Page 421 - Canine Lameness

22.2 Neoplasia of Specific eeions 393

compared to forged plates (i.e. currently used TPLO plates). This corrosion‐related increased ion
release may place patients at risk of tumor development (Sprecher et al. 2018). The risk of
developing osteosarcoma after TPLO has been described to be very low. Sartor et al. (2014) retro-
spectively evaluated 2464 dogs with at least one‐year follow‐up after TPLO. In that study, 11 dogs
developed osteosarcoma at the TPLO site (0.4% incidence) and 29 dogs developed osteosarcoma at
a different site (1.2%). The authors calculated incidence density rates of OSA at the TPLO site to
be between 10.2 and 30.4 per 10 000 dog‐years at risk. Interestingly, all dogs that developed osteo-
sarcoma at the TPLO site had cast TPLO plates implanted (Sartor et al. 2014). In a more recent
matched case‐control study, dogs that had received a TPLO in the last year were 40 times as likely
to develop proximal tibial osteosarcoma as were dogs with no history of TPLO (Selmic et al. 2018).
Unfortunately, the type of implant was not disclosed in that study. Regardless, proximal tibial
osteosarcoma should be considered as a differential after TPLO which can easily be diagnosed
with radiographs.
Presence of the classic findings of cranial cruciate ligament rupture, such as joint effusion and
cranial drawer, do not rule out the possibility of neoplasia (Lahmers et al. 2002). While extremely
rare, it is possible that stifle instability is secondary to neoplasia rather than due to degeneration.
Several tumors of the stifle joint have been described. Specifically, the stifle is one of the three most
common joints to develop periarticular histiocytic sarcoma. Villonodular synovitis has also been
described in the stifle region of two dogs, one of which was bilateral (Marti 1997). Lymphoma of
the synovium of the stifle joint has been reported in one dog (Lahmers et al. 2002).
Unfortunately, joint fluid analysis cannot be used to reliably diagnose stifle neoplasia and even
in the case of synovial lymphoma, it failed to provide the diagnosis (Lahmers et al. 2002).
Additionally, because radiographic abnormalities may be subtle, a biopsy is required to establish a
diagnosis.

22.2.4 Hip Region
Osteosarcoma is the most common bone tumor of the proximal femur. Osseous tumors of the
pelvis or soft tissue tumors of the pelvic canal can also cause a lameness. Lipomas in the inguinal
area rarely cause a lameness unless they become large enough to interfere with normal range of
motion. Another type of lipoma rarely associated with lameness is the intermuscular lipoma,
which is typically encountered in the thigh region. This lipoma grows between the muscle bellies
of the thigh, particularly those of the caudal thigh, and unlike the infiltrative lipoma does not
invade the muscle bellies. Villonodular synovitis has also been described in the hip region of one
dog (Kusba et al. 1983).
The rectal exam is an essential part to detect neoplasia of the hip region since it can reveal
tumors of the pelvic canal or the pelvis (mostly caudal aspect, depending on the size of the dog and
length of the finger of the examiner). Because of the large muscles surrounding the hip area, subtle
lesions of the bones can be more easily missed on radiographs. Therefore, computed tomography
is frequently used since it is more sensitive to show both soft tissue and bone pathology. Fine‐
needle aspirates and biopsies in this area frequently require imaging guidance. When tumors of
the femoral neck or head are treated by amputation, an acetabulectomy en bloc is recommended.

22.2.5 Nervous System
Neoplastic diseases affecting the nervous system of the pelvic limb are similar to those of the
thoracic limb (Chapter 17). Peripheral nerve sheath tumors can affect any component of the periph-
eral nervous system, but they are less commonly observed in the lumbosacral area compared to the