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Measurement of radiographic joint space width in the tibiofemoral compartment of the osteoarthritic kneeComparison of standing anteroposterior and Lyon Schuss views.

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ARTHRITIS & RHEUMATISM
Vol. 48, No. 2, February 2003, pp 378–384
DOI 10.1002/art.10773
© 2003, American College of Rheumatology
Measurement of Radiographic Joint Space Width in the
Tibiofemoral Compartment of the Osteoarthritic Knee
Comparison of Standing Anteroposterior and Lyon Schuss Views
Eric Vignon,1 Muriel Piperno,1 Marie-Pierre Hellio Le Graverand,1 Steven A. Mazzuca,2
Kenneth D. Brandt,2 Pierre Mathieu,1 Huguett Favret,1 Martine Vignon,1
Florence Merle-Vincent,1 and Thierry Conrozier1
Objective. To evaluate progression of joint space
narrowing in radiographs of osteoarthritic (OA) knees
imaged in both the standing anteroposterior (AP) and
the Lyon schuss positions, using alternative methods to
measure joint space width (JSW).
Methods. Standing AP (extended view) and Lyon
schuss (posteroanterior [PA] view, with 20–30° of flexion) radiographic images of 58 OA knees were obtained
twice (at baseline and 2 years later). With both methods,
fluoroscopy was used to align the anterior and posterior
margins of the medial or lateral tibial plateau with the
central x-ray beam. Minimum JSW, mean JSW, and
joint space area (JSA) of the medial or lateral femorotibial joint space were measured using a new digital
image analysis system. The effects of knee flexion versus
extension and parallel versus nonparallel tibial plateau
alignment were evaluated with respect to the reproducibility of JSW in repeated examinations (intraclass
correlation coefficient [ICC]), the mean of within-knee
standard deviations of repeated measurements (SDm),
and the sensitivity to changes in JSW in serial radiographs (standardized response mean [SRM]).
Results. The performance of the new software, as
assessed by the reproducibility of repeated measure-
ments of minimum JSW on the same image, was excellent in both the standing AP (ICC ⴝ 0.98) and Lyon
schuss radiographs (2 SDm ⴝ 0.5 mm, ICC ⴝ 0.98). The
reproducibility in different radiographs of the same
knee was not evaluated. However, over 2 years, the mean
(ⴞ SD) decrease in the minimum JSW of OA knees was
0.17 ⴞ 0.75 mm in standing AP radiographs (P not
significant) and 0.24 ⴞ 0.50 mm in Lyon schuss views
(P ⴝ 0.007), with SRMs of 0.23 and 0.48, respectively.
The quality of alignment of the tibial plateau was
satisfactory (<1 mm between anterior and posterior
margins of the medial tibial plateau) in 66% of the pairs
of Lyon schuss radiographs and in 57% of the pairs of
standing AP radiographs. In the Lyon schuss radiographs, SRM was highly dependent on tibial plateau
alignment. Minimum JSW was more sensitive to change
than was mean JSW or JSA, in paired Lyon schuss
radiographs that exhibited satisfactory alignment.
Conclusion. Compared with the standing AP radiograph, PA imaging of the knee in 20–30° flexion (the
schuss position) increases the reproducibility of radiographic JSW measurements in OA knees and the sensitivity to change in JSW in serial radiographs. Sensitivity to change in minimum JSW is notably increased
by aligning the medial tibial plateau with the central
x-ray beam in the Lyon schuss radiograph.
1
Eric Vignon, MD, Muriel Piperno, MD, Marie-Pierre Hellio
Le Graverand, MD, PhD, Pierre Mathieu, MD, Huguett Favret, PhD,
Martine Vignon, Florence Merle-Vincent, MD, Thierry Conrozier,
MD: Claude Bernard University, Lyon, France; 2Steven A. Mazzuca,
PhD, Kenneth D. Brandt, MD: Indiana University School of Medicine,
Indianapolis.
Address correspondence and reprint requests to Eric Vignon,
MD, Service de Rhumatologie, Centre Hospitalier Lyon Sud, 165
chemin du Grand-Revoyet, 69 495 Pierre-Bénite Cedex, France.
