The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 88, Issue suppl 3

Classification and Diagnostics | November 01, 2006

Systematic Analysis of Classification Systems for Osteonecrosis of the Femoral Head

Michael A. Mont, MD; German A. Marulanda, MD; Lynne C. Jones, PhD; Khaled J. Saleh, MD, MSc, FRCSC; Noah Gordon, MD; David S. Hungerford, MD; Marvin E. Steinberg, MD

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In support of their research for or preparation of this manuscript, one or more of the authors received grants or outside funding from Stryker Orthopaedics and Smith and Nephew. None of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. Commercial entities (Stryker Orthopaedics and Smith and Nephew) paid or directed, or agreed to pay or direct, benefits to a research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

The Journal of Bone and Joint Surgery, Incorporated

J Bone Joint Surg Am, 2006 Nov 01;88(suppl 3):16-26. doi: 10.2106/JBJS.F.00457

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Abstract

Background: Multiple classification systems for osteonecrosis of the hip have been developed to assist physicians in the diagnosis and treatment of this potentially debilitating disorder. The purpose of this analysis was to delineate the classification systems utilized in reports published since 1985 and, through a comparison of the most commonly used systems, to identify consistent factors that would allow for cross-publication comparisons to be made.

Methods: We performed a PubMed search for reports of outcome studies concerning treatment methods for osteonecrosis of the hip. All studies of reported outcomes with greater than ten patients were included in the analysis. Various classification systems were tabulated to determine usage frequencies. The four most commonly used systems were then analyzed to determine common factors used for classification.

Results: One hundred and fifty-seven studies were available for analysis. Sixteen major classification systems that made use of more than one radiographic factor were identified, and nine of these systems had one to five modifications reported throughout the literature. Additionally, eleven other systems made use of single factors obtained from either magnetic resonance imaging or anatomic data. The review revealed that four classification systems accounted for greater than 85.4% of the reported studies. Parameters for these four systems were stratified to allow for uniformity of patient or study evaluation.

Conclusions: This analysis of the reported classification systems for osteonecrosis of the femoral head revealed several similarities between the most commonly used systems. An analysis of patients can be made with any of the four major systems if specific data are collected according to various magnetic resonance imaging and radiographic findings. This approach will allow for easier comparison of studies across different centers.

Level of Evidence: Prognostic Level III. See Instructions to Authors on jbjs.org for a complete description of levels of evidence.

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Osteonecrosis of the femoral head is a devastating disease that typically affects young patients (mean age, mid-thirties)¹ and often leads to femoral head collapse if left untreated^2,3. Because these patients are young and relatively active, and because total hip arthroplasty has not always been associated with an optimal outcome in this patient population, various procedures for joint preservation have been utilized, ranging from core decompression^4-20, percutaneous drilling¹⁷, vascularized and nonvascularized bone-grafting^21-31 and osteotomies ^32-38 to hemiresurfacing^39-42, total hip arthroplasty^1,3, and metal-on-metal total hip resurfacing^43,44. Unfortunately, these methods have different indications and various reported success rates and there is tremendous controversy concerning when to use the various procedures⁴⁵. One of the major obstacles to an understanding of this issue is that there is no universally accepted classification method for assessing the severity of and making a prognosis about this disease. In addition, there is often no uniform collection of data from the various treatment centers that would allow for patient stratification, follow-up, and classification. This lack of uniformity in data collection makes it difficult, if not impossible, to perform analyses and comparisons across various centers. Some authors will classify the stages of the disease differently than other authors and institutions, which does not allow for validation of various treatment algorithms.

A classification system for any orthopaedic condition should be consistent, logical, reproducible, all-inclusive, sensitive, and clinically useful. In addition, two main functions should be easily recognized as the purpose of any classification schema. First, classification organizes and categorizes a problem to guide a decision-making process. Second, the system should clearly stratify the natural progression or resolution of a disease process^46-48. For pathologic processes such as osteonecrosis of the femoral head, for which controversy exists regarding the natural history, diagnosis, and treatment, the above-mentioned functions are critically important to allow for cross-comparison of results between centers and investigators.

