Outcomes after a Grammont-style reverse total shoulder arthroplasty?

Outcomes after a Grammont-style reverse total

shoulder arthroplasty?

Robert Z. Tashjian, MD

, Bradley Hillyard, BA

, Victoria Childress, BA

Jun Kawakami, MD, PhD

, Angela P. Presson, PhD

, Chong Zhang, MS

Peter N. Chalmers, MD

Deptartment of Orthopaedic Surgery, University of Utah, Salt Lake City, UT, USA

Division of Epidemiology, Department of Medicine, University of Utah, Salt Lake City, UT, USA

Background: The purpose of this study was to determine the factors associated with outcomes after reverse total shoulder arthroplasty (RTSA).

Methods: We retrospectively evaluated all RTSAs performed by the senior author between January 1, 2007, and November 1, 2017. We

evaluated pain visual analog scale (VAS), Simple Shoulder Test (SST), and American Shoulder and Elbow Surgeons Standardized Shoulder

Assessment Form (ASES) scores and complication and reoperation rates at a minimum of 2-year follow-up. We evaluated preoperative and

2-week postoperative radiographs for glenoid inclination (GI), medialization as distance between the center of the humeral head or

glenosphere and the line of the deltoid, and distalization via the acromial–greater tuberosity distance. We performed inter- and intrarater

reliabilities via intraclass correlation coefﬁcients (ICCs) and conducted a multivariable analysis.

Results: We included 230 RTSAs in the analysis, with 70% follow-up at a median of 3.4 years. Reliability was acceptable with all ICCs >.678.

Increased postoperative GI was signiﬁcantly associated with increased VAS pain postoperatively (P ¼ .008). Increased distalization was asso-

ciated with an increased rate of complications and reoperations (P ¼.032). Younger age (P ¼.008), female gender (P ¼ .009), and lower body

mass index (BMI) (P ¼ .006) were associated with worse ASES scores. Female gender (P < .001) and lower BMI (P ¼ .039) were associated

with worse SST scores. Female gender (P ¼ .013) and lower BMI (P ¼ .005) were associated with worse VAS-pain scores.

Conclusion: Age, gender, and BMI are associated with outcome after RTSA. In this retrospective analysis of a Grammont-style RTSA, superior

inclination is associated with increased pain postoperatively, whereas excessive arm lengthening is associated with increased risk for complication

or reoperation.

Level of evidence: Level IV; Case Series; Treatment Study

Keywords: Reverse total shoulder arthroplasty; shoulder replacement; radiographic analysis; lateralization; pati ent-repor ted out comes;

medical comorbidities

Although reverse total shoulder arthroplasty (RTSA)

generally has low reoperation rates

and excellent long-

term outcomes,

2,11,21,35

not all patients have an excellent

long-term outcome postoperatively.

Conceptually, RTSA

with a Grammont-style design shifts the center of rotation

(COR) medially and distally.

4,22

Alteration of the COR

changes the deltoid and infraspinatus function.

This shift

has been suggested to be important for postoperative

shoulder function.

However, designs with less of a shift in

the COR also have good long-term outcomes.

12,17,18,34

Biomechanically, glenosphere or baseplate lateralization

may be a trade-off between impingement-free range of

Each author certiﬁes that his or her institution approved the human pro-

tocol for this investigation, that all investigations were conducted in con-

formity with ethical principles of research, and that informed consent for

participation in the study was obtained from all subjects.

This study was performed under the University of Utah Institutional Re-

view Board as approved protocol 46622. Informed consent for participa-

tion in the study was obtained from all subjects.

The work for this manuscript was performed at the University of Utah.

*Reprint requests: Peter N. Chalmers, MD, Department of Orthopaedic

Surgery 590 Wakara Way, Salt Lake City, UT, USA.

E-mail address: [email protected] (P.N. Chalmers).

J Shoulder Elbow Surg (2020) -,1–8

www.elsevier.com/locate/ymse

https://doi.org/10.1016/j.jse.2020.04.027

motion

and deltoid forces.

Although lateralization in-

creases stability,

it does so by creating increased joint

loads and deltoid forces.

It also increases back-side forces

on the baseplate.

In addition, although lateralization may

reduce notching, it may not be as effective as inferior

overhang.

