The Orthopaedic

generous donati

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This study was

Beaumont Hosp

J Shoulder Elbow Surg (2015) 24, 1915-1925

1058-2746/$ - s

http://dx.doi.org

www.elsevier.com/locate/ymse

Elucidating trends in revision reverse totalshoulder arthroplasty procedures: a retrievalstudy evaluating clinical, radiographic, andfunctional outcomes data

Brett P. Wiater, MDa, Erin A. Baker, MSb,c, Meagan R. Salisbury, MSb,Denise M. Koueiter, MSb, Kevin C. Baker, PhDb,c, Betsy M. Nolan, MDa,J. Michael Wiater, MDa,c,*

aDepartment of Orthopaedic Surgery, Beaumont Health System, Royal Oak, MI, USAbDepartment of Orthopaedic Research, Beaumont Health System, Royal Oak, MI, USAcDepartment of Surgery, Oakland University William Beaumont School of Medicine, Rochester, MI, USA

Background: The purpose of this study was to explore relationships between damage modes in explantedreverse total shoulder arthroplasty (RTSA) components, patient and radiographic risk factors, and func-tional data to elucidate trends in RTSA failure.Methods: Fifty RTSA systems, retrieved from 44 patients, with 50 polyethylene (PE) liners, 30 gleno-spheres, 21 glenoid baseplates, 13 modular humeral metaphases, and 17 humeral stems, were examinedfor damage modes, including abrasion, burnishing, dishing, embedding, scratching, and pitting. PE linerswere also analyzed for delamination and edge deformation. Charts were reviewed for patient, surgical, andfunctional data. Pre-revision radiographs were analyzed for scapular notching and loosening.Results: Average term of implantation was 20 months (range, 0-81 months). Metallic componentsexhibited abrasion, burnishing, dishing, pitting, and scratching. PE liners displayed all damage modes.Damage was exhibited on 93% of glenospheres and 100% of PE liners. Of 29 aseptic shoulders, 13 showedevidence of scapular notching and 5 of humeral loosening. There was a moderate correlation betweenradiographically observed implant failure or dissociation and PE embedding (r ¼ 0.496; P < .001).There were weak and moderate correlations between scapular notching severity and PE dishing(r ¼ 0.496; P ¼ .006), embedding (r ¼ 0.468; P ¼ .010), and delamination (r ¼ 0.384; P ¼ .040).Conclusions: To date, this is the largest series of retrieved RTSA components and the first to relate damagemodes to radiographic and clinical data. Most damage was observed on the PE liners, on both the articularsurface and rim, and glenosphere components. Correlation of retrieval findings with radiographic and clin-ical data may help establish predictors of prostheses at risk for failure.

Implant Retrieval Program at Beaumont is underwritten by

ons to the Dorothy and Byron Gerson Implant Analysis

, the program is partially funded by the Stryker Corporation.

approved by the Human Investigation Committee at

itals Research Institute under the study ID #2011-241.

*Reprint requests: J. Michael Wiater, MD, Department of Orthopaedic

Surgery, Beaumont Health System, 3535 W 13 Mile Road, Suite 744,

Royal Oak, MI 48073, USA.

E-mail address: mwiater@beaumont.edu (J.M. Wiater).

ee front matter � 2015 Journal of Shoulder and Elbow Surgery Board of Trustees.

/10.1016/j.jse.2015.06.004

1916 B.P. Wiater et al.

Level of evidence: Level IV, Case Series, Treatment Study.� 2015 Journal of Shoulder and Elbow Surgery Board of Trustees.

Keywords: Reverse total shoulder arthroplasty; implant retrieval; implant damage; scapular notching