A cursory review of the literature reveals multiple classification methods. One of the first classification systems utilized for this disease was that of Ficat and Arlet, who developed their system in the 1960s before the advent of magnetic resonance imaging^49-51. This system has been modified at least four times. Originally having three stages, the system progressed to four stages and then to six stages, sometimes including symptoms and magnetic resonance imaging findings. Most surgeons still use the simple four-tiered method. Another frequently used classification system is the University of Pennsylvania staging system^52,53, which evolved from the Ficat and Arlet system. This system defines seven precise stages and utilizes radiographs and/or magnetic resonance imaging to stratify lesion size. Using the University of Pennsylvania system, a group of investigators from the Association Research Circulation Osseous (ARCO) tried to initiate the adoption of this system as a new classification method during various society meetings^54-56. Eventually, three different renditions of a uniform ARCO system were made, with no consensus of agreement on which of those systems to use. Japan uses a classification system that was developed by the Japanese Orthopaedic Association and their Ministry of Health⁵⁷. This system initially evaluates hips according to the four-tiered approach of Ficat and Arlet, but stages II and III are further subdivided by type and location of the lesion and stages I and IV are not included in the final classification.

It would be useful if the different centers studying this disease collected similar data so that, regardless of the classification system employed, conversion to other systems would be possible. This might allow for a better prediction of prognosis and indications for different treatment methods. In addition, authors around the world would be able to compare data uniformly.

The purpose of this study was to review the published, peer-reviewed literature since 1985 to describe the most commonly used systems. A second purpose was to describe the common factors in the most commonly used systems to decide if it is possible to agree on universal findings for data collection that would allow for easier comparison of studies across different centers.

Materials and Methods

Materials and Methods | Results | Discussion | References

Aliterature search of PubMed, the MEDLINE database of the United States National Library of Medicine, National Institutes of Health, was carried out to identify all articles that were published between January 1985 and December 2005 and that evaluated clinical outcome in patients with osteonecrosis of the femoral head. The starting year of 1985 was chosen because that was the year in which the results of magnetic resonance imaging began to be commonly included in the analysis of outcomes of patients with osteonecrosis. There was no restriction on the origin or language of the publications. The key words used in the search were "osteonecrosis," "avascular necrosis," "hip," "femoral head," "outcome," and "classification." The initial search was further refined with the addition of key words for each of the operative treatments available (such as core decompression, bone-grafting, and osteotomies). We excluded studies with a patient size of less than ten as well as studies in which only the outcome of total hip arthroplasties was reported. The bibliographies of all of the retrieved articles were also searched for further scientific reports that evaluated outcome. All articles that were identified in this way were then reviewed to determine if they met the eligibility criteria.

It was noted during the initial literature search that there were a number of published reports that had used classification systems that were initially proposed as one isolated finding or criterion. Key words that pertained to angiographic findings, changes evident on magnetic resonance imaging or computed tomography, and intraoperative findings were therefore added as key words to further refine the original search. The reports describing these isolated parameters were added with use of the same inclusion criteria.

The reports were stratified by frequency of use of various classification systems. We then identified the most commonly used classification systems and stratified them for the purpose of identifying the diagnostic factors that should be collected by investigators to enable usage of any of the commonly utilized staging systems. Finally, a comparison table, which was an amalgamation of parameters from the commonly used systems, was constructed to allow for an easier unified gathering of data.

Results

Materials and Methods | Results | Discussion | References

A total of 2,241 reports concerning osteonecrosis of the hip were found in the literature. Case reports, studies that did not report outcome, and studies that described in vitro procedures, traumatic osteonecrosis, and Legg-Calvé-Perthes disease were excluded. This left 472 reports that described the outcome of treatment methods. Articles that described less than ten patients, that made no mention of the duration of follow-up, or that included treatment with total hip arthroplasty were then excluded. This left 157 reports, which have been included in the present analysis of classification methods with reported outcomes.

