Arthroplasty Today Cementation of a monoblock dual mobility bearing in a newly-implanted porous revision acetabular component in patients undergoing revision total hip arthroplasty --Manuscript Draft-- Manuscript Number: ARTD-D-19-00024R2 Article Type: Original Research Keywords: Revision hip arthroplasty; dislocation; instability; cemented dual mobility; fully porous shell Corresponding Author: Ran Schwarzkopf, MD, MSc NYU Hospital for Joint Diseases, NYU Langone Medical Center New Rochelle, NY United States First Author: Jonathan A Gabor, BS Order of Authors: Jonathan A Gabor, BS James E Feng, MD Shashank Gupta, BE Tyler E Calkins, BS Craig J Della Valle, MD Jonathan Vigdorchik, MD Ran Schwarzkopf, MD MSc Abstract: Background: The most common indications for revision total hip arthroplasty (rTHA) are instability/dislocation and mechanical loosening. Efforts to address this have included the use of dual mobility (DM) articulations. The aim of this study is to report on the use of cemented DM cups in complex acetabular rTHA cases with a high risk of recurrent instability. Methods: A multicenter, retrospective study was conducted. Patients who received a novel acetabular construct consisting of a monoblock DM cup cemented into a fully porous metal shell were included. Outcomes data included 90-day complications and readmissions, revision for any reason, and Harris Hip Scores. Results: Thirty-eight hips in 38 patients were included for this study. At a median follow-up of 215.5 days (range, 6–783 days), the Harris Hip Score improved from a mean of 50 ± 12.2 to 78 ± 11.2 (p<0.001). One (2.6%) patient experienced a dislocation on postoperative day 1, and was closed reduced with no further complications. There was one (2.6%) reoperation for periprosthetic joint infection treated with a two-stage exchange. Conclusions: In this complex series of patients, cementation of a monoblock DM cup into a newly-implanted fully porous revision shell reliably provided solid fixation with a low risk of dislocation at short-term follow-up. While longer term follow-up is needed, utilization of this novel construct should be considered in patients at high risk for instability. Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation
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Arthroplasty Today
Cementation of a monoblock dual mobility bearing in a newly-implanted porousrevision acetabular component in patients undergoing revision total hip arthroplasty
Corresponding Author: Ran Schwarzkopf, MD, MScNYU Hospital for Joint Diseases, NYU Langone Medical CenterNew Rochelle, NY United States
First Author: Jonathan A Gabor, BS
Order of Authors: Jonathan A Gabor, BS
James E Feng, MD
Shashank Gupta, BE
Tyler E Calkins, BS
Craig J Della Valle, MD
Jonathan Vigdorchik, MD
Ran Schwarzkopf, MD MSc
Abstract: Background: The most common indications for revision total hip arthroplasty (rTHA)are instability/dislocation and mechanical loosening. Efforts to address this haveincluded the use of dual mobility (DM) articulations. The aim of this study is to report onthe use of cemented DM cups in complex acetabular rTHA cases with a high risk ofrecurrent instability.
Methods: A multicenter, retrospective study was conducted. Patients who received anovel acetabular construct consisting of a monoblock DM cup cemented into a fullyporous metal shell were included. Outcomes data included 90-day complications andreadmissions, revision for any reason, and Harris Hip Scores.
Results: Thirty-eight hips in 38 patients were included for this study. At a medianfollow-up of 215.5 days (range, 6–783 days), the Harris Hip Score improved from amean of 50 ± 12.2 to 78 ± 11.2 (p<0.001). One (2.6%) patient experienced adislocation on postoperative day 1, and was closed reduced with no furthercomplications. There was one (2.6%) reoperation for periprosthetic joint infectiontreated with a two-stage exchange.
Conclusions: In this complex series of patients, cementation of a monoblock DM cupinto a newly-implanted fully porous revision shell reliably provided solid fixation with alow risk of dislocation at short-term follow-up. While longer term follow-up is needed,utilization of this novel construct should be considered in patients at high risk forinstability.
