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20.7 ­uscle Contractures 367

terrier (Robinson 1992; Demko and McLaughlin 2005). Males and females are equally affected,
with most dogs presenting between 4 and 11 months of age. Approximately 12–16% of cases are
affected bilaterally. Dogs will present with unilateral or bilateral pelvic limb lameness (Demko and
McLaughlin 2005).

20.6.2 Physical Exam
Dogs will have pain and crepitus with range of motion of the affected hip joint(s). They may have
accompanying atrophy of the limb from disuse. Given the prevalent signalment of toy-breed dogs,
concurrent patella luxation may be present. This may confuse the veterinary exam; however, if both
are present the hip pathology generally causes more pain than the stifle pathology in these cases.

20.6.3 Diagnostics
Diagnosis of avascular necrosis of the femoral head is suspected based on signalment, history, and
physical exam findings. It is confirmed via orthogonal radiographs of the pelvis (Figure 20.13). In
the early stages of the disease, there may be an increased joint space. Once vascular necrosis has
occurred, radiographic changes will be seen within the femoral head and neck as areas of lucency.
Ultimately, there may be flattening of the femoral head, collapse of the joint space, and progressive
degeneration of the joint. CT scan may also be performed if radiographs are unequivocal (during
early stages of the disease). Differential diagnosis include fracture (slipped capital physeal fracture,
femoral neck fracture), infection, and neoplasia.

20.7 Muscle Contractures

Muscle contraction describes the normal, physiologic process of muscle shortening during activa- HIP REGION
tion. Muscle contracture, on the other hand, is a pathologic process that results in permanent
shortening of the muscle leaving it unable to stretch. The normal muscle fibers are replaced by
fibrous connecting tissue, which will shorten the affected muscle. Muscle contracture is also
referred to as “fibrotic myopathy” or “fibrotic contracture” in the literature (Taylor and Tangner
2007; Adrega Da Silva et al. 2009; Cabon and Bolliger 2013). Muscle contractures are different from
acute strain injuries because of their chronicity. However, it is possible that muscle strains trigger
muscle contractures (Section 20.9.3; Nielsen and Pluhar 2005).

20.7.1 Gracilis Contracture
A syndrome known as gracilis contracture (also referred to as gracilis myopathy), can affect not
only the gracilis muscle, but also the semitendinosus and semimembranosus, and rarely the
biceps femoris muscles, individually, or concurrently (Lewis et al. 1997; Steiss 2002; Spadari et al.
2008).
The exact etiology of gracilis contracture is not known. It has been theorized to develop
secondary to acute trauma, chronic repetitive trauma, infection, autoimmune disease, neuro-
genic disorders, vascular abnormalities and even drug reactions, though none have been proven
(Taylor and Tangner 2007). Affected dogs frequently participate in tracking-obedience- protection
work from a young age (Steiss 2002), giving some credence to repetitive stress/trauma as a cause