Facet joint geometry and intervertebral disk degeneration in the L5-S1 region of the vertebral column in German Shepherd dogs

OBJECTIVE: To evaluate the possible association between facet joint geometry and intervertebral disk degeneration in German Shepherd Dogs. ANIMALS: 25 German Shepherd Dogs and 11 control dogs of similar body weight and condition. PROCEDURE: Facet joint angles in the caudal portion of the lumbar region of the vertebral column (L5-S1) were measured by use of computed tomography, and the intervertebral discs were evaluated microscopically. The relationship between facet joint geometry and disk degeneration was evaluated by use of statistical methods. RESULTS: German Shepherd Dogs had significantly more facet joint tropism than control dogs, but an association with disk degeneration was not found. However, German Shepherd Dogs had a different facet joint conformation, with more sagittally oriented facet joints at L5-L6 and L6-L7 and a larger angle difference between the lumbar and lumbosacral facet joints, compared with control dogs. CONCLUSIONS AND CLINICAL RELEVANCE: A large difference between facet joint angles at L6-L7 and L7-S1 in German Shepherd Dogs may be associated with the frequent occurrence of lumbosacral disk degeneration in this breed.     

Effectiveness of cervical hemilaminectomy in canine Hansen Type I and Type II disc disease: a retrospective study

Medical records of 41 dogs, including 15 small breed dogs (<15 kg) and 26 large breed dogs (>15 kg), with cervical intervertebral disc disease (IVDD) that underwent a hemilaminectomy were reviewed. Dogs were diagnosed using myelography, computed tomography/myelography, or MRI, and dogs were classified as having either Hansen Type I disc extrusion or Hansen Type II disc protrusion located ventrally, ventrolaterally, or laterally within the cervical spinal canal. The most common clinical presentation was ambulatory tetraparesis and/or lameness (44%). The most affected sites for cervical IVDD were between the sixth and seventh cervical vertebrae (C6-C7; 78% of Hansen Type II discs) and C2-C3 (86% of Hansen Type I discs). Treatment was effective in 88% of dogs. Five large breed dogs (12%) did not improve. In dogs with a Hansen Type I disc extrusion, clinical signs improved in 96% of the cases. In dogs with a Hansen Type II disc protrusion, an excellent and good outcome was seen in 47% and 32% of cases, respectively. Outcome was significantly better for small breed dogs and dogs with Hansen Type I disc disease compared with large breed dogs and dogs with Hansen Type II disc disease.     

MR-imaging of lumbosacral intervertebral disc degeneration in clinically sound German shepherd dogs compared to other breeds

German shepherd dogs are overrepresented in the group of dogs with cauda equina compression syndrome due to degenerative lumbosacral stenosis. A congenital predisposition for early degeneration of the lumbosacral intervertebral disc has been suspected. Our aims were to assess the morphologic appearance of the lumbosacral intervertebral disc and the lumbosacral junction in healthy German shepherd dogs compared to other breeds and to evaluate for an early onset of degenerative changes. The lumbosacral spine of 110 clinically sound German shepherd dogs and 47 healthy dogs of other large breeds was examined using magnetic resonance (MR) imaging. The degeneration of every intervertebral disc was graded using an established classification system. Signal intensity of the entire lumbosacral disc and the nucleus pulposus was determined independently. Lumbosacral malalignment was assessed according to a previously described method. The findings for the German shepherd dogs were compared to those of the other breeds. Although most dogs were younger than 18 months at the date of examination, significantly higher grades of degeneration were detected for the lumbosacral intervertebral disc of German shepherd dogs (P < 0.003). Degeneration of the lumbosacral intervertebral disc was independent from findings in the other lumbar discs. We conclude that the German shepherd dog has a predisposition for degenerative changes in the lumbosacral intervertebral disc.     

