Advances in the Canine Cranial Cruciate Ligament, 2nd edition

Tibial Tuberosity Advancement 233

are available on postoperative evaluation of the
PTA in clinical cases; a single report has deter-
mined postoperative PTA in a series of cases
(Wolfet al. 2012). This oversight needs to be
corrected, so as to ensure that the technique is
performed appropriately. Such data will help
confirm clinically that TTA does result in sta-
bility of the stifle joint after surgery with neu-
tralization of the tibiofemoral shear forcein vivo.
Despite the many reports of successful surgical
outcomes, such evidence is not yet available.
The current recommendation, as presented
by the inventors of this technique (Tepic), is
to use the PTACTtechnique. This recommenda-
tion is based on knowledge of the variations
in the anatomy of the proximal tibial plateau
and the distal femur, and how anatomic fac-
tors affect advancement measurements when
using the common tangent between the tibial
and femoral surfaces at their contact point, or
PTACT(Boudrieau 2005; Boudrieau 2009). Less
variation has been reported with PTACTcom-
pared with PTATPA, further supporting this rec-
ommendation (Hoffmannet al. 2011).
The accuracy in planning the osteotomy and
determining amount of advancement has been
studied (Etcheparebordeet al. 2011; Milletet al.
2013; Cadmuset al. 2014). Errors will occur
because of the varied anatomy encountered,
such as positioning (tibial drawer or stifle
joint extension angle), patella tendon insertion
point (high versus low), unrecognized effects
with regard to tibial tuberosity hinge point
(maintained at the distal attachment versus
allowed to move proximally), variation in the
pre-planning measurement method (Inauen
et al. 2009; Bushet al. 2011), and loss of advance-
ment due to the saw kerf and cage position
(Botte 2013). For these reasons, virtual surgery
pre-planning is currently recommended. This
can be accomplished using digital software
(e.g., Orthoplan Elite; Sound, Carlsbad, CA,
USA) or a cut-and-paste manual method using
radiographic film. Virtual pre-planning (Fig-
ure 28.6) allows the cage advancement to be
measured at the appropriate point of cage
placement/position to achieve the desired
90 ◦PTA postoperatively. Regardless of which
pre-planning method is used, accurate transfer
of the plan to the bone is required to achieve
the desired advancement. Factors related
to saw kerf, tuberosity displacement with

patella-based advancement, and cage position-

ing all need to be recognized.

TTA case selection

Several factors specific to the anatomic configu-

ration of the limb should be considered before

selection of this surgical technique (Boudrieau

2009).

Low versus high patellar tendon

insertion point

The tibial tuberosity may be at greater risk for

fracture with TTA in cases with a low patel-

lar tendon insertion point, as a smaller plate is

applied to the tibial crest and the usual posi-

tion of the interspersed cage is above the most

proximal position of the plate, with little bone

present for support. Interestingly, this confor-

mation may be better suited for a tibial plateau

leveling osteotomy as there is increased but-

tress support of the tibial tuberosity with greater

amounts of tibial plateau rotation. In dogs with

a high insertion point the TTA is preferable,

as a larger TTA plate can be applied to the

tibial crest, and the interspersed cage that is

placed within the gap remains buttressed with

adequate bone. Finally, the larger plate better

disperses all the forces to the tibial crest (Fig-

ure 28.7). Currently, there are no experimental

or clinical studies reported that support these

assumptions.

Excessive tibial plateau angle

Cases where there is excessive TPA are not con-

ducive to TTA. The target PTAis 90◦, but achiev-

ing this angle in such cases require substantially

greater advancement, sometimes beyond that

obtained with currently available implants (the

maximal cage width for the osteotomy gap is

15 mm). More importantly, there is a conforma-

tional deformity of the joint with excessive tibial

plateau angle that places the joint in a relative

angle of hyperextension, despite the limb itself

not being in the extended position (Figure 28.8).

The TTA does not address this malformation.

The maximal TPA to perform a TTA has yet to