LITHUANIAN UNIVERSITY OF HEALTH SCIENCES

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LITHUANIAN UNIVERSITY OF HEALTH SCIENCES

FACULTY OF MEDICINE

DEPARTMENT OF PHYSICS, MATHEMATICS AND BIOPHYSICS

Influence of Primary Total Hip Arthroplasty on Patient-Reported

Quality of Life Within the First Postoperative Year

Maximilian Otto Ulrich Klug

Master’s Thesis Supervisor: Dr. Renata Paukštaitienė Consultant: Dr. Linas Pauliukėnas Kaunas, 2021

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1. SUMMARY

Author: Maximilian Otto Ulrich Klug.

Title: Influence of Primary Total Hip Arthroplasty on Patient-Reported Quality of Life Within the First

Postoperative Year.

Aim: To assess the quality of life for individuals with osteoarthritis (OA) undergoing primary total hip

arthroplasty (THA) within the first year postoperatively.

Objectives:

1. To assess the mental and physical well-being after THA measured with the SF-36 MCS and PCS at 3 months postoperatively and compare the results with the preoperative values in a meta-analysis.

Methods: A systematic electronic search of PubMed was conducted to identify reports published from

2011 to April 2021 in which primary THA for patients with osteoarthritis of the hip was performed. Studies were included which had primary OA as surgical indication, primary THA as type of surgery and reported preoperative and follow-up data on the SF-36 component summary scores PCS and MCS at 3-, 6- or 12-month follow-up. Quantitative meta-analyses of a total of 7 studies with 2867 patients was conducted to compare each of the follow-ups with their corresponding preoperative baseline data.

Results: Two meta-analyses, consisting each of five and three studies with 817 and 1186 patients,

indicated a significant increase in the MCS at the 3- and 12-month follow-up compared with the preoperative assessment (P = 0.007 and P = 0.0001). A meta-analysis consisting of five studies with 2052 patients could not report a statistically significant increase in the MCS at the 6-month follow-up compared to the baseline.

Three meta-analyses, two consisting each of five and one of two studies with 817, 2052 and 510 patients, indicated a significant increase in the PCS at the 3-,6- and 12-month follow-up compared with the preoperative assessment (P < 0.00001, P < 0.00001 and P < 0.00001).

Conclusions: This meta-analysis indicates that there is a significant and sustainable increase in the

health-related quality of life, both mental and physical, associated with total hip arthroplasty throughout the follow-up time of three to 12 months, except for mental well-being at the 6-month follow-up, for which no statistically significant effect was found.

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2. ACKNOWLEDGMENTS

I would like to thank my supervisor Dr. Renata Paukštaitienė and my consultant Dr. Linas Pauliukėnas for their help in guiding me throughout the process of this master’s thesis.

3. CONFLICTS OF INTERESTS

The author reports no conflicts of interest.

4. PERMISSION ISSUED BY THE ETHICS COMMITTEE

The ethical approval for conducting this master’s thesis was obtained from the Bioethics Center of the Lithuanian University of Health Sciences. Registration code: BEC-MF-282.

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5. ABBREVIATIONS

α – significance level in testing of statistical hypothesis

VT - Vitality

THA - Total hip arthroplasty

SMD - Standardised mean difference SF-36 - 36-item Short Form Survey SF-12 - 12-item Short Form Survey SF - Social functioning

SEM - Standard error of the mean SD - Standard deviation

RR - Response rate RP - Role-physical RE - Role-emotional

RCT - Randomized controlled trial QoL - Quality of Life

PROM - Patient-Reported Outcome Measure

PRISMA - Preferred Reporting Items for Systematic Reviews and Meta-Analyses PF - Physical functioning

PCS - Physical component summary score P – p-value in testing of statistical hypothesis OA - Osteoarthritis

MRR - Minimal response rate MH - Mental health

MeSH - Medical Subject Headings

MCS - Mental component summary score MCID - Minimal clinically important difference ISAR - International Society of Arthroplasty Registries I2_{- Measure of inconsistency}

HRQoL - Health-Related Quality of Life GH - General health

EQ-5D - EuroQol 5 Dimension Health Outcome Survey CI - Confidence interval

BP - Bodily pain BMI - Body mass index

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6. INTRODUCTION

With over one million procedures worldwide per year, total hip arthroplasty (THA) has become a common procedure [1] for patients with advanced osteoarthritis (OA) of the hip to restore function, relieve and improve pain and quality of life. The Lithuanian arthroplasty register reports a total of 12657 performed primary THAs within only the four-year period of 2011-2014 [2]. Due to the aging population in many developed countries, it is expected to see an increase in procedures performed each year in the near to mid-term future [3-6].

While the focus of outcome assessment of THA had been on the surgical and technical aspects, there is a trend in outcome research to put an increased focus on patient-centred outcomes [7]. No gold standard for patient-reported outcome measures (PROM) has emerged yet and within the last 15 years an ever-increasing variety and usage in orthopaedic research is described in the literature [8]. A commonly used PROM to assess the health-related quality of life (HRQoL) of patients after THAs is the 36-Item Short Form Survey (SF-36), which explores quality of life across eight domains and two component summary scores are derived thereof: mental (MCS) and physical (PCS) well-being [9].

A systematic review and meta-analysis of the literature of the last decade with the time scope of 3 - 12 months postoperatively is performed upon the question if THA yields statistically significant improvement of HRQoL for patients in both domains (MCS and PCS) within the early period after total hip replacement. The SF-36 was chosen as the PROM to be evaluated because of its distinct mental and physical scores.

THA as an elective procedure for patients burdened with end-stage OA comes along with the hopes and wishes regarding the functional and overall outcome for a better life postoperatively. The findings of the current study may help in moderation of realistic patient’s expectations regarding improved quality of life in the short-term.

Follow-up studies and meta-analyses evaluating PROMs have demonstrated superior mid- to long-term quality of life after THA, especially in the physical well-being domains [10-11]. This thesis aims to explore the literature for the short-term mental and physical domains of the quality of life for individuals with osteoarthritis undergoing primary THA.

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7. AIM AND OBJECTIVES

Aim:

To assess the quality of life for individuals with osteoarthritis undergoing primary total hip arthroplasty (THA) within the first year postoperatively.

Objectives:

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8. LITERATURE REVIEW

8.1. Total Hip arthroplasty (THA)

The general concept of THA, also called total hip replacement, is to resect the femoral head and replace it with a prosthetic head fixed to a metallic stem fitted into the remaining femoral shaft. Depending on the technique used, the fixation is done in a cemented or uncemented fashion. The cartilage of the acetabulum is replaced with an artificial acetabular cup. A spacer or liner between the femoral and acetabular parts of the prothesis ensures smooth gliding between the components. The bearing surfaces, e.g., the prosthetic femoral head and the acetabular liner are available in different materials, such as metal, polyethylene, and ceramic. Various combinations of them can be used together. Surgeons can choose from a variety of surgical approaches; however, the most common ones are the posterior, direct lateral, and direct anterior approach [12].

