Optimizing lateralization and distalization shoulder angles in shoulder arthroplasty: A systematic review of functional outcomes and complication

Abstract

Background

The lateralization shoulder angle (LSA) and distalization shoulder angle (DSA) are critical factors in predicting postoperative complications in shoulder surgeries. This study investigates the impact of LSA and DSA variations on functional outcomes and complications in shoulder surgery.

Methods

A systematic literature search was conducted in PubMed, Scopus, Web of Science, and the Cochrane Library up to December 2024. The primary outcomes evaluated included the impact of LSA and DSA on postoperative functional outcomes, complication rates, optimal angular parameters, and biomechanical implications.

Results

We included 14 high-quality studies encompassing 8372 patients. The synthesis demonstrated that maintaining an LSA within the optimal range of 75° to 95° is consistently linked to improved functional scores and enhanced active external rotation. Similarly, a DSA range of 40° to 65° is associated with superior anterior active elevation and abduction. The interplay between LSA and DSA is crucial, as balanced adjustments of these angles optimize deltoid tension and shoulder biomechanics, reducing the risk of different complications.

Discussion

Maintaining the LSA between 75° and 95° and the DSA between 40° and 65° significantly enhances functional outcomes and shoulder mobility following arthroplasty. Future research should aim to validate these optimal ranges.

Introduction

Successful outcomes in shoulder surgery, particularly in joint replacement and stabilization procedures, necessitate meticulous consideration of anatomical and biomechanical factors. Among these, the lateralization shoulder angle (LSA) and distalization shoulder angle (DSA) are critical determinants of joint function, surgical approach, and postoperative recovery.^1–3 The LSA was determined by the angle between two lines drawn from the acromion—one to the greater tuberosity and the other to the superior glenoid tuberosity. Similarly, the DSA was defined as the angle formed by two lines extending from the superior glenoid, one to the greater tuberosity and the other to the acromion.^4,5 These angular parameters are fundamental to shoulder stability and function, playing a pivotal role in optimizing joint mechanics, enhancing postoperative mobility, and minimizing complications.^1–3

Growing biomechanical evidence highlights the necessity of precise LSA and DSA alignment to preserve native shoulder kinematics. Proper alignment mitigates rotator cuff strain and supports optimal deltoid function during both active and passive motion.^1,6 Conversely, malalignment can induce mechanical imbalances, leading to chronic pain, restricted range of motion (ROM), and an increased risk of glenoid loosening, often necessitating revision surgery. ⁷ Research has consistently shown that precise optimization of these angles enhances pain alleviation, joint mobility, and muscle function, with well-defined LSA and DSA parameters being strongly associated with better recovery pathways and sustained functional improvement over the long term.^8,9 Moreover, the association between LSA, DSA, and postoperative complications—including scapular notching, nerve injury, and rotator cuff dysfunction—remains a key focus of ongoing research. Evidence suggests that deviations from optimal LSA and DSA values substantially increase the likelihood of these complications, negatively affecting long-term functional outcomes and patient satisfaction.^10,11 Determining the optimal LSA and DSA ranges is essential for reduced complication rates and enhancing surgical outcomes, particularly as shoulder procedures become increasingly sophisticated and technically demanding.

This systematic review evaluates the impact of LSA and DSA variations on postoperative function and complication rates in shoulder surgery. Furthermore, it investigates whether specific angular parameters are linked to optimal recovery and superior clinical outcomes. Through a comprehensive analysis of current literature, this study aims to highlight the biomechanical and clinical significance of LSA and DSA, offering key insights to refine surgical approaches, enhance implant positioning, and improve long-term patient prognosis, ultimately promoting more consistent and successful recovery following shoulder arthroplasty.

Methods

This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. ¹² Furthermore, the methodological framework adhered to the principles outlined in the Cochrane Handbook for Systematic Reviews of Interventions, ¹³ ensuring a rigorous and standardized approach to evaluating intervention effectiveness. The study protocol was prospectively registered in PROSPERO, the international database for systematic review registration, under the identifier CRD42024620974.

Data sources and search strategy

A comprehensive literature search was performed across PubMed, Scopus, Web of Science, and the Cochrane Library, covering all relevant studies up to December 2024. To enhance the accuracy and robustness of the search process, database-specific search strategies were implemented. The detailed search strategies are provided in Supplementary file 1 and Table 1.

Table 1.

Summary of the included studies.

