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FACTORS INVOLVED IN THE PROGNOSIS OF LAMINITIS IN THE UK
ROBERT A EUSTACE B.V.Sc. Cert.E.O. Cert.E.P. FRCVS.
The Laminitis Clinic, Mead House Farm, Dauntsey, Chippenham, Wiltshire. SN15 4JA.
P.J. CRIPPS B.V.Sc. B.Sc. M.Sc. PhD. MRCVS.
University of Liverpool, Department of Veterinary Clinical Science and Animal Husbandry, Leahurst, Neston, South Wirral, L64 7TE.
Keywords: laminitis; prognosis; group; founder distance
The significance of clinical and radiological parameters as prognostic indicators for laminitis, founder and sinking syndrome was studied using case records of 216 horses and ponies. Five animals were destroyed without treatment and were not included in the results of the study. 162 (77%) animals returned to athletic soundness; 7 animals (3%) did not regain full athletic function, 42 animals (20%) died or were destroyed. Cases were assigned to four groups on the basis of initial clinical examination alone. These groups were laminitis, acute founder, sinker, and chronic founder. This grouping was found in itself to be the most important prognostic parameter which was studied. Stepwise regression analysis of the data from animals by group indicated that the radiological measurement of founder distance, was the most significant radiological prognostic measurement for acute founder cases. Less significant prognostic parameters were the severity of lameness, rotation angles, the presence of solar prolapse, and the number of feet affected. The height of the animal at the withers was not significantly related to outcome. The prognosis for horses was not significantly different from that for ponies.
Many therapeutic regimes have been described to treat "laminitis" but few published reports support their efficacy. Goetz and Comstock (1985) reported that in a group of 22 horses affected with varying severity and chronicity of laminitis 46% became sound following the use of adjustable heart bar shoes as part of the treatment regime, 27% were improved by at least 2 Obel grades and 27% required euthanasia. Allen et al (1986) reported on the treatment of 13 cases of chronic refractory laminitis cases by the use of deep digital flexor tenotomy. Eleven cases improved, but did not become sound, and two were subjected to euthanasia. Baxter (1986) recorded the results of treatment of 12 cases of distal displacement of the distal phalanx, three cases survived but remained lame. Hunt et al (1991) used deep digital flexor tenotomy on 20 horses suffering from acute and chronic laminitis. Six cases survived more than six months following surgery, three of these remained lame and no case returned to athletic performance.
Little has been achieved in terms of improving the accuracy of the prognosis for laminitis cases. Colles and Jeffcott (1977) related the prognosis for a case of laminitis to the severity of onset, number of feet affected and speed of recovery although no results were clinical data was published. Stick et al (1982) produced a retrospective survey of referred laminitis cases. Their study indicated that horses with distal phalangeal rotation (relative to the dorsal hoof wall) of more than 11.5 degrees tended to remain lame. Stashak (1987) suggests that only in exceptional circumstances should treatment be considered for cases in which the distal phalanx has penetrated the sole (solar prolapse). Eustace and Caldwell (1989) demonstrated that animals with degrees of distal phalangeal rotation greater than the suggested threshold of 11.5 degrees can return to full athletic function if they are treated using a heart bar shoe and the technique of dorsal wall resection. Linford (1987) described the radiological measurement of wall thickness; an increase in this distance was found to be positively associated with laminitis and marginal fractures of the distal phalanx. Hunt (1993) considered that the greater the severity of lameness the worse the prognosis for cases of laminitis.
In this study clinical and radiological parameters were studied for clinical cases where we knew both the treatments given and the outcome. The data were subjected to statistical analysis to discover which parameters were significant predictors of successful outcome and which ones were likely to be of value for future cases.
Materials and Methods.
All cases which were referred to a specialist equine laminitis referral centre, between May 1988 and July 1993 were included in the study. No case selection was applied. The physical characteristics of the cases are listed in Table 1.
Animals were assigned to groups following clinical examination with special attention being paid to the feet and palpation of the digital arteries and coronary bands.
