
==== Front
Clin Shoulder Elb
Clin Shoulder Elb
CISE
Clinics in Shoulder and Elbow
2383-8337
2288-8721
Korean Shoulder and Elbow Society

39138944
10.5397/cise.2024.00262
cise-2024-00262
Original Article
Does preoperative forward elevation weakness affect clinical outcomes in anatomic or reverse total shoulder arthroplasty patients with glenohumeral osteoarthritis and intact rotator cuff?
http://orcid.org/0000-0002-9444-9145
Hones Keegan M. 1
http://orcid.org/0000-0002-0682-8381
Hao Kevin A. 2
http://orcid.org/0009-0002-7815-7967
Buchanan Timothy R. 2
http://orcid.org/0000-0002-5967-1031
Trammell Amy P. 1
http://orcid.org/0000-0001-5788-3463
Wright Jonathan O. 1
http://orcid.org/0000-0001-9174-9874
Wright Thomas W. 1
http://orcid.org/0009-0007-5748-8958
LaMonica Tyler J. 1
http://orcid.org/0000-0002-9355-5069
Schoch Bradley S. 3
http://orcid.org/0000-0002-9201-9408
King Joseph J. 1
1 Department of Orthopaedic Surgery and Sports Medicine, University of Florida, Gainesville, FL, USA
2 College of Medicine, University of Florida, Gainesville, FL, USA
3 Department of Orthopedic Surgery, Mayo Clinic, Jacksonville, FL, USA
Corresponding Author: Joseph J. King Department of Orthopaedic Surgery and Sports Medicine, University of Florida, 3450 Hull Rd, Gainesville, FL 32611, USA Tel: +1-352-273-7002 Fax: +1-352-273-7293 Email: kingjj@ortho.ufl.edu
9 2024
30 7 2024
27 3 316326
21 3 2024
11 5 2024
2 6 2024
© 2024 Korean Shoulder and Elbow Society
2024
https://creativecommons.org/licenses/by-nc/4.0/ This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background

This study sought to determine if preoperative forward elevation (FE) weakness affects outcomes of anatomic (aTSA) and reverse total shoulder arthroplasty (rTSA) for patients with rotator cuff-intact glenohumeral osteoarthritis (RCI-GHOA).

Methods

A retrospective review of a single institution’s prospectively collected shoulder arthroplasty database was performed between 2007 and 2020, including 333 aTSAs and 155 rTSAs for primary RCI-GHOA with a minimum 2-year follow-up. Defining preoperative weakness as FE strength ≤4.9 lb (2.2 kg), three cohorts were matched 1:1:1 by age, sex, and follow-up: weak (n=82) to normal aTSAs, weak (n=44) to normal rTSAs, and weak aTSAs (n=61) to weak rTSAs. Compared outcomes included range of motion, outcome scores, and complication and revision rates at latest follow-up.

Results

Weak aTSAs and weak rTSAs achieved similar postoperative outcome measures to normal aTSAs and normal rTSAs, respectively (P>0.05). Compared to weak rTSAs, weak aTSAs achieved superior postoperative passive (P=0.006) and active external rotation (ER) (P=0.014) but less favorable postoperative Shoulder Pain and Disability Index (P=0.032), American Shoulder and Elbow Surgeons (P=0.024), and University of California, Los Angeles scores (P=0.008). Weak aTSAs achieved the minimal clinically important difference (MCID) and substantial clinical benefit at a lower rate for abduction (P=0.045 and P=0.003) and FE (P=0.011 and P=0.001). Weak aTSAs had a higher revision rate (P=0.025) but a similar complication rate (P=0.291) compared to weak rTSAs.

Conclusions

Patients with RCI-GHOA and preoperative FE weakness obtain postoperative outcomes similar to patients with normal preoperative strength after either aTSA or rTSA. Preoperatively, weak aTSAs achieved greater ER but lower rates of clinically relevant improvement in overhead motion compared to weak rTSAs.

Level of evidence

III.

Shoulder joint
Arthroplasty
Shoulder replacement
Inverted shoulder
Joint range of motion
==== Body
pmcINTRODUCTION

The utilization of total shoulder arthroplasty (TSA), in both the reverse (rTSA) and anatomic (aTSA) configurations, is increasing in the United States [1]. Conventionally, aTSA has been the procedure of choice for rotator cuff-intact glenohumeral osteoarthritis (RCI-GHOA) with purported superior rotational motion; however, rTSA is beginning to gain popularity, with recent investigations demonstrating similar outcomes for this indication [2,3].

Overhead motion and strength in forward elevation (FE) are critical to functional outcome [4]. Poor FE strength preoperatively may indicate supraspinatus pathology or insufficiency and portend a poor prognosis after aTSA [5]. Given that the success of aTSA relies on an intact rotator cuff, patients with RCI-GHOA and poor preoperative FE strength undergoing aTSA may have a better outcome with rTSA. Additionally, modern lateralized rTSA implant designs have been shown to improve strength in other planes applicable to the posterior cuff, such as the external rotation (ER), though results directly applicable to FE are few and vary [6-9]. Trammell et al. [10] found superior outcomes in patients undergoing rTSA compared to aTSA in the context of limited preoperative FE range of motion (ROM). Hao et al. [11] demonstrated pre- to postoperative improvements in FE strength in patients undergoing either aTSA or rTSA. In the context of weak FE with the rotator cuff intact, there may be incomplete supraspinatus tears or insufficiency below the threshold of visibility, in which case rTSA may portend more of an advantage with less reliance on the supraspinatus for overhead motion compared to aTSA [12], though aTSA has been shown to have acceptable outcomes in this context [13].

To further refine the indications for aTSA versus rTSA in patients with RCI-GHOA, the purpose of this study was to compare clinical outcomes of patients with RCI-GHOA and preoperative FE weakness undergoing aTSA versus rTSA. We hypothesized that patients undergoing rTSA for this indication would have improved functional outcomes and a lower complication rate compared to those undergoing aTSA. 

