The 2019 Revised Version of Association Research Circulation Osseous Staging System of Osteonecrosis of the Femoral Head

Journal Pre-proof The 2019 revised version of Association Research Circulation Osseous staging system of osteonecrosis of the femoral head Byung-Ho Yoon, Michael A. Mont, Kyung-Hoi Koo, Chung-Hwan Chen, Edward Y. Cheng, Quanjun Cui, Wolf Drescher, Valerie Gangji, Stuart Goodman, Yong-Chan Ha, Philippe Hernigou, Marc Hungerford, Richard Iorio, Woo-Lam Jo, Lynne C. Jones, Vikas Khanduja, Harry K.W. Kim, Shin-Yoon Kim, Tae-Young Kim, Hee young Lee, Mel S. Lee, Young-Kyun Lee, Yun Jong Lee, Junichi Nakamura, Javad Parvizi, Takashi Sakai, Nobuhiko Sugano, Masaki Takao, Takuaki Yamamoto, De-Wei Zhao PII:

S0883-5403(19)31101-5

DOI:

https://doi.org/10.1016/j.arth.2019.11.029

Reference:

YARTH 57646

To appear in:

The Journal of Arthroplasty

Received Date: 9 September 2019 Revised Date:

11 November 2019

Accepted Date: 19 November 2019

Please cite this article as: Yoon B-H, Mont MA, Koo K-H, Chen C-H, Cheng EY, Cui Q, Drescher W, Gangji V, Goodman S, Ha Y-C, Hernigou P, Hungerford M, Iorio R, Jo W-L, Jones LC, Khanduja V, Kim HKW, Kim S-Y, Kim T-Y, Lee Hy, Lee MS, Lee Y-K, Lee YJ, Nakamura J, Parvizi J, Sakai T, Sugano N, Takao M, Yamamoto T, Zhao D-W, The 2019 revised version of Association Research Circulation Osseous staging system of osteonecrosis of the femoral head The Journal of Arthroplasty (2019), doi: https://doi.org/10.1016/j.arth.2019.11.029. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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. © 2019 Published by Elsevier Inc.

The 2019 revised version of Association Research Circulation Osseous staging system of osteonecrosis of the femoral head Byung-Ho Yoon1*, Michael A. Mont2*, Kyung-Hoi Koo3, Chung-Hwan Chen4, Edward Y. Cheng5, Quanjun Cui6, Wolf Drescher7, Valerie Gangji8, Stuart Goodman9, Yong-Chan Ha10, Philippe Hernigou11, Marc Hungerford12, Richard Iorio13, Woo-Lam Jo14, Lynne C. Jones15, Vikas Khanduja16, Harry K.W. Kim17, ShinYoon Kim18, Tae-Young Kim19, Hee young Lee20, Mel S. Lee21, Young-Kyun Lee3, Yun Jong Lee22, Junichi Nakamura23, Javad Parvizi24, Takashi Sakai25, Nobuhiko Sugano26, Masaki Takao25, Takuaki Yamamoto27, DeWei Zhao28 1

Department of Orthopaedic Surgery, Inje University College of Medicine, Seoul Paik Hospital, Seoul, South

Korea 2

Department of Orthopaedic Surgery, Lenox Hill Hospital, Northwell Health, New York, NY, USA.

3

Department of Orthopaedic Surgery, Seoul National University Bundang Hospital, Seongnam, South Korea.

4

Department of Orthopaedic Surgery, Kaoshiung Medical University Hospital, Kaohsiung, Taiwan

5

Department of Orthopaedic Surgery, University of Minnesota Medical School, Minneapolis, MN, USA

6

Department of Orthopaedic Surgery, University of Virginia School of Medicine, Charlottesville, VA, USA

7

Department of Orthopedic and Trauma Surgery, RWTH Aachen University, Pauwelsstrasse 30, D-52074

Aachen, Germany 8

Department of Rheumatology and Physical Medicine, Hôpital Erasme, Université Libre de Bruxelles, Brussels,

Belgium 9

Department of Orthopaedic Surgery, Stanford University School of Medicine, 450 Broadway Street, Redwood

City, CA, 94063, USA. 10

11

Department of Orthopaedic Surgery, Chung-Ang University College of Medicine, Seoul, South Korea

Hôpital Henri Mondor, Creteil, France

12

Department of Orthopedic Surgery, Mercy Medical Center, USA.

13

Department of Orthopaedic Surgery, Lahey Hospital and Medical Center, NYU Langone’s Hospital, USA.

14

Department of Orthopaedic Surgery, Seoul St. Mary's Hospital, College of Medicine, The Catholic University

of Korea, Seoul, South Korea. 15

Department of Orthopaedic Surgery, Center for Metabolism and Obesity Research Johns Hopkins University

School of Medicine

16

Department of Trauma & Orthopaedics, Addenbrooke's, - Cambridge University Hospitals, Cambridge, UK.

17

Center for Excellence in Hip Disorders, Scottish Rite Hospital for Children, UT Southwestern Medical Center,

Dallas, Texas. 18

Department of Orthopedic Surgery, Graduate School of Medicine, Kyungpook National University, Daegu

41944, Republic of Korea. 19

Department of Orthopedic Surgery, KonKuk University Medical Center, Seoul, South Korea.

