PUNCTURE WOUNDS INTO THE NAVICULAR BURSA OF THE HORSE

Radiography was used to evaluate 32 horses presented for puncture wounds into the navicular bursa. At the initial radiographic examination, 21 horses had no radiographic signs of osteomyelitis, while 11 did. The mean-time interval between injury and radiographic examination was 20.6 days for horses without evidence of osteomyelitis and 59.3 days for those with evidence of osteomyelitis. Radiographic signs of osteomyelitis of the navicular bone included flexor cortical destruction and irregularity of the flexor surface. Other abnormalities included pathologic fracture of the navicular bone, subluxation of the distal interphalangeal joint, or secondary joint disease. The lateromedial and palmaroproximal-palmarodistal oblique projections were most useful for identifying abnormalities of the navicular bone. There was a high correlation between horses that had positive presurgical radiographic signs and surgical findings. However, approximately 50% of horses that had negative radiographic findings initially had positive surgical findings. Ten of 21 horses with negative radiographic findings on initial examination had evidence of bony lesions when reevaluated from 3 weeks to 6 years later. Nine of 11 horses with radiographic signs of osteomyelitis on initial radiographic examination were euthanatized or had an unsatisfactory outcome. Seven of 10 horses with radiographic signs on reexamination were euthanatized. Thirteen of 20 horses with positive surgical findings for navicular bone infection were euthanatized or had an unsatisfactory outcome.     

RADIOGRAPHIC APPEARANCE OF THE NAVICULAR BONE AND DISTAL INTERPHALANGEAL JOINT AND THEIR RELATIONSHIP WITH OSSIFICATION OF THE COLLATERAL CARTILAGES OF THE DISTAL PHALANX IN FINNHORSE CADAVER FOREFEET

Radiographic findings in the navicular bone and distal interphalangeal joint as well as the ossification status of the collateral cartilages of the distal phalanx were evaluated in 100 Finnhorse cadaver forefeet. The most common shapes of the proximal articular margin of the navicular bone were convex and straight. Remodeling of the navicular bone was common, especially on the lateral extremity. No bony fragments were identified at the distal flexor margin even though this area appeared irregular in several feet. Several large, rounded or lollipop-shaped synovial invaginations were identified in only six feet. The thickness of the flexor cortex varied considerably, and the corticomedullary junction was uni- or bilaterally indistinct in nine feet. The shape of the sagittal ridge of the flexor cortex was commonly flat but varied. It appeared locally irregular or indistinct in 17 feet, but changes elsewhere along the flexor cortex were rare. Osteophytosis on the dorsal and palmar margins of the distal interphalangeal joint and entheseophytosis on the dorsal aspect of the middle phalanx and on the extensor process of the distal phalanx were common. "Possibly significant" ossification of the collateral cartilages (high side-bones or separate centers of ossification) was present in 36 feet; all grades of ossification in the proximal/ palmaroproximal direction as well as palmar ossification were seen. A statistically significant relationship was found between entheseophytosis on the proximal flexor margin of the navicular bone and "possibly significant" ossification. Osteophytosis on the palmarodistal margin of the middle phalanx was more common in feet with a relatively long distal phalanx, suggestive of palmar ossification. Radiographic changes in the navicular bone or in the distal interphalangeal joint did not otherwise appear to be associated with ossification of the collateral cartilages of the distal phalanx in Finnhorses.     