Study ID	Design	Setting	Population	Follow-up	Sample size	Mean age (SD)	Sex (male), N (%)
Hill et al. 2022	CC	USA	Patients were included for review if they had undergone RSA with a Zimmer Biomet TM Reverse implant construct	12 months	689	70.35 (7.22)	358 (52)
Valenti et al. 2024	RC	France	focused on patients exclusively treated with RTSA for CTA	12 months	62	74.51 (6.79)	22 (35.5)
Giovannetti et al. 2024	RC	Italy	primary RSA as a treatment for Cuff Tear Arthropathy, Massive Irreparable rotator cuff tear, Osteo arthritis or Rheumatoid arthritis, true anteroposterior radiograph of the affected shoulder in neutral rotation at final follow-up,	12 months	83	68 (12.72)	36 (43.3)
Imiolczyk et al. 2023	RC	—	primary RSA in patients with CTA	24 months	630	73.7	225 (35.7)
Berthold et al. 2021	RC	5 separate institutions and Multiple locations	Patients undergoing primary rTSA with a 135° prosthesis design	Minimum of 2 years	94	69.2 (8.2)	27 (44.3)
Tuphé et al. 2022	RC	France	patients who underwent RSA for proximal humerus fractures, with a minimum of 2 years radiological follow-up	Minimum of 2 years	49	76 (7)	4 (8)
Marsalli et al. 2021	RC	Chile	Patients who underwent primary RS) for rotator cuff arthropathy	—	51	—	—
Mahendraraj et al. 2020	RC	USA	patients undergoing RSA between May 2016 and December 2017	2 years	238	71.2 (7.2)	83 (35)
Mallett et al. 2021	RCT	France and USA	patients scheduled to undergo RSA	—	20	72 (6.6)	14 (70)
Boutsiadis et al. 2018	RC	France and USA	consecutive patients who underwent RSA for CTA	Minimum of 2 years	46	—	—
Moverman et al. 2024	RC	USA	patients who underwent RSA between June 2013 and May 2019, with a minimum of 3 months follow-up	Minimum of 3 months	6320	70.8 (8.6)	2493 (39.44)
Dainotto et al. 2023	RC	Argentina	Patients with RCA treated with RSA	Minimum 12 months	27	72 (7.1)	6 (22.3)
Longo et al. 2023	RC	USA	patients undergoing RTSAs	2 years	33	73 (8.575)	14 (42.42)
Okutan et al. 2024	simulation-based analysis from a consecutive case series.	Institutional review board-approved analysis of anonymized CT data	30 patients with cuff tear arthropathy scheduled to undergo RTSA	—	30	—	—

RCT: randomized controlled trial; CC: case control; RC: retrospective cohort; RSA: reverse shoulder arthroplasty; RTSA: reverse total shoulder arthroplasty; CTA: cuff tear arthropathy.

Eligibility criteria and selection process

The inclusion criteria encompassed primary studies published in English up to December 2024, focusing on the impact of LSA and DSA on postoperative functional outcomes in shoulder surgeries, as well as their association with surgical complications in patients with various shoulder pathologies.

Exclusion criteria included non-English studies, case reports, case series, editorials, animal studies, and studies lacking quantitative LSA or DSA data.

Study selection was conducted independently by two authors in a two-phase process, consisting of title and abstract screening, followed by full-text review. Any discrepancies were resolved through discussion or arbitration by the senior author.

Data extraction and quality assessment

The data extraction process was carried out independently by two authors using an Excel spreadsheet to systematically compile key study characteristics, including study design, setting, population, follow-up duration, sample size, mean age, and sex distribution (male).

To ensure methodological rigor, two additional authors conducted an independent quality assessment of the included studies. Randomized controlled trials (RCTs) were evaluated using The Cochrane Collaboration's Risk of Bias Tool (ROB-2), ¹⁴ while observational studies were assessed using the Newcastle–Ottawa Scale. ¹⁵ Any disagreements during the evaluation process were resolved through discussion or adjudication by the senior author.

Outcomes measurement and definitions

This systematic review focused on key areas, including the impact of LSA and DSA on postoperative functional outcomes, the association of these angles with complication rates, the identification of optimal LSA and DSA ranges, and their biomechanical implications in shoulder arthroplasty.