Since Food and Drug Administration approval in 2004,reverse total shoulder arthroplasty (RTSA) has gainedpopularity as an effective means of achieving pain reliefand improved function in a variety of complex shoulderconditions including cuff tear arthropathy,17,34,45 massive,irreparable rotator cuff tears,10,12,17 inflammatoryarthritis,15,21,23,63 acute proximal humerus fractures,7,38,64

fracture sequelae,4,39,62 and failed shoulder arthro-plasty.6,37,62 Despite promising reports of dramaticimprovement in pain scores, functional outcome scores,range of motion (ROM), patient satisfaction, and cost-effectiveness at early and midterm follow-up, primaryand revision RTSAs have been associated with relativelyhigh complication rates, with recent studies reportingranges of 4.3% to 37.5% and 19% to 50%, respec-tively.9,14,19,28,29,45,48,58,60 Postoperative complicationsare numerous and include instability, infection, peri-prosthetic fracture, hematoma and seroma, neurologicinjuries, implant loosening, acromial fracture, and scap-ular notching.8,59 A recent implant retrieval study char-acterized thewear on polyethylene (PE) humeral liners andassociated rim damage on PE liners with scapularimpingement.43 Day et al11 proposed that when thenotching reaches the level of the inferior baseplate screws,wear to the PE liner is greatly accelerated, and eventuallythe metallic humeral metaphysis becomes involved.

Implant retrieval studies in the hip and knee arthro-plasty literature are numerous and have proved to be in-tegral to the evolution of surgical technique and implantdesign.1,3,5,22,26,31,33,44,47,49,52,55,61 To date, retrievalstudies of RTSA have consisted of small observationalstudies limited to examination of wear patterns, predom-inantly of the PE component. Studies by Nam et al43 andDay et al11 found wear of the PE liner in 60% to 100% ofretrieved systems; however, no RTSA retrieval study hasbeen performed that has thoroughly examined all of theretrieved components and correlated damage modes toclinical data.

The objective of this study was to examine clinicallyfailed, retrieved RTSA metallic and PE componentsthrough a combination of clinical, radiographic, and dam-age mode analyses. We hypothesized that through datacollection and analysis, we could identify preliminarytrends and relationships between implant damage modes,patient factors, in vivo device performance, and post-operative outcomes that might eventually be used todevelop future prospective studies.

Materials and methods

Damage mode analysis

Retrieved RTSA systems were obtained and catalogued throughthe Institutional Review Board–approved orthopedic implantretrieval program at our institution between 2005 and 2013. Onretrieval, systems were de-identified and ultrasonically cleaned ina diluted Micro-90 solution (International Products Corporation,Burlington, NJ, USA) for 5 minutes, followed by an ultrasonicbath in a �85% ethanol solution for an additional 5 minutes. Allnonpolymer components were also ultrasonically bathed inacetone for 5 minutes. Devices were allowed to air dry, and themanufacturer, model, material, and relevant surgical informationwere recorded and entered into an electronic database. The de-vices were then vacuum sealed to prevent oxidation and stored atroom temperature until analysis.

Fifty RTSA implants were obtained from 44 patients. Thesenior author (J.M.W.) implanted 31 of these systems, and sur-geons from outside institutions implanted the remaining 19. Of the6 patients with explants from 2 separate revisions, both explantswere retrieved from the same shoulder and none were staged.

According to the failure mechanism of each individual case, allor some of the components were revised. Of the 50 RTSA devicescollected, 30 contained a metallic glenosphere, 50 included a PEinsert, 21 contained a glenoid baseplate, 13 included a modularmetallic humeral metaphysis, and 17 contained a humeral stem(10 monoblock, 7 modular). Devices varied by manufacturer andmodel, including 26 Trabecular Metal Reverse Shoulder System(Zimmer, Warsaw, IN, USA), 10 Aequalis Reversed II (Tornier,South Bloomington, MN, USA), 5 Reverse Shoulder System(Encore; DJO, Austin, TX, USA), 3 Anatomical Shoulder Reverse(Zimmer), 3 Delta CTA Reversed Shoulder Prosthesis (DePuy,Warsaw, IN, USA), 2 Comprehensive Reverse Shoulder System(Biomet, Warsaw, IN, USA), and 1 Equinox Reverse Platform(Exactech, Gainesville, FL, USA). Five retrieved implants usedmixed-model components, including Trabecular Metal ReverseShoulder System stem and PE liner (n ¼ 3), Delta CTA stem andPE liner (n ¼ 1), and Anatomical Shoulder Reverse system stemand PE liner (n ¼ 1), with each implant using glenoid-sideTrabecular Metal Reverse Shoulder System components. Radio-graphs and intraoperative findings confirmed that 32 of thehumeral stems were uncemented and 18 were cemented. In 33cases, humeral stems were retained at revision; of the 17 retrievedhumeral stems, 10 were uncemented and 7 were cemented.

