Dual mobility in hip arthroplasty: What evidence do we need?

No dislocation and low complication rate for a modern dual mobility cup with pre-impacted femoral head in primary hip replacement: A consecutive series of 175 hips at minimum 5-year follow-up

INTRODUCTION

Despite its excellent results in preventing dislocation, the dual mobility cup (DMC) is still struggling to be adopted by some teams due to premature wear and loosening reported on first-generation implants. Therefore, this study aimed to assess the mid-term survivorship of a modern DMC with a pre-impacted head and the radio-clinical results at a minimum follow-up of 5 years.

METHODS

This was a retrospective single-centre study performed on patients who had a primary total hip replacement for osteoarthritis in 2016. The cup was a third-generation DMC with a pre-impacted femoral head. Clinical (harris hip score (HHS)) and radiological (cup abduction, anteversion, overhang, and radiolucent lines) results were recorded, as well as complications, particularly dislocations and survivorship. A minimum of five years of follow-ups was required.

RESULTS

One hundred and seventy-five hips (167 patients) met the inclusion criteria. Five hips (2.9%, 5/175) were lost to follow-up and excluded from the postoperative analysis. The mean follow-up period was 70 ± 2.9 months [63.6-76.5]. Three cups needed revision surgery (1.8%, 3/170): one for septic loosening, and two for chronic infection. At 77 months, the global survival probability was 98.2% ± 1, and the survival probability excluding septic aetiology was 100%. There was a significant improvement in the HHS from pre-operatively (48.3 ± 6.0 [14.0-70.0]) to post-operatively (96 ± 4.5 [50-100]) (p < 0.0001). There were no postoperative dislocations recorded, nor any iliopsoas-impingement or symptomatic cam-effect.

DISCUSSION

This study showed excellent survival and good radiological and clinical results of this dual mobility cup at a mid-term follow-up. None of the patients had dislocation or any specific complication feared with dual mobility cups.

Does the Dual Mobility Cup Reduce Dislocation After Primary Total Hip Arthroplasty in Elderly Patients at High Risk of Dislocation?

OBJECTIVE

The dual mobility cup (DMC) is designed to extend the longevity of the prosthesis by improving stability, enhancing the range of motion, and decreasing impingement without increasing wear. We hypothesized that DMC would reduce the risk of dislocation in elderly patients. This study aimed to investigate the clinical and radiographic outcomes of DMC-total hip arthroplasty (THA) in elderly patients at high risk of dislocation.

METHODS

From June 2016 to March 2020, 94 patients with a mean age of 77.7 years (97 hips) who underwent a posterolateral approach for DMC-THA in our department were followed up for at least one year. Preoperative and postoperative pelvic tilt angles (PTA) and DMC orientation were prospectively collected for all patients. Intraoperative and postoperative complications were recorded. A parametric test was used for normal distribution, and a non-parametric test was used for non-normal distribution.

RESULTS

Abduction and anteversion angles of the cup were 42.4 and 18.0° in the supine position immediately postoperative. The average PTA for patients in the supine and standing positions were 26.5 and 34.5°, respectively. When moving from the supine to the standing position, patients experienced a mean posterior pelvic tilt of 9°. No intraoperative acetabular-related complications were recorded. Postoperative complications included early infection in one patient (1.0%) and dislocation in one patient (1.0%).

CONCLUSION

Our study demonstrates that DMC-THA provides satisfactory short-term outcomes in elderly patients at a high risk of dislocation, regardless of the change in PTA resulting from postural transition.

The Incidence and Temporal Trends of Dislocation After the Use of Constrained Acetabular Components and Dual Mobility Implants in Primary Total Hip Replacements: A Systematic Review and Meta-Analysis of Longitudinal Observational Studies

BACKGROUND

Dislocation after a primary total hip replacement (pTHR) remains a common cause of treatment failure. Constrained acetabular components (CACs) and dual mobility implants (DMIs) may mitigate this in patients at high risk of dislocation or with significant intraoperative instability. This meta-analysis evaluated the incidence and temporal trends of dislocation after implantation with CACs and DMIs in pTHR.

METHODS

Longitudinal studies reporting dislocation after the use of CACs or DMIs in pTHR were sought from Medline and Embase to September 2020. Secondary outcomes included revision surgery for dislocation and for all causes.

