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Obesity Does Not Affect Outcomes in Hybrid Versus Cemented Total Knee Arthroplasty in Asians
Accepted Manuscript Obesity Does Not Affect Outcomes in Hybrid Versus Cemented Total Knee Arthroplasty in Asians Jin-Guang Ernest Ang, MBBS, Hamid Rahmatullah Bin Abd Razak, MBBS, MRCS, Dip SpMed, MMed (Ortho), Tet-Sen Howe, MBBS, FRCS (Edin), FAMS, Boon-Keng Tay, MBBS, FRCS (Edin), FAMS, FACS, Seng-Jin Yeo, MBBS, FRCS (Edin), FAMS PII:
S0883-5403(17)30572-7
DOI:
10.1016/j.arth.2017.06.043
Reference:
YARTH 55969
To appear in:
The Journal of Arthroplasty
Received Date: 7 April 2017 Revised Date:
13 June 2017
Accepted Date: 27 June 2017
Please cite this article as: Ang J-GE, Bin Abd Razak HR, Howe T-S, Tay B-K, Yeo S-J, Obesity Does Not Affect Outcomes in Hybrid Versus Cemented Total Knee Arthroplasty in Asians, The Journal of Arthroplasty (2017), doi: 10.1016/j.arth.2017.06.043. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Obesity Does Not Affect Outcomes in Hybrid Versus
Jin-Guang Ernest Ang, MBBS1
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Cemented Total Knee Arthroplasty in Asians
Hamid Rahmatullah Bin Abd Razak, MBBS, MRCS, Dip SpMed, MMed (Ortho)2 Tet-Sen Howe, MBBS, FRCS (Edin), FAMS2
Boon-Keng Tay, MBBS, FRCS (Edin), FAMS, FACS2
Yong Loo Lin School of Medicine
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Seng-Jin Yeo, MBBS, FRCS (Edin), FAMS2
National University of Singapore 1E Kent Ridge Road Singapore 119228
Department of Orthopaedic Surgery
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Singapore General Hospital
20 College Road, Academia Level 4
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Singapore 169865
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Please address all correspondence to: Hamid Rahmatullah Bin Abd Razak Department of Orthopaedic Surgery, Singapore General Hospital 20 College Road, Academia Level 4 Singapore 169865
Phone: (65) 9004-5495 FAX: (65) 6224-9221 Email: [email protected]
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Obesity Does Not Affect Outcomes in Hybrid Versus
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Cemented Total Knee Arthroplasty in Asians
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Abstract
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Background: This study aims to evaluate patient reported and functional outcomes following
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hybrid versus cemented total knee arthroplasty (TKA) in patients, stratified by body mass index
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(BMI).
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Methods: Registry data of patients undergoing primary TKA between January 2004 and January
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2013 were collected. Baseline interviews were conducted preoperatively to assess
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sociodemographic characteristics, BMI and knee arthritis severity, using the Knee Society Score
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(KSS), which consists of the Knee Society Knee Score (KSKS) and the Knee Society Function
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Score (KSFS) and Oxford Knee Score (OKS). These scores were collected prospectively,
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preoperatively and postoperatively up to 2 years. 2-year outcomes and 5-year revision rates were
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then compared between (1) hybrid and cemented TKA groups and (2) BMI subclasses within the
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hybrid and cemented TKA groups.
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Results: Patients who underwent cemented TKA had marginally better flexion range, KSFS and
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OKS at 2-years postoperatively. In the overweight category, flexion range, KSFS and OKS were
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marginally lower for hybrid TKAs. There were no differences in outcomes between the two
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groups in Class I and II obesity. Within the cemented TKA group, there were no differences in
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the outcomes between BMI subclasses. There were significant differences in the KSFS (0.023)
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and OKS (0.030) between the BMI subclasses within the hybrid TKA group, with patients in
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Class II obesity faring the worst. There was no statistically significant difference in the revision
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rates.
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Conclusion: We conclude that obesity does not affect outcomes in hybrid versus cemented TKA.
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Keywords: hybrid; cemented; total knee arthroplasty; MCID; obesity; Asian; revision
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INTRODUCTION
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Total knee arthroplasty (TKA) in obese patients has been associated with poorer outcomes and
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greater postoperative complications. Commonly reported complications of obesity following
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TKA include prolonged wound drainage, delayed wound healing, as well as higher infection rates
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[1–3]. Other negative effects include more medical complications, poor mobilization, and lower
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tolerance of physical therapy [4-7]. It is believed that high body weight leads to prosthetic
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loosening as a result of increased stress across the components and increased load on the local
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bone. There are currently two commonly used approaches to fixation of TKA components,
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namely the cemented and the cementless (hybrid).
