Effect of computed tomography display window and image plane on diagnostic certainty for characteristics of dysplastic elbow joints in dogs

OBJECTIVE: To test the effects of computed tomography (CT) image plane and window settings on diagnostic certainty for CT characteristics associated with dysplastic elbow joints (elbow joint dysplasia) in dogs and to provide optimal display guidelines for these CT characteristics. SAMPLE POPULATION: CT images of 50 dysplastic elbow joints from 49 lame dogs and 10 elbow joints from 5 sound dogs. PROCEDURES: CT image data were obtained in transverse, sagittal, and dorsal planes. Each plane was examined by use of 3 Hounsfield unit (HU) window settings. Two veterinary radiologists independently evaluated sets of CT images for evidence of 7 CT characteristics. Effect of elbow joint status, image plane, and window settings on diagnostic certainty for these CT characteristics was tested by use of a visual analogue scale. RESULTS: Diagnostic certainty for abnormalities of the medial coronoid process (MCP) and radial incisure was highest in the transverse plane, subchondral defects or sclerosis of the trochlea humeri was highest in the dorsal plane, and joint incongruity was highest in the sagittal plane. Certainty for hypoattenuating subchondral defects or fissures was highest at 2,500 or 3,500 HUs, whereas certainty for subchondral sclerosis was highest at 1,500 HUs and lowest at 3,500 HUs. CONCLUSIONS AND CLINICAL RELEVANCE: Diagnostic certainty for CT characteristics of elbow joint dysplasia in dogs was affected by image display variables. Diagnostic certainty for altered subchondral bone density was primarily influenced by window settings, whereas structural MCP abnormalities and joint incongruity were influenced most by image plane.     

Use of reconstructed computed tomography for the assessment of joint spaces in the canine elbow

OBJECTIVES: To assess the accuracy of reconstructed computed tomography for imaging canine elbow joint spaces. METHODS: Computed tomography scans of eight cadaveric elbows were obtained and reconstructed computed tomography images were formatted in the dorsal and sagittal planes. Humeroradial and humeroulnar joint space measurements were obtained from these images. Intra-observer and inter-observer variations in joint space measurements were assessed, as was the effect of specimen positioning (inter-image variation). After freezing, four elbows were sectioned in the dorsal plane and four in the sagittal plane. In addition to visual comparison of the frozen sections with reconstructed computed tomography images, joint space measurements were obtained from frozen sections and compared with those from reconstructed computed tomography images. Variation was assessed using statistical calculations and graphical techniques. RESULTS: Both inter-image and intra-observer analyses revealed good agreement and low variation between data sets. Inter-observer correlation was only moderate, though variation was low. Visually, the reconstructed computed tomography images accurately reflected the frozen section anatomy. Agreement between frozen section and reconstructed computed tomography joint space measurements was good, with minimal variation. CLINICAL SIGNIFICANCE: These results indicate that reconstructed computed tomography is capable of accurately imaging elbow joint spaces and precise joint space measurements can be obtained. Reconstructed computed tomography may be useful for determining joint space measurements and detecting elbow incongruencies in dogs with elbow dysplasia.     

Correlation of ultrasonographic observations with anatomic features and radiography of the elbow joint in dogs

OBJECTIVE: To define the ultrasonographic appearance of the elbow joint of dogs and to develop an ultrasonographic imaging protocol to reliably accomplish complete evaluation of that joint. ANIMALS: 11 clinically normal mixed-breed dogs. PROCEDURE: Ultrasonographic observations (by use of a 5 to 10 MHz linear array probe) were made of 22 elbow joints in cadaveric forelimbs from clinically normal dogs. Images in standard anatomic planes were recorded with a multi-image camera, on videotape, or onto a computer. The anatomic plane of the ultrasonographic beam and position of the ultrasonographic probe were also recorded. Dissection of each elbow joint was performed, and anatomic features were correlated with ultrasonographic images. RESULTS: Structures clearly identified ultrasonographically included the lateral and medial humeral epicondyles, the humeroradial and humeroulnar joints, anconeal process, medial coronoid process, hyaline cartilage covering the proximal articular surface of the radius, collateral ligaments, tendons of triceps brachii and supinator muscles, and the supinator tendon and sesamoid in the supinator cartilage. An ultrasonographic imaging protocol for examination of the elbow joint was developed. CONCLUSIONS AND CLINICAL RELEVANCE: Precise correlations were established between the gross anatomic appearance of the elbow joint and the ultrasonographic images of its component structures. The ultrasonographic imaging protocol will enable complete examination of all regions of the joint for detection of pathologic lesions.     