Group A - Laminitis. Cases were assigned to Group A if they had clinically normal hooves, and no hoof distortions characteristic of chronic founder. These animals had abnormally strong pulsation in the digital arteries of affected feet, tended to adopt a heel-loading and toe-relieving stance, and sometimes showed pain over the dorsal part of the soles of the feet. They sometimes showed resentment to light palpation around the coronary band and shifted their weight from one foot to another.
Group B. - Acute Founder cases. Cases were assigned to Group B if their hooves were similar to Group A but additionally had palpable depressions just above the coronary band. These depressions extended a variable distance (but not all the way) around the coronary band. Coronary depressions were evaluated by running a finger down the pastern and over the coronary band: In the normal horse the finger tends to slide over the coronet and onto the hoof wall; if a depression is present the finger tends to lodge just above the coronary band. The severity of lameness was often but not always greater for Group B cases than for Group A cases.
Group C. - Sinkers All sinkers showed depressions which extended the full length of the coronary band. They also showed a bounding digital pulse and reluctance to move or to have a limb lifted. Some cases adopted a toe-relieving stance, others tended to stand flat and shift weight moving in a heavy flat-footed manner, slapping the feet down in a similar way to cases of cervical maladjustment syndrome (wobbler). However none of the sinkers in this study showed signs of chronic founder.
Group D. - Chronic Founder. These cases showed changes in the foot characteristic of chronic founder. Changes included a broken back hoof-pastern axis, over-grown or concave dorsal hoof walls, stretched white lines from quarter to quarter, and divergent growth rings on the hoof walls with the rings being wider at the heels than the toes. There was relative over-growth of the heels and the soles were flat or convex. On palpation the coronary bands often seemed soft or indistinct and the skin seemed to merge directly with the horn. Some of these animals were also demonstrating the signs of laminitis or acute founder. Nevertheless, all cases showing characteristic signs of chronic founder were classified as such in Group D.
A somewhat different lameness Grading system was used in this study from those quoted previously. A modification of those systems described by Obel (1948) and Stashak (1987) was developed. This classification aimed to describe the type of gait shown both by acute and chronic cases and spans the range of severities from soundness to near-permanent recumbency. The grading system attempts to relate to clinical rather than experimental cases of laminitis.
Grade 0; No lameness at walk nor at a straight trot on a hard surface.
Grade 1; No lameness observable at walk, the animal moves freely. Shows lameness at trot in a straight line on a hard surface. Turns carefully.
Grade 2; The animal does not move freely at walk but moves with a "stiff" gait. Animal may show overt lameness on one leg at walk. It is reluctant to trot on a hard surface and turns with great difficulty.
Grade 3; The animal is reluctant to move at walk on any surface. It is very difficult to lift a limb. The animal may be virtually non-weight bearing on one limb.
Grade 4; The animal will not move without coercion, and is particularly reluctant to move from a soft to hard surface. It is impossible to lift a limb.
Grade 5; The animal spends most of the time recumbent, and cannot stand for more than a few minutes.
All the horses were radiographed at least once. In most cases all four feet were examined radiologically.
Radiographs were taken with the horse unshod and standing on flat ground using the same flat wooden block incorporating a metal ground line and the same radiographic generator. The radiographic beam was aligned to be parallel to the ground and the long axis of the navicular bone and directed towards the centre of the distal phalanx (Figure 1). All feet were radiographed whilst bearing weight and with the limb in as normal a position as possible. The sole and wall were cleaned using a hoof pick and wire brush. The frog was trimmed so as to remove all horn overlying the collateral frog sulci and the tip of the frog. The sides of the frog were bevelled. A drawing pin with a shortened point was placed approximately 1 cm posterior to the point of frog and its position marked by drawing a line across the sole and frog with an indelible felt tipped pen. The horn on the dorsal part of the hoof just below the coronary band was rasped smooth. The proximal dorsal hoof wall was palpated, just below the coronary band and the point at which the wall horn began to yield to moderate digital pressure was marked with an indelible pen line. A straight stiff wire marker, of known length, was taped to the dorsal hoof wall with the proximal end at the pen line (Eustace 1990).
