Risk factors for liner wear and head migration in total hip arthroplasty: a systematic review

Total hip arthroplasty (THA) is a successful orthopaedic surgical procedure, and its longevity depends on bearing components and implant fixation. Optimizing polyethylene and ceramics has led to improved wear parameters and contributed to improved long-term outcomes. The present systematic review investigated whether time span from implantation, patient characteristics and performance status exert an influence on liner wear and head migration in THA. This study was conducted in conformity to the 2020 PRISMA guidelines. All the clinical investigations which reported quantitative data on the amount of liner wear and head migration in THA were considered. Only studies which reported quantitative data at least on one of the following patient characteristics were suitable: mean age, mean BMI (kg/m2), sex, side, time span between the index THA and the last follow-up (months) were eligible. A multiple linear model regression analysis was employed to verify the association between patient characteristics and the amount of liner wear and/or head migration. The Pearson Product-Moment Correlation Coefficient was used to assess the association between variables. Data from 12,629 patients were considered. The mean length of the follow-up was 90.5 ± 50.9 months. The mean age of patients at surgery was 58.4 ± 9.4 years, and the mean BMI was 27.2 ± 2.5 kg/m2. 57% (7199 of 12,629 patients) were women, and in 44% (5557 of 12,629 patients) THAs were performed on the left. The mean pre-operative Harris hip score was 46.5 ± 6.0 points. There was evidence of a moderate positive association between the amount of liner wear and the time elapsed between the index surgery to the follow-up (P = 0.02). There was evidence of a moderate positive association between the amount of head migration and the time elapsed between the index surgery to the follow-up (P = 0.01). No further statistically significant association was found. The time elapsed between the index surgery to the follow-up was the most important factor which influence the head migration and liner wear in THA. Patients’ characteristics and preoperative physical activity did not influence the amount of head migration and liner wear.

Search strategy.This study was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses: the 2020 PRISMA statement 40 .The PICOT algorithm was preliminary pointed out: • P (Problem): end-stage OA; • I (Intervention): THA; • C (Comparison): time span from THA, patient characteristics and performance; • O (Outcomes): liner wear, liner wear/year, head migration.
In July 2023, the following databases were accessed: PubMed, Web of Science, Google Scholar, Embase.No time constrain was set for the search.The following matrix of keywords were used in each database to accomplish the search using the Boolean operator AND/OR: (THA OR total hip) AND (arthroplasty OR replacement OR prosthesis) AND (wear OR migration OR creep OR liner OR head).No additional filters were used in the databases search.
Selection and data collection.Two authors (F.M. and A. B.) independently performed the database search.All the resulting titles were screened by hand and, if suitable, the abstract was accessed.The full-text of the abstracts which matched the topic were accessed.If the full-text was not accessible or available, the article was not considered for inclusion.A cross reference of the bibliography of the full-text articles was also performed by hand.Disagreements were debated and mutually solved by the authors.In case of further disagreements, a third senior author (N.M.) took the final decision.
Data items.Two authors (F.M. and A.B.) independently performed data extraction.The following generalities were extracted: author, year of publication, length of the follow-up, and number of procedures.The following data concerning patient demographic were extracted: mean age, mean BMI, percentage of women, percentage of left side, mean preoperative Harris Hip Score (HHS) 41 .Data on the following outcomes of interest were extracted: mean liner wear (mm), mean liner wear per year (mm/year), mean head migration (mm).

Assessment of the risk of bias and quality of the recommendations.
The risk of bias were evaluated in accordance with the guidelines in the Cochrane Handbook for Systematic Reviews of Interventions 42 .Two reviewers (F.M. and A.B.) evaluated the risk of bias of the extracted studies independently.Disagreements were solved by a third senior author (N.M.).All the included studies were evaluated using the risk of bias of the software Review Manager 5.3 (The Nordic Cochrane Collaboration, Copenhagen).The following endpoints were evaluated: selection, detection, performance, attrition, reporting, and other bias.
Risk of bias assessment.The Cochrane risk of bias tool was used to investigate between studies risk of bias.24% (25 of 105) of included studies randomly allocated their patients, and 69% (72 of 105 studies) were conducted in a prospective fashion leading to a low to moderate risk of selection bias.The risk of detection bias was high, as assessor blinding was seldom performed.The risk of attrition and reporting biases was low to moderate, as was the risk of other bias.Concluding, the risk of bias graph evidenced a moderate quality of the methodological assessment of RCTs (Fig. 2).

Synthesis of results.
There was evidence of a moderate positive association between the amount of wear and the time elapsed between the index surgery and the last follow-up (r = 0.22; P = 0.02).There was evidence of a moderate positive association between the amount of migration and the time elapsed between the index surgery to the last follow-up (r = 0.57; P = 0.01).No statistically significant association was found between the amount of wear and patient age (P = 0.2), BMI (P = 0.4), sex (P = 0.3), side (P = 0.4), and pre-operative HHS (P = 0.05).No statistically significant association was found between the amount of migration and patient age (P = 0.6), BMI (P = 0.3), sex (P = 0.6), side (P = 0.3), and pre-operative HHS (P = 0.1).No statistically significant association was found between the amount of wear per year and patient age (P = 0.1), BMI (P = 0.5), sex (P = 0.1), side (P = 0.8), pre-operative HHS (P = 0.6), and the time elapsed between the index surgery to the follow-up (P = 0.3).These results are shown in greater detail in Table 2.

