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Tripolar Articulations as a “High Stability Bearing” for Revision Total Hip Arthroplasty: Success Rates and Risk Factors for Failure
The Journal of Arthroplasty xxx (2020) 1e7
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The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Tripolar Articulations as a “High Stability Bearing” for Revision Total Hip Arthroplasty: Success Rates and Risk Factors for Failure Ashton H. Goldman, MD, Jeremy C. Thompson, MD, Daniel J. Berry, MD, Rafael J. Sierra, MD * Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN
a r t i c l e i n f o
a b s t r a c t
Article history: Received 2 December 2019 Received in revised form 31 January 2020 Accepted 6 February 2020 Available online xxx
Background: Unconstrained tripolar articulations have been theorized to increase hip stability. The purpose of this study is to report the performance of tripolar articulations in revision THA and identify factors associated with success and failure. Methods: Between 1994 and 2016, 67 revision THAs were performed with an unconstrained tripolar articulation. Mean follow-up was 5.4 years. Patient charts were retrospectively reviewed emphasizing factors associated with risk of instability. There were 21 patients with neither a history of instability (HI) nor abductor insufficiency (AI), 20 patients with HI alone, 13 with AI alone, and 13 had both HI and AI. Results: Twelve THAs sustained at least one postrevision dislocation at an average of 2.1 years. One bipolar dissociation occurred early (1.2 y). Nine hips had a re-revision to address these complications. Survival free from dislocation at 2, 5, and 10 years was 88%, 85%, and 74%, respectively. Survival free from re-revision at 2, 5, and 10 years was 91%, 84%, and 65%, respectively. Patients with combined AI and HI had the worst survivorship free from dislocation at 2, 5, and 10 years (77%, 68%, and 55%), respectively. In contrast, patients with neither HI nor AI experienced zero dislocations. There were no failures associated with bearing wear. Conclusion: Off-the-shelf tripolar articulations were associated with reasonable survival at midterm follow-up. In patients with both AI and HI, the risks and benefits of alternative options such as dual mobility or constrained liners should be explored as the risk of dislocation at 10 years approached 50%. © 2020 Elsevier Inc. All rights reserved.
Keywords: tripolar articulation revision THA instability abductor insufficiency re-revision THA
Postoperative instability is the most common complication following revision total hip arthroplasty (THA) [1]. In fact, the cumulative risk of redislocation in patients undergoing revision for instability is 35% at 15 years [2]. Multiple factors have been implicated in cases of postoperative instability and often more than one is present when instability occurs. Some factors are not modifiable, like abductor deficiency and a history of prior instability, while other factors are under direct surgeon control and can be modified
Investigation was performed at the Mayo Clinic, Rochester, MN. Source of funding: No external source of funding used for this study. One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to https://doi.org/10.1016/j.arth.2020.02.012. * Reprint requests: Rafael J. Sierra, MD, Department of Orthopedic Surgery, Mayo Clinic, 200 First Street SW, Rochester, MN 55905. https://doi.org/10.1016/j.arth.2020.02.012 0883-5403/© 2020 Elsevier Inc. All rights reserved.
at the time of surgery; these include achieving appropriate implant position, avoiding soft tissue, bony or implant impingement, and selection of femoral head diameter or the use of an implant that has been shown to confer a higher degree of stability [3e7]. The use of larger femoral head diameters and alternative bearing constructs have been shown to decrease dislocation rates particularly in revision THA [3,6,8,9]. Alternative constructs include dual mobility articulations, unconstrained tripolar articulations, or constrained liners. The advantages and disadvantages of using these devices have been reported previously [8,10,11]. In general, as implant constraint increases, stability increases, but at the expense of a higher risk of catastrophic failure potentially requiring revision surgery [12,13]. Less constrained devices, such as dual mobility articulations, have emerged as a viable alternative for preventing and treating instability. They consist of an acetabular component (monoblock or a modular dual mobility where a metal liner is impacted into a titanium shell) that articulates with a large polyethylene femoral head that has an additional inner diameter opening that articulates
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against a standard metal or ceramic head. The larger femoral head provides a larger jump distance, more range of motion prior to impingement, and may help with offset restoration and tensioning of the abductor mechanism. Although preliminary results are promising, there are concerns about potential corrosion between the titanium shell and cobalt chrome liner in modular dual mobility implants [14]. Additionally, there are concerns regarding the durability of these constructs and the potential for long-term wear that may occur within the smaller articulation that may lead to intraprosthetic dislocation [15]. Prior to the advent of dual mobility components in North America, one construct that provided some of the advantages of a dual mobility articulation in regard to head size and impingementfree range of motion were so-called unconstrained tripolar articulations [16e18]. They consist of a standard acetabular component consisting of a metal shell and a fixed, large inner diameter polyethylene liner (typically crosslinked polyethylene in modern incarnations). This acetabular component articulates with a bipolar femoral component (usually with an outer head diameter of 40 or 44 mm). Previous small series have reported promising results but raised some concerns with the use of a bipolar head and potential for wear of the polyethylene within the bipolar articulation leading to head dissociation. As the number of dual mobility constructs continues to increase and concerns arise regarding the potential modes of failure of those devices, the authors believe that a review of our experience with the use of unconstrained tripolar is timely in order to present a potential alternative. The purpose of this study is therefore to (1) evaluate the mid to long-term survival of tripolar articulations used in revision THA with special emphasis on survivorship free from dislocation and re-revision and (2) evaluate the risk of dislocation and re-revision as related to nonmodifiable variables of abductor deficiency and a history of pre-revision instability. Methods Using our institutional joint registry, we retrospectively identified and reviewed 73 cases from June 1994 until April 2016 (thus providing a minimum potential 2 years of follow-up) in which an unconstrained tripolar articulation was used with either a 40-mm or 44-mm diameter bipolar femoral head. All patients 18 years of age and older were included in this study. Three patients were excluded due to death before their 2-year follow-up appointment; none of these 3 had known complications prior to death. One patient died after their 2-year follow-up but was subsequently lost to follow-up prior to their death. One patient died prior to 2 years but had a postoperative dislocation; therefore, this patient was included in our study. Two patients that lived outside the country were lost to follow-up. This left 67 patients (67 hips) with minimum 2 years of follow-up and a mean follow-up of 5.4 years (range 6-184 months). The study group consisted of 61% females with an average age of 68 and mean body mass index of 29 kg/m2 (Table 1). A posterior approach was used in 45% of cases and 4 patients had an extended trochanteric osteotomy. A lateral-based approach was used in 55% of revision THAs of which 3 had a Wagner or transtrochanteric osteotomy. Twenty-nine hips (43%) had acetabular component loosening prior to the revision. The acetabular component was revised in all of these cases and in an additional 17 that were well fixed for an acetabular revision rate of 69%. The femoral component was revised in only 12 cases (18%). An isolated head/liner exchange was performed for 27% of the revision THAs. Thirty-three (49%) THAs had a history of instability (HI)deither remote or recent, prior to revision (Table 2). Abductor insufficiency (AI) was noted from operative reports or imaging. We defined AI as any patient who had a previous abductor reconstruction, severely
Table 1 Demographic and Surgical Data of 67 Revision THAs With a Tripolar Articulation. Total (N ¼ 67)
Variable Gender Female Male Side Left Right Age at surgery Mean (SD) Body mass index (kg/m2) Mean (SD) Approach Lateral Posterior Bipolar head size (mm) 40 44 Cup revision No Yes Stem revision No Yes Head/liner exchange No Yes Abductor deficiency No Yes Trochanteric deficiency No Yes Abductor insufficiency No Yes Preop instability No Yes Instability of abductor insufficiency No Yes Instability and abductor insufficiency No Yes
41 (61.19%) 26 (38.81%) 30 (44.78%) 37 (55.22%) 68.2 (10.9) 28.8 (5.8) 37 (55.22%) 30 (44.78%) 50 (74.63%) 17 (25.37%) 21 (31.34%) 46 (68.66%) 55 (82.09%) 12 (17.91%) 49 (73.13%) 18 (26.87%) 62 (92.54%) 5 (7.46%) 46 (68.66%) 21 (31.34%) 41 (61.19%) 26 (38.81%) 34 (50.75%) 33 (49.25%) 21 (31.34%) 46 (68.66%) 54 (80.60%) 13 (19.40%)
SD, standard deviation; THA, total hip arthroplasty.