Radiographs were fixed onto a horizontal viewing box, a sheet of clear film was overlaid and lines were drawn with a fine tipped pen. Six measurements were made from each latero-medial radiograph (see Figure 1).
1. Angle S, the angle between the dorsal hoof wall and the ground.
2. Angle T, the angle between the dorsal cortex of the distal phalanx and the ground.
3. Angle U, the angle between a line connecting the centres of curvature of the proximal and distal interphalangeal joints and the ground. The curvature of these joints is not uniform but a `best fit' line can be drawn.
4. The vertical distance, d, between the top of the dorsal wall wire marker and the proximal limit of the extensor process of the distal phalanx.
The length of the dorsal wall wire marker.
The length of the middle phalanx, MP.
7. The distance between the dorsal wall marker and the dorsal cortex of the distal phalanx. A point mid-way along the dorsal cortex of the distal phalanx was chosen for measurements and the line of measurement was perpendicular to the dorsal cortex.
From these measurements five calculations were made:
a. Angle H: Angle T minus Angle S, as described by Stick et al (1982).
b. Angle R: Angle T minus Angle U.
D%: 4 divided by 6 above, expressed as a percentage; = i.e.; 4 / 6 x 100 %. It is the imaged value for founder distance divided by the imaged value for the length of the middle phalanx. Thus it is calculated by relating D to the only osseous structure commonly measurable in digital radiographs which is unaffected by laminitis and founder, and it provides a measure of D which avoids having to correct for magnification.
D, the Founder Distance. The true distance between the top of the dorsal wall wire marker and the proximal limit of the extensor process of the distal phalanx after correcting for magnification. This is calculated using the following formula:
Actual length = length measured radiographically x actual length of marker / radiographic length of marker.
WT: the actual thickness of tissue between the dorsal hoof wall and the dorsal cortex of the distal phalanx after correction for magnification according to the above formula.
Where normal values or ranges are quoted for radiological measurements these refer to those found by Cripps and Eustace (1999).
The presence of solar prolapse, due to distal movement of the distal phalanx, was recorded when solar corium was visible protruding through the horny sole.
The number of feet affected was recorded. The horse's height at the withers was measured using a conventional measuring stick. The dose of analgesic which the animal was receiving on admission was recorded.
After a period of at least six months, the animals were categorised according to outcome into either Failure of Treatment (Dead or unrideable) or Success of Treatment (Sound with Grade 0 lameness and rideable). Unless the animal showed a Grade 0 lameness and was able to return to its previous type of work and remain sound during the follow-up period the case was categorised as a failure of treatment. A client questionnaire was used to obtain the results of treatment on animals not recently examined by the first author (Eustace 1991a).
The following variables were included in the statistical analysis. The animal's age, sex, breed, height, number of feet affected, presence of solar prolapse and analgesic dosage on admission. The grade of lameness, the group to which it had been assigned on admission and final outcome category. Radiological variables considered were Angle S, Angle T, Angle U, Angle H, Angle R, Wall thickness WT, D% and Founder distance D.
The treatments used in this study were based on removing or treating the initiating cause of laminitis, using acepromazine or phenoxybenzamine as peripheral vasodilators with limited doses of non-steroidal anti-inflammatory drugs, providing the animal with a deep shavings bed covering the whole stable floor area, fitting frog supports to the feet, and encouraging the animal to lie down. Animals were restricted to complete stable rest until 30 days after they appeared to be Grade 0 lame in the stable without analgesics. Thereafter they began a controlled exercise program starting with walking out in hand and building up to ridden work.
Medical treatments included phenoxybenzamine, acepromazine, phenylbutazone, flunixin, meclofenamate and aspirin. Acepromazine and phenylbutazone were the most commonly used drugs in combination. The dosage of acepromazine was adjusted to produce moderate tranquillisation, phenylbutazone was used to alleviate rather than abolish lameness. Other medical treatments were used to treat specific problems associated with laminitis e.g., antibiotics, thyroid supplementation, cyproheptadine, uterine lavage. All cases were given a diet based on forage incorporating alfalfa Alfa A and Hi Fi 1. A proprietary biotin, methionine and zinc chelate mixture (Biometh Plus) 2 was used as a specific horn supplement on the first 67 cases. Thereafter the supplement Farrier's Formula 3 was substituted.