SALINE ARTHROGRAPHY OF THE DISTAL INTERPHALANGEAL JOINT FOR LOW‐FIELD MAGNETIC RESONANCE IMAGING OF THE EQUINE PODOTROCHLEAR BURSA: FEASIBILITY STUDY

Abnormalities of the deep digital flexor tendon, navicular bone, and collateral sesamoidean ligament can be difficult to visualize using magnetic resonance imaging (MRI) if bursal fluid is absent. The use of saline podotrochlear bursography improves podotrochlear apparatus evaluation, however, the technique has disadvantages. The objective of this prospective feasibility study was to describe saline arthrography of the distal interphalangeal joint as an alternative technique for improving MRI visualization of the deep digital flexor tendon, navicular bone, collateral sesamoidean ligament, and podotrochlear bursa, and to compare this technique with saline podotrochlear bursography. Eight paired cadaver forelimbs were sampled. Saline podotrochlear bursography or saline arthrography techniques were randomly assigned to one limb, with the alternate technique performed on the contralateral limb. For precontrast and postcontrast studies using each technique, independent observers scored visualization of the dorsal aspect of the deep digital flexor tendon, palmar aspect of the navicular bone, collateral sesamoidean ligament, and podotrochlear bursa. Both contrast techniques improved visualization of structures over precontrast MR images and visualization scores for both techniques were similar. Findings from this study demonstrated that saline arthrography is feasible and comparable to saline podotrochlear bursography for producing podotrochlear bursa distension and separation of the structures of the podotrochlear apparatus on nonweight bearing limbs evaluated with low‐field MRI. Clinical evaluation of saline arthrography on live animals is needed to determine if this technique is safe and effective as an alternative to saline podotrochlear bursography in horses with suspected pathology of the podotrochlear apparatus.     

POSITIVE CONTRAST MAGNETIC RESONANCE BURSOGRAPHY FOR ASSESSMENT OF THE NAVICULAR BURSA AND SURROUNDING SOFT TISSUES

Magnetic resonance (MR) imaging is often performed to determine the cause of palmar heel pain. We evaluated how distension of the navicular bursa affected the MR appearance of the navicular bursa and associated structures. An MR evaluation was performed on normal cadaver limbs and cadaver limbs from horses with lameness localized to the foot. The normal navicular bursae were injected with 2, 4, or 6 ml of solution. The bursae of the feet from lame horses were injected with 4 or 6 ml, and the MR study was repeated. All bursae were examined grossly to verify the presence or absence of adhesions. Clinical patients that had initial MRI abnormalities suggesting adhesions were also evaluated. Distension of the proximal recess of the normal navicular bursa, proximal to the collateral sesamoidean ligament was achieved with 2 ml. Separation of the collateral sesamoidian ligament from the deep digital flexor tendon (DDFT) was achieved with 4 ml. The separation of the navicular bone from the DDFT and distal sesamoidian impar ligament required 6 ml. Adhesions were more clearly defined in the bursa of the two pathologic cadaver limbs following distension. MR bursography used on clinical patients allowed the determination of the presence or absence of adhesions. In these horses, this determination could not have been definitively made without this technique. MR bursography is useful in horses where the presence of adhesions cannot be clearly defined by MRI.     

FEASIBILITY FOR ULTRASOUND‐GUIDED INJECTION OF THE COLLATERAL LIGAMENTS OF THE DISTAL INTERPHALANGEAL JOINT IN HORSES

Desmitis of the collateral ligament of the distal interphalangeal joint is a cause of lameness in performance horses. The objective of this prospective, experimental, ex vivo feasibility study was to evaluate the success of ultrasound‐guided injection of the collateral ligaments of the distal interphalangeal joint in the equine forelimb. Seventy‐six ultrasound‐guided dye injections of the collateral ligament of the distal interphalangeal joint were performed on horses’ cadaver limbs. The hooves were sectioned transversely to verify the location of the dye relative to the collateral ligaments and surrounding structures. Evaluations of transverse sections were performed independently by two experienced observers. A scoring system was used to assess injection of the collateral ligament of the distal interphalangeal joint at the proximal, middle, and distal aspect over the length of the ligament. The collateral ligament was injected at any point in 97.4% of cases. The ligament was injected over the entire scored length in 43.2% of cases (32/74), over two scored length areas in 45.9% of cases (34/74), and in one area in 10.8% of cases (8/74). The distal interphalangeal joint and the common digital extensor tendon were also injected in 81.6% (62/76) and 43.4% (33/76) of the cases, respectively. Use of the ultrasound had a positive and negative predictive value of 98% and 9%, respectively. In this study, ultrasound guidance was useful for confirming injection of the collateral ligament of the distal interphalangeal joint but did not prevent injecting the distal interphalangeal joint and the common digital extensor tendon.     