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February 25, 2019 Ran Schwarzkopf, MD
Associate Professor, Division of Adult Reconstructive Surgery
Revision total hip arthroplasty (rTHA) is a technically challenging surgery with a high 24
risk of complications. Currently, the most common indication for revision and re-revision THA 25
is instability/dislocation, which has been reported to range from 6.6% to as high as 28% of all 26
rTHA patients [1,2,11,3–10]. Management options include the use of large femoral heads, 27
constrained acetabular liners, and dual mobility (DM) articulations. Utilization of a larger 28
femoral head confers stability by increasing the head-to-neck ratio, range of motion (ROM) prior 29
to impingement, and head-jump distance [12]. However, the effects can become diminished with 30
acetabular defects that result in cup placements which deviate from the ideal hip center of 31
rotation [13]. Additionally, larger femoral heads have been associated with increased volumetric 32
wear even with the presence of highly cross-linked polyethylene liners [14]. Finally, because 33
these larger femoral heads may require the use of a thinner liner, there remains the potential for 34
polyethylene fracture and mechanical failure in some cases [15]. Meanwhile, constrained 35
acetabular liners are designed to lock the femoral head into the inner bearing surface, which 36
leads to higher forces on the acetabular cup. Consequently, constrained liners restrict ROM 37
causing prosthetic impingement that can lead to unacceptably high failure rates [16,17], 38
including early catastrophic failures in freshly implanted revision cups. To address some of these 39
shortcomings, DM bearings have been advocated. 40
DM articulations feature an unconstrained tripolar design with two mobile articulations. 41
The first articulation is between the prosthetic head and the inner surface of the polyethylene 42
outer head, and the second is between the outer surface of the polyethylene head and the 43
monoblock metal acetabular shell or metal acetabular liner. At the extremes of ROM, the stem 44
engages the edge of the polyethylene liner, causing it to articulate with the inner surface of the 45
3
metal acetabular shell. This design affords the patient a greater impingement-free ROM while 46
enlarging the effective size of the femoral head, conferring the mechanical advantages offered by 47
a larger femoral head jump distance. The current generation of DM implants have shown 48
remarkably low dislocation rates following primary THA and rTHA [18–26]. A recent meta-49
analysis by Levin et al. reported a short- to mid-term dislocation rate of 2.2% following rTHA 50
with the use of DM articulations [27]. Early concerns over excessive early wear due to the 51
additional bearing, aseptic loosening, and intra-prosthetic dislocation (IPD) have been largely 52
alleviated, with an aseptic survivorship rate of 97.7% and aseptic loosening and IPD rates at 53
0.3% and 0.7%, respectively [27]. 54
While biomechanical studies have validated the use of cementation of a DM cup into a 55
well-fixed metal acetabular shell as a viable alternative to a standard cemented polyethylene 56
liner, clinical reports evaluating outcomes of this construct in patients at high risk for recurrent 57
instability and dislocation have been equivocal [22,28–31]. The goal of this study is to analyze 58
the short-term outcomes, and rates of complications, reoperations, and re-revisions of a DM cup 59
meant for cementation cemented into a newly-implanted highly porous revision acetabular shell. 60
Our hypothesis is that this reconstruction construct would decrease the incidence of instability 61
after complex rTHA, without an increase in early construct failure. 62
63
Methods 64
A multi-institutional retrospective study was conducted using clinical data of patients 65
who received a novel rTHA construct that utilized a monoblock DM cup that is intended for 66
insertion with cement (cemented POLARCUP◊, Smith & Nephew, Memphis, TN), cemented into 67
a fully porous revision acetabular component (REDAPT◊, Smith & Nephew, Memphis, TN). 68
4
Two institutions contributed the data of 34 patients and 4 patients, respectively, to this study. The 69
