Clinical findings, surgical techniques, prognostic factors for short-term survival and long-term outcome in horses with acquired inguinal hernias: Ninety-eight cases (2005-2020).

OBJECTIVE: To report findings, outcome and determine variables associated with survival in horses with acquired inguinal hernia (AIH). STUDY DESIGN: Retrospective study. ANIMALS: A total of 98 cases in 97 horses. METHODS: The medical records (2005-2020) of horses diagnosed with AIH were reviewed. Retrieved data included signalment, history, clinical variables, surgical aspects, postoperative complications, and short- and long-term outcomes. Logistic regression analyses were used to determine factors associated with short-term survival (p < .05). RESULTS: Manual reduction was attempted in a third of the cases (32/98, 33%) and emergency surgery to reduce the hernia was performed in 64 of 98 (65%) cases. Concurrent small intestinal (SI) volvulus was identified in 26 (26/98, 27%) cases. Castration was the most common technique used to prevent recurrence (64/94, 68%). Overall AIH recurrence rate was 11% (11/98). A total of 59 (59/98, 60%) cases survived to hospital discharge and 49 of 52 (94%) cases were still alive after 12 months. Cases admitted within 10 h of colic signs had increased odds of survival (72%) compared to those admitted after 10 h (26%; p < .001). Draft breeds (p = .021), high heart rate on admission (p = .001) and concurrent SI volvulus (p = .048) were associated with reduced survival to hospital discharge. CONCLUSIONS: Horses with AIH had a higher risk of concurrent SI volvulus and lower survival than reported. Draft breeds, high heart rate on admission and concurrent SI volvulus were associated with reduced short-term survival. CLINICAL SIGNIFICANCE: The results of this study should help in prognostication for horses with AIH.

Standing low-field MRI of the equine proximal metacarpal/metatarsal region is considered useful for diagnosing primary bone pathology and makes a positive contribution to case management: A prospective survey study.

High-field MRI of the proximal metacarpal/metatarsal region has been associated with great diagnostic potential and clinical reports of standing low-field MRI of the forelimb suggest the same. To better understand diagnostic outcomes with standing low-field MRI of the proximal suspensory region, a prospective survey study was conducted and users of a widely available system questioned on their experience, operating procedures, and interpretation of standing low-field MRI findings. Response data included scores on a modified Likert scale from which weighted ratings were calculated for statistical analyses. Depending on the question, responses were obtained from 17 to 29 of the 38 invited facilities. Users indicated that standing low-field MRI was most frequently performed in the face of equivocal diagnostic findings; compared to Sports horses, general purpose riding horses were thought less likely to have detectable abnormalities and standing low-field MRI was rated most useful for the detection of primary bone pathology in the proximal metacarpal region. Standing low-field MRI signal change involving both the suspensory ligament and adjacent bone concurrently was rated most relevant and abnormalities solely affecting the muscle/adipose tissue bundles least relevant for diagnosing suspensory ligament injury. Transverse scans and in decreasing order T1-weighted gradient echo, short-tau inversion recovery FSE, T2*-weighted gradient echo, and T2-weighted FSE sequences were most frequently acquired and judged most useful by the majority of users experienced in imaging of the target area. This survey supports the relevant impact of standing low-field MRI on clinical case management, particularly in the context of imaging the proximal metacarpal region.

LOW-FIELD MAGNETIC RESONANCE IMAGING APPEARANCE OF POSTARTHROSCOPIC MAGNETIC SUSCEPTIBILITY ARTIFACTS IN HORSES.

An awareness of magnetic susceptibility artifacts is important for interpreting prepurchase and postoperative magnetic resonance imaging (MRI) studies in horses. These artifacts occur when a metallic or a paramagnetic substance creates a local magnetic field deformity. Aims of the current experimental study were to determine prevalence of these artifacts after arthroscopy in a sample of nonlame horses, and to describe effects of time and type of pulse sequence on low-field MRI signal intensity and detection of the artifacts. Ten, nonlame Standardbred horses were prospectively recruited. All horses underwent arthroscopy of both metacarpophalangeal joints for purposes unrelated to the study. Serial low-Field MRI examinations were performed on each horse and each joint (before, and 6 and 12 weeks postsurgery). In two horses, more detailed longitudinal evaluations were performed with additional MRI examinations. Magnetic susceptibility artifacts were detected postoperatively at the surgical access sites in eight metacarpophalangeal joints at both 6 and 12 weeks after surgery (40% prevalence). Neither of the two longitudinally followed horses had artifacts at any time. Artifacts were only detected on gradient echo (GRE) sequences. Findings indicated that magnetic susceptibility artifacts can be present in postarthroscopy MRI studies in horses and can persist up to 12 weeks after arthroscopy. For this sample of horses, the artifacts did not interfere with evaluation of the joint. Further longitudinal studies are needed to determine the full duration of magnetic susceptibility artifact persistence in affected tissues.