Many articles compared the effectiveness of two or more techniques for the treatment of osteonecrosis of the hip^4-24,58-63. Forty-seven reports analyzed outcome after core decompression of the femoral head^{4-20,58,64-68}. Thirty-four articles reported outcome after femoral osteotomies (angular and/or rotational)^{32-38,45,58,59,62,63,67,69-100}. Twenty-two articles studied the success rates of nonvascularized bone-grafting^{20-22,60,82,85,86,101-112}, and twenty-nine publications reported on vascularized (fibular and/or iliac) grafting^{21-31,59,61-63,72,82,100,102,113-139}. Nineteen reports were published on limited resurfacing of the femoral head^{39-43,82,85,86,107,140-143}, and twenty seven studies reported on the outcome of nonoperative management^{3,49,60,107,144-151} (Table I).

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TABLE I Classification Systems for Osteonecrosis of the Femoral Head (In Order of Frequency)

Classification	Year Described	Number of Studies^*
Ficat and Arlet^49-51	1960s	96
University of Pennsylvania (Steinberg et al.)^52,53	1984	31
Association Research Circulation Osseous^54-56	1991	18
Japanese Orthopaedic Association^57,186,187	1987	7
Marcus et al.¹⁹²	1973	5
Sugioka⁹⁴	1978	4
Kerboul et al.¹⁶⁷	1974	2
Kokubo et al.¹⁷⁵	1987	2
Smith et al.^18,189	1995,1996	2
Jones¹⁹³	1989	1
Lafforgue et al.¹⁷⁹	1993	1
Koo and Kim¹⁵⁷	1995	1
Theodorou et al.¹⁷¹	2001	1
Atsumi and Kuroki³²	1997	1
Shimizu et al.¹⁶⁹	1994	1
Sakamoto et al.¹⁶⁸	1997	1
Springfield and Enneking¹⁹⁴	1978	1

Several published studies employed more than one classification

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TABLE I Classification Systems for Osteonecrosis of the Femoral Head (In Order of Frequency)

Classification	Year Described	Number of Studies^*
Ficat and Arlet^49-51	1960s	96
University of Pennsylvania (Steinberg et al.)^52,53	1984	31
Association Research Circulation Osseous^54-56	1991	18
Japanese Orthopaedic Association^57,186,187	1987	7
Marcus et al.¹⁹²	1973	5
Sugioka⁹⁴	1978	4
Kerboul et al.¹⁶⁷	1974	2
Kokubo et al.¹⁷⁵	1987	2
Smith et al.^18,189	1995,1996	2
Jones¹⁹³	1989	1
Lafforgue et al.¹⁷⁹	1993	1
Koo and Kim¹⁵⁷	1995	1
Theodorou et al.¹⁷¹	2001	1
Atsumi and Kuroki³²	1997	1
Shimizu et al.¹⁶⁹	1994	1
Sakamoto et al.¹⁶⁸	1997	1
Springfield and Enneking¹⁹⁴	1978	1

Several published studies employed more than one classification

Magnetic resonance imaging has had a tremendous impact on the classification and stratification of osteonecrosis of the femoral head. Eighteen different authors based their studies on the findings shown by magnetic resonance imaging alone, while another five authors incorporated these findings into the main classification systems mentioned above^{13,53,127,152-157}. Intraoperative findings, radiographic appearance, angiography results, and clinical symptoms were also used as the sole method in seven studies^153,158-166.

One or more of the four most common classification systems (Ficat and Arlet, University of Pennsylvania, ARCO, and Japanese Orthopaedic Association) were used in 86.8% of the reports (Tables II, III, IV, V). Of the four systems, the Ficat and Arlet scale⁴⁹ (Table II) was the system most commonly reported (63%). Ninety-six articles utilized this classification as the only stratification system or as a system used in association with other scales. The classification of the University of Pennsylvania⁵² (Table III) was the second most commonly used system and was employed in thirty-one studies (20%). The ARCO classification system⁵⁴ (Table IV) was used in eighteen studies (12%), while the system of the Japanese Orthopaedic Association⁵⁷ (Table V) was utilized in seven studies (5%). Eighteen (12%) of the above-mentioned studies were conducted with the use of two or more classification systems. Twenty-three other articles stratified patients and treatments through the use of modified versions of these four systems^{32,157,167-179}.