8.1.1. Prevalence, incidence and future projections of THA

With over one million procedures worldwide per year, THA has become a common procedure [1]. The number of persons living with a hip endoprosthesis is high, the annual cases for THA are rising and this is projected to yet continue over the next decades. Tarasevičius et al. [2] report from the Lithuanian arthroplasty register a total of 12657 performed primary THAs within the four-year period of 2011-2014 in Lithuania alone. The prevalence of THA among the total population in the United States was 0.83% in 2010, however, with increasing age it rises to 5.26% at eighty years, which constitutes approximately 2.5 million living with a THA performed on them. The female population exhibits a higher prevalence in comparison to males [13].

A projection for the predicted future annual use of primary THA in the United States (US) predicts an increase from 498.000 in 2020 to 1.42 million in only two decades, by 2040 [3]. In Germany the annual number of THA procedures was over 213.000 in 2010, with an incidence of 261 per 100.000 population. This figure is projected to rise to 288.000 with an incidence of 360 by the year 2040, respectively, which constitutes a growth of 38% within three decades. While the incidence in the total population is assumed to rise, the incidence within the age groups is expected to remain constant. The overall rise of the incidence is attributed to the reality of an aging population in many Western countries, such as the United States or Germany. It is aggravated by the age cohort born in the 1960s, the so called “baby boomers”, who are about to enter the average age for receiving primary THA (65 years) [4-6].

8.1.2. Indications for THA

There is no international consensus for the surgical indication of THA and the criteria appear to be different from the level of the referring physicians to regional and national practice [1, 14]. In a statement of the National Institutes of Health (US) the recommendation in favour of THA addresses the

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patient population with pathology of the hip that causes “chronic discomfort and significant functional impairment“ [15]. A common indication for THA is osteoarthritis (OA) of the hip; with OA being defined by current concepts as a functional failure of synovial joints involving “the entire joint organ, including the subchondral bone, menisci, ligaments, periarticular muscle, capsule and synovium” [16].

According to Hunter et. al. 2008 [17] the surgical option in OA should be reserved for the individuals with severe pain and functional limitations of activities of daily living refractive to non-surgical therapeutical approaches, both, non-pharmacological and pharmacological.

8.1.3. Influence of surgical approaches on outcome of THA

Commonly used surgical approaches in THA are in comparison not superior over each other in the postoperative outcome beyond the immediate to early postoperative time. A meta-analysis comparing the direct anterior approach with the posterior approach did not show any significant differences in the Harris hip score (a disease specific HRQOL instrument) at three months and one year post-op [18]. In a recent meta-analysis comparing the direct anterior approach (DAA) with other surgical approaches in THA, the DAA only displays superior functional outcome within the first 6 weeks postoperatively, but not beyond [19].

8.1.4. Influencing pre-intervention factors on postoperative outcome of THA

Among many factors, the age, BMI, various comorbidities, the level of education and waiting time for the surgical procedure of patients may influence the expected QoL outcome. Umehara et al. [20] found that that the preoperative SF-36 scores for the BMI >25kg/m2_{group were lower, than for}

groups with lower BMI, however no difference was reported in the postoperative outcome scores. Moreover, the study identified age as a possible influence on postoperative quality of life (QoL), with the age group <70 years showing significant increase in the SF-36 scores. Huddleston et al. [21] describe both, age and obesity, as well as the year of the procedure, as risk factors for experiencing adverse events postoperatively, but not female gender, chronic obstructive pulmonary disease, diabetes and smoking. The negative influence of obesity on early postoperative complication rates of THA is also reported by Friedman et al. [22].

The level of education is a prognostic factor for the QoL outcome and satisfaction after THA. Greene et al. [23] showed that a high education level was associated with a higher HRQoL and less pain postoperatively compared to patients with low and medium education status. Cardiovascular, pulmonary, metabolic diseases are a common burden among the target population for THA and may influence the QoL experienced after THA. A Danish study exploring the influence of comorbidity burden on HRQoL outcome saw a significant increase in patient-reported quality of life regardless of the extent of comorbidities reported before the intervention. Interestingly, patients with a higher degree

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of comorbidities also reported a higher gain in QoL at the 3-month follow-up and the mean responses were similar to the groups with no comorbidities. One year post-op, however, the groups with comorbidities saw a stagnation in QoL, while the patients with no comorbidities experienced a further increase thereof [24].

Often patients with end-stage OA in need of THA are facing long waiting times for the procedure, for example in Sweden the average patient waited 239 days [25]. Long waiting times can negatively influence the expected outcome. Vergara et al. [26] report, that patients enrolled in waiting lists for THA in Spain are expected to wait longer if their preoperative pain and functional status was relatively high. However, for patients waiting longer than six months the functional gain was comparably smaller, than for the prioritized patients with a higher preoperative functional impairment and burden of pain, but shorter waiting times.

8.1.5. Quality of life: mental and physical well-being after THA

Physical and mental well-being after THA for different follow-up times report generally an improvement compared to preoperative assessments of patients with end-stage OA. In a long term 16-year follow-up study of 250 THA patients it was concluded that PROMs yielded an impaired self-reported physical well-being, despite a better physical performance compared to patients with severe, untreated OA of the hip [11].

A meta-analysis on the quality of life from 3.6 to 7 years after THA exploring 20 studies and considering various generic and disease-specific instruments to assess HRQoL found the mid-term postoperative QoL outcome superior to the preoperative baseline [10]. Nguyen et al. [27] examined the mental wellbeing after THA and concluded, that there was a significant improvement one-year postoperatively, while there was an association between mental health and the improvement of pain and function.

8.2. Assessment of quality of life (QoL) and health-related quality of life (HRQoL)

The terms “quality of life”, “health-related quality of life” and “health status” are widely used, but lack in consensual and distinguishable definitions in the literature [28]. The world health organisation’s definition of health is “a state of complete physical, mental and social well-being, and not merely the absence of disease and infirmity” [29]. Various measures of QoL and HRQoL have been inspired by this definition, among them the 36-item Short Form Survey (SF-36) [28].

8.2.1. Generic patient-reported outcome measures in THA

There is no consensus on the ideal tool for researchers to use in evaluating health-related quality of life (HRQoL) in THA and different generic and disease specific outcome measures exists in the literature, with an overall increasing utilization rate of the individual instruments in the last 15 years.

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Among the different instruments, for generically assessing the quality of life there is a wide use of the Short Form-36 Health Survey (SF-36), the related 12-item Short Form Health Survey (SF-12) and the EuroQol 5 Dimension Health Outcome Survey (EQ-5D) [8]. The great variety of patient-reported outcome measures used currently in orthopaedic research is problematic due to the difficult cross-study comparison of outcomes. Siljander et al. [30] reviewed four of the major orthopaedic journals from 2004-2016 and found a total of 42 unique PROM instruments used.