Retrieved components were analyzed for damage by 2 ob-servers. Components were first evaluated macroscopically forpresence or absence of the following damage modes: abrasion,burnishing, scratching, dishing, embedding, pitting, and fracture(Fig. 1).11,24,40,43 PE components were also evaluated for evidenceof delamination and edge deformation.11,43 Components were then

Figure 1 Top left, A list of observed damage modes on RTSA components, with brief descriptions of their causes or appearances. Topright, Identification of pitting (A), embedding (B), edge deformation (C), scratching (D), and abrasion and delamination (E) on the humeralliner as well as burnishing and scratching of the glenosphere (F). Bottom, Representative scanning electron micrographs showing abrasion(A) and scratching (B) of the glenosphere as well as pitting (C) and abrasion on the rim (D) of the polyethylene liner.

Reverse shoulder arthroplasty retrieval analysis 1917

evaluated under light microscopy (LM, MZ-16; Leica Instruments,Wetzlar, Germany), during which the presence of damage modeswas confirmed and magnified images were obtained. To confirmand further evaluate damage modes, scanning electron microscopy(JEOL JSM-6400; JEOL Ltd., Tokyo, Japan) was performed onseveral devices. PE components were sputter coated with gold-palladium before evaluation under scanning electron microscopy.

Clinical records review

Medical records were retrospectively reviewed to collect pertinentpatient and surgical data, such as ages at implantation and revision,implant term of implantation, sex, body mass index (BMI), handdominance, reasons for index and revision surgery, and presence orabsence of infection. Operative reports were also reviewed todetermine intraoperative observations made by the surgeon.

Radiographic analysis

Anteroposterior and lateral radiographs from the pre-revisionprocedure were evaluated for implant alignment, grade of scap-ular notching (according to the method of Sirveaux54), humeralradiolucent lines (according to the method of Sanchez-Soteloet al50,51), cement extrusion from the humeral canal, metallosis(metallic debris visible on plain radiographs), fracture ornonunion, heterotopic ossification, bone deficiency, loosening,

instability, implant failure, and dissociation of modular compo-nents. Radiographic analysis was performed by a shoulder andelbow fellowship-trained orthopedic surgeon, blinded to patientidentification and not involved in the care of these patients.

Functional outcomes analysis

Through a separate Institutional Review Board–approved protocol,a trained, independent clinical research nurse collected outcomesdata. Outcomes data was evaluated from pre-index, immediate pre-revision, and post-revision time points when available. Post-revision data were available in 5 cases, which were collected at 1to 3 time points with an average follow-up of 37months. Functionaloutcomes were evaluated with the American Shoulder and ElbowSurgeons score, including the activities of daily living componentscore,41 and the subjective shoulder value.18 Patients were asked torate their pain on a visual analog scale of 0 (none) to 10(maximum).25 ROM measurements, including active externalrotation and active forward elevation, weremadewith a goniometer.

Statistical analysis

Study data were statistically analyzed (SPSS Statistics 20.0; IBM,Armonk, NY, USA) to examine the associations within and betweeneach study data set, including component damage, clinical review,radiographic analysis, and implant characteristics data (Table I).

Table I List of data elements captured

Damage mode Clinical data Radiographic evaluation Implant design characteristics Functional outcomes

Abrasion Age at implantation Bone fracture Model Active externalrotation (degrees)

Burnishing Age at revision Cement status/extrusion Manufacturer Active forwardelevation (degrees)

Fracture Body mass index Prosthetic instability Component materials ASES ADL scoreDelamination Sex Dissociation of PE liner Component size ASES scoreDishing Hand dominance Heterotopic ossification Component fixation Pain visual analog scaleEdge deformation Infection (organism) Humeral lucency (location) Component features

(e.g., modular humeralmetaphysis, centralglenosphere hole)

Shoulder subjective value

Embedding Intraoperatively observedbone deficiency

Implant alignment ormigration

Follow-up length

Pitting Intraoperatively observedmetallosis

Implant fracture

Scratching Intraoperatively observedsynovitis

Metallosis

Intraoperatively observedwear debris

Scapular notching (grade)

Previous arthroplasties atsurgical site

Reason for implantationReason for revisionSurgical sideTerm of implantation

ASES, American Shoulder and Elbow Surgeons; ADL, activities of daily living; PE, polyethylene.

