Closing Cranial Wedge Ostectomy and Triple Tibial Osteotomy 249CADWABFigure 29.4 Triple tibial osteotomy planning. The angle
between lines depicting the tibial plateau (TP) and the
patella tendon (PT) with the stifle at an approximately
135 ◦angle is formed. The correction angle (CA) is
calculated as the TP-PT angle minus 90◦. The length of
the PT is measured. The hole at the distal end of the tibial
tuberosity cut (B) is located by measuring the PT length
distal from the PT insertion. The first cut, depicted by the
black line extending proximad from the hole at B,
separates the tibial tuberosity from the tibial shaft. The
length of the cut is measured and a hole (D) is drilled
level with the mid-point, approximately 3 mm in from the
caudal edge of the tibia. The wedge angle (WA) is
calculated from the CA: WA=CA×0.6 + 7. The wedge
is cut, and the ostectomy reduced and stabilized with a
plate.
tibia is exposed. Then, using the length of the
patella tendon measured during planning, a
point is marked distal to the insertion of the
patella tendon (Figure 29.4, point B). A 2-mm
hole is drilled from medial to lateral and a linear
saw guide inserted and aligned parallel to the
cranial edge of the tuberosity. The bone is cut,
the saw guide removed, and the cut completed.
The tuberosity fragment is held off the caudal
fragment by a spacer tool, called awedgie.The
mid-point of the osteotomy is marked and a
2-mm hole is drilled at that level from medial
to lateral 2–3 mm in from the caudal edge of
the tibia (Figure 29.4, point D). The pin of the
combined osteometer and saw guide is placed
in the hole and the guide is positioned so that
the removed wedge is centered on the apex. It
is held in position with a purpose-made, self-
retaining forceps (a clasper) or 1.6 mm K-wire
through a hole in the distal arm of the osteome-
ter. The cuts are made in the medial cortex,
the guide is removed, and the cuts are com-
pleted through the lateral cortex. The popliteal
artery is retracted as the lateral cortex is cut.
The bone wedge is removed and used later as
a bone graft. The wedgie tool is moved distal
to the ostectomy to hold the tibial crest frag-
ment in a cranial position so that the proximal
tibial fragment can be fully reduced. A large
pointed reduction forceps is placed on the prox-
imal aspect of the proximal fragment and on
the base of the tibial tuberosity and is squeezed
until the ostectomy is reduced. A bone plate is
contoured to the medial aspect of the tibia and
secured with bone screws. The bone wedge is
cut into 2 mm-sized fragments and packed into
the defect between the tuberosity fragment and
the shaft.Patient selection
TTO is more likely to develop complications if
used to manage excessive slope. With a bone
wedge larger than 20◦, it is likely that one
or both bone bridges will fracture. In dogs
with unusual tibial tuberosity morphology, the
appropriate wedge size is harder to determine
and another technique may be more suitable.
While TTO can be performed in small dogs,
the osteotomies need to be very precise in dogs
weighing<10 kg.Implant selection
Because the osteotomy is slightly lower than
where the TPLO osteotomy is usually located,
the pre-contoured locking TPLO plate will not
be suitable in all cases. Some tibias are relatively
flat, and removing the pre-contour may result
in screws being directed towards the osteotomy.