8.2.2. The 36-Item Short Form Survey (SF-36)

The SF-36 is a generic (HRQoL) outcome tool and consists of 36 items to assess self-reported HRQoL, producing eight different domains: physical functioning (PF), role-physical (RP), bodily pain (BP), general health (GH), vitality (VT), social functioning (SF), role-emotional (RE), and mental health (MH). From the eight domains summary scores can be derived, the physical health component score (PCS) is derived from PF, RP, BP, GH and the mental health component score (MCS) from VT, SF, RE and MH, respectively. The better the self-reported health and function, the higher the value represented in the score [9].

8.2.3. Response rates of PROMs in evaluating THA

High response rates (RR) of the participants of trials on PROMs are an important factor for reliable datasets and subsequent high quality of their analyses. However, due to loss to follow-up of participants in many studies the ideal required RRs are often not met. Pronk et al. [31] conducted a retrospective analysis of prospectively collected data on PROMs of patients receiving primary THA and aimed to investigate the minimal response rate (MRR) for an adequate evaluation of the procedure. They concluded that all of the participants were needed to respond on the preoperative and at the 3-month follow-up, resulting in a MMR of 100%. Taking the reality of non-responders into consideration, they recommend a MRR of 60%, which is a threshold also corroborated by the International Society of Arthroplasty Registries (ISAR) [32].

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9. RESEARCH METHODOLOGY AND METHODS

9.1. Protocol

This systematic review and meta-analysis were conducted by following the recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) [33].

9.2. Research question

The following research question was formulated using the PICO (population, intervention, comparison, outcome) process omitting the domain of a comparison [tab. 1]:

What is the quality of life in adults with primary osteoarthritis of the hip within the first year after primary total hip arthroplasty (THA) with the evaluation of the MCS and PCS derived summary scores of the SF-36 assessed at a baseline preoperatively and at 3-, 6- and 12-months follow-up?

Table 1: PICO process of the research question Definition Description

Population Adults with primary osteoarthritis of the hip Intervention Primary total hip arthroplasty (THA)

Comparison Not applicable

Outcome Quality of life evaluated by MCS and PCS derived summary scores of the SF-36

assessed at a baseline pre-operatively and at 1-2, 3, 6 and 12 months follow-up. The comparison domain of the PICO process was found to be not applicable, because the research interest is about the general evaluation of QoL after THAs of individuals with the burden of OA, comparing the baseline (preoperative values) with the outcome values at follow-up intervals.

9.3. Eligibility criteria

Reports that met all the following criteria were considered eligible for inclusion in the systematic review:

(1) Adult patients with primary OA as surgical indication undergoing THA. (2) Primary THA as type of surgery.

(3) Data on MCS and/or PCS of the SF-36.

(4) Preoperative data and follow-up data for (at least) one of the following points of time: 3 months, 6 months, or 12 months postoperatively.

Reports that had at least one of the following criteria were excluded from the systematic review: (1) No preoperative baseline data of the SF-36 component summary scores and / or no postoperative

follow-up data available.

(2) Indication for THA is not mainly primary OA in the assessed patient population.

(3) Follow-up times do not include any of the specific intervals of 3, 6, or 12 months postoperatively. (4) Data on SF-36 summary scores are not expressed as mean.

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(5) Reports on revision THA or indication is fracture, infection or oncological conditions of patients. (6) Response rate of the participants of less than 60%.

(7) Mean BMI over 30 kg/m2_{or mean age <55 or >75 years.}

(8) Published before 2011 and / or not in the English language.

9.4. Information sources and search strategy

A search of the database PubMed for articles in English published between 2011 and 2021 was conducted, with the last search on the 04.04.2020. The search was composed of several medical subject headings (MeSH), other search terms and the Boolean operators “AND” and “OR” [ tab. 2].

Table 2: Search strategy used Description Keywords

1st_{keyword terms} _{(“Arthroplasty, Replacement, Hip”[Mesh])}

Boolean operator

(Connector) AND

2nd_{keyword terms (“Quality of Life” [Mesh] OR SF-36 OR SF36 OR SF 36 OR short}

form 36 OR 36-Item Short Form Survey OR 36-Item Short Form Questionnaire)

Filters English, from 2011 – 2021

9.5. Selection process

In the first stage of the selection process, the author independently screened the articles identified by the electronic search in PubMed by titles and abstracts for inclusion in the systematic review by the preformulated inclusion and exclusion criteria. In a second stage the successfully retrieved full-text reports were screened for the same beforementioned criteria. In the entire process there was no second reviewer involved.

9.6. Data extraction

The author independently extracted all the data from full-text articles, there was no second reviewer involved. No authors of the reviewed articles were contacted. The full-text articles were reviewed to extract data on sample size, study characteristics, study period, geographical study location, response rate of participants, patient demographics (mean age (standard deviation (SD)), mean BMI (SD), percentage of male patients included in the study, baseline (preoperative) mean of MCS and PCS (SD) and corresponding follow-up means (SD) at 3, 6 or 12 months postoperatively. Only data expressed as means was considered for extraction, if the data was not expressed as means with standard deviation (SD), but means with 95% confidence interval (CI) or means with standard error of the mean (SEM) the CI or SEM was converted to SD. This was done for confidence intervals by using

mean − t_!"#$%&$'& &)*+$#+,%

-"$./0) "+1) < m < mean + t!

"#$%&$'& &)*+$#+,% -"$./0) "+1)

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With 𝑡₂ = 𝑡!"#

$ (𝑛 − 1) and P= 0.95.

For SEMs the SD was calculated with: SEM = "#$%&$'& &)*+$#+,% -"$./0) "+1)

9.7. Study risk of bias assessment

This systematic review includes RCTs and other controlled trials with experimental and control groups, however, according to the research question formulated, the interest lays on the HRQoL after primary THA for a patient population with primary OA. Therefore, the focus of this review does not include a comparison of treatment effect of differently designed study settings for the subgroups of the included studies, but rather the overall impact of THA on physical and mental well-being. For this reason, a validated risk of bias assessment tool, which exists for other common study designs such as meta-analyses of RCTs, could not be identified for the design of the current meta-analysis. The author chose to study the risk of bias with an approach suitable for this research design inspired by the recommendations for the risk of bias of non-randomized studies of the Cochrane Handbook for Systematic Reviews of Interventions version 6.2 [34]. A hypothetical ideal “target trial” would be a trial of two study groups of the exact same demographics and same baseline scores for MCS and PCS. The experimental group would undergo surgically the same THA and receive the same aftercare, while the control group would not receive any surgery or additional treatment. Baseline and follow-up assessments with the SF-36 would be used to compare the outcome of both groups and allow a comparison and assessment of the impact of THA on the QoL in a controlled manner and with a high precision if the response rate is at 100%. This, however, would be an unethical research design, because it cannot be justified to withhold a surgical treatment for patients in need for it. With this hypothetical “ideal” trial in mind, the focus of the assessment of the risk of bias was assessed upon the degree of heterogeneity of the study participants baseline demographics including preoperative MCS, PCS, age, proportion of males to females and BMI. These pre-intervention prognostic factors represent the assessed confounding biases.

