The use of magnetic resonance imaging for the assessment of distal limb wounds in horses: A pilot study

The utility of magnetic resonance (MR) imaging in the evaluation of equine solar foot penetrations is well established. The objective of this pilot study was to evaluate the utility of MR imaging in assessment of equine distal limb wounds excluding solar penetrations. Low-field MR images of 23 horses that had previously sustained distal limb wounds were reviewed in consensus by two ECVDI diplomats. Structures (bone; synovial structure; subcutaneous tissue and skin; and ligament/tendon) were identified as normal or abnormal on MR images, radiographs and ultrasound images and reports. All abnormalities were described. The presence of artefacts and their effect on image interpretation were also noted for each modality. Comparisons were made between imaging modalities, and it was noted if MR imaging influenced case management. Abnormalities of the bone were identified in 26% of horses on MR images and 17% of horses on radiographs; there were no osseous abnormalities identified on radiographs that were not identified on MR images, and additional features and better characterisation of lesions were noted on MR images. Tendon/ligament abnormalities were identified in 57% horses on MR and 47% of horses on ultrasound images. Magnetic susceptibility artefacts compromised MR image interpretation in 17% of horses. MR imaging of equine distal limb wounds allowed identification of both osseous and tendon/ligament abnormalities in more cases than either radiography or ultrasonography, and altered case management in 20/23 horses. Although MR imaging should not replace conventional imaging, this study highlights that MR imaging of equine distal limb wounds can yield information not detected on conventional imaging which may direct treatment and affect prognostication.     

Standing computed tomography of the equine limb using a multi-slice helical scanner: Technique and feasibility study

Computed tomography (CT) is an important cross-sectional diagnostic modality for lameness localised to the equine distal limb. The necessity of general anaesthesia to perform CT scans has limited its use in the equine orthopaedic field. Therefore, many attempts have been made to perform CT of the distal limb in standing horses. This retrospective report aims to describe the technical set-up and the feasibility of using a multi-slice helical CT unit recently introduced into the equine market. The medical records of the patients undergoing a standing CT in the period between March 2019 and January 2020 were reviewed. The imaged anatomical region and the image quality were assessed. Thirty-two horses met the inclusion criteria, and the following anatomical areas have been imaged: front foot/pastern (n = 14), metacarpophalangeal joint (n = 11), front proximal suspensory ligament (n = 2), carpus (n = 2), metatarsophalangeal joint (n = 2) and tarsus (n = 1). In 97% of the cases, excellent imaging quality was obtained. Motion artefact is the main cause of poor image quality. The feet and the metacarpophalangeal region can be easily imaged. Imaging the proximal anatomical regions of the limb is more challenging but achievable.     

Computed tomographic evaluation of the distal limb in the standing sedated horse: Technique,imaging diagnoses,feasibility, and artifacts

In several veterinary institutions, adjustments of CT machines have been made that allow for imaging of the standing horse. The risk of general anesthesia is eliminated and the shorter scan completion time reduces cost to clients. The objective of this retrospective, analytical study was to evaluate the technique, imaging diagnoses, feasibility, and image artifacts of multi-slice helical CT of horses’ distal limbs acquired under standing sedation. The CT images of 250 horses of various breeds, aged 3–23 years, that underwent standing distal limb CT were evaluated. Three observers assessed the CT images for artifacts and inter-observer agreement was calculated. Eighty-six percent (95% confidence interval (CI), 81–90) of the scans were carried out on the forelimbs, while 14% (95% CI, 10–19) were of the hindlimbs. A total of 65% (95% CI, 59–71) of horses that underwent standing sedated CT had single imaging diagnoses. Seventy-one percent (95% CI, 65–77) of the cases had unilateral lesions, 27% (95% CI, 22–33) had bilateral lesions and 2% (95% CI, 1–4) had no diagnosed lesions. The average CT acquisition time was 17.5 minutes (range = 15–20). The average number of acquisitions per horse was 1.7 (median = 1; range = 1–4). There was good to excellent agreement between all three observers for the presence of motion artifact in the metacarpo/metatarsophalangeal joints, identification of marked beam hardening artifact, mild solar/ skin dirt, and photon starvation artifact (kappa 0.61-0.80). No complications were encountered. Standing examination of the distal limb achieved diagnostic image quality that was obtained with minimal acquisition attempts and in a timely manner.     

