INTRODUCTION

In Morocco, in common with many low and middle- income countries, working equids are rarely, if ever, kept in paddocks or stabled. Instead, the vast majority rest outside their owners homes while not working, usually restrained by hobbles attached around the pastern.

The choice of equipment used to hobble these animals is often entirely inappropriate and may result in serious injury. The most detrimental hobble type is that made of baling twine or wire as these materials, when neglected or forgotten, can rapidly become embedded within the soft and bony tissues of the limb. These embedded hobbles lead to a significant, and classically recognized, periosteal reaction around the affected bone, and result in severe lameness, however, clinical signs can resolve surprisingly rapidly once the hobble is removed. Despite the fact that the encircling materials are deeply and chronically embedded within the soft and bony tissues of the limb, ischemic necrosis or synovial structure contamination is apparently rarely encountered. This is in stark contrast to other reports in the veterinary literature of acute wire laceration, or entanglement causing prolonged inadequate perfusion in the distal limb, resulting in severe ischaemic damage and even hoof capsule loss (^{De Gresti et al., 2008}; ^{Jackson, 1969}; ^{Ruzickova et al., 2017}; ^{Stanek, 1981}). This retrospective case series describes the presenting signs, diagnosis, treatment and outcome of 16 donkeys presented to a working equid hospital in Morocco with severe lameness that was associated with hobbles embedded in the soft tissues and/ or the bone of the pastern region.

To the knowledge of the authors, this is the first report of neglected baling twine or wire hobbles embedded around the pastern in equids and yet it is a common and debilitating problem for vast numbers of working equids across the globe. With relatively simple and cheap treatment, the prognosis for affected animals is excellent, in our experience.

MATERIALS AND METHODS

This was a retrospective clinical study and involved a search of the clinical records of all working equids presented to the American Fondouk Hospital in Fez, Morocco, with radiographic evidence of embedded hobbles which was then confirmed at surgery, between 2012-2020.

Any animal presenting with severe lameness plus a draining fistula on the pastern or evidence of scarring or fibrosis around the pastern would routinely be radiographed at this authors hospital, for suspicion of embedded hobbles. The following information was recorded for each affected case; signalment, reason for presentation, clinical signs, any imaging performed, treatment, type of material used to hobble, length of hospitalisation, outcome, and long term follow up, if available are shown in Table 1. Radiographs were obtained using a Fujifilm (FCR) capsula system. Latero-medial and/or dorso-palmar/plantar views were available for all cases.

RESULTS

OUTCOME

The details of species, wound location, history when available, lameness grade at presentation, post-surgery and at the point of discharge, presence of wire or baling twine, radiographic changes, treatment protocol and number of days hospitalized and outcomes were all recorded and are presented in Table 1.

In all cases recovery after hobble removal was uneventful. The clinical records from our hospital record the post-operative degree of lameness in seven animals. Of these three were completely sound, immediately after hobble removal and two were rated as 2/5 lame at walk. A further two were rated 3/5 lame at walk. Each of these donkeys had presented on the same day as surgery either toe touching or non-weight bearing lame, suggesting that the presence of the foreign body, rather than associated infection or inflammation was the most significant source of pain.

Hospitalization time varied between one week and six weeks with the majority of animals discharged within a month of presentation. Details of the degree of lameness at discharge were available for 13 of the cases. Of these all were considered by the treating veterinarian to be sound enough to return to work in the context of a working equid. Five were recorded as sound, six as 2/5 and one was reported to have a residual lameness of 3/5 although even that individual returned to work effectively.

Table 1 Clinical information of cases in the study. 

NI: no information available.

IVRP: Intravenous Regional perfusion.

DISCUSSION

Working equids, that is horses, donkeys and mules, play a critical role in supporting the income generating capacity of their owners in low and middle income countries and are essential in both agricultural and urban arenas (^{Fielding, 1991}). Poor management strategies, as a result of ignorance and poverty, are at the root of many of the health problems encountered in this population (^{Lindberg et al., 2003}). The incorrect use of hobbles, or the use of incorrect material for making hobbles, is one example of poor management (^{Kay & Ouassat, 2002}).

The use of hobbles for containing working equids is ubiquitous in Morocco and in many other countries in the developing world where access to paddocks is limited (^{Pritchard et al., 2005}). The use of these hobbles entails many risks. All over the world, the safe containment of horses poses challenges. Post and rail paddocks probably represent the gold standard in horse containment and yet even this type of fencing can lead to injuries. In one survey of 180 horse owners run by The Equine Research Centre in Guelph Ontario, 27% of respondents reported accidents caused by fencing, of which 63% were caused by wire fencing and 13% caused by post and rail (Virginia Cooperative Extension, 1999). In many developing world countries, these containment issues are hugely compounded by the fact that access to grazing is transient and temporary and therefore paddocks are largely unknown. Instead, working equids are more often than not, kept tied up, often on long ropes to allow maximum grazing, and left unsupervised outside to forage. In Morocco, entanglement in these grazing ropes is very common and the resultant acute injuries range from mild rope burns to catastrophic lesions with associated musculoskeletal problems including torticollis and fractures. Attaching grazing animals using hobbles around the pasterns causes chronic limb lesions ranging from mild abrasions to tendonitis, laceration, ischaemia and tetanus (Kay et al., 2004).