RESULTS

A total of 46 studies (3 CAC and 43 DMI) comprising 582 CACs and 18,748 DMIs were included. The pooled incidence of dislocation was 1.08% (95% confidence interval [CI]: 0.00-3.72; range 0.27%-2.60%) over a weighted mean follow-up of 4.1 years for CACs, compared with 0.25% (95% CI: 0.08-0.46; range 0.00%-4.72%) over 6.2 years for DMIs. For DMIs, there was a temporal decline in dislocations from the 1980s onward, and dislocation rates remained low (<1%) until 15 years postoperatively. There were insufficient data for similar analysis of CACs. All studies were at high risk of bias. The incidence of revision for dislocation after CACs was 0.3% vs 0.1% for DMIs, and the incidence of revision for all causes after CACs was 4.8% vs 2.7% for DMIs.

CONCLUSION

DMIs demonstrated a lower incidence of dislocation compared with CACs; however, there was a relative absence of CACs used in the context of pTHR in the literature. Temporal trends in dislocation have improved over time for DMIs.

A 5-year follow-up of Girdlestone resection arthroplasty in hip infection continued by Total hip replacement: A case report

Introduction

Resection arthroplasty of the hip was already performed for recent 100 years. This kind of surgery has been used for a wide variety of hip problems such as infection, degenerative osteoarthritis and prosthetic joint infection. Total hip replacement is remarkable procedure in order to relieve pain and restore hip function. We present this report to describe our experience in treating hip infection by used two stages of surgery.

Case presentation

A 61-years old male suffered left hip infection that leads severe destruction on his joint. He felt badly pain on his hip with significant disability associated it such as limping, restriction of movements, and shortening of the limb. The hip movements were painful and caused walking in antalgic gait. Radiologic examination at that time revealed gross destruction of femoral head as well as acetabulum, irregular and hazy joint margins with diminished joint space. Patient was diagnosed with chronic non-specific inflammation of the hip joint.

Result

Two stages surgery were performed on this patient. Resection arthroplasty firstly performed in order to eradicate the infection completely and alleviate very bothersome pain for improvement of patient's quality of life. Two years later, after patient was ready for next stage mentally, cemented total hip replacement performed to achieve normal function of the hip. Five-years follow up functional outcome was performed. Patient was very satisfied with the result with Harris hip scores was 95.

Conclusion

Resection arthroplasty of the hip followed by a conversion to total hip replacement in hip infection case provide complete infection eradication, good functional outcome and satisfaction for the patient. Although the procedure was time-consuming it can be a choice if the eradication of infection still in a doubt.

Modular Dual Mobility Constructs Used for Recurrent Hip Instability

Background

Recurrent hip dislocation despite prior attempts at surgical stabilization is a dreadful and technically challenging complication. A modular dual mobility (MDM) articulation has shown promise in addressing this problem, which might seem intractable. Our purpose was to examine the outcomes of revision total hip arthroplasty (THA) with an MDM placed through a direct anterior (DA) approach when all other conservative and surgical treatments have failed.

Methods

Fifteen patients revised with an MDM for recurrent instability (RI) between 2012 and 2018 by a single surgeon at a single institution were reviewed retrospectively, with a minimum of two years' follow-up. All patients underwent full acetabular revision with an MDM articulation through a DA approach with intraoperative fluoroscopy. No stems were revised. Dislocations, complications, and clinical outcomes are reported.

Results 

All patients had recurrent posterior instability with a mean number of 4 ± 2 (range: 2 to 8) dislocations prior to MDM revision THA (MDM rTHA). Eight patients had already failed surgical intervention for instability, and seven had failed repeated closed reductions and conservative care. After MDM rTHA, there were no dislocations at a mean follow-up of 4 ± 1 years (range: 2 to 8). Similarly, there were no further revisions or reoperations. Postoperatively, the mean cup inclination improved to 45 ± 2 degrees (range: 41 to 48), and the mean anteversion improved to 20 ± 2 degrees (range: 17 to 23). All cups were well-positioned utilizing fluoroscopic guidance. The mean effective head size increased from 32 mm to 44 mm. The mean hip disability and osteoarthritis disability score (HOOS, Jr) was 73 ± 25% (range: 40 to 100).