COMPUTED TOMOGRAPHIC ANATOMY OF THE DISTAL EXTREMITY OF THE HORSE

X-ray computed tomography (CT) is an imaging tool that is becoming increasingly available for use in veterinary medicine. Advantages, including depiction of detailed cross-sectional anatomy, improved contrast resolution, and computer reformatting, make it a potentially valuable diagnostic technique. Veterinary application of CT has been primarily limited to use in small animals. Current reports describe the technique for use in the horse, but there are no published studies correlating serial CT images with equine cross-sectional anatomy. A study of the distal extremity of the horse was undertaken to facilitate interpretation of images produced using CT. Transverse CT images of the distal forelimb of equine cadavers were evaluated relative to gross anatomic dissection. Resolution of bone architecture in transverse plane images was satisfactory, but soft-tissue' resolution, although satisfactory for visualization of major structures, was relatively poor, probably due to lack of interposed fat and insufficient differences in physical density and atomic number. Thus it appears in the equine distal limb that CT may be most useful for evaluation of complex bone abnormalities.     

RADIOGRAPHIC STUDY OF DISTAL RADIAL PHYSEAL CLOSURE IN THOROUGHBRED HORSES

Monthly radiography was performed to study distal radial physeal closure in ten male and ten female Throughbred horses. The height, thoracic circumference and metacarpus circumference were also measured. Distal radial physeal closure time was sooner in females than males, and took 701 ± 37 and 748 ± 55 days respectively.     

INJURY OF THE COLLATERAL LIGAMENTS OF THE DISTAL INTERPHALANGEAL JOINT DIAGNOSED BY MAGNETIC RESONANCE

We describe the clinical, imaging, and necropsy findings of two horses with severe injury of the collateral ligaments of the distal interphalangeal (DIP) joint diagnosed using magnetic resonance (MR) imaging. In MR images it was possible to examine the collateral ligaments of the DIP joint from the origin at the middle phalanx to the insertion on the distal phalanx. Both horses in this report had abnormal high signal intensity within the collateral ligaments of the DIP joint, and one horse had abnormal high signal intensity within the bone of the distal phalanx on short tau inversion recovery (STIR) and T2-weighted imaging sequences. High signal intensity on STIR and T2-weighted images represents abnormal fluid accumulation indicative of inflammation, within ligament, tendon, or bone on these imaging sequences. Abnormalities were confirmed on necropsy in both horses. Injury of the collateral ligaments of the DIP joint should be considered as a source of pain in horses with lameness localized to the foot.     

RADIOGRAPHIC QUANTIFICATION OF TRACHEAL DIMENSIONS OF THE NORMAL THOROUGHBRED HORSE

Radiographic measurement of tracheal dimensions in the horse may be useful in evaluating upper and lower respiratory tract conditions due to the gradient of pressure changes between these areas. Lateral radiographs of the trachea of 15 normal sedated Thoroughbred horses were made at inspiration and expiration and magnification-corrected mean airway heights measured were, respectively: larynx: 5.89 and 5.86 cm; trachea at the third cervical vertebra (C3): 4.17 and 4.04 cm; at the fifth cervical vertebra (C5): 3.62 and 3.59 cm; at the first thoracic vertebra (T1): 3.4 and 3.23 cm; and carina: 3.85 and 4.12 cm. The ratio of airway height to nearby vertebral body lengths, at inspiration and expiration were, respectively: laryngeal height at C3: 0.56 and 0.56; tracheal height at C3: 0.4 and 0.39; at C5: 0.37 and 0.37; at T1: 0.59 and 0.59; and carina height: 0.91 and 0.94. The ratio of tracheal height to the thoracic inlet at inspiration and expiration was, respectively, 0.15 and 0.15. There was not a statistically significant association between airway diameter and phase of respiration. No association was found between tracheal height and body mass or height at the withers. Radiographic tracheal height can be measured independent of respiratory phase in sedated horses. It is suggested that the ratio of tracheal height to an adjacent bony landmark is more reliable for comparison between horses and tracheal height measurement should be made at C5, due to a lower standard deviation. If only thoracic radiographs are made, measurements of tracheal height at the thoracic inlet may be valuable.     