Effects of anatomic conformation on three-dimensional motion of the caudal lumbar and lumbosacral portions of the vertebral column of dogs

OBJECTIVE: To determine the association between the 3-dimensional (3-D) motion pattern of the caudal lumbar and lumbosacral portions of the canine vertebral column and the morphology of vertebrae, facet joints, and intervertebral disks. SAMPLE POPULATION: Vertebral columns of 9 German Shepherd Dogs and 16 dogs of other breeds with similar body weights and body conditions. PROCEDURE: Different morphometric parameters of the vertebral column were assessed by computed tomography (CT) and magnetic resonance imaging. Anatomic conformation and the 3-D motion pattern were compared, and correlation coefficients were calculated. RESULTS: Total range of motion for flexion and extension was mainly associated with the facet joint angle, the facet joint angle difference between levels of the vertebral column in the transverse plane on CT images, disk height, and lever arm length. CONCLUSIONS AND CLINICAL RELEVANCE: Motion is a complex process that is influenced by the entire 3-D conformation of the lumbar portion of the vertebral column. In vivo dynamic measurements of the 3-D motion pattern of the lumbar and lumbosacral portions of the vertebral column will be necessary to further assess biomechanics that could lead to disk degeneration in dogs.     

COMPUTED TOMOGRAPHY OF THE NORMAL LUMBOSACRAL INTER VERTEBRAL DISC IN 22 DOGS

Computed tomography of the lumbosacral spine was performed on 22 purpose-bred, medium-sized hound dogs between 1 and 6 years of age. Images were evaluated to determine the degree of disc bulge. All dogs were neurologically normal. Dogs were imaged in dorsal recumbency with the pelvic limbs variably extended. Sagittal reconstructions were made from transverse images. The mean (+/-SD) width of the mid-portion of the L7-S1 intervertebral disc was 0.5 +/- 0.07 cm (range 0.33-0.62 cm). All L7-S1 intervertebral discs were dorsally convex, with the mean bulge measuring 0.25 +/- 0.07 cm (range 0.17-0.50 cm). The height of the vertebral canal at L7-S1 was 0.91 +/- 0.11 cm (range 0.68-1.15 cm). The mean percentage of the vertebral canal occupied by the bulge was 26.89 +/- 5.05% (range 20.74-43.08%). Mild bulging of the L7-S1 intervertebral disc can be present without associated neuropathy in medium-sized dogs.     

Immunohistochemical demonstration of lumbar intervertebral disc innervation in the dog

Low back pain is a common ailment in dogs, particularly in specific breeds such as the German shepherd dog. A number of structures such as facet joint capsules, ligaments, dorsal root ganglia, periosteum, vertebral endplates and meninges have been associated with this condition. Yet, in spite of all diagnostic efforts, the origin of pain remains obscure in a substantial proportion of all cases. A further structure often being involved in vertebral column disorders is the intervertebral disc. The presence of nerves, however, is a precondition for pain sensation and, consequently, structures lacking innervation can be left out of consideration as a cause for low back pain. Nerve fibres have been demonstrated at the periphery of the intervertebral disc in man, rabbit and rat. With regard to the dog, however, the extent of intervertebral disc innervation is still being disputed. The goal of the present study, therefore, was to substantiate and expand current knowledge of intervertebral disc innervation. Protein gene product (PGP) 9.5 was used for immunohistochemical examination of serial transversal and sagittal paraffin sections of lumbar discs from adult dogs. This general marker revealed nerve fibres to be confined to the periphery of the intervertebral discs. These results indicate that even limited pathological processes affecting the outer layers of the intervertebral disc are prone to cause low back pain.     

Review and retrospective analysis of degenerative lumbosacral stenosis in 156 dogs treated by dorsal laminectomy.