METHODS

We performed a retrospective review and case-control study of one tertiary referral institution’s shoulder arthroplasty database for patients undergoing aTSA or rTSA for primary RCI-GHOA between 2007 and 2020 after University of Florida Institutional Review Board approval was obtained (IRB No. 202202385). Informed consent was obtained from patients prior to enrolling in the shoulder arthroplasty database. The diagnosis of an intact rotator cuff was based on preoperative imaging and examination and confirmed intraoperatively. In addition, computed tomography (CT) scans were commonly obtained preoperatively. Low-grade partial tears were considered to be intact based on surgeon discretion, while high-grade partial and full-thickness tears were not included. Patients lacking preoperative clinical data or with less than 2 years of clinical follow-up were excluded. Additionally, patients with a preoperative diagnosis of acute proximal humerus fracture, posttraumatic glenohumeral arthritis, oncologic-related diagnoses, or preoperative nerve palsy were excluded, given the demonstration of worse clinical outcomes in these populations [14,15]. All TSAs were performed by one of four fellowship-trained shoulder surgeons. Initially, 716 primary TSAs were ascertained, from which we excluded 90 for missing preoperative clinical information including strength measurements. Thus, we had clinical information on 626 shoulders (413 aTSAs and 213 rTSAs). Of this cohort, 488 had a minimum of 2 years of clinical follow-up and were included in subsequent analyses of ROM, strength, outcome scores, and postoperative complications (332 aTSAs and 153 rTSAs). The choice between aTSA and rTSA was made by the surgeon intraoperatively. Generally, rTSA was used in the following cases, all based on surgeon discretion: Walsh B2 and B3 glenoids that could not be corrected to within 10 degrees of retroversion with augments and eccentric reaming, patients with a good result with an rTSA for any reason on the contralateral side, low-grade partial thickness cuff tears, and patients who were considered to have a low chance of healing from subscapularis takedown for an aTSA.

Surgical Technique

All shoulder arthroplasties were performed through a deltopectoral approach. This study included multiple implant designs for rTSA; 85% were the medialized-glenoid lateralized-humerus design with a 145° neck-shaft angle [16]. During rTSA, the supraspinatus was left intact and was only tenotomized sequentially if there was concern for soft tissue tension preventing glenohumeral joint reduction. The subscapularis tendon was repaired based on surgeon discretion but was commonly left as a tenotomy given the lateralized implant design commonly used in this study. For aTSA, the subscapularis was either peeled or a lesser tuberosity was performed based on surgeon preference.

Rehabilitation

Postoperatively, all patients completed a standard rehabilitation protocol consisting of a physical therapist-directed home exercise program. A sling was used for 2 weeks, and patients were allowed to begin pendulum exercises, with motion limited to passive FE and ER, to neutral for a total of 3 weeks postoperatively. Active ROM was initiated without limitations at 6 weeks. Strengthening exercises were initiated at 12 weeks, with gradual return to activities.

Clinical Outcomes

ROM, shoulder strength, and outcome scores were obtained at preoperative and postoperative clinical visits, including annual postoperative visits with clinical exam and standard radiographic views after the first year postoperatively. ROM measures were evaluated using a handheld goniometer, including active and passive FE, active and passive ER, active abduction, and active internal rotation (IR). Active IR was assessed as the most cephalad vertebral level reached by the thumb behind the patient’s back and scored according to the following scale: no IR, 0; hip, 1; buttocks, 2; sacrum, 3; L5 to L4, 4; L3 to L1, 5; T12 to T8, 6; and T7 or higher, 7 [17]. ER and FE strength were measured using a hand-held dynamometer (Lafayette Instrument Company). ER strength was assessed with the shoulder in 0° ER and 0° abduction with the elbow in 90° flexion. FE strength was measured at 30° of shoulder flexion and 30° of abduction. All measurements were executed using standardized methods by a research coordinator. Outcome scores recorded included the Simple Shoulder Test (SST), the Constant score, the American Shoulder and Elbow Surgeons (ASES) score, the University of California, Los Angeles (UCLA) score, and the Shoulder Pain and Disability Index (SPADI) as previously described [18]. Pre- and postoperative radiographs at annual follow-up visits were obtained for diagnosis and evaluation of implant positioning, loosening, and periprosthetic fractures postoperatively. Postoperative advanced imaging (e.g., CT) was not standardly obtained.

Matched Cohort Comparisons

We dichotomized preoperative FE strength using the 30th percentile among aTSAs (Fig. 1) to create weak (preoperative FE strength ≤4.9 lb [2.2 kg]) and normal (>4.9 lb) cohorts. The 30th percentile was selected as it best approximated the mode of preoperative FE strength among aTSAs. Three cohorts were generated and matched: (1) weak aTSAs (n=82) to normal aTSAs (n=82), (2) weak rTSAs (n=44) to normal rTSAs (n=44), and (3) weak rTSAs (n=61) to weak aTSAs (n=61). All matching was completed based on age (within 3 years), sex, and follow-up. In addition, the third match set was further constrained by preoperative FE strength (matched within 2 lb). Matched cohorts were conceived using the MatchIt package [19]. Outcomes compared between matched cohorts included ROM, strength, functional outcomes, and pain.

Handling of Missing Data

To avoid the selection bias introduced by complete case analysis [20], missing ROM, strength, and outcome score data were alleviated using a two-step process. First, patients missing outcome data at the latest follow-up had their previous clinical visits reviewed in reverse chronological order to identify outcomes recorded at earlier time points that qualified for the minimum 2-year follow-up. If data were present at a qualifying previous clinical time point, they were used for analysis. Additionally, for patients that still had missing data, multiple imputation by predictive mean matching was used to impute data for variables with missing values. Multiple imputation utilizes existing data to reproduce conclusions that likely would have been present in a complete dataset and has been progressively more applied in shoulder surgery studies [21,22]. We set the number of imputed datasets (M) to 20 as endorsed by the literature [23]. Estimates of standard errors among these datasets were calculated using Rubin’s rules [24]. Multiple imputation was performed using the mice package [25].

