Prolonged, continuous distal limb cryotherapy in the horse

Continuous digital hypothermia for prevention and treatment of equine acute laminitis: A practical review

Laminitis is a severely debilitating and life-threatening condition that occurs as a consequence of different primary triggering factors. Continuous digital hypothermia (CDH) is recommended in horses at risk of, or diagnosed with, acute laminitis due to its several physiological and biochemical alterations that may be positive for the prevention and early treatment of the condition, representing a low risk of adverse effects. Modulation of the inflammatory response, profound vasoconstriction, and prevention of tissue damage are the most notable protective effects of cryotherapy on the lamellae. This practical review aims to summarize the published literature evaluating CDH efficacy in the prevention and early treatment of acute laminitis in horses, highlighting the most important clinical findings and discussing the best methods to provide cryotherapy. Nineteen publications evaluated different CDH methods, including the use of commercially available ice boots or fluid bags filled with iced water or crushed ice, as well as alternatives to immersion in ice, e.g., frozen gel packs and a perfused cuff prototype. Although some techniques were effective for cooling and maintaining the hooves below the optimal temperature of 10 °C, relevant limitations such as labor intensiveness, reliance on an ice source and price make its use impractical in some clinical situations. Twelve experimental studies assessed the efficacy of CDH on the prevention or early treatment of laminitis, finding multiple positive effects in terms of clinical improvement, immunological and inflammatory modulation, and histological protection. After the analysis of the literature, the clinical importance of CDH in different stages of laminitis remains clear. However, it also highlights the need for a safer, more user-friendly, and more effective method of cryotherapy that can be used both in a hospital and an ambulatory setting.

Transmural Ultrasonography in the Evaluation of Horse Hoof Internal Structures: Comparative Qualitative Findings-Part 1

Ultrasonography is commonly used to evaluate equine lameness-related structures, but traditional hoof approaches cannot adequately visualize internal structures such as the lamellar layer. To address this limitation, we used 62 healthy hooves without digital radiographic abnormalities, made up of thirty anatomical pieces (phase 1) and thirty-two hooves from living horses (phase 2). In both phases, half of the digits were submerged in water (group 1) and the other half in water and ice (group 2) for 24 h. Ultrasonographic views and temperature and humidity measurements were taken every two hours, and sagittal sections were obtained in phase 1. Good quality images were obtained in both phases. The transmural technique allowed the evaluation of several structures of the DEJ (tubular and lamellar strata of the hoof wall, sublamellar dermis, and solar and coronary papillae) and of the distal phalanx (extensor process, parietal surface, and apex). Our findings suggest that the transmural technique following hoof submersion can be useful for internal evaluation of hoof conditions, such as laminitis. However, further validation of the technique in natural or experimental cases is required.

Cryotherapy Techniques: Best Protocols to Support the Foot in Health and Disease

Treatment of equine laminitis continues to be a challenge despite recent advancements in knowledge of the pathophysiology of laminitis. With more evidence supporting its use, distal limb hypothermia or cryotherapy has become a standard of care for both prevention of laminitis and treatment of the early stages of acute laminitis. Recent studies have demonstrated that cryotherapy reduces the severity of sepsis-related laminitis and hyperinsulinemic laminitis in experimental models and reduces the incidence of laminitis in clinical colitis cases. This article reviews the recent literature supporting the use of distal limb cryotherapy in horses.

The effect of regional hypothermia on mechanical nociceptive thresholds in the equine distal forelimb

Regional hypothermia has shown promise as analgesic in horses when used to manage painful conditions of the distal limb such as laminitis. In this prospective study, the analgesic effects of regional hypothermia were assessed using mechanical nociceptive thresholds during distal limb cooling. The study population consisted of eight healthy adult Standardbred horses, selected from a teaching herd. A distal forelimb of each horse was cooled using water immersion at the following sequential target water temperatures: 34 °C, 20 °C, 10 °C, 5 °C, 1 °C, 5 °C, 10 °C, 20 °C. Limb surface temperature was measured after 30 min at each target water temperature and the mechanical force required to elicit a response (mechanical nociceptive threshold) was determined using a pneumatic actuator. Both forelimbs of each horse were tested one week apart. At skin surface temperatures above 7 °C, there was little association between skin surface temperature and the mechanical force required to elicit a response. As the skin surface temperature decreased below 7 °C, there was a rapid increase in the force required to elicit a response (P = 0.036). Skin surface temperatures of <7 °C required water temperatures below 2 °C. The results of this study suggest that hypothermia has potential to provide distal limb analgesia in horses at skin surface temperatures below 7 °C. Further evaluation of the technique is warranted.