torn abductors at the time of surgery, a trochanteric nonunion, or segmental bone loss of the greater trochanter. Patients were divided into 4 groups. Group 1 had an intact abductor complex and no HI (n ¼ 21). Group 2 had a HI without AI (n ¼ 20). Group 3 had AI without HI (n ¼ 13). Finally, Group 4 patients had both HI and an insufficient abductor mechanism (n ¼ 13). Patient risk factors including age (by decade), gender, and body mass index (per 5 kg/m2) were independently assessed. Surgical risk factors such as operative approach and components revised
Table 2 Pre-revision Diagnoses. Preoperative Diagnoses
n
%
Any history of instability Aseptic loosening acetabular component Polywear, osteolysis Second-stage reimplantation Acetabular erosion from a bipolar Fracture, osteolysis Acute infection, head/liner exchange
33 29 8 5 1 1 1
49.3 43.3 11.9 7.5 1.5 1.5 1.5
If a patient had previous dislocations but it was not the impetus for revision, their revision diagnosis is listed in addition to instability. Therefore, there are more diagnoses than there are patients in the study.
A.H. Goldman et al. / The Journal of Arthroplasty xxx (2020) 1e7
3
Fig. 1. Survivorship free of dislocation for our revision THA cohort with a tripolar construct. THA, total hip arthroplasty.
were assessed as potential risk factors for failure. The data are reported using standard summary statistics, including means and standard deviations for continuous variables, and counts and percentages for categorical variables. The analysis focused on the primary endpoints of dislocation and re-revision. These were analyzed
as time-to-event outcomes using survivorship methods, including Kaplan-Meier estimation and Cox proportional hazards regression. Kaplan-Meier rates and hazard ratios (HRs) are reported with 95% confidence intervals (CIs). All statistical tests were 2-sided and Pvalues less than .05 were considered significant.
Table 3 Nonsignificant Variables Evaluated for Survival Free of Dislocation and Re-Revision. Variable
Status
Dislocation
Re-Revision
Hazard Ratio (95% CI)
P-Value
Hazard Ratio (95% CI)
P-Value
Age Body mass index Gender
per 10 y per 5 kg/m2
0.86 (0.5-1.5) 0.94 (0.6-1.6)
.56 .82
0.87 (0.5-1.5) 0.7 (0.4-1.2)
.59 .21
Female Male
1.0 (reference) 1.6 (0.5-4.8)
.45
1.0 (reference) 0.9 (0.3-2.6)
.78
40 mm 44 mm
1.0 (reference) 2.3 (0.7-7.1)
.17
1.0 (reference) 2.4 (0.8-7.0)
.11
No Yes
1.0 (reference) 0.6 (0.2-1.9)
.37
1.0 (reference) 0.5 (0.2-1.5)
.20
No Yes
1.0 (reference) 1.3 (0.4-5.0)
.66
1.0 (reference) 1.0 (0.3-3.7)
.99
No Yes
1.0 (reference) 1.6 (0.5-5.5)
.44
1.0 (reference) 2.2 (0.7-6.9)
.17
Lateral Posterior
1.0 (reference) 1.5 (0.5-4.7)
.51 .51
1.0 (reference) 1.8 (0.6-5.4)
.27
Head size
Cup revision
Stem revision
Modular exchange
Approach
CI, confidence interval.
4
A.H. Goldman et al. / The Journal of Arthroplasty xxx (2020) 1e7
Table 4 Survival Free of Dislocation and Risk of Postrevision Dislocation Based on HI and AI. Variable Overall Instability or abductor insufficiency Pre-revision instability Abductor status
Instability and abductor insufficiency
Level No (group 1) Yes No Yes (group 2) Intact Insufficient (group 3) No Yes (group 4)
N
Events
2-y Survival (95% CI)
5-y Survival (95% CI)
10-y Survival (95% CI)
Hazard Ratio (95% CI)
P-Value
67 21 46 34 33 41 26
12 0 12 3 9 4 8
88.1% 100.0% 82.6% 94.1% 81.8% 92.7% 80.8%
84.6% 100.0% 77.4% 94.1% 74.5%, 89.8% 76.5%
74.3% 100.0% 64.5% 84.7% 63.9% 89.8% 59.0%
NA 1.0 (reference) 12.3 (0.6-233.7) 1.0 (reference) 3.2 (0.9-11.9) 1.0 (ref) 3.3 (0.9-11.0)
NA .1
54 13
7 5
(80.6-96.2) (100-100) (72.4-94.3) (86.5-100.0) (69.7-96.1) (85.0-100.0) (67.0-97.4)
90.7% (83.3-98.8) 76.9% (57.1-100.0)
(76.2-93.9) (100-100) (66.0-90.9) (86.5-100.0) (60.6-91.6) (80.7-99.8) (61.7-94.9)
88.5% (80.3-97.6) 68.4% (46.9-99.7)
(60.2-91.8) (100-100) (47.4-87.8) (67.8-100.0) (44.3-92.1) (80.7-99.8) (38.6-90.3)
83.0% (70.7-97.4) 54.7% (30.7-97.5)
1.0 (reference) 3.1 (0.9-9.8)
.08 .054
.06
CI, confidence interval; NA, not applicable.