Statistical Analysis

Toward our primary aim, we compared pooled ROM, strength, and outcome scores between matched cohorts. Two-sided unpaired Welch’s t-tests were used to compare continuous measures. Fisher’s Exact test was used to compare categorical measures. Additionally, weak aTSAs vs. weak rTSAs were further evaluated by comparing the proportion of patients exceeding the minimal clinically important difference (MCID) and substantial clinical benefit (SCB) derived for primary aTSA from prior reports utilizing the same prosthesis and including many patients from our institution [18,26,27]. All statistical analyses were performed using R Software (version 4.2.0, R Core Team) with a defined P<0.05.

RESULTS

Overall Characteristics

Patients undergoing aTSA were significantly younger (65.2±7.7 vs. 71.3±7.0 years, P<0.001) and had a longer average follow-up period (5.9±3.2 vs. 3.7±1.8 years, P<0.001) compared to those undergoing rTSA. Patients who underwent aTSA also had a significantly increased average preoperative Constant score (P=0.031), active FE ROM (P=0.001), active abduction ROM (P=0.005), ER strength (P=0.005), and FE strength (P=0.005) compared to those undergoing rTSA. Postoperatively, patients who underwent aTSA exhibited significantly lower SST score (P=0.008), ASES score (P=0.001), and Constant score (P=0.001) and significantly higher SPADI (P=0.001), active ER ROM (P=0.001), passive ER ROM (P=0.003), and active IR score (P=0.009) compared to those who underwent rTSA. Patients who underwent aTSA showed significantly larger pre- to postoperative improvement in passive ER ROM (P=0.026) and significantly smaller pre- to postoperative improvement in SPADI (P=0.001), SST score (P=0.015), ASES score (P=0.004), UCLA score (P=0.001), Constant score (P=0.001), active FE ROM (P<0.001), passive FE ROM (P<0.001), active abduction ROM (P=0.006), and FE strength (P=0.015) compared to those who underwent rTSA.

Weak vs. Normal aTSA

Patients undergoing weak aTSAs had similar age (P=0.106), sex (P=1.000), prior surgery rates (P=0.350), and body mass index (BMI) (P=0.318) compared to normal aTSAs (Table 1). Weak aTSA patients had longer average follow-up than normal aTSAs (6.4±3.4 vs. 5.1±3.0 years, P=0.012) and had poorer preoperative outcome scores, strength, and active FE and abduction compared to patients undergoing normal aTSA.

Postoperatively, ROM, strength, and outcome scores were comparable between the weak and normal aTSA cohorts (P>0.05) (Table 1). Compared to normal aTSA patients, those undergoing weak aTSAs demonstrated significantly greater pre- to postoperative improvement in ER strength (4±6 vs. 1±6 lb, P=0.008) and FE strength (4±6 vs. 1±6 lb, P=0.001). Weak aTSA and normal aTSA patients demonstrated comparable all-cause complication rates (14% and 13%, respectively; P=1.000) and revision rates (12% each, P=1.000) (Table 2).

Weak vs. Normal rTSA

Weak rTSAs had similar age (P=0.487), sex (P=1.000), prior surgery rates (P=0.446), and BMI (P=0.754) compared to normal rTSAs (Table 1). Weak rTSAs had shorter follow-up (2.8±1.2 vs. 3.5±1.5 years, P=0.011) and poorer preoperative outcome scores, strength, and active FE compared to normal rTSAs.

Postoperatively, ROM, strength, and outcome scores were comparable between the weak and normal rTSA cohorts (P>0.05) (Table 1). Compared to normal rTSAs, weak rTSAs demonstrated significantly greater improvements in active FE (64°±25° vs. 45°±29°, P=0.002) and active abduction (55°±30° vs. 39°±36°, P=0.035). Weak rTSAs and normal rTSAs demonstrated similar all-cause complication rates (8.9% and 7.3%, respectively; P=0.799) and revision rates (3.8% and 3.0%, respectively; P=1.000) (Table 2).

Weak aTSA vs. Weak rTSA

Weak aTSAs and weak rTSAs had similar sex proportions, prior surgery rates, BMI, and follow-up (Table 3). Weak aTSAs were younger than weak rTSAs (68.7±7.8 vs. 72.0±8.0 years, P=0.021). Weak aTSAs and weak rTSAs had similar preoperative outcome scores, strength, and ROM, but weak aTSAs had superior preoperative active FE (88°±25° vs. 74°±28°, P=0.004) and abduction (82°±26° vs. 69°±26°, P=0.013).

Postoperatively, compared to weak aTSAs, weak rTSAs demonstrated significantly better SPADI (19.7±16.5 vs. 27.3±22.7, P=0.032), ASES (81.1±16.3 vs. 73.4±21.7, P=0.024), and UCLA scores (29.6±5.6 vs. 26.1±7.3, P=0.008), while weak aTSAs demonstrated superior active (46±16° vs. 38±15°, P=0.014) and passive ER (59±17° vs. 49±15°, P=0.006). Compared to weak aTSAs, weak rTSAs demonstrated significantly greater pre- to postoperative improvements in UCLA score (17.5±6.4 vs. 13.8±8.1, P=0.025), active (59°±28° vs. 34°±41°, P=0.002) and passive FE (43°±30° vs. 31°±38°, P=0.043), and active abduction (51°±31° vs. 31°±38°,0.008) (Table 3). Weak rTSAs more frequently exceeded the MCID for abduction (86% vs. 70%, P=0.045), FE (90% vs. 71%, P=0.011), and UCLA score (93% vs. 71%, P=0.002) and the SCB for abduction (70% vs. 42%, P=0.003) and FE (74% vs. 42%, P=0.001) (Table 4). Weak aTSAs and weak rTSAs demonstrated comparable all-cause complication rates (14% and 8.9%, respectively; P=0.291), although weak aTSAs demonstrated higher revision rates than weak rTSAs (12% vs. 3.8%, P=0.025) (Table 2).

