Advances in the Canine Cranial Cruciate Ligament, 2nd edition

Biomechanics of the Cranial Cruciate Ligament-Deficient Stifle Treated by Tibial Osteotomies 275

2010). Differing stifle joint excursions over a gait
cycle may also mean that the amount of tib-
ial plateau rotation (TPLO) or advancement of
the patellar tendon insertion (TTA) necessary to
neutralize subluxation varies between individ-
ual dogs. Firm evidence to support specific ‘tai-
loring’ of postoperative TPAs or patellar tendon
angles is lacking. It is unlikely that the reported
optimal angles (e.g., TPA of 6◦) are universal for
every dog with CR.
Traditional surgical techniques that involve
the placement of a passive stabilizing struc-
ture, such as lateral suture stabilization, have
the advantage of decreasing rotational insta-
bility, but they hinder full stifle flexion and
restrict normal axial rotational motion of the sti-
fle, as placement of the implant cannot be not
perfectly isometric in all three planes. Flexion–
extension range of motion in stifles treated
with TPLO and TTA should not be as dimin-
ished when compared to the traditional proce-
dures (Chailleuxet al. 2007). Full flexion may be
slightly decreased after TPLO and CCWO when
compared to normal, as they move the distal
tibial segment (i.e., the longitudinal axis of the
tibia) into slight extension.
The biomechanical models on which TPLO
and TTA are based upon are two-dimensional.
Therefore, tibial osteotomies do not directly
attempt to address axial rotational instability
caused by CR (Kimet al. 2008). Axial rotation
of the tibia relative to the femur remains unre-
stricted, and the control of internal–external
rotational motion must then rely on muscular
forces about the stifle and joint adaptation. It

is uncertain whether this muscular compensa-

tion occurs in dogs, or whether abnormal axial

rotation is a clinically significant factor in stifles

treated by tibial osteotomies. Persistent axial

rotational instability may be one explanation for

the progression of osteoarthritis and the sub-

sequent meniscal tears in stifles treated by tib-

ial osteotomies (Lazaret al. 2005; Lafaveret al.

2007). When treating clinical cases with severe

internal rotation, consideration should be given

to combining extracapsular stabilization with

osteotomies. On the other hand, extracapsular

techniques create constant external rotation and

abduction of the stifle over a range of motion,

which may also be detrimental to joint home-

ostasis (Chailleuxet al. 2007).

The primary kinematic abnormality of CR is

an increase in cranial tibial translation. Tibial

osteotomies have been showed to successfully

neutralize cranial tibial thrust and reestablish

normal alignment of the stifle inex vivomodels.

However,in vivostudies have shown that TPLO

may not consistently provide stability in all

dogs (Kimet al. 2012). A currently unpublished

in vivo investigation of clinical dogs, using

lateral fluoroscopy (Figure 32.3), has shown

that TPLO resolves cranial tibial translation and

internal tibial rotation in the majority of dogs,

but creates a static caudal tibial displacement

that is present throughout the gait cycle (Fig-

ure 32.4) (Tingaet al. 2015). When cranial tibial

subluxation is resolved, internal tibial rotation

is resolved, but when cranial tibial subluxation

is not resolved, neither is internal tibial rota-

tion. Presumptively, the resolution of instability

Figure 32.3 Representative image from
shape-matching software of a stifle after tibial
plateau leveling osteotomy. Three-dimensional
computed tomography-derived bone models are
superimposed over lateral projection
fluoroscopic images that are acquired during
activity, and the relative positions of the bones
are calculated using custom-written software.