Abstract
Background
This study sought to characterize the tipping point values (the functional scores that patients deem dysfunctional enough to warrant surgery) for patients undergoing first revision reverse total shoulder arthroplasty (rTSA).
Methods
This study was a retrospective review of a prospectively collected single-institution database of patients undergoing first revision rTSA between August 2015 and December 2019. Tipping point evaluation utilized preoperative scores including the American Shoulder and Elbow Surgeons (ASES), raw and normalized Constant, Shoulder Pain and Disability Index (SPADI), Simple Shoulder Test (SST), and University of California-Los Angeles (UCLA) scores, and active range of motion including abduction, forward elevation (FE), external rotation (ER), and internal rotation score (IR) prior to elective revision rTSA.
Results
We included 125 revision rTSAs. Tipping points were 37.6 ASES score, 30.5 raw Constant score, 35.5 normalized Constant score, 68.1 SPADI, 3.7 SST, 13.2 UCLA score, 64° abduction, 69° FE, 23° ER, and 3.1 IR. Higher SST was found for older patients and patients with a lower body mass index. Lower abduction and FE tipping points were reported in patients undergoing revision rTSA for rotator cuff failure, unexplained pain, and implant wear.
Discussion
These tipping points can help surgeons counsel patients regarding when to undergo revision rTSA.
Level of evidence
Level III; retrospective cohort study; treatment study.
Keywords: tipping point, preoperative function, predictors, patient-reported outcomes, shoulder replacement, decision
Introduction
The prevalence of primary total shoulder arthroplasty (TSA; 895% increase from 2000 to 2017) and subsequent revision TSA (392% increase from 2002 to 2017) is escalating. 1 Indications for revision TSA include glenoid component loosening, rotator cuff failure, instability, and pain.2–5 In revision cases, reverse total shoulder arthroplasty (rTSA) is often utilized due to the decreased reliance on an intact rotator cuff. Furthermore, rTSA reduces the risk of glenoid loosening, and its semi-constrained design increases stability in the revision setting.6–11
Despite reports of positive outcomes with revision rTSA, the decision on whether and when to revise is challenging.12–15 The so-called tipping point, the clinical status that patients deem dysfunctional enough to warrant surgery, requires balancing of potential functional and pain improvements with the intraoperative and postoperative surgical risks.16–20 Determining the point at which a patient finds the potential improvements in pain and function worth the risks of surgery can aid surgeons in counseling patients considering surgery.17,21–24 Previous studies have defined the tipping point in the setting of primary anatomic total shoulder arthroplasty (aTSA), rTSA, hemiarthroplasty, cuff tear arthropathy arthroplasty, and ream and run arthroplasty, but no current literature applies this concept to revision rTSA.22,24
The purpose of this study was to characterize the tipping point thresholds for range of motion (ROM) and functional outcome scores in patients undergoing first revision rTSA. Secondarily, we assessed the influence of age, sex, type of primary shoulder arthroplasty, and reason for revision on tipping point thresholds.
Materials and methods
We performed a retrospective review of patients enrolled in a single-center prospectively collected database who previously underwent primary shoulder arthroplasty and subsequently underwent revision to rTSA at our institution between August 2015 and December 2019. Patients with prior revision shoulder arthroplasty surgery, oncologic diagnosis, periprosthetic fracture, or history of suspected prosthetic joint infection were excluded. We initially identified 169 shoulders that underwent rTSA that met the aforementioned criteria; of these, 13 shoulders were excluded for lacking a preoperative assessment of clinical outcome scores. We further excluded 31 shoulders undergoing revision rTSA for instability, as these patients often present dislocated and the decision to undergo revision surgery is less elective. In the remaining 125 shoulders, the decision to undergo surgery was made between the performing surgeon and patient after the failure of conservative measures, that is, medical management of infection or physical therapy for rotator cuff insufficiency in the setting of aTSA or hemiarthroplasty, and/or a possibly correctable etiology, such as aTSA or hemiarthroplasty with rotator cuff failure or glenoid component loosening, for primary arthroplasty failure was identified.
Clinical outcomes
The tipping point was defined as the value for active ROM and outcome scores at the time a patient elected to undergo revision rTSA. All patients were examined by the performing surgeon or by clinical research assistants prior to surgery. Active ROM measures were assessed using a large goniometer (degrees) and included abduction, forward elevation (FE), and external rotation (ER). Internal rotation (IR) was assessed as the most cephalad vertebral level reached by the thumb behind the patient's back and scored as follows: 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. 25 Clinical outcome scores evaluated included the Simple Shoulder Test (SST), the raw and normalized 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). 26
Statistical analysis
Demographic and surgical characteristics of included rTSAs were described descriptively. The tipping point was computed for each outcome metric as described for the overall cohort and stratified by age (<60, 60–69, 70–79, ≥80), sex, primary construct (aTSA, rTSA, hemiarthroplasty, or resurfacing), and reason for revision rTSA. To account for missing values, we utilized multivariate random forest imputation to reduce the influence of missing data on generated estimates. 27 This method has been used previously in the shoulder surgery literature. 28 First, missing values are imputed with a rough estimate; subsequently, a predictive random forest is trained and used to re-impute missing values in an iterative manner until convergence. The mean, standard deviation (SD), and 95% confidence intervals (CI) for each tipping point were computed from 500 bootstrap replicates. Multivariable linear regression was used to identify predictors of lower tipping point thresholds. All statistical analyses were performed using R Software (version 4.2.0, R Core Team, Vienna, Austria). Single imputation was performed using the simputation package. 29 Statistical significance was set at P < 0.05.