E-mail: eric.vignon@chu-lyon.fr.
Submitted for publication August 7, 2002; accepted in revised
form October 16, 2002.
The aim of treatment of patients with osteoarthritis (OA) is to improve pain and function and, ideally,
to prevent progression of structural damage. Therapeutic agents that prevent the development, or slow the
progression, of structural changes of OA have been
designated disease-modifying OA drugs (DMOADs).
Definitions of DMOAD activity have been proposed
378
COMPARISON OF AP AND LYON SCHUSS VIEWS TO MEASURE JSW
(1–3), and guidelines for radiographic evaluation of
structural damage in OA have been developed (1–4).
DMOADs may be directed at any of the structural
changes in OA, such as destruction of articular cartilage,
osteophytosis or osteosclerosis, cyst formation, or attrition of bone, although it is generally considered that the
most promising target for DMOAD development is
prevention of cartilage destruction. The clinical benefits
of effective “chondroprotective” therapy, however, remain unknown.
A variety of methods for imaging the joint have
been proposed (e.g., ultrasound, magnetic resonance
imaging), but it is generally considered that measurement of joint space width (JSW) is currently the best
available surrogate for evaluation of the progression of
cartilage destruction. Measurement of JSW is recommended by both the US Food and Drug Administration
and the European Agency for the Evaluation of Medicinal Products Human Medicines Committee as a primary end point in clinical trials of DMOADs (5,6). JSW
can be assessed by measurement of the interbone distance at its narrowest point (minimum JSW), as the
mean width, or as joint space surface area (JSA), using
a graduated eyepiece and/or image analysis systems
(7–10).
In patients with hip OA, the progression of joint
space narrowing (JSN) has been evaluated in several
studies, with good agreement that the annual rate of JSN
is ⬃0.15 mm (1,11). For evaluation of radiographic
progression of hip OA, minimum JSW has been demonstrated to be more sensitive to change compared with
mean JSW or measurement of surface area, and measurements have been shown to be optimized by use of an
image analysis system, in comparison with use of a
graduated eyepiece (12). However, measurement of
minimum JSW using a 0.1-mm–graduated eyepiece was
sufficiently sensitive to demonstrate a chondroprotective
effect of the drug diacerein in patients with hip OA (13).
The assessment of radiographic progression of
knee OA has generally been based on measurement of
JSW in the femorotibial compartment in standing anteroposterior (AP) radiographs of the extended knee.
Although evidence that glucosamine sulfate has
DMOAD activity has been reported recently in studies
using standing AP radiographs (14,15), the rate of the
progression of JSN in patients with femorotibial OA has
been extremely variable in published reports (16), due,
in large part, to differences in the reliability of the
various radiographic methods that have been used.
Measurement of femorotibial compartment JSW
is influenced by a number of variables, including the
379
degree of weight-bearing, alignment of the medial tibial
plateau with the central x-ray beam, rotation of the knee,
and the degree of knee flexion (17–19). Fluoroscopy has
been recommended as a means of standardizing the
position of the knee in serial radiographic examinations
(4). In the fluoroscopically assisted AP view described by
Buckland-Wright et al (9), the position of the x-ray beam
is fixed, and the knee is flexed (usually 7–9°) to facilitate
alignment of the medial tibial plateau with the central
x-ray beam.
The Lyon schuss view is a posteroanterior (PA)
radiograph of the knee in flexion. The degree of flexion
is a result of positioning the patient with the tips of both
great toes, the knees, and the pelvis coplanar and in
contact with the examination table. The resulting degree
of knee flexion varies from 20° to 30°, depending on the
relative length of the feet and tibiae.
It has been suggested that the greater degree of
knee flexion afforded by the Lyon schuss view, in
comparison with the standing AP view, increases the
sensitivity of the former approach to JSN (18). However,
long-term evaluation of the progression of JSN in the
OA knee using standardized radiography that combines
fluoroscopic positioning and a significant degree of fixed
flexion of the knee has not been described previously.