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In the context of this study, hybrid TKA refers to a cementless femoral component fixation and
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cemented tibial component fixation. Cementless femoral component fixation has the potential for
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biologic fixation, which may provide more durable, long-term stability, via the use of porous
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coated implant, which provides advantages such as superior bone ingrowth and improved
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stability. Little is known if obesity affects outcomes based on the type of femoral fixation in
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TKA. To our knowledge, there have been no published comparisons of cemented versus hybrid
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TKA in Asians stratified by body mass index (BMI).
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This study aims to evaluate patient reported and functional outcomes following hybrid vs
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cemented TKA in patients, stratified by BMI. We hypothesized that obesity leads to poorer
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outcomes in hybrid TKA.
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MATERIALS AND METHODS
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Study sample
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Prospective registry data of all primary unilateral unconstrained TKAs performed at our tertiary
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institution between January 2004 and January 2013 were collected. Our institutional review
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board granted a waiver for informed consent for this study as no patient identifiable data was
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used. Patients were included only if they underwent a primary unilateral TKA, with the other
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knee asymptomatic or successfully replaced and completed all appropriate follow-up
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appointments and outcome assessments for at least 2 years following index surgery. Exclusion
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criteria included: (1) Spastic or flaccid paralysis of one or both lower limbs regardless of cause
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(2) New York Heart Association Class II and III cardiac failure (3) Severe pulmonary disorders
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limiting the patient to only home ambulation (4) All revision arthroplasties including infected
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arthroplasties (5) Severe hip and/or spine conditions preventing patient from ambulating
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independently. From this registry data, we identified 542 patients who underwent hybrid TKA
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and matched them to 542 patients who underwent cemented TKA for age, gender and body mass
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index.
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Perioperative details
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All patients received a cruciate-retaining (CR) TKA with a fixed bearing tibial prosthesis. All
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surgeries were performed by fellowship-trained senior orthopaedic surgeons in a tertiary teaching
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hospital of a developed nation. Patients received mechanical or oral prophylaxis against venous
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thromboembolism and underwent a standard postoperative rehabilitation protocol. They were
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then followed up at the specialist outpatient clinic at 1 month, 3 month, 6 month, 1 year and 2
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years postoperatively.
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Assessments
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All assessments were made independently. Baseline interviews were conducted preoperatively to
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assess sociodemographic characteristics, BMI and knee arthritis severity, using the Knee Society
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Score (KSS) [8] which consists of the Knee Society Knee Score (KSKS) and the Knee Society
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Function Score (KSFS) and Oxford Knee Score (OKS) [9]. We used the 1997 “12–60” version of
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the OKS for which higher scores indicate greater severity. These scores were collected
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prospectively, preoperatively and postoperatively up to 2 years. Comorbidities and revision
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surgery were assessed via the electronic health records.
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Statistical analysis
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We stratified the patients in both groups according to the WHO BMI classification [10]
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(Overweight: 25-29.9 kg/m2; Class I Obesity: 30-34.9 kg/m2; Class II Obesity: >35). Outcomes
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at 2 years were then compared between (1) hybrid and cemented TKA groups and (2) BMI
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subclasses within the hybrid and cemented TKA groups. The Student’s T-test was used for
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comparison of means and the Z-test for comparison of proportions. Revision rates were
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calculated for both groups at a median follow-up of 5 years.
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SOURCE OF FUNDING
There was no external or internal source of funding for this study.
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RESULTS
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Preoperatively, there were no significant differences in the demographics and outcomes between
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the two groups (Table 1). Patients who underwent cemented TKA had marginally better flexion
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range, KSFS and OKS at 2 years postoperatively. In the overweight category, flexion range,
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KSFS and OKS were marginally lower for Hybrid TKAs. There were no differences in outcomes between the two groups in Class I and II obesity (Table 2).
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Within the cemented TKA group, there were no differences in the outcomes between BMI
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subclasses. However, there were significant differences in the KSFS (0.023) and OKS (0.030)
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between the BMI subclasses within the Hybrid TKA group, with patients in Class II obesity
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faring the worst (Table 3).
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There was no statistically significant difference in the revision rates of surgery between the
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hybrid TKA and cemented TKA groups across all three BMI classes. As seen in table 4, there
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were no differences between the two groups based on the reason for revision surgery as well.
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The mean follow-up duration for our patients was 4.3 years (2.5–6.3).
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DISCUSSION
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Current studies evaluating the outcomes of cemented versus hybrid TKA have mostly been done
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on Caucasian populations. Body composition and metabolic function of Asians have been
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established to be drastically different from that of Caucasians, with major differences in lean
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body mass and body fat percentage [11]. Extrapolating from this anthropometric difference, it is
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likely that for the same BMI, we would see a different trend in Asian patients undergoing TKA
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compared to their Western counterparts [12]. At present, this specific population is
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underrepresented in current literature with regards to both TKA fixation methods and the
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influence of obesity within this patient population. To the knowledge of the authors, there has
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only been one study to date comparing outcomes of cemented and cementless TKA in the Asian
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population [13]. We aimed to add more value to current literature in this particular domain.
