Modular versus monoblock stem in revision total hip arthroplasty: a systematic review and meta-analysis

Introduction

Background

The number of total hip arthroplasty (THA) is ever-growing (1). Over the decades, several studies investigated the durability of primary implants and follow-ups of up to 25 years with cementless-coated implants (2). It is estimated that THA surgeries will increase by 174% in 2030 with a consequent increase in THA revisions (rTHA), and that volume will double by 2026 (3). The main reasons for rTHA are represented by aseptic loosening (a most significant percentage of 23.19%), followed by instability (22.43%) and infection (22.13%) (4). One of the most critical problems of revision surgery is bone loss in the femoral site (5). The femur metaphyseal bone loss makes implanting a primary proximal fitting stem impracticable because of the need to achieve stability and restore the correct biomechanical parameters (offset, limb length, femoral version) (6). Revision stems are designed to overcome bone loss and restore hip function. One of the most popular was designed by Wagner in the 1980s (Figure 1). Its tapered, fluted titanium (TFT) stem wedges into the distal femur, allowing good stability. The tapered shape allows axial stability, and rotational stability is achieved by longitudinal splines along the stem (7). Wagner-type stems obtained success, also presenting some problems (8). The main drawbacks have been: subsidence and dislocation of up to 20% in some cases (9-13). Moreover, fully porous coated stems reach stability both with the overall dimensions and with the osseointegration of their particular coating. Several modular stems (Figure 2) were developed to overcome these problems and give intraoperative versatility (14). With this type of implant, the surgeon can perform immediate, reliable, distal fixation and then put a proximal segment to restore leg length, offset, anteversion, and hip biomechanics (15,16).

Figure 1 Monoblock stem.

Figure 2 Modular stem.

Rationale and knowledge gap

The rationale of the study is to compare the outcomes of modular and monoblock stems, in the lack of studies in the literature that have carried out a statistical analysis between the two types of stems. In fact, in presence of a previously published systematic review (17), this study represents the first meta-analysis that analyzes comparative studies between modular and monoblock stems evaluating clinical and radiological outcomes and perioperative complications.

Objective

This systematic review and meta-analysis aims to analyze only studies that compared modular and monoblock stems in rTHA surgery, focusing on clinical and radiological outcomes and complication rates. We present this article in accordance with the PRISMA reporting checklist (available at https://aoj.amegroups.com/article/view/10.21037/aoj-23-33/rc).

Methods

This systematic review and meta-analysis collected data from studies focused on adult patients undergoing revision total hip replacement with a modular or monoblock stem. A literature search according to Cochrane methodology was performed by two independent reviewers (Parisi FR and Luciano C) that extracted the following data: authors, year of publication, type of study, level of evidence (LOE), number of participants, age, gender, body mass index (BMI) for both groups, follow-up, and results. A flowchart was reported according to Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines. The systematic research literature was performed on 28th February 2023 using the following search strategy: ((Modular stem) OR (monolithic stem)) AND (hip review) on PubMed, Scopus, and Cochrane. No restrictions were applied to the period of the studies. After finding the articles, we manually searched the reference list of those articles to find additional documents. We included randomized controlled trials (RCTs) and observational retrospective or prospective studies in English, which compared clinical and radiological outcomes and complication rates after rTHA. We excluded trials that did not compare two different stem types (modular and monoblock) or with very short follow-up (less than 6 months), studies without clinical and radiological outcomes, and studies focused on primary THA. The comparison analysis between the two types of stems regarded the evaluation of clinical scores, radiological outcomes, dislocation rate, infection rate, and intraoperative and postoperative periprosthetic fractures. Two independent reviewers (Parisi FR and Luciano C) assessed the risk of bias for included studies using the Methodological Index for Non-Randomized Studies (MINORS) score (18). When inconsistencies occurred in the data extraction and the risk of bias assessment between the two independent reviewers, a third investigator (Zampogna B) resolved them. The Review Manager (RevMan) software version 5.4 was used to conduct a meta-analysis. Harris Hip Score (HHS) (19) was evaluated as a continuous outcome using mean difference (MD) with 95% confidence intervals (CIs). The rate of complications was assessed as dichotomous outcomes using an odds ratio (OR) with 95% CIs. We used a fixed-effect model for heterogeneity lower than 55% or random-effect in the case of I²>55% (20). The statistical significance of the results was fixed at P<0.05.

