Table 1.

Percentage of necrotic area analysis in classification and correlation with collapse.

Author	Year	Country	Study point	Classification	Relations with collapse
Kerboul et al [5]	1974	France	Necrosis radian	Large range: ≥200 Small range: ≤160 Median range: >160, <200	Large range: worse result Small range: better result
Beltran et al [25]	1990	United States	Percentage of necrotic area	—	No collapse occurs in the range <25%, 43% collapse in the range from 25% to 50%, and 87% collapse in the range of 50%.
Sugano et al [22]	1994	Japan	Necrosis portion and range (X-ray)	IA < 30% IB < 44% IC < 88%	—
Koo and Kim [26]	1994	South Korea	Necrosis range	Divided into three types: <30%, 30–40%, >40%	Collapse rate increases in the upper type.
Koo et al [23]	1995	South Korea	Necrosis index (necrosis range)	Necrosis index = (A/180)(B/180)(C/180) A, B, C are three angles	A level: <33 B level: 33–60 C level: 67–100 If the index is >40, collapse of the femoral head occurs.
Steinberg et al [27]	1999	United States	Necrosis radian	—	Necrosis radian >200, worse result
Shimizu et al [28]	1994	Japan	Necrosis range	Grade: high/low sign Grade: high sign	Grade is confer to be collapse. Grade in the critical range, like weight-bearing area, is vice versa.
Chen et al [29]	2000	China	Necrosis radian	—	In core depression operation, all the cases whose necrosis radian is >250 collapse.
Lafforgue et al [24]	1993	France	WB value (percentage of necrotic area vs. weight-bearing area)	WB = β/γ × 100% β: range of necrotic area in weight-bearing area γ: range of weight-bearing area	No collapse when WB is <45%, but collapse occurs when WB is >45%.
Zhao et al [30]	2005	China	Necrosis index Percentage of necrotic area	Some kind of index for predicting necrosis	The relative risk of the percentage of necrotic surface area is 1.043.
Ha et al [31]	2006	South Korea	Percentage of necrotic area	Modified Kerboul et al’s [5] method: Level 1: <200; Level 2: 200–250; Level 3: 250–300; Level 4: >300	—
Connolly and Weinstein [32]	2006	Turkish	Necrosis range	—	Necrotic area <33% would not favour a collapse.