Table 4.

Correlation of Joint Space Narrowing Across Radiographic Staging Systems

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

^*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

^**Defined as marked joint space narrowing

^†† Defined as complete loss of joint space