1918 B.P. Wiater et al.

Statistical correlations were used to explore potential trendswithin the multifactorial data set, with the objective of cultivatingfuture studies. Each data set was correlated internally, using aPearson product moment correlation analysis (e.g., observeddamage modes on the glenosphere were compared with oneanother). To assess relationships between damage mode observa-tions and implant characteristics, patient factors, radiographicanalyses, and intraoperative observations, additional Pearsoncorrelation analyses were performed. Terms of implantation co-horts were compared by a Fisher exact test. Nineteen cases ofconfirmed or suspected infection were removed from any corre-lation analyses, including the following radiographic analysis dataelements: scapular notching, scapular notching grade, bone defi-ciency, humeral lucencies, and heterotopic ossification.

Patients’ pre-index, immediate pre-revision, and post-revisionfunctional outcomes scores and ROM were compared with dam-age mode data by Pearson product moment correlation tests.

For all analyses, significance was determined by a ¼ .05.Correlation coefficients (r) of 0.20 to 0.40, 0.40 to 0.60, 0.60 to0.80, and 0.80 to 1.00 were considered weak, moderate, strong,and very strong, respectively.16,43

Results

Clinical records review

The patient population included 21 women and 23 men,with average ages at initial RTSA implantation and revision

RTSA of 68 years (range, 45-83 years) and 69 years (range,46-86 years), respectively, and BMI of 31 (range, 18-52).Of the 50 devices collected, 26 were left shoulder devicesand 24 were right. Twenty-five RTSAs were implanted onthe dominant side, and hand dominance data were unavai-lable for 2 patients. Reasons for implantation and revisionwere multifactorial (Tables II and III). The average term ofimplantation for the full series was 20 months (range, 0.1-81.5 months), with 98% of revisions occurring within 5years of implantation (0 to �1 year, n ¼ 32; >1 to�5 years, n ¼ 17; >5 to �10 years, n ¼ 1). The averageterm of implantation of the 19 systems revised for infection(or treated as such) was 19 months (range, 0-70 months),whereas the average term of implantation of aseptic sys-tems was 21 months (range, 0-81 months).

A transition in reasons for revision was observed whendata were sorted by term of implantation. When term ofimplantation was <9 months (range, 0.1-8.7 months),reasons for revision included only infection or acuteinstability (n ¼ 21 of 21 total cases); however, when theterm of implantation was >9 months (range, 9.2-81.5 months), revisions included component failure, loos-ening, dissociation (i.e., separation of 2 components), andscapular notching (n ¼ 21 of 29 total cases included atleast 1 of these 4 reasons). In the group with a term ofimplantation >9 months, there were also cases of infection(n ¼ 7) as well as acute and chronic instability (n ¼ 8). In

Table II Reasons for implantation of reverse total shoulderarthroplasty)

Reason for implantation No. (%)

Unknown 24 (48)Cuff tear arthropathy 10 (20)Rotator cuff tear 6 (12)Failed hemiarthroplasty 5 (10)Degenerative joint disease 3 (6)Avascular necrosis 2 (4)Arthritis 2 (4)Dislocation 2 (4)Fracture nonunion 2 (4)Postinfection 2 (4)Acromiohumeral arthropathy 1 (2)Charcot shoulder 1 (2)Chondromalacia of glenoid 1 (2)Arthrosis 1 (2)Failed total shoulder arthroplasty 1 (2)Failed reverse total shoulder arthroplasty 1 (2)Failed rotator cuff repair 1 (2)

) Ten cases had multiple reasons for implantation, 16 cases had a

single reason for implantation, and 24 cases had an unknown reason

for implantation.

Table III Reasons for revision of reverse total shoulderarthroplasty)

Reason for revision No. (%)

Instability with confirmed dislocation 19 (38)Infection 16 (32)/19 (38)y

Implant loosening (any component) 13 (26)Implant dissociation 5 (10)Instability 3 (6)Hematoma 3 (6)Pain 2 (4)Abscess 2 (4)Scapular notching 2 (4)Component malpositioning 1 (2)Periprosthetic fracture 1 (2)Implant failure (catastrophic) 1 (2)Metal wear or synovitis 1 (2)

) Twenty-one cases had multiple reasons for revision and 29 cases

had a single reason for revision. All septic and aseptic cases

included.y Sixteen cases were confirmed preoperatively or intraoperatively,

whereas an additional 3 cases were confirmed in the postoperative

period. There were 19 cases of confirmed infection in the study

population.