Clinically, lateralization may also be a trade-off. Base-

plate lateralizati on may reduce notching

but may impair

postoperative outcomes with subscapularis repair.

Later-

alization improves external rot ation but may do so at the

expense of elevation

and abduction.

A prior systematic

review found no signiﬁcant differences in postoperative

outcomes between patients with medialized and lateralized

COR implants.

Another prior retrospective study

demonstrated signiﬁcantly worse outcomes with lateralized

implants.

Finally, a randomized clinical trial between a

lateralization design and a medialized one demonstrated no

signiﬁcant differences in postoperative outcomes.

Finally,

baseplate inclination, glenosphere size, and glenosphere

inferior overhang may also inﬂuence postoperative

outcomes.

3,37,42,43,48

Thus, there is a gap within our current knowledge. This

gap remains in part because there is anatomic variation

in the preoperative position of the COR and variation in

surgical technique with reaming and implant positioning.

The same implant, placed in different patients by different

surgeons using different technique, may be more or less

distalized and medialized and inclined.

The purpose of this study was to determine the factors

associated with outcome after Grammont-style reverse total

shoulder arthroplasty (RTSA). Following Grammont’s

original concept,

we hypothesized that increased medial-

ization and distalization would be associated with improved

postoperative outcomes.

Methods

Included patients

This is a retrospective case series. A single surgeon (R.Z.T.)

performed all procedures using the same technique and post-

operative protocol. We obtained informed consent from all

included subjects. We performed this study after approval by our

Institutional Review Board. We searched the operative logs of the

(University of Utah) for all patients who underwent a surgical

procedure by a single surgeon (R.Z.T.) between January 1, 2007,

and November 1, 2017, using the Common Procedure Terminol-

ogy code 23472 to capture all patients who underwent reverse

total shoulder arthroplasty. We excluded patients who were known

to have become deceased.

Data collection

We collected demographics, body mass index (BMI), Charlson

comorbidty index at the time of the index surgery,

8,9

indication for

surgery, version of the humeral component as assessed and

documented by the surgeon intraoperatively (not as measured

radiographically), glenosphere size, documented intraoperative

complications, documented postoperative complications, and

reoperations. We contacted all patients, and the following out-

comes were collected: American Shoulder and Elbow Surgeons

Standardized Shoulder Assessment Form (ASES) score, Simple

Shoulder Test (SST) score, and visual analog scale for pain (VAS)

score and whether complications or reoperations had occurred.

When patients were willing to return for an in-person evaluation,

this was preferred; otherwise, these outcomes were collected via

mail and phone. To maximize follow-up, we contacted patients on

multiple occasions at different times of the day via different phone

numbers and using all available contact methods available,

including an electronic service that provides updated contact

information.

On preoperative and 2-week postoperative 2-dimensional

imaging, we made the following measurements: (1) glenoid

inclination (complement of the b angle

), as previously

described

; (2) acromial–greater tuberosity distance (AGT); and

(3) the center of rotation medialization (CORM; Fig. 1). We used

AGT to measure humeral distalization. To determine the inter-

observer reliability of these measurements, 2 attending orthopedic

surgeons fellowship trained in shoulder and elbow surgery

analyzed 50 radiographs. To determine the intraobserver reli-

ability of these measurements, one attending orthopedic surgeon

fellowship trained in shoulder and elbow surgery analyzed 50

radiographs twice separated by 1 month. From these measure-

ments, we calculated intraclass correlation coefﬁcients (ICCs)

using a single-rating, absolute-agreement, 2-way mixed effect

model. We interpreted ICCs based on prior guidelines.

As this

was a retrospective analysis, we took no a priori steps to adjust for

magniﬁcation. To ensure that there were no magniﬁcation effects,

we measured glenosphere size on 50 radiographs and compared

the measured glenosphere size to the known true glenosphere size

as provided by the manufacturer using ICCs and a mean difference

analysis. We made all measurements using the measurement tools

provided within the Picture Archiving and Communication Sys-

tems program in our hospital system (IntelliSpace 4.4, Philips,

Andover, MA, USA).

Statistical analysis

We summarized patient demographics, clinical variables, and

outcomes (SST, ASES, and VAS scores) descriptively (Tables I

and II). We summarized continuous variables as mean (standard

deviation), median (interquartile range), and range, and categori-

cal variables were summarized as frequency and percentage.