All cases were treated using some form of frog support; after the first 29 cases, plastic and steel glue-on adjustable heart bar shoes were developed and substituted for steel shoes (Eustace 1992a and 1992b). Animals showing a lameness of Grade 2 or more were not shod with nailed on shoes. Dorsal wall drilling was used on animals at the acute founder stage, and dorsal wall resections were made at the old founder stage (Eustace 1992a). Foot bandaging was rarely used, although latterly solar prolapses were covered with a hydrocolloid dressing (Granuflex) 4 which was left in situ for up to one week. Resection of the interior check ligament was performed on five cases; deep digital flexor tenotomy was performed on sixteen animals. In some cases just one leg was operated on whilst in one animal all four deep flexor tendons were divided.
Owners were provided with a diet and management protocol for the animals. Most animals having dorsal hoof wall resections returned to the Clinic for foot treatments and shoeing at six weekly intervals for up to a year.
A total of 216 animals were admitted to the laminitis referral centre during the period of study, and of these 5 were not treated or radiographed and were excluded from further analyses. After a period of at least six months the other 211 animals were categorised according to outcome. Statistical analysis was performed using Minitab 5, SPSS 6 and Genstat 5 7. Where the measured variables had different values for different feet of the same animal the greatest value for each animal was used. Initial basic analyses examined the differences between measured variables for the different outcome groups, using Student's t test for independent samples, the Mann-Whitney test or a x2 test as appropriate.
The ability of variables to predict outcome was investigated as follows: a) for categorical variables an individual with a certain level of a variable was assumed to show the commonest outcome for that level; b) for continuous variables the cut-off point was found that best separated groups. c) the possibility that more than one explanatory variable could be used to predict success or failure was examined using the method of maximum likelihood. Success or Failure was considered as being binomially distributed and a logit link was used; a forward stepwise regression was employed and variables were entered into the model in the order that most reduced the deviance (log-likelihood ratio statistic). Variables were added to the model until there was no longer a significant reduction in deviance. This was the final model and from it the probability of success was estimated for each animal. An estimate of less than 0.5 was predicted to be a failure and value of m 0.5 were predicted as successes. For each of methods a), b) and c) the proportion of correct predictions could be calculated, either overall or according to true outcome.
Basic analyses were performed to examine the relationship of the calculated angle H to outcome. In addition the relationship was investigated between outcome and whether the animal was a horse or a pony. Similar statistical methods were used as for the rest of this study. The same approach was used to examine the importance of solar prolapse and of the number of feet affected. Significance probabilities (P values ) were for a two-sided Null Hypothesis of no difference. Statistical Significance was set at P < 0.05.
Of the 211 animals, 162 (77%) returned to an athletic career at their original or higher level of performance: 49 (23%) animals were either destroyed or were unable to be ridden. Of the 49 animals, 7 were able to be used as pets or breeding animals without analgesics and 42 either died or were destroyed. Of the latter 42, 19 did not survive 1 week, 15 survived between 1 week and 6 months and 8 survived longer than one year.
Tables 1 to 5 show the distribution of cases by breed, age, sex, duration before referral and cause. The Clinical Groupings and outcomes following treatment are given in Table 6 and Table 7 shows the relationship between outcome and grade of lameness. Tables 8 and 9 show the relationship between outcome, horse versus pony and Group.