Results Twelve patients (12 hips; 18%) sustained at least 1 dislocation and 1 hip sustained a bipolar component dissociation during the study period. Eight of the 12 hips with dislocation eventually went onto rerevision (75%). There were an equal number of dislocations from both laterally based and posteriorly based approaches. The bipolar dissociation also was revised. Overall survival free of dislocation was 88% at 2 years, 85% at 5 years, and 74% at 10 years (Fig. 1). None of the demographic variables evaluated were associated with dislocation (Table 3). With the numbers available, surgical approach, type of revision, and outside diameter of the bipolar head did not affect the rate of instability (P ¼ .17-.66). All patients who experienced a
dislocation either had a HI and/or were considered to have an insufficient abductor mechanism (Table 4). There was a trend toward a higher risk of dislocation in patients with AI (HR 3.3, CI 0.9-11.0, P ¼ .054) and HI (HR 3.2, CI 0.9-11.9, P ¼ .08), but these factors independently did not reach significance. For patients in group 4 (patients with both AI and HI), survivorship free from dislocation at 2, 5, and 10 years was 77%, 68%, and 55%, respectively. Similarly, there was a trend toward increased risk of dislocation in group 4 compared to all others (HR 3.1, CI 0.9-9.8, P ¼ .06). In contrast, for patients in group 1 (without a history of previous dislocation or AI) a 0% risk of dislocation was observed (Fig. 2). Overall, there were 14 patients requiring re-revision during the study period. There was an equal number of re-revisions from both
Fig. 2. Survivorship free of dislocation categorized by having neither abductor insufficiency nor preop instability or having both abductor insufficiency and preoperative instability.
A.H. Goldman et al. / The Journal of Arthroplasty xxx (2020) 1e7
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Table 5 Indications for Re-Revision and Complications Following Utilization of a Tripolar Construct.
a
Indication for Re-revision
N
Months Following Surgery
Recurrent instability Periprosthetic joint infection Periprosthetic femur fracture Femoral component loosening Femoral component loosening with component fracture Acetabular loosening Bipolar head dissociation with acetabular loosening Complication not requiring reoperation Peroneal palsy Delayed wound healing Greater trochanter fracture Cerclage wire breakage
8 3 1 1 1 1 1
2a, 31, 31, 41, 66, 93, 115a, 141 1a, 32, 116a 41 100 41 34 46
1 2 1 1
0 0 1 26
Patients appear twice due to requiring multiple reoperations.
laterally based and posteriorly based approaches. Indications for rerevision and complications are shown in Table 5. One patient had an intraprosthetic dissociation that was associated with a grossly loose acetabular component requiring re-revision. No failures were associated with bearing wear. The overall survival free of rerevision for the entire groups was 91% at 2 years, 84% at 5 years, and 65% at 10 years (Fig. 3). No patient or surgical factors were found to be predictive of re-revision including independently group AI or HI (groups 2 and 3) (P ¼ .11-.78) (Table 6). Discussion Previous papers have reported the risk of instability after revision THA to be as high as 9.8% [6]. The risk is even higher when revising patients for instability, with one previous report demonstrating a cumulative risk of dislocation of 35% at 15 years [2]. As such, surgical strategies aimed at decreasing this complication are warranted. In this study, we demonstrate that an unconstrained tripolar articulation can be successful at midterm follow-up with a low risk of instability, especially when the abductor mechanism is intact and there is no prior HI. Such a bearing provides an option in patients undergoing revision THA who are presumed to be at higher risk of dislocation. Conversely, when used in patients with both HI and AI, the failure of this articulation approached 50% at 10 years. Alternative methods to prevent instability should be explored in this group of patients. To the authors’ knowledge, this study represents the largest series of tripolar articulations reported in the English literature. et al [19], in a small series of patients with pre-revision Beaule instability, had only 1 postrevision dislocation in a group of 11 patients at a mean of 6.5 years. Similarly, Levine et al [16] showed a 93% survival at a mean of 38 months utilizing a similar articulation. Our overall 5-year survival free of dislocation of 85% is lower than
what was reported in those previous studies; however, this likely represents different patient selection for use of this device and preoperative abductor status [16,19]. This study provides good evidence on the safety of tripolar articulation use. Furthermore, this unconstrained alternative demonstrated no failures associated with wear, fracture, or potential problems associated with cobalt/ chromium metal liners. Anticipating the use of a tripolar articulation at the time of revision surgery may, in certain circumstances, avoid the complications associated with removal of well-fixed implants. One example is in the case of a well-fixed nonmodular stem, in which case a tripolar bearing may provide greater stability than a fixed bearing, while avoiding the need for femoral revision. A tripolar articulation allows maintenance of the current femoral stem, usually a 22-mm or 28-mm head and placing a bipolar articulation that subsequently articulates with the 40-mm or 44-mm inner diameter polyethylene liner. Simply using a 40-mm or 44-mm femoral head is an alternative to tripolar construct; however, the concern for trunnionosis arises [20]. In cases where an acetabular component is well-fixed, well positioned, increased stability is warranted, and a dual mobility liner is not an option, a 40 or 44 inner diameter polyethylene may be cemented into the acetabular component. Furthermore, given that more than two-thirds of revision THAs in the current study required an acetabular revision, a tripolar articulation, in the same way as a dual mobility bearing, may avoid high stresses on the bone-implant interface associated with a constrained articulation. Tripolar articulations may be considered as a viable alternative to dual mobility liners in select cases. Monoblock dual mobility implants have demonstrated very good results in a number of mostly European series and there are promising early data using uncemented modular dual mobility constructs in North America [8,20e23]. Modular metal dual mobility liners usually cannot be
Table 6 Survival Free of Re-Revision Based on Abductor Status and Preoperative Instability. Variable Overall Instability or abductor insufficiency Pre-revision instability Abductor status
Instability and abductor insufficiency
Level No (group 1) Yes No Yes (group 2) Intact Insufficient (group 3) No Yes (group 4)
CI, confidence interval; NA, not applicable.