• Global lateralization: The measurement from the rim of the glenoid to the outermost edge of the greater tuberosity.^5,16

• LSA: the angle between two lines drawn from the acromion—one to the greater tuberosity and the other to the superior glenoid tuberosity.^4,5

• The lateralization index (LI) is calculated by dividing the distance from the greater tuberosity's lateral edge to the acromion's lateral edge by the distance from the glenoid plane to the lateral edge of the greater tuberosity.^5,16

• Global distalization: The measurement from the acromion down to the highest point on the greater tuberosity.^5,16

• DSA: the angle formed by two lines extending from the superior glenoid, one to the greater tuberosity and the other to the acromion.^4,5

• The distalization index (DI) is determined by dividing the distance between the highest point of the greater tuberosity and the upper margin of the glenoid by the distance from the lowest point of the acromion to the highest point of the greater tuberosity.^5,16

• Critical shoulder angle (CSA): The angle between a line drawn between the top and bottom poles of the glenoid and a line extending from the inferior glenoid pole to the lateral border of the acromion.^5,16

Data synthesis

This systematic review synthesized data across multiple key domains to assess the impact of LSA and DSA on outcomes following shoulder arthroplasty. The biomechanical implications of LSA and DSA variations were analyzed, focusing on their effects on joint mechanics, stress distribution, and overall shoulder function. Additionally, clinical outcome correlations were evaluated to determine the relationship between specific LSA and DSA values and postoperative recovery metrics, including pain levels, functional improvement, and ROM.

The role of surgical techniques and implant positioning in influencing LSA and DSA adjustments was also examined to assess their impact on postoperative functional outcomes. Furthermore, complication rates were analyzed to explore the association between varying degrees of lateralization and distalization and the incidence of implant loosening, joint instability, and other postoperative complications. This review also aimed to establish optimal LSA and DSA ranges that maximize functional recovery and minimize surgical complications.

To achieve these objectives, the interplay between LSA and DSA was investigated to identify synergistic and antagonistic effects that influence patient outcomes. This review provides novel insights into the biomechanical mechanisms underpinning LSA and DSA adjustments and offers evidence-based recommendations for optimizing surgical planning and implant positioning. Moreover, patient-specific factors, including anatomical and injury-related variations, were considered to develop guidelines for tailoring LSA and DSA adjustments in clinical practice. This synthesis aims to inform surgeons and patients about the significance of LSA and DSA in postoperative recovery expectations and functional outcomes.

Results

Study selection and data extraction

The initial search identified 436 studies, of which 52 duplicates were removed, leaving 384 studies for title and abstract screening. Following this phase, 64 studies were deemed eligible for full-text review. After applying exclusion criteria, an additional 50 studies were excluded, resulting in 14 studies being included in this systematic review.

Among the 14 studies included in this review, 13 were observational in design, and one was a RCT. Study settings spanned multiple countries, including the United States, France, Italy, Chile, and Argentina. Patient cohorts comprised individuals undergoing reverse shoulder arthroplasty (RSA), reverse total shoulder arthroplasty, or treatment for cuff tear arthropathy (CTA). Follow-up intervals varied from 3 months to 2 years. Across all studies, 8372 patients were enrolled; individual study sample sizes ranged from 20 to 6320. The mean age of participants ranged from 68 ± 12.7 to 76 ± 7 years, and the proportion of male patients varied between 8% and 70%. The screening process is illustrated in the PRISMA flow diagram (Figure 1), and a summary of the included studies is presented in (Table 1).

Figure 1.

PRISMA flow diagram. PRISMA: Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

Quality assessment

The overall risk of bias assessment for the included RCT indicated a low risk (Figure 2). Additionally, the quality evaluation of all observational studies included in this review classified them as high quality except one study was classified as low quality (Table 2). This combination of low bias and robust methodological quality enhances the strength, reliability, and validity of the findings presented in this study.

Figure 2.

Risk of bias of the included RCT. RCT: randomized controlled trial.

Table 2.