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TABLE II Classification System of Ficat and Arlet⁵¹

Stage	Radiographic Findings
1	None (only evident on magnetic resonance images)
2	Diffuse sclerosis, cysts (visualized on radiographs)
3	Subchondral fracture (crescent sign; with or without head collapse)
4	Femoral head collapse, acetabular involvement, and joint destruction (osteoarthritis)

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TABLE II Classification System of Ficat and Arlet⁵¹

Stage	Radiographic Findings
1	None (only evident on magnetic resonance images)
2	Diffuse sclerosis, cysts (visualized on radiographs)
3	Subchondral fracture (crescent sign; with or without head collapse)
4	Femoral head collapse, acetabular involvement, and joint destruction (osteoarthritis)

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TABLE III Classification System of the University of Pennsylvania (Steinberg)⁵²^,⁵³

Stage	Criteria
0	Normal radiograph, bone scan, and magnetic resonance images
I	Normal radiograph. Abnormal bone scan and/or magnetic resonance images
	A: Mild (<15% of femoral head affected)
	B: Moderate (15% to 30% of femoral head affected)
	C: Severe (>30% of femoral head affected)
II	Cystic and sclerotic changes in femoral head
	A: Mild (<15% of femoral head affected)
	B: Moderate (15% to 30% of femoral head affected)
	C: Severe (>30% of femoral head affected)
III	Subchondral collapse without flattening (crescent sign)
	A: Mild (<15% of articular surface)
	B: Moderate (15% to 30% of articular surface)
	C: Severe (>30% of articular surface)
IV	Flattening of femoral head
	A: Mild (<15% of surface and <2 mm of depression)
	B: Moderate (15% to 30% of surface and 2 to 4 mm of depression)
	C: Severe (>30% of surface and >4mm of depression)
V	Joint narrowing or acetabular changes
	A: Mild
	B: Moderate
	C: Severe
VI	Advanced degenerative changes

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TABLE III Classification System of the University of Pennsylvania (Steinberg)⁵²^,⁵³

Stage	Criteria
0	Normal radiograph, bone scan, and magnetic resonance images
I	Normal radiograph. Abnormal bone scan and/or magnetic resonance images
	A: Mild (<15% of femoral head affected)
	B: Moderate (15% to 30% of femoral head affected)
	C: Severe (>30% of femoral head affected)
II	Cystic and sclerotic changes in femoral head
	A: Mild (<15% of femoral head affected)
	B: Moderate (15% to 30% of femoral head affected)
	C: Severe (>30% of femoral head affected)
III	Subchondral collapse without flattening (crescent sign)
	A: Mild (<15% of articular surface)
	B: Moderate (15% to 30% of articular surface)
	C: Severe (>30% of articular surface)
IV	Flattening of femoral head
	A: Mild (<15% of surface and <2 mm of depression)
	B: Moderate (15% to 30% of surface and 2 to 4 mm of depression)
	C: Severe (>30% of surface and >4mm of depression)
V	Joint narrowing or acetabular changes
	A: Mild
	B: Moderate
	C: Severe
VI	Advanced degenerative changes

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TABLE IV Classification System of the Association Research Circulation Osseous⁵⁶

Stage	Findings	Techniques	Subclassification	Quantitation
0	None	Radiography, computed tomography, scintigraphy, magnetic resonance imaging	NO	NO
1	Radiography and computed tomography normal. At least ONE of the-other techniques is positive	Scintigraphy, magnetic resonance imaging	Location of lesion	Area of involvement (percentage)
			Medial	A: Minimal (<15%)
			Central	B: Moderate (15% to 30%)
			Lateral	C: Extensive
				Length of crescent
				A: <15%
				B: 15% to 30%
				C: >30%
				Surface collapse and dome depression
				A: <15% and <2 mm
				B: 15% to 30% and 2 mm to 4 mm
				C: >30% and >4 mm
2	Sclerosis, osteolysis, focal porosis	Radiography, computed tomography, scintigraphy, and magnetic resonance imaging	Same as stage 1	Same as stage 1
3	CRESCENT SIGN and/or flattening of articular surface	Radiography and computed tomography	Same as stage 1	Same as stage 1
4	Osteoarthritis, acetabular changes, joint destruction	Radiography only	NO	NO