The medical records of 156 dogs with degenerative lumbosacral stenosis (DLS) that underwent decompressive surgery were reviewed for signalment, history, clinical signs, imaging and surgical findings. The German Shepherd Dog (GSD) was most commonly affected (40/156, 25.6%). Pelvic limb lameness, caudal lumbar pain and pain evoked by lumbosacral pressure were the most frequent clinical findings. Radiography showed lumbosacral step formation in 78.8% (93/118) of the dogs which was associated with elongation of the sacral lamina in 18.6% (22/118). Compression of the cauda equina was diagnosed by imaging (epidurography, CT, or MRI) in 94.2% (147/156) of the dogs. Loss of the bright nucleus pulposus signal of the L7-S1 disc was found on T2-weighted MR images in 73.5% (25/34) of the dogs. The facet joint angle at L7-S1 was significantly smaller, and the tropism greater in GSD than in the other dog breeds. The smaller facet joint angle and higher incidence of tropism seen in the GSD may predispose this breed to DLS. Epidurography, CT, and MRI allow adequate visualization of cauda equina compression. During surgery, disc protrusion was found in 70.5% (110/156) of the dogs. Overall improvement after surgery was recorded in the medical records in 79.0% (83/105) of the dogs. Of the 38 owners that responded to questionnaires up to five years after surgery, 29 (76%) perceived an improvement.     

Influence of intervertebral disc fenestration at the herniation site in association with hemilaminectomy on recurrence in chondrodystrophic dogs with thoracolumbar disc disease: a prospective MRI study

Objective— To describe the influence of fenestration at the disc herniation site on recurrence in thoracolumbar disc disease of chondrodystrophoid dogs.
Study Design— Prospective clinical study.
Animals— Chondrodystrophic dogs (n=19).
Methods— Dogs were divided into 2 groups: group 1 (9 dogs) had thoracolumbar disc extrusion (Hansen type I) treated by hemilaminectomy and concomitant fenestration of the affected intervertebral disc and group 2 (10 dogs) had hemilaminectomy without fenestration. All dogs had 3 magnetic resonance imaging (MRI) examinations: preoperatively, immediately postoperatively to assess removal of herniated disc material, and again 6 weeks after surgery.
Results— There were 13 male and 6 female dogs; mean age, 7.1 years. Thoracolumbar disc herniation was confirmed with MRI. Immediate post surgical MRI revealed that the herniated disc removal was complete in all but 1 dog and that fenestration did not lead to complete removal of nucleus pulposus within the intervertebral disc space. On the 3rd MRI examination, none of the group 1 dogs had further disc material herniation at the fenestrated site. Six of the 10 group 2 dogs had a recurrence of herniation leading to clinical signs in 3 dogs (pain in 2 dogs, paresis in 1 dog).
Conclusion— In thoracolumbar disc herniation, fenestration of the affected intervertebral disc space prevents further extrusion of disc material.
Clinical Relevance— Fenestration reduces the risk of early recurrence of disc herniation and associated postoperative complications.     

Immunhistochemical Demonstration of Lumbar Intervertebral Disc Innervation in the Dog

Low back pain is a common ailment in dogs, particularly in specific breeds as for instance the German shepherd dog. A number of structures such as facet joint capsules, ligaments, dorsal root ganglia, periosteum, vertebral endplate, and meninges have been associated with this condition. However, in a substantial proportion of all cases, the origin of pain remains obscure. A further structure often being involved in vertebral column disorders is the intervertebral disc. However, the presence of nerves is a precondition for pain sensation and, consequently, structures lacking sensory innervation can be left out of consideration as a cause for low back pain. Nerve fibres have been demonstrated at the periphery of intervertebral discs in man, rabbit and rat. With regard to the dog, however, extent of intervertebral disc innervation still is disputed. The goal of the present study, therefore, was to assess previous findings based on silver impregnation. Protein gene product (PGP) 9.5 was used as a marker for immunohistochemical examination of serial transversal and sagittal paraffin sections of lumbar discs from adult dogs. This technique revealed nerve fibres to be confined to the periphery of the intervertebral discs. Thus, even limited pathological processes affecting the outer layers of the intervertebral disc are prone to cause low back pain.     