Furthermore, a comparison of various methods of measuring the change in JSW in knee radiographs has rarely
been reported (20). The present study was undertaken
to evaluate the progression of JSN in OA knees imaged
in both the standing AP and Lyon schuss positions, as
assessed by changes in minimum JSW, mean JSW, and
JSA, using an image analysis system.
PATIENTS AND METHODS
Patients. Radiographs of OA knees analyzed in the
present study were obtained from 32 consecutive patients (24
women, 8 men; mean [⫾ SD] age 68.8 ⫾ 8.8 years) enrolled in
a study of patients with knee OA. Using the American College
of Rheumatology (formerly, the American Rheumatism Association) criteria for knee OA (21), we selected patients older
than age 50 years who had knee pain for ⬎6 months and at
least one definite osteophyte of the femorotibial joint. Narrowing of the medial and/or the lateral femorotibial joint was an
additional eligibility criterion.
Procedures. Patients underwent radiographic examinations at baseline and again after an interval of ⬃2 years (mean
interval 23.5 months). The radiography protocol included a
standing AP view of the knee in full extension and a Lyon
schuss view (18). For both views, the angle of the x-ray beam
was adjusted to provide optimal alignment with the medial
tibial plateau, as determined fluoroscopically. The radiographs
were obtained in a variety of radiology departments by a
variety of radiology technicians who, although they had been
380
VIGNON ET AL
Figure 1. Measurement of the width of the femorotibial joint space. The treatment of the digitized image
provides a precise delineation of the bone edges. A constant area of the joint is delineated by the computer. The
outer limit of the measured region is delineated by the nonosteophytic medial or lateral edge of the femorotibial
joint.
given instructions describing the technique, had not been
trained specifically in its performance.
Radiographic severity of OA and radioanatomic alignment. Lyon schuss radiographs were read by the same observer
(EV), who scored them for osteophyte severity (scale 0–3) and
JSN (scale 0–5) with the help of an atlas, as described
previously (18). A JSN score ⬎1 in either the medial or lateral
compartment was required for inclusion in the OA cohort. The
same observer (EV) also examined the radiographs for the
degree of alignment of the medial tibial plateau with the x-ray
beam, according to the method described by Buckland-Wright
et al (9). Alignment of the medial tibial plateau was graded as
satisfactory if the anterior and posterior rims of the medial
tibial plateau were superimposed ⫾1 mm and unsatisfactory if
the distance between the margins was ⬍1 mm.
Measurement of JSW. Minimum and mean JSW and
JSA were measured in digitized radiographs using a new image
analysis system (Acticiel, Lyon, France), as previously reported
for the hip joint (12). The topography of the measured surface
area is shown in Figure 1. The outer limit of the measured
region was delineated by the nonosteophytic medial or lateral
edge of the femorotibial compartment. The inner limit of the
measured region was then delineated at a constant distance
from the outer limit, by the computer. After the bone edges
had been delineated by the examiner (HF) with the help of the
computer mouse, the computer automatically calculated the
measurements. Both radiographs in each pair were measured
concurrently, with the observer blinded to the temporal sequence of the films.
Statistical analysis. The reproducibility of the alternative measurement approaches was estimated by the intraclass
correlation coefficient and the mean of within-joint standard
deviations of repeated measurements (SDm) of baseline radiographs (22). Paired t-tests were used to evaluate whether mean
changes in JSW or JSA over 2 years were significantly greater
than zero. Sensitivity to change was evaluated by the standardized response mean (SRM).
RESULTS
Repeated measurements of the same radiographs. To assess the reproducibility of results obtained
with our image analysis system, 2 measurements of 36
Lyon schuss radiographs and of 20 standing AP radiographs were evaluated. Only knees with JSN in the
medial femorotibial compartment were selected, and
JSW was measured only in that compartment. In both
views, the intraclass correlation coefficients for minimum JSW, mean JSW, and JSA were 0.98, 0.98, and
0.97, respectively. Results for minimum JSW in Lyon
schuss radiographs, analyzed according to the method
described by Bland and Altman (22), are illustrated in
Figure 2. The difference between the repeated measurements was unrelated to JSW when minimum JSW was
⬍4 mm (Figure 2); differences ⬎2 SDm (i.e., 2 ⫻ 0.25
mm ⫽ 0.50 mm) were found only when JSW was ⬎4
mm. Similar results were obtained for mean JSW and
JSA (data not shown).
