Assessment of joint space width in patients with osteoarthritis of the knee: a comparison of 4 measuring instruments.
OBJECTIVE
To evaluate the intra and interobserver reproducibility of 4 measuring instruments for assessing joint space width in knee osteoarthritis (OA) and to estimate the effects of patients, instrument, session order, and reader variation.


METHODS
We studied 30 patients with unilateral tibiofemoral OA selected to represent a broad range of radiographic changes. Joint space width (JSW) was measured on plain anteroposterior weight bearing radiographs. Using an experimental design, 3 readers assessed JSW 3 times with 4 measuring instruments (ruler, caliper, graduated magnifying glass, digitized assessment).


RESULTS
Intra and interobserver reproducibility was high with all measuring instruments (intraclass correlation coefficients from 0.95 to 0.98 and from 0.91 to 0.97, respectively). Analysis of variance (ANOVA) showed a patient effect (p < 10(-6)), a reader effect (p = 0.0001), an instrument effect (p = 0.0001), and a session order effect (p = 0.04). The variance component estimates were patients 55%, readers 34%, session order 2%, instruments 8%. ANOVA performed separately for each instrument showed that session order differences always represented less than 1% of the total variance. The reader component accounted for 0% of the total variance for the ruler, 2% for the digitized method, 16% for the caliper, and 18% for the graduated magnifying glass.


CONCLUSIONS
Ruler and digitized assessment have better reliability than caliper and graduated magnifying glass.
Clinique de Rhumatologie, Hôpital Cochin, Paris, France.
P
P
Ravaud
C
C
Chastang
G R
GR
Auleley
B
B
Giraudeau
V
V
Royant
B
B
Amor
H K
HK
Genant
M
M
Dougados
D000704:Analysis of Variance; D003952:Diagnostic Imaging / Q000379:methods*; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging*; D015588:Observer Variation; D010003:Osteoarthritis / Q000000981:diagnostic imaging*; D011859:Radiography; D015203:Reproducibility of Results