Total Knee Replacement in the Dog 369(A)(B)Figure 44.7 Aseptic loosening of a cemented canine
total knee replacement. (A) Radiograph demonstrating a
wide, radiolucent line at the implant–cement interface of
a cemented femoral component. On retrieval, the femoral
component was found to be grossly loose, with soft tissue
between the implant and the cement mantle (B).
bacterial cultures. As with septic loosening
after total hip replacement, there is insufficient
data available to determine the incidence of
aseptic loosening in canine TKR. One case of
femoral component loosening was reported in a
preclinical study (Allenet al. 2009) (Figure 44.7)
and, more recently, was seen in a clinical case
with overt tibial loosening associated with
failure of the cement mantle, collapse of the
medial subchondral bone, and secondary wear
of the UHMWPE insert. However, the overall
clinical experience with the BioMedtrix implant
has been encouraging, with good implant
stability in the short-term and a low incidence
of loosening in the early clinical cases (Liska &
Doyle 2009).
Mannet al. (2012) investigated factors that
are likely to contribute to early loosening of
the Biomedtrix tibial component by assessing
the interfaces between the implant, cement, and
bone. They observed that the subchondral bone
of the canine proximal tibia is extremely dense,
making it difficult to achieve effective cement
intrusion and implant fixation. More cement
intrusion into cancellous bone was present
along the central keel compared to the under-
side of the tibial component body. In order
to achieve a good fixation of cement to sub-
chondral tibial bone, and therefore reduce the
chances of cement failure, it is important to
pressurize cement for intrusion. This can be
done through multiple keyholes drilled into the
dense cut surface of the tibia.Laboratory testing
Recent publications have focused on labora-
tory testing of TKR, with the goal of improv-
ing understanding of stifle joint kinematics
after TKR and ameliorating the surgical tech-
nique. Bakeret al. (2014) assessed stifle joint
kinematics before and after CrCL transection
as well as after TKR performed with various
tibial plateau angles (TPAs) and tibial com-
ponent thicknesses. These authors found that
kinematics were optimized when the TKR was
performed with an 8◦ TPA. Stifle kinemat-
ics after TKR has been assessedex vivousing
a 6-degrees-of-freedom robotic kinematic sys-
tem (Bertran & Allen 2016). The results of this
study confirmed that the BioMedtrix TKR pros-
thesis is semi-constrained, limiting rotational
instability but permitting some cranio-caudal
translation during stifle flexion and extension.
Compared with the intact stifle, cranial tib-
ial translation was significantly greater after
TKR, while internal rotation and varus torque
were significantly reduced. The clinical conse-
quences of these alterations to joint kinemat-
ics remain to be determined, and a study to
assess three-dimensional motion after TKR is
currently ongoing.
Another factor that influences long-term
outcome after TKR is accurate preparation of
the articular surfaces. Dogs undergoing TKR
often have severe intra- and extra-articular
pathology causing significant alterations to
the normal anatomy. Such alterations make
it difficult for the surgeon to achieve optimal