Results
Cohort demographics
One-hundred and twenty-five revision rTSAs were included, with 58% being female (Table 1). The average age at surgery was 67 years. Sixty-five (48%) of the revisions were from primary aTSA, 18 (15%) were from primary rTSA, 31 (28%) were from a hemiarthroplasty, and 11 (8%) were from humeral head resurfacing. The most common preoperative diagnoses for primary shoulder arthroplasty were primary osteoarthritis (52%), rotator cuff arthropathy (20%), and proximal humerus fracture (12%). The most common reasons for revision to rTSA were aseptic glenoid loosening (34%), rotator cuff failure (32%), and unexplained pain (13%).
Table 1.
Characteristics of included revision rTSAs (n = 125).
| Characteristic | Mean ± SD or % (N) |
|---|---|
| Age at surgery (years) | 66.6 ± 10.0 |
| BMI (kg/m2) | 30.2 ± 6.0 |
| Female sex | 58.4% (73) |
| Dominant side surgery | 57.6% (72) |
| Comorbidities | |
| Inflammatory arthritis | 8.8% (11) |
| Hypertension | 61.6% (77) |
| Heart disease | 12.8% (16) |
| Diabetes | 16.0% (20) |
| Tobacco use | 12.8% (16) |
| Chronic renal failure | 1.6% (2) |
| Chronic liver failure | 0.8% (1) |
| Primary shoulder arthroplasty | |
| aTSA | 52.0% (65) |
| rTSA | 14.4% (18) |
| Hemiarthroplasty | 24.8% (31) |
| Resurfacing | 8.8% (11) |
| Preoperative diagnosis of primary shoulder arthroplasty | |
| DJD | 52.0% (65) |
| Fracture | 12.0% (15) |
| Rotator cuff arthropathy | 20.0% (25) |
| Instability arthropathy | 4.0% (5) |
| Avascular necrosis | 4.8% (6) |
| Unknown | 6.4% (8) |
| Post-traumatic arthritis | 0.8% (1) |
| Indication for revision | |
| Humeral loosening | 3.2% (4) |
| Glenoid loosening | 34.4% (43) |
| Rotator cuff failure | 32.0% (40) |
| Unexplained pain | 12.8% (16) |
| DJD/implant wear | 12.0% (15) |
| Other | 5.6% (7) |
Data are presented as mean ± standard deviation or % (N).
aTSA: anatomic total shoulder arthroplasty; rTSA: reverse total shoulder arthroplasty; DJD: degenerative joint disease.
Tipping point thresholds
In the overall cohort, the tipping point thresholds for outcome scores were 37.6 for the ASES score, 30.5 for the raw Constant score, 35.5 for the normalized Constant score, 13.2 for the UCLA score, 3.7 for the SST, and 68.1 for the SPADI (Table 2). Tipping point thresholds for ROM measures in the overall cohort were 64° for abduction, 69° for FE, 23° for ER, and 3.1 for the IR score. Tipping point thresholds were stratified by age (Table 3), sex (Table 4), primary shoulder arthroplasty construct (Table 5), and reason for revision rTSA (Table 6).
Table 2.
Tipping point thresholds for patients deciding to undergo revision RSA in the overall cohort.
| Outcome metric | Raw values Mean ± SD [95% CI] |
Bootstrapped values Mean ± SD [95% CI] |
|---|---|---|
| ASES | 37.6 ± 16.5 | 37.6 ± 1.5 [35.0 to 40.8] |
| Raw Constant score | 30.4 ± 13.5 | 30.5 ± 1.2 [28.3 to 33.1] |
| Normalized Constant score | 35.5 ± 15.9 | 35.5 ± 1.4 [32.9 to 38.6] |
| UCLA | 13.2 ± 4.7 | 13.2 ± 0.4 [12.4 to 14.1] |
| SST | 3.7 ± 2.5 | 3.7 ± 0.2 [3.3 to 4.1] |
| SPADI | 67.9 ± 17.6 | 68.1 ± 1.6 [64.5 to 70.9] |
| Abduction (°) | 64 ± 30 | 64 ± 3 [59 to 69] |
| FE (°) | 69 ± 34 | 69 ± 3 [64 to 75] |
| ER (°) | 23 ± 23 | 23 ± 2 [19 to 28] |
| IR score | 3.1 ± 1.8 | 3.1 ± 0.2 [2.8 to 3.4] |
ASES: American Shoulder and Elbow Surgeons score; CI: confidence interval; ER: external rotation; FE: forward elevation; IR: internal rotation; RSA: reverse shoulder arthroplasty; SD: standard deviation; SPADI: Shoulder Pain and Disability Index; SST: Simple Shoulder Test; UCLA: University of California-Los Angeles shoulder score.
Table 3.