Conclusion

Refractory hip instability in THA may be effectively managed with an MDM articulation, even when prior attempts at surgical stabilization have failed. Intraoperative imaging and a direct anterior approach may aid the challenges of implant positioning and achieving hip stability in a revision setting.

Dual Mobility hip replacement in hip fractures offer functional equivalence and a stability advantage - A case-controlled study

BACKGROUND

Hip fracture is a common and serious injury in the elderly. Hip arthroplasty is the most frequently performed procedure for patients with an  intracapsular hip fracture. The majority of national guidelines recommend total hip arthroplasty (THA) for more active patients. Literature indicates significant stability advantages for dual mobility (DM) acetabular components in non-emergent scenarios. Evidence supporting the use of DM in hip fracture patients is limited.

AIM

We set out to ascertain if DM implants offer stability and/or functional advantages over standard THA in patients with hip fracture.

METHODS

We utilised our local National Hip Fracture Database to identify all patients undergoing either a standard or DM THA for hip fracture (n=477) We matched cohorts based on age, AMTS, mobility status pre-operatively, gender, ASA and source of admission. Our primary outcome of interest was functional status using the oxford hip score (OHS). Secondary outcome measures included  dislocation, fracture and deep infection requiring further surgery.

RESULTS

62 patient pairs were available for this study. Mean OHS for DM THA was 41.5 and for standard THA this was 42.7 (p=0.58). There were 4 dislocations in the standard THA group and 0 with DM THA. No difference was seen with infection or peri-prosthetic fracture.

CONCLUSION

This study demonstrates functional equivalence between DM and standard THA. In addition it shows a trend towards less dislocation with DM THA. Cost savings from less instability may outweigh initial prosthesis costs. This study suggests a suitably powered RCT using instability as the primary outcome measure is indicated.

Spine Fusions, Yoga Instructors, and Hip Fractures: The Role of Dual Mobility in Primary Total Hip Arthroplasty

BACKGROUND

Despite the increased use of dual mobility (DM) in primary total hip arthroplasty (THA), debate exists regarding the indications for its use. No specific algorithm exists to guide this decision-making process. Therefore, the purpose of this article is to summarize the currently available literature regarding the use of DM in primary THA and provide evidence-based guidelines based on specific patient populations and risk factors for instability.

METHODS

We reviewed the current literature for studies evaluating risk factors for dislocation in primary THA, as well as the clinical use and results of DM in primary THA. Based on the strength of the literature, we discuss the use of DM in specific patient populations. We provide a decision-making algorithm to determine whether a patient may be indicated for DM in primary THA.

RESULTS

Surgeons should consider preoperative patient demographics, risk factors for instability (eg, significant hip-spine issues), type of procedure to be performed (eg, conversion arthroplasty), and indications for surgery (eg, THA for femoral neck fracture). Based on this algorithmic assessment, DM may be warranted in the primary THA setting if a patient's combined risk reaches an established threshold based on the literature.

CONCLUSION

This evidence-based algorithm may help guide current practice in the use of DM in primary THA. We advocate the continued judicious use of DM in hip arthroplasty. Longer term studies are needed in order to evaluate the durability of DM, as well as any complications related to the DM articulation.

Dual mobility total hip arthroplasty in the treatment of femoral neck fractures

AIMS

To evaluate the rate of dislocation following dual mobility total hip arthroplasty (DM-THA) in patients with displaced femoral neck fractures, and to compare rates of dislocation, surgical-site infection, reoperation, and one-year mortality between DM-THA and bipolar hemiarthroplasty (BHA).

METHODS

Studies were selected based on the following criteria: 1) study design (retrospective cohort studies, prospective cohort studies, retrospective comparative studies, prospective comparative studies, and randomized controlled studies (RCTs)); 2) study population (patients with femoral neck fracture); 3) intervention (DM-THA or BHA); and 4) outcomes (complications during postoperative follow-up and clinical results). Pooled meta-analysis was carried out to evaluate the dislocation rate after DM-THA and to compare outcomes between DM-THA and BHA.