Sensitivity to JSN. The progression of JSN in OA
knees over the 2-year period of the study was evaluated
in paired standing AP and Lyon schuss radiographs of 58
knees (32 patients). Joint space narrowing affected the
medial femorotibial compartment in 52 knees and the
lateral compartment in 6 knees (radiographic evidence
COMPARISON OF AP AND LYON SCHUSS VIEWS TO MEASURE JSW
Figure 2. Reproducibility of the measurement of minimum joint
space width (JSW) in 36 osteoarthritic knees using the new semiautomated method. Differences between 2 measurements of the same
radiograph (minimum JSW 1⫺2) are plotted according to the method
of Bland and Altman (22). Two standard deviations of the mean of
difference ⫽ 0.50 mm.
of OA in both compartments was not noted in any of the
58 knees).
The standing AP radiographs did not demonstrate a statistically significant change in JSA or minimum or mean JSW (Table 1). Markedly different results
were obtained when Lyon schuss radiographs were
analyzed; mean (⫾ SD) decreases in minimum JSW
(0.24 ⫾ 0.50 mm), mean JSW (0.25 ⫾ 0.55 mm), and
mean JSA (3.8 ⫾ 9.0 mm2) were clearly larger in the
Lyon schuss views than in standing AP views obtained
concurrently from the same subjects (0.17 ⫾ 0.75 mm,
0.14 ⫾ 0.78 mm, and 2.5 ⫾ 13.3 mm2, respectively), and
these differences were significant for all 3 parameters
(P ⫽ 0.007, P ⫽ 0.009, and P ⫽ 0.02, respectively). In the
standing AP radiographs, SRMs for minimum JSW,
mean JSW, and JSA were 0.23, 0.17, and 0.18, respectively; in the Lyon schuss radiographs, the SRMs were
0.48, 0.45, and 0.42, respectively (Table 1).
Table 1.
knees*
381
Based on readings of Lyon schuss radiographs,
22% of 58 OA knees had minimal (grades 1–2) OA
severity at baseline, 66% had moderate (grades 2–3) OA
severity, and 12% had severe (grades 4–5) OA. Progression of JSN was unrelated to baseline severity of OA.
Reanalysis of these data after exclusion of knees with
severe OA did not alter this conclusion.
Effects of tibial plateau alignment. Approximately 72% of the standing AP radiographs and 83% of
the Lyon schuss radiographs exhibited satisfactory alignment of the tibial plateau (i.e., superimposition ⫾1 mm
of the anterior and posterior margins of the medial tibial
plateau). However, only 57% and 66%, respectively, of
these paired images exhibited satisfactory alignment in
both the baseline and 2-year radiographs.
In serial Lyon schuss views (Table 2), the mean
decrease in minimum JSW in paired radiographs with
satisfactory alignment (0.27 mm) was significantly
greater than zero (P ⬍ 0.01). In contrast, in Lyon schuss
radiographs showing unsatisfactory alignment in either
or both images in the serial pair, the mean decrease was
smaller (0.11 mm) and not significant. Results of the
measurement of mean JSW and JSA were similar to
those of minimum JSW. Paired Lyon schuss views
showing satisfactory alignment permitted detection of
statistically significant decreases in mean JSW and JSA
(0.25 mm and 3.5 mm2, respectively) within 2 years. In
contrast, 2-year changes in these parameters were not
significant in Lyon schuss views with unsatisfactory
alignment. However, the differences between satisfactorily and unsatisfactorily aligned Lyon schuss views with
respect to sensitivity to change in mean JSW and JSA
were attributable more to differences in the variability of
changes in these parameters (smaller standard deviations in well-aligned pairs) than to differences between
means. Comparison of SRMs indicates that the greatest
sensitivity to JSN was obtained with measurement of
Measurement of JSW on standing anteroposterior and Lyon schuss views of 58 osteoarthritic
Standing AP view
Minimum JSW, mm
Mean JSW, mm
Joint space area, mm2
Lyon schuss view
Minimum JSW, mm
Mean JSW, mm
Joint space area, mm2
Baseline JSW,
mean ⫾ SD
JSN at 2 years,
mean ⫾ SD
P†
SRM
3.55 ⫾ 1.14
4.2 ⫾ 1.19
72.2 ⫾ 23.0
0.17 ⫾ 0.75
0.14 ⫾ 0.78
2.5 ⫾ 13.3
NS
NS
NS
0.23
0.17
0.18
2.92 ⫾ 1.30
3.47 ⫾ 1.31
57.9 ⫾ 22.4
0.24 ⫾ 0.50
0.25 ⫾ 0.55
3.8 ⫾ 9.0
0.007
0.009
0.02
0.48
0.45
0.42
* JSW ⫽ joint space width; JSN ⫽ joint space narrowing; SRM ⫽ standardized response mean; AP ⫽
anteroposterior; NS ⫽ not significant.
