Clinical implications of scapular notching at 2 and 5-year follow-up after reverse total shoulder arthroplasty

Robert J. Shelley; Mikalyn T. DeFoor; Stephen A. Parada; Lynn A. Crosby

doi:10.1016/j.jor.2020.08.006

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Original Article

21 (); 384-389

doi:

10.1016/j.jor.2020.08.006

Clinical implications of scapular notching at 2 and 5-year follow-up after reverse total shoulder arthroplasty

Robert J. Shelley^a, Mikalyn T. DeFoor^b, Stephen A. Parada^a,, Lynn A. Crosby^c

a Department of Orthopaedics, Medical College of Georgia at Augusta University Medical Center, Augusta, GA, USA

b School of Medicine, Medical College of Georgia at Augusta University, Augusta, GA, USA

c Veterans Affairs Nebraska-Western Iowa Health Care System, Omaha, NE, USA

∗Corresponding author: Stephen A. Parada. sparada@augusta.edu

Received: 2020-4-21, Accepted: 2020-8-11, Published: 2020-8-19

Professor P K Surendran Memorial Education Foundation

Disclaimer:
This article was originally published by Reed Elsevier India Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.

Abstract

Scapular notching is a unique radiographic sequela of reverse total shoulder arthroplasty (rTSA) with unclear long-term clinical consequences.

Our retrospective review of a single surgeon, single implant, primary rTSA database investigates the incidence of scapular notching at 2 and 5-year follow-up. Various patient outcome scores were also obtained.

Of 158 primary rTSAs performed, 82 (52%) patients completed 2-year and subsequent 5-year follow-up. The incidence of scapular notching at 2 and 5-years was 11.9% and 19.5%, respectively.

Scapular notching negatively affects validated post-operative outcome scores, active range of motion and total complications, and furthermore increases with time.

Keywords

Reverse total shoulder arthroplasty (rTSA)

Scapular notching

Complications

Clinical outcomes

Retrospective study

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1 Introduction

Reverse total shoulder arthroplasty (rTSA) has been proven to decrease pain and improve function for patients with rotator cuff arthropathy, and its use in the United States has continued to increase since its introduction to that market in 2003.^1–3 Although initially utilized for patients with rotator cuff arthropathy (RCA),⁴ indications have evolved to include patients with rheumatoid arthritis, acute and chronic proximal humerus fractures, chronic rotator cuff tears with pseudoparalysis, osteoarthritis with severe glenoid wear, and revision of unsatisfactory or failed anatomic total shoulder arthroplasties (TSA).¹^,⁵^,⁶ Major complication rates are reported as high as 26%, despite the improved implant designs and increased surgeon experience.⁷ These well documented complications include scapular notching, acromial/scapular fracture, post-operative hematoma, instability, glenosphere dissociation, and periprosthetic infection.^8–10

Scapular notching is a radiographic sequela unique to rTSA that initially occurs when the polyethylene liner of the humeral component mechanically impacts the inferior scapular neck.^11–18 This phenomenon results in bone loss under the inferior glenoid baseplate and can ultimately lead to component loosening through further osteolysis. Scapular notching is classified by the Nerot-Sirveaux grading scale,¹⁸ with grade 1 or 2 representing mechanical impingement of the humeral polyethylene linear on the inferior scapular neck, and 3 or 4 representing a further osteolytic process as the notching progresses superior to the inferior glenoid screw.^18–21

Roche et al.²² demonstrated that scapular notching increases baseplate micromotion and diminishes component fixation in a biomechanical study, possibly leading to glenoid baseplate instability. However, the clinical effects of scapular notching in orthopaedic practice remain unclear and are widely variable throughout the reported literature. Mollon et al.²³ reported a 10.1% rate of scapular notching in patients with a minimum 2-year follow-up, with significantly lower functional outcome scores, strength, and active abduction, as well as higher complication rate as compared to the patient cohort without notching. Conversely, Werner et al.²¹ reported a 96% incidence in scapular notching but reported no clinical significance, deeming notching as simply “asymptomatic osteolysis of the distal scapular neck.” The purpose of this study was to further investigate the incidence and clinical implications of scapular notching at 2 and 5-year follow-up after primary rTSA through retrospective review of a prospectively collected single surgeon, single implant, primary rTSA database. Our hypothesis was that scapular notching does increase with time and negatively impacts patient outcome measures in clinical practice.

2 Methods

2.1

2.1 Level of evidence

Level III.