study procedures were reviewed and approved by the university Institutional Review Board 70
(Study #i17-00535). 71
Data Collection 72
All institutions participating in this study performed a retrospective chart review of a 73
consecutive cohort of patients who underwent rTHA surgery and received the rTHA construct. 74
Baseline demographics (age, gender, race, and insurance type), preoperative status (body mass 75
index [BMI], and Charlson Comorbidity Index [CCI], laterality, radiographic Paprosky 76
Classification of the acetabular defects, number of previous revision surgeries, time interval from 77
last hip arthroplasty, surgical indication, surgical factors (extended trochanteric osteotomy [ETO] 78
performed, allograft use, number of screws used, concomitant acetabular cage usage, 79
intraoperative complications), and quality outcomes (length of stay, inpatient complications, 30- 80
and 90-day readmissions, all-cause re-revisions) were collected. 81
Patients 82
Thirty-eight patients treated by seven fellowship-trained arthroplasty surgeons between 83
May 2016 and June 2018 were included. All patients who received the POLARCUP◊ cemented 84
into a REDAPT◊ acetabular component over this time period were included in this study. No 85
patients were excluded. The decision was made to use this construct if it was felt by the 86
operating surgeon that the patient would be at a high risk of instability following a complex 87
acetabular reconstruction in which a fully porous acetabular shell was used. Risk was defined by 88
the degree of acetabular bone loss (as defined by the Paprosky classification), as well as the 89
patient history and indication for revision [32]. 90
5
The mean patient age was 62.7 ± 9.7 years. There were 18 males (47.4%) and 20 females 91
(52.6%) with a mean body mass index of 29.7 ± 7.0 kg/m2. Patients underwent a mean of 1.6 92
prior reconstructive hip surgeries (range, 1–4), including the primary THA. The mean amount of 93
time between the primary THA and the revision surgery of interest was 12.7 ± 9.2 years. 94
Preoperatively, the majority of patients ambulated with either a rolling walker (13, 34.2%) or 95
cane (16, 42.1%). According to the Paprosky Classification, 4 (10.5%) patients were Type IIA, 96
10 (26.3%) patients were Type IIB, 6 (15.8%) patients were Type IIC, 9 (23.7%) patients were 97
Type IIIA, and 9 (23.7%) patients were Type IIIB [32]. Additional demographics can be found in 98
Table 1. Specific indications for rTHA included 23 (60.5%) patients for aseptic loosening of the 99
acetabulum, 9 (23.7%) for periprosthetic joint infection, 4 (10.5%) for instability, and 2 (5.3%) 100
for malorientation of the acetabular cup and soft tissue impingement. (Table 2). 101
Surgical Technique 102
Twenty-seven (71.1%) cases were performed using a posterior approach and 11 cases 103
(28.9%) were performed using a modified direct lateral approach. Femoral stems were revised in 104
addition to the acetabular components in 20 (52.6%) cases. Extended trochanteric osteotomies 105
were performed to extract well-fixed femoral components in seven (20%) cases. Fresh frozen 106
cancellous allograft was used to fill contained defects in 18 (47.4%) cases, and concomitant 107
acetabular cages were used in 11 (28.9%) cases. Mean surgical time was 208.6 ± 62.9 minutes. 108
The revision shell is unique, offering a combination of locking and non-locking 109
cancellous bone screws. Following final cup insertion, the DM monoblock acetabular cup was 110
then cemented in place, when the cement had reached a doughy consistency (Figure 1). The 111
metal acetabular cup intended for cementation is manufactured from stainless steel. Its backside 112
design features anti-rotation fins as well as 0.35 mm equatorial teeth that further enhance 113
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primary stability. The monoblock dual mobility shell was a minimum of 11 mm smaller in outer 114
diameter than the revision shell utilized. The median porous metal shell size was 60 mm (range, 115
54–76 mm), the median polyethylene outer head size was 47 mm (range, 43–63 mm), and the 116
inner femoral head sizes were 28 mm (in cups ≥47 mm) and 22 mm (43 mm and 45 mm cups). 117