Effect of anesthetizing individual compartments of the stifle joint in horses with experimentally induced stifle joint lameness.

OBJECTIVE: To evaluate the effects of sequential anesthesia of the individual compartments of the equine stifle joint on lameness induced by intra-articular deposition of interleukin (IL)-1ß. ANIMALS: 6 horses. PROCEDURES: For each horse, baseline hind limb lameness was first evaluated. A randomly selected compartment of 1 stifle joint was then injected with IL-1ß to induce synovitis and lameness; subsequently, the same compartment was anesthetized with 2% mepivacaine hydrochloride, and lameness was reevaluated. Two weeks later, baseline lameness was evaluated, and lameness was similarly induced; thereafter, the 2 synovial compartments of the stifle joint not injected with IL-1ß were anesthetized sequentially in random order (ie, first and second blocks); lameness was evaluated after each block. Finally, the IL-1ß-treated compartment was anesthetized (third block); lameness was again evaluated. This second experiment was repeated for the contralateral stifle joint 2 weeks later. Throughout the study, lameness was quantified objectively by assessing vertical pelvic movement asymmetry with a wireless, inertial sensor-based system. RESULTS: Intra-articular deposition of IL-1ß induced lameness in all injected limbs. In the first experiment, anesthesia of the compartment injected with IL-1ß resulted in a significant decrease in lameness, with vertical pelvic movement asymmetry approaching baseline. In the second experiment, lameness improved significantly after the second and third blocks and was almost completely abolished after all 3 synovial compartments were anesthetized. CONCLUSIONS AND CLINICAL RELEVANCE: In horses, lameness caused by a lesion in 1 compartment of a stifle joint can be improved more by instillation of local anesthetic solution into that compartment than by anesthesia of the other compartments.

MRI features of metacarpo(tarso)phalangeal region lameness in 40 horses.

Lameness originating from the metacarpo(tarso)phalangeal (MP) joint has a significant effect on the use and athletic competitiveness of a horse. The identification of the cause of lameness originating from the MP joint can be challenging, given the limitations of radiography, ultrasonography, and nuclear scintigraphy. Our purpose was to describe the injury types and incidence in magnetic resonance imaging (MRI) studies from 40 horses with lameness attributable to the MP joint region where it was not possible to reach a clinically plausible diagnosis using other imaging modalities. Horses were examined in a 1.5 T magnet (Siemens Medical Solutions) under general anesthesia. The frequency of occurrence of MR lesions was subchondral bone injury (19), straight or oblique distal sesamoidean desmitis (13), articular cartilage injury and osteoarthritis (eight), suspensory branch desmitis (seven), osteochondral fragmentation (seven), proximal sesamoid bone injury (seven), inter-sesamoidean desmitis (four), deep digital flexor tendonitis (four), collateral desmitis (three), superficial digital flexor tendonitis (two), enostosis-like lesions of the proximal phalanx or MCIII (two), desmitis of the palmar annular ligament (one), desmitis of the proximal digital annular ligament (one), and dystrophic calcification of the lateral digital extensor tendon (one). Twenty-five horses had multiple MR abnormalities. MRI provided information that was complementary to radiography, ultrasonography, and nuclear scintigraphy and that allowed for a comprehensive evaluation of all structures in the MP joint region and a diagnosis in all 40 horses.

Clinical, magnetic resonance, and sonographic imaging findings in horses with proximal plantar metatarsal pain.