2.2

2.2 Study design

This study was a retrospective review of a prospectively collected database of patients who received a primary rTSA between 2009 and 2013 and completed clinical and radiographic follow-up at both 2 and 5 years post-operatively. Patients were treated with rTSA at a single institution for various surgical indications including rotator cuff arthropathy, previously failed arthroplasty/resurfacing, or post-traumatic pathology. Any primary rTSA completed during this study period that successfully completed all follow up visits was included. All revision rTSAs performed during this time period were excluded.

Approval was obtained by the Institutional Review Board (IRB) at our institution for initial patient recruitment and enrollment in the large clinical database for rTSA outcomes. Written informed consent and approval to enroll in the rTSA clinical database was obtained from all patients. Patient demographic data was entered into a database and outcomes were updated at yearly post-operative follow-up visits. Standard shoulder radiographs were obtained pre-operatively, post-operatively, and at subsequent 1, 2, and 5-year follow-up intervals. Primary clinical database records were reviewed including patient demographics, surgical and perioperative notes, and both initial and follow-up radiographs for all patients that received a rTSA. All patients with 5-year follow-up were included in the study, and any patient that did not meet 5-year follow-up was then excluded. The primary outcome of interest in this study was the presence or absence of scapular notching.

2.3

2.3 Surgical methods

A single, fellowship trained shoulder surgeon performed all procedures with a single rTSA implant (Equinoxe Reverse Total Shoulder Arthroplasty, Exactech, Gainesville, FL, USA) via a deltopectoral approach. This medial glenoid/lateral humerus implant design²⁴^,²⁵ has a well-defined and relatively low scapular notching rate compared to the traditional Grammont style prosthesis.^12–14^,²³^,²⁶ Each procedure was performed in the beach chair position with the standard deltopectoral approach. The subscapularis was taken down and not repaired in any case, per standard technique by the surgeon. Care was taken to circumferentially expose the entire glenoid, particularly the inferior rim. After exposure of the glenoid was achieved, all soft tissue including any remaining labrum was removed so the entire glenoid could be visualized. A drill guide for the center peg of the baseplate was utilized to ensure that the baseplate would have slight inferior offset from the native glenoid. Approximately 1 mm but not more than 3 mm was used as the guide for inferior offset. The glenosphere in the system utilized fits over the baseplate and is then secured in place with a screw, creating even further inferior offset.

Post operatively, each patient received a standardized and guided occupation therapy protocol. The first two weeks after surgery were guarded with full time sling wear and limited passive range of motion of the shoulder. Sling wear was slowly weaned over the next four weeks while initiating active-assisted range of motion, with an emphasis on limited internal rotation behind the back during this period. The six to twelve week period focused on regaining full frontal plane motion, deltoid/rotator cuff isometric strengthening, and closed chain scapular stabilization. After regaining full range of motion (to include internal rotation behind the back) and scapular strength, endurance strengthening was initiated at the three-month mark. The patient then progressed back to the normal activities of daily living by six months.

2.4

2.4 Clinical assessment

Pre-operative information collected included age at surgery, gender, diagnosis, body mass index (BMI), weight, height, pain scores, shoulder outcome scores, and active range of motion (forward flexion, abduction, and internal/external rotation). The four validated shoulder outcome scores collected included the American Shoulder and Elbow Surgeons (ASES) score, Constant Score, Simple Shoulder Test (SST) score, and the University of California, Los Angeles (UCLA) Shoulder Rating Scale. Intraoperative data obtained included operative side and component sizes. Post-operative data collection included radiographic analysis, pain scores, validated shoulder outcome scores, active range of motion (ROM) and any post-operative complication.

2.5

2.5 Radiographic assessment

Two fellowship trained shoulder surgeons (LAC & SAP) independently completed analysis of the post-operative radiographic findings. The presence and severity of scapular notching was recorded in reference to the Nerot-Sirveaux classification (Fig. 1).¹⁸ Whenever a discrepancy in grading scale existed between the two reviewers, the higher grade was recorded. Rates of humeral radiolucency were also recorded.

Radiographic illustration of the Nerot-Sirveaux classification system of scapular notching with Grade 1 limiting to the inferior pillar of the scapular neck, Grade 2 contacting the inferior screw of the baseplate, Grade 3 extending beyond the inferior screw, and Grade 4 invading under the baseplate and approaching the central peg.

2.6

2.6 Data analysis

A Shapiro-Wilk test found the data was not normally distributed, therefore data analysis was performed using nonparametric tests. As a result, a Mann-Whitney test was used to identify differences in data, where P = .05 was used to determine significance. Descriptive data are reported as mean ± standard deviation for continuous variables and as percentages for categorical data.