Tipping point thresholds for patients deciding to undergo revision rTSA stratified by age derived from 500 bootstrap replicates.
| Outcome metric | <60 years (n = 29) | 60–69 years (n = 42) | 70–79 years (n = 44) | ≥80 years (n = 10) |
|---|---|---|---|---|
| ASES | 31.8 ± 2.4 [27.8 to 36.5] | 37.7 ± 2.6 [32.7 to 42.6] | 41.1 ± 2.5 [36.5 to 46.0] | 38.3 ± 5.6 [28.3 to 50.2] |
| Raw Constant score | 29.7 ± 2.1 [26.0 to 33.9] | 29.0 ± 2.2 [24.9 to 33.3] | 32.1 ± 2.1 [28.1 to 36.6] | 31.8 ± 4.4 [25.0 to 41.5] |
| Normalized Constant score | 33.6 ± 2.2 [29.5 to 38.0] | 33.2 ± 2.5 [28.3 to 38.3] | 38.3 ± 2.5 [33.6 to 43.9] | 38.7 ± 5.4 [30.1 to 50.9] |
| UCLA | 12.3 ± 0.6 [11.3 to 13.4] | 13.2 ± 0.8 [11.8 to 14.8] | 14.1 ± 0.7 [12.9 to 15.4] | 12.6 ± 2.2 [9.0 to 17.5] |
| SST | 2.9 ± 0.4 [2.1 to 3.7] | 3.6 ± 0.4 [2.9 to 4.4] | 4.3 ± 0.4 [3.5 to 5.1] | 3.5 ± 0.7 [2.2 to 4.9] |
| SPADI | 71.9 ± 2.6 [66.9 to 76.9] | 68.7 ± 2.8 [62.6 to 73.9] | 64.6 ± 2.6 [59.3 to 69.4] | 68.0 ± 7.1 [53.7 to 80.1] |
| Abduction (°) | 65 ± 4 [57 to 75] | 60 ± 4 [52 to 68] | 67 ± 6 [57 to 78] | 62 ± 8 [49 to 80] |
| FE (°) | 69 ± 5 [60 to 80] | 66 ± 6 [55 to 77] | 72 ± 5 [62 to 82] | 69 ± 10 [52 to 89] |
| ER (°) | 25 ± 4 [17 to 32] | 27 ± 4 [20 to 34] | 20 ± 4 [13 to 27] | 11 ± 8 [−4 to 28] |
| IR score | 3.3 ± 0.3 [2.7 to 3.9] | 3.0 ± 0.3 [2.4 to 3.6] | 3.1 ± 0.3 [2.6 to 3.6] | 3.0 ± 0.6 [2.0 to 4.1] |
Values presented are mean ± SD [95% CI].
ASES: American Shoulder and Elbow Surgeons score; CI: confidence interval; ER: external rotation; FE: forward elevation; IR: internal rotation; rTSA: reverse total shoulder arthroplasty; SD: standard deviation; SPADI: Shoulder Pain and Disability Index; SST: Simple Shoulder Test; UCLA: University of California-Los Angeles shoulder score.
Table 4.
Tipping point thresholds for patients deciding to undergo revision rTSA stratified by sex derived from 500 bootstrap replicates.
| Outcome metric | Male | Female |
|---|---|---|
| ASES | 38.4 ± 2.0 [34.9 to 42.6] | 36.8 ± 2.2 [32.3 to 41.1] |
| Raw Constant score | 30.1 ± 1.6 [27.1 to 33.3] | 31.1 ± 1.9 [27.6 to 34.9] |
| Normalized Constant score | 36.4 ± 2.0 [32.6 to 40.2] | 34.5 ± 2.1 [30.6 to 38.5] |
| UCLA | 13.2 ± 0.6 [11.9 to 14.4] | 13.4 ± 0.5 [12.4 to 14.4] |
| SST | 3.4 ± 0.3 [2.9 to 4.0] | 4.0 ± 0.3 [3.4 to 4.7] |
| SPADI | 68.1 ± 2.3 [63.9 to 72.4] | 67.7 ± 2.2 [63.2 to 71.8] |
| Abduction (°) | 61 ± 4 [54 to 69] | 68 ± 4 [61 to 76] |
| FE (°) | 67 ± 4 [58 to 75] | 72 ± 5 [64 to 82] |
| ER (°) | 23 ± 3 [18 to 28] | 23 ± 3 [17 to 29] |
| IR score | 3.1 ± 0.2 [2.7 to 3.5] | 3.1 ± 0.2 [2.6 to 3.6] |
Values presented are mean ± SD [95% CI].
ASES: American Shoulder and Elbow Surgeons score; CI: confidence interval; ER: external rotation; FE: forward elevation; IR: internal rotation; rTSA: reverse total shoulder arthroplasty; SD: standard deviation; SPADI: Shoulder Pain and Disability Index; SST: Simple Shoulder Test; UCLA: University of California-Los Angeles shoulder score.
Table 5.
