Low rate of dislocation of dual-mobility cups in primary total hip arthroplasty

Dual-mobility implants prevent hip dislocation following hip revision in obese patients

PURPOSE

Revision total hip arthroplasty (THA) is associated with increased rates of dislocation in obese patients. It is not known whether dual-mobility implants decrease dislocation in these patients with obesity.

METHODS

We retrospectively reviewed two groups of revision THAs to compare the dislocation rate between 32 obese patients (BMI >30 kg/m²) with standard cups, and 35 obese patients (BMI >30 kg/m²) with dual-mobility cups. All patients received the same implants except for diameter head (32-mm head with standard cups and 28-mm head with dual mobility) and had the same cemented stem that was not changed at revision. The patients were followed at routine intervals and were specifically queried about dislocation. The two groups were similar in terms of age, gender, causes of revision and follow-up since the primary arthroplasty.

RESULTS

With standard liners, more hips in obese patients dislocated than did hips in obese patients who received dual-mobility implants. The number of dislocations in standard hips was at one year follow-up 15.6 % (5 of 32) compared with 0 % in dual-mobility hips and was at five year follow-up 21.8 % (7 of 32) compared with 2.8 % (1 of 35). After a mean follow-up of seven years no cases of loosening were found. Five patients in the obese group with a standard liner underwent re-revision surgery, the additional re-operations being necessary to treat recurrent postoperative dislocation.

CONCLUSIONS

Obese patients should be counselled about the important risk of dislocation that occurs with standard liners after revision THA. Dual-mobility liners in these patients with hip revision is an efficient technique to prevent post-operative hip dislocation.

Dual-mobility or Constrained Liners Are More Effective Than Preoperative Bariatric Surgery in Prevention of THA Dislocation

BACKGROUND

Obesity is associated with an increased risk of dislocation after total hip arthroplasty (THA). However, in patients with obesity, it is not known whether the risk is only in the early postoperative period or whether it persists several years after surgery, and whether having bariatric surgery before undergoing THA and/or receiving a specific device (such as a dual-mobility or constrained acetabular liner) is more effective in terms of decreasing the risk of dislocation.

QUESTION/PURPOSES

(1) What is the cumulative risk of dislocation in patients with obesity after THA in the absence of a dual-mobility or constrained liner, and is this related to component positioning? (2) Does bariatric surgery before undergoing THA decrease dislocation risk in patients with obesity? (3) Are dual-mobility and constrained liners efficient in preventing dislocation in patients with obesity?

METHODS

At our university-based practice, all surgeons adhered to the following treatment approaches: Before 2000 no dual-mobility implants or constrained liners were used for primary THAs. Between 2000 and 2008, all patients whose body mass index (BMI) was greater than 30 kg/m(2) received dual-mobility liners (or constrained liners), except when they had previously had bariatric surgery. After 2008, all patients with BMIs over 30 kg/m(2) as well as those patients who were previously treated with bariatric surgery (regardless of BMI at the time of the index THA) received dual-mobility or constrained liners. This case-control study compared the dislocation percentage between 215 hips in nonobese patients (BMI ≤ 30 kg/m(2)), 215 hips in patients with obesity (BMI > 30 kg/m(2)) who received standard cups, 85 hips in patients with bariatric surgery before THA using standard cups (with reduction to a BMI < 30 kg/m(2)), and 155 hips in patients with obesity who received dual-mobility (when younger than 70 years) or constrained liners (when older than 70 years). All patients received the same implants except for different femoral head diameters (32-mm head with standard cups and 28-mm head with dual-mobility or constrained liners). The patients were followed at routine intervals and were specifically queried about dislocation. All the 670 hips had a minimum followup of 5 years with a mean followup of 14 years (range 5-25 years). At the most recent followup, 101 (15%) hips were lost to followup (respectively, 36 of 215, 34 of 215, five of 85, 24 of 155), which is the same ratio as observed among the underlying populations from which the patients were drawn.