Micro Total Hip Replacement for Dogs and Cats: Surgical Technique and Outcomes

Objective: To describe the surgical technique for the micro total hip replacement (Micro THR) system and report clinical outcomes. Study Design: Prospective study. Animals: Dogs (n=49) and cats (n=8) with coxofemoral arthropathy. Methods: Small breed dogs and cats with coxofemoral arthritis were enrolled for Micro THR. Patient data were recorded. Implant positioning and cement mantle quality were evaluated radiographically. Orthopedic examinations and client interviews were used to assess outcome. Results: Micro THR was performed unilaterally (40 dogs, 8 cats) and staged bilaterally (9 dogs) to resolve pain associated with osteoarthritis or trauma. Mean body weight was 7.2 kg. Postoperative complications included prosthesis luxation (9), cup aseptic loosening (1), and sciatic neurapraxia (1). Mean radiographic follow up was 96.1 weeks; 10 joints were followed for ≥3.0 years. Sixty of the 66 (91%) Micro THRs had excellent outcomes. Two dogs (<2.75 kg) were too small for the prosthesis and 4 dogs with unmanageable luxation had explantation. Conclusions: Micro THR is considered a satisfactory procedure for management of small breed dogs and cats with coxofemoral disease unresponsive to medical management. Clinical Relevance: Micro THR is a viable option to treat disabling disorders of the hip. More than 170 cat and small dog breeds, and many mixed breeds, could benefit from Micro THR surgery.     

Reoperative neurosurgery in dogs with thoracolumbar disc disease

OBJECTIVE: To characterize the subset of dogs in our neurosurgical practice that underwent spinal surgery for thoracolumbar (TL) disc herniation and subsequently underwent additional decompressive TL surgery. STUDY DESIGN: A retrospective case series. SAMPLE POPULATION: Thirty dogs that underwent reoperation for TL disc herniation. A comparison group of Dachshunds that underwent only one decompressive TL disc surgery was also studied. METHODS: Dogs that underwent reoperation were divided into two groups based on the interval between their first and second surgery. The early reoperation group included those dogs having a second surgery less than 4 weeks after the initial operation. The late reoperation group included those dogs having a second surgery more than 4 weeks after the initial operation. For each Dachshund in the late reoperation group, two Dachshunds that underwent only one decompressive TL disc surgery were selected and formed the comparison group. Dogs in the comparison group were matched with reoperated cases based on the severity of preoperative neurologic deficit and site of disc herniation. These two groups were compared to determine: (1) if age and body weight were risk factors for reoperation, and (2) if dogs had a poorer functional outcome after their second decompressive surgery than did those in the comparison group after their first (and only) decompressive surgery. RESULTS: A total of 30 of 467 (6.4%) dogs that underwent decompressive TL disc surgery were reoperated. In the early reoperative cases (n = 5 dogs), the inciting cause in all cases was residual compression from disc material at the site of the initial surgery. In the late reoperation group, 22 of 25 (88%) cases had a second disc herniation at a site distinct from the initial lesion. Dachshunds had a significantly higher risk for late reoperation (odds ratio and 95% CI = 3.67, 1.46 to 10.03); other small and medium-sized breeds (<20 kg) were underrepresented. Age and body weight were not significant predictors for reoperation. A total of 21 of 23 (91%) dogs had functional recovery after late reoperation. Complete sensorimotor loss was a significant negative predictor of functional recovery in the late reoperative cases (P = .01). Likelihood of functional recovery in dogs after their second decompressive surgery was identical to the functional recovery of dogs in the comparison group. CONCLUSIONS AND CLINICAL RELEVANCE: Our results show that a second disc herniation occurring at a site distinct from the initial lesion is the most common cause for reoperation and that Dachshunds have a significantly greater risk than other breeds.     