106 (49.1%) of the cases were female, 102 (47.2%) were geldings and 8 (3.7%) were stallions. Onset of laminitis was recently preceded by consumption of an excess of carbohydrate rich food in 146 (67%) of the cases, many of which were already obese. 22 (10%) animals were diagnosed as suffering from hyperadrenocorticism (Cushing's Disease) from clinical signs and a positive response to a thyroid releasing hormone (TRH) response test (Beech and Garcia 1985: Eustace 1991b). In six cases the animal was examined post-mortem and a pituitary adenoma was present in each case. 12 (6%) of the animals had foot distortion or imbalance which was considered to have initiated the attack of "laminitis". Twenty animals (9%) had contracture of the deep digital flexor apparatus on the affected limbs which required surgery to either the inferior check ligament or the deep digital flexor tendon. Six animals had chronically elevated AST, Gamma GT, GLDH and bile acid concentrations which were considered to be causally related to the laminitis. Four animals (2%) suffered laminitis following injections of corticosteroids, five (2%) had traumatically induced laminitis, two suffered from thyroid insufficiency (as determined by TRH response testing), one animal suffered a chemical toxaemia, and one case followed dystocia.
The Prediction of Outcome
Table 10 Shows the ability of a number of different models to predict success or failure together with their overall accuracy. Where all cases were considered the stepwise regression model chose Group membership as the single most important predictor of outcome (P< 0.001). It was able correctly to predict 171/211 (81%) of outcomes. If Group membership was not offered then founder distance (D), Grade of lameness, Angle U and Sex were chosen; these correctly identified 20/47 (47%) of failures and 154/158 (94%) of successes, giving an overall accuracy of 174/205 (86%). The effect of Sex appeared to be because all eight stallions were successes compared to 72% of females and 80% of geldings. When information about sex was not offered the model chose D, Grade of Lameness, Angle T and Angle R: the corresponding figures for success, failure and overall accuracy were 94%, 43% and 82% respectively.
When chronic founder cases were excluded and information on Group membership was not offered D was the only predictor chosen in the stepwise regression. It could correctly identify 85% of outcomes; this compares with an accuracy of 83% that was obtained by using information on Group membership alone.
Since all laminitis grouped cases became successes the prediction success was completely accurate. For acute founder the use of D increased the accuracy from 81% to 86%. Figure 2 illustrates the relationship between founder distance D and the actual percentage success for cases with acute founder. For sinkers angle U was chosen by the regression model but it could correctly predict only 71% of outcomes (compared with 80% by assuming all cases failed). The model chose angle U and Grade of lameness for cases of chronic founder and with these the accuracy of prediction increased from 79% to 83%.
The results show that the single most important predictor of outcome was the clinical group to which the animal belonged. Once this was known a number of variables measured from radiographs (and in particular founder distance D) significantly improved the logistic regression models. However, once the animals had been assigned to their clinical groups the overall ability of radiological measurements to increase the accuracy of prediction was somewhat limited. Further examination of D did however suggest that for very high or low values it was a useful guide to outcome. For instance when cases of chronic founder were examined it was found that no animal out of the 32 with a founder distance of <7.9 mm failed whilst only one of the 11 with a value above 15.2 mm was a success. The logistic regression equation suggests that values of founder distance of 14.0 mm and above have a probability of success of less than 50%. This confirmed that the proportion of success is higher for low values of D than for high values. For example, when chronic founder is excluded 2/11 (18.2%) of cases with D over 15 mm became successes and 31/34 (91%) with a D under 8 mm were successful.
There was not a direct relationship between the four clinical groupings and the radiological measurements and many cases had values which were within the range of those found in normal animals (Eustace & Cripps 1999). For example, all first time laminitis cases (Group A) had a founder distance within the normal range of -2 to 10 mm and an angle H of less than 4 degrees. It is therefore not possible to diagnose laminitis from the examination of digital radiographs alone. Some acute founder cases (Group B) had a founder distance within the normal range but others did not. The deeper the coronary band depression appears to palpation, and the greater the medio-lateral extent of the depression, the greater the measured founder distance tends to be. Similarly with sinker cases, it is possible to diagnose a sinker clinically and yet find a founder distance within the normal range. This is uncommon and such cases may have a better prognosis than sinkers with a founder distance without the normal range: in our series of 15 sinkers only one had a 'normal' recorded value for D (3.5 mm) and this was one of the 3 successes.