RESULTS

With standard liners, more hips in patients with BMI > 30 kg/m(2) dislocated than did hips in nonobese (BMI < 30 kg/m(2)) patients. The cumulative number of dislocations (first time without recurrent dislocation) was 6% (13 of 215) at 1-year followup in obese patients compared with 2% (four of 215) in nonobese patients (odds ratio [OR], 3.4; 95% confidence interval [CI] 1.09-10.58; p = 0.03) and was 13% (28 of 215) at 15 years followup compared with 4% (eight of 215) in nonobese patients (OR, 3.9; 95% CI 1.72-8.71; p = 0.001). When bariatric surgery was performed before THA, BMI declined from 42 kg/m(2) to 28 kg/m(2), but with the same standard liners, more hips after bariatric surgery dislocated at 1-year followup than did hips in patients with obesity without preoperative bariatric surgery (13% [11 of 85] compared with 6% [13 of 215]; OR, 0.43; 95% CI 0.18-1.01; p = 0.05). Dual-mobility or constrained implants decreased the risk of dislocation, and fewer hips in patients with obesity with dual-mobility or constrained liners at 7 years followup had dislocated than did hips with standard liners (2% [three of 155] compared with 9% [20 of 215]; OR, 0.19; 95% CI 0.05-0.66; p = 0.01) bringing this number in line with the number observed in nonobese subjects with standard cups.

CONCLUSIONS

With standard liners, the risk of dislocation is increased in patients with obesity. Preoperative decrease of BMI (with bariatric surgery) in patients with obesity did not prevent the risk of dislocation with standard liners. Use of dual-mobility or constrained liners in these patients is an effective technique to reduce the risk of postoperative hip dislocation. However, we do not yet know the full risks of loosening of dual-mobility and constrained liners in this obese population.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Midterm Survivorship of the Lefèvre Constrained Liner: A Consecutive Multisurgeon Series of 166 Cases

BACKGROUND

Constrained liners are used as part of a salvage procedure to provide stability for patients at high risk for dislocation after a total hip arthroplasty. However, no recent studies exist highlighting their effectiveness and/or limitations.

METHOD

This prospective review included 166 consecutive hip arthroplasties, either primary (27%) or revision (73%), with a unique design of a constrained liner: Lefèvre retentive cup. There were 113 females (69%), and the average age at index surgery was 75.9 years (range, 35-94). The mean follow-up was 6.2 years (range, 0.3-11).

RESULTS

Twenty patients had a reoperation; 10 for infection (4 acute and 6 chronic joint infection) and 10 for cup failure (5 fixation failure, 3 aseptic loosening, and 2 dislocation). Ten-year survivals for cup revision were 89% (CI, 83-94) and 92% (CI, 89-97) for all revision and revision for noninfectious reasons, respectively. When solely evaluating for dislocation, the survival at 10 years was 99% (CI, 97-100). Considering primary and revision cases, 10-year survivals cup revision for aseptic reasons were 92.4% (CI, 84-100) and 92.5% (CI, 87-98), respectively.

CONCLUSIONS

The Lefèvre retentive cup demonstrated excellent 10-year's survivorship. With the rate of aseptic loosening around 2% and a dislocation rate around 1%, the cup is as effective as other available devices and is therefore a cost-effective tool to reduce the risk of dislocation in at-risk patients undergoing hip arthroplasty.

Dual-Mobility Articulations for Patients at High Risk for Dislocation

BACKGROUND

The purpose of this study was to evaluate the performance of dual-mobility articulations in patients at high risk for dislocation after revision total hip arthroplasty.

METHODS

We reviewed the results of 36 consecutive revision total hip arthroplasties performed on patients considered high risk for instability. Indications for inclusion included abductor insufficiency, recurrent instability, failure of constrained liner, or inadequate intraoperative stability when trialing.

RESULTS

At a minimum of 2 years, there were 4 (11.1%) repeat revisions including both dual-mobility liners that were cemented into an acetabular shell and 2 for deep infection treated with a 2-stage exchange. There was one dislocation that was successfully closed reduced but no revisions for recurrent instability. The mean Harris hip score improved from 45 to 90 points (P < .001).

CONCLUSION

Dual-mobility articulations are associated with a low rate of failure with no revisions for instability in this challenging group of patients.

Assessment of Damage on a Dual Mobility Acetabular System

BACKGROUND

Dual mobility designs were introduced to increase stability and reduce the risk of dislocation, both being common reasons for surgical revision after total hip arthroplasty. The in vivo behavior of dual mobility constructs remains unclear, and to our knowledge, no data have been published describing in vivo surface damage to the polyethylene bearing surfaces.

METHODS

We used surface damage assessed on the inner and outer polyethylene bearing surfaces in 33 short-term retrieved dual mobility liners as evidence of relative motion at the 2 bearings. A lever out test was performed to determine the force required for dislocation of the cobalt-chromium femoral head from the polyethylene liner.

RESULTS

Both bearings showed damage; however, the inner polyethylene bearings had higher damage scores, lower prevalence of remaining machining marks, and higher incidence of concentric wear, all consistent with more motion at the inner polyethylene bearing. The inner polyethylene bearings also had a higher occurrence of embedded titanium debris. The damage sustained in vivo was insufficient to lead to intraprosthetic dislocation in any of the retrieved components. Lever out tests of 12 retrievals had a mean dislocation load of 261 ± 52 N, which was unrelated to the length of implantation.