Table 3: Assessment of bias questionnaire Item Question

1 By how much does the response rate deviate from the ideal 100%?

2 By how much does the mean age of the participants deviate from the calculated median age

of all included studies?

3 By how much does the mean preoperative MCS of the participants deviate from the

calculated median baseline MCS of all included studies?

4 By how much does the mean preoperative PCS of the participants deviate from the

calculated median baseline PCS of all included studies?

5 By how much does the mean BMI of the participants deviate from the calculated median

BMI of all included studies?

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Selection bias was considered with the extent of loss to follow-up of the participants in the form of the response rate (RR) within the time scope of interest of this review, e.g. the RR from baseline to a maximum of 12 months - independently of a different RR reported for a later follow-up present in the individual included study. This method of a risk of bias assessment for the purpose of this research has not been validated and thus the results are reported in table 6 descriptively for each item and study without a scoring system. Each report’s risk of bias was assessed according to six items shown in table

3. For each item the reference value of the evaluated parameter, such as mean age or BMI, was set by

finding the median of it across all included studies. Each degree of deviation from the calculated median of one of the individual parameters was assigned a significance of deviation: “0” for 0-4.9%, “+” for 5 – 9.9%, “++” for 10-15% and “+++” for >15% deviation.

9.8. Statistical analysis

Meta-analyses of a total of seven studies with 2867 patients was used to assess the quality of life for individuals with osteoarthritis (OA) undergoing primary total hip arthroplasty (THA) within the first year postoperatively. A meta-analysis is a statistical approach to combine the results of multiple studies on the same or similar subject and aims to determine an overall weighted average of the estimated intervention effects of the included reports [35]. The effect measures were the patient-reported response means of either MCS or PCS at a preoperative and at one of the follow-up intervals (3, 6, 12 months). A higher value indicates better self-reported mental or physical well-being [36]. All meta-analyses were conducted with the use of the software Review Manager (RevMan 5) version 5.4.

Two statistical models were used for meta-analysis: fixed-effect model and random-effect model. The fixed effect model is based on the assumption, that the estimated effect of intervention is the same for all studies and observed differences appear due to sampling error. The random-effect model works with the assumption, that the estimated effects follow a distribution in which the centre represents the average effect and its width the extent of heterogeneity, while the differences in intervention effects are considered to be random [35].

In a meta-analysis of preoperative versus follow-up data of either MCS or PCS means, using the inverse variance method with a random-effects model, the standardized mean difference across the analysed studies was estimated with a 95% confidence interval. The standardized mean difference is in the current study calculated by the difference in mean outcomes between preoperative baseline and a follow-up outcome of the same group divided by the standard deviation of outcomes among the participants [37]. This method was used in all cases where heterogeneity was detected. In case heterogeneity was low to moderate the fixed-effects model was used.

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Statistical heterogeneity across studies was assessed with the chi-squared (c2_{) test. The null}

hypothesis of the test states that all studies are homogeneous. If the null hypothesis of the test is rejected (if P < 0.05), heterogeneity across studies is present. Additionally, a measure of inconsistency (index I2₎

was determined to represent the variation in treatment effect among the studies that is not due to chance. The I2_{index was determined by using the formula:}

𝐼3 _{= 3}𝜒3− 𝑑𝑓

𝜒3 7 ∙ 100%

where 𝜒3_{is a test statistic for the chi-squared (c}2_{) test and df – degrees of freedom.}

Rough interpretation of the index I2_{: if I}2_{is 0 – 40% heterogeneity is low, 30-60% – moderate, 50-90%}

– substantial and 75-100% considerable heterogeneity [35].

Statistical threshold of heterogeneity for choice of statistical model was: if I2_{< 50% and P > α,}

the fixed-effects model was used, if I2_{> 50% or P < α – random-effect model was used. In all statistical}

analyses significance level (α) equal to 0.05 was used.

The results of the meta-analyses were presented using forest plots. A forest plot is an illustration of the effect estimates and confidence intervals of both the individual included studies, and the meta-analysis itself. Every study is displayed by a rectangle at the point estimate of intervention effect, the area of which represents the weight allocated to the study within the meta-analysis. A horizontal line crossing through the rectangle depicts the corresponding confidence interval [35]. Below, the summary result of the meta-analysis is represented in the illustration by a diamond shape, which displays in its vertical axis the combined point estimate of the studies, while the horizontal axis shows the corresponding 95% confidence interval.

Publication bias was evaluated by creating funnel plots. A funnel plot scatters the individual study’s effect estimates against their corresponding precision, with the horizontal axis assigned to the standardized mean difference (SMD) and the vertical axis representing the standard error of the SMD in this current review. An inverted and symmetrical funnel-shaped distribution indicates absence of publication bias, while a skewed and asymmetrical distribution could indicate its presence [38].

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10. RESULTS

10.1. Study selection

The search strategy described in table 2 identified 701 reports (see Fig. 1) which were screened by title and abstract according to the inclusion and exclusion criteria for eligibility. 66 reports were sought for retrieval, 10 reports could not be retrieved. 56 reports were, in a second phase, screened by a thorough full-text screening for enrolment in the systematic review, of which seven [39-45] were included in the meta-analysis while 49 reports were excluded because they did not provide data on the SF-36 component summary scores (n = 26), the follow-up assessment times did not match the inclusion criteria or no preoperative baseline was provided (n = 13), the response rate of the participants in the study was less < 60% or not described (n = 5), data of the MCS/ PCS was not expressed as mean (n=4) or the study population was the same as an already included study [43] (n = 1).

Fig.1: Prisma flow diagram describing study selection according to Page et al. [33]

Records identified in PubMed (Last searched on 04.04.2021):

Search strategy:

("Arthroplasty, Replacement, Hip"[Mesh]) AND ("Quality of Life"[Mesh] OR SF-36 OR SF36 OR SF 36 OR short form 36 OR 36-Item Short Form Survey OR 36-Item Short Form Questionnaire) Filters: English, from 2011 – 2021 (n = 701)

Records screened (by title and

abstract) (n = 701) Records excluded (n = 635) Irrelevant (n = 151) SF-36 not used (n = 201) Fracture (n = 55) Resurfacing (n = 17) Revision/Infection (n = 45) Not THA (n = 6)

Follow-up times not of interest (n = 97) Indication not osteoarthritis (n = 37) Study protocol (n = 23)

Not human (n = 2) Paediatric: (n = 1)

Reports sought for retrieval

(n = 66)

Reports not retrieved

(n = 10)

Reports assessed for eligibility

(n = 56)

Reports excluded (n = 49)

No data on MCS/PCS reported (n =26) No follow-up times of interest/ no preoperative baseline (n =13)

Response rate <60%/ or not reported (n = 5) Data not expressed as mean (n = 4) Same patient population (n = 1)

Studies included in meta-analysis [39-45] (n = 7) Id en ti fi cat ion Sc re eni ng In cl ud ed

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10.2. Study characteristics

The seven studies consisting of 14 subgroups included in this meta-analysis all have either a prospective study design [39,42,44-45] or reviewed retrospectively data [40-41,43] from other published or partially unpublished trials with exclusively prospectively collected data [tab. 5]. Total hip arthroplasty was the type of surgery for all studies, only two studies reported the surgical approach applied: Coulter et al. [39] used either the lateral or posterolateral approach; Reichert et al. [44] compared the single-incision direct anterior with the direct transgluteal lateral approach. The study objectives, methods, results and conclusions are described in detail in table 4.

