The sacroiliac joints of dogs are closely opposed joints composed of ligamentous and synovial components.1 The ligamentous component is located at the craniodorsal and central aspects of the joint and is composed of fascicles of collagen fibers separated by adipose tissue. The synovial component is crescent shaped and located at the caudoventral aspect. Sacroiliac joints transmit propulsive forces from hind limbs to the vertebral column and support the weight of the torso but may also have a role in buffering ground impact forces.2–5 These functions of sacroiliac joints may require both rigidity (required for force transmission) and flexibility (required for the joint to function as a buffer to high-frequency motion in this region of the body).
Although such conclusions are controversial, sacroiliac joints have been determined to be a source of pain in humans6 and signs of pain in horses have been attributed to sacroiliac joint problems7; however, it is not known whether sacroiliac joints are a source of pain in dogs.1,8 The clinical signs of sacroiliac joint pain in humans are similar to those attributable to other causes of back pain.9 Pain provocation tests for detection of sacroiliac joint dysfunction in humans may not be specific for the sacroiliac joint because such tests also stress lumbosacral, intervertebral, and hip joints.10 Dogs can have signs of lumbosacral region pain,8 which is typically attributable to diseases of lumbosacral vertebral facets, lumbosacral intervertebral disks, and hip joints.11 Physical manipulations intended to detect signs of pain of sacroiliac joints of dogs, such as the thigh thrust and shear tests, have not been validated.12 Therefore, it is not known whether sacroiliac joints are a site of pain in dogs. German Shepherd Dogs are predisposed to diseases that cause lumbosacral region pain.13 German Shepherd Dogs are commonly used as working police and military dogs.14,15 These dogs are socially and economically valuable, and lumbosacral region pain in such animals can be career limiting.
Forces from hind limbs are transmitted to the vertebral column through the hip, sacroiliac, and lumbosacral joints.3 Other authors5,16,17 have proposed that overloading of sacroiliac joints in dogs (caused by activities such as repetitive, intense activity) may lead to instability of those joints. Such instability could lead to secondary disease and development of osteophytes in sacroiliac joints, which could limit motion of the joints and increase loading of adjacent hip and lumbosacral joints.17 Therefore, it is possible that (in dogs) secondary joint disease could cause pain in the sacroiliac joints or adjacent structures.1,18 Alternatively, degenerative changes in sacroiliac joints could develop secondary to diseases of the lumbosacral and hip joints that alter loading of the sacroiliac joints.8 It is important to understand the biomechanically normal motion of sacroiliac joints before theories regarding sources of sacroiliac joint pain can be determined.
Motion of sacroiliac joints in dogs has been measured in another study,1 in which soft tissues surrounding sacroiliac joints of canine cadavers were removed with retention of the periarticular and sacrotuberous ligaments; results indicated a mean rotational motion of 7° (range, 4° to 13°). To the authors’ knowledge, no in vivo studies have been conducted to assess motion of sacroiliac joints in dogs. Skin-mounted sensors,19,20 bone marker implants,19 and indirect measurement via ultrasonography of the dorsal sacroiliac ligament21 have been used in in vivo studies to measure motion of sacroiliac joints in horses. In vivo motion studies of humans have been performed by use of roentgen stereophotogrammetry of tantalum implants,22 plain-light stereophotogrammetry of Kirschner wire implants,23 and transcutaneous palpation and digitization of anatomic landmarks.24 Computed tomography is a reliable method for detection of motion in vivo24; however, to the authors’ knowledge, no studies have been conducted to directly measure motion between the sacrum and ilium by use of CT in animals of any species.
Inclination angles of the sacroiliac joint are defined as the angle of the axis of the joint relative to a dorsally positioned reference line, as measured on transverse plane images. The transmission of the force of an animal's weight through such joints is affected by the inclination angle, which may therefore determine the loading capacity of the joint.16 Canine sacroiliac joints are aligned close to the sagittal axis.16 As the alignment of the sacroiliac joints approach the sagittal plane, the direction of loading forces may become closer to parallel with the joint surfaces than it is when the joint is obliquely aligned. Therefore, sagittally oriented sacroiliac joints may have higher shear forces than obliquely oriented joints. German Shepherd Dogs had the most sagittally aligned sacroiliac joints of any breed of dog evaluated in another study.16 Furthermore, results of that study16 indicated small-breed dogs have more oblique (ie, less sagittal) orientation of their sacroiliac joints versus large-breed dogs. Sacroiliac joint inclination angles may be related to gait characteristics or body mass. Sacroiliac joint inclination angles have not been measured in active working dogs, to the authors’ knowledge.
Sacroiliac joint inclination angles have been measured in canine cadavers and symmetric ventrodorsal radiographic images of pelvises of dogs.16 That radiographic technique involves observation of the sacral wings rather than direct observation of the sacroiliac joint space. The locations of the borders of sacroiliac joint spaces are inconsistent in radiographic images of pelvises of dogs.8 Although sacroiliac joints have been successfully imaged via CT, that modality has not been used to quantify the inclination angles of such joints.25
The purpose of the study reported here was to develop a novel noninvasive in vivo method for measurement of the motion and inclination angles of sacroiliac joints of dogs by use of CT. Two large performance dog breeds (German Shepherd Dogs and Greyhounds) were selected for evaluation in this study; one of these breeds (German Shepherd Dogs) is predisposed to lumbosacral region pain. We hypothesized that motion and inclination angles of sacroiliac joints would be measureable by use of CT, and differences in rotational and translational motions of sacroiliac joints and inclination angles of such joints would be detected between German Shepherd Dogs and Greyhounds.
Brilliance, Philips Healthware, Eindhoven, The Netherlands.
Pfizer Animal Health, West Ryde, NSW, Australia.
Troy Laboratories Pty Ltd, Glendenning, NSW, Australia.
Norbrook NZ Ltd, Auckland, New Zealand.
Piramal Healthcare Ltd, Mumbai, India.
Brilliance Workstation, version 188.8.131.52007, Philips Healthware, Eindhoven, The Netherlands.
ClearCanvas RIS/PACS Freeware, version 2.0.12729.37986 SP1, ClearCanvas Inc, Toronto, ON, Canada.
eFilm, version 2.1, Merge Healthcare, Chicago, Ill.
R, version 15.1, R Foundation for Statistical Computing, Vienna, Austria.
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