CONCLUSION

Our short-term retrieval data of 33 highly cross-linked polyethylene dual mobility components suggest that although motion occurs at both bearing articulations, the motion of the femoral head against the inner polyethylene bearing dominates. Although damage was not severe enough to lead to intraprosthetic dislocation, failure may occur long term and should be assessed in future studies.

Late Anterior Dislocation Due to Posterior Pelvic Tilt in Total Hip Arthroplasty

Background:

Excessive pelvic tilt may be one of the factors leading to instability in total hip arthroplasty (THA), even when the acetabular cup is placed properly. To our knowledge, only a few studies have described late anterior dislocation due to posterior pelvic tilt. We present 3 cases with late anterior dislocations possibly due to posterior pelvic tilt.

Cases Presentations:

Case-1: An 84-years-old woman fell and presented with an anterior dislocation 12-years after THA. Her pelvis had tilted to approximately 30° posteriorly in a supine position. After conservative treatment, she presented with 10 recurrent anterior dislocations. She had thoracolumbar kyphosis due to multiple compression fractures. Revision with anterior placement of an elevated liner and a 32-mm head corrected the dislocation, and no further dislocations occurred.

Case-2: A 78-years-old woman fell and presented with an anterior dislocation 4-years after THA. Her posterior pelvic tilt had increased 23° due to a lumbar compression fracture. Revision by decreasing the cup anteversion was performed, but recurrent posterior dislocations occurred. Owing to her worsened general condition, further treatment was abandoned.

Case-3: A 79-years-old woman twisted her body and presented an anterior dislocation 3-years after THA. After manual reduction and conservative treatment, the dislocation recurred. Her posterior pelvic tilt had increased 16°.

Conclusion:

Although minor trauma triggered the anterior instability in these patients, the underlying pathomechanism existed in the progressive pelvic posterior tilt due to thoracolumbar kyphosis. As longer life expectancy as well as implant survivorship is predicted, attention must be paid to the change of pelvic tilt in elderly patients.

Do Dual-Mobility Cups Reduce the Risk of Dislocation in Total Hip Arthroplasty for Fractured Neck of Femur in Patients Aged Older Than 75 Years?

BACKGROUND

Total hip arthroplasty (THA) for intracapsular neck of femur (NOF) fracture remains debatable as it is associated with higher rates of dislocation, notably in the older part of the population. We hypothesized this risk could be limited using dual-mobility cups (DMCs).

METHODS

Eighty-two patients (83 hips) aged older than 75 years underwent DMC-THA using a posterolateral approach for an intracapsular NOF fracture.

RESULTS

Clinical data were collected in 45 patients at a mean of 23.8 ± 9.4 months (12.1-42 months). The mortality rates were 19% (16 patients) and 36.5% (30 patients) at 1 year postoperatively and at the last follow-up, respectively. Postoperatively, there were 2 dislocations of the large articulation (4.4%) and one intraprosthetic dislocation (2.2%), all related to technical errors. Functional results were rated at least good in 71% cases, whereas the Parker and Devane scores were stable, indicating optimal restoration of autonomy and physical activity.

CONCLUSION

Although technically demanding, DMC-THA may prevent dislocation in intracapsular NOF fracture in elderly patients, while consistently limiting the risk of loss of independence.

The dual mobility cup: what problems does it solve?

Dual mobility cups have two points of articulation, one between the shell and the polyethylene (external bearing) and one between the polyethylene and the femoral head (internal bearing). Movement occurs at the inner bearing; the outer bearing only moves at extremes of movement. Dislocation after total hip arthroplasty (THA) is a cause of much morbidity and its treatment has significant cost implications. Dual mobility cups provide an increased range of movement and a may reduce the risk of dislocation. This paper reviews the use of these cups in THA, particularly where stability is an issue. Dual mobility cups may be of benefit in primary THA in patients at a high risk of dislocation, such as those who are older with increased comorbidities and a higher American Association of Anesthesiology grade and those with a neuromuscular disease. They may be used at revision surgery where the risk of dislocation is high, such as in patients with many prior dislocations, or those with abductor deficiency. They may also be used in THA for displaced fractures of the femoral neck, which has a notoriously high rate of dislocation.