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Our results showed marginally better flexion and functional outcomes in the cemented group
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compared to hybrid. However, this is not likely to be clinically significant, as it does not meet the
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minimal clinically important difference (MCID) criteria. MCID is an important concept used to
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determine whether a medical intervention improves perceived outcomes in patients. Prior to the
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introduction of the concept in 1989, studies focused primarily on statistical significance [14]. The
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MCID was defined as representing one-half of the standard deviation of the difference between
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the preoperative and postoperative outcome scores [15]. In an earlier study done by Bin Abd
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Razak et al, the calculated MCID value for patients undergoing TKA in our institution was 5 for
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the OKS [16]. In another study done by Demey et al, there was no difference between hybrid and
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cemented TKA when comparing clinical examination, range of motion, IKS score or pain score
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at 2-year follow-up [17]. Rorabeck et al and Gao et al, in their respective studies did not find a
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clinical difference between hybrid and cemented TKA [18, 19]. Furthermore, Park JW et al in
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their prospective, randomised study of 100 knees in 50 patients did not find any advantage of
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cementless over cemented components in TKA [13]. This is coherent with our findings, which
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show no clinical significance in the difference between the cemented and the hybrid groups.
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We found that BMI does not affect outcomes when comparing hybrid and cemented TKA,
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including revision rates. This is corroborated by a recent study on Western populations by
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Richard et al. They have found comparable rates of revision between hybrid TKA and cemented
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TKA [20].
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However, outcomes of hybrid TKA in Class II obesity might require further evaluation as there is
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some evidence from our study that these patients have poorer outcomes compared to Class I
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obese and overweight patients. Patients with Class II obesity had worse KSFS and OKS within
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the hybrid TKA group. The difference in KSFS between the overweight patients and those with
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Class II obesity satisfied the MCID criteria. However, the difference in OKS between Class I and
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Class II obesity did not satisfy the MCID criteria. This finding is consistent with that of Jackson
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et al [21]. In their study of 535 consecutive primary cementless TKA with a mean follow-up of
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9.2 years, they found significantly lower mean improvements in the clinical score and lower
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postoperative total clinical scores in the obese group. However, in a more recent study by Lizaur-
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Utrilla et al [22], it was found that when comparing outcomes of cementless TKAs between 171
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knees in obese patients and 171 non-obese patients with a 7-year follow-up, there were no
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significant differences in overall functional outcomes or component alignment. We postulate that
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in hybrid TKA, the process of osseointegration continues till 3 to 4 years postoperatively and
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hence the fixation may not yet be stable at 2 years of follow-up [23]. This might have an effect on
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the patient-reported outcome measures (PROMs) such as the KSFS and OKS. The jury is still out
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with respect to the impact of obesity on the outcomes of hybrid TKA.
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The major limitation of our study is that we utilized outcomes at 2 years following index surgery,
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which is at best short-term. Rothwell et al [24] evaluated the relationship of the OKS to early
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revision surgery in the New Zealand Joint Registry. They confirmed that the OKS at six months
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was a useful predictor of early revisions after TKA. Their findings showed that 70% of the
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revisions within two years for TKA would have been captured by monitoring the lowest 22% of
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the OKS. Extrapolating the results of their study, an OKS of >33 would be associated with a 7%
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risk of revision within 2 years following index TKA. It is interesting to note that the mean OKS
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for both the groups in our study were in the good to excellent categories [25]. Despite that, our
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revision rates mirrored that of Rothwell et al albeit at a longer mean follow-up of 4.3 years. The
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next limitation of our study is that of retrospective analysis which means that bias will be
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inevitable. Another potential limitation is the fact that a large proportion of our patients were not
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obese but rather overweight. Hence, the BMI of our cohort may not have reached the level at
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which fixation may be affected. Bagsby et al reported in their multicentre review of 298 TKAs in
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292 morbidly obese patients (BMI > 40 kg/m2) that there were significantly more revisions in the
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cemented group than in the cementless group [26]. Similarly, Dewan et al in their case control
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study found that patients in the morbidly obese group were approximately five times more likely
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to develop patellar radiolucencies [27]. In spite of these limitations, the strengths of our study is
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the use of registry data, which was collected prospectively. We also had a matched control group
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to account for the effect of confounders.
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Current literature regarding predictors of outcomes following TKA has contradictory findings.
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Higher body mass index (BMI) was associated with worse post-TKA function in some studies
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[28–31] but other studies found no such association between a higher BMI and a worse post-
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TKA function. [32–34]. Larger scale, randomized, prospective cohort studies are required to fully
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evaluate the impact of obesity on outcomes following cemented and hybrid TKA.
