtesy of Dr. George S. Athwal.

Acromiohumeral distance and humeral lengthening

Post-operative evaluation of the acromiohumeral distance (AHD) provides indirect information regarding humeral lengthening and deltoid tension as demonstrated in Fig. 2. AHD is influenced by both implant design and surgical technique, including the level of humeral head resection and whether the humeral component is implanted in an inlay or onlay configuration.¹⁸ Although several studies have investigated the relationship between AHD and post-operative range of motion, the findings remain inconsistent. Jobin et al²⁰ reported that an increase in AHD of >38 mm predicted achieving ≥135° of active forward flexion with 90% accuracy, whereas Kim et al²² found that an AHD of <29 mm was associated with greater forward flexion and external rotation. In contrast, Sabesan et al³¹ observed no significant correlation between AHD and post-operative range of motion. Collectively, these findings suggest that AHD alone may not reliably predict functional outcomes. Nevertheless, AHD remains a valuable radiographic parameter because it reflects humeral lengthening and deltoid tensioning, factors that have been associated with complications such as nerve injury^23,26 and acromial or scapular spine fractures.^6,27

Figure 2.

True anteroposterior (Grashey) radiograph of a right reverse shoulder arthroplasty demonstrating measurement of the acromiohumeral distance (AHD), defined as the shortest distance between the inferior aspect of the acromion and the most superior aspect of the greater tuberosity. Radiographs courtesy of Dr. George S. Athwal.

The neck–shaft angle

Abdic et al¹ measured the NSA. The anatomic NSA of the humerus is defined as the angle between the line traversing the central intramedullary axis of the humeral shaft and a line perpendicular to the anatomic head–neck junction. Most patients fall within a narrow range of NSAs of 135°–140°, although variabilities exist which averaged 149°, and reported that around 27% of stems were not aligned correctly, showing either valgus or varus deviation, The majority of malaligned components (86%) were implanted in valgus, corresponding to an NSA of >150°¹ Fig. 3. Lädermann et al²⁵ reported increased risk of valgus stem misalignment among female gender, older age, and patient with subscapularis- and deltoid-sparing approaches.

Figure 3.

True anteroposterior (Grashey) radiograph of a left reverse shoulder arthroplasty demonstrating measurement of the neck–shaft angle (NSA), defined as the angle between the humeral diaphyseal axis and a line perpendicular to the humeral tray. Radiographs courtesy of Dr. George S. Athwal.

The filling ratio of the implant

The filling ratio of the implant within the humeral intramedullary canal was measured both at the metaphyseal as well as the diaphyseal level as shown in Fig. 4. The average filling ratio at metaphysis (FRmet) and filling ratio at diaphysis (FRdia) were 0.68 ± 0.11 and 0.72 ± 0.11, respectively. Raiss et al²⁹ described that a filling ratio of >0.8 in uncemented convertible short stem has a 7.0-fold higher risk for radiographic stress shielding and recommended the use of smaller stems when used in an uncemented fashion in rTSA. Furthermore, Yokoya et al³⁷ conducted a multicenter study they reported that a filling ratio above 0.7 was an independent predictor of stress shielding post-rTSA. A recent review supported these findings as they reported that low filling ratio can decrease the stress shielding.³⁵

Figure 4.

True anteroposterior (Grashey) radiograph of a left reverse shoulder arthroplasty demonstrating measurement of the humeral implant stem filling ratios at the metaphyseal (FR_met) and diaphyseal (FR_dia) levels. The green line represents the humeral shaft axis. The red line represents the prosthetic stem width, and the blue line represents the intramedullary canal width, both measured perpendicular to the humeral shaft axis. The filling ratios are calculated as the ratio of the prosthetic stem width (red line) to the intramedullary canal width (blue line) at the level of the distal medial border of the humeral head resection (FR_met) and at the junction of the proximal two-thirds and distal one-third of the stem (FR_dia). Radiographs courtesy of Dr. George S. Athwal.

Measurement of inferior glenosphere overhang

The increased distance between the scapular pillar and the humeral component theoretically decreases post-operative notching. As shown in Figure 5, the glenoid component can be shifted inferiorly relative to the glenoid; however, there also is some concern that shifting the glenoid component too far inferiorly resulting in component overhang may compromise long-term stability of the glenoid component. Collotte et al⁸ found that an IGO of at least 3.5 mm relative to the inferior rim of the glenoid was associated with a lower notching rate and severity without negatively affecting the complication rate in rTSA. Several studies have demonstrated lower notching rates with inferiorly positioned glenospheres in the short or midterm follow-up evaluation.

Figure 5.

True anteroposterior (Grashey) radiograph of a right reverse shoulder arthroplasty demonstrating measurement of inferior glenosphere overhang (IGO), defined as the vertical distance by which the inferior aspect of the glenosphere extends beyond the inferior glenoid rim. Radiographs courtesy of Dr. George S Athwal.

