Table 6.

Correlation of joint space narrowing across radiographic staging systems.

Joint space	International Knee Documentation Committee (IKDC)	Kellgren and Lawrence	Ahlback	Rosenberg	Fairbank
Normal	A	1*		Normal	Absent
Minimal narrowing	B†	2‡
Moderate narrowing	C§	3|	I¶	Major#	Present
Severe narrowing	D#	4**	II – V††

^*Defined as doubtful narrowing

^†Defined as joint space greater than 4 mm

^‡Defined as possible narrowing

^§Defined as joint space 2 – 4 mm

^|Defined as definite joint space narrowing

^¶Defined as joint space < 3 mm

^#Defined as joint space 2 mm less than the contralateral side

^**Defined as marked joint space narrowing

^††Defined as complete loss of joint space