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TABLE IV Classification System of the Association Research Circulation Osseous⁵⁶

Stage	Findings	Techniques	Subclassification	Quantitation
0	None	Radiography, computed tomography, scintigraphy, magnetic resonance imaging	NO	NO
1	Radiography and computed tomography normal. At least ONE of the-other techniques is positive	Scintigraphy, magnetic resonance imaging	Location of lesion	Area of involvement (percentage)
			Medial	A: Minimal (<15%)
			Central	B: Moderate (15% to 30%)
			Lateral	C: Extensive
				Length of crescent
				A: <15%
				B: 15% to 30%
				C: >30%
				Surface collapse and dome depression
				A: <15% and <2 mm
				B: 15% to 30% and 2 mm to 4 mm
				C: >30% and >4 mm
2	Sclerosis, osteolysis, focal porosis	Radiography, computed tomography, scintigraphy, and magnetic resonance imaging	Same as stage 1	Same as stage 1
3	CRESCENT SIGN and/or flattening of articular surface	Radiography and computed tomography	Same as stage 1	Same as stage 1
4	Osteoarthritis, acetabular changes, joint destruction	Radiography only	NO	NO

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TABLE V Radiographic Classification System of the Japanese Orthopaedic Association⁵⁷^,¹⁸⁶^,¹⁸⁷

Stage	Finding
1	Demarcation line, subdivided by relationship to weight-bearing area (from medial to lateral)
	1A
	1B
	1C
2	Early flattening WITHOUT demarcation line around necrotic area
3	Cystic lesions, subdivided by site in the femoral head
	3A (medial)
	3B (lateral)

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TABLE V Radiographic Classification System of the Japanese Orthopaedic Association⁵⁷^,¹⁸⁶^,¹⁸⁷

Stage	Finding
1	Demarcation line, subdivided by relationship to weight-bearing area (from medial to lateral)
	1A
	1B
	1C
2	Early flattening WITHOUT demarcation line around necrotic area
3	Cystic lesions, subdivided by site in the femoral head
	3A (medial)
	3B (lateral)

The similarities among the four most commonly used systems allow for a uniform collection of data and cross-study comparison. Magnetic resonance imaging and radiographic findings were found to be fundamental elements of the main classifications (Table VI). The following parameters were found to be the most useful: (1) presence or absence of collapse; (2) size of lesion; (3) head depression; (4) acetabular involvement; (5) crescent sign; and (6) diffuse sclerosis and the presence of cysts.

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TABLE VI Definition of Parameters Included in Classification Systems of Osteonecrosis^*

Magnetic resonance imaging findings

Size of lesion† (St, A)

<15% of femoral head affected

15% to 30% of femoral head affected

>30% of femoral head affected

Radiographic Findings

A: Diffuse sclerosis or cysts (F, St, A)

B: Crescent sign and/or sequestrum (F, St, A)

C: Head depression and/or collapse (mm) (F, St)

D: Acetabular changes (mild, moderate, or severe) (F, St, A)

E: Size of Lesion†‡ (A, J, St)

<15% of articular surface

15% to 30% of articular surface

>30% of articular surface

F: Extent of Collapse (A, St)

<15% of surface or <2 mm of depression

15% to 30% or 2 mm to 4 mm of depression

>30% or >4 mm of depression

F = Ficat and Arlet. St = Steinberg (University of Pennsylvania). J = Japanese Orthopaedic Association. A = Association Research Circulation OsseousThe Japanese Orthopaedic Association and the Association Research Circulation Osseous added location of lesion as determinants, which included stratification by medial, central, and lateral lesionsThe extent of the crescent sign has been used but appears to be less predictable depending on the manner in which the radiograph is made and the degree of hip flexion