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CONCLUSION
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We conclude that obesity does not affect short-term outcomes in hybrid TKA when compared to
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conventional cemented TKA.
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Table 1 Patient characteristics Characteristics
Hybrid TKA (Cases)
Cemented TKA (Controls)
n = 542
n = 542
P-value
Mean Age (± SD) (years)
66.1 ± 7.6
Gender: Female (%)
449 (83)
Mean Body Mass Index (± SD) (kg/m2)
65.7 ± 7.7
0.389
449 (83) 31.3 ± 3.3
0.347
4.8 ± 2.3
4.6 ± 1.8
0.111
369 (68)
384 (71)
22 (4)
28 (5)
115 ± 19
115 ± 16
1.00
38 ± 18
37 ± 19
0.374
49 ± 17
50 ± 17
0.333
36 ± 8
36 ± 8
1.00
113 ± 15
115 ± 13
0.019
84 ± 13
86 ± 11
0.641
Mean Knee Society Function Score (± SD)
69 ± 21
72 ± 19
0.014
Mean Oxford Knee Questionnaire Score (± SD)
20 ± 6
19 ± 5
0.003
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31.5 ± 3.7
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Demographics
Health Services Utilization
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Hospital LOS (± SD) (days) Discharge directly home (%) Surgical
Mean range of motion (± SD) (degrees) Mean Knee Society Knee Score (± SD) Mean Knee Society Function Score (± SD)
Two-year postoperative scores Mean range of motion (± SD) (degrees) Mean Knee Society Knee Score (± SD)
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Mean Oxford Knee Questionnaire Score (± SD)
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Table 2 Comparison of outcomes by body mass index between cases and controls at 2 years post-TKA p-value
Cemented TKA
(BMI 25 – 29.9 kg/m2)
(BMI 25 – 29.9 kg/m2)
n = 235
n = 227
Mean range of motion (± SD) (degrees)
114 ± 15
117 ± 13
0.022
Mean Knee Society Knee Score (± SD)
85 ± 12
86 ± 11
0.351
Mean Knee Society Function Score (± SD)*
71 ± 21
75 ± 19
0.033
Mean Oxford Knee Questionnaire Score (± SD)*
20 ± 6
18 ± 5
< 0.001
2 (1)
0.681
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Hybrid TKA
Number of Revision TKA (%)
3 (1)
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p-value
Cemented TKA 2
(BMI 30 – 34.9 kg/m )
(BMI 30 – 34.9 kg/m )
n = 227
n = 254
113 ± 17
114 ± 14
0.480
84 ± 13
86 ± 11
0.068
68 ± 20
71 ± 19
0.092
19 ± 6
19 ± 5
1.000
4 (2)
2 (1)
0.336
Hybrid TKA
Cemented TKA
p-value
(BMI > 35 kg/m2)
(BMI > 35 kg/m2)
n = 80
n = 61
113 ± 13
113 ± 12
1.000
81 ± 17
84 ± 15
0.277
Mean Knee Society Function Score (± SD)*
64 ± 19
66 ± 20
0.546
Mean Oxford Knee Questionnaire Score (± SD)*
21 ± 7
21 ± 7
1.000
1 (1)
3 (5)
0.194
Mean range of motion (± SD) (degrees)
Mean Knee Society Function Score (± SD)* Mean Oxford Knee Questionnaire Score (± SD)*
Mean range of motion (± SD) (degrees) Mean Knee Society Knee Score (± SD)
Number of Revision TKA (%)
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Number of Revision TKA (%)
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Mean Knee Society Knee Score (± SD)
* ANOVA testing shows significant differences between the BMI subclasses within the Hybrid TKA group.