We descriptively summarized preoperative and 2-week post-

operative radiographic outcomes for GI, CORM, and AGT

shoulder measures. We tested differences between preoperative

and postoperative measures using paired t tests.

We performed univariable and multivariable regressions to

assess relationships between postoperative shoulder measures and

patient outcomes. The distribution of each outcome variable

dictated the type of regression model, where for ASES and SST

we used linear regression, as these variables were approximately

normally distributed, and for reoperation we used logistic

regression, which is common for binary outcomes.

For VAS, we

used negative binomial regression, because of its heavy skew and

notable fraction of 0 values (30%).

Multivariable models

2 R.Z. Tashjian et al.

adjusted for age, sex, BMI, Charlson comorbidty index, implant

company, humeral version, length of follow-up, and postoperative

diagnosisdexcept for reoperation, which was limited by the

number of events (we adjusted for age, sex, Charlson comorbidty

index, and length of follow-up).

We reported results from linear

regression models as mean differences, results from logistic

regression models as odds ratios (ORs), and results from negative

binomial models as ratios. We reported 95% conﬁdence intervals

(CIs) and P values with all point estimates from the regression

models. We examined potential nonlinear relationships between

shoulder measures and outcomes. We assessed statistical signiﬁ-

cance at the 0.05 level, and all tests were 2-tailed. We conducted

these analyses in R, version 3.6.1 (R Foundation for Statistical

Computing, Vienna, Austria).

Sample size determination

The authors assumed that an association with the strength for a

correlation coefﬁcient of 0.3 would be clinically signiﬁcant, as it

is consistent with multiple prior shoulder arthroplasty radio-

graphic and outcome association analysis studies.

7,32

To have a

90% chance to ﬁnd an association of at least a value of r equal to

0.3, should one exist, a sample size of 112 patients would be

needed. Based on an expected loss to follow-up rate of 30%, our

target sample size was 160, and thus this was our minimum target

sample size.

Results

Study cohort

During the 10-year period in question, the senior author

performed 369 RTSAs, of which 40 patients were deceased

at the time of follow-up and 99 were lost to follow-up. Of

the 329 eligible for follow-up, 230 had patient-reported

outcome scores available at a minimum of 2-year follow-

up, providing a rate of follow-up of 70% at a minimum of 2

years, a maximum of 12 years, and a mean  standard

deviation of 4.01.9 years. We performed these procedures

on 216 unique patients, with 14 patients undergoing bilat-

eral RTSA. This cohor t was elderly, mostly female, and

mostly right-sided (Table I). Rotator cuff tear arthropathy

was the most common indication for surgery in 46% of

patients, with 24% of patients being revision

arthroplasties and 8% being fractures or their sequelae. The

Figure 1 Radiographic measurement technique. The solid white

line demonstrates the acromial–greater tuberosity distance (AGT),

a measure of humeral distalization, which was measured as the

shortest distance between the greater tuberosity and the acromion.

The dashed white line shows the line of pull of the deltoid, and the

solid black line shows the medialization of the center of rotation

relative to the line of pull of the deltoid (CORM), which was

measured as the distance between the center of the best-ﬁt circle

of the humeral head or glenosphere on preoperative and post-

operative radiographs and a line between the most lateral aspect of

the acromion and the deltoid tuberosity

Table I Demographics of the included patients

Variable MeanSD,

median (IQR),

or % (n/N)

Age, yr 7010

Body mass index (n¼222) 297

Charlson comorbidty index (n¼225) 2.81.2

Length of follow-up, yr, median (IQR) 3.4 (2.5, 5.2)

Female sex, % (n/N) 71 (163/230)

Right operative side, % (n/N) 69 (158/229)

Implant, % (n/N)

Wright Medical 64 (146/229)

Zimmer 36 (82/229)

Humeral version, % (n/N)

<10



16 (33/203)



-20



74 (150/203)



10 (20/203)

Indication for surgery, % (n/N)

Degenerative 63 (143/228)

Rotator cuff tear arthropathy 39 (89/228)

Glenohumeral osteoarthritis (GHOA) 9 (21/228)

Rotator cuff tear (RCT) 8 (17/230)

GHOAþRCT 7 (16/228)