SPONTANEOUS RESOLUTION OF A PSEUDOANEURYSM IN A HORSE FOLLOWING ANGIOGRAPHIC DIAGNOSIS

Angiography in a horse was used to confirm a pseudoaneurysm of the dorsal metatarsal artery originating from trauma. Gradual clinical resolution of the pseudoaneurysm occurred within days following the procedure. A follow-up angiogram confirmed the clinical impression. An etiology of the spontaneous resolution is presented. Probable influences included technical factors of the injection procedure that caused prolonged presence of the contrast medium within the aneurysmal sac and factors that enhance thrombus formation during angiography.     

MAGNETIC RESONANCE IMAGING FINDINGS OF DESMOPATHY OF THE COLLATERAL LIGAMENTS OF THE EQUINE DISTAL INTERPHALANGEAL JOINT

We report the use of a low-field magnetic resonance (MR) imaging system for the detection of desmopathy of the collateral ligament of the distal interphalangeal joint and the long-term outcome. Twenty horses were studied and their medical records and MR images were reviewed retrospectively. Long-term follow-up information was obtained by telephonic questionnaires of owners, trainers, or referring veterinarians. Desmopathy of the medial collateral ligament (80%) and enthesopathy of the affected collateral ligament (80%) were common MR imaging features. Treatment consisted of stall rest followed by a rehabilitation period. Additional treatments included shoeing, extracorporeal shock wave therapy, application of a half limb or foot cast, and medication of the distal interphalangeal joint. Twelve (60%) horses returned to their previous level of exercise and maintained their previous level, whereas eight horses had a poor outcome. Low-field MR imaging in the standing patient can be used to detect collateral ligament desmopathy of the distal interphalangeal joint without a need for general anesthesia.     

ULTRASONOGRAPHY OF THE SOLAR ASPECT OF THE DISTAL PHALANX IN THE HORSE

Ultrasonographic examinations were performed on the solar aspect of the distal phalanx of 10 feet of five normal live horses (Group 1), 22 feet of seven normal cadavers (Group 2), and nine feet of five horses with pathology of the dorsal solar aspect of the distal phalanx (Group 3). Lateromedial radiographs of the distal phalanx were made in all groups, and in Group 2, digits were sagitally sectioned after imaging. The ultrasonographic and radiographic appearance of the sagittal solar aspect of the distal phalanx was described. Measurements of the distance between the sole and the distal tip of the distal phalanx (A), the solar aspect of the apex of the frog and the distal phalanx (B), and the body of the frog's surface and flexor surface of the distal sesamoid bone (C) were made ultrasonographically, radiographically, and on the sectioned cadaver specimens. There was no statistical difference between the radiographic, ultrasonographic, and direct cadaver measurements in A and C. In B, there was a statistical difference between the radiographic, ultrasonographic, and cadaver measurements-most likely as a result of the difference in trimming of the frog apex. Ultrasonographic and radiographic examination of the nine feet of the five horses in Group 3 were performed and the abnormalities described. Color flow and power Doppler ultrasonography were performed on the normal sagittal solar distal phalanx, on the impar distal sesamoidean ligament, and at the insertion of the deep digital flexor tendon on the facies flexoria of the distal phalanx. Power Doppler in these horses showed blood flow at 0.16-0.48 kHz at the tip of the distal phalanx and at 0.16 kHz at the deep digital flexor tendon insertion and in the impar distal sesamoidean ligament. Using color flow Doppler in normal horses mean blood flows ranged from 1.8 to 5.4 cm/s at the tip of the distal phalanx and 1.8-2.0 cm/s at the deep digital flexor tendon insertion and in the impar distal sesamoidean ligament.     