Tipping point thresholds for patients deciding to undergo revision rTSA stratified by primary arthroplasty construct derived from 500 bootstrap replicates.
| Outcome metric | aTSA | rTSA | Hemiarthroplasty | Resurfacing |
|---|---|---|---|---|
| ASES | 38.4 ± 2.1 [34.4 to 42.6] | 42.6 ± 4.6 [34.4 to 52.4] | 35.4 ± 2.6 [30.1 to 40.4] | 31.4 ± 3.0 [25.8 to 37.3] |
| Raw Constant score | 31.6 ± 1.7 [28.4 to 35.0] | 31.1 ± 3.5 [24.8 to 38.4] | 26.5 ± 1.9 [22.9 to 30.4] | 35.1 ± 4.2 [27.8 to 44.2] |
| Normalized Constant score | 36.8 ± 2.0 [33.0 to 41.0] | 37.0 ± 4.4 [29.1 to 45.5] | 30.7 ± 2.1 [26.8 to 35.0] | 40.5 ± 4.7 [32.4 to 50.0] |
| UCLA | 13.1 ± 0.6 [12.1 to 14.4] | 15.2 ± 1.4 [12.7 to 18.0] | 12.3 ± 0.7 [11.0 to 13.6] | 13.8 ± 0.6 [12.5 to 15.1] |
| SST | 3.8 ± 0.3 [3.2 to 4.5] | 3.9 ± 0.6 [2.8 to 5.1] | 3.3 ± 0.4 [2.4 to 4.1] | 3.9 ± 0.7 [2.7 to 5.3] |
| SPADI | 67.0 ± 2.4 [62.2 to 71.2] | 65.6 ± 5.0 [54.2 to 74.2] | 71.7 ± 2.4 [67.3 to 76.5] | 66.6 ± 3.6 [59.3 to 73.8] |
| Abduction (°) | 64 ± 4 [57 to 72] | 66 ± 8 [51 to 84] | 58 ± 5 [48 to 67] | 77 ± 10 [59 to 96] |
| FE (°) | 70 ± 4 [62 to 78] | 69 ± 8 [54 to 86] | 60 ± 5 [49 to 70] | 91 ± 11 [70 to 111] |
| ER (°) | 29 ± 3 [23 to 35] | 13 ± 5 [2 to 24] | 14 ± 3 [7 to 20] | 29 ± 4 [22 to 36] |
| IR score | 3.4 ± 0.2 [3.0 to 3.9] | 2.8 ± 0.4 [2.0 to 3.6] | 2.5 ± 0.3 [2.0 to 3.0] | 3.8 ± 0.4 [3.0 to 4.5] |
Values presented are mean ± SD [95% CI].
ASES: American Shoulder and Elbow Surgeons score; CI: confidence interval; ER: external rotation; FE: forward elevation; IR: internal rotation; rTSA: reverse total shoulder arthroplasty; SD: standard deviation; SPADI: Shoulder Pain and Disability Index; SST: Simple Shoulder Test; UCLA: University of California-Los Angeles shoulder score.
Table 6.
Tipping point thresholds for patients deciding to undergo revision RSA stratified by reason for revision surgery derived from 500 bootstrap replicates.
| Outcome metric | Glenoid loosening | Humeral loosening | Implant wear | Rotator cuff failure | Other | Unexplained pain |
|---|---|---|---|---|---|---|
| ASES | 38.4 ± 2.6 [33.8 to 44.0] | 42.4 ± 13.9 [12.5 to 67.5] | 26.3 ± 3.7 [18.6 to 33.7] | 52.0 ± 6.6 [39.5 to 64.8] | 36.5 ± 2.1 [32.2 to 40.5] | 40.9 ± 3.2 [34.7 to 47.4] |
| Raw Constant score | 33.8 ± 2.2 [30.1 to 38.5] | 27.7 ± 7.0 [12.4 to 40.5] | 26.2 ± 3.9 [19.0 to 34.5] | 38.8 ± 6.1 [28.1 to 51.3] | 26.8 ± 1.5 [23.8 to 29.7] | 31.8 ± 3.0 [26.5 to 38.2] |
| Normalized Constant score | 39.3 ± 2.7 [34.9 to 44.7] | 32.7 ± 8.1 [14.8 to 46.7] | 30.0 ± 4.2 [22.3 to 38.8] | 46.5 ± 7.8 [32.8 to 62.4] | 31.2 ± 1.8 [27.6 to 34.8] | 36.9 ± 3.3 [31.1 to 43.8] |
| UCLA | 13.7 ± 0.9 [12.1 to 15.6] | 12.2 ± 1.5 [8.9 to 14.8] | 11.3 ± 1.0 [9.3 to 13.2] | 17.1 ± 2.5 [13.1 to 22.2] | 12.5 ± 0.5 [11.5 to 13.7] | 14.0 ± 0.9 [12.3 to 15.7] |
| SST | 4.1 ± 0.4 [3.4 to 5.0] | 4.2 ± 1.9 [0.7 to 8.0] | 2.9 ± 0.7 [1.6 to 4.3] | 4.3 ± 0.7 [3.0 to 5.7] | 3.1 ± 0.3 [2.6 to 3.7] | 4.0 ± 0.6 [3.0 to 5.2] |
| SPADI | 65.6 ± 3.3 [59.6 to 71.6] | 65.1 ± 12.3 [42.3 to 86.5] | 74.2 ± 4.0 [66.8 to 82.0] | 55.9 ± 7.4 [40.7 to 68.9] | 71.6 ± 2.0 [67.3 to 75.3] | 65.6 ± 3.3 [58.9 to 71.3] |
| Abduction (°) | 74 ± 4 [66 to 82] | 65 ± 21 [20 to 100] | 58 ± 8 [44 to 73] | 80 ± 16 [53 to 111] | 53 ± 3 [47 to 59] | 62 ± 9 [46 to 80] |
| FE (°) | 80 ± 5 [70 to 90] | 63 ± 11 [41 to 79] | 65 ± 9 [48 to 83] | 85 ± 16 [53 to 117] | 59 ± 4 [52 to 67] | 64 ± 11 [45 to 84] |
| ER (°) | 23 ± 4 [16 to 30] | 14 ± 13 [−9 to 40] | 18 ± 5 [8 to 28] | 17 ± 11 [−4 to 38] | 29 ± 3 [23 to 36] | 15 ± 5 [4 to 25] |
| IR score | 3.6 ± 0.3 [3.1 to 4.2] | 1.7 ± 0.4 [1.0 to 2.5] | 2.7 ± 0.5 [1.8 to 3.7] | 3.5 ± 0.8 [2.0 to 4.9] | 2.7 ± 0.3 [2.2 to 3.3] | 3.3 ± 0.3 [2.6 to 3.9] |
Values presented are mean ± SD [95% CI].