The quality evaluation of all observational studies (NOS).

study ID	selection				Comparability	outcome			Quality rating	overall quality
	Representativeness of the exposed cohort	Selection of the non-exposed cohort	Ascertainment of exposure	Demonstration that outcome of interest was not present at start of study	Comparability of cohorts on the basis of the design or analysis controlled for confounders	Assessment of outcome	Was follow-up long enough for outcomes to occur	Adequacy of follow-up of cohorts
Mahendraraj et al. 2020	*	—	*	*	**	*	*	*	8	Good
Marsalli et al. 2021	*	*	*	*	**	*	*	*	9	Good
Moverman et al. 2024	*	*	*	*	**	*	*	*	9	Good
Boutsiadis et al. 2018	*	—	*	*	**	*	*	*	8	Good
Berthold et al. 2021	*	—	*	*	**	*	*	*	8	Good
Imiolczyk et al. 2023	*	—	*	*	**	*	*	*	8	Good
Giovannetti et al. 2024	*	—	*	*	**	*	*	*	8	Good
Tuphé et al. 2022	*	—	*	*	**	*	*	*	8	Good
Valenti et al. 2024	*	—	*	*	**	*	*	*	8	Good
Longo et al. 2023	*	—	*	*	**	*	*	*	8	Good
Hill et al. 2022	*	—	*	*	**	*	*	*	8	Good
Dainotto et al. 2023	*	*	*	*	*	*	*	*	8	Good
Okutan et al. 2024	*	—	*	—	—	*	—	—	3	Poor

NOS: Newcastle–Ottawa Scale.

Influence of lateralization shoulder angle on postoperative outcomes

The analysis of 13 studies consistently underscores the critical role of the LSA in determining postoperative functional outcomes following shoulder surgeries. Berthold et al. (2021) ¹⁷ reported a negative correlation between LSA and functional scores, including the American Shoulder and Elbow Surgeons (ASES) score (p = 0.03; r = −0.281) and the Simple Shoulder Test (p = 0.001; r = −0.41), suggesting that lower LSA values are associated with superior functional recovery. This finding is supported by Valenti et al. (2024), ¹⁸ who observed a moderate negative correlation between LSA and both ASES (ρ = −0.43, p = 0.001) and Constant scores (ρ = −0.35, p = 0.005), further reinforcing the notion that reducing LSA enhances postoperative function.

Similarly, Boutsiadis et al. (2018) ⁴ identified an optimal LSA range of 75° to 95°, with a cutoff value of 75° demonstrating high sensitivity (0.90) and specificity (0.80) for predicting active external rotation (AER) > 16° (p < .001). In line with these findings, Mallett et al. (2021) ¹⁹ reported that lower postoperative LSA was associated with significant improvements in elevation and external rotation (p = .0118 and p = .0002, respectively), reinforcing the trend observed in other studies.

Additionally, Dainotto et al. (2024) ²⁰ demonstrated a negative Pearson correlation between LSA and abduction (ABD) (r² = −0.38; p = 0.047), further supporting the idea that a lower LSA benefits specific functional movements. Conversely, Longo et al. (2023) ²¹ reported that higher LSA values were linked to increased internal rotation (IR) peak values and ROM, suggesting that LSA may have a nuanced, movement-specific impact on different functional parameters. In contrast, Imiolczyk et al. (2024) found that LSA does not predict the 2-year functional and clinical outcomes of RSA in patients who have CTA. ²²

From another point of view, Okutan et al. (2024), ⁵ which looks at the LI rather than angular measurement, LSA demonstrated a weak but statistically significant correlation with lateralization (r = 0.36, p < 0.01). In contrast, no significant association was observed between LSA and lateralization arm change (LAC). In contrast, the LI—an index-based measure—showed moderate correlations with both lateralization (r = 0.72, p < 0.01) and LAC (r = 0.78, p < 0.01). Additionally, LSA exhibited a moderate correlation with the CSA (r = 0.54). No significant correlation was found between glenoid inclination (GI) and any of the lateralization measures (LSA, LI). Also, Okutan et al. concluded that LI is more reliable than angular radiographic measurement (LSA) for estimating implant lateralization, though their prognostic value for clinical outcomes remains unestablished.