118
Results 119
Thirty-eight patients were available for both clinical and radiographic evaluation at a 120
median follow-up of 215.5 days (range, 6–783 days). There were no intraoperative 121
complications. There were seven (18.4%) inpatient complications. Two (5.3%) were surgical 122
complications and included an anterior hip dislocation on postoperative day 1 in one patient and 123
proximal DVT in another patient. The dislocation was spontaneous and not precipitated by any 124
trauma/falls, and a closed reduction was performed with no complications. At latest follow-up, 125
the patient was doing well with 5/5 abductor strength and had no hip instability since the 126
dislocation. The DVT was treated with heparin and IVC filter placement; heparin was stopped 127
and the patient resumed aspirin therapy for prophylaxis prior to discharge, with no further 128
complications. Five (13.2%) were medical complications and included supraventricular 129
tachycardia, atrial fibrillation, urinary retention, UTI, and myocardial infarction in one patient 130
each. Four (11.8%) patients had postoperative anemia treated with blood transfusion. Additional 131
surgical information can be found in Table 3. 132
The majority of patients were discharged home with health services (26, 68.4%), 133
followed by skilled nursing facilities (9, 23.7%), acute rehabilitation facilities (1, 2.6%), and 134
home with self-care (2, 5.3%). Postoperatively, four (10.5%) patients experienced complications 135
– three (7.9%) within 30 days and one (2.6%) within 90 days following discharge. One patient 136
7
experienced a non-displaced fracture of the greater trochanter, which was treated non-137
operatively. Two patients experienced infection – one was treated with an irrigation and 138
debridement due to continued wound drainage, with no further returns to the operating room; the 139
other underwent a two-stage exchange for a periprosthetic joint infection 10 months after the 140
index revision surgery. One patient was admitted for dehydration and acute renal failure; this 141
patient expired due to cardiac complications and so had an orthopedic follow-up time of only six 142
days. 143
The mean Harris Hip Score at last follow-up was 78 (range, 49–95), significantly 144
improved from the mean preoperative score of 50 (range, 35–78) (p < 0.001). At latest 145
radiographic follow-up, there were no dissociations at the DM-cement interface. All outcome 146
information is summarized in Table 4. 147
148
Discussion 149
Recurrent instability is the most common cause of failure requiring repeat revision 150
following rTHA. A number of surgical treatment modalities have been proposed to decrease the 151
incidence of hip instability in high-risk patients, including the use of dual mobility bearings [16]. 152
The unconstrained tripolar design of the DM implant enhances stability by effectively increasing 153
the femoral head size while increasing the ROM to impingement and jump distance needed for 154
dislocation. The long-term survivorship as well as rates of dislocation following rTHA with DM 155
have been excellent [27,33]. However, a fraction of high-risk patients will continue to experience 156
dislocation despite these enhanced implant designs. In these patients, novel constructs may be of 157
unique benefit. In this report, we describe a low risk of dislocation amongst a complex cohort of 158
patients where a novel construct was utilized, including the use of a monoblock DM cup 159
8
specifically intended for insertion with cement, cemented into a cementless revision acetabular 160
component. While biomechanical studies have suggested that this type of construct is sound and, 161
in fact, stronger than cemented polyethylene liners which have been commonly used in clinical 162
practice, there has been little clinical data to support the use of this construct [28,34,35]. 163
In many rTHA cases, a well-fixed acetabular shell can be retained; however, all of the 164
cases included in the present study required an acetabular shell revision. Due to the extent of the 165
bone loss and bony defects, it was felt by the operating surgeons that a fully porous revision shell 166