3 Results

Of the 158 primary rTSAs performed during this period, 82 patients (52%) completed both 2-year and subsequent 5-year follow-up. Scapular notching was observed in 11.9% of patients at 2-year follow-up and 19.5% of patients at 5-year follow-up. At final 5-year follow up, 31% (5 of 16) of patients with scapular notching were grade 1, 12.5% (2 of 16) were grade 2, and 56% (9 of 16) were grade 4, as graded by the Nerot-Sirveaux classification (Figs. 2 and 3). No patients had grade 3 notching at 5-year follow-up in this cohort.

Radiographs of a 69-year-old female at immediate post-operative (A), 2 years (B), and 5 years (C) demonstrate low-grade notching (Grade 1) present on the 5-year radiographs (C).

Radiographs of a 71-year-old female at immediate post-operative (A), 2 years (B), and 5 years (C) demonstrate high-grade notching (Grade 4) present on the 5-year radiographs (C).

There was no significant difference in pre-operative patient demographics (age, height, weight, BMI or gender) or recorded operative factors (size of glenosphere, polyethylene liner or humeral tray) in patients that developed scapular notching at 2 or 5-year follow-up versus those that did not. The average age of patients with and without scapular notching was not statistically different, 65.5 ± 10.9 and 66.8 ± 11.6, respectively (P = .68). The incidence of scapular notching was similar between men and women (8/16 men vs 26/62 women, P = .57). There was also no difference in incidence based on BMI (30.9 ± 6.1 vs 29.5 ± 5.1, P = .38), weight (126.7 ± 43.2 vs 136.5 ± 48.5, P = .45) or height (126.5 ± 44.3 vs 108.9 ± 39.8, P = .17) between the scapular notching and control groups. In regard to implant size parameters, there was no difference in glenosphere (39.1 ± 1.8 vs 39.5 ± 2.4, P = .43), polyethylene liner (1.3 ± 1.3 vs 0.9 ± 1.2, P = .03), or humeral tray (1.7 ± 4.1 vs 1.5 ± 2.7, P = .87) size between the scapular notching and control patient cohorts (Table 1).

Table 1 Demographic comparison of patients with and without scapular notching at 5 years.

Variable	No Scapular Notching (n = 16)	Scapular Notching (n = 66)	Significance (P)
Patient Demographics
Age (yr)	65.5 ± 10.9	66.8 ± 11.6	0.68
Height (cm)	108.9 ± 39.8	126.5 ± 44.3	0.17
Weight (kg)	136.5 ± 48.5	126.7 ± 43.2	0.45
BMI (kg/m²)	29.5 ± 5.1	30.9 ± 6.1	0.38
Male Gender	50 (8/16)	42 (26/62)	0.57
Preoperative Function
UCLA Score	8.5 ± 2.2	7.9 ± 2.4	0.43
ASES Score	13.8 ± 12.2	8.5 ± 10.9	0.12
Simple Shoulder Test Score	0.7 ± 1.6	0.8 ± 2.0	0.89
Constant Score	18.9 ± 15.2	15.4 ± 16.8	0.48
Active Forward Flexion (°)	71.0 ± 39.5	73.6 ± 40.7	0.83
Active Abduction (°)	52.3 ± 26.2	54.6 ± 23.2	0.75
Active External Rotation (°)	4.5 ± 11.3	0.7 ± 9.6	0.21
Operative Factors
Glenosphere Size (mm)	39.5 ± 2.4	39.1 ± 1.8	0.43
Poly Size (mm)	0.9 ± 1.2	1.3 ± 1.3	0.30
Humeral Tray (mm)	1.5 ± 2.7	1.7 ± 4.1	0.87

Post-operatively, every patient had statistically significant improvements in every active ROM and functional outcome scores compared to pre-operative scores regardless of the development of scapular notching. However, at 5-year follow-up, patients with scapular notching had significantly lower ASES (87.5 ± 13.5 vs 93.7 ± 3.8, P = .007), Constant (81.6 ± 13.9 vs 88.9 ± 4.4, P = .02), UCLA (32 ± 4.1 vs 34 ± 1.6, P = .008), and SST (10.1 ± 1.9 vs 10.9 ± 0.5, P = .009) scores, compared with patients without scapular notching. At 5-year follow-up, patients with scapular notching also had significantly less active forward flexion (130° ± 46.1° vs 162.5° ± 16.6°, P = .017) and external rotation (26.7° ± 9.9° vs 32.7° ± 6.6°, P = .039), but no significant difference in active abduction (84.4° ± 1.3° vs 89.6° ± 1.9°, P = .085) (Table 2). Additionally, patients with scapular notching at 5 years had similar visual analog scale (VAS) pain scores to those that did not (0.3 ± 0.7 vs 0.1 ± 0.4, P = .27).