RESULTS

A total of 17 studies (ten cohort studies on DM-THA and seven comparative studies of DM-THA and BHA) were selected. These studies included 2,793 patients (2,799 hips), made up of 2,263 DM-THA patients (2,269 hips) and 530 BHA patients (530 hips). In all, 16 studies were analyzed to evaluate dislocation rate after DM-THA. The cumulative dislocation rate was 4% (95% confidence interval (CI) 3 to 5). Seven studies were analyzed to compare the rates dislocation and surgical-site infection. The rate of dislocation was significantly lower in the DM-THA group than in the BHA group (risk ratio (RR) 0.3; 95% CI 0.17 to 0.53, p < 0.001, Z -4.11). There was no significant difference in the rate of surgical-site infection between the two groups (p = 0.580). Six studies reported all-cause reoperations. The rate of reoperation was significantly lower in the DM-THA group than in the BHA group (RR 0.5; 95% CI 0.32 to 0.78, p = 0.003, Z -3.01). Five studies reported one-year mortality. The mortality rate was significantly lower in the DM-THA group than in the BHA group (RR 0.58 95% CI 0.45 to 0.75, p < 0.0001, Z -4.2).

CONCLUSION

While the evidence available consisted mainly of non-randomized studies, DM-THA appeared to be a viable option for patients with displaced fractures of the femoral neck, with better reported rates of dislocation, reoperation, and mortality than BHA. Cite this article: Bone Joint J 2020;102-B(11):1457-1466.

Study protocol: The DUALITY trial-a register-based, randomized controlled trial to investigate dual mobility cups in hip fracture patients

Background and purpose - Physically and mentally fit patients with a displaced femoral neck fracture (FNF) are mostly treated with total hip arthroplasty (THA). Dislocation is a severe and frequent complication in this group, and dual mobility cups (DMC) were developed to reduce the risk of dislocation after THA. The DUALITY trial investigates whether the use of DMC in FNF patients treated with a THA reduces the risk of dislocation.Patients and methods - The trial is a national, multicenter, register-based, randomized controlled trial (rRCT). Patients ≥ 65 years with a non-pathological, displaced FNF (Type Garden 3-4/AO 31-B2 or B3) who are suitable for a THA according to local guidelines are assessed for eligibility using the web-based registration platform of the Swedish Fracture Register (SFR). 1,600 patients will be randomized 1:1 to either insertion of a DMC (intervention group) or a standard cup (control group). The study is pragmatic in that the choice of implant brands, surgical approach, and peri- and postoperative protocols follow the local routines of each participating unit. All outcome variables will be retrieved after linkage of the study cohort obtained from the SFR with the Swedish Hip Arthroplasty Register and the National Patient Register.Outcomes - The primary outcome is the occurrence of any dislocation of the index joint treated with closed or open reduction within 1 year after surgery, expressed as a relative risk when comparing groups, and a risk reduction of at least 45% is considered clinically relevant. Secondary outcomes are the relative risk of any reoperation of the index joint, periprosthetic joint infection, and mortality within 90 days and 1 year. Patient-reported outcomes and health economics are evaluated.Start of trial and estimated duration - The DUALITY trial started recruiting patients in January 2020 and will continue for approximately 5 years.Trial registration - The trial is registered at clinicaltrials.gov (NCT03909815; December 12, 2019).

Dual mobility total hip arthroplasty in the treatment of femoral neck fractures

Aims

To evaluate the rate of dislocation following dual mobility total hip arthroplasty (DM-THA) in patients with displaced femoral neck fractures, and to compare rates of dislocation, surgical-site infection, reoperation, and one-year mortality between DM-THA and bipolar hemiarthroplasty (BHA).

Methods

Studies were selected based on the following criteria: 1) study design (retrospective cohort studies, prospective cohort studies, retrospective comparative studies, prospective comparative studies, and randomized controlled studies (RCTs)); 2) study population (patients with femoral neck fracture); 3) intervention (DM-THA or BHA); and 4) outcomes (complications during postoperative follow-up and clinical results). Pooled meta-analysis was carried out to evaluate the dislocation rate after DM-THA and to compare outcomes between DM-THA and BHA.