ACCURACY OF SURVEY RADIOGRAPHIC DIAGNOSIS OF INTERVERTEBRAL DISC PROTRUSION IN DOGS

To assess the diagnostic accuracy of survey radiography for canine thoracolumbar intervertebral disc protrusion, survey radiographs (lateral and ventrodorsal) of 64 dogs with surgically-confirmed thoracolumbar intervertebral disc protrusion, 51 dogs with negative myelograms and 29 dogs with various spinal conditions other than disc protrusion were reviewed by three independent observers who were unaware of any clinical information. There were marked differences in observer performance for diagnosis of intervertebral disc protrusion, although there were no significant differences in intraobserver diagnostic accuracy for small vs. large dogs. Accuracy of observers for determining sites of intervertebral disc protrusion using survey radiography was in the range 51-61%. All observers had low accuracy for identification of second sites of intervertebral disc protrusion. The most useful radiographic sign, narrowed intervertebral space, had only moderate sensitivity (range 64-69%) and moderate predictive value (range 63-71%) for intervertebral disc protrusion. Vacuum phenomenon was an infrequent but accurate sign of intervertebral disc protrusion. Recognition of multiple radiographic signs of intervertebral disc protrusion at one site was associated with increased accuracy of diagnosis. No observer was accurate enough to justify attempting targeted surgical treatment of intervertebral disc protrusion without myelography.     

Refractive states of eyes and association between ametropia and breed in dogs

OBJECTIVE: To assess the refractive state of eyes in various breeds of dogs to identify breeds susceptible to ametropias. ANIMALS: 1,440 dogs representing 90 breeds. PROCEDURES: In each dog, 1 drop of 1% cyclopentolate or 1% tropicamide was applied to each eye, and a Canine Eye Registration Foundation examination was performed. Approximately 30 minutes after drops were administered, the refractive state of each eye was assessed via streak retinoscopy. Dogs were considered ametropic (myopic or hyperopic) when the mean refractive state (the resting focus of the eye at rest relative to visual infinity) exceeded +/- 0.5 diopter (D). Anisometropia was diagnosed when the refractive error of each eye in a pair differed by > 1 D. RESULTS: Mean +/- SD refractive state of all eyes examined was -0.05 +/- 1.36 D (emmetropia). Breeds in which the mean refractive state was myopic (< or = -0.5 D) included Rottweiler, Collie, Miniature Schnauzer, and Toy Poodle. Degree of myopia increased with increasing age across all breeds. Breeds in which the mean refractive state was hyperopic (> or = +0.5 D) included Australian Shepherd, Alaskan Malamute, and Bouvier des Flandres. Astigmatism was detected in 1% (14/1,440) of adult (> or = 1 year of age) dogs; prevalence of astigmatism among German Shepherd Dogs was 3.3% (3/90). Anisometropia was detected in 6% (87/1,440) of all dogs and in 8.9% (8/90) of German Shepherd Dogs. CONCLUSIONS AND CLINICAL RELEVANCE: Refractive states of canine eyes varied widely and were influenced by breed and age. In dogs expected to have high visual function (eg, performance dogs), determination of refractive state is recommended prior to intensive training.     

Prevalence and characterization of urinary tract infections in dogs with surgically treated type 1 thoracolumbar intervertebral disc extrusion