COMPUTED TOMOGRAPHY AND POSITIVE CONTRAST COMPUTED TOMOGRAPHIC ARTHROGRAPHY OF THE CANINE SHOULDER: NORMAL ANATOMY AND EFFECTS OF LIMB POSITION ON VISIBILITY OF SOFT TISSUE STRUCTURES

Soft tissue injuries of the shoulder are an important cause of forelimb lameness in dogs. The objectives of this canine cadaver study were to describe normal anatomy of shoulder soft tissue structures using computed tomography (CT) and computed tomographic arthrography (CTA) and to determine the effects of positioning on visualization of shoulder soft tissue structures. Thirteen forelimbs were removed from eight canine cadavers. Two forelimbs were used for contrast dose optimization. For the remaining 11 forelimbs, shoulder CT and CTA were performed using three defined joint angles (140°, 90°, and 70°). For three forelimbs, CT and CTA images were compared with frozen anatomic sections to describe normal anatomy. Ten forelimbs were used for analysis of positioning effects. Soft tissue structures evaluated were the joint capsule, cartilage, ligaments, tendons, and muscles. A visual assessment score was assigned to each structure using a consensus of two observers. The range and mode of scores were calculated and compared for each modality and limb position. The shoulder joint capsule and medial and lateral glenohumeral ligaments were completely visible with CTA. All tendons and muscles were visualized in all the examinations except for the teres minor muscle tendon and the coracobrachialis muscle, which were not visible on all scans. Positioning the limb in an extended position significantly improved visualization of most soft tissue shoulder structures. Shoulder cartilage was best seen with CTA and with neutral or flexed positioning of the shoulder. Findings indicated that both CT and CTA are feasible imaging techniques for visualization of soft tissue structures of the canine shoulder.     

Computed tomographic osteoabsorptiometry of the elbow joint in clinically normal dogs

OBJECTIVE: To evaluate subchondral bone density patterns in elbow joints of clinically normal dogs by use of computed tomographic (CT) osteoabsorptiometry. SAMPLE POPULATION: 20 cadaver forelimbs from 10 clinically normal dogs. PROCEDURE: Each elbow joint was imaged in parasagittal and transverse planes of 1.5-mm thickness. Slice data were converted to dipotassium phosphate equivalent density (PPED) values. Sagittal, parasagittal, and transverse medial coronoid process topographic maps were constructed. Defined zones were created for each of the 3 CT planes, and confluence and peak PPED values were determined. RESULTS: The lowest PPED value was 340 mg/ml (articular and subchondral confluence), and the highest was 1780 mg/ml (peak subchondral density). Detectable effects of joint laterality were not found in the confluence or peak PPED measurements or in the peak-to-confluence PPED ratio for all 3 CT planes. Significant differences were found among zones in all 3 planes for confluence and peak PPED measurements and between sagittal and transverse planes for peak-to-confluence PPED ratios. Subjectively, the pattern of density distribution among dogs was fairly consistent for the sagittal and parasagittal slices. Three specific patterns of density distribution were apparent on the transverse topographic maps of the medial coronoid process that corresponded to conformational differences. CONCLUSIONS AND CLINICAL RELEVANCE: The use of CT osteoabsorptiometry provides a repeatable technique that can be used to noninvasively examine bone density and the effects of stress acting on joints in vivo. Variability in density values for any of the CT planes was not identified among clinically normal dogs.     

Spectrum of computed tomographic findings in 58 canine elbows with fragmentation of the medial coronoid process

O bjective : To describe in detail the computed tomographic findings in elbows of dogs with fragmentation of the medial coronoid process of the ulna.
M ethods : Retrospective review of computed tomographic images of 58 elbows that had displaced medial coronoid process fragment(s), non-displaced medial coronoid process fragment or a stable fissure in the articular cartilage of the medial coronoid process at arthroscopy.
R esults : Bone fragments were observed in 85 per cent elbows with a displaced fragment at arthroscopy, in 18 per cent elbows with a non-displaced fragment and in 29 per cent elbows with a stable fissure. Fissures in the subchondral bone were observed in computed tomographic images of 43 per cent elbows that had a stable fissure at arthroscopy. Abnormal shape, sclerosis and lucency affecting the medial coronoid process, subchondral sclerosis of the ulna and humerus, irregular radial incisure of the ulna and periarticular osteophytes were observed in a similar proportion in dogs regardless of the arthroscopic findings. Kissing lesions affecting the medial aspect of the humeral condyle were mainly associated with displaced fragments. Signs of joint incongruity were observed in dorsal and sagittal reconstructed computed tomographic images in 24 per cent elbows.
C linical S ignificance : A wide range of abnormalities may be observed in computed tomographic images of dogs with fragmented medial coronoid process. Computed tomographic is moderately sensitive for detection of fragments.     