N
Events
2-y Survival (95% CI)
5-y Survival (95% CI)
10-y Survival (95% CI)
Hazard Ratio (95% CI)
P-Value
67 21 46 34 33 41 26
14 3 11 6 8 6 8
90.9% 95.2% 88.9% 94.1% 87.6% 92.7% 88.1%
83.9% 89.9% 80.9% 87.6% 79.7% 89.8% 74.4%
64.7% 72.0% 62.6% 67.6% 61.5% 70.7% 57.4%
NA 1.0 1.7 1.0 1.4 1.0 2.0
NA .41
54 13
9 5
(84.3-98.1) (86.6-100) (80.2-98.6) (86.5-100) (76.9-99.8) (85.0-100) (76.4-100)
92.6% (85.9-99.8) 83.9% (65.7-100)
(75.1-93.6) (77.6-100) (69.7-93.9) (77.0-99.8) (66.3-95.9) (80.7-99.8) (58.6-94.5)
88.3% (79.9-97.6) 63.9% (40.7-100)
(48.8-85.9) (45.3-100) (44.8-87.6) (45.8-99.7) (40.8-92.7) (49.8-100) (37.1-88.9)
69.2% (51.3-93.3) 51.1% (27.3-96.0)
(reference) (0.5-6.2) (reference) (0.5-4.1) (reference) (0.7-5.8)
1.0 (reference) 2.2 (0.7-6.8)
.51 .21
.16
6
A.H. Goldman et al. / The Journal of Arthroplasty xxx (2020) 1e7
Fig. 3. Survivorship free of reoperation for our revision THA cohort with a tripolar construct.
impacted into older cups, so surgeons must choose to revise the acetabular component or cement a monoblock cup or liner into a well-fixed shell to obtain a dual mobility construct. This practice is limited by the size of the liner to be cemented into place. Alternatively, most implant companies today manufacture an off-theshelf 40 or 44 mm polyethylene liner that snap into or can be cemented into an appropriately sized shell and thus would be compatible with a tripolar construct. The current study is important to understand in the changing landscape of the ideal revision THA articulation. Larger femoral heads were shown to decrease the risk of postoperative instability [3,6,9,19]. Hartzler et al [8] demonstrated that dual mobility had a lower risk of instability compared to large femoral heads including patients with a previous HI. With the rise in utilization of dual mobility, stratification of patients based on AI or HI becomes paramount [2,6e8]. In the current study, the risk of instability in patients with a HI was 3.2 times higher than those without. Although a direct comparison was not made, the favorable results published by Hartzler et al [8] would favor using a dual mobility over an unconstrained tripolar articulation in patients with a HI. The current results show that an unconstrained tripolar articulation is a reasonable option in select cases without a history of AI or HI. There are several limitations to this retrospective study. First, the decision to use a tripolar articulation was based on surgeon preference and on compatibility with implants that were revised and did not follow a specific algorithm. Along these lines, there is a lack of homogeneity in our cohort as operative approach was at the
discretion of the surgeon and could affect the risk of dislocation and re-revision. Second, we do not present comparative data for other articulations as the intent of this study was to examine the survival and safety of the 67 tripolar constructs performed at our institution. Next, we do not present patient reported outcomes data, as we would expect these data to be similar to that reported with any complex revision cohort, and not be specific to the use of the tripolar articulation. We rather focused on the risk of subsequent dislocation and complications as our endpoints as they are directly associated with the use of the articulation. Fourth, the small cohort limited our ability to achieve statistical significance in certain variables studied; however, this is the largest series to date reporting the use of this articulation to the authors’ knowledge. Finally, with a mean follow-up of 5.4 years, complications related to polyethylene wear were not observed; however, it would be expected that longer follow-up may be associated with some degree of polyethylene failure, especially if the bipolar head uses conventional polyethylene. In conclusion, this report supports the use of off-the-shelf tripolar articulations as a safe alternative for patients undergoing revision THA. Tripolar articulations were associated with reasonable survival at midterm follow-up, and with minimal risk of polyethylene wear or bearing dissociation. Patients without HI or AI were identified as having the lowest risk of failure with this articulation, while patients with both AI and HI demonstrated a risk of dislocation of nearly 50% at 10 years. Larger studies are needed to compare unconstrained tripolar constructs to large femoral heads and dual mobility articulations.
A.H. Goldman et al. / The Journal of Arthroplasty xxx (2020) 1e7
Acknowledgments The authors would like to thank Dirk R. Larson, MS for his assistance with the statistical analysis. References [1] Springer BD, Fehring TK, Griffin WL, Odum SM, Masonis JL. Why revision total hip arthroplasty fails. Clin Orthop Relat Res 2009;467:166e73. [2] Jo S, Almonte JHJ, Sierra RJ. The cumulative risk of re-dislocation after revision THA performed for instability increases close to 35% at 15 years. J Arthroplasty 2015;30:1177e82. [3] Hummel MT, Malkani AL, Yakkanti MR, Baker DL. Decreased dislocation after revision total hip arthroplasty using larger femoral head size and posterior capsular repair. J Arthroplasty 2009;24:73e6. [4] Kosashvili Y, Backstein D, Safir O, Lakstein D, Gross AE. Dislocation and infection after revision total hip arthroplasty comparison between the first and multiply revised total hip arthroplasty. J Arthroplasty 2011;26:1170e5. [5] Kung PL, Ries MD. Effect of femoral head size and abductors on dislocation after revision THA. Clin Orthop Relat Res 2007;465:170e4. [6] Wetters NG, Murray TG, Moric M, Sporer SM, Paprosky WG, Della Valle CJ. Risk factors for dislocation after revision total hip arthroplasty. Clin Orthop Relat Res 2013;471:410e6. [7] Yoshimoto K, Nakashima Y, Aota S, Kaneuji A, Fukui K, Hirakawa K, et al. Redislocation after revision total hip arthroplasty for recurrent dislocation: a multicentre study. Int Orthop 2017;41:253e8. [8] Hartzler MA, Abdel MP, Sculco PK, Taunton MJ, Pagnano MW, Hanssen AD. Otto Aufranc Award: Dual-mobility constructs in revision THA reduced dislocation, rerevision, and reoperation compared with large femoral heads. Clin Orthop Relat Res 2018;476:293e301. [9] Garbuz DS, Masri BA, Duncan CP, Greidanus NV, Bohm ER, Petrak MJ, et al. Large (36 or 40-mm) femoral heads decreased the rate of dislocation after revision total hip arthroplasty. J Bone Joint Surg Am 2012;94:2095. [10] Guyen O, Chen QS, Bejui-Hugues J, Berry DJ, An KN. Unconstrained tripolar hip implants: effect on hip stability. Clin Orthop Relat Res 2007;455:202e8. [11] Lachiewicz PF, Watters TS. The use of dual-mobility components in total hip arthroplasty. J Am Acad Orthop Surg 2012;20:481e6.