OBJECTIVE: To determine the prevalence of urinary tract infections (UTI), factors that correlate positively with UTI, and whether identified UTI are most likely community- or hospital acquired in dogs with surgically treated type 1 thoracolumbar intervertebral disc (IVD) extrusions. STUDY DESIGN: Prospective cross-sectional clinical study. SAMPLE POPULATION: Dogs (n=92) that were surgically treated for a thoracolumbar extradural compressive spinal cord lesion that was consistent with type 1 IVD extrusion. METHODS: Dogs were evaluated for bacterial lower UTI when possible by cystocentesis and urine culture before surgery, and 48-72, 96-120 hours, and 7 days after surgery while hospitalized. Paraparesis, confirmation of thoracolumbar extruded nucleus pulposus, and informed owner consent were required for study inclusion. Urine specimens (n=297) were cultured and both objective and subjective clinical data were obtained. RESULTS: Prevalence of UTI in dogs with surgically treated type 1 thoracolumbar IVD extrusion was 27% (25 dogs). Temporal prevalence of UTI was 15% (13/89) before surgery, 12% (11/91) at 2-3 days, 16% (12/76) at 4-5 days, and 20% (8/41) at 7 days after surgery. Statistically significant factors affecting UTI prevalence included neurologic and urinary status, sex, administration of perioperative antibiotics, and amount of time body temperature was <35 degrees C during anesthesia. CONCLUSION: UTI are common in dogs with surgically treated type 1 thoracolumbar IVD extrusion. Females, dogs that cannot ambulate or voluntarily urinate, dogs not administered perioperative cefazolin, and dogs whose body temperature falls <35 degrees C during anesthesia have a higher incidence of UTI. CLINICAL RELEVANCE: All dogs with surgically treated type 1 thoracolumbar IVD extrusion should be monitored for the presence of UTI; however, close attention should be paid to females and dogs that cannot ambulate or voluntarily urinate.     

Surgical Decompression in Dogs with Thoracolumbar Intervertebral Disc Disease and Loss of Deep Pain Perception: A Retrospective Study of 46 Cases

The case details and outcome after surgical decompression of 46 dogs with thoracolumbar intervertebral disc disease with loss of deep pain perception prior to surgery were reviewed. Nineteen dogs (41.3%) recovered with a median follow-up period of 12.5 months. Recovery was defined as an ambulatory paraparesis, or better, with urinary and fecal continence. There was a better outcome in dogs with loss of deep pain for less than 24 hours prior to surgery (19/41; 46.3% recovered) than in dogs without deep pain perception for more than 24 hours (0/5; 0% recovered). Dogs with deep pain perception present at two weeks postoperatively had significantly higher success rate (8/12; 66.7% recovered) than dogs without deep pain perception at this time period (1/10; 10.0% recovered). The return of deep pain perception by two weeks postoperatively can be a useful positive prognostic indicator.     

Surgical decompression in dogs with thoracolumbar intervertebral disc disease and loss of deep pain perception: A retrospective study of 46 cases

The case details and outcome after surgical decompression of 46 dogs with thoracolumbar intervertebral disc disease with loss of deep pain perception prior to surgery were reviewed. Nineteen dogs (41.3%) recovered with a median follow-up period of 12.5 months. Recovery was defined as an ambulatory paraparesis, or better, with urinary and fecal continence. There was a better outcome in dogs with loss of deep pain for less than 24 hours prior to surgery (19/41; 46.3% recovered) than in dogs without deep pain perception for more than 24 hours (0/5; 0% recovered). Dogs with deep pain perception present at two weeks postoperatively had significantly higher success rate (8/12; 66.7% recovered) than dogs without deep pain perception at this time period (1/10; 10.0% recovered). The return of deep pain perception by two weeks postoperatively can be a useful positive prognostic indicator.     

Complications of Methylprednisolone Sodium Succinate Therapy in Dachshunds with Surgically Treated Intervertebral Disc Disease

Objective: To compare the incidence of clinically evident post-operative complications, financial cost and length of hospital stay for Dachshunds with acute intervertebral disc disease treated with decompressive surgery with and without the use of methylprednisolone sodium succinate (MPSS).
Design: Retrospective clinical study
Setting: Veterinary Teaching Hospital
Animals: Dachshunds that presented to the Veterinary Hospital of the University of Pennsylvania between January 1994 and December 1999 with acute intervertebral disc disease that were treated with decompressive surgery.
Intervention: None
Measurements and Main Results: Dogs were divided into 2 groups dependent upon whether they had received MPSS. Medical records were examined for evidence of post-operative complications. Other parameters recorded included details of drugs administered (principally corticosteroids and gastrointestinal protectant drugs), length and cost of hospital stay and neurological status at 24 hours post-operatively and at suture removal. Compared to other corticosteroids, dogs receiving MPSS had a significantly higher incidence of clinically evident post-operative gastrointestinal complications, an increased use of gastrointestinal protectant drugs, and an increased cost for hospital stay (p<0.01).
Conclusions: The use of MPSS inDachshunds with acute intervertebral disc disease is associated with an increased post-operative complication rate and an increased financial cost to the client. The use of MPSS should be carefully evaluated for each patient.     