ACCURACY OF LOW‐FIELD MAGNETIC RESONANCE IMAGING VERSUS RADIOGRAPHY FOR GUIDING INJECTION OF EQUINE DISTAL INTERPHALANGEAL JOINT COLLATERAL LIGAMENTS

Desmopathy of the distal interphalangeal joint collateral ligament is a common cause of lameness in the horse and carries a variable prognosis for soundness. Intralesional treatment has been proposed for improving outcome; however, limited reports describe methods for injecting this ligament. The purpose of this study was to compare accuracy of low‐field magnetic resonance imaging (MRI) vs. radiography for injecting the collateral ligament of the distal interphalangeal joint. Equine cadaver digit pairs (n = 10) were divided by random assignment to injection of the ligament by either technique. An observer unaware of injection technique determined injection success based on postinjection MRI and/or gross sections acquired from the proximal, middle, and distal portions of the ligament. McNemar's test was performed to determine statistical difference between injection techniques, the number of injection attempts, and injection of the medial or lateral collateral ligament. Magnetic resonance imaging guided injection was successful more frequently than radiographic‐guided injection based on postinjection MRI (24 of 30 vs. 9 of 30; P = 0.0006) and gross sections (26 of 30 vs. 13 of 30; P = 0.0008). At each level of the ligament (proximal, middle, and distal), MRI‐guided injection resulted in more successful injections than radiographic guidance. Statistical significance occurred at the proximal aspect of the collateral ligament based on postinjection MRI (P = 0.0143) and the middle portion of the ligament based on gross sections (P = 0.0253). Findings supported future testing of standing, low‐field MRI as a technique for delivering intralesional regenerative therapy in live horses with desmopathy of these collateral ligaments.     

USE OF RADIOGRAPHY, COMPUTED TOMOGRAPHY AND MAGNETIC RESONANCE IMAGING FOR EVALUATION OF NAVICULAR SYNDROME IN THE HORSE

Radiographic evaluation of navicular syndrome is problematic because of its inconsistent correlation with clinical signs. Scintigraphy often yields false positive and false negative results and diagnostic ultrasound is of limited value. Therefore, we assessed the use of computed tomography and magnetic resonance imaging in a horse with clinical and radiographic signs of navicular syndrome. Cadaver specimens were examined with spiral computed tomographic and high-field magnetic resonance scanners and images were correlated with pathologic findings. Radiographic changes consisted of bony remodeling, which included altered synovial fossae, increased medullary opacity, cyst formation and shape change. These osseous changes were more striking and more numerous on computed tomographic and magnetic resonance images. They were most clearly defined with computed tomography. Many osseous changes seen with computed tomography and magnetic resonance imaging were not radiographically evident. Histologically confirmed soft tissue alterations of the deep digital flexor tendon, impar ligament and marrow were identified with magnetic resonance imaging, but not with conventional radiography. Because of their multiplanar capability and tomographic nature, computed tomography and magnetic resonance imaging surpass conventional radiography for navicular imaging, facilitating earlier, more accurate diagnosis. Current advances in imaging technology should make these imaging modalities available to equine practitioners in the future.     

