Stress Imaging of the Stifle 129including the presence of moderate rotational
stifle laxity and limb deformity. Furthermore,
these measurements are sensitive to changes
in stifle flexion angle because the femur ‘rolls’
caudally on the tibial plateau as the stifle flexes.
Flexion angle must, therefore, be kept consis-
tent between stressed and non-stressed views.
Most techniques advocate using a flexion angle
of 90◦.
In functionalin vivostudies where subjects
are imaged during activities (e.g., standing), it
may not be possible to keep the flexion angle
consistent between stressed and non-stressed
views. This renders the techniques for quanti-
fying subluxation described above inaccurate.
An alternate method for quantifying alignment
is available when flexion angle cannot be con-
trolled, which involves simply measuring the
direct distance between the proximal and dis-
tal attachment sites of the CrCL (Figure 18.2);
increases in this distance under stress views are
interpreted as being indicative of cranial tib-
ial subluxation. The measurement is also unaf-
fected by any change in tibial geometry due
to tibial plateau leveling osteotomy. However,
there is still a susceptibility to error associated
with oblique projections.
When stressed views are compared to
non-stressed views, it is important to assess
whether there is already cranial tibial sublux-
ation present on the non-stressed image. As
the detection of subluxation is pathognomonic
for CR, performing an additional stress view is
probably unnecessary. Furthermore, the mag-
nitude of calculated subluxation will be lower
if the difference in alignment between the two
views is quantified, and it may thus be possible
to get a false-negative result. One potentially
helpful method of more objectively assessing
for subluxation if cranial tibial subluxation is
suspected in the non-stressed stifle is to com-
pare femorotibial alignment to the contralateral
stifle, provided that the contralateral stifle is
normal.
Tibial compression radiography
With tibial compression radiography, the
stressed views are obtained while perform-
ing the tibial compression test. With the dog
in lateral recumbency, a standard lateral
Figure 18.2 Lateral projection radiograph showing the
method by which the proximal and distal attachment sites
of cranial cruciate ligament were defined. The proximal
attachment was defined as the point on the cranio-
proximal margin of the femoral condyles immediately
caudal to the roof of the intercondylar notch, and the
distal attachment site was defined as the point at the
cranial margin of the medial tibial condyle (double-
headed arrow).radiographic view of the stifle is obtained with
the stifle at 90◦of flexion (neutral position).
While maintaining the same stifle flexion angle,
a second radiograph is performed with the
tarsal joint being maximally flexed by hand
(tibial compression position) (Figure 18.3).
Noticeable cranial movement of the tibia rela-
tive to the distal femur between stressed and
non-stressed views is considered indicative of
CrCL rupture (see Figure 18.1). In a study using
a subjective method of assessing for subluxa-
tion where the positions of the caudal femoral
condyle relative to the tibial plateau were
determined, the test was found to have 97%
sensitivity and 100% specificity for detection of
CR (de Roosteret al. 1998).