20

Center for preventive medicine and public health, Seoul National University Bundang Hospital, Seongnam,

South Korea. 21

Department of Orthopaedic Surgery, Kaohsiung Chang Gung Memorial Hospital, Kaohsiung, Taiwan.

22

Department of Internal Medicine, Seoul National University Bundang Hospital and Medical College of Seoul

National University, Seongnam, South Korea. 23

Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, 1-8-1 Inohana, Chuo-ku,

Chiba City, Chiba, 260-8677, Japan. 24

Department of Orthopedic Surgery, Rothman Orthopaedic Institute, Philadelphia, PA, USA.

25

Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, Japan.

26

Department of Orthopaedic Medical Engineering, Osaka University Graduate School of Medicine, Suita,

Osaka, Japan. 27

Department of Orthopaedic Surgery, Faculty of Medicine, Fukuoka University, 7-45-1 Nanakuma, Jonan-ku,

Fukuoka, 840-8571, Japan. 28

Department of Orthopedics, Affiliated Zhongshan Hospital of Dalian University, Dalian, China.

Correspondence to: Kyung-Hoi Koo, MD (corresponding author) Department of Orthopaedic Surgery, Seoul National University Bundang Hospital 166 Gumi-ro, Bundang-gu, Seongnam,463-707, South Korea, KS009 Tel: 82-31-787-7204 Fax: 82-31-787-4056 E-mail: [email protected]

Byung-Ho Yoon and Michael A. Mont equally contributed to this work, and should be considered co-first author.

page 1 / 15 1

The 2019 revised version of Association Research Circulation Osseous staging system of

2

osteonecrosis of the femoral head

page 2 / 15 3 4 5

Abstract Objective: The Association Research Circulation Osseous (ARCO) presents the 2019 revised staging system of osteonecrosis of the femoral head (ONFH) based on the 1994 ARCO classification.

6

Methods: In October 2018, ARCO established a task force to revise the staging system of ONFH. The task

7

force involved 29 experts who used a web-based survey for international collaboration. Content validity ratios

8

for each answer were calculated to identify the levels of agreement. For the rating queries, a consensus was

9

defined when more than 70% of the panel members scored a ‘‘4’’ or “5” rating on a 5-point scale.

10

Results: Response rates were 93.1 to 100%, and through the four-round Delphi study, the 1994 ARCO

11

classification for ONFH was successfully revised. The final consensus resulted in the following 4-staged system:

12

1) Stage 1: x-ray is normal, but either magnetic resonance (MRI) or bone scan is positive; 2) Stage 2: x-ray

13

abnormal (subtle signs of osteosclerosis, focal osteoporosis, or cystic change in the femoral head), but without

14

any evidence of subchondral fracture, fracture in the necrotic portion, or flattening of the femoral head; 3) Stage

15

3: fracture in the subchondral or necrotic zone as seen on x-ray or computed tomography (CT) scans. This stage

16

is further divided into stage 3A (early, femoral head depression ≤ 2 mm) and stage 3B (late, femoral head

17

depression > 2 mm); and 4) Stage 4: x-ray evidence of osteoarthritis with accompanying joint space narrowing,

18

acetabular changes, and/or joint destruction. This revised staging system does not incorporate the previous

19

subclassification or quantitation parameters, but the panels agreed on the future development of a separate

20

grading system for predicting disease progression.

21

Conclusion: A staging system has been developed to revise the 1994 ARCO classification for ONFH by an

22

expert panel-based Delphi survey. ARCO approved and recommends this revised system as a universal staging

23

of ONFH.

24 25

Key words: staging; hip; osteonecrosis; avascular necrosis; Delphi

page 3 / 15 26

Introduction

27

Osteonecrosis of the femoral head (ONFH), previously described as avascular necrosis, usually affects

28

adults younger than 50 years.1,2 It frequently leads to collapse of the femoral head and hip arthritis. Many cases

29

of non-traumatic ONFH are associated with the use of glucocorticoids or excessive alcohol intake. Other

30

associated disorders and risk factors include sickle cell disease, human immunodeficiency virus infection,

31

systemic lupus erythematosus, organ transplantation, Gaucher disease, and coagulation abnormalities such as

32

anti-phospholipid antibody syndrome.3 In the United States, 10,000 to 20,000 new patients are affected with

33

ONFH annually.3 In Korea and Japan, the annual prevalence is more than 10,000.4,5 It has been reported to

34

account for about 50% of the total hip arthroplasties (THAs) performed in Asia and sub-Saharan Africa6-8 and

35

over 10% of those in the United States.9

36

Because patients with non-traumatic ONFH tend to be young and active, their THAs generally have a

37

higher rate of revision10,11 and worse outcomes12 than those performed for primary hip osteoarthritis. Thus,

38

clinical researchers have attempted to develop effective treatments for joint preservation in patients who have

39

ONFH. However, effective treatments remain less-reliable, as varying indications and outcomes have been