The effect of continuous digital hypothermia on lamellar energy metabolism and perfusion during laminitis development in two experimental models

BACKGROUND

Continuous digital hypothermia (CDH) prevents lamellar failure in the euglycaemic hyperinsulinaemic clamp (EHC) and oligofructose (OF) laminitis models, but the mechanisms remain unclear.

OBJECTIVES

To evaluate the effects of CDH on lamellar energy metabolism and perfusion in healthy horses and during EHC and OF laminitis models.

STUDY DESIGN

In vivo experiment.

METHODS

Archived samples were used from Standardbred geldings that received no treatment (CON) (n = 8) or underwent EHC (n = 8) or OF (n = 6) laminitis models. Both forelimbs were instrumented with a lamellar microdialysis system, and one forelimb was cooled (CDH) with the other maintained at ambient temperature (AMB). Microdialysate was collected every 6 hours and analysed for glucose, lactate and pyruvate concentrations and lactate to pyruvate ratio (L:P). Microdialysis urea clearance was used to estimate lamellar tissue perfusion. Data were analysed using a mixed-effects linear regression model.

RESULTS

Glucose did not change in CDH limbs relative to AMB in CON (P = .3), EHC (P = .3) or OF (P = .6) groups. There was a decrease in lactate (P < .001) and pyruvate (P < .01) in CDH limbs relative to AMB in all groups. L:P decreased in CON CDH relative to CON AMB (P < .001) but was not different in EHC (P = .6) and OF (P = .07) groups. Urea clearance decreased in CDH limbs relative to AMB in CON (P = .002) and EHC (P < .001), but not in OF (P = .4).

MAIN LIMITATIONS

The EHC model may not mimic natural endocrinopathic laminitis.

CONCLUSIONS

CDH caused a marked decrease in lamellar glucose metabolism (CON, EHC and OF) and perfusion (CON and EHC) without affecting lamellar glucose concentration. Although cellular energy failure is not a primary pathophysiological event in EHC and OF laminitis models, CDH may act by limiting energy supply to pathologic cellular processes whilst preserving those critical to lamellar homoeostasis.

Evaluation of digital cryotherapy using a commercially available sleeve style ice boot in healthy horses and horses receiving i.v. endotoxin

BACKGROUND

Continuous digital cryotherapy experimentally prevents development and reduces severity of sepsis-associated laminitis. A sleeve style ice boot where ice is in direct contact with the skin, and water drains from the boot is being used clinically for distal limb cryotherapy. The degree of cooling achieved by this boot is unknown.

OBJECTIVES

Evaluate skin and lamellar cooling after application of the ice sleeve in healthy horses, and the same horses during an endotoxaemia model.

STUDY DESIGN

Prospective study, crossover design.

METHODS

In eight healthy horses thermocouples were inserted into dorsal lamellae of both front feet, and under skin on both metacarpi. One forelimb received cryotherapy using sleeve style ice boot, with contralateral limb as control. Temperature was recorded on data logging devices at 5 min intervals during each cryotherapy session. Day 1: temperature data was collected for healthy horses. Day 2: data was collected for the same horses during i.v. administration of endotoxin.

RESULTS

In healthy and endotoxaemic horses, the sleeve style ice boot significantly decreased mean skin (7.2°C and 5.8°C respectively) and lamellar (10.8°C and 9.6°C respectively) temperatures compared with control limbs (P<0.001). Skin and lamellar temperatures in endotoxaemic horses undergoing cryotherapy were significantly colder than in healthy horses (P = 0.01).

MAIN LIMITATIONS

Order of treatment not randomised.

CONCLUSIONS

The boot caused significant decreases in lamellar temperatures compared with untreated control limbs in all horses. Endotoxaemic horses had significantly colder lamellae and skin than healthy horses. This study is the first to show that a sleeve style boot, where ice does not cover the hoof, can cause significant decreases in lamellar temperatures through cooling of blood as it travels to the foot.

