Long-term outcomes of uncemented or cemented arthroplasty revision following metal-on-metal total hip replacement

Background Which device(uncemented or cemented total hip replacementUTR or CTR) is more conducive to the revision of metal-on-metal total hip replacement(MoM-TR) is inconclusive. The purpose of this study was to assess the long-term outcomes of individuals who had undertaken UTR versus CTR following initial MoM-TR. Methods Two hundred and thirty-four individuals(234 hips) had received UTR or CTR following initial MoM-TR during 2007-2018 were reviewed . Outcomes reported in this analysis involving Harris Hip Scores(HHS) as well as the major orthopaedic complications(MOC) were gathered 3 months, 6 months, 12 months, and then every one year after revision. Results From the 12th month after revision to final follow-up, CTR yielded superior HHS than UTR. The MOC rates were 47.4% and 16.1% in the UTR and CTR groups, respectively. Between-group noteworthy divergences were noted regarding the rates of re-revision, prosthesis loosening, and periprosthetic fracture(10.3% for UTR vs 2.5% for CTR, p =0.015; 16.3% for UTR vs 5.9% for CTR, p = 0.011; and 12.0% for UTR vs 4.2% for CTR, p =0.045, respectively). The decreasing


Background
Which device(uncemented or cemented total hip replacementUTR or CTR) is more conducive to the revision of metal-on-metal total hip replacement(MoM-TR) is inconclusive. The purpose of this study was to assess the long-term outcomes of individuals who had undertaken UTR versus CTR following initial MoM-TR.

Methods
Two hundred and thirty-four individuals(234 hips) had received UTR or CTR following initial MoM-TR during 2007-2018 were reviewed . Outcomes reported in this analysis involving Harris Hip Scores(HHS) as well as the major orthopaedic complications(MOC) were gathered 3 months, 6 months, 12 months, and then every one year after revision.

Results
From the 12th month after revision to final follow-up, CTR yielded superior HHS than UTR. The MOC rates were 47.4% and 16.1% in the UTR and CTR groups, respectively. Between-group noteworthy divergences were noted regarding the rates of re-revision, prosthesis loosening, and periprosthetic fracture(10.3% for UTR vs 2.5% for CTR, p =0.015; 16.3% for UTR vs 5.9% for CTR, p = 0.011; and 12.0% for UTR vs 4.2% for CTR, p =0.045, respectively).

Conclusion
The superiority of CTR over UTR in terms of improving HHS and decreasing the MOC rate.

Background
In recent years, the utilisation of metal-on-metal total hip arthroplasty(MoM-THA) has sharply declined as a result of the reported low 10-year survivorship and high failure rates associated with a host of issues(i.e., adverse reactions to metal debris[ARMD]) [1][2][3][4]. Failure that occurs secondary to MoM wear tends to be a concern [5][6][7]. Poor bone stock could be attributed to the substantial osteolysis triggered by ARMD which is closely related to the failure of MoM-THA, resulting in the high rate of revision [8].
This growing rate of MoM-THA failure may also conduce to the increase in the utilisation of uncemented or cemented THA(UTHA or CTHA) [8,9]. Several reports have reviewed major orthopaedic complications(MOC) following the conversion of MoM-THA to UTHA or CTHA [3,7]. Interest in CTHA has been growing over the last decade, with reported superior Harris hip scores(HHS) and fewer MOC for CTHA than for UTHA [5,[10][11][12].
So far, no definitive consensus exists regarding the long-term outcomes of conversion from initial MoM-THA to UTHA or CTHA [11]. Thus, we performed a retrospective review to assess the long-term outcomes of the conversions.

Study population
An initial study cohort of 326 patients(326 hips) were identified from our joint registration database who were treated using UTHA or CTHA following primary MoM-THA from March, 2007 to January, anterior approach, as reported [13]. The main exclusion criteria involved cases without a MoM-bearing surface at the time of conversion; lacking study data; dyskinesia or bone-related diseases; tumours, organ dysfunction.
Data were collected according to a standard protocol. Follow-up occurred 3 months, 6 months, 12 months, and then every one year after conversion. The primary endpoint was the HHS; secondary endpoints were the MOC rate.

Statistical analysis
Revision was defined as the removal of the entire endo-prosthesis. Prosthesis loosening was assessed according to previous reports [8,14]. Continuous data were compared using Student's t-test.
Categorical data were compared using Chi-squared tests or Fisher's exact tests, as appropriate. All statistical analyses were done using SPSS 24.0(IBM, Armonk, NY). A 2-sided p<0.05 was considered significant.

Results
In total, 234 individuals(234 hips) undertaking conversion from initial MoM-THA to UTHA or CTHA were  (Table 1).