Reducing the distal profile of dual mobility liners can mitigate soft-tissue impingement and liner entrapment without affecting mechanical performance

Soft-tissue impingement with dual mobility liners can cause anterior hip pain and intra-prosthetic dislocation. The hypothesis of this study was that reducing liner profile below the equator (contoured design) can mitigate soft-tissue impingement without compromising inner-head pull-out resistance and hip joint stability. The interaction of conventional and contoured liners with anterior soft tissues was evaluated in cadaver specimens via visual observation and fluoroscopic imaging. Resistance to inner-head pull-out was evaluated via finite element analyses, and hip joint stability was evaluated by rigid-body mechanics simulation of dislocation in two modes (A, B). Cadaveric experiments showed that distal portion of conventional liners impinge on anterior hip capsule and cause iliopsoas tenting at low flexion angles (≤30°). During hip extension, the rotation imparted to the liner from posterior engagement with femoral neck was impeded by anterior soft-tissue impingement. The iliopsoas tenting was significantly reduced with contoured liners (p ≤ 0.04). Additionally, the contoured and conventional liners had identical inner-head pull-out resistance (901 N vs. 909 N), jump distance (9.4 mm mode-A, 11.7 mm mode-B) and impingement-free range of motion (47° mode-A, 29° mode-B). Thus, soft-tissue impingement with conventional dual mobility liners may be mitigated by reducing liner profile below the equator, without affecting mechanical performance. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:889-897, 2016.

Salvage of Monoblock Metal-on-Metal Acetabular Components Using a Dual-Mobility Bearing

BACKGROUND

Large-diameter, monoblock acetabular components have been used for both hip resurfacing arthroplasty and metal-on-metal (MoM) total hip arthroplasty (THA). If revision is required, one solution is to retain the shell and use a dual-mobility bearing.

METHODS

We reviewed the results of 25 revision THAs including 11 hip resurfacing arthroplasty and 14 MoM THAs where a monoblock acetabular component was mated to a dual-mobility bearing.

RESULTS

At a mean of 29 months, there was one failure, an intraprosthetic dislocation of the dual-mobility bearing. There was a significant decrease in serum metal ion levels postoperatively.

CONCLUSION

Retention of a well-fixed, monoblock MoM acetabular shell and mating it to a dual-mobility bearing in the setting of revision surgery seems to be a reasonable, low-morbidity option at short-term follow-up in appropriately positioned cups.

A forty millimetre head significantly improves range of motion compared with a twenty eight millimetre head in total hip arthroplasty using a computed tomography-based navigation system

PURPOSE

Larger-diameter (≥40 mm) femoral heads decrease the incidence of post-operative dislocation in total hip arthroplasty (THA). This study was conducted to discover whether larger-diameter femoral heads result in greater range of motion of the hip with the use of a computed tomography (CT)-based navigation system.

METHODS

Thirty-nine primary THAs were performed via a posterolateral approach using a CT-based navigation system. The stem was inserted in the femur in line with the original femoral neck anteversion. Considering the range of motion during various daily activities which could occur without impingement, the cup anteversion was decided at 10 ° increments according to the stem anteversion. While the cup inclination was set at 40 ° in order to avoid a high inclination angle to prevent the edge roading between the HXLPE liner and ceramic head. After implantation, trial liners and femoral heads were used with either 28 or 40 mm diameter. Maximal hip flexion, extension, abduction, external rotation in extension at 0° and internal rotation angles in flexion at 90 ° were measured. The differences between the ranges of motion with the 40-mm and 28-mm heads were tested. The results were assessed with paired Student t-tests.

RESULTS

The ranges of motion in flexion, extension, abduction and internal rotation angles improved significantly with the 40-mm heads compared with the 28-mm heads. The ranges of motion of cases where maximal flexion angle was 90° or less were excluded, improved significantly with the 40 mm heads.

CONCLUSIONS

We concluded that the larger-diameter 40-mm femoral prosthetic heads result in greater ranges of motion in flexion, extension, abduction and internal rotation.

Is There a Benefit to Head Size Greater Than 36 mm in Total Hip Arthroplasty?

This study compares the rate of dislocation and revision for instability between 36-mm and anatomic femoral heads (large diameter metal-on-metal THA, dual-mobility bearings, and hip resurfacing arthroplasty) in patients at high risk for dislocation. A total of 501 high-risk patients, over a 10-year period, were identified (282 36-mm THA, 24 dual-mobility bearings, 83 metal-on-metal arthroplasty, and 112 hip resurfacing arthroplasty). There were 13 dislocations in the 36-mm group compared to 1 in the anatomic group (4.6% vs 0.5%; P = .005). Four patients dislocated more than once in the 36-mm group (1.4% vs 0%; P = .04), and 2 patients in the 36-mm group required a revision for instability (0.7% vs 0%; P = .11). These results suggest that anatomic head sizes significantly lower the risk of dislocation in high-risk patients.

