Advances in the Canine Cranial Cruciate Ligament, 2nd edition

Surgical Management of Cruciate Ligament Rupture Combined with Patella Luxation 263

the tibial plateau and distal articular surface
on a CC radiographic view (Jaegeret al. 2007).
The mechanical medial proximal tibial angle
(mMPTA) and mechanical medial distal tibial
angle (mMDTA) can be calculated for the tibia
on CC view after drawing the mechanical tibial
axis from the center of the intercondylar fossa
of the femur through the intertubercular emi-
nence of the tibia and the distal intermediate
ridge of the tibia (Dismukeset al. 2007; Dis-
mukeset al. 2008a). CC radiographic views of
the complete femur with coxofemoral and sti-
fle joints and complete tibia with stifle and hock
joints are recommended. This may require two
radiographs, since many dogs are too large to
be imaged on one large radiographic plate. The
radiographic beam should be centered over the
stifle joint and the femoral cortices should bisect
the fabellae. However, it may be difficult to
accurately assess varus angulation of the femur
by use of CC radiographs (Aiken & Barnes
2014). In dogs with Grade 2, 3, or 4 medial PL,
the patella may luxate during imaging, mak-
ing evaluation of the shape of the femur more
challenging because it is more difficult to ori-
ent the femur (Figure 31.1). Varus and valgus
femoral angulation is assessed on the CC view
of the femur. That assessment includes mea-
surement of the anatomic long axis of the femur
and the aLDFA (Figure 31.2) (Tomlinsonet al.
2007). The mean aLDFA reportedly is 97◦ in
Labrador Retrievers and 93◦in German Shep-
herd dogs (Tomlinsonet al. 2007). In one study,
the mean aLDFA, mLDFA and femoral varus
angle obtained using CT imaging in Toy Poo-
dles with Grade 2 medial PLdid not differ statis-
tically from that of normal Toy Poodles, but they
were 15◦larger for Toy Poodles with Grade 4
medial PL (Yasukawaet al. 2016). Hip dysplasia
with low femoral neck inclination (coxa vara)
and low femoral head anteversion angles has
been associated with medial PL (Roush 1993;
Kaiseret al. 2001). However, CT-based review
of femoral shape in Toy Poodles with medial
PL identified no association between medial PL
and hip dysplasia (Yasukawaet al. 2016). Varus
orientation of the tibia is determined by measur-
ing the mMPTA and mMDTA on a CC view and
the mechanical cranial distal tibial angle and the
mechanical proximal tibial angle on the sagit-
tal or mediolateral view (Dismukeset al. 2008b).
A mediolateral view of the entire femur with

Figure 31.1 Craniocaudal radiographic view of the

femur of 1-year-old male Akita Inu with medial patellar

luxation. The patella is medial to the medial trochlear

ridge, and it is therefore more challenging to determine

whether the view of the distal portion of the femur is truly

craniocaudal.

the coxofemoral joint and stifle joints included

and a mediolateral view of the tibia with sti-

fle and hock joints included are also recom-

mended. Mediolateral views with the femoral

condyles superimposed are recommended, but

these may be difficult to obtain in dogs with

torsional or angular deformities of the femur.

A ‘condylar offset sign’ may be seen in cases

of femoral torsion, in that in a mediolateral

projection one of the femoral condyles is off-

set cranially or distally in relation to the other.

Excessive femoral varus results in a distal off-

set, whereas femoral torsion or underdevelop-

ment of the medial or lateral trochlear ridge

results in a cranial offset (Figure 31.3). Femoral