Sonography is commonly used for diagnosis of desmopathy of the proximal part of the suspensory ligament in horses. However, magnetic resonance (MR) imaging has been stated to be superior for detecting disease and localizing lesions. In this retrospective study of 39 horses or 46 hind limbs with lameness due to proximal plantar metatarsal pain, the clinical and diagnostic findings are discussed and sonography and MR imaging compared for examination of the proximal part of the suspensory ligament. With MR imaging interpreted as the clinical gold standard, desmopathy of the proximal part of the suspensory ligament was diagnosed in 21 hind limbs, proximal plantar metatarsal pain of unknown cause in 12, an osseous injury at the origin of the suspensory ligament in four and a condition unrelated to the suspensory ligament in nine. Based on these findings, sonography had a sensitivity of 0.77 and 0.66 and specificity of 0.33 and 0.31 for diagnosing proximal suspensory desmopathy and for accurately localizing lesions, respectively. MR imaging changes consistent with proximal suspensory desmopathy were signal hyperintensities and an increase in cross-sectional area compared with the contralateral limb. Anesthesia of the deep branch of the lateral plantar nerve is not specific neither for proximal suspensory desmopathy, as conditions unrelated to the suspensory ligament were diagnosed, nor for diagnosis of proximal plantar metatarsal pain, as conditions outside the proximal plantar metatarsal region were also diagnosed.

Magnetic resonance imaging characteristics of the foot in horses with palmar foot pain and control horses.

Palmar foot pain is a common cause of lameness. Magnetic resonance imaging (MRI) has the potential to detect damage in all tissues of the equine foot, but an understanding of the differences in magnetic resonance (MR) images between feet from horses with and without palmar foot pain is required. This study aimed to describe MR findings in feet from horses with no history of foot-related lameness, and to compare these with MR findings in horses with lameness improved by palmar digital local analgesia. Thirty-four limbs from horses euthanized with a clinical diagnosis of navicular syndrome (ameness >2 months duration, positive response to palmar digital nerve blocks and absence of other forelimb problems) (Group L), and 25 feet from age-matched horses with no history of foot pain (Group N) were examined. For each anatomic structure, MR signal intensity and homogeneity, size, definition of margins, and relationships with other structures were described. Alterations in MR signal intensity and homogeneity were graded as mild, moderate, or severe and compared between Groups L and N. Results revealed that there were significant differences in MR images between Groups N and L. Multiple moderate-severe MR signal changes were present in 91% of limbs from Group L and moderate (none were graded severe) in 27% of limbs from Group N. In most Group L limbs, more than three structures and frequently six to eight structures were abnormal. Concomitant abnormalities involved most frequently the deep digital flexor tendon, distal sesamoidean impar ligament, navicular bone, collateral sesamoidean ligament, and navicular bursa (with significant associations in severity grade between these structures), sometimes with involvement of the distal interphalangeal joint and/or its collateral ligaments. It was concluded that findings on MR images were different between horses with and without foot pain, and that pain localized to the foot was associated with MR changes in a variety of structures, indicating that damage to several structures may occur concurrently and that MR imaging was useful for evaluation of foot pain.

How does magnetic resonance imaging represent histologic findings in the equine digit?

Magnetic resonance (MR) imaging is increasingly used in the diagnosis of equine foot pain, but improved understanding of how MR images represent tissue-level changes in the equine foot is required. We hypothesized that alterations in signal intensity and tissue contour would represent changes in tissue structure detected using histologic evaluation. The study objectives were to determine the significance of MR signal alterations in feet from horses with and without lameness, by comparison with histopathologic changes. Fifty-one cadaver feet from horses with a history of lameness improved by palmar digital analgesia (n = 32) or age-matched control horses with no history of lameness (n = 19) were stored frozen before undergoing MR imaging and subsequent histopathological examination at standard sites (deep digital flexor tendon, navicular bone, distal sesamoidean impar ligament, collateral sesamoidean ligament, and navicular bursa). Using MR images, signal intensity and homogeneity, size, definition of anatomic margins, and relationships with other structures were described. Alterations were graded as mild, moderate, or severe for each structure. For each anatomic site examined histologically the structures were described and scored as no changes, mild, moderate, or severe abnormalities, also taking into account adhesion formation within the navicular bursa detected on macroscopic examination. Alterations in MR signal intensity were related to changes at the tissue level detected by histologic examination. A sensitivity and specificity comparison of MR imaging with histologic examination was used to evaluate the significance of MR signal alterations for detection of moderate-to-severe lesions of the deep digital flexor tendon (DDFT), navicular bone, distal sesamoidean impar ligament (DSIL), collateral sesamoidean ligament (CSL) and navicular bursa. Agreement between the MR and histologic grading was assessed for each structure using a weighted kappa agreement. Direct comparison between histology and MR imaging for individual limbs revealed that signal alterations on MR imaging did represent tissue-level changes. These included structural damage, fibroplasia, fibrocartilaginous metaplasia, and hemosiderosis in ligaments and tendons; trabecular damage, osteonecrosis, fibroplasia, cortical defects, and increased vascularity in bone; and fibrocartilage defects. MR imaging had a high sensitivity and specificity for most structures. MR imaging had high specificity for lesions of the DDFT, CSL and navicular bursa, quite high specificity for lesions of the medulla of the navicular bone and its proximal aspect, with moderate specificity for the DSIL, and distal, dorsal and palmar aspects of the navicular bone, and was sensitive for detection of abnormalities in all structures except the dorsal aspect of the navicular bone. When MR and histologic grades alone were compared, there was good agreement between MR and histologic grades for the navicular bursa, DDFT, navicular bone medulla and CSL; moderate-to-good agreement in grades of the distal and palmar aspects of the navicular bone; fair to moderate in grades of the DSIL, and poor agreement for the dorsal and proximal aspects of the navicular bone. The results of this study support our hypothesis and indicate the potential use and limitations of MR imaging for visualization of structural changes within osseous and soft tissue structures of the equine foot.

