262 Surgical Treatment
period of the TPLO procedure (Slocum &
Slocum 1993). In two large studies, the reported
incidence of PL after a variety of CR stabiliza-
tion methods was 0.18% and 0.3%, respectively
(Arthurs & Langley-Hobbs 2007; Fitzpatrick &
Solano 2010).
Patient evaluation
Clinical signs
Patients with combined CR and PL often have
no history of trauma and present with an acute
unilateral pelvic limb lameness after exercise.
In two studies, the mean age at presentation
was 19 and 24 months, respectively (Fitzpatrick
et al. 2010; Langenbach & Marcellin-Little 2010).
By comparison, dogs presenting because of CR
alone tend to be older: the median age at pre-
sentation for dogs with CR was 67 months in a
study involving 1000 dogs (Fitzpatrick & Solano
2010). Owners may report occasional to fre-
quent skipping and hopping on the affected leg
before CR, suggesting that the PL preceded CR.
The duration of lameness varies from acute to
chronic lameness lasting several months. Com-
bined CR and PL has been reported in several
breeds. Labrador Retrievers are the most com-
monly affected dogs. In the authors’ experience,
English Bulldogs and American Pit Bull Terriers
are also commonly affected. These two breeds
were also the most common in a study describ-
ing the management of combined medial PL
andCRusingTTA(Yeadonet al. 2011).
Physical examination findings include cranial
tibial thrust, positive cranial drawer motion and
PL with varying degrees of luxation. Grades
2 and 3 are most common, but Grades 1 and
4 have also been reported. In dogs with com-
bined CR and PL most luxations are medial,
but lateral PL is possible. In one report, two
lateral PL were described as a complication of
CR stabilization surgery: one in a Bull Mas-
tiff and one in a sighthound cross (Lurcher)
(Arthurs & Langley-Hobbs 2007). However, in
areportof65dogswithlateralPL,nodoghad
concurrent CR (Kalffet al. 2014). In that report,
a breed shift from large and giant breeds to
medium and large breeds was described: the
most commonly affected breed was the Cocker
Spaniel.
Palpation
The diagnosis of combined CR and PL is
made by palpation. Pelvic limb radiographs are
needed to provide an adequate understanding
of the condition and underlying deformities,
and to select treatment options. PL are graded
using Putnam’s grades: Grade 1 being man-
ual dislocation of the patella with spontaneous
reduction upon release; Grade 2 being the spon-
taneous and frequent PL with self-reduction;
Grade 3 being a near-constant luxation that can
be manually reduced; and Grade 4 being a per-
manent luxation (Putnam 1968).Imaging
For dogs with combined CR and PL, the focus
of assessment is to detect malalignment of the
quadriceps femoris extension apparatus. This
includes angulation and torsion of the femur,
tibial tuberosity malposition, and angulation
and torsion of the tibia. The minimum val-
gus or varus femoral or tibial angles leading
to medial or lateral PL are not known. Assess-
ment of femoral and tibial geometry can be
made using radiographs or computed tomogra-
phy (CT) scanning. Radiographs should ideally
be made under sedation or general anesthesia
to allow for correct alignment and positioning.
A change in distal femoral elevation influences
the measurement of mediolateral angulation
of the femoral shaft (Jackson & Wendelburg
2012). In that study, measurements of the
anatomic lateral distal femoral angle (aLDFA)
were increased when the distal aspect of the
femur was elevated by> 5 ◦.A10◦elevation led
to an increase in aLDFA of∼ 1 ◦. Radiographic
views of the femurs and tibias are warranted
because limb conformation is often abnormal,
and because the problem is generally bilateral.
For the femur and tibia, angulation in a frontal
plane is assessed by use of a craniocaudal (CC)
radiographic view by evaluating lateral devia-
tion (valgus) or medial deviation (varus) of the
lower extremity relative to the proximal por-
tion of the bone. This has been done using the
aLDFA and mechanical lateral distal femoral
angle (mLDFA) (Palmeret al. 2011). For the
tibia, angulation in a frontal plane is evalu-
ated by measuring the relative orientation of