ASES: American Shoulder and Elbow Surgeons score; CI: confidence interval; ER: external rotation; FE: forward elevation; IR: internal rotation; RSA: reverse shoulder arthroplasty; SD: standard deviation; SPADI: Shoulder Pain and Disability Index; SST: Simple Shoulder Test; UCLA: University of California-Los Angeles shoulder score.
Multivariable linear regression for outcome scores identified an association between increasing age and higher tipping point thresholds for the SST (β=0.06, P = 0.022) and normalized Constant score (β=0.32, P = 0.032) (Table 7). The finding is reflected in the age-stratified tipping point thresholds (Table 3). For example, the normalized Constant score shows an overall increase with age from 33.6 to 33.2, 38.3, and 38.7 in age groups <60, 60–69, 70–79, and ≥80, respectively. Increasing body mass index (BMI) was associated with a higher SPADI (β=0.07, P = 0.015) and lower SST (β=−0.09, P = 0.035), raw Constant (β=−0.61, P = 0.004), and normalized Constant score (β=−0.72, P = 0.003) thresholds. Compared to revision rTSA for glenoid loosening, patients undergoing revision rTSA for rotator cuff failure were associated with lower tipping point thresholds in the raw (β=−7.4, P = 0.023) and normalized Constant score (β=−8.5, P = 0.024). No association with tipping point thresholds for outcome scores was found for sex, whether surgery was performed on the dominant shoulder, or the primary shoulder arthroplasty construct.
Table 7.
Multivariable linear regression performed to identify predictors of lower tipping point thresholds in outcome score measures.
| Preoperative predictor | Regression coefficient (standard error), P-value | |||||
|---|---|---|---|---|---|---|
| SPADI | SST | ASES | UCLA | Raw Constant | Normalized Constant | |
| Intercept | 58.5 (14.1), P = 0.000 | 3.5 (2.0), P = 0.083 | 36.1 (13.0), P = 0.007 | 13.2 (3.8), P = 0.001 | 40.6 (10.3), P = 0.000 | 40.6 (12.0), P = 0.001 |
| Age at surgery (years) | −0.22 (0.17), P = 0.190 | 0.06 (0.02), P = 0.022 | 0.22 (0.16), P = 0.158 | 0.06 (0.05), P = 0.158 | 0.20 (0.12), P = 0.106 | 0.32 (0.15), P = 0.032 |
| Body mass index (kg/m2) | 0.69 (0.28), P = 0.015 | −0.09 (0.04), P = 0.035 | −0.47 (0.26), P = 0.073 | −0.13 (0.08), P = 0.089 | −0.61 (0.21), P = 0.004 | −0.72 (0.24), P = 0.003 |
| Female sex | 0.66 (3.31), P = 0.843 | −0.72 (0.47), P = 0.127 | 1.33 (3.07), P = 0.666 | −0.43 (0.89), P = 0.632 | −1.35 (2.42), P = 0.579 | 1.48 (2.82), P = 0.600 |
| Dominant side surgery | 2.13 (3.41), P = 0.532 | −0.50 (0.48), P = 0.298 | 0.20 (3.15), P = 0.949 | −0.11 (0.91), P = 0.906 | −2.38 (2.49), P = 0.342 | −2.63 (2.90), P = 0.366 |
| Primary construct (ref = aTSA) | ||||||
| rTSA | 3.05 (5.39), P = 0.573 | −0.38 (0.76), P = 0.622 | −0.37 (4.98), P = 0.941 | 0.93 (1.44), P = 0.522 | −4.54 (3.94), P = 0.251 | −5.38 (4.59), P = 0.244 |
| Hemiarthroplasty | 1.38 (4.58), P = 0.764 | 0.26 (0.65), P = 0.690 | −1.11 (4.24), P = 0.794 | −0.01 (1.23), P = 0.990 | −0.70 (3.35), P = 0.834 | −1.12 (3.90), P = 0.775 |
| Resurfacing | −5.55 (6.45), P = 0.392 | 1.10 (0.91), P = 0.233 | −2.39 (5.97), P = 0.689 | 1.90 (1.73), P = 0.273 | 9.16 (4.71), P = 0.054 | 10.74 (5.49), P = 0.053 |
| Reason for revision rTSA (ref = glenoid loosening) | ||||||
| Rotator cuff failure | 4.96 (4.38), P = 0.260 | −0.86 (0.62), P = 0.170 | −0.05 (4.05), P = 0.991 | −0.89 (1.17), P = 0.448 | −7.40 (3.20), P = 0.023 | −8.53 (3.73), P = 0.024 |
| Unexplained pain | −0.89 (5.64), P = 0.875 | 0.00 (0.80), P = 0.999 | 4.52 (5.21), P = 0.388 | 0.56 (1.51), P = 0.710 | −2.24 (4.12), P = 0.587 | −2.14 (4.80), P = 0.656 |
| Other | −7.67 (8.04), P = 0.342 | 0.08 (1.14), P = 0.941 | 9.80 (7.43), P = 0.190 | 2.72 (2.15), P = 0.209 | 6.18 (5.87), P = 0.295 | 8.05 (6.84), P = 0.241 |