DETECTION OF A RADIOGRAPHICALLY OCCULT FRACTURE OF THE LATERAL PALMAR PROCESS OF THE DISTAL PHALANX IN A HORSE USING COMPUTED TOMOGRAPHY

A horse with a suspected injury of the distal phalanx was examined using radiography at day two and 19 after the onset of the lameness, with no definite diagnosis. Using computed tomography an incomplete fracture of the lateral wing of the distal phalanx was diagnosed at day 25. Based on computed tomography it was determined that the fracture probably did not enter the joint or involve the palmar cortex throughout its length which were of prognostic importance. The day following the CT examination a new oblique radiographic projection was made. In this radiography which was based on, and never would have been attempted without, the information about the geometric pattern of the fracture achieved by CT examination, a radiolucent area indicative of a wing fracture was seen. This report emphasizes the value of computed tomography in diagnosing a geometric complicated nonarticular oblique fracture of the palmar process of the pedal bone in a horse.     

IMPROVED IDENTIFICATION OF THE PALMAR FIBROCARTILAGE OF THE NAVICULAR BONE WITH SALINE MAGNETIC RESONANCE BURSOGRAPHY

Fibrocartilage degeneration is the earliest pathologic finding in navicular disease but remains difficult to detect, even with magnetic resonance (MR) imaging. We hypothesized that injection of the navicular bursa with saline would improve accuracy of MR imaging evaluation of palmar fibrocartilage. Thoracic limbs were collected from 11 horses within 6 h of death. Imaging was performed with a 1.5 T magnet using sagittal 2D proton density and transverse 3D FLASH sequences with fat saturation. For the purpose of determining sensitivity and specificity of the MR images, fibrocartilage was classified as normal or abnormal, based on combination of the findings of gross and microscopic pathology. Thickness of fibrocartilage was measured on histologic sections and corresponding transverse FLASH MR images before and after injection of saline. A paired Student's t- test was used for comparison of measurements. Partial thickness fibrocartilage loss was present in 6 of 22 limbs. Sensitivity of precontrast MR images for detection of lesions was 100% while specificity was 6%. Saline MR arthrography resulted in both sensitivity and specificity of 100% based on consensus review. Mean histologic fibrocartilage thickness was 0.75±0.12 mm. Mean fibrocartilage thickness on precontrast transverse FLASH images was 0.93±0.065 and 0.73±0.09 mm on postsaline images. The histologic cartilage thickness was signficantly different from that in precontrast images ( P <0.001) but not in images acquired after saline injection ( P =0.716). Based on our results, and using pulse sequences as described herein, navicular fibrocartilage can only be evaluated reliably for the presence of partial thickness lesions after intrabursal injection of saline.     

NEGATIVE CONTRAST PERITONEOGRAPHY IN THE HORSE

A method of negative contrast peritoneography using CO₂ peritoneal insufflation technique was investigated in adult horses. Radiographic visualization of anatomic structures in the dorsal abdomen, including the kidneys, portions of the spleen and liver, dorsal stomach and mesenteric root region, was enhanced. Visualization of ventral abdominal structures was not enhanced. Negative contrast peritoneography allowed reduction in the radiographic technique from 140 kVp and 40 mAs before insufflation to 100 kVp and 5–10 mAs following insufflation. The technique was easily and safely performed with minimal patient discomfort and risk.     

RADIOGRAPHIC APPEARANCE OF THE NAVICULAR BONE IN SOUND HORSES

Radiographs of the navicular bone in 523 sound horses were reviewed. Detailed evaluation criteria were used. The incidence of radiographic changes and variations in normal horses were recorded. Results were tested for right-left limb difference and for age relationship. Variation in shape and bone structure was commonly seen in the navicular bone. Radiographic changes with an incidence of less than 2% included flexor cortex defects and calcification on the flexor surface. Fragments at the distal navicular bone border, calcification in the impar ligament and enthesiophytes at the proximal border were radiographic findings with an incidence of 2% to 10%. Abnormal canals at the distal border were found in 11% horses. Elongation of the lateral proximal extremity was commonly found. The mean width of the flexor cortex was 3.6 mm.