DISCUSSION

This study found that, while patients with RCI-GHOA and preoperative weakness in FE can achieve clinically relevant improvements after both aTSA and rTSA, patients that underwent aTSA achieved greater postoperative ER that did not exceed the MCID or SCB. On the other hand, patients that underwent rTSA achieved greater overhead ROM exceeding clinically-relevant thresholds and had lower rates of revision surgery. In patients with primary RCI-GHOA, aTSA has been purported to offer superior postoperative axial ROM over rTSA [28]. Historically, rTSA has been utilized in patients with non-functional rotator cuffs and severe glenoid bone loss [29,30]. These indications have been expanded with increasing use in RCI-GHOA with good clinical outcomes [31], especially as contemporary designs have demonstrated improved function and strength from the original Grammont design [9].

There are limited data assessing the influence of FE weakness on outcomes after TSA. Hao et al. [11] previously studied 374 primary aTSAs and 601 primary rTSAs and found that aTSA demonstrated significantly greater FE strength than rTSAs at baseline, 6 months, 1 year, and 2 years postoperatively. However, the present study included patients undergoing aTSA and rTSA for a wide variety of indications. rTSA confers certain advantages over aTSA that may enable superior postoperative overhead motion, particularly in patients with poor FE strength preoperatively. First, the improved moment arm of the deltoid after rTSA may provide greater clinical improvement in both ROM and strength in abduction and FE. Biomechanically, contemporary medialized glenoid-lateralized humerus rTSA designs placed with inferior overhang optimize the deltoid moment arm, assisting with overhead ROM [32]. Intraoperatively, the rTSA design allows greater soft tissue release, potentially decreasing limitations on ROM. Further, the subscapularis, which acts as an adductor, may not need to be repaired in rTSA, which may allow greater overhead motion [33], although repair is associated with lower rates of postoperative instability [34]. Additionally, multiple techniques for subscapularis repair exist, including tenotomy with tendon-to-tendon repair, tuberosity osteotomy, peel technique, and over-the-top repair, with unclear results concerning the superior technique [35-37]. The greater improvement in active FE observed in weak rTSA compared to weak aTSA cohorts supports these biomechanical principles (59°±28° vs. 34°±41°, P=0.002). Furthermore, while not statistically significant, FE strength trended higher after weak rTSA compared to weak aTSA (7±6 vs. 5±6 lb, P=0.064).

Consistent with prior findings [2,28], weak aTSAs obtained greater postoperative active (46°±16° vs. 38°±15°, P=0.014) and passive ER (59°±17° vs. 49°±15°, P=0.006) compared to weak rTSAs. In a prior study comparing matched aTSA versus rTSA for RCI-GHOA with preoperative ER stiffness (passive ER ≤0°), Hao et al. [2] found that stiff aTSAs had greater postoperative active ER (40°±19° vs. 28°±17°, P<0.001) compared to stiff rTSAs; however, postoperative outcome scores were similar between groups. Unlike the aforementioned study that showed similar postoperative functional outcome scores between stiff aTSAs and stiff rTSAs, weak aTSAs had inferior postoperative SPADI (27±23 vs. 19±17, P=0.032), ASES (73±22 vs. 81±6, P=0.024), and UCLA (26±7.3 vs. 30±5.6, P=0.008) scores compared to weak rTSAs.

Overall, weak aTSAs were found to have higher revision rates than weak rTSAs in our study (12% vs. 3.8%, P=0.025) (Table 2), with similar revision rates regardless of preoperative weakness (normal aTSA: 12%, normal rTSA: 3.0%). Previously, Parada et al. [38] reviewed 2224 aTSAs and 4158 rTSAs and found higher revision rates in aTSA compared to rTSA (5.6% and 2.5%, respectively), with aTSAs most commonly requiring revision secondary to cuff failure, aseptic loosening, and infection. This may indicate a clinical benefit of rTSA over aTSA in patients who may be at high risk for revision, including those who may suffer from rotator cuff insufficiency [5] or patients who are older [39]. Notably, glenoid loosening was the most common complication and reason for failure in normal and weak aTSA (3% each). Parada et al. [38] similarly reported a glenoid loosening rate of 2.5% in aTSA. Our aTSA revision rate was higher than theirs, which may reflect the older average age of our matched cohorts and the long-term follow-up (average 5.1 years in normal and 6.4 years in weak aTSAs).

Our study demonstrated that both patients who are preoperatively weak and those with normal preoperative strength can experience postoperative clinical improvements, with no significant differences between groups, further showing that both aTSA and rTSA confer different strengths and weaknesses. However, we recognize that this study has several limitations. By nature, retrospective study designs are subject to bias, which limits the strength of our conclusions. Further, while we matched our aTSA and rTSA cohorts, there are many preoperative characteristics that were not controlled for that could contribute to outcomes, including previous surgery to the ipsilateral shoulder [40], glenoid deformity, and subscapularis repair [33]. While unable to be truly assessed, it is also possible that preoperative strength could be limited secondary to pain and associated with poor effort rather than purely true muscle weakness. Poor FE in patients with an intact rotator cuff may reflect increased fatty degeneration or atrophy of the supraspinatus; unfortunately, preoperative magnetic resonance imaging scans are not routinely acquired in patients undergoing TSA at our institution, and this parameter could not be evaluated in our retrospective investigation. Further, selection bias remains a possible limitation; although we only included patients with RCI-GHOA, surgeon preference and clinical decision-making based on glenoid deformity or intraoperative rotator cuff status may affect the rates at which aTSA versus rTSA were utilized in patients.

CONCLUSIONS

Patients with RCI-GHOA and preoperative FE weakness obtain similar postoperative outcomes to patients with normal preoperative strength after either aTSA or rTSA. While preoperatively weak aTSAs achieved greater postoperative ER compared to weak rTSAs, they had slightly inferior postoperative functional outcome scores and lower rates of clinically relevant improvement in overhead motion. While patients with RCI-GHOA undergoing either aTSA or rTSA benefitted significantly from these operations, rTSA may be advantageous in the setting of poor preoperative FE strength.

