Introduction
Femoral neck fracture is a common fracture in senior patients, which can decrease mobility and increase mortality [
1]. There are many options for these fractures including internal fixation, hemiarthroplasty, and total hip arthroplasty [
2]. Among these procedures, hemiarthroplasty has become the most preferred treatment option for surgeons according to the surveys [
1-
3]. There are two types of options, including unipolar hemiarthroplasty (UH) and bipolar hemiarthroplasty (BH), when using a hemiarthroplasty. In comparison to UH, BH has an additional inner bearing between the stem and the endoprosthetic head component. In theory, this design would decrease acetabular erosion, decrease protrusion, and decrease dislocation, as well as maintain joint stability and improve hip function [
4,
5]. However, whether UH or BH is preferable for the patient population remains uncertain [
6-
13].
Although several randomized controlled trials (RCTs) on this topic have been published, these studies showed inconclusive and controversial results [
14-
23]. The previous systematic reviews demonstrated that further well-designed RCTs were needed to draw a definitive conclusion, indicating the scientific evidence was still insufficient [
24,
25]. However, many RCTs have been published [
14,
18,
19,
21,
23,
26], since the latest meta-analysis conducted in 2010 [
25]. The need remains for strong evidence including the recent RCTs to make a more precise estimation [
27]. Therefore, the objective of this meta-analysis was to include all available RCTs and to evaluate the relative effects between UH and BH for displaced femoral neck fractures.
Materials and methods
This study was performed and reported following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement [
28]. This study was approved by the ethical review committee of Navy General Hospital and Wuhan Pu’Ai Hospital.
Search strategy
A comprehensive search (up to April, 2014) without restriction on language was independently conducted by two reviews (ZJ and FD) through the databases of Pubmed, Embase, and Cochrane Library. The MeSH terms (hip fractures, femoral neck fractures, arthroplasty, hemiarthroplasty, hip prosthesis) and multiple keywords (unipolar, bipolar, arthroplasty, hemiarthroplasty, replacement, prosthesis, fractur*) were used to ensure inclusion of all possible studies. These terms were connected by the Boolean operators “AND” and “OR”. Additionally, the reference lists of included articles and relevant reviews were also examined for potential studies.
Inclusion and exclusion criteria
The eligible articles should meet the following inclusion criteria: (1) RCTs comparing UH with BH; (2) patients with displaced femoral neck fractures; (3) at least one of the following main clinical outcomes: surgical information and postoperative outcomes. Studies were excluded if they had any of the following characteristics: (1) reviews, abstracts, letters, or meeting proceedings; (2) patients with immature skeleton, delayed union, nonunion, previous surgery, or pathological fractures; (3) duplicate reports of an earlier trial or no interest outcomes reported.
Two reviewers (ZJ and FD) independently extracted the data from all eligible RCTs with the use of a standardized data recording form. Disagreements were resolved by discussion, a third review (YW) was consulted for the final decision when necessary. The data of interest included the following categories: (1) study characteristics such as year of publication, sample size, age, gender, and follow-up duration; (2) surgical information including operation time, blood loss, blood transfusion, and hospital stay; (3) primary outcomes comprising functional scores, pain, range of motion (ROM), 6-min walk, quality of life and cost (4) secondary outcomes including mortality, reoperation, dislocation, complications, and acetabular erosion. In addition, complications were sorted into four categories, including implant-related complications (periprosthetic fractures, prosthesis loosening, dislocation, etc.), cardiovascular and cerebrovascular complications (cardiac arrest, myocardial infarction, acute cardiac arrhythmia, cerebrovascular accidents, pulmonary embolism, deep venous thrombosis, etc.), local complications (wound infection, wound hematoma, incision rupture, heterotopic ossification, etc.), and general complications (pneumonia, urinary tract infection, bedsore, gastrointestinal bleed, acute renal failure, etc.).
Risk of bias assessment
Two reviewers (ZJ and FD) independently assessed each of the included study. Disagreements were resolved by means of discussion, with arbitration by a third reviewer (HL), when differences of opinion remained. The risk of bias of the included studies was evaluated using the bias assessment tool recommended by the Cochrane Handbook for Systematic Reviews of Interventions (version 5.1.0) [
29]. For each trial, the risk of bias was categorized as low risk, high risk, or unclear risk. Bias assessment was carried out using RevMan 5.2.10 software (Cochrane Collaboration, UK).