rather than a modular acetabular cup was needed to achieve adequate fixation and reconstruction 167
of the acetabulum. The advantage of using a newly-implanted fully porous shell, aside from the 168
location and number of screw holes and shell porosity, is having the ability to place the 169
acetabular shell in the best reconstruction position possible. However, as this may not be the best 170
position for hip stability, a liner is cemented within the shell in a better “safe-zone” position. The 171
use of cement is necessary as these shells have no locking mechanism. In order to impart greater 172
stability to the construct, the decision was made to use a DM shell rather than a polyethylene 173
liner in these cases. An example of this is shown in Figure 3; the revision shell is placed in over 174
55° of abduction and in a more neutral version in order to achieve good construct fixation, and 175
the DM cup is placed in a more stable fixation around 40° of abduction and 15° of anteversion. 176
To our knowledge, this is the largest US study to date reporting on the clinical outcomes 177
of a cemented DM cup in a newly-implanted fully porous acetabular shell. Our results show that 178
cementation of a DM cup designed for cemented use into a newly-implanted highly porous, 179
revision acetabular shell can lead to enhanced hip stability in the early postoperative period with 180
a low-risk of early dislocation or mechanical failure. One (2.6%) patient experienced a 181
spontaneous dislocation on postoperative day 1, which was closed reduced later that day with no 182
9
further recurrence of instability. In our cohort, there were no IPD or failures at the DM-cement 183
interface, nor were there any instances of re-revision for early aseptic loosening. Only one 184
(2.6%) patient required a re-revision with removal of hardware, which was due to a 185
periprosthetic joint infection. However, at the time of explant, all the components were noted to 186
be well-fixed. Evidence of functional improvements in this cohort was demonstrated by 187
significant improvements in hip range of motion, as well as a significant improvement in Harris 188
Hip Scores. 189
Studies on the clinical performance of cemented DM cups have been generally limited, 190
but have been more common in Europe where the use of DM is more widespread. Hamadouche 191
et al. reviewed 47 patients treated with cemented DM cups for recurrent dislocation following 192
primary or revision THA [36]. After a minimum follow-up of 2 years, two patients (4.3%) had 193
further episodes of dislocation, which occurred between the polyethylene outer head and the 194
metal shell in one hip, and the femoral inner head and the outer polyethylene head (IPD) in the 195
other. The authors suspected that improper placement of the acetabular shell in excessive 196
abduction was responsible for the former, and wear and fatigue deformation due to excessive 197
activity was responsible for the latter. A later follow-up study reporting on the 5–13 year results 198
of this cohort was performed [37]. Three patients (5.6%) experienced recurrent dislocation, two 199
of which were intra-prosthetic. The cumulative survival rate at ten years was 86.1% using re-200
dislocation as the end-point, and the authors concluded that DM represents the best 201
reconstructive option for the treatment of recurrent hip instability after THA. Schneider et al. 202
explored the outcomes of 96 rTHAs with cemented DM constructs intended for cement use 203
(Novae Stick, SERF, Décines, France) and acetabular cages. Despite the majority of patients 204
having severe acetabular bone loss, they found a high dislocation rate of 10.4% and an aseptic 205
10
survivorship rate of 99.3% at 8 years [29]. Haen et al. found that when there is a moderate 206
deficiency in bone stock, rates of mechanical loosening are comparable regardless of whether an 207
acetabular reinforcement device is used in conjunction with a cemented DM cup [38]. 208
Plummer and colleagues were the first US group to report on the clinical performance of 209
a construct that was similar to the one used in this series [22]. Nine of the 36 revised hips in their 210
series received DM components cemented into well-fixed or new acetabular shells. Of these, two 211