Table IV Frequency of radiographically observed scapularnotching by grade at the pre-revision time point (n ¼ 29)

Grade No. (%)

1 4 (14)2 3 (10)3 3 (10)4 3 (10)

Cases with confirmed infections were excluded from the data set.

Reverse shoulder arthroplasty retrieval analysis 1919

the shoulders revised because of infection (n ¼ 19), theknown organisms included Propionibacterium (n ¼ 4),enterococcus (n ¼ 1), methicillin-resistant Staphylococcusaureus (n ¼ 1), gram-negative bacilli (n ¼ 2), methicillin-resistant Staphylococcus epidermidis (n ¼ 1), gram-positive cocci (n ¼ 1), and yeast (n ¼ 1). In 8 cases, the

patients were treated as infected despite negative intra-operative cultures. Intraoperative observations includedbone deficiencies of the glenoid only (n ¼ 7 total; 2 septic,5 aseptic), humerus only (n ¼ 3 total; 2 septic, 1 aseptic),and both glenoid and humerus (n ¼ 2 total; 2 septic) aswell as synovitis (n ¼ 5 total; 3 septic, 2 aseptic), PE weardebris (n ¼ 2 total; 2 aseptic), and metallic wear debris(n ¼ 4 total; 4 aseptic). This series included 6 cases ofimplant failure or dissociation, which included 1 linerdissociation, 2 dissociated glenospheres-baseplates, 2grossly loose baseplates, and 1 catastrophic in vivo fractureof a modular implant. Fracture occurred through the screwconnecting the metaphyseal and diaphyseal portions of thehumeral stem, and the distal portion of the humeral stemwas not included in the damage mode analysis because itwas not retrieved.

Radiographic analysis

Forty-one patients (n ¼ 47 cases; 94%) had pre-revisionradiographs available for review. Prosthetic instability wasobserved radiographically in 21 patients (45%) beforerevision. One patient exhibited metallosis on radiographicexamination, and 2 shoulders showed cement extrusionbefore revision. Greater tuberosity nonunion was noted in 2patients (4%). Glenoid tilt averaged 137� (range, 105-175).A change in humeral alignment was recorded in 4 cases(n ¼ 3 subsided, n ¼ 1 loose).

To eliminate infection as a confounding factor, scapularnotching and lucencies were assessed only in asepticpatients. Of the 29 aseptic cases, scapular notching waspresent in 13 shoulders (45%), and lucency surrounding thehumeral component was observed in 5 shoulders (17%)(Table IV). The average grade of scapular notching was1.7 � 1.5 (range, 0-4). In addition, bone deficiency of theproximal humerus was observed in 4 aseptic shoulders(9%).

Damage mode analysis

All PE liners exhibited some form of damage, and thedamage modes with the highest incidence of occurrencewere scratching and pitting damage, observed on 43 and 36PE liners, respectively. Damage was observed on only thearticular surface of 21 liners (40%) and on both the

Figure 2 Percentage of observed damage modes on retrieved RTSA systems, including glenosphere, glenoid baseplate, polyethylene(PE) liner, humeral metaphysis, and humeral stem. One humeral stem fractured in vivo, but it was not retrieved or included in the damagemode analysis (A), percentage of observed damage modes on retrieved RTSA components implanted for 0 to 9 months (B), or percentage ofobserved damage modes on retrieved RTSA components implanted >9 months (C). Significance between 2 terms of implantation cohorts:PE liner dishing* (P ¼ .002); PE liner edge deformation** (P ¼ .004).

1920 B.P. Wiater et al.

articular surface and rim of 29 liners (60%). Of the metalliccomponents, the glenosphere exhibited the most damage,with 93% (n ¼ 28) showing at least 1 damage mode, themost common of which was scratching (n ¼ 26) (Fig. 2, A).

Damage mode data were divided into 2 groups: terms ofimplantation <9 months vs. terms of implantation >9months (Fig. 2, B and C). There were significantly greaterincidences of dishing (P ¼ .002) and edge deformation(P ¼ .004) of the PE liner when the term of service of theimplant exceeded 9 months compared with devicesimplanted for <9 months.