| Implant wear | 4.59 (6.53), P = 0.484 | −0.86 (0.92), P = 0.356 | −6.93 (6.04), P = 0.253 | −1.58 (1.75), P = 0.369 | −5.79 (4.77), P = 0.227 | −6.71 (5.56), P = 0.230 |
| Humeral loosening | −0.64 (9.29), P = 0.946 | −0.09 (1.31), P = 0.947 | 3.55 (8.59), P = 0.680 | −2.32 (2.48), P = 0.353 | −5.64 (6.78), P = 0.407 | −5.79 (7.90), P = 0.465 |
Statistically significant predictors are denoted in bold.
ASES: American Shoulder and Elbow Surgeons score; aTSA: anatomic total shoulder arthroplasty; CI: confidence interval; rTSA: reverse total shoulder arthroplasty; SD: standard deviation; SPADI: Shoulder Pain and Disability Index; SST: Simple Shoulder Test; UCLA: University of California-Los Angeles shoulder score.
Multivariable linear regression for ROM revealed an association between increasing BMI and lower tipping point threshold for IR (β=−0.11, P < 0.001) (Table 8). Compared to revision rTSA for a primary aTSA, patients undergoing revision rTSA for a primary humeral head resurfacing had higher FE (β=39°, P = 0.001) and abduction (β=28°, P = 0.008) measurements at the time they elected for revision surgery. Similarly, patients undergoing revision rTSA for a primary hemiarthroplasty had lower ER measurements (β=−16°, P = 0.010) compared to revision rTSA for a failed primary aTSA. Compared to revision rTSA for glenoid loosening, revision rTSA for rotator cuff failure, unexplained pain, and implant wear had lower FE (β=−28°, P = 0.001; β=−23°, P = 0.025; and β=−25°, P = 0.035; respectively) and abduction (β=−27°, P < 0.001; β=−19°, P = 0.045; and β=−23°, P = 0.032; respectively) measurements. No association with tipping point thresholds for ROM-based tipping point thresholds was found for age, sex, or whether surgery was performed on the dominant shoulder.
Table 8.
Multivariable linear regression performed to identify predictors of lower tipping point thresholds in range of motion measures.
| Preoperative predictor | ||||
|---|---|---|---|---|
| ER (°) | FE (°) | IR score | Abduction (°) | |
| Intercept | 57.1 (18.3), P = 0.002 | 94.4 (24.9), P = 0.000 | 6.5 (1.3), P = 0.000 | 92.1 (22.9), P = 0.000 |
| Age at surgery (years) | −0.29 (0.22), P = 0.198 | 0.29 (0.30), P = 0.339 | 0.01 (0.02), P = 0.449 | 0.20 (0.28), P = 0.471 |
| Body mass index (kg/m2) | −0.36 (0.37), P = 0.322 | −0.84 (0.50), P = 0.093 | −0.11 (0.03), P = 0.000 | −0.82 (0.46), P = 0.077 |
| Female sex | 0.21 (4.30), P = 0.962 | −6.15 (5.86), P = 0.297 | −0.06 (0.31), P = 0.855 | −6.53 (5.40), P = 0.229 |
| Dominant side surgery | −0.24 (4.42), P = 0.956 | −7.20 (6.02), P = 0.234 | −0.50 (0.32), P = 0.115 | −4.58 (5.54), P = 0.410 |
| Primary construct (ref = aTSA) | ||||
| rTSA | −12.50 (7.00), P = 0.077 | −12.84 (9.53), P = 0.181 | −0.70 (0.50), P = 0.165 | −9.61 (8.77), P = 0.276 |
| Hemiarthroplasty | −15.57 (5.95), P = 0.010 | 6.36 (8.10), P = 0.434 | −0.43 (0.43), P = 0.320 | 8.06 (7.46), P = 0.282 |
| Resurfacing | −3.44 (8.38), P = 0.682 | 39.25 (11.41), P = 0.001 | 0.96 (0.60), P = 0.111 | 28.44 (10.50), P = 0.008 |
| Reason for revision rTSA (ref = glenoid loosening) | ||||
| Rotator cuff failure | 7.82 (5.69), P = 0.172 | −27.60 (7.75), P = 0.001 | −0.84 (0.41), P = 0.041 | −26.91 (7.13), P = 0.000 |
| Unexplained pain | −4.87 (7.32), P = 0.507 | −22.64 (9.97), P = 0.025 | −0.28 (0.52), P = 0.596 | −18.61 (9.18), P = 0.045 |
| Other | −2.07 (10.44), P = 0.843 | 19.50 (14.22), P = 0.173 | −0.32 (0.75), P = 0.669 | 13.81 (13.08), P = 0.294 |
| Implant wear | 2.29 (8.48), P = 0.787 | −24.62 (11.55), P = 0.035 | −0.33 (0.61), P = 0.583 | −23.06 (10.63), P = 0.032 |
| Humeral loosening | −5.12 (12.06), P = 0.672 | −15.60 (16.43), P = 0.344 | −1.72 (0.86), P = 0.048 | −9.51 (15.12), P = 0.531 |
Statistically significant predictors are denoted in bold.