Table 4: Objectives, methods, results, conclusions of included reports Author

(Year) Objective Method Result Conclusion

Coulter, 2017 [39] Comparison of effectiveness of unsupervised, home-based versus supervised outpatient-based physiotherapy after THA.

Single-blind RCT with 98 patients after THA either assigned to a supervised 4-week outpatient physiotherapy program or an unsupervised physiotherapy program with written and pictorial instructions. Outcome was assessed preoperatively and at a maximum follow-up of 6 months with following instruments: WOMAC, SF-36 (MCS, PCS), UCLA, TUG.

No significant difference for any measure between the groups. Clinical and statistical similar outcome after THA between supervised and unsupervised physiotherapeutic rehabilitation. Goh,

2020 [40] Assessment of the impact of psychological distress on PROM after THA.

Retrospective analysis of

prospectively collected data on SF-36 (MCS, PCS), OHS, WOMAC preoperatively and at a maximum 2-year follow-up of 1384 patients undergoing THA. Stratification of patients into a distressed and non-distressed group according to a baseline MCS value of 50 and subsequent multiple regression analysis was conducted.

For the PCS, the distressed group had a lower score at 6 months, but not at 2 years compared to non-distressed group.

THA may lead to an improved mental well-being in preoperatively distressed patients. Jaiswal, 2019 [41] Assessment of impact of preoperative mental well-being on functional outcome after THA.

Prospective cohort study relying on data of a RCT with 677 patients undergoing THA with assessment of SF-36 (MCS) and WOMAC preoperatively and at a 12-month follow-up to conduct a multiple linear regression to determine the effect of mental health on the WOMAC index.

Mean WOMAC and SF-36 MCS were significantly increased at 12 months, strong correlation between pre-operative MCS and improvement in WOMAC index at 12 months. There is a correlation between pre-operative-mental health and the resolution of pain and better function.

Kuchálik,

2017 [42] Assessing the long-term outcome of THA using local infiltration analgesia (LIA).

Secondary analysis of data of a RCT with 80 patients with an

experimental group receiving local infiltration analgesia and a control group receiving intrathecal morphine (ITM) for post-operative pain management. Outcome was assessed with HOOS, EQ-5D, SF-36 (MCS, PCS), NRS at a preoperative baseline and with a maximum follow-up of 2 years.

No significant differences between groups on outcome scales, except for a group by time interaction in favour of the LIA on the EQ-5D index.

The study did not reveal significant differences between patients receiving LIA and those with ITM

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Table 4 (continued) Author

(Year) Objective Method Result Conclusion

Liebs, 2014 [43]

Evaluation of the impact of femoral offset after THA on quality of life.

Secondary analysis of data of RCTs evaluating different methods of rehabilitation to assess the correlation of femoral offset with pain after THA. 362 patients were assessed with post-operative radiographs for femoral offset as well as WOMAC, SF-36 (MCS, PCS) as outcome measure pre-operatively and with a maximum follow-up of 2 years.

The amount of offset had an association with the WOMAC pain subscale, with the low offset group showing less pain, than the normal- and high-offset group. MCS and PCS were not different between groups.

Low femoral offset after THA displays less pain than normal or high offset.

Reichert,

2018 [44] Comparison of clinical outcome of THA between the single-incision direct anterior (DAA) and the direct transgluteal lateral surgical approach.

A RCT of 123 patients randomized into two different surgical

approaches of THA were evaluated by post-operative x-rays as well as HHS, XSFMA, SF-36, SAM and T25-FW pre-operatively and at a maximum follow-up of 12 months.

The DAA group showed higher self-reported patient activity, no other differences between groups. No difference between surgical approaches in function are evident, while the DAA group showed higher patient activity compared to the lateral approach group. Tristaino, 2016[45] Assessment of effectiveness of psychological support for patients receiving total joint arthroplasty.

A non-randomized prospective controlled cohort study with 200 patients undergoing THA or TKA alternately assigned to either receive routine care or in addition

psychological support from the preoperative to the rehabilitation period. Assessment of outcome was conducted with SF-36 (MCS, PCS) and HADS pre-operatively and with a 4-month maximum follow-up.

The THA group with psychological support reached the physiotherapy goal one day earlier than the control. The experimental group showed on the HADS a lower percentage of anxiety and depression. The patients receiving psychological support had a lower incidence of anxiety and depression as well as better mental well-being.

WOMAC = Western Ontario and McMaster Universities Osteoarthritis Index; UCLA=University of California, Los Angeles activity scale, TUG=timed Up and Go test, HOOS= Hip dysfunction and Osteo-arthritis Outcome Score; NRS= Numeric rating score; LIA= local infiltration analgesia; ITM= intrathecal morphine; RCT= Randomized controlled trial; HHS= Harris hip score, XSFMA= extra short musculoskeletal functional assessment questionnaire, SAM= Stepwatch Activity Monitor; T25-FW= timed 25 m foot walk; TKA= Total knee arthroplasty; HADS= Hospital Anxiety and Depression scale; OHS= Oxford hip score

The mean age of the participants ranged from 59.9 [45] to 73.0 years [43] and the mean BMI from 25.8 [40] to 28.4 kg/m2_{[41]. Goh et al. [40] have the largest sample size (total of 1364 participants)}

and with 14 years the longest study period as well. The lowest sample size is the home-based physiotherapy group of Coulter et al. [39] with a total of 42 patients. Four reports are from Europe [42-45], one from Australia [39], one from Asia [40] and one from Northern America [41]. The response rate ranges from 70.42% [44] to 96.83% [45]. A more detailed description of the demographics of each study is presented in table 5.