† P values were determined by paired t-test. The null hypothesis was a mean JSN of zero.
382
VIGNON ET AL
Table 2. Effect of alignment of the medial tibial plateau on sensitivity to JSN over 2 years, in serial Lyon schuss radiographs of 38 knees
with satisfactory alignment and 20 knees with unsatisfactory
alignment*
Parameter
Minimum JSW, mm
Satisfactory alignment
Unsatisfactory alignment
Mean JSW, mm
Satisfactory alignment
Unsatisfactory alignment
Joint space area, mm2
Satisfactory alignment
Unsatisfactory alignment
JSN, mean ⫾ SD
P†
SRM
0.27 ⫾ 0.53
0.11 ⫾ 0.44
⬍0.01
NS
0.51
0.25
0.25 ⫾ 0.56
0.25 ⫾ 0.62
⬍0.01
NS
0.44
0.40
3.5 ⫾ 8.9
4.4 ⫾ 10.2
⬍0.02
NS
0.39
0.42
* JSN ⫽ joint space narrowing; SRM ⫽ standardized response mean;
JSW ⫽ joint space width; NS ⫽ not significant. See Patients and
Methods for definitions of satisfactory alignment and unsatisfactory
alignment.
† P values were determined by paired t-test. The null hypothesis was a
mean JSN of zero.
minimum JSW in well-aligned pairs of Lyon schuss views
(Table 2).
The effects of alignment on sensitivity to JSN
were different using the standing AP view compared
with the Lyon schuss view: neither minimum JSW, mean
JSW, nor JSA showed statistically significant changes
over 2 years in standing AP views (Table 3). This was
true regardless of the quality of alignment of the medial
tibial plateau and the x-ray beam. With one exception
(minimum JSW in unsatisfactorily aligned radiographs),
SRMs for changes in minimum JSW, mean JSW, and
JSA in standing AP radiographs were smaller than in
Lyon schuss radiographs (Table 2).
DISCUSSION
The 3 joint space measurements performed in the
present study were highly reproducible using the new
image analysis system. Reproducibility of measurement
was unrelated to JSW, especially when the minimum
JSW was ⬍4 mm. A comparison of the reproducibility of
this method with those previously described is difficult,
however, because the kappa statistic has not been reported systematically in earlier studies. Nonetheless,
acceptable coefficients of variation for manual and
automated methods of joint space width measurement
have been reported previously (16).
In the present study, the reproducibility of measurements of JSN was evaluated by repeated measurement of the same image. However, in evaluating the
progression of JSN, measurement of JSW must involve
analysis of serial radiographs of the same knee. It is
important to note, therefore, that the rate of JSN may
vary because of differences in radioanatomic positioning
between examinations. For example, the coefficient of
variation for hip JSW varied from 1.1% to 3.3% in
repeated measurements of the same radiograph and also
in different radiographs of the same joint (10).