Computed tomographic anatomy of the temporomandibular joint in the young horse

Reasons for performing study: The equine temporomandibular joint (TMJ) and its surrounding structures can be difficult to investigate in cases with a clinical problem related to the region. Little previous attention has been given either to a computed tomographic (CT) imaging protocol for the joint or an interpretation of the structures displayed in CT images of the normal joint. Objectives: To provide a CT atlas of the normal cross‐sectional anatomy of the equine TMJ using frozen and plastinated sections as anatomical reference. Methods: Eight TMJs from 4 immature pure‐bred Spanish horses were examined by helical CT. Scans were processed with a detailed algorithm to enhance bony and soft tissue. Transverse CT images were reformatted into sagittal and dorsal planes. Transverse, sagittal and dorsal cryosections were then obtained, photographed and plastinated. Relevant anatomic structures were identified in the CT images and corresponding anatomical sections. Results: In the CT images, a bone window provided excellent bone detail, however, the soft tissue components of the TMJ were not as well visualised using a soft tissue window. The articular cartilage was observed as a hyperattenuating stripe over the low attenuated subchondral bone and good delineation was obtained between cortex and medulla. The tympanic and petrous part of the temporal bone (middle and inner ear) and the temporohyoid joint were seen in close proximity to the TMJ. Conclusions: Helical CT provided excellent images of the TMJ bone components to characterise the CT anatomy of the normal joint. Potential relevance: Detailed information is provided that may be used as a reference by equine veterinarians for the CT investigation of the equine TMJ and serve to assist them in the diagnosis of disorders of the TMJ and related structures (middle and inner ear). The study was performed at an immature stage and further studies of mature individuals are required in order to confirm that the clinical interpretation is not affected by changes occurring with age.     

Radiographic measurement of canine tibial angles in the sagittal plane

Objective— To describe a method for radiographic measurement of the mechanical joint angles of the tibia in the sagittal plane and report reference ranges for a population of dogs with cranial cruciate ligament disease, and specifically for Labrador Retrievers.
Study Design— Retrospective evaluation of radiographs.
Animals— Canine tibia (n=150) of dogs evaluated for cranial cruciate ligament disease; 104 tibiae were from Labrador Retrievers, 46 tibiae were from other medium- to large-breed dogs.
Methods— Medial-lateral radiographs were used to establish anatomic landmarks and measure the mechanical cranial distal tibial angle (mCrDTA) and mechanical caudal proximal tibial angle (mCaPTA).
Results— For all tibiae mean mCrDTA was 81.6° and mCaPTA, 63.6°. For Labrador Retriever tibiae mean mCrDTA was 81.7° and mCaPTA, 63.8°. For non-Labradors, means mCrDTA was 81.5° and mCaPTA, 63°. Labrador Retrievers were significantly younger than non-Labradors in our study population. No significant differences were noted between Labrador Retrievers and non-Labradors for mCrDTA or mCaPTA and correlations between mCrDTA and mCaPTA were neither strong nor significant.
Conclusion— A method was established for radiographic measurement of mechanical joint angles of the canine tibia in the sagittal plane. Reference ranges are reported for a population of Labrador Retrievers and a population of non-Labradors with cranial cruciate ligament disease.
Clinical Relevance— Measurement method and reference ranges provided for mechanical tibial angles may be used to aid in diagnosis, surgical planning, and postoperative critique for hindlimb angular deformities.     

Heritabilities and genetic trends for elbow score as recorded by the New Zealand Veterinary Association Elbow Dysplasia Scheme (1992–2013) in four breeds of dog

AIM: To estimate the heritability of the New Zealand Veterinary Association (NZVA) elbow phenotype, obtain estimated breeding values (EBV) for the worst-elbow score and estimate the genetic trends for this trait in four populous breeds of dogs, using the records from the NZVA Canine Elbow Dysplasia Scheme database (1992–2013).