Primary endpoint
The mean HHS in Group UTHA and CTHA were 79.14 (±8.  Table 2). Between-group differences in HHS were not significant 3 months or 6 months after conversion.

Discussion
The revision of initial MoM-THA using CTHA yielded superior long-term clinical outcomes compared to the use of UTHA. For all we know, this is the largest report regarding outcomes of conversion after MoM-THA.
The MOC of MoM-THA related to ARMD could be the occasion of increased metal ion levels, potentially increasing the risk of endo-prothesis failure [8,5]. These ions reduce the number and activity of osteoblasts by inhibiting the expression of osteoblast genes, eventually leading to intraosseous growth disorder [3,7,14]. The result of the metal ion is a challenge to UTHA or CTHA. In response to this challenge, the force on UTHA may be transmitted to one part of the bone, while it acts as a stress shielding to other bones [15][16][17]. On account of the limitation of stress buffering or conduction [4], UTHA can lead to further bone destruction, which will form a vicious cycle, and eventually lead to the failure of the prosthesis [11,18,19].
The risk of converting from MoM-THA to UTHA or CTHA remains an increasing concern [14,8,3].
Nonetheless, the reported literature on the outcomes of these conversions is underprovided [20,4,21]. Several studies have revealed noteworthy distinctions in clinical outcomes, although they are constrained by small sample sizes [3,13,8]. Undeniably, revision MoM-THA is related to a high rate of MOC [8]. Even so, we failed to detect noteworthy distinctions regarding the rates of MOC 1 year after conversion. There has been increasing concern as to whether there are substantial differences in the long-term results of these two types of conversions [3,8,17]. In 2009, Eswaramoorthy et al. [23] reviewed 76 cases who undertook conversion from MoM-THA to UTHA. Consistent with the current findings, a high rate of MOC (24%) was observed involving prosthesis loosening and periprosthetic fracture, predominantly attributable to a high rate of revision (7%).
The reason for the conversion has a significant effect on the result of the conversion [4,7]. With the continuous updating of arthroplasty equipment and further development of surgical technology, the total re-revision rate due to MoM wear is low, regardless of whether long-or short-stem UTHA is used for THA [11,15]. Periprosthetic fractures frequently result in high re-revision rates for UTHA [16,19]. Consistent with our results. A possible explanation for these phenomena is that the stress transmission is severely disrupted by the periprosthetic fractures [20,21]. It may be difficult to reconstruct the supporting structure by using long-or short-stem of UTHA [15,18]. In this way, it is unlikely that long-or short-stem of UTHA will resist stress under the weight-bearing [2,8]. However, for CTHA, the situation may be different, because cemented fixation itself is an antagonistic relationship to fracture or stress [6][7][8]. It can enhance the friction coefficient of the bone-cement interface, and also promote the tension of the entire femoral part, which is crucial for the hip stability after revision [13,18].
Several limitations should be acknowledged in this study. Firstly, this is a retrospective study, and bias is inevitable. However, the results are basically quantitative because clinical outcomes are the focus of our attention. In addition, because there were no significant differences in baseline data in this comparative study, the effect of data on retrospective collection is limited. Secondly, subjective factors may play a key role in assessing baseline comorbidities in the absence of objective diagnostic data, which may result in unexplained baseline variables, which reduces the ability to draw reliable conclusions. Thirdly, the subjects we included have a large time span (more than 11 years), which may have limited the reliability of our conclusions. Because the clinical experience of surgeons is not fixed. With the accumulation of surgical volume, the surgeon's experience may be a potential variable, which plays an important role in postoperative outcomes.

Conclusions
The long-term results reported in the current study provide a growing body of evidence that conversion to CTHA following primary MoM-THA is associated with more significant improvements in functional outcomes and lower MOC rate compared to conversion to UTHA.

Availability of data and materials
The data used during our study are available from the corresponding author upon reasonable request.

Authors' contributions
WC, SM, JL, and BC carried out the data collection and analysis. MZ, XZ, WY, and GH performed the surgical procedures and participated in the study design and manuscript writing. All authors have read and approved the final manuscript.

Ethics approval and consent to participate
This study was approved by the Investigational Ethics Review Board (The First Affiliated Hospital, Sun Yat-sen University), and an exemption from informed consent was gained from the review board.

Consent for publication
Not applicable.

22.
Sierra RJ, Cabanela ME.   Figure 1 Flow diagram exhibiting methods for identification and exclusion of patients to compare the long-term outcomes of uncemented or cemented total hip arthroplasty (UTHA or CTHA, respectively) following initial metal-on-metal THA (MoM-THA).