Distal limb pathologic conditions in horses treated with sleeve-style digital cryotherapy (285 cases)

Digital cryotherapy (DC) is frequently used as laminitis prophylaxis for horses. While DC with ice-water slurries is reported to be safe for up to 48 h, the safety of sleeve-style digital cryotherapy (SSDC) with ice in direct contact with the distal limb has not been evaluated. Our objective was to determine the incidence of distal limb pathologic conditions (DLPC) among horses treated with SSDC. A retrospective study of cases from 2011 to 2015 identified 285 horses treated with SSDC for a minimum of 12 h. Data collected from medical records included demographic, treatment, diagnostic, and SSDC treatment parameters. Bivariate statistics and a generalized linear regression model were created to evaluate risk factors associated with increased incidence of DLPC. Among horses treated with SSDC, 7% had tissue injury of the distal limb. Increasing duration of SSDC was associated with increased incidence of DLPC. Lesions observed included dermatitis, cellulitis, alopecia, coronitis, tissue necrosis, and distal limb edema. These lesions were similar to frostbite, non-freezing cold injury, and prolonged water immersion injuries seen in other species. While the incidence of DLPC was low, the authors recommend that horses undergoing SSDC with ice in direct contact with the skin should be monitored closely for injury when prolonged cryotherapy is clinically indicated. Further studies to improve safety, efficacy, and convenience of alternative methods of DC for horses are warranted.

Novel dry cryotherapy system for cooling the equine digit

Objectives

Digital cryotherapy is commonly used for laminitis prophylaxis and treatment. Currently validated methods for distal limb cryotherapy involve wet application or compression technology. There is a need for a practical, affordable, dry cryotherapy method that effectively cools the digit. The objective of this study was to evaluate the hoof wall surface temperatures (HWSTs) achieved with a novel dry cryotherapy technology.

Design

Repeated-measures in vivo experimental study.

Setting

Experimental intervention at a single site.

Participants

6 systemically healthy horses (3 mares, 3 geldings).

Interventions

Cryotherapy was applied to six horses for eight hours with a commercially available rubber and rubber and welded fabricice boot, which extended proximally to include the foot and pastern. Reusable malleable cold therapy packs were secured against the foot and pastern with the three built-in hook-and-loop fastener panels.

Primary and secondary outcome measures

HWST and pastern surface temperature of the cryotherapy-treated limb, HWST of the control limb and ambient temperature were recorded every five minutes throughout the study period.

Results

Results were analysed with mixed-effects multivariable regression analysis. The HWST (median 11.1°C, interquartile range 8.6°C–14.7°C) in the cryotherapy-treated limb was significantly decreased compared with the control limb (median 29.7°C, interquartile range 28.9°C–30.4°C) (P≤0.001). Cryotherapy limb HWST reached a minimum of 6.75°C (median) with an interquartile range of 4.1°C–9.3°C. Minimum HWST was achieved 68 minutes after cryotherapy pack application.

Conclusions

Dry application of cryotherapy significantly reduced HWST and reached minimums below the therapeutic target of 10°C. This cryotherapy method might offer an effective alternative for digital cooling.

Principles and Application of Hydrotherapy for Equine Athletes

Hydrotherapy has become a key element within equine rehabilitation protocols and is used to address range of motion, proprioception, strength, neuromotor control, pain, and inflammation. Various forms of hydrotherapy can be tailored to the individual's injury and the expected return to athletic performance. This article describes the mechanisms of action of hydrotherapies and potential use in the clinical management of equine musculoskeletal injuries.

A comparison of seven methods for continuous therapeutic cooling of the equine digit

REASONS FOR PERFORMING STUDY

Digital hypothermia may be effective for laminitis prophylaxis and therapy, but the efficacy of cooling methods used in clinical practice requires evaluation.

OBJECTIVES

To use hoof wall surface temperature (HWST) to compare several cooling methods used in clinical practice.

STUDY DESIGN

Experimental crossover design with a minimum washout period of 72 h.

