228 Surgical Treatment
(A)(B)(C)Knee
AngleTPSPTAPTA120°110°100°90°80°180° 150°90° 60°120°180° 150° 90°60°120°
Knee AngleKnee Angle600400200–2000Fs (N)FpFigure 28.1 (A) Anatomic landmarks of the radiographic
and morphologic studies of the knee. The patellar tendon
force (Fp) is shown, which is approximately of the same
magnitude and direction of the tibiofemoral compressive
force, and results in a variable amount of tibiofemoral
shear force depending on the knee flexion angle and
tibial plateau slope (TPS), both of which influence the
patellar tendon angle (PTA). (B) The relationship between
was suggested as the crossover point at 135◦of
stifle joint extension; thus, the TTA technique
was developed so as to achieve this PTA (Fig-
ure 28.2). These assumptions were supported in
four experimentalex vivomodels (Apeltet al.
2007; Milleret al. 2007; Kipferet al. 2008; Hoff-
mannet al. 2011). These models were used to
evaluate cranial tibiofemoral shear force either
indirectly with cranial tibial subluxation (Apelt
et al. 2007; Milleret al. 2007; Kipferet al. 2008)
or directly with cranial tibial thrust under vary-
ing loading conditions (Hoffmannet al. 2011)
(Figure 28.3). A recent 3D quasi-static rigid
body pelvic limb computer model simulating
the stance phase of gait predicted improved
joint loading in the CrCL-deficient stifle, but not
restoration of normal CrCL-intact biomechan-
ics (Brownet al. 2015). In this model, the TTA
effectively reduced tibial translation, but did
not stabilize tibial rotation (Brownet al. 2015).
These results were similar whether using either
the tibial plateau angle (TPA) or common tan-
gent planning methods to achieve a target PTA
of 90◦(Brownet al. 2015). The findings in this
model were consistent with anin vivoassess-
ment of the TTA during weight-bearing, which
demonstrated that craniotibial translation was
reduced, but not eliminated (Skinneret al. 2013).
A 3D nonlinear joint finite element model
reconstruction, which was based on a cadaver
knee joint of a human, was used to evalu-
ate the reduction in retropatellar pressure and
patellar tendon force. The analysis confirmed
not only a decrease in patellofemoral contact
forces after TTA, but also femorotibial contact
forces with stifle joint extension (Shirazi-Adl &
Figure 28.1 (Continued) the PTA (y-axis) and knee
flexion angle (x-axis); note that the PTA= 90 ◦at a knee
flexion angle of∼ 100 ◦; the 95% confidence intervals of
the means are shown for men (filled circles) and women
(open circles). (C) Tibiofemoral shear force (Fs; y-axis)
during isometric knee extension at various knee flexion
angles (x-axis) for men (filled circles) and women (open
symbols). During knee extension, the application of
posteriorly directed external forces of 100 N (squares and
circles) and 50 N (diamonds) against the anterior tibia at
0.4 m, 0.4 m and 0.2 m distal to the tibial plateau,
respectively. Positive values (Fs) indicate that the tibia
tends to slide anteriorly in relation to the femur (anterior
tibiofemoral shear). Source: Nisell 1985. Reproduced
with permission from Taylor & Francis.