Results

Results of the search

The literature research identified 1,334 articles. After duplicate removal, 949 articles were screened on title and abstract. The full text of 48 articles was read, and 36 were excluded for the reasons: not comparative studies between types of stems (n=14); primary THA (n=8); not requested outcomes (n=9); non-adequate follow-up (n=5). The articles included in this review were 12 (Figure 3).

Figure 3 PRISMA 2020 flow diagram. THA, total hip arthroplasty; PRISMA, Preferred Reporting Items for Systematic Review and Meta-Analyses.

Included studies

We included 11 retrospective observational studies (ROS) and one RCT. The studies compared clinical and/or radiographic outcomes and complications between two groups of patients who underwent revision THA with a modular or monoblock stem.

Demographic data

The study included a total number of participants of 3,671 patients (Table 1). The mean age of the patients involved was 68.4 years old (from 27 to 93 years of age). The BMI ranged from 23.3 to 39.8 kg/m², averaging 28.55 kg/m². The mean follow-up was 46.9 months (from 193 days to 101.5 months). Stem manufacturer and brand of each study are reported in Table 2. MINORS score was calculated for non-randomized studies. The mean value was 17, ranging from 15 to 19 (Table 3).

Radiological outcomes

Most of the studies in the review analyzed the subsidence of the prosthetic revision stem on follow-up radiographic exams (Table 4). Among the studies, there was no prevalence of subsidence for one type of stem. Mean subsidence was from 0.92 to 10 mm for the modular stem and from 1 to 15 mm for the monoblock stem. Only two of the studies included showed a statistically significant difference in subsidence between the two types of stems: Clair et al. (21) reported that subsidence was higher for modular stems than non-modular (P<0.001), while Feng et al. (23) reported lower subsidence for modular stem than monoblock (P<0.05).

Effect of intervention

The meta-analysis compared clinical outcomes and perioperative complications between modular and monobloc stem in revision THA. Postoperative HHS showed better results with modular stems but without statistical significance (MD =1.32; 95% CI: −1.62 to 4.27; P=0.38; I²=76%) (Figure 4). The rate of dislocations was lower for revisions with monoblock stems. However, no statistical difference was observed between the groups (OR =2.48; 95% CI: 0.67 to 9.14; P=0.17; I²=50%) (Figure 5). The infection rate was similar among the two groups (OR =1.07; 95% CI: 0.51 to 2.23; P=0.86; I²=0%) (Figure 6). The rate of intraoperative fracture was lower in the monoblock stem group than in the modular stem group but with no statistical significance (OR =1.62; 95% CI: 0.42 to 6.21; P=0.48; I²=87%) (Figure 7). The rate of postoperative periprosthetic fracture was lower with monoblock stems compared with modular stems, but no statistical difference was reported (OR =1.60; 95% CI: 0.55 to 4.64; P=0.39; I²=0%) (Figure 8).

Figure 4 Harris Hip Score. SD, standard deviation; IV, inverse variance; CI, confidence interval.

Figure 5 Dislocation. M-H, Mantel-Haenszel; CI, confidence interval.

Figure 6 Infection. M-H, Mantel-Haenszel; CI, confidence interval.

Figure 7 Intraoperative fracture. M-H, Mantel-Haenszel; CI, confidence interval.

Figure 8 Postoperative periprosthetic fracture. M-H, Mantel-Haenszel; CI, confidence interval.