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[12] Chalmers BP, Arsoy D, Sierra RJ, Lewallen DG, Trousdale RT. High failure rate of modular exchange with a specific design of a constrained liner in high-risk patients undergoing revision total hip arthroplasty. J Arthroplasty 2016;31: 1963e9. [13] Della Valle CJ, Chang D, Sporer S, Berger RA, Rosenberg AG, Paprosky WG. High failure rate of a constrained acetabular liner in revision total hip arthroplasty. J Arthroplasty 2005;20(7 Suppl 3):103e7. [14] Matsen Ko LJ, Pollag KE, Yoo JY, Sharkey PF. Serum metal ion levels following total hip arthroplasty with modular dual mobility components. J Arthroplasty 2016;31:186e9. [15] Philippot R, Farizon F, Camilleri J, Boyer B, Derhi G, Bonnan J, et al. Survival of dual mobility socket with a mean 17 years follow-up. Rev Chir Orthop Reparatrice Appar Mot 2008;94:43e8. [16] Levine BR, Della Valle CJ, Deirmengian CA, Breien KM, Weeden SH, Sporer SM, et al. The use of a tripolar articulation in revision total hip arthroplasty: a minimum of 24 months’ follow-up. J Arthroplasty 2008;23: 1182e8. [17] McClelland SJ, Godfrey JD, Benton PC, Slemmons BK. Revision of failed hip surface replacement arthroplasties with a bipolar prosthesis. Three case reports with two-to three-year follow-up observations. Clin Orthop Relat Res 1986:243e8. [18] Ries MD, Wiedel JD. Bipolar hip arthroplasty for recurrent dislocation after total hip arthroplasty. A report of three cases. Clin Orthop Relat Res 1992: 121e7. PE, Schmalzried TP, Udomkiat P, Amstutz HC. Jumbo femoral head for [19] Beaule the treatment of recurrent dislocation following total hip replacement. J Bone Joint Surg Am 2002;84:256e63. [20] Lavernia CJ, Iacobelli DA, Villa JM, Jones K, Gonzalez JL, Jones WK. Trunnionehead stresses in THA: are big heads trouble? J Arthroplasty 2015;30: 1085e8. [21] Hamadouche M, Biau DJ, Huten D, Musset T, Gaucher F. The use of a cemented dual mobility socket to treat recurrent dislocation. Clin Orthop Relat Res 2010;468:3248e54. [22] Jauregui JJ, Pierce TP, Elmallah RK, Cherian JJ, Delanois RE, Mont MA. Dual mobility cups: an effective prosthesis in revision total hip arthroplasties for preventing dislocations. Hip Int 2016;26:57e61. [23] Langlais FL, Ropars M, Gaucher F, Musset T, Chaix O. Dual mobility cemented cups have low dislocation rates in THA revisions. Clin Orthop Relat Res 2008;466:389e95.
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The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Tripolar Articulations as a “High Stability Bearing” for Revision Total Hip Arthroplasty: Success Rates and Risk Factors for Failure Ashton H. Goldman, MD, Jeremy C. Thompson, MD, Daniel J. Berry, MD, Rafael J. Sierra, MD * Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN
a r t i c l e i n f o
a b s t r a c t
Article history: Received 2 December 2019 Received in revised form 31 January 2020 Accepted 6 February 2020 Available online xxx
Background: Unconstrained tripolar articulations have been theorized to increase hip stability. The purpose of this study is to report the performance of tripolar articulations in revision THA and identify factors associated with success and failure. Methods: Between 1994 and 2016, 67 revision THAs were performed with an unconstrained tripolar articulation. Mean follow-up was 5.4 years. Patient charts were retrospectively reviewed emphasizing factors associated with risk of instability. There were 21 patients with neither a history of instability (HI) nor abductor insufficiency (AI), 20 patients with HI alone, 13 with AI alone, and 13 had both HI and AI. Results: Twelve THAs sustained at least one postrevision dislocation at an average of 2.1 years. One bipolar dissociation occurred early (1.2 y). Nine hips had a re-revision to address these complications. Survival free from dislocation at 2, 5, and 10 years was 88%, 85%, and 74%, respectively. Survival free from re-revision at 2, 5, and 10 years was 91%, 84%, and 65%, respectively. Patients with combined AI and HI had the worst survivorship free from dislocation at 2, 5, and 10 years (77%, 68%, and 55%), respectively. In contrast, patients with neither HI nor AI experienced zero dislocations. There were no failures associated with bearing wear. Conclusion: Off-the-shelf tripolar articulations were associated with reasonable survival at midterm follow-up. In patients with both AI and HI, the risks and benefits of alternative options such as dual mobility or constrained liners should be explored as the risk of dislocation at 10 years approached 50%. © 2020 Elsevier Inc. All rights reserved.
Keywords: tripolar articulation revision THA instability abductor insufficiency re-revision THA
Postoperative instability is the most common complication following revision total hip arthroplasty (THA) [1]. In fact, the cumulative risk of redislocation in patients undergoing revision for instability is 35% at 15 years [2]. Multiple factors have been implicated in cases of postoperative instability and often more than one is present when instability occurs. Some factors are not modifiable, like abductor deficiency and a history of prior instability, while other factors are under direct surgeon control and can be modified
Investigation was performed at the Mayo Clinic, Rochester, MN. Source of funding: No external source of funding used for this study. One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to https://doi.org/10.1016/j.arth.2020.02.012. * Reprint requests: Rafael J. Sierra, MD, Department of Orthopedic Surgery, Mayo Clinic, 200 First Street SW, Rochester, MN 55905. https://doi.org/10.1016/j.arth.2020.02.012 0883-5403/© 2020 Elsevier Inc. All rights reserved.