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Table 5: Demographics of participants in the included reports

Author

(Year) Study period Subgroup Study design Location RR N Age mean (SD) Male % Mean BMI (SD) Coulter, 2017 [39] 2010-2014 P Australia 64 (53 -86) A _{41.8 NR} Supervised 92.86 56 Home-based 90.48 42 Goh, 2020 [40] 2001-2015 R Singapore 72.3 Distressed 720 61.1 (12.8) 25.4 25.8 (4.8) Non-distressed 644 62.5 (11.7) 35.6 25.8 (4.8) Jaiswal, 2019 [41] 2005-2006 R Canada 85.36 677 67.5 (12.0) 41.8 28.4 (5) Kuchálik, 2017 [42] 2011-2012 P Sweden 80 50 to 85 (NR) NR NR ITM 90 LIA 87.5 Liebs, 2014 [43] 2003-2006 R Germany 87.2 Low offset 75 67.8 (7.8) 26.6 27.5 (4.7) Normal offset 195 69.3 (8.1) 32.8 27.1 (4.4) High offset 92 73.0 (7.2) 52.1 26.6 (3.2) Reichert, 2018 [44] 2011-2014 P Germany Anterior 94.81 77 63.2 (8.2) 58.4 28.1 (3.7) Lateral 70.42 71 61.9 (7.8) 54.9 28.3 (3.4) Tristaino, 2016 [45] 2011-2012 P Italy NR EXP 96.83 61 59.9 (8.4) 59.0 CTR 95.45 63 63.7 (8.7) 49.2

A= median and interquartile range; P = prospective; R= retrospective; NR= not recorded; RR = response rate; N= number of participants

10.3. Risk of bias in studies

Considering the baseline demographics of the included studies, the calculated medians functioning as reference values to assess the deviation thereof are: 63.7 years median age, 27.3 kg/m2

median BMI, median baseline MCS of 50.45 and 27.8 median baseline PCS. According to these medians the assessment of risk of bias (see tab. 3) was done and its results are demonstrated in table 6. Overall, there is a high degree of heterogeneity among the included studies in their demographic features at baseline, this is especially the case for the proportion of male to female participants, baseline MCS and PCS results and the response rates. Relatively low heterogeneity was found for the mean age and BMI.

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Table 6: Evaluation of risk of bias according to assessment questionnaire (see tab. 3)

Author (Year) Subgroup Item 1

(RR) Item 2 (AGE) Item 3 (MCS) Item 4 (PCS) Item 5 (BMI) Item 6 (Gender) Coulter, 2017 [39] Supervised + 0 +++ +++ NR +++ Home-based + 0 +++ +++ NR +++ Goh, 2020 [40] Distressed +++ 0 +++ 0 0 +++ Non-distressed +++ 0 ++ 0 0 +++ Jaiswal, 2019 [41] ++ + +++ NR 0 +++ Kuchálik, 2017 [42] ITM + NR 0 + NR NR LIA ++ NR 0 0 NR NR

Liebs, 2014 [43] Low offset ++ + 0 0 0 +++

Normal offset ++ + 0 0 0 +++ High offset ++ ++ 0 0 0 0 Reichert, 2018 [44] Anterior Lateral +++ + 0 0 ++ ++ 0 + 0 0 +++ + Tristaino, 2016 [45] EXP 0 + 0 +++ NR +++ CTR 0 0 +++ ++ NR 0

Each degree of deviation from the calculated median of one of the individual parameters is assigned a power of deviation: “0” for 0-4.9%, “+” for 5 – 9.9%, “++” for 10-15% and “+++” for >15% deviation. If a parameter is not reported in the study, it is assigned “NR” for “not recorded”.

Coulter et al. [39] report data with by far the largest standard deviation of the included studies indicating low precision, they did not report the mean BMI of the participants. The baseline MCS and PCS are comparatively high and the differences in means between baseline and follow-up values are the largest reported among the included studies [tab. 7]. The response rate is with 90.48 and 92.86 % for both subgroups relatively high. Goh et al. [40] have the second lowest response rate (after the lateral approach group of Reichert et al. [44] with 70.42 %) of the included reports (72.3%), both of their subgroups together have the highest sample size of this review.

The stratification of patients into a distressed and non-distressed group according to their baseline MCS value yields a risk of bias because of different preintervention conditions, considering the heterogenous baseline values on MCS and PCS among the remaining studies enrolled in this review, the differences do not stand out. Jaiswal et al. [41] report a relatively low response rate of 85.36%, but a high sample size of 677. The precision of the reported data is, with the second largest standard deviation after Coulter et al. [39], of lower quality.

Kuchálik et al. [42] do not report sufficient demographic data on the included patient population, neither the mean BMI nor the proportion of male to female participants are presented. The stratification of patients by their femoral offset by Liebs et al. [43] yields a confounding bias, the outcome of the subgroups shows results with a high similarity, however. Reichert et al. [44] report in the lateral approach subgroup the lowest response rate of the included studies with 70.42 %. Tristaino et

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al. [45] yield a confounding bias, because the experimental group (EXP) received psychological support from the preoperative to the rehabilitation phase, which may have a direct influence on the PROM outcome beyond the THA itself.

10.4. Results of individual studies

Across the included studies there is a wide variety of outcomes for the mean mental (MCS) and physical (PCS) summary scores [tab. 7]. The mean difference from baseline to the 3-month follow-up ranges from a mean increase of 10.3 in the high-offset group of Liebs et al. [43] to 36.24 in the supervised group of Coulter et al. [39]. The same groups also constitute the range for the 6-month follow up, with Liebs et al. [43] improving further to a 13.97 and Coulter et al. [39] slightly decreasing to a 35.84 difference in means.

Table 7: Reported means of the MCS and PCS at baseline (preoperative) and at follow-up at 3, 6 and 12 months across the included studies

AUTHOR

(YEAR) GROUP SUB- N SUMMARY SCORE MEAN (SD) PRE-OP FOLLOW-UP MEAN (SD) IN MONTHS

3 6 12 COULTER, 2017 [39] Supervised 56 MCS 58.53 (20.44) 84.6 (23.18) 81.1 (22.96) Home-based 42 MCS 59.59 (19.99) 79.8 (22.36) 78.6 (22.04) Supervised 56 PCS 35.56 (15.11) 71.8 (28.49) 71.4 (28.49) Home-based 42 PCS 36.96 (17.3) 71.9 (27.62) 68.5 (27.34) GOH, 2020 [40] Distressed 720 MCS 39.4 (8.8) 55.1 (13.7) Non-distressed 644 MCS 58.0 (5.4) 55.1 (11.9) Distressed 720 PCS 26.8 (8.8) 42.9 (11.6) Non-distressed 644 PCS 29.1 (10.9) 44.9 (10.8) JAISWAL, 2019 [41] 676 MCS 72.2 (18.4) (15.7) 81.1 KUCHÁLIK, 2017 [42] ITM 40 MCS 49.2 (11.9) 54.2 (8.9) 54.5 (8.2) LIA 40 MCS 51.7 (11.8) 54.6 (10.0) 53.5 (9.4) ITM 40 PCS 26.2 (8.0) 41.3 (10.0) 45 (9.4) LIA 40 PCS 28.3 (7.9) 39.8 (10.03) 46.7 (11.2) LIEBS, 2014 [43] Low offset 75 MCS 48.9 (12.1) 51.77 (11.49) (10.02) 53.57 (8.91) 53.54 Normal offset 195 MCS 48.7 (12.4) (10.54) 52.33 52.33 (9.41) (10.04) 51.85 High offset 92 MCS 49.1 (11.3) 53.27 (10.47) 51.89 (9.87) (9.63) 52.1 Low offset 75 PCS 27.1 (8.7) 38.75 (9.24) 42.83 (9.38) 44.46 (9.93) Normal offset 195 PCS 26.9 (7.3) 38.62 (8.99) 42.57 (9.4) 44.19 (9.91) High offset 92 PCS 27.8 (6.9) 38.1 (9.48) 41.77 (9.49) 43.16 (10.44)