required re-revision due to failure at the DM-cement interface within the first 90 postoperative 212
days. Importantly, these cases utilized a technique that involved roughening the backside of a 213
modular DM liner (modular dual mobility, Stryker, Mahwah, NJ) with a high-speed burr and 214
then cementing it into a shell [22]. The authors, currently, strongly recommend against the use of 215
this technique. At a minimum follow-up of 2 years, no failures had been observed with the other 216
cemented DM cups in their study. Chalmers et al. reviewed the results of 18 patients that had 217
undergone rTHA with a monoblock DM construct cemented into a well-fixed or new acetabular 218
component [30]. At mean follow-up of three years, three patients (17%) experienced 219
postoperative dislocations, and no cups failed at the DM-cement interface. The dislocations 220
occurred at a mean of four months postoperatively. Two were treated with open reduction and 221
one with revision to a cemented constrained liner. Evangelista et al. assessed the outcomes of 18 222
patients who underwent cementation of a DM monoblock cup, designed for cementation, into a 223
well-fixed or new revision acetabular cup [31]. At a mean follow-up of 36 months, there were no 224
cases of hip dislocation nor any dissociations at the DM-cement interface. 225
Though DM implants may present a promising solution for preventing hip instability, a 226
potential disadvantage is their increased cost relative to traditional THA implants [39–41]. 227
However, given the economic burden posed by rTHA procedures, which can exceed $50,000 in 228
11
hospital charges alone, the use of DM implants may actually be more cost-effective from a 229
societal perspective, especially in complex rTHA with an increased risk of instability [1]. 230
Our study has several limitations that must be taken into consideration. Only one type of 231
fully porous acetabular shell and DM cup was used in this study, and therefore the results may 232
not be generalizable to other designs and constructs. The cohort of patients in this study was 233
relatively small and the follow-up time was limited. Despite this, the incidence rates of 234
dislocation in both primary and revision THA are highest in the immediate postoperative period 235
and remain elevated throughout the first three postoperative months, which is adequately covered 236
in the present study [42]. Still, further follow-up will be required to ensure long-term durability 237
of this construct. Future studies may be needed to directly compare outcomes between cemented 238
DM cups, constrained liners, and large femoral heads utilized in complex THA revision cases. 239
240
Conclusion 241
Cementation of a DM monoblock cup into a newly-implanted fully porous revision shell 242
was associated with a low risk of surgical complications and re-revision at short-term follow-up. 243
This technique allows for placement of the porous cup such that bony purchase is maximized, 244
and allows for improved placement of the DM cup with regards to abduction, and anteversion, 245
and the hip’s natural center of rotation. Considerations for this construct should be made in 246
patients at high risk of dislocation in order to provide durable fixation and improved stability. 247
248
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377
Table 1: Baseline Patient Demographics (n = 38)
Age (years) 62.7 ± 9.7 Gender Male 18 (47.4%) Female 20 (52.6%) BMI 29.7 ± 7.0 Race African American (Black) 8 (21.1%) Asian 1 (2.6%) White 22 (57.9%) Other 5 (13.2%) ASA 1 0 (0.0%) 2 16 (42.1%) 3 20 (52.6%) 4 2 (5.3%) Charlson Comorbidity Index 2.8 ± 1.6 Smoking Status Current Smoker 5 (13.2%) Former Smoker 17 (44.7%) Never Smoker 16 (42.1%) Marital Status Married 11 (28.9%) Divorced 3 (7.9%) Single 15 (39.5%) Other 9 (23.7%) Insurance Type Commercial 12 (31.6%) Medicare 16 (42.1%) Medicaid 8 (21.1%) Workers Comp 2 (5.3%) Laterality Left 17 (44.7%) Right 21 (55.3%) Previous Reconstructive Surgeries 1.6 ± 0.8 Paprosky Classification IIA 4 (10.5%) IIB 10 (26.3%) IIC 6 (15.8%) IIIA 9 (23.7%) IIIB 9 (23.7%) Preoperative Ambulatory Status Rolling Walker 13 (34.2%) Cane 16 (42.1%) Crutches 2 (5.3%) Unassisted 5 (13.2%) Unknown 2 (5.3%) Mean Time from Primary to Revision (years) 12.7 ± 9.2