Can cemented dual-mobility cups be used without a reinforcement device in cases of mild acetabular bone stock alteration in total hip arthroplasty?

INTRODUCTION

Cemented versions of dual-mobility cups (DMCs), helpful in cases of bone stock alteration, are usually used in association with a reinforcement device. To simplify the intervention in elderly subjects or those with a poor bone stock, the cups can be cemented directly into the bone, but the long-term result remains uncertain. We conducted a retrospective study in this population so as to: (1) assess whether cemented fixation of a DMC without a reinforcement device leads to a higher loosening rate, (2) confirm its efficacy in preventing dislocations in subjects at high risk of instability, and (3) measure the functional results.

HYPOTHESIS

Cemented fixation of a DMC is reliable in cases of moderate alteration of bone stock.

MATERIAL AND METHODS

Sixty-four patients (66 hips) undergoing implantation of a cemented DMC (Saturne™) without a reinforcement device were included in this single-center retrospective study. Their mean age was 79.8 years (range, 40-95 years). The indications varied: hip osteoarthritis (30.3%), prosthesis revision (44.0%), and trauma (25.8%). The patients were evaluated radiologically and clinically at follow-up. The main evaluation criterion was the revision rate for aseptic loosening. Dislocations, the infection rate, and the Postel Merle d'Aubigné (PMA) score were noted.

RESULTS

At the mean follow-up of 4.2 years, three (4.6%) patients had been lost to follow-up and 22 (33.3%) had died. There was one case of aseptic loosening (1.5%). Cup survival was 98% at 5 years (95%CI [94-100]). There were no dislocations. There was one revision for infection. The mean PMA score was 15.5 (range, 9-18).

DISCUSSION

The frequency of acetabular loosening was comparable to the frequency in cemented DMCs with a reinforcement device. A cemented DMC without a reinforcement device is possible and is a simple and viable option when there is moderate bone stock alteration.

LEVEL OF EVIDENCE

IV, retrospective cohort study.

Intra-prosthetic dislocation of dual-mobility cups after total hip arthroplasty: potential causes from a clinical and biomechanical perspective

INTRODUCTION

Recurrent dislocation of total hip arthroplasty is a frequent indication for revision surgery. Hip joint stability depends on implant design, cup position and crucially on femoral head diameter. Due to an effective ultra-large diameter femoral head, dual-mobility cups are considered an attractive solution to prevent dislocation in unstable conditions. Although patients obviously benefit for many years in terms of mobility and pain, an increase of intra-prosthetic dislocation reports using dual-mobility cups has been recently observed. However, the failure mechanism of this implant-specific complication, which is characterized by the loss of the positive-locking between the femoral head and the mobile liner, is not yet completely understood.

METHODS

A comprehensive search was performed with the PubMed database and a search engine to overview this topic and to identify potential causes for this implant-specific failure from a clinical and biomechanical perspective.

RESULTS

Peri-operative findings indicate extensive fibrosis at the large articulation as well as cup loosening as potential causes. In addition, current research has shown that the failure mechanism is affected by the surface topography of the femoral neck and in particular by the design of the mobile liner.

DISCUSSION

In clinical practice it is necessary to differentiate a classic dislocation between the mobile liner and the metallic shell from an intra-prosthetic dislocation between the femoral head and the liner.

CONCLUSION

Due to the increasing popularity of dual-mobility cups in total hip arthroplasty, the understanding of which implant-specific features or tissue response may increase the risk of intra-prosthetic dislocation is of major importance for reduced revision rates by using optimized surgical techniques and implant designs.

Dual mobility cup in revision total hip arthroplasty: dislocation rate and survival after 5 years

BACKGROUND

Dislocation is a common complication of total hip arthroplasty (THA), particularly when performed as revision surgery. Dual mobility cups (DMCs) minimize the risk of instability when implanted during primary THA. However, their usefulness and survival in revision THA remain unclear. We therefore conducted a retrospective study to assess DMC stability and survival at a minimal follow-up period of 5years after revision THA.

HYPOTHESIS

The dislocation rate associated with DMCs for revision THA is similar to that seen after primary THA.

MATERIALS AND METHODS

Cup exchange with implantation of a DMC was performed in 71 patients (74 hips) between 2000 and 2007, for the following reasons: recurrent dislocation (n=22), aseptic loosening (n=38), and infection (n=14). The DMCs were cemented in 47 cases and cementless in 27 cases. The clinical variables (Merle d'Aubigné-Postel score and Harris Hip Score) and radiological findings were collected retrospectively from the medical records and compared with those obtained at the last follow-up visit.