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Table 7 (continued) AUTHOR

(YEAR) GROUP SUB- N SUMMARY SCORE MEAN (SD) PRE-OP FOLLOW-UP MEAN (SD) IN MONTHS

3 6 12 REICHERT, 2018 [44] MCS Anterior 77 MCS 57.2 (8.5) 56 (9.2) 56.0 (10.0) 55.0 (9.8) MCS Lateral 71 MCS 56.3 (9.2) 56.7 (8.3) 55.8 (7.2) 56.2 (6.9) PCS Anterior 77 PCS 27.4 (8.2) 44.6 (9.2) 46.0 (10.0) 47.5 (9.9) PCS Lateral 71 PCS 25.6 (8.7) 40.7 (10.1) 42.7 (5.6) 42.9 (11.9) TRISTAINO, 2016 [45] EXP 63 MCS 48.1 (11.1) 47.1 (13.1) CTR 66 MCS 39.9 (11.9) 38.2 (14.4) EXP 63 PCS 35.1 (9.1) 53.7 (7.6) CTR 66 PCS 31.5 (8.1) 47.8 (11.4)

N = number of participants MCS= mental component summary score PCS= physical component summary score

After one year the mean differences compared to the preoperative assessment is 15.36 for Coulter et al. [39] to 20.1 reported by Reichert et al. [44] for their anterior approach group. While the dynamic for the PCS response means across all studies show an increase in respect to the preoperative data at all follow-up times, the mental well-being represented by the MCS demonstrates a more mixed picture. At the 3-month follow-up the MCS response mean decreases by -1.7 for the control group of Tristaino et al. [45] while it rises by 26.07 for the supervised group reported by Coulter et al. [39]. The latter also reports the highest difference in means for the 6-month follow-up, with 22.57, while the lowest is the non-distressed group of Goh et al. [40] with a decrease in MCS of -2.9 compared to preoperative assessments. One year after THA the anterior approach group of Reichert et al. [44] worsened by -2.2 mean difference compared to the baseline and Jaiswal et al. [41] increased from a very high baseline of 72.2 to 81.1, which is a difference in means of 8.9.

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10.5. Results of synthesis and risk of bias assessment 10.5.1. MCS and PCS at 3-month follow-up

Among the seven studies and their 14 subgroups enrolled in this meta-analysis there were five studies (consisting of 11 subgroups) [39,42-45] including 817 treatment cases with baseline and follow-up data three months after THA that assessed the MCS [Fig. 2 A].

Fig. 2: Meta-analysis (A) with forest plot (B) and funnel plot (C) of MCS means 3-month follow-up versus preoperative baseline

The results of a meta-analysis [Fig. 2A-B] indicate that the three months postoperative state of mental well-being is superior compared with the preoperative baseline, there was a significant difference between the two assessment times (SMD = 0.30; 95% CI 0.08 to 0.52; P = 0.007). Statistical heterogeneity was substantial to considerable (I2 _{= 79%;}_𝜒3_{= 47.14; P < 0.00001). The skewed and} asymmetric funnel plot [Fig. 2C] indicates a risk of publication bias.

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There were five studies (consisting of 11subgroups) [39,42-45] including 817 treatment cases with baseline and follow-up data three months after THA that assessed the PCS [Fig. 3A].

Fig. 3: Meta-analysis (A) with forest plot (B) and funnel plot (C) of PCS means 3-month follow-up versus preoperative baseline

The results of a meta-analysis [Fig. 3A-B] indicate that the 3-month postoperative state of physical well-being is superior compared with the preoperative baseline, there was a significant difference between the two assessment times (SMD = 1.56; 95% CI 1.39 to 1.73; P < 0.00001). Statistical heterogeneity was moderate to substantial (I2 _{= 53%; 𝜒}3_{= 21.4; P = 0.02). The funnel plot [Fig. 3C]} indicates no evident risk of publication bias.

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10.5.2. MCS and PCS at 6-month follow-up

Five studies (consisting of 11 subgroups) [39-40, 42-44] including 2052 treatment cases with baseline and follow-up data six months after THA that assessed the MCS [Fig. 4A].

Fig. 4: Meta-analysis (A) with forest plot (B) and funnel plot (C) of MCS means 6-month follow-up versus preoperative baseline

The results of a meta-analysis [Fig. 4A-B] indicate that the 6-month postoperative state of mental well-being is superior compared with the preoperative baseline, however, there was no significant difference between the two assessment times (SMD = 0.41; 95% CI -0.07 to 0.88; P = 0.10). Statistical heterogeneity was considerable (I2 _{= 98%;}_𝜒3 _{= 467,35; P < 0.00001). The skewed and asymmetric} funnel plot [Fig. 4C] indicates a risk of publication bias.

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The same five studies (consisting of 11 subgroups) [39-40, 42-44] including 2052 treatment cases with baseline and follow-up data six months after THA that assessed the PCS [Fig. 5A].

The results of a meta-analysis [Fig. 5A-B] indicate that the 6-month postoperative state of physical well-being is superior compared with the preoperative baseline, there was a significant difference between the two assessment times (SMD = 1.74; 95% CI 1.58 to 1.89; P < 0.00001). Statistical heterogeneity was substantial (I2_{=69%; 𝜒}3 _{= 31,93; P = 0.0004). The distribution in the funnel plot [Fig.} 5C] does not indicate an evident risk of publication bias.

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10.5.3. MCS and PCS at 12-month follow-up

Three studies (consisting of six subgroups) [41, 43-44] including 1186 treatment cases with baseline and follow-up data 12 months after THA that assessed the MCS [Fig. 6A].

Fig. 6: Meta-analysis (A) with forest plot (B) and funnel plot (C) of MCS means 12-month follow-up versus preoperative baseline

The results of a meta-analysis [Fig. 6A-B] indicate that the 12-months postoperative state of mental well-being is superior compared with the preoperative baseline, there was a significant difference between the two assessment times (SMD= 0.32; 95% CI 0.16 to 0.48; P=0.0001). Statistical heterogeneity was moderate to substantial (I2 _{= 64%;}_𝜒3_{=13,6; P=0.02). The skewed and asymmetric} funnel plot [Fig. 6C] indicates a risk of publication bias.

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Two studies (consisting of 5 subgroups) [43-44] including 510 treatment cases with baseline and follow-up data 12 months after THA that assessed the PCS [Fig. 7A].

The results of a meta-analysis [Fig. 7A-B] indicate that the postoperative state at one year of physical well-being is superior compared with the preoperative baseline, there was a significant difference between the two assessment times (SMD = 1.89; 95% CI 1.75 to 2.04; P<0.00001). Statistical heterogeneity was low (I2_{=24%; 𝜒}3_{=5.26; P = 0.26). The funnel plot [Fig. 7C] does not indicate a risk} of publication bias.