Adequate evaluation of the reproducibility of a
radiographic method requires the analysis of multiple
radiographs of the same joint, obtained in different
centers on the same day. Although a protocol of this
type was not authorized for the present study by the
ethics committee at our institution, we previously reported an intraobserver kappa value of 0.76 for minimum JSW in Lyon schuss radiographs (18). The large
difference between the kappa values obtained for repeated measurements of JSW in the same radiograph
and in repeated images of the same knee (0.98 and 0.76,
respectively) clearly indicates that the reproducibility of
measurements in a longitudinal trial is highly dependent
on the quality of the radiograph and emphasizes that
measurements of serial changes in JSW in the femorotibial joint are highly dependent on changes in the
radioanatomic position of the knee (16–20). It is an
advantage of the Lyon schuss view, relative to the
standing AP view that, because the knee is in contact
with the examination table, the effects of radiographic
magnification are minimal. Magnification in the standing AP view has been reported to be as great as 34% (9).
Additional advantages of the Lyon schuss radiograph are the fixed degree of flexion of the tibiofemoral
angle it provides (because the patient is positioned with
both knees and the pelvis in contact with the table), and
the good alignment of the tibial plateau with the central
x-ray beam (which is achieved by use of fluoroscopy).
Table 3. Effect of alignment of the medial tibial plateau on sensitivity to JSN over 2 years, in serial standing AP radiographs of 33 knees
with satisfactory alignment and 25 knees with unsatisfactory
alignment*
Parameter
Minimum JSW, mm
Satisfactory alignment
Unsatisfactory alignment
Mean JSW, mm
Satisfactory alignment
Unsatisfactory alignment
Joint space area, mm2
Satisfactory alignment
Unsatisfactory alignment
JSN, mean ⫾ SD
SRM
0.15 ⫾ 0.77
0.19 ⫾ 0.74
0.19
0.26
0.08 ⫾ 0.77
0.20 ⫾ 0.86
0.10
0.23
2.6 ⫾ 18.3
5.1 ⫾ 15.1
0.14
0.33
* JSN ⫽ joint space narrowing; SRM ⫽ standardized response mean;
JSW ⫽ joint space width. See Patients and Methods for definitions of
satisfactory alignment and unsatisfactory alignment. P values (as
determined by paired t-test) were not significant, for all comparisons.
The null hypothesis was a mean JSN of zero.
COMPARISON OF AP AND LYON SCHUSS VIEWS TO MEASURE JSW
Another benefit, as shown in the present study, is greater
sensitivity to change in JSW with the Lyon schuss
technique, in comparison with the standing AP radiograph, because the Lyon schuss position, due to its
degree of flexion of the knee, places the areas of the
femorotibial surfaces that exhibit the greatest cartilage
damage in contact. The results of the present study
confirm that PA radiographs obtained with the knee in
20–30° of flexion afford greater sensitivity to change in
JSN than does the standing AP radiograph. In theory,
the relatively poor sensitivity of the standing AP view to
progressive changes in articular cartilage thickness in
knee OA may be compensated for in the design of
studies of OA progression by using an appropriate
increase in sample size, based on an estimate of error
variation in JSN estimates. However, it has been demonstrated recently that the increase in sample size
necessary to negate an error of such magnitude is
prohibitively large (i.e., 10-fold to 16-fold greater than
that needed with fluoroscopically standardized radiography) for studies of 2–3 years duration (23).
Indeed, in the present study, a statistically significant reduction in minimum JSW over the 2-year interval
of followup was noted only in the Lyon schuss radiographs and was not detected in the standing AP views
(Table 1). Furthermore, the SRMs were nearly twice as
great in the Lyon schuss images as in the standing AP
radiographs. JSW, both at baseline and at the 2-year
examination, was significantly smaller in the Lyon schuss
radiographs than in the standing AP views (P ⬍ 0.01),
probably related to the greater contact of the joint
surfaces at the site of maximum cartilage destruction.
The degree of knee flexion in the Lyon schuss view, as
judged from the depth of the intercondylar notch, is less
than that in the tunnel view, but considerably greater
than that in the semiflexed fluoroscopically positioned
AP radiograph described by Buckland-Wright (9), in
which it averages 7–9°.