Table 1
Table 2: Indication for revision THA of interest (n = 38)
Aseptic Loosening 23 (60.5%)
Septic Failure 9 (23.7%)
Instability 4 (10.5%)
Malorientation of the acetabular cup 2 (5.3%)
Table 2
Table 3: Surgical Information (n = 38) Anesthesia Type
General 30 (68.4%) Regional (Spinal/Epidural) 8 (21.1%) Surgeon
Surgeon 1 1 (2.6%) Surgeon 2 1 (2.6%) Surgeon 3 11 (28.9%) Surgeon 4 14 (36.8%) Surgeon 5 2 (5.3%) Surgeon 6 5 (13.2%) Surgical Time (minutes) 208.6 ± 62.9 Median Porous Metal Shell Size (mm) 62 (54 – 76) Median Number of Screws 5 (3 – 14) Median Dual Mobility Outer Cup Size (mm)
48 (43 – 63)
Median Femoral Head Size (mm) 28 (22 – 28)
Femoral stem revised 20 (52.6%) Bone Allograft Used
Surgical 2 (5.3%) Patient 13 - DVT Patient 37 - Anterior hip dislocation on POD1
Postoperative Anemia Requiring Blood Transfusion
4 (10.5%)
Length of Stay (days) 4.7 ± 2.9
Table 3
Table IV. Outcomes (n = 38) Median follow-up (days) 215.5 (range, 6–783) Discharge Disposition Home or Self-Care 2 (5.3%)
Home with Health Services
26 (68.4%)
Skilled Nursing Facility 9 (23.7%)
Acute Rehabilitation Facility
1 (2.6%)
Inpatient Complications 7 (18.4%)
30-Day Complications 3 (7.9%) Patient 11 - Hip pain, x-ray showed avulsion fracture of the greater trochanter Patient 32* - Hip pain/drainage; treated with irrigation and debridement Patient 36* - Dehydration and acute renal failure
Readmissions 2 (5.3%)
90-Day Complications 1 (2.6%) Patient 24* - Irrigation and debridement of hip wound
Readmissions 1 (2.6%)
Re-Revisions 1 (2.6%)
Patient 28 - Removal of hardware Deep Infection 1 (2.6%)
Dislocation 0 (0.0%)
Aseptic Loosening 0 (0.0%)
Ambulatory Status at Latest Follow-Up Rolling Walker 11 (28.9%) Cane 13 (34.2%) Crutches 1 (2.6%) Unassisted 12 (31.6%) Unknown 1 (2.6%)
*Resulted in hospital readmission
Table 4
Figure 1: (A) POLARCUP
◊ intended for cementation prior to implantation. (B) REDAPT
◊ fully
porous shell impacted in place following acetabular preparation. (C) Trial placement of DM
monoblock cup. (D) DM cup cemented into revision acetabular shell.
Figure 1
Figure 2: Pre-/postoperative pelvic radiographs.
Figure 2
Figure 3: Representative example of a fully porous acetabular shell implanted in a position for
maximum bony coverage but less than ideal for hip stability (abduction >55°, anteversion <10°)
with the DM cup cemented within in a better position for hip stability.
Figure 3
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Encouraging Short Term Outcomes with a Novel Acetabular Reconstruction Construct
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Response to reviewers’ comments 4/15/2019
We would like to thank the reviewers for their time and effort helping us improve this work and prepare
it for publication.
Reviewer #1: The authors addressed my comments and concerns appropriately.
Response:
Thank you
Reviewer #2: I appreciate the effort the authors have put forth to make this a better paper, but still have some
suggestions/questions:
1. Line 82: Were all cases performed by one surgeon or a number of different surgeons?
Response: Cases were performed by seven surgeons. This has been clarified in the text below.
Lines 82-83: Thirty-eight patients treated by seven fellowship-trained arthroplasty surgeons between
May 2016 and June 2018 were included.
2. Lines 134-141: Which of the four complications happened within 30 days, and which one happened within
90 days following discharge?
Response: Although this distinction was not made in the text, this information can be found in Table
4. The corresponding section of Table 4 has been copied below.
30-day complications
Patient 11 - Hip pain, x-ray
showed avulsion fracture of the
greater trochanter
Patient 32* - Hip pain/drainage;
treated with irrigation and
debridement
Patient 36* - Dehydration and
acute renal failure
90-day complications Patient 24* - Irrigation and
debridement of hip wound
3. Lines 171-172: Why do the authors think the stability obtained in their study could not have been obtained
with uncemented, modular DM cups? The authors should compare the survivorship/outcomes or rates of
dislocation of uncemented DM cups in rTHA reported in literature to their study.