Discussion

Key findings

Periprosthetic femoral bone loss recognizes several causes as osteolysis, stress shielding, periprosthetic infections and fractures, aseptic loosening, metastases, or iatrogenic bone defects after component removal (29-31). Femoral stem loosening due to femoral bone loss account for a complication rate ranging from 58% to 84% in hip revision surgery (32,33). In 1987, the first monoblock, tapered, fluted, coated revision stem was developed in Europe with quick diffusion in the USA (7). In recent decades, new modular stems have been designed to restore biomechanical parameters like offset and limb length without sacrificing implant stability (34). The principal differences between the use of modular and monoblock stem have been evaluated in several studies (35). Modular stems reported a higher chance of intraoperative periprosthetic fracture than monoblock, which reported a higher subsidence risk (17). Compared to a similar systematic review (17), our study analyzed only studies that compared monoblock and modular stems in hip revision surgery. We analyzed 12 articles with a total population of 3,671 patients. A meta-analysis was conducted on the clinical outcomes (HHS) and intraoperative and postoperative complications. The results did not show statistically significant differences between the two stems. In particular, analyzing the results obtained with HHS, Feng et al. (23), Li et al. (24), and Moreta et al. (13) showed better results for modular stems, although Huang et al. (15) and Cohn et al. (27) reported higher values in favor of the monoblock ones. No statistically significant differences existed between the monoblock and modular stem dislocation rate. According to studies by Huang et al. (15), Cohn et al. (27), Moreta et al. (13), Wang et al. (25), and Weiss et al. (10), the monoblock stems had a reduced dislocation rate. Only one study, published by Feng et al. (23), showed dislocation results in supporting modular stems. Data regarding infection rate resulted similar between the two groups without a clear prevalence. There was no statistically significant difference between modular and monoblock stems in intra and postoperative fractures rate. Once more, data analysis reveals that monoblock stems had a lower but not significant rate of intraoperative fractures than modular stems. Especially, studies conducted by Feng et al. (23), Huang et al. (15), and Cohn et al. (27) demonstrated a decreased incidence of intraoperative fractures with the monoblock stems, while Richards et al. (26) showed a lower risk of intraoperative fractures with the modular ones. According to current results of postoperative fractures, Cohn et al. (27) and Weiss et al. (10) showed a higher risk with modular stems. Radiological results showed that monoblock stems had subsidence (measured in millimeters) more frequently than modular stems, according to Clair et al. (21), Feng et al. (23), Huang et al. (15), Wang et al. (25), and Cohn et al. (27). Possible reasons are due to surgeon inexperience, wrong sizing, misdiagnosed intraoperative fractures (36). Studies comparing implant survival with 5-year follow-up reported comparable data. Li et al. (24) reported the modular stem at 92.31% and the monoblock stems at 85.71%, while Wang et al. (25) reported a rate of 91.3% and 88.2%, respectively. The literature analysis has highlighted many data without significant differences in clinical and postoperative outcomes using modular and monoblock stems in revision total hip replacement. An important factor is highlighted by Clair et al. (37) about the cost of implants: nonmodular stems are significantly less expensive than modular implants. This analysis should be considered, because all hospitals have a budget cap today.

Strengths and limitations

To our knowledge, our systematic review and meta-analysis is the first that analyzes only comparative studies between modular and monoblock stems evaluating clinical and radiological outcomes and perioperative complications. The main limitation of this study is the small number and low quality of enclosed studies that compared the two stems. Moreover, the modular stem is usually used for more complex cases with lower quality femoral bone stock, even if many authors did not analyze the femoral bone stock with radiographic scores. In addition, differences in surgeon experience and surgical skill may differ as well and influence the preference of implant.

Comparison with similar research

A paper published by Koutalos et al. (17) analyzed 46 non-comparative studies reporting the outcome of modular or monoblock stems. This review analyzed clinical and perioperative outcomes demonstrating that monoblock stems had a lower intraoperative fracture rate but a greater risk of failure with statistically significant data. Moreover, their data reported a statistically significant HHS favoring the modular stems.

Explanations of findings

In clinical practice, the significance of the given data should be helpful in the planning and decision-making process for the revision of total hip replacement with femoral deficiency. In the literature, few reviews analyze modular and monoblock stems in hip revision surgery. Both modular and monoblock stems can be used in rTHA as they show similar and satisfactory clinical and radiological outcomes.

Implications and actions needed

Further research must consider a more homogeneous evaluation of clinical parameters: the return to activity and daily living, the assessment of bone mineral density over time, the influence of BMI on the onset of stress shielding, and revision implant failure, in addition to clinical scores. Moreover, there is a lack of data stratification according to the surgical approach used, the type of bone damage, and the number of hip procedures the patient underwent.

Conclusions

The modular and monoblock stems present satisfactory and comparable clinical and postoperative outcomes. Both revision stems are a valid and effective option for managing femoral bone deficit in hip revision surgery.

Acknowledgments

Funding: None.

Footnote

Provenance and Peer Review: This article was commissioned by the editorial office, Annals of Joint for the series “Modular Implants for Revision Arthroplasty in Orthopedics”. The article has undergone external peer review.

Reporting Checklist: The authors have completed the PRISMA reporting checklist. Available at https://aoj.amegroups.com/article/view/10.21037/aoj-23-33/rc

Peer Review File: Available at https://aoj.amegroups.com/article/view/10.21037/aoj-23-33/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://aoj.amegroups.com/article/view/10.21037/aoj-23-33/coif). The series “Modular Implants for Revision Arthroplasty in Orthopedics” was commissioned by the editorial office without any funding or sponsorship. GM served as the unpaid Guest Editor of the special series. RP serves as an unpaid editorial board member of Annals of Joint from June 2016 to November 2024. The authors have no other conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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