Influence of distalization shoulder angle on postoperative outcomes

The DSA also plays a crucial role in postoperative functional outcomes, although its impact appears to exhibit greater variability across studies. Berthold et al. (2021) ¹⁷ identified a significant positive correlation between DSA and final active forward elevation (p = 0.02; r = 0.299), suggesting that increased distalization enhances elevation capacity. Similarly, Valenti et al. (2024) ¹⁸ reported a moderate positive correlation between DSA and ASES scores (ρ = 0.39, p = 0.002) as well as Constant scores (ρ = 0.36, p = 0.004), reinforcing the association between greater distalization and improved functional outcomes. These findings align with those of Boutsiadis et al. (2018), ⁴ who established an optimal DSA range of 40° to 65° for maximizing anterior active elevation (AAE) and abduction. A cutoff value of 65° demonstrated high sensitivity (0.90 for AAE >106° and 0.95 for abduction >78°) and specificity (0.70 and 0.90, respectively) (p = .02 and p = .03), highlighting the functional benefits of maintaining DSA within this range. Furthermore, Dainotto et al. (2024) ²⁰ identified a direct proportional Spearman association between postoperative Acromiohumeral Distance and active elevation (AE) (rs = 0.49), supporting an optimal DSA range of 40° to 45° for achieving AE >106°, corroborating the findings of Boutsiadis et al. (2018). ⁴ Conversely, Mahendraraj et al. (2020) ²³ and Imiolczyk et al. (2023) ²² found minimal or no significant correlations between DSA and various functional outcomes, suggesting inconsistencies in the influence of DSA across different patient cohorts and surgical techniques. Additionally, Longo et al. (2023) ²¹ reported that while DSA was significantly associated with IR ROM, its correlation with other kinematic variables remained non-significant, indicating a more movement-specific impact of DSA on functional recovery.

Finally, Okutan et al. (2024), ⁵ which looked at the DI rather than angular measurement, found that DSA did not correlate significantly with distalization (r = 0.17, p = 0.113) or Distalization Arm Change (DAC) (r = 0.06, p = 0.214). In contrast, the DI demonstrated moderate correlations with both distalization (r = 0.69, p < 0.01) and DAC (r = 0.62, p < 0.01). DSA also showed a moderate negative correlation with CSA (r = −0.74). Similar to the lateralization metrics, GI did not correlate significantly with DSA or DI. Finally, Okutan et al. concluded that DI is more reliable than angular radiographic measurements (DSA) for estimating implant distalization, though their prognostic value for clinical outcomes remains unestablished.

Complication rates associated with lateralization and distalization shoulder angles

Complication rates varied among the included studies, with associations between LSA, DSA, and postoperative complications being inconsistently reported. Berthold et al. (2021) ¹⁷ documented an overall complication rate of 28%, which included radiolucent lines, heterotopic ossification, and tuberosity resorption, all identified as potential predictors of poorer clinical outcomes.

Hill et al. (2022) ²⁴ specifically linked higher preoperative LSA and greater postoperative reductions in LSA to an increased incidence of acromial stress fractures (ASF), suggesting that excessive lateralization followed by medialization may predispose patients to structural compromise.

Similarly, Moverman et al. (2024) ²⁵ reported a 3.8% overall incidence of stress fractures, including 2.8% acromial stress fractures and 0.9% scapular spine stress fractures. Notably, greater glenoid lateralization was associated with reduced rates of scapular notching and impingement, though no direct correlation between LSA/DSA and implant loosening or instability was established.

Conversely, other studies, such as Tuphé et al. (2022) ²⁶ and Marsalli et al. (2021), ²⁷ found no significant association between LSA/DSA and complication rates, suggesting that other factors, including surgical technique and patient-specific anatomical variations, may influence complication risk independently of these angles

Optimal angle ranges for lateralization and distalization shoulder angles

The reviewed studies collectively establish optimal ranges for LSA and DSA to enhance postoperative functional outcomes and minimize complications in shoulder surgery.

For LSA, a strong consensus among Boutsiadis et al. (2018), ⁴ Berthold et al. (2021), ¹⁷ and Valenti et al. (2024) ¹⁸ supports an optimal range of 75° to 95°, consistently linked to improved AER and superior functional scores. Specifically, Boutsiadis et al. (2018) ⁴ identified a cutoff value of 75°, which demonstrated high sensitivity (0.90) and specificity (0.80) for predicting favorable AER outcomes, reinforcing the clinical importance of maintaining LSA within this range.

However, Dainotto et al. (2024) ²⁰ proposed a broader optimal LSA range of 80° to 100° for abduction (ABD > 76°) and 80° to 90° for AE ( > 106°), suggesting that slightly higher LSA values may enhance specific functional movements without compromising overall shoulder mechanics.

For DSA, studies by Boutsiadis et al. (2018), ⁴ Valenti et al. (2024), ¹⁸ and Hill et al. (2022) ²⁴ frequently reported an optimal range of 40° to 65°, correlating with improved AAE and abduction. Boutsiadis et al. (2018) ⁴ further refined this by identifying a cutoff value of 65°, which demonstrated high sensitivity (0.90) and specificity (0.70) for predicting AAE > 106°, along with high accuracy (sensitivity 0.95; specificity 0.90) for abduction >78°. These findings reinforce the importance of maintaining DSA within this range to optimize functional outcomes.