Quantitative evaluation of equine deep digital flexor tendon morphology using magnetic resonance imaging.

Injury of the distal aspect of the deep digital flexor tendon (DDFT) is a recognized cause of lameness, but diagnosis is difficult. This study aimed to improve understanding of DDFT morphology and pathology using retrospective evaluation of magnetic resonance (MR) images. We hypothesized that: (1) The distal aspect of the DDFT in normal horses would have a repeatable proximal/distal pattern and symmetry between limbs and between lobes; (2) DDFT dimensions would be related to bodyweight, navicular bone dimensions and hoof size; (3) this symmetry and pattern would be lost in DDFT injury; and (4) DDFT size would increase with injury. MR images of 64 live horse limbs, 26 with no identified DDFT lesion and 38 with identified DDFT abnormalities, and 19 normal cadaver limbs were analyzed. Using standardized transverse images, measurements of DDFT cross-sectional area, medial-lateral (ML) width and dorsal-palmar depth were obtained at six preselected sites. A uniform distal to proximal shape pattern was identified in all horses. The flattened crescent shape at the insertion changed to a deeper bilobed shape more proximally, with the mid-navicular area having the greatest cross-sectional area. Strong ML (P < 0.0006) and left/right symmetry (P < 0.02) were observed. In addition, there was a strong association between DDFT cross-sectional area and horse weight (P = 0.005) and between DDFT and navicular bone ML width (P = 0.004). Symmetry between sides or between lobes was lost at sites with a unilateral lesion and correlation between horse weight and DDFT cross-sectional area was lost in the presence of lesions. DDFTs with core lesions had a consistent increase in cross-sectional area overall, but other lesion types had no significant increase in size. The shape and symmetry seen in normal tendons could be related to the mechanical demands placed upon individual lobes. The limited increase in cross-sectional area with injury may be explained by the restrictive structures of the hoof, possibly explaining the ongoing pain seen in such lesions.

Magnetic resonance imaging of the equine digit with chronic laminitis.

Chronic laminitis is a severe disease affecting the equine digit. It was hypothesized that magnetic resonance (MR) imaging would improve visualization of structures within the foot and pathology associated with chronic laminitis. This study aimed to describe the MR imaging findings in chronic laminitis, compare different pulse sequences for visualization of pathology, and to compare MR imaging with standard radiography. Twenty (10 forelimb, 10 hindlimb) cadaver limbs from 10 horses clinically diagnosed with chronic laminitis (group L) and 10 limbs without laminitis (group N) were used. Lateromedial radiographs and sagittal and transverse MR images of the foot were obtained. Radiographs and MR images were evaluated for anatomic definition and evidence of pathology. Dorsal hoof wall thickness and angle of rotation and displacement distance of the distal phalanx were measured. Comparisons were made between group L and N, forelimb and hindlimb within each horse, and MR imaging and radiography. Features consistently noted with MR images in group L, but not detected using radiography, included laminar disruption, circumscribed areas of laminar gas, laminar fluid, and bone medullary fluid. Other findings seen only on MR images included increased size and number of vascular channels, alterations in the corium coronae, and distal interphalangeal joint distension. Magnetic resonance imaging allowed better definition of laminar gas lines and P3 surface irregularity observed on radiographs. Based on measurements, group L had a greater angle of rotation, distal displacement, and dorsal hoof wall thickness than group N; forelimb hoof wall thickness was greater than hindlimb; and distal displacement and hoof wall thickness measurements were smaller using MR imaging than radiography, but had a similar pattern. It is concluded that there are features of chronic laminitis consistently observed using MR imaging and that these may be additional to features observed radiographically.