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Table 3 Comparison of outcomes between BMI subclasses within Hybrid TKA group p-value
Hybrid TKA
Hybrid TKA
(BMI 25 – 29.9 kg/m2)
(BMI 30 – 34.9 kg/m2)
(BMI > 35 kg/m2)
n = 235
n = 227
n = 80
Mean range of motion (± SD) (degrees)
114 ± 15
113 ± 17
113 ± 13
0.761
Mean Knee Society Knee Score (± SD)
85 ± 12
84 ± 13
81 ± 17
0.067
Mean Knee Society Function Score (± SD)1
71 ± 21
68 ± 20
64 ± 19
0.023
Mean Oxford Knee Questionnaire Score (± SD)2
20 ± 6
19 ± 6
21 ± 7
0.030
4 (2)
1 (1)
0.353
3 (1)
Significant difference seen between “overweight” and “Class II obesity”
2
Significant difference seen between “Class I obesity” and “Class II obesity”
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Number of Revision TKA (%)
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Hybrid TKA
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Cemented TKA, number
p-value
Aseptic loosening of the tibial component
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3
0.703
Deep infection
1
2
0.561
Addition of patella
1
0
0.317
Fracture of the femur
1
0
0.317
Fracture of the tibia
2
0.561
Reasons for revision
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Table 4 Reasons for revision
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S0883-5403(17)30572-7
DOI:
10.1016/j.arth.2017.06.043
Reference:
YARTH 55969
To appear in:
The Journal of Arthroplasty
Received Date: 7 April 2017 Revised Date:
13 June 2017
Accepted Date: 27 June 2017
Please cite this article as: Ang J-GE, Bin Abd Razak HR, Howe T-S, Tay B-K, Yeo S-J, Obesity Does Not Affect Outcomes in Hybrid Versus Cemented Total Knee Arthroplasty in Asians, The Journal of Arthroplasty (2017), doi: 10.1016/j.arth.2017.06.043. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Obesity Does Not Affect Outcomes in Hybrid Versus
Jin-Guang Ernest Ang, MBBS1
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Cemented Total Knee Arthroplasty in Asians
Hamid Rahmatullah Bin Abd Razak, MBBS, MRCS, Dip SpMed, MMed (Ortho)2 Tet-Sen Howe, MBBS, FRCS (Edin), FAMS2
Boon-Keng Tay, MBBS, FRCS (Edin), FAMS, FACS2
Yong Loo Lin School of Medicine
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Seng-Jin Yeo, MBBS, FRCS (Edin), FAMS2
National University of Singapore 1E Kent Ridge Road Singapore 119228
Department of Orthopaedic Surgery
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Singapore General Hospital
20 College Road, Academia Level 4
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Singapore 169865
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Please address all correspondence to: Hamid Rahmatullah Bin Abd Razak Department of Orthopaedic Surgery, Singapore General Hospital 20 College Road, Academia Level 4 Singapore 169865
Phone: (65) 9004-5495 FAX: (65) 6224-9221 Email: [email protected]
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Obesity Does Not Affect Outcomes in Hybrid Versus
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Cemented Total Knee Arthroplasty in Asians
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Abstract
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Background: This study aims to evaluate patient reported and functional outcomes following
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hybrid versus cemented total knee arthroplasty (TKA) in patients, stratified by body mass index
5
(BMI).
6
Methods: Registry data of patients undergoing primary TKA between January 2004 and January
7
2013 were collected. Baseline interviews were conducted preoperatively to assess
8
sociodemographic characteristics, BMI and knee arthritis severity, using the Knee Society Score
9
(KSS), which consists of the Knee Society Knee Score (KSKS) and the Knee Society Function
10
Score (KSFS) and Oxford Knee Score (OKS). These scores were collected prospectively,
11
preoperatively and postoperatively up to 2 years. 2-year outcomes and 5-year revision rates were
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then compared between (1) hybrid and cemented TKA groups and (2) BMI subclasses within the
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hybrid and cemented TKA groups.
14
Results: Patients who underwent cemented TKA had marginally better flexion range, KSFS and
15
OKS at 2-years postoperatively. In the overweight category, flexion range, KSFS and OKS were
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marginally lower for hybrid TKAs. There were no differences in outcomes between the two
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groups in Class I and II obesity. Within the cemented TKA group, there were no differences in
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the outcomes between BMI subclasses. There were significant differences in the KSFS (0.023)
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and OKS (0.030) between the BMI subclasses within the hybrid TKA group, with patients in
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Class II obesity faring the worst. There was no statistically significant difference in the revision
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rates.
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Conclusion: We conclude that obesity does not affect outcomes in hybrid versus cemented TKA.
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Keywords: hybrid; cemented; total knee arthroplasty; MCID; obesity; Asian; revision
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INTRODUCTION
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Total knee arthroplasty (TKA) in obese patients has been associated with poorer outcomes and
28
greater postoperative complications. Commonly reported complications of obesity following
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TKA include prolonged wound drainage, delayed wound healing, as well as higher infection rates
30
[1–3]. Other negative effects include more medical complications, poor mobilization, and lower
31
tolerance of physical therapy [4-7]. It is believed that high body weight leads to prosthetic
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loosening as a result of increased stress across the components and increased load on the local
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bone. There are currently two commonly used approaches to fixation of TKA components,
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namely the cemented and the cementless (hybrid).
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In the context of this study, hybrid TKA refers to a cementless femoral component fixation and
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cemented tibial component fixation. Cementless femoral component fixation has the potential for
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biologic fixation, which may provide more durable, long-term stability, via the use of porous
39
coated implant, which provides advantages such as superior bone ingrowth and improved
40
stability. Little is known if obesity affects outcomes based on the type of femoral fixation in
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TKA. To our knowledge, there have been no published comparisons of cemented versus hybrid
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TKA in Asians stratified by body mass index (BMI).
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This study aims to evaluate patient reported and functional outcomes following hybrid vs
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cemented TKA in patients, stratified by BMI. We hypothesized that obesity leads to poorer
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outcomes in hybrid TKA.