Correlation of damage modes with clinical recordsdata

The presence of damage modes and radiographicallyobserved findings were compared against clinical data

obtained from medical record review. Pitting on the artic-ular surface of the PE humeral liner was negativelycorrelated with patient BMI (r ¼ �0.384; P ¼ .006) andweakly associated with female patients (r ¼ 0.284;P ¼ .046). Edge deformation damage to the liner wasmoderately correlated with implant dissociation(r ¼ 0.443; P ¼ .001). Delamination was positivelycorrelated with the RTSA system being implanted in thedominant limb of the patient (r ¼ 0.423; P ¼ .003).Scratching on the articular surface of the glenosphere waspositively associated with the patient’s BMI (r ¼ 0.368;P ¼ .045). Presence and severity of scapular notching weremoderately positively correlated with both term of im-plantation (r ¼ 0.481, P ¼ .008 and r ¼ 0.491, P ¼ .007,respectively) and implant failure or dissociation as a reasonfor revision (r ¼ 0.367, P ¼ .050 and r ¼ 0.530, P ¼ .003,respectively).

Table V Average functional outcomes score for 28 patients at 3 time points

Pre-index Pre-revision Post-revision

American Shoulder and Elbow Surgeons score 26.6 � 21.4 41.8 � 27.1 59.9 � 25.1Activities of daily living 7.7 � 5.5 12.5 � 7.8 13.3 � 7.9Pain 7.3 � 3.1 5.8 � 3.0 2.4 � 2.7Subjective shoulder value 17.9 � 23.0 48.0 � 30.8 56.3 � 28.9Active forward elevation 60 � 33.7 87.5 � 35.6 89.9 � 19.8Active external rotation 8.1 � 19.3 17.2 � 19.6 24.25 � 10.6

Reverse shoulder arthroplasty retrieval analysis 1921

Correlation of damage modes with implant designcharacteristics

Of the retrieved RTSA systems, 8 of the baseplates had aporous tantalum backing, whereas 9 of the baseplates werehydroxyapatite coated. Hydroxyapatite-coated baseplateswere positively associated with dissociation of the PE linerfrom the humeral component (r ¼ 0.613; P ¼ .001).Baseplates with a threaded central peg were moderatelypositively associated with PE delamination (r ¼ 0.533;P ¼ .003), whereas baseplates with a grooved central pegwere strongly positively associated with dissociation of thePE liner from the humeral component and weakly corre-lated with loosening as a reason for revision (r ¼ 0.642,P < .001 and r ¼ 0.386, P ¼ .043, respectively).

The presence of a hole in the articulating surface of theglenosphere (to facilitate attachment to the baseplate) waspositively correlated with dissociation of the PE liner(r ¼ 0.451; P ¼ .012). Glenosphere diameter was stronglynegatively correlated with the severity of scapular notching(r ¼ �0.600; P ¼ .030).

Correlation of damage modes with radiographicdata

Severity of scapular notching was positively correlated withdishing (r ¼ 0.496; P ¼ .006), delamination (r ¼ 0.384;P ¼ .040), and embedding of third-body particles(r ¼ 0.468; P ¼ .010) in the articular surface of the PEcomponent. In addition, a moderately positive relationshipwas found between retrieved liners with damage on boththe articular and rim surfaces and scapular notching(r ¼ 0.455; P ¼ .013). A negative correlation was observedbetween the severity of scapular notching and burnishing ofthe articular surface of the glenosphere component(r ¼ �0.675; P ¼ .016).

A negative relationship was found between radiograph-ically observed glenohumeral joint instability and the PEdamage modes of delamination (r ¼ �0.344; P ¼ .018),dishing (r ¼ �0.328; P ¼ .024), pitting (r ¼ �0.350;P ¼ .016), and edge deformation (r ¼ �0.330; P ¼ .024).This decreased incidence of damage on the PE componentin patients with instability may be due to the significantlydecreased implant term of service in patients with

instability (r ¼ �0.335; P ¼ .021). Whereas patients withinstability were less likely to exhibit damage on the PEliners, they demonstrated an increased incidence of abra-sion on the articular surface of the glenosphere (r ¼ 0.503;P ¼ .006) and burnishing at the glenosphere-baseplateinterface (r ¼ 0.630; P ¼ .003). There were no significantcorrelations found between implant alignment (pre-revisionglenoid tilt) and damage modes on any components.