Baseplate screw orientation

Screw orientation plays a critical role in glenoid baseplate fixation. Earlier biomechanical studies suggested that a divergent screw configuration, where the superior and inferior screws are angled away from each other, could reduce micromotion at the glenoid–baseplate interface compared with a parallel orientation, thereby enhancing primary stability by increasing bone–implant contact and resisting shear forces. On post-operative radiographs, screw orientation should be assessed in both axillary and true AP (Grashey) views (Fig. 6). Ideally, the inferior screw should be directed toward the dense scapular pillar and the superior screw toward the coracoid base, creating a divergent spread that improves fixation in osteopenic bone. However, recent cadaveric biomechanical data indicate that screw position may not have a statistically significant effect on glenoid baseplate micromotion in the early post-operative fixation period. These findings show that screw divergence bore no statistically significant difference in micromotion compared to a parallel screw orientation, result consistent with other biomechanical investigations.⁷ Therefore, the 3-column concept was proposed as it provides a practical framework for understanding optimal screw placement. The scapula can be conceptualized as 3 key bony columns anchoring the glenoid baseplate:

• 1.The base of the coracoid, representing the anterosuperior column.
• 2.The scapular spine, forming the posterior column.
• 3.The scapular pillar, constituting the inferior column.

Figure 6.

True anteroposterior (Grashey) radiograph of a left reverse shoulder arthroplasty demonstrating the ideal divergent configuration of the baseplate screws to optimize glenoid fixation. Radiographs courtesy of Dr. George S. Athwal.

This 3-column model guides surgeons to aim screws toward these denser regions of bone, maximizing purchase and stability.¹⁹ Figure 7 demonstrates the scapular ‘‘safe zone’’ for avoiding suprascapular nerve injury as described by Shishido and Kikuchi.³³ Penetrating the cortex with a drill bit medial to the safe zone may potentially lead to injury of the suprascapular nerve. Shishido and Kikuchi reported that it was safe to penetrate the cortex up to 1.4 cm medial to the face of the glenoid. It should be kept in mind that during rTSA, the glenoid face is reamed away, so the safe zone distance will likely be less than 1.4 cm. Furthermore, penetrating the posterior cortex increases the risk of scapular spine fractures therefore it should be avoided.

Figure 7.

Schematic illustration of the scapular safe zone (red highlight), representing the maximum safe extent of baseplate medialization. The yellow line depicts the course of the suprascapular nerve. Medialization beyond 1.4 cm from the superior glenoid rim may increase the risk of suprascapular nerve injury.

The humeral offset

The HO was defined as the distance from the lateral edge of the acromion to the lateral edge of the proximal humerus on an AP (Grashey view) shoulder radiograph. (Fig. 8) The post-operative value was subtracted from the pre-operative value to determine the change in the HO (ΔHO. PostHO–PreHO). A negative value was defined as medialized HO and a positive value was defined as lateralized HO, Carrazana-Suarez et al,⁵ found that restoring the pre-operative HO or lateralization beyond the baseline may be favorable for improving ER and decreasing complications, such as scapular notching and instability (Fig. 9).

Figure 8.

True anteroposterior (Grashey) radiograph of a left reverse shoulder arthroplasty demonstrating measurement of the humeral offset (HO), defined as the distance between the lateral border of the acromion and the lateral cortex of the humerus. Radiographs courtesy of Dr. George S. Athwal.

Figure 9.

Pre-operative humeral offset (HO) (A) and post-operative humeral offset (HO) (B) measurements. ΔHO represents the difference between post-operative and pre-operative humeral offset (ΔHO = PostHO − PreHO). This example illustrates a medialized Right reverse shoulder arthroplasty. Radiographs courtesy of Dr. George S. Athwal.

The reverse total shoulder arthroplasty angle

Placement of the baseplate appeared to be consistent across most studies, with authors generally reporting that it was flush with the native glenoid, and precise pre-operative determination of glenoid inclination is important to correctly plan the positioning of the baseplate.¹¹ Boutsiadis et al⁴ confirmed a 10° inferior tilt in their series, while Boileau et al³ emphasized targeting a 0° inclination to correct glenoid alignment. Although the actual measurement of inferior tilt was often not stated numerically, several studies implied its use as part of their surgical protocol. (Fig. 10) Glenosphere overhang, an important factor in avoiding impingement and notching, was not consistently reported, though studies like Boutsiadis and Boileau implied its improvement using lateralizing strategies such as BIO-rTSA or augmented baseplates.^21,34 Table I summarizes post-operative parameters.

Figure 10.

Post-operative true anteroposterior (Grashey) radiograph of a right reverse shoulder arthroplasty demonstrating a neutral reverse shoulder arthroplasty (rTSA) angle following angled Bio-rTSA. The horizontal red line is drawn along the scapular spine and is parallel to the Center post of the baseplate. The vertical red line passes through the medial edge of the glenosphere and is perpendicular to the horizontal reference line. A 90° angle indicates a neutral rTSA angle. Radiographs courtesy of Dr. George S. Athwal.