40

reported. This confusion may in part be due to absence of a reliable, widely accepted patient stratification

41

system.[12]

42

In 1991, the Association Research Circulation Osseous (ARCO) developed the first international

43

classification system based on the system of Ficat and Arlet13 and that of Steinberg et al. (University of

44

Pennsylvania classification).14 The original ARCO classification was composed of 7 stages of disease

45

progression with a subdivision of location and size of the necrotic lesion.15 Because this classification was not

46

practical or easy to apply in clinical and research settings, ARCO tried to simplify the original classification in

47

1994. The modified ARCO classification system had 5 stages with the same subdivisions as the 1991

48

classification; with the original stage III and IV merged into stage 3 and the original stage V and VI integrated

49

into stage 4.16 Unfortunately, this modified version has not been widely used, and only the staging without the

50

subdivisions has been used due to several reasons.17-19 First, the system appears to be too complicated for

51

practical use. Second, the stage 0 lesions, was poorly defined and did not always result in osteonecrosis. Third,

52

stage 3 lesions with minimal collapse of the femoral head do not always progress to more advanced stages, and

53

they might have better prognosis than lesions with definite collapse after joint-preserving treatments.20-23

54

Therefore, to improve on the prognostic impact of stage 3 in the 1994 ARCO system, the Nijmegen modification

55

had been proposed to divide stage 3 into an early and late substages.24 In 2013, ARCO held an international

page 4 / 15 56

consensus meeting with the goal of revising the classification system once again. Unfortunately, consensus was

57

not achieved despite intensive discussion, because of a disagreement about the lesion size/extent subdivisions

58

that are closely related to the prognosis of ONFH. Under these circumstances, in October 2018, another attempt,

59

with 5 orthopaedic surgeons, 1 rheumatologist, and 1 specialist in consensus methodology, was undertaken to

60

revise the 1994 classification system of ONFH using a Delphi approach.

61

The Delphi method is a structured communication technique for achieving convergence of expert

62

opinions.25,26 After each round, a facilitator provides an anonymous summary of the experts' opinions from the

63

previous round as well as the reasons underlying their judgments. Through this process, the range of the answers

64

will converge towards a consensus. The Delphi technique is particularly suitable when the issues are

65

controversial or when there is not firm scientific evidence.27 Thus, the task force employed a modified Delphi

66

method for the revision of the ARCO classification system. After conducting a four-stage modified Delphi

67

process using anonymous web-based internet surveys, a consensus was built on the 2019 revised ARCO staging

68

system for ONFH.

69

Materials and Methods

70

Selection of Expert panel members

71

To recruit panel members, each of the ARCO board members recommended two or three experts based on the

72

following criteria: (1) at least 10 years of clinical/research experience and (2) three or more publications on

73

osteonecrosis. The number of participants in a Delphi panel has usually been between 15 and 30, because a

74

larger sample size (beyond 30) has rarely been found to improve the results.25 Thirty experts, including nine

75

ARCO board members, were invited to the Delphi panel. Among the 30 invitees, one, who had retired from

76

academic activity, declined the invitation. The remaining 29 experts accepted the invitation and participated in

77

the Delphi procedure. The elected participants had a mean of 19 years (range, 11 to 32 years) of clinical and/or

78

research experience on osteonecrosis (Table 1).

79 80

The modified Delphi procedure

81

The ARCO task force initially raised 3 issues: (1) whether the panel members use the ARCO

82

classification system in their clinical practice and research and if not why not; (2) what are problems in the

83

current ARCO classification system: and (3) how to revise the system.

84 85

In the first survey, the panel members were asked to answer 2 open-ended questions about the above three issues.

Replies to the first survey were analyzed to determine whether consensus was reached or

page 5 / 15 86

not. In the second to fourth rounds, the panel members were asked to answer the revised questionnaires on the

87

issues on which the panel members did not reach consensus in the previous round. The rounds were continued

88

until final consensus was obtained. Each round lasted 2 weeks with a 2-week gap for the analysis and for

89

controlled feedback. Thus, each participant was informed of anonymized other responses as a simple tabulated

90

descriptive summary. This ensured that all participants contributed to the discussion.

91 92 93

Cut-off point for consensus The content validity ratio (CVR)28 in which the linear transformation of a proportional level of

94

agreement on

95

represents the proportion of panel participants who rate an item as essential. The CVR was calculated according

96

to the following formula, using the total number of experts (N) and the number who rated the object as essential

97

(E): CVR = [(E - (N / 2)) / (N / 2)].

98

means that 20 is the minimum panel number to reach a consensus.29 Concerning queries with rates, we defined

99

that a consensus was reached when more than 70% of panel members scored a ‘‘4’’ or “5” rating on a 5-point

100

how

many

“experts”

within

a

panel

rate

an

item

“essential” was used. It

In the case of 29 responders, the cut off value of CVR was 0.379, which

scale. 30

101 102

Data synthesis and analysis

103

Data from each Delphi round were extracted from the online survey database and were anonymously

104

reported back to all panel members. Opinions or rationales provided by panel members were also anonymously

105

circulated. The open-ended responses in the first round were integrated, categorized, and described in terms of

106

frequency and percentages. In the second and third round, the answers were collected and the percentage and

107

CVR were calculated for each answer. In the fourth round, the proportion of the panel who rated 4 or more on a

108

5-point scale was computed for each question.