Statistical analysis
For each included study, mean differences (MD) and confidence intervals (CIs) were calculated for continuous outcomes, while risk ratios (RRs) and 95% CI were calculated for dichotomous outcomes. Heterogeneity across trials was assessed with use of both the chi-square (
χ
2) test and the
I-squared (
I
2) test. Statistical heterogeneity was considered significant when
P < 0.10 for the
χ
2 test or
I
2 > 50% [
30]. A random effects model was used to ensure that these studies represented a random sample of all potentially available studies [
31]. Subgroup analysis was carried out according to specific complication categories and follow-ups. Sensitivity analysis was performed to test the strength and robustness of pooled results by sequential omission of individual studies. Publication bias was assessed using a funnel plot of the most frequently reported outcome. All reported
P values were two-sided, and
P < 0.05 was regarded as statistically significant. Statistical analyses were conducted by RevMan 5.2.10 software (Cochrane Collaboration, UK).
Discussion
Hemiarthroplasty, as an effective technique for displaced femoral neck fractures, could help early ambulation and satisfied function recovery and is increasingly performed by the surgeons [
1-
3]. However, controversy has persisted for a long time regarding the use of bipolar versus unipolar prosthesis. This study suggests that (1) BH is associated with similar or better improvement in hip functionality, hip pain, and quality of life compared with UH while with a higher cost and that (2) there are no significant differences between BH and UH with regard to operation time, blood loss, blood transfusion, hospital stay, mortality, reoperation, dislocation, and complications, and that (3) BH could not decrease acetabular erosion rate in the long term.
Compared with UH, bipolar prosthesis with an additional inner articulation has the theoretical advantages of less acetabular erosion and less dislocation [
4,
5]. This study demonstrates that the incidence of acetabular erosion in BH is less than that in the UH group at the follow-ups (Figure
3). These findings are consistent with the previous studies [
6,
13]. However, statistical difference was only noted at 1 year follow-up and the acetabular erosion rate increased at the later follow-ups with no significance observed (Figure
3). This may be because the bipolar articulation loses mobility with time and functions as a UH [
18,
26,
32-
35]. In addition, it should be recognized that this result should be interpreted with caution until confirmed by future studies, because the number of the pooled studies is small and the studies are of small sample size. Regarding to dislocation, it is not proved to be less comparing BH with UH in this study. Other studies have also failed to find this benefit [
3,
36,
37]. However, the close reduction of bipolar head is more difficult than the unipolar prosthesis, and BH typically requires open reduction [
38,
39]. Moreover, BH could not increase the risk of operation in terms of surgical and postoperative results, including operation time, blood loss, blood transfusion, hospital stay, mortality, reoperation, dislocation, and complications. It may be demonstrated that BH is an alternative treatment as safe as UH.
It is also hypothesized that BH with lower acetabular erosion rate will produce a less painful arthroplasty and improve hip function and quality of life [
4,
5]. However, this meta-analysis failed to find the statistical difference in HSS score between BH and UH. Other hip functional scores, hip pain, and quality of life according to SF-36 and EQ-5D scores found inconsistent results (similar or better). It may be demonstrated that BH with a higher cost can achieve no less outcomes, so further studies are needed to perform the cost-effective analysis of BH versus UH. However, it should be recognized that these results were from the qualitative descriptive analysis of the available studies, not the meta-analysis, due to the heterogeneity among the studies. Therefore, more RCTs with the same outcome assessment scores are suggested and may help to get a more reliable conclusion.
The latest systematic review on this topic was published in 2010 and demonstrated that there was no significant difference in clinical outcomes between BU and UH [
25]. However, there were several limitations in that study. It included both RCTs and quasi-RCTs, indicating a lower level of evidence of that study. Moreover, although seven studies were included in that study, only five studies were used for analysis, because two studies were conference abstracts without sufficient data. Therefore, there are several strengths in this meta-analysis. Firstly, more strict inclusion criteria were conducted. Only RCTs were included in this study, so the reliability of the results was ensured. Secondly, more RCTs published in recent years were included in this study, making the evidence much stronger. Thirdly, complications were further sorted. The potential bias risk from pooling all complications was decreased.
However, this meta-analysis also has several potential limitations. Firstly, publication bias which is common to all meta-analysis may be still unavoidable in this study. Secondly, various prostheses used in the included studies may induce related bias, whereas a subgroup analysis according to prosthesis type was not conducted due to insufficient data. Thirdly, different outcome measures were reported in the included studies, so a meta-analysis to statically strengthen the evidence could not be performed. Instead, a descriptive systematic review was conducted in these results.
Conclusions
This systematic review and meta-analysis suggest that BH for displaced femoral neck fractures could not have benefit over UH in terms of surgical information and postoperative results, including operation time, blood loss, blood transfusion, hospital stay, mortality, reoperation, dislocation, and complications. BH may achieve similar or better outcomes compared with UH with respect to clinical outcomes, including hip functionality, hip pain, and quality of life. However, BH is associated with higher cost and could not decrease the incidence of acetabular erosion in the long term.
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Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
DR and QH conceived and designed the study. ZJ, FD, and YW performed the study. WL, HL, and DW analyzed the data. ZJ, FD, and YW wrote the manuscript. All authors read and approved the final manuscript.