244 Surgical Treatment
caudal cortices). If this is done, the functional
axis shift will be around 5◦for a 25◦wedge, and
7–8◦for a 35–40◦wedge.
Technique: planning
The principles of CCWO for either managing
proximal tibial deformity or reducing the TPA
are similar to those used when correcting defor-
mities in other bones, though there are cer-
tain considerations that are specific to this loca-
tion. In early descriptions of the procedure,
the osteotomy was located more distal because
only straight plates were available for stabiliza-
tion, and sufficient space was needed to ensure
purchase for three bicortical screws. With the
development of purpose-designed plates (TWO
plates; Veterinary Instrumentation, Sheffield,
UK, and TPLO plates from various manufac-
turers), the level of the osteotomy is now posi-
tioned more proximal, and the amount of func-
tional axis shift is smaller. The size of the wedge
to be removed is planned on the ‘90–90’ lateral
view of the tibia, named after the fact that the
stifle and tarsus are position at 90◦of flexion,
with the beam centered over the stifle. The TPA
is measured. The optimal postoperative TPA
is considered to be 6◦. The appropriate wedge
size will depend on the magnitude of the TPA,
the level of the osteotomy, and whether the
cranial cortices of the tibial will be aligned. If
the osteotomy is proximal and the cranial cor-
tices are aligned, wedge sizes are usually 2–3◦
less than the TPA for TPAs of 25–32◦.Fora
TPA greater than 35◦, the wedge size should be
the same as the TPA. The limb and the radio-
graphs should be assessed to determine if there
is significant varus/valgus or tibial torsion that
should be addressed. Varus and valgus can be
corrected by adjusting the plane of one of the
osteotomies relative to the other. Torsion can
be corrected by rotation of the fragments at
the level of the osteotomy. The stabilizing plate
must be contoured appropriately to maintain
the intended rotation correction.
When planning corrections of large TPAs, it
may be helpful to print an image of the lateral
tibial radiograph, draw the planned wedge in
the anticipated location, cut out the wedge, and
reposition the ‘fragments’ to simulate reduc-
tion. The TPA can be measured on this paper
model, and the effect of the cranial shift on the
functional axis appreciated. If the final TPA is
not appropriate, the size of the wedge can be
adjusted accordingly and the exercise repeated.
This same process can be performed digitally
using some of the planning software packages
that allow the ‘cutting’ and repositioning of
image fragments (Figure 29.1).
A recent modification described by Freder-
ick & Cross (2017) results in less length loss for
the same wedge size. The position of the prox-
imal cut is planned similarly to that described
above. The level of the distal cut is adjusted
proximally such that the proximal and distal
osteotomies will be of equal length (Figure 29.2).
The cranial edges are aligned in the same way as
usual.Technique: intraoperative
The medial aspect of the proximal tibia is
exposed and the muscles elevated caudally and
laterally at the proposed level of the osteotomy.
The joint level is identified and the planned
stabilizing implant positioned on the proxi-
mal fragment to assist in identifying the most
proximal level of the ostectomy. The proxi-
mal osteotomy line is scored, ensuring that it
is approximately parallel to the tibial plateau
and that it is 3–5 mm distal to the insertion of
the patella tendon. Using a goniometer, wedge
set, or custom wedge guide (sterilized radio-
graphic film), the second osteotomy line is
scored, with the apex at the caudal cortex. The
two cuts are made ensuring that they are copla-
nar. The wedge is removed and the fragments
reduced, with the cranial cortices aligned. If
a large wedge was removed, the intact fibula
may prevent complete reduction. It should be
cut or fractured at the level of the osteotomy.
A Kirschner wire placed from cranial to cau-
dal across the osteotomy may help to main-
tain reduction while the plate is contoured and
applied.Patient selection
CCWO can be used to level the plateau of any
tibia. It has been superseded by TPLO based