Outcomes of Dual Mobility Bearings in Revision Total Hip Replacements

Background Dual mobility bearings have gained attention in the prevention of instability in revision total hip replacement. This study aimed to evaluate the use of dual mobility bearings in revision total hip replacement. The primary outcome was the rate of dislocation. Secondary outcomes included the rate of re-operation for any reason, surgical complications, serious medical adverse events, and 90-day mortality rate. Methods A single-centre case series of 55 consecutive operations in 49 patients who underwent revision total hip replacement using dual mobility bearings with a minimum follow-up of three months was studied. Results Early dislocation occurred in one case (2%), and there were no intra-prosthetic dislocations at a mean follow-up of 16 months. The rate of re-operation for any reason was 6/55 (11%) cases, and the post-operative infection rate was 2/55 (4%) cases. Serious medical adverse events occurred in 2/55 (4%) cases. The 90-day mortality rate was 1/55 (2%) cases. Two cases (2%) had cup abduction or anteversion angles outside of the safe zones although there were no dislocations in these patients. Conclusion This case series demonstrates a low dislocation rate in the early post-operative period for dual mobility bearings in revision total hip replacement. Dual mobility bearings show promise as an early low dislocation implant in revision total hip replacement. It remains to be determined whether dual mobility bearings are low-wear implants in the long term.


Introduction
Total hip replacement is the most commonly performed adult reconstructive hip procedure, with nearly one million performed worldwide each year [1].Increasing life expectancy has increased the number of procedures and consequently increased the requirement for revision total hip replacement surgery [2].Over the last five years, the most common reasons for revision total hip replacement surgery were aseptic loosening, dislocation/subluxation, periprosthetic fracture, infection, and adverse soft tissue reaction to particulate debris [3].
Instability after a total hip replacement remains a significant cause of readmission and revision surgery [4,5].The rate of instability after revision total hip replacement surgery has been reported to be as high as 9.8-25% [3,[6][7][8].The need for subsequent re-revision surgery is strongly associated with the time to the first revision, with 19.6% of total hip replacements revised within a year of primary surgery requiring re-revision within 10 years [3].Techniques to treat instability in revision total hip replacement include modular component upsizing (increasing femoral head size), increasing femoral offset, use of constrained cups, and correcting component malposition [9].
Dual mobility bearings have gained attention in the prevention of instability in revision total hip replacement.They consist of a smaller-diameter femoral head that articulates with a larger-diameter polyethylene liner, which in turn articulates with an acetabular component (Figure 1).This design increases the jump distance and impingement free range of movement.Reported outcomes of several studies using dual mobility bearings in revision total hip replacement support their effectiveness [10].The rate of dislocation after revision surgery using dual mobility bearings has been reported to be as low as 0-3.5% [11].Polyethylene wear was a significant problem for first-generation dual mobility bearings [12].This problem appears to have lessened over the short and medium term through improved polyethylene fabrication, use of thinner and smoother trunnions, chamfered rims, and eccentric centres of insert and shell rotation [13][14][15].Intra-prosthetic dislocation is an additional complication specific to dual mobility bearings and is characterised by dislocation of the outer polyethylene bearing surface from the inner femoral head, resulting in articulation between the inner femoral head and acetabular liner [16,17].
This study aimed to evaluate the use of dual mobility bearings in revision total hip replacement.The primary outcome was the rate of dislocation.Secondary outcome measures included the rate of re-operation for any reason, surgical complications, serious medical adverse events, and 90-day mortality rate.

Materials And Methods
A retrospective single-centre case series of 55 consecutive operations in 49 patients who underwent revision total hip replacement using dual mobility bearings was studied.Patients underwent surgery between 2019 and 2022.Inclusion criteria were patients undergoing revision total hip replacement with the use of dual mobility bearings with a minimum follow-up of three months.
Data was collected retrospectively using the Electronic Patient Record Systems and Centricity Picture Archiving and Communications Systems (PACS).Data collected included age, sex, body mass index, date of primary surgery and type of implant, any previous revision surgery, the indication for revision surgery and type of implant, peri-operative length of stay, blood transfusion requirement, requirement for critical care admission, and medical and surgical complications.A serious medical adverse event was defined as an untoward medical occurrence that resulted in prolonged hospitalisation or persistent or significant disability.Data was inputted and analysed using Microsoft Excel (Version 16.16.27).
Radiographic cup abduction and anteversion angles were measured using PACS on post-operative radiographs.The cup abduction angle was calculated as the angle formed by the intersection of a line passing through the inferior aspect of the radiographic teardrops and a line tangential to the rim of the cup on pelvic anteroposterior radiographs [18].The cup anteversion angle was calculated as the angle between a line touching the opening surface of the acetabular component and a line perpendicularly drawn to the table on cross-table lateral hip radiographs (Woo and Morrey method) [19].Acceptable ranges were defined as an inclination of 30-45 degrees and an anteversion of 5-25 degrees [20,21].
Patients undergoing elective surgery attended a pre-operative assessment clinic for pre-surgery optimisation.During surgery, patients were positioned in a lateral decubitus position, and a posterior approach to the hip was used.Patient preoperative skin preparation was performed using ChloraPrep (Becton, Dickinson).Repair of the capsule, short external rotators, and fascia was performed using a size 2 Vicryl suture (Ethicon).Skin closure was performed using size 3-0 Monocryl suture (Ethicon) (39/55), surgical skin staples (Medtronic) (15/55), and 3-0 Ethilon suture (Ethicon) (1/55).Revision procedures were performed by a fellowship-trained consultant orthopaedic surgeon specialising in revision hip surgery using a standard surgical technique.Patients received peri-operative antibiotic prophylaxis and post-operative venous thromboembolism prophylaxis.
The case series has been reported in line with the Preferred Reporting Of CasESeries in Surgery (PROCESS) Guideline [22].