Spontaneous hoof capsule loss following lacerations of the equine distal limb

In this article, 3 cases of an infrequent complication of lower limb trauma that presented as a cellulitis and deteriorating comfort a few days after lower limb laceration are described. All 3 horses sloughed the hoof capsule 10 days after initial trauma to that particular limb. Development of subsequent cellulitis/lymphangitis contributed to deterioration of distal limb perfusion. The exact pathophysiological mechanisms remain unknown but clinicians should be aware of this unusual but major complication following limb trauma.     

A review of regional limb perfusion for distal limb infections in the horse

Regional limb perfusion (RLP) is a technique widely used for the treatment of limb infections in horses. The objective is to deliver high concentrations of an antimicrobial to a focal region to optimise the bacterial kill with minimal systemic effects. However, experimentally, realising these objectives has been unreliable because conflicting methodologies have produced highly variable results. The aim of this study is to review all of the experimental and clinical literature on RLP between 1990 and 2019 to determine whether there is evidence that RLP has a consistent and practical application for the treatment of distal limb infections in equine practice. A large number of reports have been published on RLP in the horse; however, there are many variations in the technique including the drug used, dose, volume and concentration of perfusate, dosing interval, the type, method and duration of application of the tourniquet and whether the procedure is performed standing or anaesthetised. Prospective clinical studies are lacking, retrospective studies are limited by their nature, while wide differences in treatment regimen and methodology in retrospective and experimental studies have complicated the interpretation of the findings and make it difficult to rationalise an approach that provides a reliable and repeatable outcome. The optimal method of performing RLP has not been established, so the apparent clinical benefits of the technique are often difficult to confirm and quantify. Future studies need to standardise methodologies to enable meaningful comparisons.     

Distal limb cast sores in horses: Risk factors and early detection using thermography

Reasons for performing study: There is a lack of evidence‐based data on the prevalence, outcome and risk factors of distal limb cast sores, and no objective tool has been described for the early detection of cast sores. Objectives: To investigate the prevalence, location, outcome and risk factors of cast sores after application of a distal limb cast and to determine whether static thermography of the cast is a valuable tool for the assessment of sores. Methods: A prospective study was conducted on horses treated with a distal limb cast. At each cast removal, cast sores were graded as superficial sores (SS), deep dermal sores (DS) or full thickness skin ulcerations (FS). In several cases, a thermographic evaluation of the cast was performed immediately prior to removal and differences in temperature (ΔT) between the coolest point of the cast and 2 cast regions predisposed for sore development (dorsoproximal mc/mtIII and palmar/plantar fetlock) were calculated. Results: Mean ± s.d. total casting time of 70 horses was 31 ± 18 days. Overall, 57 legs (81%) developed at least SS. Twenty‐four legs (34%) ultimately developed DS and one horse had an FS. Multivariable analysis showed that the severity of sores was positively associated with increasing age (OR: 1.111, P = 0.028), a normal (vs. swollen) limb (OR: 3.387, P = 0.023) and an increase in total casting time (OR per week: 1.363, P = 0.002). The thermographic evaluation (35 casts) revealed that the severity of sores was positively associated with increasing ΔT (OR: 2.100, P = 0.0005). The optimal cut‐off values for the presence of SS and DS were set at, respectively, ΔT = 2.3 and 4.3°C. Conclusion and potential relevance: Distal limb cast is a safe coaptation technique with increasing risk of developing sores with time. Thermography is a valuable and rapid clinical tool to monitor the development of cast sores.     

Glucocorticoid therapy and the risk of equine laminitis

Although glucocorticoids have been used successfully for the treatment of noninfectious inflammatory diseases of horses for more than 35 years, their use has been attended by a fear of the induction of laminitis. This paper reviews the evidence for this fear and the possible mechanisms whereby glucocorticoids could participate in laminitis induction. Although the association of laminitis with elevated serum cortisol in pituitary pars intermedia dysfunction suggests that chronic exposure to glucocorticoids may be part of laminitis pathogenesis, review of published reports and databases suggests that glucocorticoid‐induced laminitis is a relatively rare occurrence. However, several of the actions of glucocorticoids are similar to those known to be involved in laminitis pathogenesis. Glucocorticoid administration can induce insulin resistance, lead to vascular dysfunction that potentiates vasoconstriction, and interfere with keratinocyte proliferation and differentiation as well as matrix integrity, all mechanisms that could possibly induce laminitis. Drug formulation, dose and route of administration, and the systemic and hoof disease history of the horse must all be considered when assessing laminitis risk during glucocorticoid treatment. Generally, local glucocorticoid administration presents little risk as does systemic treatment of recurrent airway obstruction without concurrent disease. Caution should be used however in horses that are overweight and/or insulin resistant, or have had a recent bout of acute laminitis of alimentary or endotoxic origin. Overall, however, the risk of laminitis after glucocorticoid treatment, especially local use, is acceptable compared to the many benefits of these drugs.     