109 110

Source of Funding

111

112 113 114

No external funding was received in support of this work.

Results Four Delphi rounds were successfully performed from January 1 to April 30, 2019.

page 6 / 15 115

Round 1: Open question round

116

Two questionnaires were sent to the panel members: Q1. “Do you use the ARCO classification system in

117

your clinical practice and research? Please answer 'Yes' or 'No'. If 'No', please describe the reason(s).” Second,

118

panel members were also required to provide their own opinions regarding the current classification system. Q2.

119

“Do you think the ARCO classification system should be revised? Please answer 'Yes' or 'No'. If 'Yes', please

120

describe what problems the ARCO classification system has and how to solve them.”

121

The response rate was 100%. Eighteen panel members (62.1%) answered that they used the current ARCO

122

classification system, while 11 (39.3%) answered that they did not. The most common reasons for non-usage

123

was “too complicated and not helpful” (5/29, 17.2%) and the second most common reason was “use another

124

classification” (3/29, 10.3%). Twenty-five panel members (86.2%) agreed with the necessity of revision of the

125

current ARCO system.

126 127 128

Round 2: Questions on whether each stage or definition for sub-classification needs to be changed. Panel members received 9 queries on which stage(s) had to be revised or not. The response rate was 96.5%

129

(28/29) in the second round. The nine queries and panel members’ responses are shown in Table 2. Through the

130

second round, consensus was reached (1) to delete stage 0 and (2) to maintain stages 1 and 4 (Table 2) with the

131

same definition as previously presented in 1994 version of the ARCO staging. However, experts’ opinions were

132

divided about stage 2 and 3 and had not converged in Round 2.

133 134

Round 3: Questions focused on stage 2 and 3.

135

In this round, we re-tried to get a consensus on the unresolved issues of Round 2 and the participants

136

had the opportunity to express an opinion on whether they agreed with the majority opinions in the previous

137

round (Table 3). The response rates were 93.1% (27/29) in Round 3. After each re-voting process, all questions

138

resulted in a consensus. In the revised staging system, the definition of stages 2 and 3 was kept unchanged and

139

stage 3 was further divided by the degree of femoral head depression. Additionally, the revised system did not

140

incorporate the subdivisions according to the size/location/length of the necrotic area, even though they are a

141

strong predictor for further collapse of the femoral head. The experts proposed to design a new classification

142

system of size/location/length or prognostic grading system for ONFH, separately from its progression staging

143

system, at a later date.

144

page 7 / 15 145

Round 4: Questions for the detailed definition of stage 3.

146

To establish the definition of early and late stage 3, we moved to Round 4. Participants were asked

147

whether or not they agreed on the opinion that stage 3 would be divided into early and late sub-stages according

148

to the degree of femoral head depression. Moreover, two cut-off values (2 mm and 3 mm) for the depression

149

were scored for agreement on a 5-point scale. The response rates in this Delphi procedure were 100% in Round

150

4 (Table 4). Through Round 4, the revised ARCO staging system had two sub-stages according the depression

151

depth (2 mm); early stage 3 (3A) defined as the status with a crescent sign alone or a mild head depression (≤ 2

152

mm) and late stage 3 (3B) as the status with depression of the femoral head (> 2 mm).

153

After four consecutive Delphi rounds, a full and final consensus was achieved on the revised version of

154

the ARCO staging system for ONFH (Table 5) (Fig 1). This version was presented and approved on May 3,

155

2019 at the 2019 ARCO Conference in Dalian, China.

156

Discussion

157

Osteonecrosis of the femoral head is a progressive disease, which results in collapse of the femoral

158

head in a large proportion of patients. Collapse of the femoral head is irreversible in its natural history and is a

159

crucial event that often leads to intolerable symptoms and secondary hip arthritis with an impaired quality of life.

160

The collapse usually occurs within 2 years in 32 to 79% of patients who have symptomatic ONFH,31 and

161

untreated asymptomatic ONFH has a progression to symptomatic disease or collapse in about 60% during a

162

maximal 20-year follow-up.32

163

Because ONFH often affects young patients who want to maintain high levels of activity in their life,

164

joint-preserving treatments appear to be appropriate. Generally, these conservative treatments are recommended

165

for pre-collapse ONFH with a low risk for progression, while advanced cases with post-collapse and/or

166

acetabular involvement require hip arthroplasty. In addition, various joint-preserving techniques such as core

167

decompression, bone grafting, and osteotomies may be indicated, if a patient has pre-collapse lesions with a

168

lower risk for disease progression. Therefore, treatment decisions should be based on the current status of

169

ONFH – “where is it?” – and risk factors for predicting further progression – “where is it going?”