Results
The case series was composed of 23 men and 26 women with a mean age of 78 years (53-93 years) (Table 1).
The mean body mass index was 27 kg/m 2 (17-51 kg/m 2 ).The mean follow-up duration was 16 months, and the median follow-up duration was 12 months (range: 3-36 months).There were no patients lost to followup.The mean time from the primary procedure to revision surgery was 10 years (one month to 32 years).
The mean radiographic cup abduction angle was 36 degrees (30-45 degrees), and the mean radiographic cup anteversion angle was 20 degrees (9-30 degrees) measured on post-operative radiographs (Figure 2 and Figure 3).Acceptable ranges of radiographic cup inclination angle were defined as abduction of 30-45 degrees and anteversion of 5-25 degrees [20,21].Two cases (4%) had cup angles outside of the safe zones (Table 1 and Figure 4).There were no dislocations in these patients.

FIGURE 2: Radiographic cup abduction angle measurement.
The cup abduction angle was calculated as the angle formed by the intersection of a line passing through the inferior aspect of the radiographic teardrops and a line tangential to the rim of the cup on pelvic anteroposterior radiographs.

FIGURE 3: Radiographic cup anteversion angle measurement.
The cup anteversion angle was calculated as the angle between a line touching the opening surface of the acetabular component and a line perpendicularly drawn to the table on cross-table lateral hip radiographs.This case series demonstrates a low dislocation rate in the early post-operative period.This data is comparable to published literature on dual mobility bearings in revision total hip replacements [7,11].A recent UK case series of revision total hip replacements using dual mobility bearings to treat recurrent instability demonstrated a re-dislocation rate of 0% in early-to mid-term follow-up [23].Similarly, the rate of dislocation in revision total hip replacement surgery has been reported as low as 3.5% with dual mobility bearings [11].A retrospective comparison of the dislocation rate following revision total hip replacement in obese patients found a dislocation rate of 15.6% with fixed implants compared with 0% with dual mobility bearings at one-year follow-up [24].A meta-analysis of level 3 and 4 studies found a significantly lower odds of dislocation in revision surgery with dual mobility bearings compared to fixed implants [25].Moreover, in a retrospective comparative study, dual mobility bearings had a significantly lower dislocation rate compared to large femoral heads in revision surgery [26].A recent systematic review of studies involving dual mobility bearings in revision total hip replacement demonstrated an overall dislocation rate of 2.2% with dual mobility bearings versus 7.1% in the control group at a mean follow-up of 4.1 years [27].
Limitations of this study include its lack of long-term follow-up.Nonetheless, it has been reported that the majority of dislocations after revision total hip replacement occur within three months of surgery [28].Polyethylene wear was a significant problem for first-generation dual mobility bearings, but newergeneration designs seem to have improved this issue over the short and medium term [12][13][14][15].A recent systematic review of comparative studies concerning dual mobility bearings in primary and revision total hip replacement demonstrated excellent mid-term survivorship [27].A meta-analysis of studies from five national joint registries demonstrated dual mobility construct all-cause survivorship of 97.8% at five years and 96.3% at 10 years [29].It remains to be determined whether dual mobility bearings are low-wear implants in the long term.
This case series includes a range of indications for revision total hip replacement surgery.Revision surgery performed ranged from isolated acetabular component revision to total femoral replacement.Thus, the study results may be applicable to a broad population and may have good generalisability.This data is comparable to published literature regarding indications for revision total hip replacements.A retrospective study of 38,377 revision total hip replacements demonstrated that dislocation was the most common indication for revision surgery, followed by infection and aseptic loosening [30].

Conclusions
This case series demonstrates a low dislocation rate in the early post-operative period for dual mobility bearings in revision total hip replacement.Based on current evidence, dual mobility bearings show promise as an early low dislocation implant in revision total hip replacement.However, further long-term follow-up data is needed to fully understand the effectiveness of dual mobility bearings in revision total hip replacement.

FIGURE 1 :
FIGURE 1: Diagram of a dual mobility bearing.

FIGURE 4 :
FIGURE 4: Scatterplot of radiographic cup abduction and anteversion angles for the 55 operations in this case series.