METHODS

Seven cooling methods (commercially available ice packs, wraps and boots) and one prototypical dry-sleeve device were applied to a single forelimb in 4 horses for 8 h, during which HWST of the cooled forelimb and the uncooled (control) forelimb was recorded hourly. Results were analysed descriptively.

RESULTS

The median (range) HWST from 2-8 h was lowest for the ice and water immersion methods that included the foot and extended proximally to at least include the pastern: 5.2°C (range: 4.8-7.8°C) for the fluid bag and 2.7°C (2.4-3.4°C) for the ice boot. An ice boot that included the distal limb but not the foot resulted in a median HWST of 25.7°C (20.6-27.2°C). Dry interface applications (ice packs) confined to the foot only resulted in a median HWST of 21.5°C (19.5-25.5°C) for the coronet sleeve and 19.8°C (17.6-23°C) for a commercial ice pack. For the dry interface applications that included the foot and distal limb, the median HWST was much higher for the ice pack device, 19.9°C (18.7-23.1°C), compared with the perfused cuff prototype of 5.4°C (4.2-7°C).

CONCLUSIONS

Immersion of the foot and at least the pastern region in ice and water achieved sustained HWST <10°C as did a prototype perfused cuff device with a dry interface. Variation between cooling methods may have a profound effect on HWST and therefore efficacy in clinical cases where laminitis prophylaxis or therapy is the goal.

The management of equine acute laminitis

Laminitis is an extremely painful condition resulting in damage to the soft tissues anchoring the third phalanx to the hoof, which can result in life-threatening debilitation. Specific therapy is not available. The most important principles of therapy include aggressive nutritional and medical management of primary disease processes, cryotherapy, anti-inflammatory therapy, pain management, and biomechanical support. This review focuses on the principles of evidenced-based therapies.

The anatomy and physiology of the suspensory apparatus of the distal phalanx

The equine hoof capsule protects the softer, more sensitive, structures within. Failure of the connection between hoof and bone (suspensory apparatus of the distal phalanx or SADP) results in the crippling lameness of laminitis. Active basal cell proliferation occurs principally in tubular hoof and proximal and distal lamellae. The remaining lamellae are virtually non-proliferative and the hoof wall moves past the stationary distal phalanx, by controlled activation and inhibition of constituent proteases. The lamellar corium derives most of its blood supply from the branches of the terminal arch which perforate the distal phalanx. Valveless veins within the foot can be exploited clinically for retrograde venous therapy or contrast radiography (venography). The basement membrane (BM) forms the interface between the lamellar epidermis and the adjacent dermis and the plasma membrane of each lamellar basal cell is attached to the BM by numerous electron dense adhesion plaques or hemidesmosomes the ultimate attachment unit of the SADP. Laminitis destroys and dislocates the BM and its components and without an intact, functional BM, the structure and function of the lamellar epidermis is pathologically compromised. Transcription and activation of constituent proteases occurs in normal hoof lamellae but in increased amounts during laminitis.

Therapeutic hypothermia (cryotherapy) to prevent and treat acute laminitis

Digital hypothermia successfully reduces the severity of experimentally induced laminitis. Continuous-distal limb cryotherapy may be a useful technique in clinical cases that are at risk of developing laminitis. This article examines the effects of hypothermia on tissue as well as the rationale, and suggested protocols for the usage of distal limb cryotherapy in the prevention and treatment of laminitis.

Equine laminitis model: cryotherapy reduces the severity of lesions evaluated seven days after induction with oligofructose

REASONS FOR PERFORMING STUDY

A previous preliminary study demonstrated the potential of distal limb cryotherapy (DLC) for preventing laminitis. Clinically, DLC must be effective for periods longer than 48 h and the preventive effect must extend beyond its discontinuation.

OBJECTIVES

To evaluate the effect of DLC, applied during the developmental phase of induced laminitis, on the severity of clinical laminitis and lamellar histopathology 7 days after dosing.

METHODS

Eighteen normal Standardbred horses were divided into 3 groups of 6. Continuous cryotherapy was applied for 72 h to the distal limbs of the first group. The second and third groups were administered laminitis inducing doses of oligofructose and 72 h of cryotherapy applied (immediately after dosing) to the second group. After clinical assessment all horses were subjected to euthanasia 7 days after dosing and hoof lamellar tissues were harvested and analysed.