170

Since 1980, when the first ONFH staging system was developed by Ficat, at least 16 classification

171

systems have been proposed.[29] Among them, the Ficat and Arlet classification, the Steinberg classification,

172

the ARCO classification, and the Japanese Investigation Committee (JIC) classification have been used in many

173

studies. However, none has been considered to be ideal with adequate reliability and reproducibility. The Ficat

174

and Arlet classification consists of 5 stages (including stage 0) based on the findings on plain radiographs, and it

page 8 / 15 175

has no quantitative evaluation of the necrotic extent.33 After the introduction of magnetic resonance imaging

176

(MRI) in clinical practice and research for ONFH, the Steinberg and ARCO classifications incorporated 7 or 5

177

stages respectively, reflecting radiographic or pathological progression status and 3 quantitative parameters of

178

necrotic area as prognostic risk factors.[12] The 1994 ARCO classification also included 3 location parameters

179

for sub-classification according to the JIC system and thw Steinberg system. The 2001 revised JIC classification

180

was comprised of four lesion types based on the location in the central coronal images and separately describing

181

a modified ARCO staging with the deletion of stage 0 and with the subdivision of stage 3 according to the depth

182

of the head depression (< 3 mm versus ≥ 3 mm).34 Nevertheless, there had been no subdivision of stage 3 in the

183

1994 ARCO classification, and a need had been subsequently recognized to subdivide stage 3 into early and late

184

stages because some lesions with minimal collapse do not necessarily progress.

185

Although the Steinberg, 1994 ARCO, and JIC classification systems were comprehensively designed to

186

improve performance and to enhance clinical application, they have not been user-friendly when compared to

187

the Ficat and Arlet classification. In a systematic review, the Ficat and Arlet classification was used in 63% of

188

the published literature, the Steinberg classification in 20%, the ARCO system in 12%, and the JIC system in

189

5%.[29] Additionally, in a recent survey study for skeletal radiologists, only half of them used a specific

190

classification system and the majority used the Ficat and Arlet classification.35 Moreover, the Ficat and Arlet,

191

Steinberg, and 1994 ARCO classification showed poor inter-observer reliability (Kappa statics (κ), 0.31 to 0.56)

192

and intra-observer reproducibility in validation studies18,36,37 with the exception of the study by Kay et al.19

193

Although the kappa value for inter-observer reliability of JIC classification system was reported to be about

194

0.72,18,38 the JIC system classified only size and location of necrotic portion, but not stages. Further modification

195

of the 1994 ARCO classification system has not been successful, due to the lack of consensus on the staging,

196

sub-classification, and/or quantitation.

197

When compared to the 1994 classification system, the current version of the ARCO staging system

198

has 3 main changes (Table 6): (1) Stage 0 is deleted; (2) stage 3 is subdivided into early and late sub-stages

199

according to the amount of femoral head depression (≤2 mm versus >2 mm); and (3) the subdivision according

200

to the size/location/length of the necrotic area is not included.

201

The concept of stage 0 was proposed by Ficat as both pre-radiographic and pre-clinical status (“silent

202

hip”) in patients with unilateral ONFH. In the Steinberg et al. and 1994 ARCO systems, stage 0 was also

203

defined as the status with normal or non-diagnostic images in suspected patients, except histological changes.

204

Because stage 0 was assigned under the idea that a staging system had

to include the disease onset, stage 0 is

page 9 / 15 205

not practical, but rather theoretical.24 Furthermore, pathological evaluation is not routinely performed in recent

206

clinical practice and a pathological necrosis of the bone marrow necrosis does not always progress to definitive

207

osteonecrosis. Thus, the consensus opinion was to delete stage 0 in the current revised system.

208 209

In the 1994 ARCO classification, stage 3 was characterized by a crescent sign; a curvilinear subchondral fracture line on the x-ray.

210

Late radiographs of stage 3 may show articular surface flattening of the femoral head without hip

211

joint space narrowing or acetabular involvement.24 However, it was established that the prognosis in stage 3 can

212

be different according to the depth of the head depression. Some of stage 3 patients who had

213

head depression do not rapidly progress to more advanced stages and may respond favorably to joint-preserving

214

procedures.39,40 The Nijmegen modification of the ARCO classification has already proposed to sub-classify

215

stage 3

216

current revised version subdivides stage 3 into an early and late phase by using the cutoff of head depression as

217

2 mm.

24

minimal femoral

, but the criteria for early and late sub-stages was the presence of femoral head collapse alone. The

218

Multiple studies have shown that the extent of necrosis predicts the outcome of the disease and is an

219

important determinant of prognosis and management in ONFH. Given this background information, many

220

classification systems have tried to develop and include methods of assessing and characterizing the extent of

221

necrosis. The Steinberg system categorizes the extent of involvement into 3 subsets in stage I to V. The 1994

222

ARCO system subdivided stages into 3 categories according to the extent of the femoral head involvement and

223

the location of the necrotic region. To date, however, there is no general agreement as to which method for

224

determining the extent of involvement is most valid, reproducible, and convenient to use.41 In addition, the

225

optimal cutoff values of the necrotic extent on disease progression have not been obtained. Furthermore, in the

226

later stages, the other factors including the size/depth of the collapsed segment, joint narrowing, and acetabular

227

involvement could also potentially determine the prognosis and the type of treatment indicated.35 During the

228

Delphi process, we realized that the Ficat and Arlet system does not have subcategories based on the extent of

229

necrosis and is much simpler and more popular than the other classification systems. Thus, this revised ARCO

230

staging system does not include a prognostic categorization by using the location or quantitation of the necrosis.