Correlation of damage modes with functionaloutcomes

Pre-index (n ¼ 27) and immediately pre-revision (n ¼ 17)outcomes data were available for 28 patients who under-went a late revision. Eleven patients did not have pre-revision outcomes data available as these patients presentedto either the emergency department or the clinic with aproblem necessitating immediate revision (e.g., obviousperiprosthetic infection). Post-revision data were analyzedfor a smaller cohort of these patients with minimum 1-yearpost-revision follow-up (i.e., at least 1 year after retrievedimplant was removed or revised; n ¼ 12). There were nosignificant correlations with damage modes and pre-index,pre-revision, or post-revision outcomes scores. Averagescores at each time point are listed in Table V.

Discussion

Although RTSA has proved to be effective in managementof complex shoulder conditions, the complication rateremains high.9,14,19,28,29,45,48,58,60 The goal of this studywas to gain a comprehensive understanding of the rela-tionship between in vivo implant damage, clinical compli-cations, and functional outcomes. We found severalsignificant correlations between implant damage modes andradiographic data, implant design characteristics, patientdemographic data, and clinical outcomes, using the largestreported series of retrieved RTSA implants to date.

Few prior studies have examined implant damagemodes in RTSA. In 2010, Nam et al,43 in a 14-deviceretrieval series, first characterized in vivo damage modesof RTSA and focused primarily on the PE humeral liner.They observed scratching, abrasion, embedding, and

1922 B.P. Wiater et al.

pitting damage on the surface of the PE components andreported an increased frequency and severity of wear anddeformation in the inferior quadrant of the humeral liner,attributed to impingement of the humeral component onthe lateral aspect of the scapula. In another retrieval study,Day et al11 observed rim damage on all of the 7 retrievedRTSA systems from their case series but little or noarticular surface damage. In addition, they demonstrateddamage arising from unintended contact between the hu-meral components and the inferior baseplate screws, whichresulted in the production of both metallic and PE weardebris.

Similar to the study of Nam et al,43 our analysis ofretrieved RTSA systems also showed high rates ofscratching and abrasion damage to the retrieved PE linersas well as evidence of impingement and edge deformationon 48% and 26% of PE liners, respectively. In contrast tothe study of Day et al,11 our analysis showed that 21 liners(42%) exhibited damage to the articular surface withoutevidence of rim damage, whereas 29 liners (58%) demon-strated damage to both the articular surface and rim. Thehighest incidences of damage modes observed on thearticular surface of the PE were scratching (86%), pitting(72%), and burnishing (52%). This difference may be dueto the use of differing analysis techniques or the differencein the term of service among the cohorts. The minimumterm of service in the study by Day et al was 1.3 years, incontrast to our study, in which the majority of implantswere removed before 1 year.

Whereas the glenohumeral joint is not subjected to thehigh biomechanical loads in the hip or knee, there is stillobservation of significant damage to the articulating sur-face of both the PE liner and the metallic glenosphere,which may indicate the need to investigate alternativebearing surfaces. Other studies have described the potentialfor PE wear in RTSA systems in well-functioning systems,with the absence of rim loading. Finite element analysesperformed by Terrier et al56 described the potential forsignificantly increased wear in RTSA systems comparedwith anatomic total shoulder arthroplasty in the absence ofrim damage. A recent in vitro wear simulation that usedalternating movements of glenohumeral flexion andabduction without rim loading also demonstrated high wearrates over 5 million loading cycles.57 PE wear in RTSAsystems may have both mechanical and biologic conse-quences, including wear-through of the PE liner, as hasbeen shown in total shoulder arthroplasty systems,46 aswell as an inflammatory or immune reaction to weardebris.20