Fig. 1. Density plots depicting the distribution of preoperative forward elevation (FE) strength with lines indicating the 30th percentile for anatomic total shoulder arthroplasty (aTSA; blue, 4.9 lb [2.2 kg]) and reverse total shoulder arthroplasty (orange, 4.9 lb) separately (A) and the 30th percentile for aTSA (4.9 lb) overlayed on the overall cohort (B).

Table 1. Demographics and clinical outcomes of aTSAs and rTSAs with preoperative FE strength ≤6.1 lb

Outcome measure	aTSA	rTSA	
Normal (n=82)	Weak (n=82)	P-value	Normal (n=44)	Weak (n=44)	P-value	
Age at surgery (yr)	65.9±7.0	67.8±7.5	0.106	70.8±6.9	71.9±7.9	0.487	
Female	75.6 (62)	75.6 (62)	1.000	61.4 (27)	61.4 (27)	1.000	
Prior surgery	15.9 (13)	9.8 (8)	0.350	27.3 (12)	18.2 (8)	0.446	
BMI (kg/m2)	31.7±6.8	30.6±7.4	0.318	30.5±6.1	30.1±5.8	0.754	
Follow-up (yr)	5.1±3.0	6.4±3.4	0.012	3.5±1.5	2.8±1.2	0.011	
Preoperative							
 SPADI score	62.5±13.7	72.1±13.2	<0.001	61.2±14.7	73.4±13.3	<0.001	
 SST score	4.5±2.5	3.2±2.2	0.001	5.0±2.2	3.2±2.1	<0.001	
 ASES score	42.3±14.4	33.0±14.7	<0.001	41.6±15.4	32.2±13.7	0.004	
 UCLA score	15.5±4.0	12.8±4.4	0.002	14.8±3.3	11.9±3.8	<0.001	
 Constant score	46.4±14.1	37.2±13.0	<0.001	44.9±12.7	31.9±12.4	<0.001	
 Active ER (°)	22.6±17.0	19.9±20.0	0.351	22.0±20.2	15.7±19.7	0.140	
 Active FE (°)	98±24	84±25	0.001	94±27	69±29	<0.001	
 Passive ER (°)	35±18	32±19	0.248	34±22	31±19	0.548	
 Passive FE (°)	125±25	111±24	0.248	118±26	98±25	0.548	
 Active IR score	3.1±1.7	2.9±1.7	0.438	2.6±1.5	2.6±1.6	0.891	
 Active abduction (°)	91±27	77±25	0.002	89±26	67±26	<0.001	
 ER strength (lb)	12±6	6±3	<0.001	11±6	6±3	<0.001	
 FE strength (lb)	10±4	4±2	<0.001	9±3	4±2	<0.001	
Postoperative							
 SPADI score	26.2±25.9	32.1±24.6	0.145	16.4±19.0	19.6±17.6	0.429	
 SST score	9.1±3.5	8.2±3.6	0.114	10.3±2.5	9.8±2.4	0.362	
 ASES score	73.5±24.3	68.3±24.1	0.173	83.1±19.8	79.8±18.1	0.426	
 UCLA score	27.1±7.4	25.5±8.2	0.299	30.5±5.5	29.6±5.8	0.499	
 Constant score	72.2±20.5	66.8±21.6	0.138	81.5±15.9	75.5±16.4	0.145	
 Active ER (°)	47±17	42±19	0.160	40±19	39±13	0.789	
 Active FE (°)	127±32	118±33	0.157	139±16	133±18	0.176	
 Passive ER (°)	55±18	53±19	0.490	48±17	49±14	0.700	
 Passive FE (°)	147±22	137±29	0.053	153±14	147±18	0.140	
 Active IR score	4.9±1.5	4.7±1.8	0.437	4.7±1.7	4.4±1.6	0.405	
 Active abduction (°)	118±33	111±34	0.213	127±26	122±27	0.356	
 ER strength (lb)	12±7	11±7	0.284	15±8	12±7	0.117	
 FE strength (lb)	10±6	8±6	0.077	15±7	12±6	0.108	
Improvement							
 SPADI score	-	–40.0±23.4	0.336	-	-	0.073	
 SST score	4.6±3.5	5.0±3.5	0.458	5.3±2.9	6.5±3.4	0.074	
 ASES score	31.2±25.6	35.3±24.5	0.312	41.6±22.1	47.7±23.2	0.225	
 UCLA score	11.7±8.1	12.7±8.8	0.489	15.9±5.7	17.9±6.6	0.148	
 Constant score	26.2±21.4	29.9±22.5	0.339	37.2±17.7	43.8±17.8	0.112	
 Active ER (°)	24.2±17.4	22.6±23.1	0.640	17.8±22.4	22.7±19.3	0.311	
 Active FE (°)	29±35	34±40	0.449	45±29	64±25	0.002	
 Passive ER (°)	20±22	21±22	0.723	14±22	18±23	0.440	
 Passive FE (°)	22±27	27±32	0.326	38±33	50±30	0.123	
 Active IR score	1.8±2.1	1.8±2.1	0.937	2.1±2.0	1.8±2.1	0.512	
 Active abduction (°)	28±39	33±40	0.404	39±36	55±30	0.035	
 ER strength (lb)	1±6	4±6	0.008	4±7	6±5	0.181	
 FE strength (lb)	1±6	4±6	0.001	5±7	8±6	0.094	
Values are presented as mean±standard deviation or percent (number). Normal: based on age, sex, and follow-up, Weak: matched 1:1 to a cohort with preoperative FE strength >4.9 lb (2.2 kg).

aTSA: anatomic total shoulder arthroplasty, rTSA: reverse total shoulder arthroplasty, FE: forward elevation, BMI: body mass index, SPADI: Shoulder Pain and Disability Index, SST: Simple Shoulder Test, ASES: American Shoulder and Elbow Surgeons, UCLA: the University of California, Los Angeles, ER: external rotation, IR: internal rotation.

