<prompt> Ahlback Grade2 changes of Osteoarthritis of the knee means:Joint space obliterated or almost obliteratedMinor bone attrition 5 mmModerate bone attrition 5-15 mmSevere bone attrition 15 mm  <response>: Ans. A. Joint space obliterated or almost obliteratedAhlback Radiographic Grading Scale of Osteoarthritis of the Tibiofemoral Joint:Grade of OsteoarthritisDescription0 No radiographic findings of osteoarthritis1 Joint space narrowing 3mm2 Joint space obliterated or almost obliterated3 Minor bone attrition 5mm4 Moderate bone attrition 5-15mm5 Severe bone attrition 15mm 