231

By deleting the subcategorization system used in the 1994 ARCO classification, the revised ARCO staging

232

system is simpler and is more practical for use in clinical and research settings. While our revised system of 4

233

stages may appear similar the Ficat and Arlet system, the proposed system has major differences

234

compared to Ficat and Arlet’s classification system which was used before the advent of MRI. In addition,

page 10 / 15 235

the Ficat and Arlet system was confusing in that it did not sufficiently clarify collapse. For example, it

236

designated a crescent sign without collapse as a Stage 2 lesion, which we now consider a Stage 3 collapsed

237

lesion.

238

these are major differences between the historical system and the ARCO system proposed in this report.

There was also no subclassification of amount of head depression, which affects prognosis. All of

239

The simple 4-staged system of the 2019 ARCO system might result in a limitation – a progression

240

from one stage to the next can be captured only after a substantial pathologic or radiographic change. The

241

previous validation studies reported a poor reliability of the ONFH classification systems, especially in middle

242

stages.18,19,35,37 Stage 1 and 4 represented distinct images of either a normal hip without any ONFH change or a

243

severely arthritic hip with joint space narrowing, acetabular changes, and/or or joint destruction. Therefore,

244

opinions about the assignment into stage 1 and 4 did not vary markedly among assessors. But the discrepancy

245

between their opinions would increase if x-ray findings are not clear or if they introduce subjective non-

246

quantitative definitions of stage 2 or 3 that are open to various interpretations.37 Plakseychuk et al. found that the

247

presence of a crescent sign in Steinberg stage III and joint space narrowing in stage V were a main cause for the

248

diminished reliability.35 The authors reported that the definitions of the crescent stage have been ambiguous in

249

all classifications through a review of literature. In fact, it is a pathological term representing subchondral

250

fracture or collapse; collapse of necrotic bone produces a crescent-like void in the subchondral region. The

251

radiographically clear definition of the crescent sign, or the precise radiographic distinction between

252

subchondral collapse and cyst formation has never been clearly delineated.35

253

It has been difficult to reach a consensus regarding which characteristics of the various

254

classification systems are significantly unique across different countries and continents. Therefore, we

255

believed that the Delphi method would be appropriate, as it has been utilized in many fields of medicine

256

and has demonstrated reliability and validity for reaching a consensus when the available literature on a

257

given topic is limited. In addition, we believe that this new system will be useful because it provides

258

simplicity without eliminating significantly unique characteristics. For example: (1) Stage 0 of the

259

previous ARCO system that was characterized by normal imaging studies could only be assigned after

260

histologic diagnosis. We do not believe that including this stage is clinically useful with the advent of MRI;

261

(2) Solidifying Stage 1 and 2 lesions as pre-collapse disease is important, as these two categories represent

262

lesions that warrant joint preserving surgery and do not necessitate hip arthroplasty; (3) We subdivided

263

Stage 3 into early and late sub-stages according to the amount of femoral head depression (≤2 mm versus

264

>2 mm). The degree of head depression has been repeatedly shown to be a significant factor that

page 11 / 15 265

influences the clinical outcomes of various joint preserving procedures (Table 7); (4) Stages 5 and 6 are

266

not included as found in the Steinberg classification because these do not alter treatment methods past

267

Stage 4. We believe that for the purposes of this treatment-driven classification system, Stage 4

268

sufficiently indicates that hip arthroplasty is the most appropriate treatment modality without including

269

Stages 5 and 6, which have been encompassed into stage 4.

270

We acknowledge several limitations of our study. First, inter-observer and intra-observer

271

reliabilities were not verified. While this was not the purpose of the current study, we will certainly do

272

this in the future for this new staging system. In addition, certain radiologic elements of this staging

273

system have been assessed in previously published studies.37,42,43 Second, we used the Delphi method to

274

reach consensus among the experts. However, we did not recruit all experts who have been involved in

275

the previous classification systems. Third, we adopted a 2 mm cut-off for subdividing collapse into early

276

(3A) and late (3B) stages. While the significance of the 2mm cut-off was not established in this publication,

277

it has been demonstrated in many previous works.21,44-48 The preoperative level of collapse has been

278

shown to significantly influence the clinical outcome of non-vascularized bone grafting,47,48 vascularized

279

bone grafting,44,46 as well as posterior45 and anterior21 rotational osteotomies (Table 7). As mentioned

280

previously, the authors of the current study will determine the validity of this cut-off in future work.

281

Lastly, the significance of Steinberg V and VI categories was not included because they do not change the

282

treatment approach. Rather, these categories refer to the extent of joint degeneration after collapse has

283

occurred. In both of these stages, the most appropriate treatment method would be a hip arthroplasty.