aTSA: anatomic total shoulder arthroplasty; CI: confidence interval; ER: external rotation; FE: forward elevation; IR: internal rotation; rTSA: reverse total shoulder arthroplasty; SD: standard deviation.
Discussion
This study reports the tipping point thresholds for ROM and outcome scores in patients undergoing first revision rTSA. Patients below 60 years old were more likely to accept worse shoulder pain and deterioration of function before undergoing revision rTSA. Patients with a greater BMI were more likely to tolerate a poorer IR with minimal difference in other planes of motion before undergoing revision rTSA. No sex-based differences in tipping point were observed. Additionally, we reported significantly lower overhead motion thresholds (FE and abduction) in patients undergoing revision rTSA for rotator cuff failure and implant wear.
Compared to the tipping point thresholds for primary rTSA reported by Schoch et al., 22 patients undergoing revision rTSA herein had lower overhead motion but higher axial rotation and outcome scores at the time patients elected for revision surgery. The primary rTSA cohort exhibited greater abduction (70° vs 64°) and FE (80° vs 69°), but poorer ER (15° vs 23°), IR score (2.0 vs 3.1), Constant score (33 vs 35.5), ASES score (33 vs 37.6), SPADI score (88 vs 68.1), and SST score (3 vs 3.7) compared to our revision rTSA cohort (Table 2). Low preoperative overhead motion has been reported in prior revision rTSA cohorts.30–34 As these planes of motion significantly affect activities of daily living, it is possible that patients with loss of overhead motion will sooner seek revision rTSA despite higher rotational motion and lower SPADI tipping points compared to primary rTSA.
Younger patients exhibited worse SST and normalized Constant scores before undergoing revision rTSA compared to older patients (Table 7). This trend was contrary to Somerson et al. 24 in that patients who underwent primary TSA of all types (aTSA, rTSA, hemiarthroplasty, cuff tear arthropathy prosthesis, and ream and run arthroplasty) reported a lower tipping point for SST (0.14 for each one-year increase in age, P < 0.001); however, there was no significant trend in primary rTSA alone (β=0.03, P = 0.822) as the age-based trend was driven by the hemiarthroplasty group (β=−0.33, P = 0.004). Similarly, the preoperative findings (i.e. tipping points) in revision rTSA specifically in young patients (<55 years) reported by Otto et al. 35 compared to the results herein revealed an expected decreased mean age (49 vs 67 years) but also decreased preoperative ASES (28 vs 39) and SST (1.3 vs 3.8). It is possible that younger patients have lower tipping points as a result of previously described variability in increased pain sensitivity in lower age groups, which could possibly be limiting their function. 36 Alternatively, surgeons may counsel younger patients to delay surgery longer due to the increased lifetime risk of requiring a subsequent re-revision surgical procedure, as their likelihood of outliving their implant will increase with younger age at surgery.
On multivariable analysis, we found patients with increased BMI to have a lower tipping point for IR but no other functional (Table 7) and ROM scores (Table 8). Our findings aligned with those of other studies on rTSA which found trends of increasing BMI and decreased preoperative IR (R = −0.09, P = 0.002; R = −0.18, P = 0.003; respectively).37,38 Obese patients may have decompensated motion in planes required for IR; Sulkar et al. 39 attributed mechanical limitations in IR to decreased ability to tilt the scapula and limited scapulothoracic ROM. In fact, Eichinger et al. 37 found some of the lowest IR values in patients with BMI > 35. The lower IR tipping point associated with increased BMI is possibly related to mechanical limitations rather than differences in patients’ ability to withstand decreasing ROM in this plane when deciding to undergo surgery. 37
No significant difference in tipping points prior to revision rTSA was identified between sexes (Table 7, Table 8). This finding contrasted that of Schoch et al. 22 who found that females had lower tipping points prior to primary rTSA, specifically ASES (32 vs 38, P = 0.001), SPADI (93 vs 68, P = 0.004), and SST (2 vs 4, P < 0.001), and ER (15° vs 23°, P = 0.001). While our study found the same effect direction in our cohort of revision rTSA for these same metrics except ASES (Table 4), none of these functional and ROM metrics showed statistically significant differences on multivariable regression between patients of differing sex (Table 7, Table 8). Thus, sex may not play as critical a factor in patients electing to undergo revision arthroplasty given other factors involved with revisions compared to primary shoulder arthroplasty.