RESULTS

Of the 74 cases, 2 were lost to follow-up. At last follow-up, the mean Merle d'Aubigné-Postel score was 15.2 (11-18) and the mean Harris Hip Score was 80.4 (51-98). Of the 8 failures, 2 (2/72, 2.7%) were related to mechanical factors (1 case each of aseptic loosening and dislocation) and 6 were changed because of infection (recurrent infection, n=4). Mechanical failure was not linked to a specific reason for revision THA. A radiolucent line was visible in 4 cases but this finding was not associated with clinical manifestations. When failure was defined as cup revision for any non-infectious complication, 5-year implant survival was 99% (95% confidence interval, 93-100%).

DISCUSSION

Use of a DMC in revision THA was associated with a slightly higher dislocation rate (1/72, 1.4%) than in primary THA, whereas 5-year survival was comparable. Cemented DMCs were not associated with a greater risk of loosening.

CONCLUSION

DMCs are useful to decrease the risk of dislocation in revision THA performed for any reason. The low rate of loosening indicates that DMCs do not result in high stresses at the bone-implant interface.

LEVEL OF EVIDENCE

IV, retrospective study.

Revision of Failed Hip Resurfacing and Large Metal-on-Metal Total Hip Arthroplasty Using Dual-Mobility Components

Revision of metal-on-metal (MoM) total hip arthroplasty (THA) or hip resurfacing is associated with high complication rates. The authors propose dual-mobility components as a surgical option and present short- to mid-term results of MoM hips revised with dual-mobility components. Eighteen consecutive hips that underwent revision of MoM THA or hip resurfacing using dual-mobility components were identified. At final follow-up (mean, 17.5 months), the visual analog scale, modified Harris Hip Score, and SF-12 scores had all improved (P<.05, P<.01, and P<.05, respectively). There were no dislocations or other complications. Revision of failed MoM THA or hip resurfacing using a dual-mobility device is an effective strategy.

Reconstruction with modular megaprostheses for sarcomas of the lower extremity

Limb-preserving surgery using modular megaprostheses for the reconstruction of large skeletal defects is currently the preferred treatment for sarcomas. The authors report the postoperative outcomes after skeletal resection for lower extremity sarcomas and the use of the METS cemented modular implant system (Stanmore Implants, Hertfordshire, United Kingdom) for reconstruction. They retrospectively studied 52 consecutive patients operated on from 2003 to 2012. There were 27 distal femur prostheses, 13 proximal femur, 11 proximal tibia, and 1 total femur implants. Patients were followed for a mean of 4.3 years. Overall patient survival, prosthesis survival, limb salvage rate, and secondary complications were documented. Five years postoperatively, prosthesis survival was 79%. Complications warranting implant revision surgery were documented in 15% of patients, whereas complications warranting surgery of any kind were observed in 27% of the patients. Nonmechanical complications, namely local relapse of the tumor and prosthetic infection, were the most common cause of prosthetic failure, accounting for 88% of major revision surgeries and 100% of amputations. Mechanical complications were rare, observed in only 6% of patients. No patients required secondary revision surgery. The limb salvage rate was 89%. Overall patient survival was 79% at 5 years and 71% at 10 years. The low risk for mechanical complications and the high limb salvage rate support the use of the METS modular megaprostheses for the reconstruction of skeletal defects following lower limb sarcoma surgery.

Can Dual Mobility Cups prevent Dislocation in All Situations After Revision Total Hip Arthroplasty?

The outcome of a single design of dual mobility cup was prospectively evaluated in a continuous series of 994 revision THAs with respect to dislocation and intra-prosthetic dislocation (IPD). At a 7.3-year mean follow-up, the dislocation rate was 1.5% and the IPD rate was 0.2%. The 2 IPD occurred in acetabular-only revisions and were related to a poor head-to-neck ratio with early impingement and wear at the polyethylene mobile component chamfer. Dual mobility cups demonstrated a low dislocation rate in revision THA but did not compensate for potential perioperative technical errors. In addition, IPD did not appear to be a concern with respect to the benefit in term of instability prevention though caution is advised in acetabular-only revision associated with a poor head-to-neck ratio.

LEVEL OF EVIDENCE

Therapeutic study-Level IV.