The Relationship between outcome, founder distance (D) and D%
Although D% was strongly associated with outcome and with D the association with outcome was always stronger with the actual founder distance than with D%.
The Relationship between outcome and angle of rotation (Angle H).
The mean and median values for Angle H were greater overall for failures than for successes (P<0.01). This was partially related to the low central value (mean 3.87o, median 3.00o) for the laminitis cases, all of which recovered; the mean for the other 3 clinical groups varied between 10o and 11.2o with medians of 8.5o-11o. Within clinical groups Angle H was only significantly different between outcomes for chronic founder where the mean (median) value was 18o (20o) for failures as against 10.2o (9o) for successes, [P<0.001]. When all clinical groups were considered together the raw data suggested that low values of Angle H might indicate success and high values failure: 54% (15/28) of cases with Angle H > 20o were successes compared with 88% (21/24) of those with Angle H <2o. Logistic regression suggested that overall Angle H could significantly predict outcome (P<0.01) but within clinical groups this did not apply (P>0.5) except for the chronic founder cases (P<0.001). If information on group membership was not given Angle H could correctly identify 4% (2/47) of failures and 99% (156/158) of successes, giving an accuracy of 77% (158/205). Within the chronic founder group the corresponding values are 29% (6/21), 96% (77/80) and 82%.
The Relationship between outcome and Grade of lameness (Table 7)
There was a significant association (P < 0.001) between outcome and the grade of lameness with the proportion of failures increasing with increasing grade of lameness. Part of this association could be explained by the relationship between grade and clinical group: none of the 16 laminitis cases had a lameness grade greater than 3 whilst 14 of the 15 sinkers had a grade of 3 or more.
The Relationship between outcome and Breed (Table 2)
The combined failure rate for Arabs, Arab Cross and Thoroughbred animals was 20/37 (54.1%). This was significantly greater (P < 0.001) than for most of the other breeds whose combined failure rate was 29/174 (16.7%). Regression analysis suggested that the effect of breed was acting independently to that of group membership, grade of lameness or founder distance.
The Relationship between outcome and Horse versus Pony (Tales 8 & 9)
The distribution of clinical groupings was different for horses and ponies (P < 0.001) and this was mainly due to there being a greater proportion of ponies than horses with Chronic Founder (62.2% Vs 34%) and a lower proportion with Acute Founder (25.2% Vs 49%). The outcome of success or failure was not significantly associated with being a horse or a pony (P>0.35) and this was true both overall and when looking at individual clinical groups.
The Relationship between outcome and prolapse of the sole
There was a significant association between outcome and solar prolapse (P<0.001). A total of 36 cases had prolapses and of these 20 (56%) were successes compared with 142/175 (81%) of unprolapsed cases. Although the likelihood of failing was greater for prolapsed cases than for non-prolapsed ones the overall accuracy of prediction (78%) was less than that obtained if Group membership alone was used. (81%).
The Relationship between outcome and number of feet affected
The outcome was significantly associated with the number of feet affected (P<0.01) and this was true whether the number of feet were considered in four separate categories or as up to 2 versus more than 2 affected. Although the mean number of feet affected was different in successes and failures (P<0.05) there is not a clear cut relationship between increased number of feet affected and increased risk of failure. Of the three horses with only one foot affected 1 (33%) became a success. Overall 82% of animals with 2 affected feet were successes and 62% of those with 4 feet affected. However when success rate was examined by clinical group it was found that for acute founder there was 74% success for 2 affected feet and 88% success for 4 affected feet: corresponding values for chronic founder were 85% and 73%.
The results of treatment in this study compare favourably with previous reports in which the success rate, judged by a return to athletic soundness (Grade 0 lameness and a return to previous activity), has varied between 0% to 62% (Stick et al 1982; Goetz and Comstock 1985; Allen et al 1986; Baxter 1986; Hunt et al 1991; Hunt 1993; Peremans 1991).