METHODS: Overall, 4,070 elbow records from a pedigree of 11,311 dogs were available for animals scored between 1992 and 2013. The worst elbow score between the left and right elbows was identified for each dog and used for EBV analysis. Estimates of heritability and EBV for the elbow score of dogs from German Shepherd dog, Labrador Retriever, Golden Retriever and Rottweiler breeds were obtained using restricted maximum likelihood procedures with a within-breed linear animal model. The model included the fixed effects of sex and birth year, with age at scoring as a covariable, and the random effect of animal. Genetic trends for the worst-elbow score were calculated as the regression coefficient of the EBV, weighted by reliabilities, on year of birth.

RESULTS: The estimates of heritability for worst-elbow score were 0.25 (SE 0.06) in German Shepherd dogs, 0.46 (SE 0.06) in Labrador Retrievers, 0.18 (SE 0.07) in Golden Retrievers and 0.29 (SE 0.11) in Rottweilers. The genetic trend for German Shepherd dogs was ?0.0082 (SE 0.0015), for Labrador Retrievers was ?0.0016 (SE 0.0016), for Golden Retrievers was ?0.0033 (SE 0.0010) and for Rottweilers was ?0.0070 (SE 0.0023) units per annum, which were different from zero (p<0.01) in all breeds except Labrador Retrievers.

CONCLUSIONS AND CLINICAL RELEVANCE: A small but favourable response to selection was achieved by three of the four breeds in the study period; during which selection for elbow traits has been largely voluntary. While the magnitude of genetic change in terms of elbow units per annum may appear small, it must be remembered that elbow scoring grades only range from 0–3. Greater improvement may be possible if compulsory screening was a requirement for pedigree breeding stock, and if greater selection pressure were applied on the basis on an individual’s EBV, rather than the worst-elbow score alone. The maintenance of an open registry, with transparency of EBV information made available to all breeders, may enhance selection intensity opportunities and potentially assist with the process and progress of breeding selection.     

Incomplete ossification of the humeral condyle in two Labrador retrievers

Incomplete ossification of the humeral condyle (IOHC) was identified in two Labrador retrievers using computed tomography. Both dogs were non-weightbearing on the affected forelimbs. The dogs were treated by means of a bone screw placed across the humeral condyle. IOHC was originally reported in spaniel and chondrodystrophic breeds. The pathogenesis of the condition remains unknown, but may be related to impaired antebrachial bone growth, similarly to the pathogeneses of elbow dysplasia and radius curvus.     

Computed Tomography of the Normal Bovine Tarsus

The objective of this study was to provide a detailed multiplanar computed tomographic (CT) anatomic reference for the bovine tarsus. The tarsal regions from twelve healthy adult cow cadavers were scanned in both soft and bone windows via a 16‐slice multidetector CT scanner. Tarsi were frozen at ?20^o C and sectioned to 10‐mm‐thick slices in transverse, dorsal and sagittal planes respecting the imaging protocol. The frozen sections were cleaned and then photographed. Anatomic structures were identified, labelled and compared with the corresponding CT images. The sagittal plane was indispensable for evaluation of bone contours, the dorsal plane was valuable in examination of the collateral ligaments, and both were beneficial for assessment of the tarsal joint articulations. CT images allowed excellent delineation between the cortex and medulla of bones, and the trabecular structure was clearly depicted. The tarsal soft tissues showed variable shades of grey, and the synovial fluid was the lowest attenuated structure. This study provided full assessment of the clinically relevant anatomic structures of the bovine tarsal joint. This technique may be of value when results from other diagnostic imaging techniques are indecisive. Images presented in this study should serve as a basic CT reference and assist in the interpretation of various bovine tarsal pathology.     

