Table 2.

Ahlbäck grade in the series

Ahlbäck grading	N	%
I Narrowing of the joint space (with or without subchondral sclerosis) (*)	243	18.3
II Obliteration of the joint space	358	26.9
III Bone defect/loss <5 mm	416	31.3
IV Bone defect/loss between 5 and 10 mm	241	18.1
V Bone defect/loss >10 mm, often with subluxation and arthritis of the other compartment	71	5.3
Total	1329	100.0

(*) Joint space narrowing is defined by a space inferior to 3 mm or inferior to half of the space in the other compartment (or in the homologous compartment of the other knee).