at the time of surgery; these include achieving appropriate implant position, avoiding soft tissue, bony or implant impingement, and selection of femoral head diameter or the use of an implant that has been shown to confer a higher degree of stability [3e7]. The use of larger femoral head diameters and alternative bearing constructs have been shown to decrease dislocation rates particularly in revision THA [3,6,8,9]. Alternative constructs include dual mobility articulations, unconstrained tripolar articulations, or constrained liners. The advantages and disadvantages of using these devices have been reported previously [8,10,11]. In general, as implant constraint increases, stability increases, but at the expense of a higher risk of catastrophic failure potentially requiring revision surgery [12,13]. Less constrained devices, such as dual mobility articulations, have emerged as a viable alternative for preventing and treating instability. They consist of an acetabular component (monoblock or a modular dual mobility where a metal liner is impacted into a titanium shell) that articulates with a large polyethylene femoral head that has an additional inner diameter opening that articulates
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against a standard metal or ceramic head. The larger femoral head provides a larger jump distance, more range of motion prior to impingement, and may help with offset restoration and tensioning of the abductor mechanism. Although preliminary results are promising, there are concerns about potential corrosion between the titanium shell and cobalt chrome liner in modular dual mobility implants [14]. Additionally, there are concerns regarding the durability of these constructs and the potential for long-term wear that may occur within the smaller articulation that may lead to intraprosthetic dislocation [15]. Prior to the advent of dual mobility components in North America, one construct that provided some of the advantages of a dual mobility articulation in regard to head size and impingementfree range of motion were so-called unconstrained tripolar articulations [16e18]. They consist of a standard acetabular component consisting of a metal shell and a fixed, large inner diameter polyethylene liner (typically crosslinked polyethylene in modern incarnations). This acetabular component articulates with a bipolar femoral component (usually with an outer head diameter of 40 or 44 mm). Previous small series have reported promising results but raised some concerns with the use of a bipolar head and potential for wear of the polyethylene within the bipolar articulation leading to head dissociation. As the number of dual mobility constructs continues to increase and concerns arise regarding the potential modes of failure of those devices, the authors believe that a review of our experience with the use of unconstrained tripolar is timely in order to present a potential alternative. The purpose of this study is therefore to (1) evaluate the mid to long-term survival of tripolar articulations used in revision THA with special emphasis on survivorship free from dislocation and re-revision and (2) evaluate the risk of dislocation and re-revision as related to nonmodifiable variables of abductor deficiency and a history of pre-revision instability. Methods Using our institutional joint registry, we retrospectively identified and reviewed 73 cases from June 1994 until April 2016 (thus providing a minimum potential 2 years of follow-up) in which an unconstrained tripolar articulation was used with either a 40-mm or 44-mm diameter bipolar femoral head. All patients 18 years of age and older were included in this study. Three patients were excluded due to death before their 2-year follow-up appointment; none of these 3 had known complications prior to death. One patient died after their 2-year follow-up but was subsequently lost to follow-up prior to their death. One patient died prior to 2 years but had a postoperative dislocation; therefore, this patient was included in our study. Two patients that lived outside the country were lost to follow-up. This left 67 patients (67 hips) with minimum 2 years of follow-up and a mean follow-up of 5.4 years (range 6-184 months). The study group consisted of 61% females with an average age of 68 and mean body mass index of 29 kg/m2 (Table 1). A posterior approach was used in 45% of cases and 4 patients had an extended trochanteric osteotomy. A lateral-based approach was used in 55% of revision THAs of which 3 had a Wagner or transtrochanteric osteotomy. Twenty-nine hips (43%) had acetabular component loosening prior to the revision. The acetabular component was revised in all of these cases and in an additional 17 that were well fixed for an acetabular revision rate of 69%. The femoral component was revised in only 12 cases (18%). An isolated head/liner exchange was performed for 27% of the revision THAs. Thirty-three (49%) THAs had a history of instability (HI)deither remote or recent, prior to revision (Table 2). Abductor insufficiency (AI) was noted from operative reports or imaging. We defined AI as any patient who had a previous abductor reconstruction, severely
Table 1 Demographic and Surgical Data of 67 Revision THAs With a Tripolar Articulation. Total (N ¼ 67)
Variable Gender Female Male Side Left Right Age at surgery Mean (SD) Body mass index (kg/m2) Mean (SD) Approach Lateral Posterior Bipolar head size (mm) 40 44 Cup revision No Yes Stem revision No Yes Head/liner exchange No Yes Abductor deficiency No Yes Trochanteric deficiency No Yes Abductor insufficiency No Yes Preop instability No Yes Instability of abductor insufficiency No Yes Instability and abductor insufficiency No Yes
41 (61.19%) 26 (38.81%) 30 (44.78%) 37 (55.22%) 68.2 (10.9) 28.8 (5.8) 37 (55.22%) 30 (44.78%) 50 (74.63%) 17 (25.37%) 21 (31.34%) 46 (68.66%) 55 (82.09%) 12 (17.91%) 49 (73.13%) 18 (26.87%) 62 (92.54%) 5 (7.46%) 46 (68.66%) 21 (31.34%) 41 (61.19%) 26 (38.81%) 34 (50.75%) 33 (49.25%) 21 (31.34%) 46 (68.66%) 54 (80.60%) 13 (19.40%)
SD, standard deviation; THA, total hip arthroplasty.
torn abductors at the time of surgery, a trochanteric nonunion, or segmental bone loss of the greater trochanter. Patients were divided into 4 groups. Group 1 had an intact abductor complex and no HI (n ¼ 21). Group 2 had a HI without AI (n ¼ 20). Group 3 had AI without HI (n ¼ 13). Finally, Group 4 patients had both HI and an insufficient abductor mechanism (n ¼ 13). Patient risk factors including age (by decade), gender, and body mass index (per 5 kg/m2) were independently assessed. Surgical risk factors such as operative approach and components revised
Table 2 Pre-revision Diagnoses. Preoperative Diagnoses
n
%
Any history of instability Aseptic loosening acetabular component Polywear, osteolysis Second-stage reimplantation Acetabular erosion from a bipolar Fracture, osteolysis Acute infection, head/liner exchange
33 29 8 5 1 1 1
49.3 43.3 11.9 7.5 1.5 1.5 1.5
If a patient had previous dislocations but it was not the impetus for revision, their revision diagnosis is listed in addition to instability. Therefore, there are more diagnoses than there are patients in the study.
A.H. Goldman et al. / The Journal of Arthroplasty xxx (2020) 1e7
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Fig. 1. Survivorship free of dislocation for our revision THA cohort with a tripolar construct. THA, total hip arthroplasty.
were assessed as potential risk factors for failure. The data are reported using standard summary statistics, including means and standard deviations for continuous variables, and counts and percentages for categorical variables. The analysis focused on the primary endpoints of dislocation and re-revision. These were analyzed
as time-to-event outcomes using survivorship methods, including Kaplan-Meier estimation and Cox proportional hazards regression. Kaplan-Meier rates and hazard ratios (HRs) are reported with 95% confidence intervals (CIs). All statistical tests were 2-sided and Pvalues less than .05 were considered significant.
