Is Cemented Dual-Mobility Cup a Reliable Option in Primary and Revision Total Hip Arthroplasty: A Systematic Review

Background: Instability is a common complication following total hip arthroplasty (THA). The dual mobility cup (DMC) allows a reduction in the dislocation rate. The goal of this systematic review was to clarify the different uses and outcomes according to the indications of the cemented DMC (C-DMC). Methods: A systematic review was performed using the keywords “Cemented Dual Mobility Cup” or “Cemented Tripolar Cup” without a publication year limit. Of the 465 studies identified, only 56 were eligible for the study. Results: The overall number of C-DMC was 3452 in 3426 patients. The mean follow-up was 45.9 months (range 12–98.4). In most of the cases (74.5%) C-DMC was used in a revision setting. In 57.5% DMC was cemented directly into the bone, in 39.6% into an acetabular reinforcement and in 3.2% into a pre-existing cup. The overall dislocation rate was 2.9%. The most frequent postoperative complications were periprosthetic infections (2%); aseptic loosening (1.1%) and mechanical failure (0.5%). The overall revision rate was 4.4%. The average survival rate of C-DMC at the last follow-up was 93.5%. Conclusions: C-DMC represents an effective treatment option to limit the risk of dislocations and complications for both primary and revision surgery. C-DMC has good clinical outcomes and a low complication rate.


Introduction
The use of the dual mobility cup (DMC) is an established practice in hip replacement surgery, which could ensure higher implant stability, physiological mobility of the hip joint and reduce wear. DMC is considered one of the major current strategies to prevent and treat hip instability, which is the first reason for total hip arthroplasty (THA) revision. The excellent long-term results of DMC justify their steady increase in recent years, both in primary complex cases and in recurrent hip instability after THA [1][2][3][4][5].
DMC can be used as the first implant surgery in complex cases of osteoarthritis (OA), including obese patients or those with neuromuscular or neurological diseases; and in fractures, such as acetabular fractures, femoral neck fractures (FNF), or pathological fractures [6][7][8][9]. Another common use of DMC is in revision surgery of total or partial hip arthroplasties or following the failure of a previous osteosynthesis [10,11].
In complex cases, including bone defects, DMC can be cemented directly into the bone or acetabular brace, such as primary or revision surgery [12,13]. While many reviews in the literature investigate and describe DMC [14,15], there is no specific analysis of cemented DMC (C-DMC).

Methodological Quality Assessment
The study quality of all included studies was evaluated using the MINORS (Methodological Index for Non-Randomized Studies) criteria. Each item was scored from 0 to 2, with maximum scores of 16 for non-comparative studies and 24 for comparative studies. Each study included was scored by 2 authors (C.G. and M.G.).

Statistical Analysis
The kappa (k) value was used to evaluate consensus among reviewers in item selection. The agreement was classified as poor when k < 0.30, partial 0.30 < k < 0.60 and total with k > 0.60. Given the high heterogeneity among the studies, a meta-analysis was not performed; however, indirect comparisons were made.

Literature Search and Study Characteristics
The initial search found 465 studies. After removing the duplicates, the remaining items were screened based on the title and abstract. The full texts of the remaining 86 articles were examined. Finally, according to the eligibility criteria, 56 articles were included in the systematic review [12, (Figure 1).  Among the reviewers, there was excellent agreement involving the title (k = 0.90; 95% CI, 0.88 to 0.92), the abstract (k = 0.91; 95% CI, 0.89 to 0.93), and the full text (k = 0.93; 95% CI, 0.92 to 0.94). Of the selected articles published between 2008 and 2021, ten reports are comparative studies (17.9%).

Overall Demographic Data
The overall number of patients was 4675 (4701 hips). Finally, 3452 C-DMC in 3426 patients were found. The patients who reached the last follow-up and who were evaluated for clinical and radiographic outcomes are 3162 (92.3%).

Operative Technique and Implants
Overall, 3452 C-DMCs are included. The posterolateral approach was the most used surgical approach (75.3%). The anterior approach was used in 14% of cases, the lateral approach in 5.3% of cases, and an extensive approach was used in 5.4% of cases. The most used implant was the Avantage dual mobility cup (Zimmer Biomet©, Warsaw, IN, USA), used in 17 studies and 54.2% of all cases, followed by the DM Novae cemented cup (Serf©, Décines-Charpieux, France) (7 studies, 14.2%) (Tables 2 and 3).

Complications and Cup Survival Rate
The overall dislocation rate from 51 studies was 3.1%. The systematic review reported 7 cases of IPD, in four different studies. The overall IPD rate is 0.2%. The most frequent postoperative complications were periprosthetic infections (3%); aseptic loosening (1.3%) and mechanical failure (0.5%). A total of 138 revisions are reported (revision rate of 4%), in 48 studies reporting data eligible for the study. The average survival rate of the DMC at the last follow-up was evaluated in 43 studies (76.8%). At 45.9 months follow-up, the overall survival rate was 93.5% (range 83.1-100) ( Table 4).