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MATERIALS AND METHODS
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Study sample
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Prospective registry data of all primary unilateral unconstrained TKAs performed at our tertiary
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institution between January 2004 and January 2013 were collected. Our institutional review
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board granted a waiver for informed consent for this study as no patient identifiable data was
54
used. Patients were included only if they underwent a primary unilateral TKA, with the other
55
knee asymptomatic or successfully replaced and completed all appropriate follow-up
56
appointments and outcome assessments for at least 2 years following index surgery. Exclusion
57
criteria included: (1) Spastic or flaccid paralysis of one or both lower limbs regardless of cause
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(2) New York Heart Association Class II and III cardiac failure (3) Severe pulmonary disorders
59
limiting the patient to only home ambulation (4) All revision arthroplasties including infected
60
arthroplasties (5) Severe hip and/or spine conditions preventing patient from ambulating
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independently. From this registry data, we identified 542 patients who underwent hybrid TKA
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and matched them to 542 patients who underwent cemented TKA for age, gender and body mass
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index.
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Perioperative details
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All patients received a cruciate-retaining (CR) TKA with a fixed bearing tibial prosthesis. All
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surgeries were performed by fellowship-trained senior orthopaedic surgeons in a tertiary teaching
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hospital of a developed nation. Patients received mechanical or oral prophylaxis against venous
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thromboembolism and underwent a standard postoperative rehabilitation protocol. They were
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then followed up at the specialist outpatient clinic at 1 month, 3 month, 6 month, 1 year and 2
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years postoperatively.
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Assessments
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All assessments were made independently. Baseline interviews were conducted preoperatively to
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assess sociodemographic characteristics, BMI and knee arthritis severity, using the Knee Society
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Score (KSS) [8] which consists of the Knee Society Knee Score (KSKS) and the Knee Society
77
Function Score (KSFS) and Oxford Knee Score (OKS) [9]. We used the 1997 “12–60” version of
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the OKS for which higher scores indicate greater severity. These scores were collected
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prospectively, preoperatively and postoperatively up to 2 years. Comorbidities and revision
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surgery were assessed via the electronic health records.
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Statistical analysis
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We stratified the patients in both groups according to the WHO BMI classification [10]
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(Overweight: 25-29.9 kg/m2; Class I Obesity: 30-34.9 kg/m2; Class II Obesity: >35). Outcomes
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at 2 years were then compared between (1) hybrid and cemented TKA groups and (2) BMI
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subclasses within the hybrid and cemented TKA groups. The Student’s T-test was used for
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comparison of means and the Z-test for comparison of proportions. Revision rates were
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calculated for both groups at a median follow-up of 5 years.
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SOURCE OF FUNDING
There was no external or internal source of funding for this study.
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RESULTS
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Preoperatively, there were no significant differences in the demographics and outcomes between
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the two groups (Table 1). Patients who underwent cemented TKA had marginally better flexion
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range, KSFS and OKS at 2 years postoperatively. In the overweight category, flexion range,
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KSFS and OKS were marginally lower for Hybrid TKAs. There were no differences in outcomes between the two groups in Class I and II obesity (Table 2).
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Within the cemented TKA group, there were no differences in the outcomes between BMI
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subclasses. However, there were significant differences in the KSFS (0.023) and OKS (0.030)
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between the BMI subclasses within the Hybrid TKA group, with patients in Class II obesity
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faring the worst (Table 3).
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There was no statistically significant difference in the revision rates of surgery between the
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hybrid TKA and cemented TKA groups across all three BMI classes. As seen in table 4, there
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were no differences between the two groups based on the reason for revision surgery as well.
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The mean follow-up duration for our patients was 4.3 years (2.5–6.3).
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DISCUSSION
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Current studies evaluating the outcomes of cemented versus hybrid TKA have mostly been done
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on Caucasian populations. Body composition and metabolic function of Asians have been
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established to be drastically different from that of Caucasians, with major differences in lean
118
body mass and body fat percentage [11]. Extrapolating from this anthropometric difference, it is
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likely that for the same BMI, we would see a different trend in Asian patients undergoing TKA
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compared to their Western counterparts [12]. At present, this specific population is
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underrepresented in current literature with regards to both TKA fixation methods and the
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influence of obesity within this patient population. To the knowledge of the authors, there has
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only been one study to date comparing outcomes of cemented and cementless TKA in the Asian
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population [13]. We aimed to add more value to current literature in this particular domain.