IMAGE FUSION OF COMPUTED TOMOGRAPHIC AND MAGNETIC RESONANCE IMAGES FOR THE DEVELOPMENT OF A THREE-DIMENSIONAL MUSCULOSKELETAL MODEL OF THE EQUINE FORELIMB

Biomechanical models that compute the lengths and forces of muscle-tendon units are broadly applicable to the study of factors that promote injury and the planning and effects of orthopedic surgical procedures in equine athletes. A three-dimensional (3D) generic musculoskeletal model of the equine forelimb comprised of bony segment, muscle-tendon, and ligament information, was developed based on high-resolution computed tomographic (CT) and T1-weighted magnetic resonance (MR) images from an isolated forelimb of a Thoroughbred racehorse. Image fusion was achieved through coregistration of CT and MR images with an image analysis program (Analyze) by adjustment of the relative position and orientation of fiducial markers visible in both modalities until the mutual information between the images was maximized. 3D surfaces of the bones and origin/insertion sites, centroid paths and volumes of the muscle-tendon and ligamentous structures were obtained from the multimodal (CT/MR) images using semiautomated and manual segmentation combined with sagittal and transverse color-cryosection anatomic images obtained from three other cadaveric equine forelimbs. Once bony and soft-tissue structures were reconstructed in the same coordinate system, data were imported to a software package for interactive musculoskeletal modeling (SIMM). The combination of integrated CT and MR acquisitions and anatomical images provided an accurate and efficient means of generating a 3D model of the musculoskeletal structures of an average-sized equine adult horse.     

EVALUATION OF MAGNETIC RESONANCE IMAGING TECHNIQUES IN THE EQUINE DIGIT

An anatomic study of the equine digit using magnetic resonance imaging (MRI) was performed. Seventeen isolated forelimbs and one hindleg of nine warmblood horses were imaged in transverse, sagittal, and dorsal planes with a 1.5 Tesla magnet using T1-, T2- proton density-weighted spin echo sequences as well as T2 gradient echo sequences. One scan plane in each horse was compared with corresponding anatomic and histologic sections. The best imaging planes to visualize various anatomic structures were determined. Fibrocartilage was visualized in the insertion of the deep digital flexor tendon and the suspensory ligament as well as in the distal sesamoidean ligaments. The correlation of MRI images with anatomic and histologic sections confirmed that all of the anatomic structures in the equine digit could be evaluated in PD and T2 studies.     

Helical computed tomographic anatomy of the canine abdomen

The purpose of this study was to provide an atlas of the normal anatomy of the canine abdomen using helical computed tomographic (CT) images of the abdomen in four mature cross-breed dogs. The dogs were supported in sternal recumbency under general anaesthesia and scans were performed with 5 mm collimation and a pitch of 1. All sections were imaged with soft-tissue window settings and the cranial abdomen was also imaged with mediastinum-vascular window settings. CT scans were performed immediately after iodinated contrast medium was injected into the cephalic vein at 2 mL/kg. Iodinated contrast medium (10 mL/kg) was administered orally 2 h before the scan with a further 3 mL/kg administered immediately prior to scanning. A cross-sectional anatomy atlas was used to identify the structures of the abdominal cavity. Clinically relevant anatomical structures were identified and labelled in the CT images.     

COMPUTED TOMOGRAPHIC ARTHROGRAPHY OF THE NORMAL CANINE ELBOW

Comprehensive evaluation of canine elbow joint dysfunction includes assessment of articular cartilage, which can noninvasively be performed with contrast arthrography. Aims of this prospective study were to compare positive contrast computed tomographic (CT) arthrography and histomorphometry measures of cartilage thickness in normal canine elbows, and to determine the optimal contrast medium concentration. Thirty‐two canine cadaver elbows were examined using multidetector CT, before and after intra‐articular administration of iohexol at one of three different concentrations. Articular cartilage thickness was measured on both the CT arthrography images and corresponding histologic specimens. Mean difference (bias) between the CT arthrography and histomorphologic measurements was 0.18 and 0.19 mm in the sagittal and dorsal planes, respectively. Mean bias and precision of CT arthrography measurements made in the sagittal or dorsal reformations were not significantly different from one another. Computed tomographic arthrography measurements from elbows with 75 mg I/ml were significantly larger and had greater bias compared to other contrast medium groups (150 and 37.5 mg I/ml). There was no significant difference in CT arthrography measurement precision between different contrast medium concentrations. Histomorphologic thickness of the articular cartilage overlying the cranial aspect of the ulna (mean 0.32 mm) was significantly thinner than cartilage of the radius (0.36 mm) or humerus (0.36 mm). Findings from this cadaver study indicated that CT arthrography delineates articular cartilage of the normal canine elbow; yields cartilage thickness measures slightly greater than histomorphometry measures; and provides high measurement precision regardless of image plane, contrast medium concentration, or anatomic zone.