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TABLE VI Definition of Parameters Included in Classification Systems of Osteonecrosis^*

Magnetic resonance imaging findings

Size of lesion† (St, A)

<15% of femoral head affected

15% to 30% of femoral head affected

>30% of femoral head affected

Radiographic Findings

A: Diffuse sclerosis or cysts (F, St, A)

B: Crescent sign and/or sequestrum (F, St, A)

C: Head depression and/or collapse (mm) (F, St)

D: Acetabular changes (mild, moderate, or severe) (F, St, A)

E: Size of Lesion†‡ (A, J, St)

<15% of articular surface

15% to 30% of articular surface

>30% of articular surface

F: Extent of Collapse (A, St)

<15% of surface or <2 mm of depression

15% to 30% or 2 mm to 4 mm of depression

>30% or >4 mm of depression

Discussion

Materials and Methods | Results | Discussion | References

Classification systems are excellent tools that are widely used to stratify the severity, prognosis, and indications for treatment of many orthopaedic conditions. Osteonecrosis of the femoral head is characterized by a lack of consensus regarding diagnostic methods, evaluation of natural history or progression of the disease, and indications for various treatment options. The use of a reliable and comprehensive classification system is further justified when the results from different centers and investigators must be compared^{48,57,180,181}. Because there are common denominators present in all of the four staging systems that we identified (Ficat and Arlet, University of Pennsylvania, ARCO, and Japanese Orthopaedic Association), we propose that centers can use their preferred system but that they should also collect data that would enable easy conversion to any of the four commonly used systems so that cross-comparison of results can be made at any time, if necessary. The following discussion will review the parameters in each of the major classification systems. The tables describing the classification systems include factors that conform to current usage and may not necessarily be in agreement with the materials as originally published.

Ficat and Arlet (Table II) were the first to introduce a classification system for osteonecrosis of the femoral head; their system delineated three stages⁵⁰. Later, a fourth stage was added, completing the classification system that is most often used today⁵¹. In 1985, another modification of this system was made to include a stage 0 and a transitional stage⁴⁹. Stage I is defined by normal radiographic findings and by an increased uptake of tracer on bone scintigraphy. Stage II represents the reparative stage before flattening of the femoral head occurs. Stage III is characterized by subcortical lucency, representing a fracture beneath the articular cortex. This is termed the crescent sign. Stage IV denotes further flattening of the femoral head with an evident loss of its anatomical sphericity. This collapse and destruction of the femoral head lead to progressive degeneration (narrowing of the joint space), osteophyte formation, and the presence of subchondral cysts. Although Ficat and Arlet deserve credit for initiating this first classification, there are some drawbacks to this system. At the time that the system was developed, the clinical use of magnetic resonance imaging was not available and the system depended on invasive diagnostic techniques, such as core decompression. In addition, the descriptions of various stages were ambiguous and overlapping. There was controversy as to whether hips with a crescent sign but without femoral head flattening should be grouped together with hips that had already shown gross flattening of the femoral head. This controversy was addressed and clarified in the third modification to the system. The most important drawback, however, is that the system did not allow quantitation of the size of the lesion, making it impossible to measure subtle degrees of progression.