Failed arthroplasty 24 (54/228)

Traumatic 14 (31/228)

Acute proximal humerus fractures 4 (10/228)

Proximal humeral fracture sequelae 8 (17/228)

Other 2 (4/228)

Rtsa XR COR 3

senior author used Aequalis (Wright Medical Technology,

Memphis TN, USA) and Trabecular Metal Reverse (Zim-

mer, Warsaw, IN, USA) components during the study

period, in which most humeral components were placed in



-20



retroversion. Both systems are Grammont-style

RTSAs with inlay, medialized humeral components and

without glenosphere lateralization options. For the initial 3

years, we performed the Zimmer RTSA exclusively and

then we switched to implants manufacturered by Wright

Medical exclusively after that point.

At ﬁnal follow-up, the SST score was 73 (range 0-12,

data available for 210/230 patients), the ASES score was

6721 (5-100, data available for 224/230 patients), the

VAS score was 23 (0-1, data available for 224/230

patients). Of the included shoulders, 18% (41/230) suffered

either a complication or reoperation postoperatively; 3.4%

of shoulders had postoperative instability (8/230). One

percent of shoulders developed a recurrence of a prior

known infection (3/230), and 4% (9/230) of shoulders

suffered a new postoperative infection (3 in primary RTSAs

and 6 in revision RTSAs). Of these, 1% (3/230) were deep

infections requiring operative irrigation and d



ebridement

and the other 3% (6/230) were superﬁcial infections

responding to antibiotics. Three percent of shoul ders had a

postoperative acromial fracture (7/230), and none of these

patients had a history of trauma. One percent of shoulders

had persistent pain at the strap tendon requiring operative

release (3/230), and 1% of shoulders had postoperative

hematomas (2/230). Two percent of shoulders had glenoid

loosening (2 in the context of a glenoid bone graft and 1 in

the context of infection, 4/230). One percent (3/230) of

shoulders had nerve injuries (1 median, 1 ulnar, and 1

diffuse plexopathy), all of which resolved. Two percent of

shoulders (5/230) had other complications including a

postoperative seizure, a postoperative fall with a glenoid

neck fracture, and postoperative thromboembolic events.

Radiographic measures

Inter- and int rarater reliability was generally excellent for

all radiographic measures (Table II). There were minimal

effects from magniﬁcation, as the ICCs comparing the

radiographically measured glenosphere size and the recor-

ded glenosphere size had an ICC of 0.79 (95% CI 0.652,

0.877) with a mean difference of 0.104 (95% CI –0.014,

0.222) mm. GI changed 9



into a more inferior inclination

(range 15



superior to 40



inferior), CORM change was 24

mm medial (11 mm lateralization to 55 mm medialization),

and AGT increased 29 mm (0 to 51 mm); all of these

changes were statistica lly signiﬁcant (Table III).

Associations with outcomes

There were no notable nonlinear relationships between

shoulder measures and outcomes. Our multivariable

regression analyses found no associations between any of

the measured radiographic factors and functional outcomes

as measured with the ASES or SST scores at ﬁnal follow-up

(Table IV). However, there were multiple patient factors

associated with outcome. Adjusting for the other variables

in the model, a 1-year increase in age was associated

with a 0.6-point increase in ASES score (95% CI 0.2, 1.1,

P ¼ .008); women had on average an 11-point lower ASES

score relative to men (95% CI –2.7, –18.4, P ¼ .009), and a

1-point increase in BMI was associated with a 0.7-point

increase in ASES score (0.2 to 1.2, P ¼ .006). Adjusting

for the other variables in the model, females had a 2.1-po int

reduced SST score relative to males (–0.83 to –3.3,

P < .001), and a 1-point increase in BMI was associated

with a 0.1-point increase in SST (0.0 to 0.2, P ¼ .039).

Postoperative pain was associated with postoperative GI,

sex, and BMI. Adjusting for the other variables in the

model, a 1



increase in postoperative GI into superior

inclination was associated with a 3% (95% CI 1%, 6%,

P ¼ .008) increase in VAS pain, female gender was asso-

ciated with a 95% (95% CI 11%, 343%, P ¼ .013) increase

in VAS pain, and a 1-point increase in BMI was associated

with a 4% (95% CI 1%, 7%, P ¼ .005) decrease in VAS

pain.