Table 3 Nonsignificant Variables Evaluated for Survival Free of Dislocation and Re-Revision. Variable
Status
Dislocation
Re-Revision
Hazard Ratio (95% CI)
P-Value
Hazard Ratio (95% CI)
P-Value
Age Body mass index Gender
per 10 y per 5 kg/m2
0.86 (0.5-1.5) 0.94 (0.6-1.6)
.56 .82
0.87 (0.5-1.5) 0.7 (0.4-1.2)
.59 .21
Female Male
1.0 (reference) 1.6 (0.5-4.8)
.45
1.0 (reference) 0.9 (0.3-2.6)
.78
40 mm 44 mm
1.0 (reference) 2.3 (0.7-7.1)
.17
1.0 (reference) 2.4 (0.8-7.0)
.11
No Yes
1.0 (reference) 0.6 (0.2-1.9)
.37
1.0 (reference) 0.5 (0.2-1.5)
.20
No Yes
1.0 (reference) 1.3 (0.4-5.0)
.66
1.0 (reference) 1.0 (0.3-3.7)
.99
No Yes
1.0 (reference) 1.6 (0.5-5.5)
.44
1.0 (reference) 2.2 (0.7-6.9)
.17
Lateral Posterior
1.0 (reference) 1.5 (0.5-4.7)
.51 .51
1.0 (reference) 1.8 (0.6-5.4)
.27
Head size
Cup revision
Stem revision
Modular exchange
Approach
CI, confidence interval.
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Table 4 Survival Free of Dislocation and Risk of Postrevision Dislocation Based on HI and AI. Variable Overall Instability or abductor insufficiency Pre-revision instability Abductor status
Instability and abductor insufficiency
Level No (group 1) Yes No Yes (group 2) Intact Insufficient (group 3) No Yes (group 4)
N
Events
2-y Survival (95% CI)
5-y Survival (95% CI)
10-y Survival (95% CI)
Hazard Ratio (95% CI)
P-Value
67 21 46 34 33 41 26
12 0 12 3 9 4 8
88.1% 100.0% 82.6% 94.1% 81.8% 92.7% 80.8%
84.6% 100.0% 77.4% 94.1% 74.5%, 89.8% 76.5%
74.3% 100.0% 64.5% 84.7% 63.9% 89.8% 59.0%
NA 1.0 (reference) 12.3 (0.6-233.7) 1.0 (reference) 3.2 (0.9-11.9) 1.0 (ref) 3.3 (0.9-11.0)
NA .1
54 13
7 5
(80.6-96.2) (100-100) (72.4-94.3) (86.5-100.0) (69.7-96.1) (85.0-100.0) (67.0-97.4)
90.7% (83.3-98.8) 76.9% (57.1-100.0)
(76.2-93.9) (100-100) (66.0-90.9) (86.5-100.0) (60.6-91.6) (80.7-99.8) (61.7-94.9)
88.5% (80.3-97.6) 68.4% (46.9-99.7)
(60.2-91.8) (100-100) (47.4-87.8) (67.8-100.0) (44.3-92.1) (80.7-99.8) (38.6-90.3)
83.0% (70.7-97.4) 54.7% (30.7-97.5)
1.0 (reference) 3.1 (0.9-9.8)
.08 .054
.06
CI, confidence interval; NA, not applicable.
Results Twelve patients (12 hips; 18%) sustained at least 1 dislocation and 1 hip sustained a bipolar component dissociation during the study period. Eight of the 12 hips with dislocation eventually went onto rerevision (75%). There were an equal number of dislocations from both laterally based and posteriorly based approaches. The bipolar dissociation also was revised. Overall survival free of dislocation was 88% at 2 years, 85% at 5 years, and 74% at 10 years (Fig. 1). None of the demographic variables evaluated were associated with dislocation (Table 3). With the numbers available, surgical approach, type of revision, and outside diameter of the bipolar head did not affect the rate of instability (P ¼ .17-.66). All patients who experienced a
dislocation either had a HI and/or were considered to have an insufficient abductor mechanism (Table 4). There was a trend toward a higher risk of dislocation in patients with AI (HR 3.3, CI 0.9-11.0, P ¼ .054) and HI (HR 3.2, CI 0.9-11.9, P ¼ .08), but these factors independently did not reach significance. For patients in group 4 (patients with both AI and HI), survivorship free from dislocation at 2, 5, and 10 years was 77%, 68%, and 55%, respectively. Similarly, there was a trend toward increased risk of dislocation in group 4 compared to all others (HR 3.1, CI 0.9-9.8, P ¼ .06). In contrast, for patients in group 1 (without a history of previous dislocation or AI) a 0% risk of dislocation was observed (Fig. 2). Overall, there were 14 patients requiring re-revision during the study period. There was an equal number of re-revisions from both
Fig. 2. Survivorship free of dislocation categorized by having neither abductor insufficiency nor preop instability or having both abductor insufficiency and preoperative instability.
A.H. Goldman et al. / The Journal of Arthroplasty xxx (2020) 1e7
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Table 5 Indications for Re-Revision and Complications Following Utilization of a Tripolar Construct.
a
Indication for Re-revision
N
Months Following Surgery
Recurrent instability Periprosthetic joint infection Periprosthetic femur fracture Femoral component loosening Femoral component loosening with component fracture Acetabular loosening Bipolar head dissociation with acetabular loosening Complication not requiring reoperation Peroneal palsy Delayed wound healing Greater trochanter fracture Cerclage wire breakage
8 3 1 1 1 1 1
2a, 31, 31, 41, 66, 93, 115a, 141 1a, 32, 116a 41 100 41 34 46
1 2 1 1
0 0 1 26
Patients appear twice due to requiring multiple reoperations.
