Page 330 - Canine Lameness

302 18 Tarsal Region

limited to the distal limb but may clinically affect. Depending on the severity of the deformity,
surgical correction may be considered.

18.7.2 Idiopathic Tarsal Hyperflexion

Luxation or subluxation of the distal tarsal joints is usually of traumatic origin, but it can also
develop in the later stages of erosive immune-mediated arthropathies (Figure 18.11). Some dogs
(especially Shetland Sheepdogs and Collies) without history of trauma or evidence of immune
disease develop the instability gradually, and it may happen in both tarsi, sometimes in concert
with carpal hyperextension. If arthrocentesis and testing for antinuclear antibody and rheumatoid
TARSAL REGION factors speak against underlying immune-mediated disease, either inherent connective tissue
weakness or degeneration of the plantar support structures is suspected but not proven (Carmichael
and Marshall 2018). Dogs with this idiopathic, atraumatic presentation gradually develop a gait
abnormality that often appears to be more mechanical than painful in nature. Treatment is chal-
lenging due to the number of joints affected but generally involves partial tarsal arthrodesis,
although orthotic support can be considered.

18.7.3 Idiopathic Tarsal Hyperextension
Tarsal hyperextension can occur at multiple levels but most prominently involves the tarsocrural
joint. This condition may accompany talar OCD and is a feature of some myopathies (Marioni-
Henry et al. 2014). Additionally, tarsal hyperextension may be due to painful conditions more proxi-
mal in the limb, such as cranial cruciate ligament rupture, hip dysplasia, or lumbosacral stenosis. In
cases with more proximal pathology, tarsal hyperextension is thought to develop as a compensation
mechanism in which the associated weight shifting towards the thoracic limbs results in tarsal
hyperextension to gain pelvic limb length. Alternatively, pain in a more proximal joint may result in
a changed stance angle (i.e. a dog with stifle pathology may prefer to stand with increased flexion of
the stifle and therefore the tarsus is hyperextended to compensate). The presence of tarsal hyperex-
tension should therefore alert the diagnostician to the possibility of pathology located more proxi-
mally, even though the tarsal abnormality may be the most noticeable clinical sign.
In some cases, no other pathology can be identified. A congenital laxity of the fibularis musculo-
tendinous region has been implicated in calves (Kilic et al. 2015), but tarsal hyperextension is seldom
evident during the first few months of life in dogs. The hyperextension typically develops gradually,
usually during the first year of life. Dogs of any breed, age, or sex can be affected. The degree of hyper-
extension varies between cases and in some dogs, the abnormality may be intermittent. The tarsus
extends up to or beyond 180° by the end of the stance phase of the gait. The tarsocrural joint may
abruptly flip forward just before the foot is lifted. The affected tarsus may rock into and out of hyper-
extension when the dog is standing (Figure 18.12). Affected tarsi seldom appear to be painful on
manipulation. Range of motion in flexion is unaffected, but the abnormal tarsus can be extended at
least to 180°. Effusion or crepitus is usually absent unless there is concurrent talar OCD.
Radiographs of the tarsus are also usually normal unless talar OCD is present. If the tarsus is
stressed in extension, a lateral view will document the abnormally high tarsocrural angle without
other pathology (Figure 18.12). Degenerative changes may be seen, although they are observed
infrequently and may be secondary to other pathology in some cases. Radiography of the stifle and
the hip in the affected limb should be considered to evaluate for concurrent orthopedic abnormali-
ties. Since lumbosacral stenosis is occasionally associated with tarsal hyperextension, radiographs
and possibly MRI of this region may be indicated if lower back pain is evident.