Although satisfactory alignment of the tibial plateau in both members of the pair of Lyon schuss
radiographs was achieved in only 66% of cases, it should
be noted that the radiographs were obtained in a variety
of radiology departments by a variety of radiology
technicians who had not been trained formally in its
performance (although they had received written instructions describing the technique). In the present
study, a trained radiology technician in our department
at Lyon obtained the radiographs, and nearly 90% of the
pairs exhibited good alignment in both images. This
point is relevant, because the sensitivity to changes in
JSW in the Lyon schuss view was highly dependent on
383
the quality of tibial plateau alignment: the highest value
for SRM (i.e., 0.51) was observed in minimum JSW
measurements in pairs of Lyon schuss radiographs that
exhibited satisfactory alignment in both images. In contrast, in the standing AP radiographs, the SRM for JSN
was unrelated to alignment. This discrepancy may have
been attributable to the fact that alignment alone is
insufficient to assure high sensitivity to change in JSW,
and that fixation of the femorotibial angle, which is
achieved in the Lyon schuss view but not in the standing
AP view, is a major determinant of sensitivity to change.
It should be noted that in the present study, the
percentage of poorly aligned Lyon schuss radiographs
was only marginally smaller than that of poorly aligned
standing AP views. This is not surprising, insofar as
fluoroscopically assisted positioning of the knee was
used in both protocols. Because fluoroscopy was used to
optimize the quality of tibial plateau alignment in the
standing AP radiographs, the difference between results
obtained with the 2 imaging protocols could result only
from the greater degree of knee flexion required in the
Lyon schuss view and the minimal impact of radiographic magnification associated with that technique.
For this reason, the proportion of standing AP radiographs that exhibited adequate alignment in both members of the pair was much higher in this study than in a
study of conventional standing AP radiographs obtained
without use of fluoroscopy (19). A nonfluoroscopic
protocol for radiography of the knee in fixed flexion, in
which positioning of the joint is essentially identical to
that in the Lyon schuss view, was recently described by
Peterfy et al (24), but results of longitudinal studies in
patients imaged with that protocol have not been published.
In the present study, serial pairs of well-aligned
standing AP radiographs were notably less sensitive to
JSN than were those identified by Mazzuca et al (19) in
their analysis of alignment in standing AP radiographs
from extant research cohorts (SRM ⫽ 0.19 and 0.96,
respectively). This discrepancy may be explained by the
fact that Mazzuca et al identified paired radiographs in
which fortuitous alignment of the tibial plateau occurred
relative to a fixed horizontal x-ray beam; because of the
fixation of the beam, the investigators did not have an
opportunity to compensate for changes in the amount of
joint loading and/or degree of knee extension in the 2
examinations, although an adjustment of the beam angle, as was possible in the present study, might have
negated the effects of such changes. In contrast, fluoroscopically assisted adjustment of the angle of the x-ray
beam in the present study resulted in a greater propor-
384
VIGNON ET AL
tion of knees exhibiting good tibial plateau alignment in
both radiographs compared with the proportion in the
study by Mazzuca et al (57% and 14%, respectively). In
many cases, however, negation of a change in alignment
may not have compensated for a change in the degree of
joint extension (as reflected in the femorotibial angle),
which results in unpredictable changes in JSW.
It is clear that highly reproducible radioanatomic
positioning is essential for accurate evaluation of the
progression of femorotibial JSN in patients with knee
OA (19). Although the parameters used to evaluate JSN
in the present study (i.e., changes in minimum JSW,
mean JSW, and JSA) displayed similarly high levels of
reproducibility in repeated measurements of the same
image, in both the Lyon schuss and standing AP radiographs the SRM for minimum JSW was greater than that
for mean JSW or JSA (Table 1). However, the SRM of
minimum JSW was very much dependent on alignment
of the tibial plateau, while the SRMs of mean JSW and
JSA were apparently less influenced by this. Measurement of minimum JSW has been widely used in previous
studies of JSN (7,9,10,13–15,19). Based on the results of
the present study, when highly standardized radioanatomic positioning of the knee is achieved in serial
examinations, minimum JSW is the preferred parameter
for determination of OA progression in serial radiographs.
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