Front Matter

Chapter 14 Disorders of the Pelvic Limb: Diagnosis and Treatment 375

2007; Stein & Schmoekel, 2008; Christopher &
Cook, 2011; Hurt et al., 2011). This procedure
is  less technically demanding than the TPLO;
however, there is still significant risk for surgi­
cal error. The TTA is best used in patients with
a low tibial plateau angle and no tibial angula­
tion abnormalities (Boudrieau, 2009). There can
be issues with preoperative planning for appro­
priate cage size selection (Cadmus et al., 2011).
The advancement of the tibia can change the
external appearance of the tibia, particularly in
dogs with short hair, which may be a disadvan­
tage in the show ring. The TTA also carries a risk
of major complications. Infections of the spacer
cage, although uncommon, can be extremely
challenging to resolve. Recent research shows
that at a trot, the TTA procedure and LFS proce­
dure do not return dogs to normal function at
12 months, while TPLO does when compared
with a control population (Krotscheck et al., 2016).

Patellar luxation

Anatomy and pathophysiology

Patellar luxation occurs when one or several
structures that comprise the quadriceps mecha­
nism are misaligned, resulting in partial or com­
plete deviation of the patella from the trochlea
(L’Eplattenier & Montavon, 2002a; Bevan &
Taylor, 2004; Alam et al., 2007). In fact, some have
speculated that the condition should actually be
termed “femoral trochlear luxation” as the
patella will always find its natural position cre­
ated by the origin and insertion of the  quadri­
ceps mechanism, and the distortion of anatomy
results in an incorrect position of the trochlea in
line with the quadriceps mechanism. The actual
bony distortion leading to patellar luxation may
be a distortion of the femur or the tibia and it has
been speculated that with medial patella luxa­
tion asynchronous growth of the distal femoral
physis may be a major contributing cause that
perpetuates the distortion. As the patella is
tracked medially, increased tension develops lat­
erally in the distal femoral physis, which leads to
an increase in femoral torsion and distal femoral
varus. This increases the forces resulting in
medial patellar luxation. In addition, the femoral
sulcus does not develop because there is not
appropriate retropatellar pressure, and the

medialized forces on the tibial tubercle results in

abnormalities in tibial growth.

Medial patellar luxation (MPL) occurs

significantly more frequently than lateral patel­

lar luxation in all dogs (Alam et al., 2007). Small

breed dogs are most commonly affected by

MPL, and the condition is considered heritable

in some breeds (Alam et al., 2007). Large‐breed

dogs are also commonly affected with MPL,

with Labrador Retrievers being overrepre­

sented (Gibbons et al., 2006). Patellar luxation

occurs bilaterally in 50% of affected dogs, with

females affected more commonly than males

(L’Eplattenier & Montavon, 2002a; Gibbons

et al., 2006; Alam et al., 2007).

Patellar luxation is divided into four grades

based on the severity of the luxation (L’Eplattenier

& Montavon, 2002a; Bevan & Taylor, 2004)

(Table 14.1). MPL predisposes dogs to cranial

cruciate ligament rupture (CCLR) and the higher

the grade of MPL, the higher the incidence of

concurrent CCLR (Campbell et al., 2010). One

study found that 40% of dogs with MPL had

concurrent CCLR (Campbell et al., 2010).

Diagnosis

Intermittent hopping or skipping and reluctance

to jump are typical historical findings in dogs

Table 14.1 Grades of patellar luxation

Grade Features

I Patella can be manually luxated but is

reduced when released

II Patella can be manually luxated or it can

spontaneously luxate with flexion of the

stifle joint. The patella remains luxated until

it is manually reduced or when the animal

extends the joint and derotates the tibia in

the opposite direction of luxation

III Patella remains luxated most of the time but

can be manually reduced with the stifle joint

in extension. Flexion and extension of the stifle

results in reluxation of the patella

IV Patella is permanently luxated and cannot be

manually repositioned. There may be up to 90

degrees of rotation of the proximal tibial plateau.

The femoral trochlear groove is shallow or

absent, and there is displacement of the quadri­

ceps muscle group in the direction of luxation