284

Thus, we do not believe this information is relevant to the purpose of this study as the proposed Stage IV

285

encompasses Steinberg Stages IV, V, and VI categories, where the treatment would be the same.

286

The 2019 revised ARCO staging system adopted the definition of stages from the 1994 ARCO

287

classification system, and the inter-observer and intra-observer reliabilities are not verified. To improve the

288

performance of the revised ARCO staging system, further studies will be needed using standardized imaging

289

tools for ONFH staging.

290 291

Conclusion

292

In the 2019 revised ARCO staging system, 1) stage 0 is deleted, 2) stage 3 is divided into early (3A)

293

and late stage (3B) according to the depth (2 mm) of head depression and 3) sub-classification of location and

294

size is not incorporated. ARCO recommends clinician and researchers use the 2019 revised ARCO staging

page 12 / 15 295

system for ONFH studies. Additionally, ARCO is developing a reliable and valid classification for predicting

296

the progression of disease.

297

Role of the funding source None

298

Acknowledgement None

299

Disclosure statement The authors declare no conflicts of interest.

page 13 / 15 300

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Figure legend

414

Figure 1. antero-posterior images of the right hip of a patient in condition progressed from ARCO stage I to IV.

415

(A) stage 1: a low-intensity outer rim on T1-weighted coronal MR image is noted. (B) stage 2: focal

416

osteoporosis and osteosclerosis are seen in the femoral head. (C) stage 3A: subchondral collapse lesser than

417

2mm and marginal sclerosis along the lesion are seen (D) stage 3B: marked collapse of thewe femoral head

418

more than 2mm is noted. (E) stage 4: fragmentation of the necrotic lesion and progress of the joint space

419

narrowing with acetabular change are seen.

420

Table 7. The Influence of the 2 mm Cut-Off on Clinical Outcomes of Various Joint-Preserving Procedures Result Study (year) Procedure Collapse < 2mm

Collapse > 2mm

Zuo et al. (2016)

Non-vascularized bone grafting

17/105 hips (16.2%) were considered clinical failures based on progressive collapse, need for total hip arthroplasty, or Harris Hip score

16/26 hips (61.5%) were considered clinical failures based on progressive collapse, need for total hip arthroplasty, or Harris Hip score

p < 0.001

Wang et al. (2009)

Non-vascularized bone grafting

Good/excellent results achieved in 30/40 hips (75%)

Good/excellent results achieved in 26/40 hips (65%)

p = 0.001

Sun et al. (2019)

Non-vascularized bone grafting versus Core Decompression

Satisfactory results can be achieved with core decompression

Survival rate is improved with bone grafting compared to core decompression

NR

Vascularized iliac bone graft

18/26 hips (69.2%) converted to total hip arthroplasty within a mean 85 months

7/7 hips (100%) converted to total hip arthroplasty within a mean 35 months

p=0.016

Vascularized greater trochanter bone graft

36/38 hips (94.7%) had a good to excellent clinical outcome based on Harris Hip score

20/26 hips (76.9%) had a good to excellent clinical outcome based on Harris Hip score

NR

Sugioka et al. (2008)

Transtrochanteric posterior rotational osteotomy

1/19 hips (5.3%) had progression of osteoarthritis

12/24 hips (50%) had progression of osteoarthritis

p=0.0004

Kubo et al. (2017)

Transtrochanteric anterior rotational osteotomy

30/47 hips (63.8%) did not have progressive collapse postoperatively

17/47 hips (36.2%) had progressive collapse postoperatively

Chen et al. (2009)

Zeng et al. (2013)

p < 0.0001

Table 1. Characteristics of Delphi respondents. Queries Country

USA South Korea Japan Taiwan United Kingdom Germany France Belgium China

Number of publications authored concerning osteonecrosis *Data are expressed as mean ± standard deviation

Total (n=29) 9 (31.0%) 8 (27.6%) 5 (17.2%) 2 (6.9%) 1 (3.4%) 1 (3.4%) 1 (3.4%) 1 (3.4%) 1 (3.4%) 20.8 ± 11.8*

Table 2. The Delphi questionnaires and results of round 2 Delphi questionnaire Responses (n=28) (Which stage should be revised or deleted?) Question 1 Revise (2, 7.1%) Stage 0 Delete (20, 71.4%) Maintain (6, 21.4%) Question 2 Revise (6, 21.4%) Stage 1 Delete (1, 3.6%) Maintain (21, 75.0%) Question 3. Revise (9, 32.1%) Stage 2 Delete (1, 3.6%) Maintain (18, 64.3%) Question 4 Revise (19, 67.9%) Stage 3 Delete (1, 3.6%) Maintain (8, 28.6%) Question 5 Revise (3, 10.7%) Stage 4 Delete (0, 0%) Maintain (25, 89.3%) Question 6 Revise (6, 21.4%) Sub-classification - location Delete (13, 46.4%) Maintain (9, 32.1%) Question 7 Revise (7, 25.0%) Sub-classification - area Delete (13, 46.4%) Maintain (8, 28.6%) Question 8 Revise (5, 17.9%) Sub-classification - length Delete (15, 53.6%) Maintain (8, 28.6%) Question 9 Revise (6, 21.4%) Sub-classification - depth Delete (15, 53.6%) Maintain (7, 25.0%) The cut off value of content validity ratio was 0.379

content validity ratio

Delete (0.428)

Maintain (0.5)

Maintain (0.285) Revise (0.357)

Maintain (0.785) Unavailable

Unavailable

Unavailable

Unavailable

Table 3. The Delphi questionnaire and results of round 3 Delphi questionnaire Question 1. Do you agree with current definition of Stage 2? Question 2. Do you agree with current definition of Stage 3?