Scapular notching, a frequent radiographic finding inRTSAwith a reported incidence as high as 92%,13,42 is theresult of mechanical impingement between the medial rimof the humerosocket and the lateral border of the scapuladuring adduction, which has been associated with factorsrelated to implant design, surgical technique, and patientcharacteristics.2,30,32,36,53 Despite the suspected causal

relationship between mechanical impingement, PE wear,and osteolysis with notch progression, as proposed byNyffeler et al,46 clinical studies have failed to convinc-ingly correlate scapular notching, especially lower gradenotching (Sirveaux54 grades 1 and 2), with significant painor dramatic changes in functional outcomes30,36,65; how-ever, in advanced cases of notching, component looseninghas been reported.53 A positive correlation between theterm of implantation of the RTSA device and the severityof scapular notching was found in our study, suggesting aprogressive phenomenon similar to that reported by Lev-igne et al35 in their series of 337 shoulders. In our study,PE liners demonstrating both articular surface and rimdamage had a higher incidence of radiographicallyobserved scapular notching than those with articular sur-face damage alone. This may be attributed to the fact thatboth PE liner rim damage and scapular notching areassociated with impingement during ROM. Damagemodes significantly correlated with severity of scapularnotching were third-body embedding, dishing, anddelamination damage to the PE liners. In devices withterms of implantation >9 months and when scapularnotching, component failure, loosening, and dissociationwere reasons for revision, there were significantly greaterincidences of dishing and edge deformation damage of thePE liners. Burnishing damage of the metallic glenosphereand glenosphere diameter were inversely related to theseverity of scapular notching. Increasing the glenospherediameter leads to lateralization of the center of rotation ofthe shoulder, which has been shown to improve theimpingement-free ROM.2

In this series, no significant correlations were foundbetween damage modes and pre-index procedure, imme-diate pre-revision or post-revision functional scores, andROM. Previous studies have shown that wear debrisremaining in the joint has potential deleterious biologiceffects.20 Recent data suggest that revision total hiparthroplasty performed because of excessive componentwear may be associated with worse outcomes anddecreased implant survivorship.27 Future series with morepatients and longer follow-up can elucidate whether higherdegrees of wear negatively affect outcomes after revision.

This investigation has several limitations. Because ofthe retrieval-based nature of this study, there were nowell-functioning implants to serve as a control to validatethe role of implant damage in revision rates. We wereunable to grade glenoid components through surfacemapping, as previously described in the literature,because symmetric PE liner and glenosphere designs didnot allow accurate determination of the orientation of theimplant as it existed in vivo. This data set includes aheterogeneous population of implants, which weredistilled into implant characteristics that were entered as adata element during statistical analyses. Statistical cor-relations did not take variable interactions or confoundingeffects into account, which excluded the possibility of

Reverse shoulder arthroplasty retrieval analysis 1923

results regarding multifactorial relationships betweendata elements. Likewise, the correlations do not provideevidence of causation, only the association between thevariables listed.

Conclusion

This series is the largest and most comprehensiveRTSA retrieval study to date and the first in the liter-ature to correlate damage modes with validated func-tional outcome measures. The multimodal analysisemployed in this study demonstrated significant corre-lations between several different implant damagemodes of the PE liner, metallic glenosphere, baseplate,humeral metaphysis, and humeral stem componentswith radiographic and clinical data. Accelerated pros-thetic wear or damage may lead to early device failureor need for revision, and the results of this study mayaid in determining patients and prostheses at risk forclinical failure and may contribute to future implantdesign.

Acknowledgment

This manuscript is dedicated in memory of Harry N.Herkowitz, MD. A generous gift provided by Byron andDorothy Gerson to establish the Byron and DorothyGerson Implant Analysis Fund has supported thisresearch. The Implant Retrieval Program at BeaumontHospital, Royal Oak, is partially funded by the StrykerCorporation.

Disclaimer

J. Michael Wiater is a paid consultant of Zimmer Inc.and DePuy-Synthes and has received research supportfrom Zimmer, Tornier, and DePuy-Synthes.

Kevin C. Baker is a paid consultant of Globus Med-ical and receives research support as a principal inves-tigator from Zimmer Inc., Globus Medical, and Arthrex,Inc.

An immediate family member of Erin A. Baker is apaid consultant of Globus Medical and receives researchsupport as a principal investigator from Zimmer Inc.,Globus Medical, and Arthrex, Inc.

J. Michael Wiater and Brett P. Wiater are brothers.All the other authors, their immediate families, and

any research foundation with which they are affiliatedhave not received any financial payments or otherbenefits from any commercial entity related to the sub-ject of this article.

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