Table 2 Post-operative outcome comparison with and without scapular notching at 5 years.

Patient Outcomes	ASES Score	Constant Score	UCLA Score	SST Score	Active Forward Flexion (°)	Active Abduction (°)	Active External Rotation (°)
No Notching	93.7 ± 3.8	88.9 ± 4.4	34 ± 1.6	10.9 ± 0.5	162.5 ± 16.6	89.6 ± 1.9	32.7 ± 6.6
Notching	87.5 ± 13.5	81.6 ± 13.9	32 ± 4.1	10.1 ± 1.9	130 ± 46.1	84.4 ± 1.3	26.7 ± 9.9
Significance	.007	.02	.008	.009	.017	.085	.039

There was a total of 15 (18.2%) complications reported for both patient cohorts. Comparatively, there were 8 (12.9%) complications in patients without scapular notching and 7 (43.7%) complications in patients with scapular notching, a statistically significant difference (P = .006). Additionally, there were 12 patients (14.6%) with medial humeral radiolucent lines at 5-year follow-up, 8 (75%) in patients with scapular notching and 4 (25%) in patients without notching, also being a statistically significant finding (P = .0002).

4 Discussion

This clinical study provides a retrospective review of a single surgeon, single implant, primary rTSA database of patients that completed 2 and 5-year radiographic and clinical follow-up, noting an incidence of scapular notching at 2 and 5 years of 11.9% and 19.5%, respectively. Our study demonstrates several noteworthy clinical findings associated with the presence or absence of scapular notching, including no difference among cohorts in regard to demographic patient characteristics, pre-operative functional outcome scores and ROM, or size of implant components placed intraoperatively. Post-operatively, however, lower functional outcome scores and less active forward flexion and external rotation, as well as increased overall complication rates and higher presence of medical humeral lucency was observed at 5-year follow-up.

It is noteworthy to recognize that every patient had statistically significant improvements in every range of motion and functional outcome score after rTSA compared to pre-operative scores, regardless of the development of scapular notching. However, this study does support previous literature suggesting that scapular notching negatively affects patient outcome scores, and furthermore increases with time.¹³^,²²^,²³ Our data reported at 2-year follow-up is similar to the findings by other authors utilizing the same implant system. Roche et al.¹³ demonstrated a scapular notching rate of 13.2% in 151 patients at a mean follow-up of 28.3 months after rTSA. Mollen et al.²³ reported a 10.1% incidence of scapular notching in 476 patients at mean follow-up of 38 months, with notching associated with significantly worse functional outcome scores.

Recent in vivo studies have demonstrated that scapular notching is subsequent to osseous impingement of the humeral implant and the scapula, particularly with external rotation of the shoulder with the arm at the side.²⁷ The post-operative three-dimensional computed tomographic (3D CT) kinematic simulation software used by Kolmodin et al.²⁷ demonstrated that notching is significantly reduced with inferior, lateral and posterior glenosphere placement for implant systems with a medialized center of rotation. However, notching was observed in 59% of patients in this study using the medialized glenoid/medialized humerus Grammont design, similar to Lévigne et al.²⁰ who reported notching rates of 68.2% with the same prosthesis. Studies confirm a significant reduction in scapular notching by recent improvements in implant design, specifically designs with larger glenospheres with inferior tilt, a humeral/neck liner angle of 145°, and a lateralized center of rotation.^28–32 These technical designs are suggested to increase resting arm adduction, decreasing the mechanical chances of impingement leading to scapular notching, which can also be correlated to increased patient BMI.³³ Although these studies agree that implant position can impact the presence of scapular notching, the translation of these findings to influence on patient outcomes is widely variable.

Medialization of the glenohumeral joint in rTSA implant designs has been associated with the development of scapular notching due to mechanical impingement.³⁴ However, the lower rate of scapular notching in the medialized glenoid/lateralized humerus design of the implant utilized during our study is consistently associated with relatively lower rates of scapular notching compared to the medialized glenoid/medialized humerus design of the Grammont prosthesis, a finding similarly reported in other studies using our same implant design.^12–14^,²³^,²⁶ It has furthermore been suggested that prosthesis designs with lower rates of scapular notching are associated with longer follow-up for notch formation,²⁶^,³¹ suggesting that continued long-term follow-up of these patients, even if asymptomatic, may be warranted due to the progressive nature of scapular notching.