RESULTS

In the laminitis induced horses clinical lameness and laminitis histopathology was significantly reduced in horses that underwent 72 h of DLC compared with untreated controls. Cryotherapy alone produced no significant lameness or other ill effect.

CONCLUSIONS

Continuous, medium- to long-term (72 h) cryotherapy applied to the distal limbs of horses safely and effectively ameliorates the clinical signs and pathology of acute laminitis.

POTENTIAL RELEVANCE

Pre-emptive distal limb cryotherapy is a practical method of ameliorating laminitis in ill horses at risk of developing the disease.

Evidence for vascular and enzymatic events in the pathophysiology of acute laminitis: which pathway is responsible for initiation of this process in horses?

To date, there is a substantial amount of data to support the hypotheses that vascular and enzymatic changes are ongoing in experimental laminitis. Furthermore, there is substantial in vitro evidence that the enzymatic changes weaken the dermo-epidermal attachments leading to mechanical failure of the hoof-bone interface of the equine digit. However, investigators of both the vascular and enzymatic theories have, to date, been unable to substantiate the effects of these pathophysiological changes in vivo on laminar tissues of horses afflicted with experimentally induced or naturally acquired laminitis. In addition, the effects of laminitis-inducing treatment have not been prevented or reversed by treatment with an MMP inhibitor or a vasoactive antagonist. It is possible that there is simultaneous activation of the vascular and enzymatic pathways and/or other inflammatory processes. Moreover, the third theory involving mechanical factors cannot be discounted simply because strong evidence for vascular and enzymatic changes exists. It is common for horses with severe musculoskeletal disease affecting weightbearing on a limb to develop laminitis in the contralateral limb. It remains to be determined what factors are responsible for initiation of laminitis in these individuals. Evidence has not been presented that precludes the possibility of coincident occurrence of vascular and enzymatic changes. In fact, many of the inflammatory mediators (e.g. interleukin-1beta) found in laminitic tissues can concurrently stimulate synthesis of vasoactive substances and activate MMPs. Because enzymatic action on proteins is largely dependent on the concentrations of proteins and enzyme, the enzymatic theory is not dependent upon increased delivery of enzymes via increased capillary flow. Likewise, because vascular changes can alter tissue function via increased capillary flow and oedema formation, the vascular theory is not dependent upon decreased capillary flow. It is true that naturally acquired laminitis is widely variable in severity and predisposing diseases. Therefore, most probably there are multiple mechanisms involved in the initiation and propagation of the pathophysiologic cascade(s) and, therefore, successful intervention will necessitate multiple treatment modalities.

Equine laminitis: cryotherapy reduces the severity of the acute lesion

REASONS FOR PERFORMING STUDY

The hypometabolic and vasoconstrictive effects of cryotherapy could prevent the development of laminitis.

OBJECTIVES

To use distal limb cryotherapy to prevent laminitis induced by alimentary carbohydrate overload.

METHODS

Laminitis was induced in 6 Standardbred horses that had one front limb continuously cooled in an ice/water mixture. Lameness evaluation, blinded lamellar histological grading and analysis for lamellar matrix metalloproteinase-2 (MMP-2) mRNA expression were used to evaluate the severity of laminitis.

RESULTS

Cryotherapy was well tolerated and effective in cooling the feet. In each horse no lameness was observed in the treated limbs. Laminitis histology scores in the treated limbs were significantly less than those of the corresponding untreated forelimbs (P < 0.05). Laminitis histology scores in the treated limbs were also significantly less than those of the untreated limbs (fore- and hind) as a group (P < 0.05). Expression of MMP-2 mRNA in the iced feet was significantly (P < 0.05) less than that detected in the untreated feet.

CONCLUSIONS

Cryotherapy, when applied to one foot, markedly reduced the severity of acute laminitis in this study. We propose that vasoconstriction (preventing delivery of haematogenous trigger factors) and hypometabolism (reduction in lamellar MMP activity) were the primary therapeutic mechanisms.

POTENTIAL RELEVANCE

Although further research is needed, we suggest cryotherapy as a potentially effective prophylactic strategy in horses at risk of developing acute laminitis.