Intraprosthetic Dislocation of Dual-Mobility Bearings Associated with Closed Reduction

CASE

We present two patients with dual-mobility total hip arthroplasty components who underwent closed reduction of posterior dislocations with conscious sedation in the emergency room. Following closed reduction, both patients had immediate pain, clicking, and grinding of the hip. Radiographs identified intraprosthetic dislocation of the dual-mobility components, and revision surgery was required.

CONCLUSION

When dislocation of a dual-mobility bearing occurs, the surgeon should consider performing a careful closed reduction with muscle paralysis and use of fluoroscopic guidance in the operating room to avoid intraprosthetic dislocation.

Dual mobility bearings withstand loading from steeper cup-inclinations without substantial wear

Steep cup abduction angles with adverse joint loading may increase traditional polyethylene bearing wear in total hip arthroplasties. However, there have been few reports evaluating the effect of cup inclination on the wear of dual-mobility devices. In a hip joint simulation, we compared the short-term wear of two-sizes of modular highly cross-linked dual-mobility bearings (28 mm femoral head diameter/42 mm polyethylene insert outer diameter/54 mm acetabular shell diameter; 22.2 mm femoral head diameter/36 mm polyethylene insert outer diameter/48 mm acetabular shell diameter) at 50 and 65° of cup inclination with modular 28 mm femoral head on 54 mm cup diameter metal-on-highly cross-linked polyethylene bearings. Increasing inclination from 50-65° had no changes in volumetric wear of 28/42/54 mm (mean, 1.7 vs. 1.2 mm3 /million cycles, respectively; p = 0.50) and 22.2/36/48 mm (mean, 1.7 vs. 1.2 mm3/million cycles, respectively; p = 0.48) dual mobility bearings. At 65°, 22.2/36/48 mm dual-mobility bearings had lower volumetric loss (mean, 2.2 vs. 6.3 mm(3) ; p = 0.03) and wear rates (mean, 1.2 vs. 2.7 mm3/million cycles; p = 0.02) compared to metal-on-highly cross-linked polyethylene bearings. Modern-generation dual-mobility designs with highly cross-linked polyethylenes may potentially withstand edge-loading from steeper cup-inclinations without substantial decreases in wear.

Intraprosthetic dislocation of a contemporary dual-mobility design used during conversion THA

Although dual-mobility sockets have been in clinical use for decades in other parts of the world, they recently gained popularity in the United States as an option for primary and revision total hip arthroplasty (THA). Improvements in dual-mobility socket technology include articulation with a metal insert impacted into a metal shell and a femoral head made of highly cross-linked polyethylene. The results and complications associated with the use of dual-mobility sockets employing these technologic advancements are not known. Specifically, intraprosthetic dislocation is a well-known complication of these implants and has been reported extensively in the literature. To the authors' knowledge, its occurrence in a modern dual-mobility socket has not been reported. The authors report a case of early intraprosthetic dislocation of a contemporary dual-mobility design used to convert a patient to THA after failed fixation of intertrochanteric hip fracture. At retrieval, there was evidence that the outer bearing may have ceased moving, causing localized focal impingement of the implant neck on the retentive ring. The authors theorized that external hip impingement (pelvic against trochanter) and previous surgery that led to the formation of scar tissue could have caused the outer bearing surface to cease its motion. This ultimately led to impingement of the femoral component neck on the retentive ring, which led to the intraprosthetic dislocation. Dual-mobility cups provide an attractive option to decrease wear and improve stability. Further research is needed to establish the ideal construct design and materials.

Outcomes of dual-mobility acetabular cup for instability in primary and revision total hip arthroplasty

Background

The concept of a dual-mobility hip socket involves the standard femoral head component encased in a larger polyethylene liner, which in turn articulates inside a metal shell implanted in the native acetabulum. The aim of this study was to assess outcomes from using a Serf Novae^® Dual Mobility Acetabular cup (Orthodynamics Ltd, Gloucestershire, UK) to address the problem of instability in primary and revision total hip arthroplasty (THA).

Materials and methods

A retrospective review was carried out of all hip arthroplasties performed in a District General Hospital utilising the dual-mobility socket from January 2007 to December 2012. Clinical and radiological outcomes were analysed for 44 hips in 41 patients, comprising 20 primary and 24 revision THA. The average age of the study group was 70.8 years (range 56–84 years) for primary and 76.4 years (range 56–89 years) for revision arthroplasty. Among the primary THA, always performed for hip osteoarthritis or in presence of osteoarthritic changes, the reasons to choose a dual mobility cup were central nervous system problems such as Parkinson’s disease, stroke, dementia (10), hip fracture (5), failed hip fracture fixation (2), severe fixed hip deformity (2) and diffuse peripheral neuropathy (1). The indications for revisions were recurrent dislocation (17), aseptic loosening with abductor deficiency (4), failed hemiarthroplasty with abductor deficiency (2) and neglected dislocation (1).