Table 2. Incidence of surgical complications and revision surgery amongst all shoulder arthroplasties performed during the study period

Complication	aTSA (n=413)	rTSA (n=213)	P-value (weak aTSA vs. weak rTSA)	
Weak (n=123)	Normal (n=290)	P-value	Weak (n=90)	Normal (n=123)	P-value	
All-cause complication	17 (13.8)	38 (13.1)	1.000	8 (8.9)	9 (7.3)	0.799	0.291	
 Rotator cuff tear and subscapularis failure	1 (0.8)	0	-	0	0	-	-	
 Rotator cuff tear	0	5 (1.7)	-	0	0	-	-	
 Subscapularis failure	1 (0.8)	2 (0.7)	-	0	0	-	-	
 Combined humeral and glenoid loosening	2 (1.6)	1 (0.3)	-	0	0	-	-	
 Humeral stem loosening	1 (0.8)	1 (0.3)	-	0	0	-	-	
 Glenoid loosening	4 (3.3)	8 (2.8)	-	1 (1.3)	4 (3.0)	-	-	
 Glenosphere loosening	1 (0.8)	2 (0.7)	-	0	0	-	-	
 Component failure	1 (0.8)	7 (2.4)	-	0	3 (2.2)	-	-	
 Infection	1 (0.8)	10 (3.4)	-	0	0	-	-	
 Glenoid fracture	0	0	-	1 (1.3)	0		-	
 Periprosthetic fracture	2 (1.6)	1 (0.3)	-	4 (5.0)	0	-	-	
 Unexplained pain	2 (1.6)	0	-	0	1 (0.7)	-	-	
 Nerve injury	1 (0.8)	0	-	0	0	-	-	
 Intraoperative fracture: humeral shaft cortex	0	1 (0.3)	-	2 (2.5)	1 (0.7)	-	-	
Re-revision rate	15 (12.2)	35 (12.1)	1.000	3 (3.8)	4 (3.0)	1.000	0.025	
Values are presented as number (%). This includes procedures that met inclusion criteria and were eligible for 2-year follow-up, stratified by prosthesis (aTSA and rTSA) and whether they had preoperative weakness (preoperative FE strength ≤6.1 lb) (n=626).

aTSA: anatomic total shoulder arthroplasty, rTSA: reverse total shoulder arthroplasty, FE: forward elevation.

Table 3. Demographics and clinical outcomes of aTSA and rTSA with preoperative FE strength ≤6.1 lb

Outcome measure	Weak aTSA (n=61)	Weak rTSA (n=61)	P-value	
Age at surgery (yr)	68.7±7.8	72.0±8.0	0.021	
Female	48.4 (30)	49.5 (30)	0.558	
Prior surgery	73.8 (45)	73.8 (45)	1.000	
BMI (kg/m2)	7.0±0.0	10.0±0.0	0.602	
Follow-up (yr)	4.0±1.8	3.5±1.7	0.092	
Preoperative				
 SPADI score	71.5±12.9	71.5±13.3	0.988	
 SST score	3.3±2.2	3.4±2.0	0.759	
 ASES score	32.3±15.4	34.0±13.3	0.546	
 UCLA score	12.4±4.2	12.2±3.7	0.775	
 Constant score	37.6±12.5	34.7±13.0	0.283	
 Active ER (°)	22.4±20.2	16.1±18.0	0.090	
 Active FE (°)	88±25	74±28	0.004	
 Passive ER (°)	34±20	31±19	0.495	
 Passive FE (°)	111±32	102±26	0.495	
 Active IR score	3.0±1.9	2.9±1.8	0.835	
 Active abduction (°)	82±26	69±26	0.013	
 ER strength (lb)	6±3	5±3	0.158	
 FE strength (lb)	4±2	4±2	0.437	
Postoperative				
 SPADI score	27.3±22.7	19.2±16.5	0.032	
 SST score	9.0±3.2	9.8±2.3	0.080	
 ASES score	73.4±21.7	81.1±16.3	0.024	
 UCLA score	26.1±7.3	29.6±5.6	0.008	
 Constant score	71.3±18.6	76.1±15.6	0.221	
 Active ER (°)	45.9±16.2	37.6±15.1	0.014	
 Active FE (°)	122±30	132±20	0.086	
 Passive ER (°)	59±17	49±15	0.006	
 Passive FE (°)	141±26	145±20	0.351	
 Active IR score	5.0±1.6	4.6±1.5	0.141	
 Active abduction (°)	112±33	120±27	0.225	
 ER strength (lb)	11±6	11±5	0.752	
 FE strength (lb)	8±6	10±6	0.108	
Improvement				
 SPADI score	-44.2±23.9	-52.3±21.3	0.075	
 SST score	5.7±3.6	6.5±3.2	0.259	
 ASES score	41.1±24.2	47.1±21.3	0.192	
 UCLA score	13.8±8.1	17.5±6.4	0.025	
 Constant score	34.6±19.8	41.5±18.2	0.098	
 Active ER (°)	23.6±21.0	21.5±20.8	0.630	
 Active FE (°)	34±41	59±28	0.002	
 Passive ER (°)	25±23	18±23	0.145	
 Passive FE (°)	31±34	43±30	0.043	
 Active IR score	2.0±2.2	1.6±2.0	0.328	
 Active abduction (°)	31±38	51±31	0.008	
 ER strength (lb)	5±6	6±5	0.220	
 FE strength (lb)	5±6	7±6	0.064	
Values are presented as mean±standard deviation or percent (number). Weak: matched 1:1 to a cohort of rTSAs with preoperative FE strength ≤6.1 lbs.

aTSA: anatomic total shoulder arthroplasty, FE: forward elevation, rTSA: reverse total shoulder arthroplasty, BMI: body mass index, SPADI: Shoulder Pain and Disability Index, SST: Simple Shoulder Test, ASES: American Shoulder and Elbow Surgeons, UCLA: the University of California, Los Angeles, ER: external rotation; IR: internal rotation.