Detailed Response to Reviewers
Response: We do not think that the hip stability/risk of dislocation could not have been achieved
with the use of uncemented DM cups; we agree completely with the reviewer that any DM cup
placed in the proper position would achieve the same hip stability. The surgeons that performed
these cases thought they need to use a fully porous acetabular cup in order to achieve proper implant
fixation and decrease the risk of construct failure of fixation (due to increased screw fixation/hole
options and fixation stability achieved with fully porous cups). In these cases, due to the decision to
use these fully porous cups, the surgeons are forced to cement a liner, as there is no locking
mechanism; that’s why a cemented DM was chosen and not an uncemented one. There is no claim
that cemented DM perform better than uncemented DM cups, placed in the same position, in hip
stability/dislocation.
Lines 162-174: In many rTHA cases, a well-fixed acetabular shell can be retained or a modular
acetabular cup used; however, all of the cases included in the present study required an acetabular
shell revision. Due to the extent of the bone loss and bony defects, it was felt by the operating
surgeons that a fully porous revision shell rather than a modular acetabular cup was needed to
achieve adequate fixation and reconstruction of the acetabulum. The advantage of using a newly-
implanted fully porous shell, aside from the location and number of screw holes and shell porosity, is
having the ability to place the acetabular shell in the best reconstruction position possible. However,
as this may not be the best position for hip stability, a liner is cemented within the shell in a better
“safe-zone” position. The use of cement is necessary as these shells have no locking mechanism. In
order to impart greater hip stability to the construct, the decision was made to use a DM shell rather
than a polyethylene liner in these cases. An example of this is shown in Figure 3; the revision shell is
placed in over 55° of abduction and in a more neutral version in order to achieve good construct
fixation, and the DM cup is placed in a more stable fixation around 40° of abduction and 15° of
anteversion.
4. Lines 165-168: Is this more of a technique in the hands of the authors? If so, it should be stated as such.
Certainly, joint reconstruction surgeons have done revision cases before this study placing the acetabular
components in the best position (with and without adjuncts), and still obtaining good stability and fixation
without using cemented DM cups. A short term follow up study of 6-783 days might not be long enough to
see the effects/failures of potentially implanting malpositioned cups for excellent bony coverage and fixation
and correcting for the malpositioning by using cemented DM cups.
Response: Many surgeons have used fully porous cups to achieve acetabular construct fixation since
the Zimmer TM revision shell was introduced to the market nearly 20 years ago. When using the TM
revision shell, and now the Smith & Nephew Redapt shell, the surgeon must cement a liner as neither
cup has a locking mechanism. Until recently, reports have only described the use of these shells in
combination with regular cemented polyethylene liners. We report here the first series of cementing
a DM cup instead of a polyethylene liner, thus presenting a construct that benefits from a known
fixation technique (use of a fully porous cup) and the stability of a DM articulation.
5. Can the authors include the longest follow up representative x-rays of shell(s) implanted in less than ideal
position for maximum bony coverage.
Response: We have added a new figure with a revision cup placed in over 55° of abduction and in
neutral version in order to achieve good construct fixation and the DM cup is placed in a more stable
fixation around 40° of abduction and 15° of anteversion. The follow-up time for this case is
approximately 2.5 years.
6. Can this cemented DM cup be used with shells from other companies or stems from other companies? If
not, can the authors explain why not.
Response: Yes, the Polar DM cemented acetabular shell can be used as a primary cemented cup, and
can be cemented into any acetabular construct such as a cage, other fully porous acetabular cups, etc.
Any stem can be used with the proper head, which can be placed into the outer polyethylene DM
head. Mixing inner and outer heads by different companies in DM is not recommended and an off-
label use, but is still done by many revision surgeons.