Results

A total of 17 studies (ten cohort studies on DM-THA and seven comparative studies of DM-THA and BHA) were selected. These studies included 2,793 patients (2,799 hips), made up of 2,263 DM-THA patients (2,269 hips) and 530 BHA patients (530 hips). In all, 16 studies were analyzed to evaluate dislocation rate after DM-THA. The cumulative dislocation rate was 4% (95% confidence interval (CI) 3 to 5). Seven studies were analyzed to compare the rates dislocation and surgical-site infection. The rate of dislocation was significantly lower in the DM-THA group than in the BHA group (risk ratio (RR) 0.3; 95% CI 0.17 to 0.53, p < 0.001, Z −4.11). There was no significant difference in the rate of surgical-site infection between the two groups (p = 0.580). Six studies reported all-cause reoperations. The rate of reoperation was significantly lower in the DM-THA group than in the BHA group (RR 0.5; 95% CI 0.32 to 0.78, p = 0.003, Z −3.01). Five studies reported one-year mortality. The mortality rate was significantly lower in the DM-THA group than in the BHA group (RR 0.58 95% CI 0.45 to 0.75, p < 0.0001, Z −4.2).

Conclusion

While the evidence available consisted mainly of non-randomized studies, DM-THA appeared to be a viable option for patients with displaced fractures of the femoral neck, with better reported rates of dislocation, reoperation, and mortality than BHA.

Absence of instabilities and intra-prosthetic dislocations at 7 to 11 years following THA using a fourth-generation cementless dual mobility acetabular cup

PURPOSE

Dual-mobility (DM) cups are increasingly used in total hip arthroplasty (THA) but there lacks literature on their long-term results. We aimed to investigate outcomes of a fourth-generation cementless DM acetabular cup at 7-11 years.

METHODS

We retrospectively evaluated 240 consecutive hips that received cementless THA using the same dual mobility cup (Novae Sunfit TH) and femoral stem (Corail). Patients were recalled at ≥7 years to collect Oxford hip scores (OHS), Harris hip scores (HHS), and inspect for radiolucent lines and granulomas. Multi-variable analyses were performed to determine whether HHS or OHS were associated with pre- or intra-operative variables.

RESULTS

At 8.4 ± 0.8 years (range, 7-11), 6 hips were revised (2.5%), 54 deceased (22.5%), and 14 could not be reached (5.8%). Four revisions (2 cup+stem, 2 liners only) were due to sepsis (1.7%), one (cup and stem) for trauma (0.4%), and one (stem) due to aseptic loosening (0.4%). For the remaining 166 hips, HHS was 83.6 ± 13.2 and OHS was 20.3 ± 6.7. Multi-variable analysis confirmed that HHS (β = - 0.38; p = 0.039) and OHS (β = 0.36; p < 0.001) worsened with age, and that OHS was worse for Charnley C patients (β = 3.17; p = 0.009). Neither granulomas nor radiolucenies were observed around any cups, but radiolucenies were seen around 25 stems (20.3%).

CONCLUSIONS

This fourth-generation DM cup demonstrated satisfactory outcomes at 7-11 years, with no instabilities or cup revisions due to aseptic loosening. Better OHS was observed for younger patients and those presenting higher Charnley grade.

LEVEL OF EVIDENCE

Level IV, retrospective case study.

Bipolar hemiarthroplasty versus total hip arthroplasty in allograft-prosthesis composite reconstruction of the proximal femur following primary bone tumour resection

AIMS

The consensus is that bipolar hemiarthroplasty (BHA) in allograft-prosthesis composite (APC) reconstruction of the proximal femur following primary tumour resection provides more stability than total hip arthroplasty (THA). However, no comparative study has been performed. In this study, we have compared the outcome and complication rates of these two methods.

METHODS

In a retrospective study, 57 patients who underwent APC reconstruction of proximal femur following the primary tumour resection, either using BHA (29) or THA (28), were included. Functional outcome was assessed using the Musculoskeletal Tumour Society (MSTS) scoring system and Harris Hip Score (HHS). Postoperative complications of the two techniques were also compared.

RESULTS

The mean follow-up of the patients was 8.3 years (standard deviation (SD) 5.5) in the BHA and 6.9 years (SD 4.7) in the THA group. The mean HHS was 65 (SD 16.6) in the BHA group and 88 (SD 11.9) in the THA group (p = 0.036). The mean MSTS score of the patients was 73.3% (SD 16.1%) in the BHA and 86.7% (SD 12.2%) in the THA group (p = 0.041). Limping was recorded in 19 patients (65.5%) of the BHA group and five patients (17.8%) of the THA group (p < 0.001). Dislocation occurred in three patients (10.3%) of the BHA group and two patients (7.1%) of the THA group.