Table 4. Proportion of weak aTSAs and weak rTSAs that exceeded the MCID and SCB for active ROM and outcome scores after aTSA

Outcome measure	Reference valuea)	Weak aTSA+rTSA (n=122)	Weak aTSA (n=61)	Weak rTSA (n=61)	P-value	
MCID						
 Abduction (°)	13.9	78.2 (95)	70.3	86.1	0.045	
 FE (°)	23.1	80.2 (98)	70.6	89.8	0.011	
 ER (°)	14.5	70.2 (86)	70.7	69.8	1.000	
 SST	1.7	91.8 (112)	87.2	96.4	0.095	
 Constant	8.6	92.9 (113)	89.5	96.3	0.272	
 ASES	14.2	89.9 (110)	85.2	94.5	0.126	
 UCLA	8.1	82.0 (100)	71.2	92.7	0.002	
 SPADI	–19.7	88.2 (108)	83.6	92.7	0.154	
SCB						
 Abduction (°)	36.1	56.0 (68)	42.0	69.9	0.003	
 FE (°)	45.5	57.8 (71)	42.0	73.7	0.001	
 ER (°)	20.1	52.7 (64)	52.6	52.9	1.000	
 SST	3.5	78.5 (96)	72.5	84.5	0.121	
 Constant	20.4	80.5 (98)	76.9	84.1	0.495	
 ASES	33.2	71.6 (87)	68.4	74.8	0.545	
 UCLA	12.6	70.7 (86)	63.4	78.0	0.109	
 SPADI	–44.3	60.1 (73)	52.2	68.0	0.099	
Values are presented as percent (number).

aTSA: anatomic total shoulder arthroplasty, rTSA: reverse total shoulder arthroplasty, MCID: minimal clinically important difference, SCB: substantial clinical benefit, ROM: range of motion, FE: forward elevation, FE: forward elevation, ER: external rotation, SST: simple shoulder test, ASES: American shoulder and elbow surgeons, UCLA: University of California, Los Angeles, SPADI: shoulder pain and disability index.

a)Reference values adopted from Roche et al. [18] and Simovitch et al. [26,27] for aTSA.

Author contributions

Conceptualization: KMH, KAH. Data curation: KMH, KAH, TRB. Formal analysis: KAH. Investigation: KMH, KAH, TRB, APT, JOW, TWW, BSS, JJK. Methodology: KMH, KAH, JOW, TWW, BSS, JJK. Project administration: TJL. Resources: TJL. Supervision: APT, JOW, TWW, TJL, BSS, JJK. Validation: KAH, JJK. Visualization: KAH. Writing – original draft: KMH, KAH, TRB. Writing – review & editing: KMH, KAH, TRB, APT, JOW, TWW, TJL, BSS, JJK.

Conflict of interest

KAH is a paid consultant for LinkBio Corp. BSS is a consultant and receives royalties from Exactech, Innomed, and Responsive Arthroscopy. JJK is a consultant for Exactech, Inc. and LinkBio Corp. TWW is a consultant and receives royalties from Exactech, Inc. No other potential conflicts of interest relevant to this article were reported.

Funding

None.

Data availability

Contact the corresponding author for data availability.