Despite advances in prosthetic design, our study demonstrates that the presence of scapular notching continues to negatively impact patient outcome scores. This data supports the work originally by Mollen et al.²³ and later updated by Simovitch et al.²⁶ These two studies examined the same patient database with the same implant after short-term and then 5-year minimum follow-up, reporting a 14.5% incidence of scapular notching at a mean follow-up of 75.1 months with continued worse functional outcome scores and complication rates, as well as higher notching grades associated with increasing time to notch development. The average time to notch development as determined by radiographs was 51.4 ± 24.1 months and was positively related to increased notching grade.

Overall, our study corroborates the findings by Simovitch et al.²⁶ with some key differences. First, it is interesting to note that the average age for rTSA in our study population was 66.8 ± 11.6 years (notching) and 65.5 ± 10.9 years (no notching), compared to 72.2 ± 6.2 years (notching) and 72.0 ± 7.1 years (no notching) in the data presented by Simovitch et al.²⁶ Additionally, patient BMI, weight and height are not statistically significant demographic characteristics between the notching and no notching patient groups in our study. This is a significant finding compared to other studies that show higher BMI and weight are protective against scapular notching presumably due to less physical activity, movement ability and increased resting shoulder adduction due to body habitus. As grade 3 and 4 scapular notching appear to be more clinically significant due to the additional factor of osteolysis producing debris from the polyethylene liner, it is also clinically significant that our study reports grade 4 notching (56%) as the most common notching grade among patients at 5-year follow up, whereas Simovitch et al.²⁶ did not reveal any patients with grade 4 notching at 5 years, although they did report one-fifth of scapular notching cases to be progressive over follow-up.

Unlike the previously mentioned studies, our study method includes a single surgeon database and an independent review and grading of post-operative radiographs by two fellowship trained shoulder surgeons, which allows for a more standard analysis of scapular notching without the inherent biases associated with multicenter, multi-surgeon, and multi-implant studies. This data is also strengthened by the length of follow-up with all patients completing 5-year clinical and radiographic follow-up. However, longer follow-up is still essential to confirm the incidence, level of progression, and long-term effects of scapular notching on clinical outcomes.

5 Limitations

This study is weakened by its relatively low follow-up rate with only 52% of surgical patients completing full 5-year follow-up, which introduces a transfer bias. The data also failed to demonstrate an effect of hand dominance for the development of scapular notching as this was inconsistently recorded in the medical records, and therefore excluded in our data analysis. Patient factors including comorbidity, activity level and bone mass density were not compared within this study, which may impact level and rate of notching. Pre-operative analysis of glenoid wear morphology and scapular neck length, final glenoid component placement, and glenosphere tilt were also not included in data collection, all of which are important technical factors in reducing the incidence of scapular notching.³⁵ In order to report on the effects of scapular notching among a robust sample size in a single-surgeon practice, multiple surgical indications for rTSA were included. However, this has the potential of introducing a confounding variable impacting functional outcomes. Selection bias is introduced as a single surgeon determined the indication of all surgeries, as well as a performance bias due to all surgeries being performed by that same surgeon. However, this study design proposes a similar patient population with a single implant design and similar rehabilitation protocol, which leads to more standardization to decrease any inherent bias that comes with multicenter, multi-surgeon databases. This study is also limited by its small number of radiographic reviews. Although both reviewers are fellowship trained shoulder surgeons, multiple studies have demonstrated that the anteroposterior radiograph may not reliably provide adequate information for surgeons to classify notching according to Sirveaux, leading to low interobserver reliability.³⁶^,³⁷

6 Conclusion

This single surgeon, single implant study, with 5-year follow-up data demonstrates that scapular notching negatively affects outcome scores and active range of motion, and furthermore increases with time. Based on our findings in this current study, we recommend paying close attention to glenoid exposure and subsequent baseplate placement as well as annual follow-up radiographs in patients who exhibit any initial scapular notching. Continued follow-up is required to validate these observations and further delineate the causes and solutions to this unique problem.

Author contributions

RJS, MTD and LAC researched literature and conceived the study. RJS, LAC and SAP were involved in protocol development, gaining ethical approval, patient recruitment and data analysis. RJS wrote the first draft of the manuscript, and MTD carried out all major section revisions with input from all authors. All authors reviewed and edited the manuscript and approved the final version for publication.

Disclosures

Stephen A. Parada has received research grants from Exatech, Inc. Stephen A. Parada and Lynn A. Crosby are consultants for Exactech, Inc.

Funding

This study did not receive any specific grant from funding agencies in the public, commercial, or not-for profit sections.

Ethical approval

This study data was collected from an Augusta University IRB approved registry following all patients receiving arthroplasty under a single surgeon. Written consent has been obtained for their anonymized information to be included in the registry.

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