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Our results showed marginally better flexion and functional outcomes in the cemented group
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compared to hybrid. However, this is not likely to be clinically significant, as it does not meet the
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minimal clinically important difference (MCID) criteria. MCID is an important concept used to
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determine whether a medical intervention improves perceived outcomes in patients. Prior to the
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introduction of the concept in 1989, studies focused primarily on statistical significance [14]. The
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MCID was defined as representing one-half of the standard deviation of the difference between
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the preoperative and postoperative outcome scores [15]. In an earlier study done by Bin Abd
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Razak et al, the calculated MCID value for patients undergoing TKA in our institution was 5 for
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the OKS [16]. In another study done by Demey et al, there was no difference between hybrid and
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cemented TKA when comparing clinical examination, range of motion, IKS score or pain score
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at 2-year follow-up [17]. Rorabeck et al and Gao et al, in their respective studies did not find a
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clinical difference between hybrid and cemented TKA [18, 19]. Furthermore, Park JW et al in
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their prospective, randomised study of 100 knees in 50 patients did not find any advantage of
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cementless over cemented components in TKA [13]. This is coherent with our findings, which
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show no clinical significance in the difference between the cemented and the hybrid groups.
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We found that BMI does not affect outcomes when comparing hybrid and cemented TKA,
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including revision rates. This is corroborated by a recent study on Western populations by
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Richard et al. They have found comparable rates of revision between hybrid TKA and cemented
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TKA [20].
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However, outcomes of hybrid TKA in Class II obesity might require further evaluation as there is
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some evidence from our study that these patients have poorer outcomes compared to Class I
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obese and overweight patients. Patients with Class II obesity had worse KSFS and OKS within
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the hybrid TKA group. The difference in KSFS between the overweight patients and those with
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Class II obesity satisfied the MCID criteria. However, the difference in OKS between Class I and
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Class II obesity did not satisfy the MCID criteria. This finding is consistent with that of Jackson
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et al [21]. In their study of 535 consecutive primary cementless TKA with a mean follow-up of
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9.2 years, they found significantly lower mean improvements in the clinical score and lower
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postoperative total clinical scores in the obese group. However, in a more recent study by Lizaur-
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Utrilla et al [22], it was found that when comparing outcomes of cementless TKAs between 171
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knees in obese patients and 171 non-obese patients with a 7-year follow-up, there were no
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significant differences in overall functional outcomes or component alignment. We postulate that
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in hybrid TKA, the process of osseointegration continues till 3 to 4 years postoperatively and
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hence the fixation may not yet be stable at 2 years of follow-up [23]. This might have an effect on
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the patient-reported outcome measures (PROMs) such as the KSFS and OKS. The jury is still out
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with respect to the impact of obesity on the outcomes of hybrid TKA.
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The major limitation of our study is that we utilized outcomes at 2 years following index surgery,
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which is at best short-term. Rothwell et al [24] evaluated the relationship of the OKS to early
166
revision surgery in the New Zealand Joint Registry. They confirmed that the OKS at six months
167
was a useful predictor of early revisions after TKA. Their findings showed that 70% of the
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revisions within two years for TKA would have been captured by monitoring the lowest 22% of
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the OKS. Extrapolating the results of their study, an OKS of >33 would be associated with a 7%
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risk of revision within 2 years following index TKA. It is interesting to note that the mean OKS
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for both the groups in our study were in the good to excellent categories [25]. Despite that, our
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revision rates mirrored that of Rothwell et al albeit at a longer mean follow-up of 4.3 years. The
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next limitation of our study is that of retrospective analysis which means that bias will be
174
inevitable. Another potential limitation is the fact that a large proportion of our patients were not
175
obese but rather overweight. Hence, the BMI of our cohort may not have reached the level at
176
which fixation may be affected. Bagsby et al reported in their multicentre review of 298 TKAs in
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292 morbidly obese patients (BMI > 40 kg/m2) that there were significantly more revisions in the
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cemented group than in the cementless group [26]. Similarly, Dewan et al in their case control
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study found that patients in the morbidly obese group were approximately five times more likely
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to develop patellar radiolucencies [27]. In spite of these limitations, the strengths of our study is
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the use of registry data, which was collected prospectively. We also had a matched control group
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to account for the effect of confounders.
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Current literature regarding predictors of outcomes following TKA has contradictory findings.
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Higher body mass index (BMI) was associated with worse post-TKA function in some studies
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[28–31] but other studies found no such association between a higher BMI and a worse post-
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TKA function. [32–34]. Larger scale, randomized, prospective cohort studies are required to fully
188
evaluate the impact of obesity on outcomes following cemented and hybrid TKA.
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CONCLUSION
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We conclude that obesity does not affect short-term outcomes in hybrid TKA when compared to
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conventional cemented TKA.