Responses (n=27) Yes, I agree (24, 88.9%) No, I do not agree (3, 11.1%)

Yes (0.777)

Yes, I agree (23, 85.2%) No, I do not agree (4, 14.8%)

Yes (0.703)

Question 3. Among 19 panels, who answered “to revise Stage Yes, I agree (25, 92.6%) 3”, 13 (68.4%) proposed to further divide the No, I do not agree (2, 7.4%) current Stage 3 according to the degree of collapse. Do you agree with that? Question 4. Among 18 panels, who described rationales for his or her answer to questions 6,7,8,9 of the previous survey, 10 (55.6%) proposed to delete size/location from the ARCO staging. Do you agree with that?

Content validity ratio

Yes (0.851)

Yes, I agree to delete the Yes (0.407) size/location from the staging. (19, 70.4%) No, I want to retain size/location in the new version. (8, 29.6%)

Yes (18, 94.7%) Question 5. (n=19 from Question 3) If you answer yes (I agree to delete the No, I do not agree (1, 5.3%) size/location from the staging), do you think it is necessary to separately establish a classification of size/location as a predictor for further

Yes (0.894)

collapse? The cut off value of content validity ratio was 0.379

Table 4. Questionnaire and replies of round 4 Questionnaire Replies (n=29) Question 1. Among the 17 panel members, who described his or Yes, I agree (28, 96.6%) her opinion about dividing stage 3, 14 (82.4%) No, I do not agree (1, 3.5%) suggested to divide stage 3 into 3A (early: crescent without collapse or slight collapse) and 3B (late: definite collapse). Do you agree with that? Question 2. How do you define “definite collapse”? Please rank the level of adequacy of the following definition, using a scale of '0 = not at all adequate' to '5 = very adequate'. Collapse by more than 2 mm (> 2 mm) Question 3. How do you define “definite collapse”? Please rank the level of adequacy of the following definition, using a scale of '0 = not at all adequate' to '5 = very adequate'. Collapse by more than 3 mm (> 3 mm)

1 (3, 10.3%) 2 (3, 10.3%) 3 (2, 6.9%) 4 (7, 24.1%) 5 (3, 48.3%) 1 (6, 20.7%) 2 (4, 13.8%) 3 (8, 27.6%) 4 (2, 6.9%) 5 (9, 31.0%)

Table 5. The 2019 revised Association Research Circulation Osseous staging criteria for osteonecrosis of the femoral head. ARCO stage 1

Image findings X-ray normal MRI abnormal

Description

A band lesion of low signal intensity around the necrotic area is seen on MRI. A cold spot is seen on bone scan. No changes are seen on plain radiographs. X-ray abnormal Osteosclerosis, focal osteoporosis or cystic changes are seen in the femoral head on plain 2 radiographs or CT scan. MRI abnormal Still there is no evidence of subchondral fracture, fracture in the necrotic portion or flattening of the femoral head. 3 Subchondral fracture Subchondral fracture, fracture in the necrotic portion and/or flattening of the femoral head is seen on X-ray or CT on plain radiography or CT scan. 3A (early) Femoral head depression ≤ 2 mm 3B (late) Femoral head depression >2 mm 4 X-ray osteoarthritis Osteoarthritis of the hip joint with joint space narrowing, acetabular changes and destruction are seen on plain radiographs. MRI: magnetic resonance image, CT: computed tomography

Table 6. Comparison of staging systems of femoral head osteonecrosis

Preclinical and preradiographic Evident change on MRI Evident change on X-ray Subchondral fracture Head collapse ≤ 2 mm Head collapse >2 mm Joint space narrowing or acetabular changes Advanced osteoarthritis

Ficat and Arlet stage 0

Steinberg stage 0

ARCO stage in 1994 0

ARCO stage in 2019

1 2 3

1 2 3

1 2 3

1 2 3A

4

4 5

4

3B 4

6

page 1 / 1 1

Figure legend

2

Figure 1. antero-posterior images of the right hip of a patient in condition progressed from ARCO stage I to IV.

3

(A) stage 1: a low-intensity outer rim on T1-weighted coronal MR image is noted. (B) stage 2: focal

4

osteoporosis and osteosclerosis are seen in the femoral head. (C) stage 3A: subchondral collapse lesser than

5

2mm and marginal sclerosis along the lesion are seen (D) stage 3B: marked collapse of thewe femoral head

6

more than 2mm is noted. (E) stage 4: fragmentation of the necrotic lesion and progress of the joint space

7

narrowing with acetabular change are seen.