Results

At a mean follow-up of 22 months (range 6–63 months), none of the hips had any dislocation, instability or infection and no further surgical intervention was required. Radiological assessment showed that one uncemented socket in a revision arthroplasty performed for recurrent dislocation had changed position, but was stable in the new position. The patient did not have complications from this and did not need any surgical intervention.

Conclusions

Even though postoperative hip stability depends on several factors other than design-related ones, our study shows promising early results for reducing the risk of instability in this challenging group of patients undergoing primary and revision hip arthroplasty.

Level of evidence

IV.

Dual mobility cups in total hip arthroplasty

Total hip arthroplasty (THA) is considered one of the most successful surgical procedures in orthopaedics. With the increase in the number of THAs performed in the world in the next decades, reducing or preventing medical and mechanical complications such as post-operative THA instability will be of paramount importance, particularly in an emerging health care environment based on quality control and patient outcome. Dual mobility acetabular component (also known as unconstrained tripolar implant) was introduced in France at the end of the 1970s as an alternative to standard sockets, to reduce the risk of THA dislocation in patients undergoing primary THA in France. Dual mobility cups have recently gained wider attention in the United States as an alternative option in the prevention and treatment of instability in both primary and revision THA and offer the benefit of increased stability without compromising clinical outcomes and implant longevity. In this article, we review the use of dual mobility cup in total hip arthroplasty in terms of its history, biomechanics, outcomes and complications based on more than 20 years of medical literature.

Dual mobility in total hip arthroplasty

Dual-mobility articulations have shown promising results. Postoperative instability remains the most common reason for revision of a total hip arthroplasty (THA). Dual-mobility cups have been shown to decrease the rate of dislocation in primary THA and have been used to treat and prevent instability in revision THA. Greater range of motion and a greater head-to-neck ratio and a greater jump distance are achieved, resulting in a lower risk of instability. Concerns with dual-mobility cups include wear and intraprosthetic dislocation. Specific design modifications have aimed to improve cup fixation and decrease polyethylene wear and the risks of intraprosthetic dislocation.

Evora® chromium-cobalt dual mobility socket: results at a minimum 10 years' follow-up

INTRODUCTION

The Evora chromium-cobalt alloy dual mobility socket claims to display a large articulation tribology different from that of stainless steel models, limiting the risk of intraprosthetic dislocation and wear. The present study reports a minimum of 10years' follow-up in a multicenter prospective series of 200 sockets previously reported on at 5years.

HYPOTHESIS

The use of chromium-cobalt in dual mobility sockets provides a low rate of failure at 10years, especially as regards to osteolysis and intraprosthetic dislocation.

MATERIALS AND METHODS

Two hundred hydroxyapatite-coated molded chromium-cobalt sockets without titanium interface were implanted without cement in 194 patients with a mean age of 70 years (range, 32-91 years). Clinical results were assessed on Postel Merle d'Aubigné and Harris scores, plain radiographs and survival analysis.

RESULTS

At a mean 11 years' follow-up (10-13 years), 56 patients had died and 31 were lost to follow-up. Four underwent surgical revision (3 femoral components, and 1 socket for migration at 9 years with complete disappearance of the hydroxyapatite). A total of 109 implants were analyzable in 107 patients with a mean age of 81 years (55-93 years). At follow-up, the mean Harris score was 90 (75-96) and the PMA score 16.3 (14-18). There were no cases of loosening (except for the case reoperated on at 9 years) and no acetabular radiolucency or cysts. There were 2 cases of non-evolutive femoral radiolucency and 10 of femoral granuloma, involving head size > 22 mm (P<0.0001) and a cemented titanium stem (P=0.004) as risk factors. There were no dislocations in the large or small articulation. Ten-year survival was 99% (95% CI: 97.3%-100%) with socket revision as censorship criterion.

DISCUSSION

The absence of dislocation in both small and large articulations confirmed the efficacy of the dual mobility concept and suggested an advantage for chromium-cobalt sockets in reducing the rate of intraprosthetic dislocation and preventing blockage of the large articulation by a better performance in the friction couple. Granulomas were associated with wear in cemented titanium stems and with heads greater than 22 mm in diameter. Ten-year survival was 99% (censorship criterion: revision for socket failure); there was, however, one case of socket loosening with disappearance of the hydroxyapatite, indicating that surveillance should be continued in this cohort.