Previous studies in working equid populations from a number of low and middle-income countries have shown that nearly all working equids have visible lesions or scars from hobbles. In Ethiopia a study of 497 equids reported 98-100% of animals had hobble lesions (Mekuria et al., 2013) and in a multi country study from Afghanistan, India, Egypt, Jordan and Pakistan involving over 4000 animals, between 62 and 88.8% of animals showed lesions or scars from hobbles (^{Pritchard et al., 2005}). In Morocco a study of 1713 equids showed 10% of animals with current lesions and a further 20% with evidence of previous lesions (^{Kay & Ouassat, 2002}).

The severity of the lesions associated with hobbling the limb of an individual animal will depend on the material used for the hobble and how long the hobble is left on (^{Kay & Ouassat, 2002}). In the 16 cases reported here, hobbling had been carried out with baling twine or wire, the cheapest, most readily available and probably most inappropriate of materials. Hobbles are sometimes left on the animal permanently, irrespective of underlying inflammation and this explains how these hobbles, with time, had come to embed themselves deeply within the soft tissues of the pastern.

Diagnosing the presence of an embedded hobble is reasonably straightforward. Presenting signs are almost pathognomonic and all equids suspected of having embedded hobbles were subject to radiographic views. All the donkeys in this case series presented with one or all of the following signs: a small draining tract at the level of mid pastern, an associated circumferential lesion (Figure 1 A), which may have been almost entirely healed by the time of presentation or may show massive soft tissue proliferation and severe lameness (4/5 to 5/5 on AAEP lameness scale). The severe lameness was a feature of all the animals in this case series. Notably the hobble could not be visualized, nor palpated at the skin surface on any of our cases. Radiography confirmed the diagnosis in all cases with wire hobbles (Figure 2 A) and in all but one of the animals with a baling twine hobble, periosteal changes were evident that suggested the presence of a non-radio-opaque foreign body (Figure 2 B). The majority of the cases presented here had evidence of massive periosteal and bony reactions to the presence of the foreign body, both wire and baling twine. An image of the first phalanx of a donkey that had presented many years previously and been euthanased prior to hobble removal shows the typical effect of this wire on the periosteum of the pastern (Figure 2 C).

Figure 1 A) Circumferential wound on the right hind pastern with a draining tract and soft tissue swelling around and above the hobbling materiel (wire in this case); B) Extensive circumferential fibrosis with severe swelling (the hobbling materiel in this case was a bailing twine). 

Figure 2 A) Latero-medial radiographic projection of the right forelimb. Note the encircling radiopaque foreign body at the mid first phalanx with extensive periosteal reaction; B) Dorso-palmar view of the right forelimb first phalanx with axial and abaxial extensive periosteal reaction forming an outline of the embedded foreign body (baling twine); C) Post mortem findings of a donkey with embedded wire in the pastern associated with extensive periosteal reaction. 

Embedded hobbles are a problem of equids in low and middle income countries where most veterinarians will not have access to radiography, however the clinical picture is so consistent that even without radiographic evidence, exploring the pastern for an embedded hobble would be worthwhile in any equid presenting with the clinical signs described here. Once diagnosed, treatment is remarkably simple and effective and requires no special equipment or even hospitalization. Recovery can be dramatic with many animals being immediately sound after removal of the foreign body, and all of our cases were discharged as sound enough to be useful as a working equid. There was no evidence in any of our cases that the hobble had penetrated any joint or synovial structure. Any joint contamination or osteomyelitis would be expected to result in severe lameness even after hobble removal which was not the case in our series of animals. Similarly, there was no evidence of associated tendon injury despite radiographic evidence that indicated extreme constriction and even penetration of the cortex (Case 1 and Case 14). Any palmar constriction around the pastern might logically have been expected to lead to tendon transection, tendon laceration or severe tendonitis, however, post-surgery, no individual showed any evidence of loss of support to the limb, or alteration in posture or function, any of which would be indicative of severe tendon injury or transection. Complete tendon transection is associated with significant alterations in limb conformation under loading, although partial severance or tears may not alter tendon function (^{Smith, 2008}). Because of this, palpation of the palmar or plantar aspect of the pastern was routinely performed once wound healing was complete and if the animal remained lame.

Donkeys showing evidence of heat or pain focused on the palmar aspect of the pastern would have an ultrasonographic assessment. None of the animals that were evaluated showed any discernible tendon abnormality either in shape or size, however longitudinal tears of the DDFT are often difficult to assess ultrasonographically (^{Smith, 2008}) and the very small size of the donkey pastern makes ultrasonography of this region challenging. The existence of tendon tears or mild tendonitis cannot therefore, be completely ruled out as a cause of the mild residual lameness that was seen in 7 of our cases at discharge.