laterally based and posteriorly based approaches. Indications for rerevision and complications are shown in Table 5. One patient had an intraprosthetic dissociation that was associated with a grossly loose acetabular component requiring re-revision. No failures were associated with bearing wear. The overall survival free of rerevision for the entire groups was 91% at 2 years, 84% at 5 years, and 65% at 10 years (Fig. 3). No patient or surgical factors were found to be predictive of re-revision including independently group AI or HI (groups 2 and 3) (P ¼ .11-.78) (Table 6). Discussion Previous papers have reported the risk of instability after revision THA to be as high as 9.8% [6]. The risk is even higher when revising patients for instability, with one previous report demonstrating a cumulative risk of dislocation of 35% at 15 years [2]. As such, surgical strategies aimed at decreasing this complication are warranted. In this study, we demonstrate that an unconstrained tripolar articulation can be successful at midterm follow-up with a low risk of instability, especially when the abductor mechanism is intact and there is no prior HI. Such a bearing provides an option in patients undergoing revision THA who are presumed to be at higher risk of dislocation. Conversely, when used in patients with both HI and AI, the failure of this articulation approached 50% at 10 years. Alternative methods to prevent instability should be explored in this group of patients. To the authors’ knowledge, this study represents the largest series of tripolar articulations reported in the English literature. et al [19], in a small series of patients with pre-revision Beaule instability, had only 1 postrevision dislocation in a group of 11 patients at a mean of 6.5 years. Similarly, Levine et al [16] showed a 93% survival at a mean of 38 months utilizing a similar articulation. Our overall 5-year survival free of dislocation of 85% is lower than
what was reported in those previous studies; however, this likely represents different patient selection for use of this device and preoperative abductor status [16,19]. This study provides good evidence on the safety of tripolar articulation use. Furthermore, this unconstrained alternative demonstrated no failures associated with wear, fracture, or potential problems associated with cobalt/ chromium metal liners. Anticipating the use of a tripolar articulation at the time of revision surgery may, in certain circumstances, avoid the complications associated with removal of well-fixed implants. One example is in the case of a well-fixed nonmodular stem, in which case a tripolar bearing may provide greater stability than a fixed bearing, while avoiding the need for femoral revision. A tripolar articulation allows maintenance of the current femoral stem, usually a 22-mm or 28-mm head and placing a bipolar articulation that subsequently articulates with the 40-mm or 44-mm inner diameter polyethylene liner. Simply using a 40-mm or 44-mm femoral head is an alternative to tripolar construct; however, the concern for trunnionosis arises [20]. In cases where an acetabular component is well-fixed, well positioned, increased stability is warranted, and a dual mobility liner is not an option, a 40 or 44 inner diameter polyethylene may be cemented into the acetabular component. Furthermore, given that more than two-thirds of revision THAs in the current study required an acetabular revision, a tripolar articulation, in the same way as a dual mobility bearing, may avoid high stresses on the bone-implant interface associated with a constrained articulation. Tripolar articulations may be considered as a viable alternative to dual mobility liners in select cases. Monoblock dual mobility implants have demonstrated very good results in a number of mostly European series and there are promising early data using uncemented modular dual mobility constructs in North America [8,20e23]. Modular metal dual mobility liners usually cannot be
Table 6 Survival Free of Re-Revision Based on Abductor Status and Preoperative Instability. Variable Overall Instability or abductor insufficiency Pre-revision instability Abductor status
Instability and abductor insufficiency
Level No (group 1) Yes No Yes (group 2) Intact Insufficient (group 3) No Yes (group 4)
CI, confidence interval; NA, not applicable.
N
Events
2-y Survival (95% CI)
5-y Survival (95% CI)
10-y Survival (95% CI)
Hazard Ratio (95% CI)
P-Value
67 21 46 34 33 41 26
14 3 11 6 8 6 8
90.9% 95.2% 88.9% 94.1% 87.6% 92.7% 88.1%
83.9% 89.9% 80.9% 87.6% 79.7% 89.8% 74.4%
64.7% 72.0% 62.6% 67.6% 61.5% 70.7% 57.4%
NA 1.0 1.7 1.0 1.4 1.0 2.0
NA .41
54 13
9 5
(84.3-98.1) (86.6-100) (80.2-98.6) (86.5-100) (76.9-99.8) (85.0-100) (76.4-100)
92.6% (85.9-99.8) 83.9% (65.7-100)
(75.1-93.6) (77.6-100) (69.7-93.9) (77.0-99.8) (66.3-95.9) (80.7-99.8) (58.6-94.5)
88.3% (79.9-97.6) 63.9% (40.7-100)
(48.8-85.9) (45.3-100) (44.8-87.6) (45.8-99.7) (40.8-92.7) (49.8-100) (37.1-88.9)
69.2% (51.3-93.3) 51.1% (27.3-96.0)
(reference) (0.5-6.2) (reference) (0.5-4.1) (reference) (0.7-5.8)
1.0 (reference) 2.2 (0.7-6.8)
.51 .21
.16
6
A.H. Goldman et al. / The Journal of Arthroplasty xxx (2020) 1e7
Fig. 3. Survivorship free of reoperation for our revision THA cohort with a tripolar construct.
impacted into older cups, so surgeons must choose to revise the acetabular component or cement a monoblock cup or liner into a well-fixed shell to obtain a dual mobility construct. This practice is limited by the size of the liner to be cemented into place. Alternatively, most implant companies today manufacture an off-theshelf 40 or 44 mm polyethylene liner that snap into or can be cemented into an appropriately sized shell and thus would be compatible with a tripolar construct. The current study is important to understand in the changing landscape of the ideal revision THA articulation. Larger femoral heads were shown to decrease the risk of postoperative instability [3,6,9,19]. Hartzler et al [8] demonstrated that dual mobility had a lower risk of instability compared to large femoral heads including patients with a previous HI. With the rise in utilization of dual mobility, stratification of patients based on AI or HI becomes paramount [2,6e8]. In the current study, the risk of instability in patients with a HI was 3.2 times higher than those without. Although a direct comparison was not made, the favorable results published by Hartzler et al [8] would favor using a dual mobility over an unconstrained tripolar articulation in patients with a HI. The current results show that an unconstrained tripolar articulation is a reasonable option in select cases without a history of AI or HI. There are several limitations to this retrospective study. First, the decision to use a tripolar articulation was based on surgeon preference and on compatibility with implants that were revised and did not follow a specific algorithm. Along these lines, there is a lack of homogeneity in our cohort as operative approach was at the
discretion of the surgeon and could affect the risk of dislocation and re-revision. Second, we do not present comparative data for other articulations as the intent of this study was to examine the survival and safety of the 67 tripolar constructs performed at our institution. Next, we do not present patient reported outcomes data, as we would expect these data to be similar to that reported with any complex revision cohort, and not be specific to the use of the tripolar articulation. We rather focused on the risk of subsequent dislocation and complications as our endpoints as they are directly associated with the use of the articulation. Fourth, the small cohort limited our ability to achieve statistical significance in certain variables studied; however, this is the largest series to date reporting the use of this articulation to the authors’ knowledge. Finally, with a mean follow-up of 5.4 years, complications related to polyethylene wear were not observed; however, it would be expected that longer follow-up may be associated with some degree of polyethylene failure, especially if the bipolar head uses conventional polyethylene. In conclusion, this report supports the use of off-the-shelf tripolar articulations as a safe alternative for patients undergoing revision THA. Tripolar articulations were associated with reasonable survival at midterm follow-up, and with minimal risk of polyethylene wear or bearing dissociation. Patients without HI or AI were identified as having the lowest risk of failure with this articulation, while patients with both AI and HI demonstrated a risk of dislocation of nearly 50% at 10 years. Larger studies are needed to compare unconstrained tripolar constructs to large femoral heads and dual mobility articulations.
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