In patients undergoing revision rTSA for rotator cuff failure, unexplained pain, and implant wear, there were significantly lower tipping points for FE and abduction compared to those of patients undergoing revision rTSA for glenoid loosening (Table 8). Prior studies have found low preoperative overhead ROM in patients undergoing rTSA for rotator cuff failure. 32 Additionally, Day et al. 40 showed an association between implant wear and increased subacromial impingement, which could also limit overhead motion due to rotator cuff insufficiency and tearing. The lower overhead ROM tipping points in this study may be attributed to muscular insufficiency in rotator cuff failure. Despite poor overhead motion, these patients may elect to delay revision surgery because they still have good pain relief from their index procedure and therefore the risks of revision surgery may not outweigh potential benefits in overhead motion, which have been shown to be modest after revision rTSA. 7 Alternatively, patients undergoing revision rTSA for unexplained pain may have been limited in overhead motion by their pain. Thus, decreased overhead ROM would be expected in patients undergoing revision rTSA for these failure modalities.
There are several limitations to this study. This study was a retrospective review of patients from a prospectively collected database from a single institution. This may limit the generalizability of our findings to other settings and patient populations. Motion and outcome measurements were recorded by different providers; however, outcomes were collected using standardized techniques. Psychosocial factors and patient pain, which may affect functional outcome scores, were not specifically evaluated in this study. The effect these factors have on the decision to undergo revision rTSA would likely best be determined in a prospective, cross-sectional survey-based study rather than a retrospective cohort study. Such a study may include direct patient input on their reasons for undergoing revision rTSA rather than examining retrospective tipping points. The decision of when to undergo surgery also may have differed depending on the provider or by other patient factors not evaluated in this study. Additionally, we acknowledge the relatively small sample size. This limited our ability to meaningfully sub-stratify our findings, such as determining failure modalities more common in different primary TSA modalities. This is an inherent limitation of many revision rTSA studies because revision rTSA is performed less commonly than primary TSA. To mitigate potential biases due to a limited sample size, we reported the tipping point as the mean (along with SD and 95% CIs) of a set of threshold values derived from 500 bootstrap replicates of the original dataset. In doing so, our threshold values represent a more robust estimation of the true values based on the distribution of included patients. While the tipping points we report are meant to compare the differences between patient groups in deciding to undergo revision rTSA, they are not meant to provide definitive measures at which patients should undergo revision rTSA as this decision should be individualized to each patient. Similarly, this study did not include a comparison group of patients that elected not to undergo revision rTSA despite similar pain and dysfunction. However, keeping in mind which patients may have a lower tipping point threshold than others can help surgeons to gauge when to advise each individual patient to consider revision rTSA. Despite these limitations, this study provides valuable information to surgeons to aid in counseling patients determining when to undergo revision rTSA.
The choice to undergo revision rTSA is a multifactorial decision that encompasses numerous physical and social factors; however, this study provides surgeons data about the tipping point in revision shoulder arthroplasty that can help guide decision making. In our study, younger patients were more likely to accept worse shoulder function as assessed by functional outcome scores prior to undergoing revision rTSA. Patients undergoing revision rTSA due to rotator cuff failure or implant wear had lower tipping point FE and abduction. Surgeons should consider these tipping points for individuals unsure of proceeding with surgery when indicating patients for revision rTSA.
Acknowledgement
This work is not based on a previous communication to a society or meeting.
Footnotes
Contributorship: KAH, RJC, DSO’K, KMH, and JJK researched literature and conceived the study. KAH, JOW, TWW, KWF, AMS, BSS, and JJK were involved in protocol development. TWW was involved in gaining ethical approval. JOW, TWW, KWF, AMS, BSS, and JJK were involved in patient recruitment. TRB, KAH, and JOW were involved in data analysis. TRB wrote the first draft of the manuscript. All authors reviewed and edited the manuscript and approved the final version of the manuscript.
The authors declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: KAH has a consultancy agreement with LinkBio Corp. TWW is a paid consultant and receives royalties from Exactech, Inc. KWF is a paid consultant for Arthrex, Inc. and Exactech, Inc. BSS receives royalties from Exactech, Innomed, and Responsive Arthroscopy. JJK is a paid consultant for Exactech, Inc. and LinkBio Corp. The other authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.
Ethical approval: Ethical approval for this study was obtained from the University of Florida Healthcare Center Institutional Review Board #IRB201902620.
Funding: The authors received no financial support for the research, authorship, and/or publication of this article.
Informed consent: Written informed consent was obtained from all subjects before the study.
Guarantor: JJK.
ORCID iDs: Timothy R Buchanan https://orcid.org/0009-0002-7815-7967
Kevin A Hao https://orcid.org/0000-0002-0682-8381
Robert J Cueto https://orcid.org/0000-0002-8905-3269
Daniel S O’Keefe https://orcid.org/0000-0003-3115-227X
Jonathan O Wright https://orcid.org/0000-0001-5788-3463
Bradley S Schoch https://orcid.org/0000-0002-9355-5069
Joseph J King https://orcid.org/0000-0002-9201-9408
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