CONCLUSION

While the dislocation rate was not higher in THA than with BHA, the functional outcome was significantly superior. Based on our results, we recommend THA in APC reconstruction of the proximal femur. Cite this article: Bone Joint J 2020;102-B(4):524-529.

Midterm Clinical and Radiographic Outcomes of a Contemporary Monoblock Dual-Mobility Cup in Uncemented Total Hip Arthroplasty

BACKGROUND

The efficacy of contemporary monoblock dual-mobility (DM) cups to prevent dislocations in total hip arthroplasty (THA) is well reported, but there is little published data on their mid- to long-term outcomes. The authors aimed at reporting the 10-year survival of a contemporary DM cup as well as its clinical and radiographic outcomes.

METHODS

From a retrospective consecutive multicentric series of 516 patients (541 hips) that received uncemented THA between June 2007 and June 2010, 6 patients (6 hips) had cup and stem revisions, 5 patients (5 hips) had isolated stem revision, and 2 patients (2 hips) had isolated insert revision. A total of 103 patients (111 hips) died with their original implants, and 41 patients (42 hips) were lost to follow-up. This left 358 patients (375 hips) for clinical assessment at a median follow-up of 8.7 years (range, 6.8-10.5 years), including 279 patients (290 hips) with postoperative radiographs. Implant survival was calculated using the Kaplan-Meier method, and multivariable analyses were performed to determine whether clinical outcomes are associated with patient or surgical factors.

RESULTS

The 10-year survival considering revision for aseptic loosening as end point was 100% for the cup and 99.2% for the stem. No dislocations were observed, and radiographic assessment revealed 1 acetabular granuloma (0.3%), but no radiolucencies nor fractures. The Harris hip score improved from 49.6 ± 15.5 to 85.2 ± 14.5, and the postoperative Oxford hip score was 19.2 ± 7.6. Multivariable analyses revealed that improvement in Harris hip score increased with cup diameter (beta, 1.28; P = .039).

CONCLUSION

Our data confirmed satisfactory midterm outcomes of uncemented THA using a contemporary DM cup, with no dislocations nor cup revisions due to aseptic loosening.

LEVEL OF EVIDENCE

Level IV, retrospective cohort study.

Long-term outcomes of a dual-mobility cup and cementless triple-taper femoral stem combination in total hip replacement: a multicenter retrospective analysis

BACKGROUND

The separate design concepts of dual-mobility cups and triple-taper femoral stems were developed to improve survivorship following total hip replacement (THR) by reducing instability/dislocation and enabling enhanced fixation. Successful outcomes at over two decades have been reported with earlier-generation devices based on these concepts. The current study aimed to provide the first long-term results with a unique pairing of later-generation dual-mobility cup and triple-taper cementless femoral stem after a decade of use in patients undergoing THR.

METHODS

In this retrospective analysis, records were reviewed for all subjects implanted with this dual-mobility cup/cementless femoral stem combination at three centers between 2002 and 2005. Any subject who had not already had follow-up visit beyond 10 years, was not previously revised, and still living were invited for a single follow-up visit consisting of Merle d'Aubgine Scores, the Western Ontario and McMaster Universities Osteoarthritis (WOMAC) index, and standard radiographs.

RESULTS

There were 244 THRs available for analysis. At a mean follow-up of 11.9 years, the Kaplan-Meier survivorship (endpoint: revision for any reason) was 99.1% (95% CI, 97.6-99.7) for the stem and 95.9% (95% CI, 93.1-97.6) for the cup. Merle d'Aubigne Scores were significantly improved from baseline and WOMAC scores were in the satisfactory range at the final follow-up. Radiographic analysis revealed no cases of stem subsidence, no cases of bone hypertrophy, 1 (0.4%) case of bone atrophy, and 3 (1.2%) cases of osteolysis around the stem. No subjects had radiolucent lines greater than 1 mm in any femoral Gruen zone. Evidence of cup migration was seen in 1 (0.4%) subject and 1 (0.4%) subject had evidence of osteolysis that was seen in Gruen zones I, II, IV, and V.

CONCLUSIONS

This combination of a later-generation dual-mobility cup and cementless triple-taper stem was associated with excellent survivorship and satisfactory functional outcomes at over 10 years follow-up.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT02648152. Date of registration: January 6, 2016. Retrospectively registered.