Scintigraphic evaluation of intra-arterial and intravenous regional limb perfusion of allogeneic bone marrow-derived mesenchymal stem cells in the normal equine distal limb using (99m) Tc-HMPAO

Reasons for performing study: Mesenchymal stem cells (MSCs) are commonly injected intralesionally for treatment of soft tissue injuries in the horse. Alternative routes of administration would be beneficial for treatment of lesions that cannot be accessed directly or to limit needle‐induced iatrogenic damage to the surrounding tissue. Objectives: The purpose of our study was to evaluate MSC distribution after intra‐arterial (IA) and intravenous (IV) regional limb perfusions (RLP) using scintigraphy. We hypothesised that MSCs would persist in the distal limb after tourniquet removal and that both techniques would lead to diffuse MSC distribution. Methods: Six horses were used in the study. MSCs were labelled with hexamethyl propylene amine oxime (HMPAO) and technetium‐99m. RLP was performed through the median artery of one forelimb and the cephalic vein of the opposite limb under general anaesthesia. The tourniquet was left in place for 45 min. Scintigraphic images were obtained at 0, 45, 75 min, 6 h and 24 h post injection. Results: Distribution of labelled MSCs through the entire distal limb was achieved with all 6 IA RLP, but 3 out of 6 IV RLP showed poor or absent uptake distal to the metacarpus. Mesenchymal stem cell persistence was 39% (30–60%) and 28% (14–50%) (median [minimum–maximum]) at 6 h for IA and IV RLP, respectively. Severe arterial thrombosis occurred in one horse after IA RLP. Conclusions: Both IA and IV RLP of the distal limb result in MSC persistence in perfused tissues. The IA perfusion resulted in more reliable cell distribution to the pastern and foot area. Potential relevance: Regional limb perfusion of MSCs might be used in cases where intralesional injection is not possible or in order to avoid iatrogenic needle damage. Further work is needed to assess the safety of IA RLP before its clinical use.     

Comparison of conventional and alternative arthroscopic approaches to the palmar/plantar pouch of the equine distal interphalangeal joint

Reasons for performing the study: The conventional arthroscopic approach to the palmar/plantar aspect of the distal interphalangeal joint (DIPJ) may result in the inadvertent penetration of the digital flexor tendon sheath (DFTS) and the navicular bursa (NB). This iatrogenic communication would be undesirable subsequent to arthroscopic lavage of a septic DIPJ. Hypothesis: A lateral/medial approach to the palmar/plantar aspect of the DIPJ will result in a significantly lower rate of inadvertent penetration of the DFTS and NB, whilst still providing adequate intra‐articular evaluation. Methods: The conventional palmar/plantar approach or a novel lateral/medial approach to the DIPJ was performed on cadaver fore‐ and hindlimbs (30 limbs/approach). Subsequently, India ink was injected into the dorsal pouch of the DIPJ, and the DFTS (n = 60) and NB (n = 20) were examined for the presence/absence of ink. In addition, observations of the number of attempts made to access the joint, evidence of iatrogenic intra‐articular trauma and occurrence of incomplete visualisation of the palmar/plantar pouch were recorded. Results: With the conventional approach, DFTS penetration was noted in 18/30 (60%) of the limbs, compared to 1/30 (3.3%) with the lateral/medial approach (P≤0.001). NB penetration was seen in 5/10 limbs with the palmar/plantar approach compared to 0/10 with the lateral/medial approach (P = 0.01). No significant differences were found between the approaches in the number of attempts made to access the joint, the incidence of iatrogenic intra‐articular trauma, or the occurrence of incomplete visibility of the palmar/plantar pouch. Conclusions: The novel lateral/medial approach to the DIPJ significantly decreases the risk of inadvertent penetration of the DFTS and NB. Potential relevance: The novel lateral/medial approach to the DIPJ is an effective technique to gain access to the palmar/plantar pouches, and is particularly advantageous for arthroscopic lavage of a septic DIPJ.     

Mechanisms of aquatic therapy and its potential use in managing equine osteoarthritis

Aquatic therapy has become increasingly popular in its use for rehabilitation of equine musculoskeletal injuries. Unfortunately, there has been no scientific evaluation of its clinical application for the treatment of osteoarthritis (OA) or associated musculoskeletal injuries in horses. The purpose of this review is to describe mechanisms of action of aquatic therapy and its potential use in the clinical management of equine OA.