Ahlbäck grading of osteoarthritis of the knee: poor reproducibility and validity based on visual inspection of the joint.
BACKGROUND
Staging of osteoarthritis (OA) of the knee is commonly based on the Ahlbäck classification. Its value has been questioned, however. We therefore evaluated the reproducibility and validity of this classification of knee osteoarthritis.


METHODS
48 patients (48 knees) (medial OA: n = 30; lateral OA: n = 8) operated with total knee prostheses were studied. Weight-bearing radiographs were evaluated twice by 4 observers. Presence of bone attrition on radiographs was compared with observations of the resected parts of the distal femur and proximal tibia.


RESULTS
When the same observer classified the radio-graphs twice according to Ahlbäck, the repeatability was fair in both medial OA (kappa values = 0.15-0.65) and lateral OA (0.59-0.76), and between different observers it was poor (kappa: 0.1). Comparison between radiographic classification and classification based on visual inspection of the bone pieces removed during arthroplasty revealed an acceptable sensitivity in both medial (67-95%) and lateral OA (43-86%), but the specificity was low (medial: 11-67%; lateral: 25-75%).


CONCLUSIONS
The main problem with the Ahlbäck classification was that a joint space could often be seen radiographically despite the presence of bone attrition on the preparations. According to our study, conventional radiographs do not give sufficient information for correct grading.
Weidow
Jonas
J
Department of Orthopedics, Sahlgrenska University Hospital, Göteborg, SE-413 45, Sweden. jonas@weidow.se
Cederlund
Claes-Göran
CG
Ranstam
Jonas
J
Kärrholm
Johan
J
D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D020370:Osteoarthritis, Knee / Q000145:classification / Q000000981:diagnostic imaging* / Q000601:surgery; D011859:Radiography; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016474:Weight-Bearing