Conversely, Dainotto et al. (2024) ²⁰ suggested a more narrowly defined optimal DSA range of 40° to 45° for achieving AE > 106°, indicating that excessive distalization beyond this range may not provide additional functional benefits and could increase complication risks.

The agreement among Boutsiadis et al. (2018), ⁴ Berthold et al. (2021), ¹⁷ and Valenti et al. (2024) ¹⁸ on optimal LSA and DSA ranges underscores a general consensus on their importance in optimizing surgical outcomes. However, the variability introduced by Dainotto et al. (2024) ²⁰ suggests that LSA and DSA should be tailored based on specific functional demands and patient characteristics. These discrepancies highlight the complexity of implant positioning and emphasize the influence of surgical technique and patient anatomy on postoperative recovery and success.

Combined influence of lateralization and distalization shoulder angles

The interplay between LSA and DSA was found to be a key determinant of postoperative outcomes. Boutsiadis et al. (2018) ⁴ reported a strong negative correlation (rs = −0.7, p < .001) between LSA and DSA, indicating that modifications in one angle directly influence the other. This relationship is crucial for optimizing deltoid tension and overall shoulder biomechanics, as an imbalance may lead to deltoid dysfunction or increased mechanical stress on the implant and surrounding structures.

The importance of maintaining an appropriate LSA-DSA balance was further emphasized by Berthold et al. (2021) ¹⁷ and Valenti et al. (2024), ¹⁸ who highlighted its role in achieving optimal functional recovery and reducing complication rates. Additionally, Longo et al. (2023) ²¹ found that while LSA and DSA were strongly correlated, their combined impact was particularly significant in influencing IR but had less pronounced effects on other functional outcomes, illustrating the complex and multifaceted nature of their interaction in shoulder biomechanics.

Discussion

Summary of key findings

This systematic review highlights the critical influence of LSA and DSA on postoperative outcomes following shoulder surgery. The synthesis of 13 studies demonstrates that maintaining LSA within an optimal range of 75° to 95° is consistently linked to improved functional scores and enhancedAER. Similarly, a DSA range of 40° to 65° is associated with greater AAE and abduction, contributing to superior postoperative mobility. The interplay between LSA and DSA is particularly crucial, as their balanced adjustment optimizes deltoid tension and shoulder biomechanics, thereby reducing the risk of complications such as acromial stress fractures and implant instability. These findings underscore the importance of precise implant positioning in enhancing functional recovery and long-term surgical success.

Biomechanical implications and clinical relevance

The biomechanical basis of LSA and DSA underscores their critical role in modulating deltoid muscle function and shoulder joint mechanics. Optimal lateralization (LSA) enhances the deltoid's moment arm, improving arm elevation while reducing scapular notching and impingement risks, as shown by Berthold et al. (2021) and Valenti et al. (2024).^17,18 Similarly, appropriate distalization (DSA) optimizes the deltoid's length–tension relationship, promoting a greater ROM in elevation and abduction, as evidenced by Boutsiadis et al. (2018) ⁴ and Hill et al. (2022). ²⁴ However, the strong negative correlation between LSA and DSA necessitates a balanced approach to implant positioning, as excessive adjustments in either parameter may disrupt joint stability and increase complication risks. ⁴ These biomechanical principles directly inform clinical practice, guiding surgeons to target an LSA of 75°–95° and DSA of 40°–65° during preoperative planning and intraoperative decision-making. Advanced tools such as intraoperative imaging, patient-specific instrumentation, and surgical planning software further enable precise implant positioning, allowing customized adjustments based on individual anatomy and surgical conditions.^27,28 Integrating biomechanical evidence and personalized strategies aims to optimize functional outcomes while minimizing complications in shoulder arthroplasty.

Patient-Specific factors and customization

While optimal LSA and DSA ranges serve as a general guideline, individual patient-specific factors, including anatomical variations, the extent of rotator cuff deficiency, and preoperative functional status, necessitate personalized adjustments to achieve optimal surgical outcomes. Giovannetti et al. (2024) ²⁸ and Valenti et al. (2024) ¹⁸ emphasize that tailoring LSA and DSA modifications based on patient-specific biomechanics and deltoid muscle function can further enhance functional recovery and joint stability. This individualized approach ensures that LSA-DSA balance is adjusted in a way that aligns with the patient's unique anatomical and functional requirements, thereby maximizing the efficacy of shoulder arthroplasty and improving long-term clinical outcomes.

