Tibial Tuberosity Advancement 231(A) (B) (C)Post-opPre-opFigure 28.5 Schematic representation of the tibiofemoral forces in the stifle joint, according to Tepic, before (A) and
after (B) tibial tuberosity advancement (TTA). The resultant compressive force (large white arrow) across the stifle joint is
parallel to the patellar tendon. Using the common tangent at the tibiofemoral contact point as the baseline (solid red
line), whereby the femur can move along this surface if the cranial cruciate ligament (CrCL) is deficient, the resultant
force can be broken down into its two orthogonal components (small blue arrows), one perpendicular and one parallel
to the tibial plateau. The latter represents the tibiofemoral shear force. If the angle of the tibial tuberosity is advanced
cranially until the patellar tendon angle (PTA) is reduced to 90◦, the tibiofemoral shear force vector becomes zero, and
the joint compressive force and resultant force become one and the same. Note that the cranial tibiofemoral shear force
is smaller than that depicted with the PTA using the tibial plateau slope (TPS), which is indicated by the green dotted
line. Note that the common tangent and TPS are similar in stifle joint flexion (C). The insets clarify the force vectors
depicted on the schematic bone models. Compare with Figure 28.2. Source: Boudrieau 2009. Reproduced with
permission from John Wiley & Sons, Inc.
Surgical Summit; Pre-Symposium Laboratories:
TTA Laboratory; Chicago, IL, USA). Support
for this concept has been demonstrated experi-
mentally, whereby less variability was observed
with PTACTversus PTATPAto achieve the target
PTA of 90◦(Hoffmannet al. 2011). These find-
ings have recently been questioned in a study
that found a poor agreement between PTACT
and PTATPA, moderate intra-observer reliability
and poor inter-observer reliability with PTACT,
with good intra-observer reliability and moder-
ate inter-observer reliability with PTATPA, thus
concluding that PTACT is not recommended
(Milletet al. 2013). Reconciling the differences
between the different studies is problematic
(Dennler 2006; Hoffmann et al. 2011; Millet
et al. 2013). An agreement between PTACTand
PTATPAis certainly not expected due to the com-
plex joint anatomy that differs between dogs,
including differing stifle joint extension angles
and change of femoral position as the femoral
condyles roll backwards with stifle joint flex-
ion (Boudrieau 2009). The latter factors are the
arguments supporting the rationale for using
the PTACTin the pre-planning, as described by
the originators of the surgical technique (Tepic
et al. 2002).Implants and techniques
Currently there are two general techniques
to perform the TTA, described as the first-
and second-generation methods. The first-
generation method is the initial method as pro-
posed by Tepic (Kyon; Boston, MA, USA), using
a titanium cage to maintain the advancement
and a corresponding titanium plate with forks