Table I.

Summarizes post-operative parameters in different shoulder X-ray views.

X-ray view	Parameter	Normal value	Interpretation
AP	Lateralization shoulder angle (LSA)	74–95°	<75°: insufficient lateralization, reduced external rotation >95°: excessive lateralization, possible over tensioning
AP	Distalization shoulder angle (DSA)	40°–65°	<40°: insufficient Distalization, reduced forward elevation >65°: excessive Distalization, increased deltoid tension and nerve injury risk.
AP	Acromiohumeral distance (AHD)	No universally accepted normal value	Low AHD <29 mm: may improve forward flexion and external rotation High AHD >38 mm indicates excessive deltoid tensioning
AP	Neck–shaft angle (NSA)	135°-140°	<135° varus stem malalignment >150° Valgus stem malalignment
AP	Filling Ratio	<0.7	>0.7-0.8 increase the risk of stress shielding
AP	Inferior glenosphere overhang (IGO)	≥ 3.5 mm	<3.5 mm increased scapular notching
AP	Humeral offset (HO)	Restoration of pre-operative humeral offset	Decreased HO: reduced external rotation, higher risk of instability
AP	rTSA angle	0°-10° inferior tilt	Superior tilt: increased notching and loosening Inferior tilt: 0-10° improved glenoid mechanics and reduced notching.
Axial view	Baseplate screws orientation	Posterior screw: directed toward scapular spine	Poor trajectory: reduced bone purchase and fixation strength
Scapular Y view	Baseplate screws orientation	Inferior screw position: directed toward scapular pillar Superior screw position: directed toward coracoid base	Poor trajectory: reduced bone purchase and fixation strength
Scapular Y view	Scapular safe zone	<1.4 cm medial to glenoid face	Risk of suprascapular nerve injury

rTSA, reverse total shoulder arthroplasty; AP, anteroposterior.

Discussion

Post-operative radiographic evaluation remains a fundamental component of follow-up after rTSA. This review highlights the radiographic parameters most commonly used to assess implant positioning, alignment, and shoulder reconstruction on standard radiographs. Among these, LSA, DSA, AHD, NSA, HO, filling ratio, IGO, rTSA angle, and baseplate screw orientation represent the principal measurements described in the literature.

Although several studies have reported associations between these radiographic parameters and clinical outcomes, the evidence remains heterogeneous. Parameters such as LSA and DSA have been associated with post-operative range of motion and provide a practical assessment of humeral lateralization and distalization.⁴ Similarly, AHD serves as an indirect measure of humeral lengthening and deltoid tension,^20,22,31 whereas HO and NSA reflect implant reconstruction and shoulder biomechanics. IGO has been shown to reduce the incidence and severity of scapular notching when appropriately optimized.⁸ Collectively, these measurements offer a comprehensive radiographic assessment of the reconstructed shoulder following rTSA.

A major finding of this review is the substantial variability in how radiographic parameters are defined and measured across studies. Differences in imaging techniques, measurement methods, and reporting standards limit direct comparison between investigations and make it difficult to establish universally accepted thresholds. This heterogeneity likely contributes to the inconsistent associations reported between certain radiographic measurements and post-operative outcomes.

Based on the available literature, a standardized post-operative radiographic assessment should include AP, axillary, and scapular Y radiographs, with routine evaluation of component position, alignment, lateralization, distalization, humeral reconstruction, glenosphere overhang, and fixation characteristics. Consistent reporting of these parameters would improve communication among surgeons, facilitate comparison across studies, and enhance the clinical utility of post-operative radiographs.

The findings of this review should be interpreted in light of several limitations. As a narrative review, study selection was not performed using systematic review methodology. Furthermore, the available literature consists primarily of retrospective studies with heterogeneous patient populations, implant designs, and radiographic protocols. Despite these limitations, the reviewed studies consistently demonstrate the importance of standardized radiographic assessment following rTSA.

Future studies should focus on validating reproducible measurement techniques and establishing standardized radiographic reporting protocols. Such efforts may improve the reliability of post-operative assessment and allow more meaningful comparisons across implant designs and clinical investigations.

Conclusion

Post-operative radiographic evaluation is fundamental to the long-term assessment of rTSA. Standardized interpretation of AP, axillary, and scapular Y radiographs allows reliable evaluation of implant positioning, alignment, and early signs of mechanical failure. Proper reconstruction of the baseplate, glenosphere, and humeral components particularly restoration of appropriate inferior tilt and HO is associated with improved function and implant durability.

Disclaimers:

Funding: No funding was disclosed by the authors.

Conflicts of interest: The author, their immediate family, and any research foundation with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.