Postoperative distalization was associated with reoper-

ation or complication. Adjusting for the other variables in

the model, a 1-mm increase in distalization was associated

with a 6% increased odds of reoperation or complication

(95% CI 1.01, 1.11, P ¼ .032; Table IV). Postoperative

Table III Radiographic measures

Variable Preoperative,

mean  SD

Postoperative,

mean  SD

Change,

mean  SD

value

GI, degrees 1028938–910 <.001

CORM, mm 208448248 <.001

AGT, mm 96388299 <.001

GI, glenoid inclination, measured as the complement of the b angle;

CORM, center of rotation medialization; AGT, acromial–greater

tuberosity distance; SD, standard deviation.

Table II Reliability analysis for the included radiographic

measures

Variable Inter-rater ICC

(95% CI)

Intrarater ICC

(95% CI)

GI 0.948 (0.910, 0.970) 0.981 (0.967, 0.989)

CORM 0.803 (0.678, 0.883) 0.914 (0.854, 0.951)

AGT 0.971 (0.949, 0.983) 0.973 (0.953, 0.985)

GI, glenoid inclination, measured as the complement of the b angle;

CORM, center of rotation medialization; AGT, acromial–greater

tuberosity distance; ICC, intraclass correlation coefﬁcient; CI, conﬁ-

dence interval.

4 R.Z. Tashjian et al.

glenoid inclination was not associated with any change in

the odds of reoperation or complication (OR 1.01, 95% CI

0.97, 1.07, P ¼ .550; Table IV). There were no differences

in outcomes or reoperation rates between implant manu-

facturers (Table IV).

Discussion

We analyzed 230 RTSAs with a minimum of 2-year,

short-term, follow-up but with an average of 4-year,

medium-term, follow-up, with patient-reported outcomes.

Baseplate superior inclination was associated with

increased postoperative pain (P ¼ .008), and distalization

was associated with increased reoperations and complica-

tions (P ¼ .032). There were also signiﬁcant associations

between patient factors and patient-reported outcomes.

Overall, these analyses suggest that preoperative patient

demographics and com orbidities are important for outcome

after RTSA. Older, higher-BMI, men with inferiorly in-

clined baseplates and without excess distalization had the

best outcome and the lowest risk for reoperation or

complication.

Association between outcomes and radiographic

implant position

Our study demonstrated overall excellent outcomes and

low complication and reoperation rates after RTSA.

Multiple pri or studies have simi larly demonstrated

excellent outcomes and low reope ration rate s using a

Grammont-style implant.

2,11,21 ,35

In addition, although

our study demonstrated an overall medialization and

distalization of the COR and tilt into inferior inclina-

tion, we found substantial variation in these factors,

with 55



variation in incl ination change, 66-mm varia-

tion in medialization change, and 51-mm variation in

distalization change. A prior study demonstrated simi lar

variation.

We also found a wide variation in post-

operative outcomes, with ASES scores ranging from 5-

100, suggesting that t he outcome after RTSA does vary

widely. Inferiorly inclined baseplates demonstrated

decreased pain postoperatively. The a uthors speculate

that this association is due to the decreased impinge-

ment at the inferior glenoid w ith an inferiorly inclined

baseplate. We also found that excess distalization led to

an increased risk for reoperation or complication. The

authors speculate that this association is due to the

increased soft tissue t ension, which may increase the

risk for acromial fractures, strap tendonitis, and nerve

injuries. As each of these individual complications is

uncommon, likely multicenter studies will be necessary

to better elucidate the associations between each and

distalizatio n. However, our data set demonstrates t hat

excess distalization does increase the risk for reopera-

tion or complication. Since collection of this series and

based on this experience, the senior author has

decreased intraoperative tension, particularly in elderly

individuals who are at risk for acromial fractures, strap

tendonitis, and nerve injuries.