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Table 1 Patient characteristics Characteristics
Hybrid TKA (Cases)
Cemented TKA (Controls)
n = 542
n = 542
P-value
Mean Age (± SD) (years)
66.1 ± 7.6
Gender: Female (%)
449 (83)
Mean Body Mass Index (± SD) (kg/m2)
65.7 ± 7.7
0.389
449 (83) 31.3 ± 3.3
0.347
4.8 ± 2.3
4.6 ± 1.8
0.111
369 (68)
384 (71)
22 (4)
28 (5)
115 ± 19
115 ± 16
1.00
38 ± 18
37 ± 19
0.374
49 ± 17
50 ± 17
0.333
36 ± 8
36 ± 8
1.00
113 ± 15
115 ± 13
0.019
84 ± 13
86 ± 11
0.641
Mean Knee Society Function Score (± SD)
69 ± 21
72 ± 19
0.014
Mean Oxford Knee Questionnaire Score (± SD)
20 ± 6
19 ± 5
0.003
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31.5 ± 3.7
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Demographics
Health Services Utilization
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Hospital LOS (± SD) (days) Discharge directly home (%) Surgical
Mean range of motion (± SD) (degrees) Mean Knee Society Knee Score (± SD) Mean Knee Society Function Score (± SD)
Two-year postoperative scores Mean range of motion (± SD) (degrees) Mean Knee Society Knee Score (± SD)
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Mean Oxford Knee Questionnaire Score (± SD)
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Preoperative scores
TE D
In-hospital complications (%)
ACCEPTED MANUSCRIPT
Table 2 Comparison of outcomes by body mass index between cases and controls at 2 years post-TKA p-value
Cemented TKA
(BMI 25 – 29.9 kg/m2)
(BMI 25 – 29.9 kg/m2)
n = 235
n = 227
Mean range of motion (± SD) (degrees)
114 ± 15
117 ± 13
0.022
Mean Knee Society Knee Score (± SD)
85 ± 12
86 ± 11
0.351
Mean Knee Society Function Score (± SD)*
71 ± 21
75 ± 19
0.033
Mean Oxford Knee Questionnaire Score (± SD)*
20 ± 6
18 ± 5
< 0.001
2 (1)
0.681
SC
RI PT
Hybrid TKA
Number of Revision TKA (%)
3 (1)
M AN U
Hybrid TKA
2
p-value
Cemented TKA 2
(BMI 30 – 34.9 kg/m )
(BMI 30 – 34.9 kg/m )
n = 227
n = 254
113 ± 17
114 ± 14
0.480
84 ± 13
86 ± 11
0.068
68 ± 20
71 ± 19
0.092
19 ± 6
19 ± 5
1.000
4 (2)
2 (1)
0.336
Hybrid TKA
Cemented TKA
p-value
(BMI > 35 kg/m2)
(BMI > 35 kg/m2)
n = 80
n = 61
113 ± 13
113 ± 12
1.000
81 ± 17
84 ± 15
0.277
Mean Knee Society Function Score (± SD)*
64 ± 19
66 ± 20
0.546
Mean Oxford Knee Questionnaire Score (± SD)*
21 ± 7
21 ± 7
1.000
1 (1)
3 (5)
0.194
Mean range of motion (± SD) (degrees)
Mean Knee Society Function Score (± SD)* Mean Oxford Knee Questionnaire Score (± SD)*
Mean range of motion (± SD) (degrees) Mean Knee Society Knee Score (± SD)
Number of Revision TKA (%)
AC C
EP
Number of Revision TKA (%)
TE D
Mean Knee Society Knee Score (± SD)
* ANOVA testing shows significant differences between the BMI subclasses within the Hybrid TKA group.
ACCEPTED MANUSCRIPT
Table 3 Comparison of outcomes between BMI subclasses within Hybrid TKA group p-value
Hybrid TKA
Hybrid TKA
(BMI 25 – 29.9 kg/m2)
(BMI 30 – 34.9 kg/m2)
(BMI > 35 kg/m2)
n = 235
n = 227
n = 80
Mean range of motion (± SD) (degrees)
114 ± 15
113 ± 17
113 ± 13
0.761
Mean Knee Society Knee Score (± SD)
85 ± 12
84 ± 13
81 ± 17
0.067
Mean Knee Society Function Score (± SD)1
71 ± 21
68 ± 20
64 ± 19
0.023
Mean Oxford Knee Questionnaire Score (± SD)2
20 ± 6
19 ± 6
21 ± 7
0.030
4 (2)
1 (1)
0.353
3 (1)
Significant difference seen between “overweight” and “Class II obesity”
2
Significant difference seen between “Class I obesity” and “Class II obesity”
AC C
EP
TE D
M AN U
1
SC
Number of Revision TKA (%)
RI PT
Hybrid TKA
ACCEPTED MANUSCRIPT
Cemented TKA, number
p-value
Aseptic loosening of the tibial component
4
3
0.703
Deep infection
1
2
0.561
Addition of patella
1
0
0.317
Fracture of the femur
1
0
0.317
Fracture of the tibia
2
0.561
Reasons for revision
RI PT
Hybrid TKA, number
SC
Table 4 Reasons for revision
AC C
EP
TE D
M AN U
1