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11. DISCUSSION OF RESULTS

The current study demonstrates the superiority of both, mental and physical well-being of all postoperative follow-ups to the preintervention baseline measurements. While a significant association of total hip arthroplasty and mental well-being three months (P = 0.007) after surgery as well as one year (P < 0.001) postoperatively could be demonstrated, no statistically significant increase could be found for the 6-month follow-up (P = 0.10). More unambiguous findings can be reported for the postoperative outcome in physical well-being, which was statistically significantly superior to the preoperative assessment of PCS at all follow-ups (all P < 0.001). These findings are corroborated by another meta-analysis on the quality of life after THA, albeit with the focus on a substantially longer follow-up time. Shan et al. [10] explored the mid-term QoL after THA. Their results show, that at 3.6 to 7 years after THA and across 20 studies, considering various generic and disease-specific instruments to assess HRQoL, the mid-term postoperative QoL outcome was superior to the preoperative baseline for the majority of the eight domains of the SF-36. While there were no meta-analyses performed on the component summary scores, they report in the domains of mental well-being results favouring the postoperative state compared to the preoperative baseline, however, only social functioning (SF) and role emotional (RE) were statistically significant differences. In the physical domains there were statistically significant improvements in mean responses in physical functioning (PF), bodily pain (BP) and role physical (RP).

Despite the importance of statistical validity of PROMs, the individual patient’s perspective on the weight of the perceived change is paramount in understanding the results in the context of a patient-centred approach to gain in quality of life by THA. For this reason, the definition of a minimal clinically important difference (MCID) for a PROM used for an intervention as THA could be very useful. MCID is the minimal size of change that a patient acknowledges as important [46]. To the knowledge of the author, there has been only one approach in attempting to define a MCID for primary THA for the SF-36. Quintana et al. [47] have tried to establish the MCID in the SF-36 in patients undergoing THA, they strongly advised however to use their results with caution and not as absolute thresholds. Moreover, they did not report data on MCID for the MCS nor PCS and thus were unfortunately not used in the analysis of the results of this review.

As Ponk et al. [31] have advised, that an adequate evaluation of PROMs in total hip replacements would need a response rate (RR) of 100%, it needs to be mentioned that one caveat of the current review is that none of the included and analysed studies were able to fulfil this requirement. The RRs ranged from as low as 70.42% [44] to as high as 96.83 % [45]. With increasing sample size an ideal RR without loss to follow-up is in many circumstances of external difficulties researchers encounter hard to achieve. The minimal requirement for drawing valid conclusions of PROM results is set to 60%

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according to the PROM-Group of the International Society of Arthroplasty Registries (ISAR) [32]. The current review included no study with a RR lower than 70%, which is a moderate strength of the current study.

The method of calculating the SF-36 summary and component scores can be done by using either the US or country-specific scoring coefficients to allow a cross-cultural comparability of the MCS and PCS [48]. The lack of information regarding the scoring method used in the included studies bears a risk for reduced comparability of the absolute results of the individual studies.

The current study analysed the comparison of preoperative to postoperative outcomes in QoL influenced by THA. To gain a deeper understanding of the raw numbers it is essential to compare the outcome with the reference population, in this case the general population of a comparable age range as the included studies.

Maglinte et al. [49] established general population norms for the summary scores PCS and MCS of the SF-36 administered by telephone for the general population of the USA. The age- and gender-stratified mean scores with standard deviation are for the PCS for the age group 55-64 years 48.34 (15.54) for males and 46.76 (17.11) for females, respectively. In the age cohort 65-74 years the corresponding mean scores were 46.95 (14.69) and 45.55 (17.32). The MCS mean scores were for males and females aged 55-64 54.34 (12.7) and 53.40 (13.89) and in the cohort of 65-74 years 56.56 (8.81) and 54.62 (13.14).

Ellert et al. [50] report similar mean summary component scores for the German population. The population norm for 60-69 years is for PCS 46.44 (11.05) for males and 44.83 (11.71) for females. The corresponding values for MCS are 52.20 (9.73) for males and 50.94 (9.38) for females. Since the data of the included studies do not provide age- and gender-stratified results on the MCS and PCS, the range of the beforementioned norms are used for comparison, with the PCS ranging from 44.83 to 48.34 and the MCS from 50.94 to 56.56, respectively.

Looking at the preoperative mental well-being (see tab. 7 for MCS), four studies or one of their subgroups [40, 42] report higher values compared with the reference population [39-41, 44], while four studies or their subgroups [40, 42-43, 45] show lower values before surgery. At all follow-up interval data included in the analysis (3,6,12 month postoperatively) all studies report MCS values within or above the reference population, apart from Tristaino et al. [45], who report at 3-month follow-up values lower compared to both, their own preoperative baseline and the reference norms used for comparison. The preoperative physical well-being (see tab. 7 for PCS) is substantially lower than the reference population across all studies, which recorded the PCS [39-40, 42-45]. All studies which assessed PCS, report an increase of the mean PCS compared to the baseline across all follow-up intervals. The studies which provided data on the 3-month follow-up showed an increase in the PCS values, two [39, 45] reached or exceeded the reference norm and three remained below it. [42-44]. At

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the 6-month follow-up, four studies report for at least one of their subgroup values within or above the reference range [39-40, 42, 44] on the other hand three reports had at least one subgroup not reaching the normative values [40, 43-44], however they are close to the lower limit of the reference range.

The meta-analyses conducted bear several limitations. The baseline demographics of the included studies are highly heterogenous, especially the difference in pre-interventional MCS and PCS [tab. 7] are a concern for confounding bias. Other demographic features such as mean age, proportion of males to females and the BMI of the participants vary as well [tab. 5]. Another concern for the assessment of the findings of this study is the potential publication bias detected in all three meta-analyses assessing the mental well-being with the MCS, while no such risk was detected for the PCS and physical well-being, respectively. The response rates are suboptimal across all studies. Moreover, there are potential confounders, which are not accounted for in this review, among them are the percentage of patients with remaining contralateral hip pathology, the waiting time for surgery [26], comorbidity status, medication use, psychological profile, extent of pre- and postoperative rehabilitation, socioeconomic factors, and the degree of education [23].

A thorough study, which accounts for these potential confounders and also aims to include other reports which used different instruments of assessing HRQoL, such as the SF-12 and EQ-5D would be warranted to explore the influence of THA on short-term quality of life.

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12. CONCLUSIONS

1. Three months after THA, there is a significant increase in self-reported mental (P = 0.007) and physical (P < 0.001) well-being, which was demonstrated by two meta-analyses each consisting of five studies with a total of 817 participants.

2. Half a year after THA a significant (P < 0.001) increase in the self-reported physical well-being could be shown in a analysis of five studies with a total of 2052 participants, while a meta-analysis of the same studies and participants could not demonstrate a statistically significant (P = 0.10) increase in the mental well-being domain.

3. At the one-year follow-up, both, the mental (P < 0.001) and physical (P < 0.001) well-being are statistically significantly superior to the preoperative baseline measurements in patients undergoing THA, which was shown in two meta-analyses consisting of three studies with a total of 1186 participants, and two studies with a total of 510 participants, respectively.

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