Table IV Results of multivariate regression analyses to determine associates with each ﬁnal outcome variable

Variable ASES SST VAS Reop./Complication

Coefﬁcient P value Coefﬁcient P value Ratio P value OR P value

GI –0.26 (–0.67, 0.14) .200 –0.01 (–0.07, 0.05) .760 1.03 (1.01, 1.06) .008 1.01 (0.97, 1.07) .550

CORM 0.05 (–0.40, 0.50) .830 –0.01 (–0.08, 0.06) .710 1.00 (0.98, 1.03) .800 0.97 (0.92, 1.02) .260

AGT 0.03 (–0.38, 0.44) .890 –0.01 (–0.07, 0.06) .830 1.00 (0.98, 1.03) .850 1.06 (1.01, 1.11) .032

Age 0.64 (0.17, 1.12) .008 0.04 (–0.04, 0.11) .330 0.99 (0.96, 1.02) .460 0.98 (0.92, 1.04) .520

Sex –10.52 (–18.37, –2.66) .009 –2.05 (–3.25, –0.84) <.001 1.95 (1.11, 3.43) .013 0.46 (0.20, 1.06) .070

BMI 0.68 (0.20, 1.16) .006 0.08 (0.00, 0.15) .039 0.96 (0.93, 0.99) .005 NA NA

CCI –3.15 (–6.66, 0.35) .080 –0.43 (–0.98, 0.11) .120 0.93 (0.74, 1.16) .520 0.68 (0.39, 1.08) .130

Implant 0.56 (–7.86, 8.99) .900 0.68 (–0.61, 1.98) .300 0.90 (0.53, 1.52) .700 NA NA

Vers. >20



–3.29 (–16.05, 9.46) .610 0.33 (–1.62, 2.28) .740 1.91 (0.86, 4.39) .110 NA NA

FU length –0.48 (–2.34, 1.38) .610 –0.02 (–0.30, 0.26) .880 0.98 (0.87, 1.09) .700 0.95 (0.77, 1.17) .640

Reop Diag. –4.78 (–12.83, 3.28) .240 –1.15 (–2.38, 0.07) .060 0.90 (0.53, 1.53) .680 NA NA

Frx. Diag. 0.69 (–8.82, 10.21) .890 0.04 (–1.39, 1.46) .960 0.68 (0.36, 1.33) .230 NA NA

GI, glenoid inclination, measured as the complement of the b angle; CORM, center of rotation medialization; AGT, acromial–greater tuberosity distance;

BMI, body mass index; CCI, Charlson comorbidity index; Vers., Version; FU, follow-up length; Reop Diag., indication for surgery of a failed arthroplasty;

Frx Diag., indication for surgery of a fracture or fracture sequelae; ASES, American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form;

SST, Simple Shoulder Test score; VAS, visual analog scale for pain; Reop., reoperation; OR, odds ratio; NA, not applicable.

For ASES and SST, we performed linear regression and have shown coefﬁcient and 95% conﬁdence intervals. For VAS, we performed negative binomial

regression and have shown ratio and 95% conﬁdence intervals. For reoperations and complications, we performed logistic regression but reduced the

number of covariates because only 41 of these events occurred. Statistically signiﬁcant differences are bolded.

Because of the limited number of events, only variables signiﬁcantly associated with the outcome in the univariable analysis and length of follow-up

were included.

Rtsa XR COR 5

Association between demographics and outcome

Within our study, patient factors were ass ociated

with patient-reported functional outcome after RTSA

but implant position was not. Prior studi es have

demonstrated sex

20,35

and age to be a predictor of

patient-reported outcomes after RTSA.

20,26

Apriorstudy

demonstrated male sex to be associated with complica-

tions after RTSA,

partially because Cutibacterium

acnes is more common in males.

Preoperative patient

expectations predict outcomes,

and these likely differ

depending on patient demographics and m edical

comorbidities. Workers’ compensation status, which is

associated with patient demographics, also affects

outcome and complication r ates after sh oulder arthro-

plasty.

However, some studies have demonstrated BMI,

gender, age, or medical comorbidities to either have no

association with postop erative outcome or to be associ-

ated in directions different from those seen in our own

studies.

15,33,46,49

Also, one study de monstrated signiﬁ-

cantly better pain with more medialization.

The

difference in our ﬁndings and the ﬁndings of th ese

studies may be explained by the different patient pop-

ulations, smaller sample sizes, dichotimization of

outcome variables, and use of logistic regression within

these study designs.