Steinberg et al. at the University of Pennsylvania^52,53 (Table III) proposed a system based on earlier classification methods (Ficat and Arlet and Marcus et al.). Their important modifications included the incorporation of magnetic resonance imaging findings and the clear distinction into seven stages. Stage 0 is both preclinical and preradiographic. Stage I demonstrates normal radiographic findings with abnormal findings on bone scans or magnetic resonance images. Stage II shows diffuse or localized areas of sclerosis and/or lucencies in the femoral head. Stage III is characterized by the crescent sign (subchondral fracture). Stage IV demonstrates collapse and fracture involving the articular surface along with segmental flattening of the femoral head but no acetabular involvement. Stage V is characterized by the development of acetabular changes in addition to the collapse of the femoral head, and Stage VI is defined by advanced degenerative changes of the joint. This system was the first major one to incorporate size-of-lesion measurements as part of a complete system. Kerboul and colleagues¹⁶⁷ utilized size-of-lesion measurements as a method to predict the outcome of treatment of stage-III osteonecrosis with femoral osteotomy. They defined the size as the sum of the angles delineating the necrotic lesion as measured on both anteroposterior and lateral radiographs. Their studies showed that favorable results were correlated to smaller-sized lesions. If the sum of the angles was <180°, patients had a better prognosis than when the sum of the angles was >230°. Many studies have confirmed this finding for various treatment options since that time^66,182-184. Steinberg et al.^53,185 expanded on the concept of lesion size and were the first to assess lesion size with use of magnetic resonance imaging and to incorporate these findings into a classification system. At the present time, several investigators are trying to evaluate the best way to determine size-of-lesion measurements with use of radiographs and/or magnetic resonance imaging. It remains to be determined which method will ultimately prove to be the most optimal for assessing lesion size.

Another attempt to develop a classification system occurred after a meeting of the ARCO in 1991⁵⁴. Although a "Committee on Terminology and Staging" was appointed to establish the most comprehensive and reproducible classification, several amendments and modifications have been made to the ARCO system over the years, and there is no consensus in support of this system as yet^54-56. This system originated from the University of Pennsylvania classification. The ARCO system that is most commonly used can be found in Table IV and is the same information as originally published in 1993⁵⁶.

The Japanese Orthopaedic Association (Table V) added to its classification the location of the lesion and stratification of this disease^57,186,187. However, several authors have argued that location of the lesion is not as helpful as size and should therefore not be universally adopted in a classification system^184,188. Originally, the system was added to the four-tiered system of Ficat and Arlet with a further subdivision of Ficat stages II and III, but a drawback to the final classification system is that it only evaluates Ficat stages II and III and not stages I and IV. It makes use of only anteroposterior, not lateral, radiographs. It assumes that lesions start medially and begin to extend centrally and then laterally as they increase in size. This may not be correct physiologically, and only approximately 5% of the lesions reported in the Japanese series are Type 1A. It is known that large lesions are almost always lateral in location and that smaller lesions may be central and/or medial, so there may not be any advantage added to size measurements by knowing location. In addition, this system does not provide a method to evaluate either preradiographic lesions or lesions in which the joint line and the acetabulum have become involved. In summary, while the location of the lesion may be added as a supplement to any staging system, its specific value is uncertain.

Several other articles that made use of individual variables for classification systems were found. We believe that an individual variable, such as an intraoperative or angiographic finding, should not be used as the exclusive method to advise patients on the best treatment option available. These findings have value as ancillary methods that will help improve the follow-up and management of patients with osteonecrosis of the femoral head, but further studies will be needed to validate whether these factors have enough prognostic importance to be incorporated into the main classification groups.

Symptomatology was only utilized in one of the commonly used classification systems (Ficat and Arlet). We agree with Steinberg and Steinberg¹⁸⁸ that "patient symptoms and physical findings, although important in management, should not be a part of the classification per se." It is unclear whether symptomatology has direct prognostic relevance, and, until this is proven, it is our opinion that it should not be included in the classification systems.

One limitation of this analysis of classification systems is that although the systems have been widely used and applied, few have been scientifically tested for accuracy, lack of variability, and reliability. For instance, Smith et al.¹⁸⁹ showed that the classification system of Ficat and Arlet had "poor" interobserver reliability and "fair" intraobserver reproducibility (kappa >0.75) among orthopaedic surgeons. In addition, Kay et al.¹⁹⁰ reported a clinically important interobserver variability in ten (40%) of the twenty-five hips assessed with use of the Ficat and Arlet classification. Intraobserver variability resulted in clinically important differences for ten (40%) of the twenty-five hips as well. The most experienced readers in their study (a total joint specialist and a musculoskeletal radiologist) disagreed with one another on the staging of nine of the twenty-five hips.