Functional Outcomes
The preoperative level of function was assessed with the HHS in 22 studies (59.3%). The mean preoperative HHS value was on average 43. The mean postoperative HHS value, evaluated in 34 studies (60.7%), was 76.7 ( Table 5). The mean pre-operative PMA was 10.4 in 10 studies (17.9%). Instead, the post-operative PMA was 14.7, in 14 studies (25%) ( Table 5).

Cemented Dual Mobility Cups in the Primary Setting
C-DMCs were used in 25.5% of cases as the primary setting, in 19 different studies (33.9%). In 40.5% of those cases, C-DMCs were used for the treatment of FNF, in 27.9% of cases as a treatment of OA complex cases, in 25.2% of cases as a treatment of pathological lesions (all cases of peri-acetabular metastasis cases except one case of pathological femur fracture) [59].
Finally, in 6.4% of the cases, a C-DMC was used in the treatment of acetabular fractures (Table 6).

Cemented Dual Mobility Cups in the Revision Setting
In 74.5% of cases, a C-DMC was used in the revision setting, such as the revision of previous THA or fixation failures. The use of C-DMC in revision cases was described in 42 studies (75%) ( Table 7).

Acetabular Reinforcement
In most cases (57.5%), the C-DMCs were used without acetabular reinforcement, cementing the acetabular component directly on the bone resulting in a low loosening rate and good cup survivorship, between 93 and 100% at the last followup (Table 8).
In 39.6% of the total cases, in 30 studies, a DMC was cemented into an acetabular reinforcement.
The most common AR used were the Kerboull cross-plates and Burch-Schneider Cage (Table 9).

Cup-in-Cup Technique
DMC was cemented into a pre-existing cup following the "cup-in-cup" technique, in 106 cases (3.1%) ( Table 3). In all cases, this procedure was used as a revision setting after the failure of a previous THA (Table 10).

Acetabular Bone Grafting
In the current study, the use of bone grafting was observed in 22 (39.3%) manuscripts. Overall, acetabular bone grafting has been used in 16.3% of C-DMC. In most cases, it was an allograft (93.2%), while in a minor part it was a synthetic graft (4.9%) or autograft (1.9%).

Discussion
This review allowed us to appreciate the satisfactory results of C-DMC. Dislocation rates found are low and the survivorship of the implants in both primary and revision surgery is satisfactory. Clinically, the improvement of the functional outcomes is significant, and radiologically, RLLs are rare.

Cemented Dual Mobility Cup in the Setting of Primary Surgery
In the present study, was observed the use of C-DMC in a primary setting in about a quarter of the surgeries (25.5%). C-DMC is an established treatment of hip OA, especially in association with other comorbidities that could increase the risk of dislocation and loosening, such as acetabular deficiency, abductor deficiency, prior acetabular fracture fixation or high-demanding physical activity patients [32].
Tabori-Jensen et al. [61] in a randomized controlled study in elderly osteoarthrosis patients with 2 years' follow-up comparing cementless DMC with C-DMC have demonstrated that cemented fixation of the Avantage DMC seems safer in elderly patients, with less implant migration.
Moreover, C-DMC represents an option in the management of FNF. In those cases, Tarasevicius et al. [15] reported a 100% survival rate one year after treatment of 42 patients with C-DMC. Lamo-Espinosa et al. [67], in a series of 69 elderly (>75 years) and frail patients with a high risk of instability with a median follow-up time of 49.04 months, reported only one case of revision due to aseptic loosening.
Another well-recognized use of C-DMC is in cases of pathological fractures. Lavignac et al. [58] used DMC in the treatment of peri-acetabular metastasis, but although the rate of complications and revisions is low, the mean patient survivorship was 19.5 months due to the progression of the primary disease. Similarly, Wegrzyn et al. [46], in a continuous series of 131 cases of periacetabular metastatic disease treated using a DMC cemented into an acetabular reinforcement device, observed an improvement in the postoperative functional outcome and pain relief, no mechanical failure or aseptic loosening of the acetabular reconstruction and a dislocation rate of 2%.
Finally, in some cases of acetabular fractures, C-DMC could be used. In those cases, it is associated with the combined treatment of fracture reduction and fixation. As reported by Giunta et al. [38], primary C-DMC for acetabular fracture in the elderly population might be a good therapeutic option that allows a return to previous daily life activity. Lannes et al. [57] found that DMC combined with internal fixation, also known as the combined hip procedure (CHP), could be an efficient procedure in selected elderly patients, with a lower level of revision rate compared to the ORIF group alone. In the CHP group, internal fixation was performed before the hip replacement. When the anterior column was involved, a suprapectineal quadrilateral buttress plate was used through a modified Stoppa approach; otherwise, a Kocher-Langenbeck approach was performed with a posterior column or wall osteosynthesis [81,82].
These findings are important and demonstrate that primary surgery with C-DMC is an excellent treatment in complex cases of OA, FNF, acetabular fractures or periacetabular metastases in terms of survival and reduced number of complications.