15,33,46,49

Limitations

Our study has several limitations. This was a retro-

spective study and thus no standardized protocol was

used to follow-up prospectively for preoperative radio-

graphs, surgical technique, postoperative rehabilitation,

postoperative radiographs, etc. Although this is a

single-surgeon series using all G rammont-style implants,

there were likely subtle changes in surgical technique,

postoperative rehabilitation, etc during the study p eriod.

Theauthorshavemaximizedthestudyperiodtomaxi-

mize sample size. In particular, the angle of arm

abduction was not standardized. Because the arm rotates

about the COR, abduction moves the shortest distance

from the COR to the line of pull of the deltoid proxi-

mally, a nd thus substantially reduces any effect of

abduction on this distance (Fig. 2). In addition, this is a

single-surgeon, single-institution study, and thus our

ﬁndings may not be generalizable. In particular,

during the study period, the author exclusively used a

medialized-COR, valgu s neck-shaft angle implant

design. Our ﬁndings thus m ay not app ly to lateral ized

(humerus or glenospher e) or varus neck-shaft angle

implant designs . However, subst antial variation was seen

in both distalization and medialization of the COR

(CORM c hang e varied from 1 1-m m lateralization to 55-

mm medialization, and AGT change varied from 0-51

mm), which mitigates thi s limitation. We also did not

analyze radiographic position relative to the pre-

deformity or ‘‘normal’’ sc apula . Our st udy do es n ot

include radiogra phs at ﬁnal follow-up a nd thus does not

allow us to assess for loosening, notching, and other

radiographic complications. Two implant designs are

included to maximize the sample size, and they do

differ slightly, although we have included im plant

manufacturer as a covariate in our multivariate analysis

and it was not associated wit h outcome. Some patients

were lost to follow-up and the population included is

heterogeneous, although diagnosis is included as a co-

variate in our analysis. It also i s an assessment of im-

mediate postoperative radiographic implant position and

not radiographic implant position at ﬁnal follow-up. It is

thus possible that some implants may h ave shifted in

position. Cl inically, it has been the authors’ experience

that substantial shifts in impl ant position in the setting

of RTSA are almost always associated w ith clinical

symptoms and reoperation, and thus this limitation

likely contributes minimal bias. Finally, humeral version

is based on the surgeon’s intraoperative assessment, and

thus no reliability data are presented for this variable.

We did not measure glenoid version as it was not felt

that this could b e reliably or accurately measured on

axillary radiographs.

Conclusion

Age, gender, and BMI are associated with outcome after

RTSA. In this retrospective analysis of a Grammont-

style RTSA, superior inclination is associated with

Figure 2 Example of robustness of center of rotation mea-

surement to angle of glenohumeral abduction.

6 R.Z. Tashjian et al.

increased pain postoperatively, whereas excessive arm

lengthening is associated with increased risk for

complication or reoperation.

Disclaimer

This investigation was supported by the University of

Utah Population Health Research (PHR) Foundation

(authors A.P.P., C.Z.), with funding in part from the

National Center for Research Resources and the Na-

tional Center for Advancing Translational Sciences,

National Institutes of Health, through Grant

UL1TR002538 (formerly 5UL1TR001067-05,

8UL1TR000105, and UL1RR025764). Our research

team is supported by the National Institutes of Health

grant UL1TR002538.

Disclosure

Peter Chalmers is a paid consultant for Arthrex and

Mitek, is paid speaker for DePuy, serves on the editorial

board for the Journal of Shoulder and Elbow Surgery,

receives intellectual property royalties from DePuy, and

has received other support from Tornier.

Robert Tashjian is a paid consultant for Zimmer/

Biomet, Wright Medical, and DePuy-Mitek; has stock in

Conextions, INTRAFUSE, Genesis, and KATOR; re-

ceives intellectual property royalties from Wright

Medical, Shoulder Innovations, and Zimmer/Biomet;

receives publishing royalties from Springer and the

Journal of Bone and Joint Surgery, and serves on the

editorial board for the Journal of Shoulder and Elbow

Arthroplasty and the Journal of the American Academy

of Orthopaedic Surgeons.

The institution of one or more of the authors (P.N.C.,

R.Z.T.) has received funding from the National Institute

of Arthritis and Musculoskeletal and Skin Disease of the

National Institutes of Health (R01 AR067196). The

content is solely the responsibility of the authors and

does not necessarily represent the ofﬁcial views of the

National Institutes of Health.

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