Acknowledgments

None.
==== Refs
REFERENCES

1 Farley KX Wilson JM Kumar A Prevalence of shoulder arthroplasty in the United States and the increasing burden of revision shoulder arthroplasty JB JS Open Access 2021 6 e20.00156
2 Hao KA Greene AT Werthel JD Clinical outcomes of anatomic vs. reverse total shoulder arthroplasty in primary osteoarthritis with preoperative rotational stiffness and an intact rotator cuff: a case control study J Shoulder Elbow Surg 2023 32 e355 65 36737034
3 Marigi EM Hao KA Friedman RJ Exactech Equinoxe anatomic versus reverse total shoulder arthroplasty for primary osteoarthritis: case controlled comparisons using the machine learning–derived Shoulder Arthroplasty Smart score J Shoulder Elbow Surg 2023 32 793 802
4 Pike JM Singh SK Barfield WR Schoch B Friedman RJ Eichinger JK Impact of age on shoulder range of motion and strength JSES Int 2022 6 1029 33 36353423
5 Schoch BS Tams C Eichinger J Wright TW King JJ Friedman RJ Anatomic total shoulder arthroplasty after healed rotator cuff repair: a matched cohort J Shoulder Elbow Surg 2020 29 2221 8 33070868
6 Hamilton MA Diep P Roche C Effect of reverse shoulder design philosophy on muscle moment arms J Orthop Res 2015 33 605 13 25640775
7 Henninger HB Barg A Anderson AE Bachus KN Burks RT Tashjian RZ Effect of lateral offset center of rotation in reverse total shoulder arthroplasty: a biomechanical study J Shoulder Elbow Surg 2012 21 1128 35 22036546
8 Herrmann S König C Heller M Perka C Greiner S Reverse shoulder arthroplasty leads to significant biomechanical changes in the remaining rotator cuff J Orthop Surg Res 2011 6 42 21846390
9 Langohr GD Giles JW Athwal GS Johnson JA The effect of glenosphere diameter in reverse shoulder arthroplasty on muscle force, joint load, and range of motion J Shoulder Elbow Surg 2015 24 972 9 25547853
10 Trammell AP Hao KA Hones KM Clinical outcomes of anatomical versus reverse total shoulder arthroplasty in patients with primary osteoarthritis, an intact rotator cuff, and limited forward elevation Bone Joint J 2023 105 1303 13 38037676
11 Hao KA Wright TW Schoch BS Rate of improvement in shoulder strength after anatomic and reverse total shoulder arthroplasty JSES Int 2021 6 247 52 35252921
12 Péan F Favre P Goksel O Influence of rotator cuff integrity on loading and kinematics before and after reverse shoulder arthroplasty J Biomech 2021 129 110778 34670177
13 Edwards TB Boulahia A Kempf JF Boileau P Nemoz C Walch G The influence of rotator cuff disease on the results of shoulder arthroplasty for primary osteoarthritis: results of a multicenter study J Bone Joint Surg Am 2002 84 2240 8 12473715
14 Coscia AC Matar RN Espinal EE Shah NS Grawe BM Does preoperative diagnosis impact patient outcomes following reverse total shoulder arthroplasty?: a systematic review J Shoulder Elbow Surg 2021 30 1458 70 33197589
15 Dezfuli B King JJ Farmer KW Struk AM Wright TW Outcomes of reverse total shoulder arthroplasty as primary versus revision procedure for proximal humerus fractures J Shoulder Elbow Surg 2016 25 1133 7 26897312
16 Werthel JD Walch G Vegehan E Deransart P Sanchez-Sotelo J Valenti P Lateralization in reverse shoulder arthroplasty: a descriptive analysis of different implants in current practice Int Orthop 2019 43 2349 60 31254018
17 Flurin PH Marczuk Y Janout M Wright TW Zuckerman J Roche CP Comparison of outcomes using anatomic and reverse total shoulder arthroplasty Bull Hosp Jt Dis (2013) 2013 71 Suppl 2 101 7 24328590
18 Roche C Kumar V Overman S Validation of a machine learning-derived clinical metric to quantify outcomes after total shoulder arthroplasty J Shoulder Elbow Surg 2021 30 2211 4 33607333
19 Ho DE Imai K King G Stuart EA MatchIt: nonparametric preprocessing for parametric causal inference J Stat Softw 2011 42 1 28
20 Ondeck NT Fu MC Skrip LA McLynn RP Su EP Grauer JN Treatments of missing values in large national data affect conclusions: the impact of multiple imputation on arthroplasty research J Arthroplasty 2018 33 661 7 29153865
21 Song A Cannon D Kim P Risk factors for degenerative, symptomatic rotator cuff tears: a case-control study J Shoulder Elbow Surg 2022 31 806 12 34687917
22 Song A DeClercq J Ayers GD Comparative time to improvement in nonoperative and operative treatment of rotator cuff tears J Bone Joint Surg Am 2020 102 1142 50 32618921
23 White IR Royston P Wood AM Multiple imputation using chained equations: issues and guidance for practice Stat Med 2011 30 377 99 21225900
24 Rubin DB Multiple imputation for nonresponse in surveys. Vol. 81 John Wiley & Sons 2004
25 van Buuren S Groothuis-Oudshoorn K Mice: multivariate imputation by chained equations in R J Stat Softw 2011 45 1 67
26 Simovitch R Flurin PH Wright T Zuckerman JD Roche CP Quantifying success after total shoulder arthroplasty: the minimal clinically important difference J Shoulder Elbow Surg 2018 27 298 305 29162305
27 Simovitch R Flurin PH Wright T Zuckerman JD Roche CP Quantifying success after total shoulder arthroplasty: the substantial clinical benefit J Shoulder Elbow Surg 2018 27 903 11 29398395
28 Kim H Kim CH Kim M Is reverse total shoulder arthroplasty (rTSA) more advantageous than anatomic TSA (aTSA) for osteoarthritis with intact cuff tendon?: a systematic review and meta-analysis J Orthop Traumatol 2022 23 3 34993646
29 Collin P Hervé A Walch G Boileau P Muniandy M Chelli M Mid-term results of reverse shoulder arthroplasty for glenohumeral osteoarthritis with posterior glenoid deficiency and humeral subluxation J Shoulder Elbow Surg 2019 28 2023 30 31405717
30 Lindbloom BJ Christmas KN Downes K Is there a relationship between preoperative diagnosis and clinical outcomes in reverse shoulder arthroplasty?: an experience in 699 shoulders J Shoulder Elbow Surg 2019 28 6S S110 7 31196504
31 Rabinowitz J Kothandaraman V Lin J Li X Friedman RJ Eichinger JK Utilization of shoulder arthroplasty in the United States: an analysis of current trends and future predictions Semin Arthroplasty 2020 30 200 9
32 Goetti P Denard PJ Collin P Ibrahim M Mazzolari A Lädermann A Biomechanics of anatomic and reverse shoulder arthroplasty EFORT Open Rev 2021 6 918 31 34760291
33 Friedman RJ Flurin PH Wright TW Zuckerman JD Roche CP Comparison of reverse total shoulder arthroplasty outcomes with and without subscapularis repair J Shoulder Elbow Surg 2017 26 662 8 28277259
34 Bethell MA Hurley ET Welch J Subscapularis repair for reverse shoulder arthroplasty: a systematic review and meta-analysis J Shoulder Elbow Surg 2023 32 2631 40 37473906
35 Lachance AD Peebles AM McBride T Eble SK Provencher MT Subscapularis repair techniques for reverse total shoulder arthroplasty: a systematic review J ISAKOS 2022 7 181 8 35597429
36 King JJ Greene AT Hamilton MA The over-the-top subscapularis repair in reverse shoulder arthroplasty: biomechanical evaluation of a novel technique JSES Open Access 2019 3 304 10 31891030
37 Cueto RJ Hao KA O’Keefe DS Clinical outcomes of over-the-top subscapularis repair in reverse shoulder arthroplasty JSES Int 2024 8 866 72 39035640
38 Parada SA Flurin PH Wright TW Comparison of complication types and rates associated with anatomic and reverse total shoulder arthroplasty J Shoulder Elbow Surg 2021 30 811 8 32763380
39 Keener JD Patterson BM Orvets N Chamberlain AM Degenerative rotator cuff tears: refining surgical indications based on natural history data J Am Acad Orthop Surg 2019 27 156 65 30335631
40 Marigi EM Tams C King JJ Shoulder arthroplasty after prior anterior shoulder instability surgery: a matched cohort analysis Eur J Orthop Surg Traumatol 2023 33 961 9 35230545