Cemented Dual Mobility Cup in the Setting of Revision Surgery
As demonstrated by the results of the study, the most frequent use of C-DMC is in revision settings (74.5%).
In cases of failure of a previous THA, C-DMC has shown an excellent role in avoiding further failures and reducing the number of complications. In fact, from the Swedish Hip Arthroplasty Register, Hailer, et al. [18] revealed in a series of 228 patients that DMCs for revision due to instability are associated with a low rate (8%) of re-revisions due to dislocation.
In patients with first-time revision hip arthroplasty due to dislocation, Mohaddes et al. [31] found better short to mid-term implant survival for C-DMC compared with cemented polyethylene cups at four years of follow-up. Stucinskas et al. [44], from the Lithuanian arthroplasty register, observed a significantly lower short-term re-revision rate for dislocations at five-year follow-up, in patients treated with C-DMC (2%) compared to different surgical concepts (9%) when used for first-time hip revisions due to recurrent dislocations.
As emerges from the results of the current review, C-DMC is a valid option in a revision setting with a dislocation rate of 3% and a survival rate of approximately 95% (with a mean follow-up of 49.6 months).

Cemented Dual Mobility Cup into an Acetabular Reinforcement
In the present study, DMC was cemented in an acetabular reinforcement in the revision setting in 83.6%, while in the primary setting only in 16.4% of the cases.
Neri et al. [74] suggested the use of DMC cemented into a reinforcement cage (Kerboull cross-plate or custom reinforcement cage) in cases of acetabular defects 2C or more according to Paprosky's classification. In a single-center continuous series of 62 patients, Lebeau et al. [30] evidenced that DMC cemented into an acetabular reinforcement at a minimum FU of five years presented good outcomes (PMA 14, HHS score 73) and only 2 cases of dislocation, while Brüggemann et al. [35], in a case series of 69 patients, demonstrated a 4-year survival of 96% and only one case of dislocation.

Cemented Dual Mobility Cup into a Pre-Existing Cup
Among the studies, a minor part (3.2%) of the DMCs was cemented into a pre-existing cup following the surgical technique described by Blumenfeld [83], known as the "Cupin-cup" technique. This technique, developed for the treatment of acetabular defects, in the current study showed good results in terms of fewer complications and guaranteed a survival rate of 93.6% at a mean follow-up of 35.7 months (Table 10).

Bone Grafting
In the current study, the use of bone grafting was observed in 16.3% of C-DMC. In most cases, bone grafting was used in a revision setting, in combination with acetabular reinforcement, using an allograft. Bone grafting could help the surgeon in cases of loss of acetabular bone stock and unstable components fixation and can be easily combined with cemented fixation of the DMC [84].

C-DMC Complications and Outcomes
In the current review, the overall dislocation rate was 2.9%, and at 45.9 months followup, the overall survival rate was 93.5%. These data are similar to the mean rates of dislocation and medium-term survival of single-mobility THA or cementless DMC [25,85,86]. These results must be considered even more due to the use of the C-DMC especially in complex cases or in revision settings.
The overall IPD rate was 0.2%. First described in 2004 by Lecuire [87], intra-prosthetic dislocation (IPD) is a specific complication of DMC. IPD is defined as excessive "wear" of the head-liner interface which induces the separation of the head from the polyethylene, but the present systematic review reported only 7 cases of IPD, showing that this complication is now extremely rare.
Overall, C-DMC demonstrates to be a valid treatment in primary complex cases, such as in revision settings, in terms of survival and reduced number of complications.
The greatest strength of the article is to represent the only systematic review specifically focused on the C-DMC present in the literature. Moreover, over three thousand C-DMCs are considered in the systematic review. Limitations of the study are represented by the low average level of evidence, most of the studies have a level IV of evidence. Furthermore, the nature of the inclusion criteria may have minimally altered the results, due to the wide heterogeneity of the patients included. However, it is assumed that in such a large case series, this possible bias could be minimized.

Conclusions
The use of C-DMCs is an option used mainly in THA revision surgery, although it also exists in a primary setting. It represents an effective treatment option with good clinical outcomes. The complication rate remains moderate, with a low rate of dislocation in both primary and revision surgery. The loosening and revision rates are also low. These results can be observed whether the implant is cemented directly into the bone or cemented in acetabular reinforcement or a previous well-fixed cup. An acetabular reinforcement was used in almost 40% of cases."

Data Availability Statement:
The authors confirm that the data supporting the findings of this study are available within the article.