Clinical implications and recommendations

Based on the synthesized evidence, key clinical recommendations emerge, providing guidance for surgeons in optimizing implant positioning and enhancing patient outcomes following shoulder arthroplasty (Figure 3).

1. Guidelines for Surgeons

   • Target Optimal Ranges: Maintain an LSA between 75° and 95° and a DSA between 40° and 65° to optimize functional recovery, joint stability, and biomechanical efficiency.
   • Utilize Advanced Surgical Tools: Leverage intraoperative imaging, computer-assisted navigation, and patient-specific instrumentation to achieve precise implant placement within these optimal ranges.
   • Achieve LSA-DSA Balance: Carefully adjust and balance LSA and DSA to optimize deltoid tension, ensure proper shoulder biomechanics, and minimize complications such as implant instability, deltoid dysfunction, and stress fractures.
2. Patient Counseling

   • Establish Realistic Expectations: Educate patients on the critical role of implant positioning in postoperative functional recovery, emphasizing its impact on pain reduction, ROM, and long-term joint function.
   • Discuss Potential Risks: Inform patients about the complications associated with suboptimal LSA and DSA adjustments, including deltoid dysfunction, acromial stress fractures, and altered biomechanics, to facilitate informed decision-making and promote adherence to rehabilitation protocols.

Figure 3.

Clinical implications and recommendation.

These recommendations underscore the importance of a precision-based approach in shoulder arthroplasty, ensuring that LSA and DSA adjustments are tailored to individual patient anatomy to achieve optimal clinical outcomes and long-term surgical success.

Strengths of the review

This systematic review presents several notable strengths, reinforcing its contribution to orthopedic research and its clinical relevance in shoulder arthroplasty.

Firstly, by incorporating data from 13 high-quality studies, this review establishes a strong evidence base for evaluating the impact of LSA and DSA on postoperative functional outcomes and complications. The consistent identification of optimal LSA and DSA ranges across multiple studies enhances the reliability and validity of the conclusions, providing clinically applicable guidance for surgical decision-making.

Additionally, this review offers a detailed analysis by examining functional outcomes, complication rates, and the biomechanical interplay between LSA and DSA, facilitating a comprehensive understanding of their roles in shoulder biomechanics and implant positioning. The rigorous quality assessment of all included studies ensures that the review is grounded in high-quality evidence, further strengthening the credibility of its findings.

Furthermore, as the most recent and comprehensive systematic review on this topic, it is the first to thoroughly examine the combined influence of LSA and DSA on postoperative outcomes, offering new insights and advancing current knowledge in shoulder arthroplasty research.

These strengths collectively emphasize the clinical significance of this review, providing surgeons with evidence-based recommendations for optimizing implant positioning, minimizing complications, and improving patient outcomes.

Limitations

Despite its strengths, this review has several limitations. First, heterogeneity in surgical techniques, implant designs, and measurement methods across studies reduces comparability. Second, the predominance of retrospective designs limits causal inference and may introduce selection bias. Third, small sample sizes in many studies reduce statistical power and generalizability. Fourth, inconsistent measurement of LSA and DSA may affect the reliability of reported outcomes. Finally, incomplete reporting of complication rates prevents a comprehensive assessment of their relationship to LSA and DSA, highlighting the need for prospective, standardized investigations.

Future research directions

Given the ethical challenges of randomizing patients to intentionally high or low LSA/DSA, future investigations might instead focus on extensive, multicenter registry data with standardized radiographic protocols to establish thresholds associated with optimal function. Additionally, advanced imaging (e.g. CT-based 3D modeling) may help refine implant positioning without subjecting patients to unnecessary risk.

Conclusion

Maintaining LSA within 75° to 95° and DSA within 40° to 65° emerges as a consensus among multiple studies, correlating with enhanced AER, AAE, and overall functional recovery. The balanced interplay between LSA and DSA is crucial for optimizing deltoid tension and shoulder biomechanics, thereby minimizing the risk of complications such as acromial stress fractures and implant instability. Future research should aim to validate these optimal ranges through standardized, prospective studies and explore the integration of advanced technologies to further refine shoulder surgeries techniques.