THORACOLUMBAR INTRADURAL DISC HERNIATION IN EIGHT DOGS: CLINICAL,LOW‐FIELD MAGNETIC RESONANCE IMAGING,AND COMPUTED TOMOGRAPHIC MYELOGRAPHY FINDINGS

Intradural disc herniation is a rarely reported cause of neurologic deficits in dogs and few published studies have described comparative imaging characteristics. The purpose of this retrospective cross sectional study was to describe clinical and imaging findings in a group of dogs with confirmed thoracolumbar intradural disc herniation. Included dogs were referred to one of four clinics, had acute mono/paraparesis or paraplegia, had low field magnetic resonance imaging (MRI) and/or computed tomographic myelography, and were diagnosed with thoracolumbar intradural disc herniation during surgery. Eight dogs met inclusion criteria. The prevalence of thoracolumbar intradural disc herniation amongst the total population of dogs that developed a thoracolumbar intervertebral disc herniation and that were treated with a surgical procedure was 0.5%. Five dogs were examined using low‐field MRI. Lesions that were suspected to be intervertebral disc herniations were observed; however, there were no specific findings indicating that the nucleus pulposus had penetrated into the subarachnoid space or into the spinal cord parenchyma. Thus, the dogs were misdiagnosed as having a conventional intervertebral disc herniation. An intradural extramedullary disc herniation (three cases) or intramedullary disc herniation (two cases) was confirmed during surgery. By using computed tomographic myelography (CTM) for the remaining three dogs, an intradural extramedullary mass surrounded by an accumulation of contrast medium was observed and confirmed during surgery. Findings from this small sample of eight dogs indicated that CTM may be more sensitive for diagnosing canine thoracolumbar intradural disc herniation than low‐field MRI.     

Assessment of the geometry of the cubital (elbow) joint of dogs by use of magnetic resonance imaging

OBJECTIVE: To assess joint geometry and highlight potential evidence of physiologic incongruity in cubital (elbow) joints of large, small, and chondrodystrophic breeds of dogs. SAMPLE POPULATION: Nonarthritic elbow joints obtained from cadavers of mature dogs of large breeds (n = 19), small breeds (14), or chondrodystrophic breeds (8). PROCEDURE: Magnetic resonance imaging was used to quantify interosseous gaps at 6 defined positions and 2 sagittal planes of the humeroantebrachial region by use of a fat-suppressed 3-dimensional gradient-echo sequence. RESULTS: Interosseous gaps in the more medially located sagittal plane were significantly narrower at the level of the anconeal process than at any other position of the joint in large-breed dogs, compared with results for small- or chondrodystrophic-breed dogs. In both sagittal planes, the gaps were significantly wider at the center of the ulnar trochlear notch than at any other position. Significant correlation between body weight and width of the interosseous gaps was found only in large-breed dogs and was found in both sagittal planes at the center of the ulnar trochlear notch (r, 0.834 and r, 0.680, respectively). CONCLUSIONS AND CLINICAL RELEVANCE: In large-breed dogs, the interosseous gap was especially narrow at the level of the anconeal process and its diametric position. This suggests less ability to compensate intra-articular steps in dogs with short ulna syndrome, which predisposes to failure of the union between the anconeal process and olecranon. Geometric incongruity may be regarded as clinically normal in nonarthritic humeroulnar joints. The degree of geometric incongruity increases with body weight.