Discussion
According to the main findings of the present study, the time elapsed between the index surgery to the followup was the most important factor which influences head migration and liner wear in THA.Moreover, patient age, BMI, sex, side, and preoperative HHS did not exert an influence in the amount of head migration and liner wear.The postoperative activity level as a potential parameter affecting head migration and liner wear could not be analysed because of missing relevant data in this regard.
The use of conventional polyethylene versus highly cross-linked polyethylene (HXPE) or vitamin E-infused highly cross-linked polyethylene (VE-HXPE) leads to higher wear rates and shorter implant survival, whereas no difference could be found between HXPE and VE-HXPE materials 34 .A recent study on 137 patients showed less wear rate in HXPE THA than in conventional polyethylene THA (0.028 mm/year and 0.086 mm/year, respectively) 49 .Survival rate after 18 years follow up was 95.5% in the HXPE group and 90.9% in the conventional polyethylene group 49 .In a randomised controlled trial study on 94 patients, 51 received a VE-HXPE THA and 43 received a HXPE THA 44 .After 5 years, there was no statistically significant difference in wear rate (24.0 μm/ year in VE-HXPE group and 23.2 μm/year in HXPE group).VE-HXPE demonstrated better results than HXPE after 10 years follow-up given the reduction of oxidative embrittlement.In general, HXPE, VE-HXPE, or ceramic on ceramic components exhibit the best wear and life span properties 47 .A positive association between the time elapsed between the index surgery to the follow-up and the amount of wear migration was evidenced.Migration results from the plastic deformation of polyethylene that occurs during the first 12-24 months, known as the bedding-in period 148,149 .The duration of the migration phase is debated.It is probably an overlapping process, time-dependent, as confirmed by our results 150 .Eliminating migration from total wear estimation resulted in an adjusted value that was nearly 50% lower than previously estimated total wear values 151 .
Metal on metal bearings lead to higher amounts of metal ions in the surrounding tissue and serum 152 .This could be seen as an indirect sign of component wear 153 , and leads to local inflammation, which promotes implant loosening through osteolysis 154 .Additionally, the metal ions can produce toxic systemic complications and deterioration of organ functions 155 .Metal on metal bearings is no longer recommended given these effects 156 .
Metal heads can be safely used with a polyethylene liner 157 .It is not clear whether any difference exists using metal head or ceramic head with HXPE 158,159 .Guadiani et al. 60 in a study on 120 patients showed a wear rate of 0.0135 mm/year using a ceramic head and 0.0171 mm/year using metal head.No differences were found in functional scores.
The most common materials are ceramic on ceramic, ceramic on polyethylene and metal on polyethylene 32 .A randomised controlled trial analysed the long-term functional and radiographic outcomes in 133 patients after bilateral THA 46 .In one hip, a ceramic-on-ceramic THA was implanted and in the other hip a ceramic-on-highly cross-linked polyethylene was implanted.conducted a 10 years follow-up study analysing factors that can predict wear in ceramicon-ceramic and ceramic-on-polyethylene THA.In accordance with our results, they showed that BMI, age and gender do not influence wear rate.Another study with 20 years follow-up confirms these results 161 .Garvin et al. 81 showed a very low wear rate in patients under 50 years old, at 0.022 mm/year.A recent study conducted by Sax et al. 162 on 130 THAs, using second-generation highly cross-linked polyethylene THA, showed opposite results, identifying an association between age and volumetric wear and an association between BMI and volumetric and linear wear.Younger patients have higher activities level than older patients 163 , but 10 years follow up study demonstrated that sport activities have no influence on migration and wear rate 164 .Low impact sport activities such as walking were included in the study 164 .There is an increasing number of young patients who undergo a THA, and the positive effect of sport on health and quality of life is well demonstrated 165,166 .Guy et al. 167 analysed wear rate in patients who practised high-impact sports.34 patients received a ceramic on HXLPE implant, and 34 patients received ceramic on conventional polyethylene implant.The HXLPE group showed a statistically significant lower wear rate and osteolysis rate than the conventional polyethylene group.Consensus guidelines for returning to sport after THA suggested that return to sport should be allowed for low-impact and moderateimpact sports, but not for high-impact sports 168 .The patients' main reason not to return to sport was surgeon's advice 169 .However, no difference in revision rate was found when comparing a sporting population with less active controls 170,171 .Two studies comparing obese with non-obese patients did not show an association between BMI and aseptic loosening, although the higher the BMI, the higher the reactive force through the hips 172,173 .
A major strength of the present study is the comprehensive analysis of the main demographic factors that can influence liner wear and head migration.To our knowledge, no other study examined the effect of these variables on THA, including all types of materials.The presence of a large number of RCTs in our study strengthens our results.Given the lack of quantitative data, it was not possible to analyse all the possible combinations of head  www.nature.com/scientificreports/and liner materials.The grey literature, i.e. unpublished or non-peer-reviewed research, was not included in the present study.It would be difficult to locate and assess for quality.Heijnens et al. 45 presented disappointing long-term results because of aseptic loosening in four of their 29 patients using carbon-fibre-reinforced polyether-ether-ketone (CFR-PEEK) liners, which might have influenced our results.Some studies did not differentiate between patients who had unilateral or bilateral THA.In unilateral THA, the forces distributed unequally between the two joints.Moreover, frequently the contralateral side is osteoarthritic and symptomatic.A painful contralateral hip, knee, or ankle might lead to increased weight-bearing of the operated leg.This could not be appreciated in most studies analysed for this systematic review.The size of the femoral head is another factor that can influence wear rate and migration: unfortunately, this could not be analysed given the lack of relevant data.Further investigations are necessary to investigate the association between liner wear and sport load. Vol

Figure 1 .
Figure 1.PRISMA flow chart of the literature search.

Table 1 .
Generalities and patient baseline of the included studies (RCT randomised controlled trial).

Table 2 .
Results of the linear regressions.