A recent study did obtain reasonable agreement when classifying osteonecrotic lesions. With use of radiographs and magnetic resonance imaging, Cherian et al.¹⁹¹ evaluated thirty-nine hips in twenty-five patients who had stage-I or II disease according to the ARCO grading system. They found that various methods to measure the size of lesions could be used with confidence because they were highly reliable and reproducible. Independent grading on two separate occasions by three observers with different medical specialty backgrounds and experience led to correlation coefficients that demonstrated substantial agreement for all sizes of lesions. As further information becomes available, the goal of achieving one unified classification system may be reached.

In summary, all of the parameters for the commonly used systems can be found in Table VI. Although there have been many iterations of each of these systems, we believe the table represents the way in which the systems are utilized in present studies.

The classification systems for osteonecrosis of the femoral head include the following key points:

Histological examination of the hip (biopsy) is no longer needed for diagnosis;Magnetic resonance imaging is the most sensitive and specific diagnostic method;Symptomatology, although important for planning treatment strategies for individual patients, is not a reliable indicator of disease severity because it is quite variable; thus, it should not be part of a classification system;A major determinant of prognosis is whether the femoral head is at the precollapse or postcollapse stage;Size of lesion is important for prognosis; however, the best method of assessing the size of the lesion has yet to be fully elucidated or defined;Acetabular articular cartilage involvement is an important determinant of disease severity in classification systems. Again, the method to determine this, whether preoperatively or with intraoperative inspection, has not been fully elucidated or previously used;The amount of femoral head depression is a major prognostic indicator of disease progression;Measurement of the amount of the depressed femoral head that is involved as well as the length of the crescent may not be reproducible;The location of the lesion may not be as important as size when dealing with large lesions, since lateral lesions are usually large. Medial lesions, although quite rare, are typically small and are associated with the best prognosis.

Histological examination of the hip (biopsy) is no longer needed for diagnosis;

Magnetic resonance imaging is the most sensitive and specific diagnostic method;

Symptomatology, although important for planning treatment strategies for individual patients, is not a reliable indicator of disease severity because it is quite variable; thus, it should not be part of a classification system;

A major determinant of prognosis is whether the femoral head is at the precollapse or postcollapse stage;

Size of lesion is important for prognosis; however, the best method of assessing the size of the lesion has yet to be fully elucidated or defined;

Acetabular articular cartilage involvement is an important determinant of disease severity in classification systems. Again, the method to determine this, whether preoperatively or with intraoperative inspection, has not been fully elucidated or previously used;

The amount of femoral head depression is a major prognostic indicator of disease progression;

Measurement of the amount of the depressed femoral head that is involved as well as the length of the crescent may not be reproducible;

The location of the lesion may not be as important as size when dealing with large lesions, since lateral lesions are usually large. Medial lesions, although quite rare, are typically small and are associated with the best prognosis.

The collection of the data related to osteonecrosis can be done at centers studying this disease even when investigators use their own preferred system. Hopefully, as more studies regarding the individual variables that can have an impact on prognosis become available, these tabulated systems may eventually be merged into one universally agreed-on and accepted method.

The goals in the treatment of osteonecrosis are to relieve pain and preserve the femoral head for as long as possible. We believe that an optimal treatment algorithm should be based on an appropriate classification of the lesion. Centers should collect radiographic and magnetic resonance imaging data that are relevant to the major classification systems. This will permit comparison of studies and of the results reported by different authors and centers, and it will improve stratification of patients to facilitate the appropriate application of traditional and new treatment modalities for this disease in the future. ?

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Topics

head of femur ; femur head necrosis ; hip region ; osteonecrosis ; vibration ; crescent sign

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Michael A. Mont, German A. Marulanda, Lynne C. Jones, Khaled J. Saleh, Noah Gordon, David S. Hungerford, Marvin E. Steinberg; Systematic Analysis of Classification Systems for Osteonecrosis of the Femoral Head. The Journal of Bone & Joint Surgery. 2006 Nov;88(suppl_3):16-26.

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