Localized infection was evident in most of our cases although generally this was restricted to the pastern. The extensive cellulitis, that is a common sequelae to many distal limb injuries in horses (^{Ruzickova et al., 2017}), was not evident in any of our cases, although all were treated with distal limb IVRP and/or systemic broad spectrum antibiotics as a precautionary measure. Many donkeys presenting with embedded hobbles had few external wounds except for single draining tracts, and wound treatment in these cases was restricted to flushing the tract after wire or twine removal, followed by bandaging as support and prevention of further contamination. Where cutaneous wounds were evident, sterile Manuka honey dressings were applied and changed daily. Whilst the evidence for the use of medical grade honey is somewhat conflictual, it has been shown in several recent studies on iatrogenically inflicted wounds on both forelimbs, that application of Manuka honey dressings reduces wound area by reducing retraction and that treated wounds remain smaller than contralateral controls and heal faster overall (^{Bischofberger et al., 2011}; ²⁰¹³).

It is hypothesized that Manuka honey owes its antibacterial properties to a number of factors, most important of which are the small quantities of hydroperoxide and methylglyoxal (MGO) otherwise known as UMF - Unique Manuka Factor. These factors combined with the low pH (around 4) of honey inhibit bacterial growth and potentially stimulate fibroblastic activity (^{Carnwarth et al., 2014}). Contaminated sloughing and necrotic wounds, particularly those which require ongoing debridement are ideal candidates for the use of medical grade Manuka Honey (^{Carnworth et al., 2014}) and this made it the dressing of choice for the more severe cutaneous wounds in our group of donkeys. The downside of this dressing is cost and availability. Manuka honey dressings are a relatively expensive option in a working equid context and not available in many developing world countries. Localized infection was evident in most of our cases although generally this was restricted to the pastern. The extensive cellulitis that is a common sequelae to many distal limb injuries in horses (^{Ruzickova et al., 2017}), was not evident in any of our cases, although all were treated with distal limb IVRP and/or systemic broad spectrum antibiotics as a precautionary measure.

Some hobbling injuries can be associated with fatal outcomes, either through fractures or the development of tetanus, particularly so in parts of the world where working equids are not routinely vaccinated. All animals in this case series were treated with tetanus antitoxin as hobble lesions have been reported as one of the main causes of tetanus infection amongst working equids. In one study of 56 equids with tetanus, and 7 animals were thought to have developed tetanus through contamination of hobble lesions (^{Kay & Knottenbelt, 2007}).

Distal limb lacerations, in all equidae, frequently involve vascular compromise with subsequent ischeamic damage and even sloughing of the hoof capsule (Ruzickova et al., 2016). In our series despite the apparent tightness and bilateral constriction of the hobble identified radiographically in most animals, hoof sloughing or ischaemic damage was not a feature. It is probable that the chronic, insidious, nature of vascular compromise associated with hobbling allowed the development of alternative vasculature. Indeed, it has been shown that collateral vessels can develop in the 2-4 weeks following vascular damage (^{Keen et al., 2008}) and this adaptability may have been protective in these cases. Imaging modalities such as digital venography or arteriography have been used to visualize the vascularity of the equine digit (^{Redden, 2001}; ^{Walker et al., 2017}) and it would have been interesting to evaluate any compromise of the vessels of the digit in our cases.

The species distribution of our case series is notable. Despite having a case load in this hospital of approximately equal numbers of horses, mules and donkeys, it is only donkeys that have ever been presented with hobbles embedded around the pastern. This may be a function of their intrinsic value; being of less value than the horse or mule, less care is taken over their wellbeing. Or alternatively it may be a function of their stoic nature; owners may feel that they are less likely to cause themselves harm therefore less care is required in their maintenance and therefore owners may choose to use wire rather than a more appropriate material. It is also striking that in both of the studies on the incidence of hobbling lesions, donkeys are much more likely to show lesions than horses or mules. In the Pritchard study, 88.8% of donkeys had lesions or scars compared with 62% of horses and, in the Kay study from Morocco, 45% of donkeys as opposed to 28% of horses showed lesions or scars. This is some indication that owners will expend more thought and care on the choice of hobble materials for more valuable animals and that there is some understanding of the risks of using wire and twine to tether horses. Much work has been done in various countries and by various Governmental and non-governmental organizations to educate owners on improved hobbling practices and limit the devastating consequences of this poor management practice.

A program of owner education and supply of appropriate non traumatic hobbles has been in place for many years in Morocco, set up by this author at working equid clinics throughout the country (^{Kay & Ouassat, 2002}). Although it is clear that much benefit to welfare can be achieved through educating owners on the use of non-traumatic hobble material such as thick cotton rope, it is much more challenging to suggest a cost effective means of allowing animals to graze that does not rely on long grazing ropes. An obvious answer would be to use electric fencing which would allow animals to temporarily graze different areas. Unfortunately, the cost involved in purchasing such a set up would make this unworkable for the vast majority of working equid owners.

In conclusion, this is the first report on the treatment and successful outcome of a group of working donkeys treated for chronic encircling hobbling injuries of the distal limb. Clinicians treating working equids, should be aware of the clinical signs, classical radiographic appearance, even in the absence of radio-opaque hobbling material, and excellent prognosis following treatment despite severe presenting clinical signs.