Whilst we cannot be certain why these good results were obtained it could be that we had particularly simple cases to treat. This explanation seems unlikely because all cases were referred from other veterinary surgeons, most cases had already received some treatments, and no case selection was made; this report includes all cases that were referred to the clinic. It is however difficult to compare results when authors do not use the same classification system to describe cases. We suggest that the time has come to abandon the use of the all encompassing term 'laminitis' to describe our clinical categories laminitis, acute founder, chronic founder and sinker. Similarly the terms acute, sub-acute and chronic laminitis do not provide an accurate reflection of the digital pathology. When descriptive criteria have been established (e.g., Baxter (1986)) the results of treatment have been very similar to our own. Other factors which may have influenced our results are the use of a single disease clinic, the same operator treating all the cases, adequate rest following lameness, good after care and follow up shoeing treatments.
Baxter (1986) and Hunt (1993) described distal displacement of the distal phalanx and reported generally poor results of treatment; this study confirms their findings. If laminitis is a condition requiring prompt treatment then distal displacement (sinker) cases constitute true clinical emergencies. Our experience suggests that a delay of only a few hours can leave the clinician with little chance of a successful outcome.
It is uncommon for sinkers to have founder distances within the normal range and in our series it occurred in only 1 of 15 animals. This animal made a successful recovery and this suggests that such cases may have a better prognosis than sinkers with a founder distance outside the normal range.
The animals were hospitalised from between 1 week and seven months. Our clinical impression is that this and the 30 days' box rest gives the laminar tissue time to heal and reduces the risk of cases progressing to founder, thereby contributing to the overall success rate. We also believe that the substitution of a biotin/methionine/zinc mixture with the supplement Farrier's Formula did lead to the production of horn with a more normal physical appearance and improved strength when horses were returned to nailed on shoes. Such findings are in agreement with the work of Kempson (1990).
Some cases were referred to the clinic wearing steel heart bar shoes; in most cases the shoes had been fitted incorrectly and were causing the animals pain. The common problems were incorrect placement of the frog piece, this resulted from failure to trim back the frog sufficiently prior to shoeing and misinterpretation of radiographs, if any had been taken. In some cases the shoes had been fitted with excessive pressure from the frog piece, or the shoes had been left on too long. If machine made heart bar shoes were used they had usually not been seated out sufficiently so that the shoe was causing painful sole pressure. Such shoes are usually made from too thin a steel section. Walking acute founder or sinker cases risks increasing the degree of founder. If the horse has steel heart bar shoes fitted, the digital tissues become pinched, this increases the lameness. In our opinion the fitting of open toes bar shoes to acute founder cases is contraindicated, such treatment seems to induce contraction of the deep digital flexor muscle to an abnormal degree resulting in refractory cases and an unsuccessful outcome. In chronic founder cases the most common foot dressing fault was that the dorsal hoof wall had not been trimmed back to be parallel with the dorsal cortex of the distal phalanx.
The majority of predisposing circumstances listed under causes were associated with over-consumption of high soluble carbohydrate food. These findings suggest that careful management to control the weight of the animal and avoidance of high carbohydrate feeds would prevent the occurrence of most of the cases seen in this study. No published results of the prevalence of equine pituitary neoplasia are available. A limited survey (Eustace, RA, unpublished observations) revealed that 1.5% of pituitary glands from slaughterhouse material showed histological evidence of neoplasia. Interestingly, in our material, islets of neoplastic tissue were present in the pars distalis as well as the more common site in the pars intermedia (Donnelly, MS and Eustace, RA, unpublished observations). In our experience recurrent cases of laminitis, particularly in animals over ten years of age, which do not have an obvious cause, often show an abnormal response to the thyroid releasing hormone (TRH) response test. The rise in cortisol increased by 50-60% fifteen minutes after intravenous injection of 1 mg of TRH. Such animals may not show the clinical signs of hirsuitism, polydipsia, polyuria associated with Cushingoid horses and ponies. Preliminary evidence suggests that these animals are developing pituitary tumours (Eustace unpublished observations). When performing the TRH response test, it can be helpful in establishing a diagnosis to measure the serum insulin concentration in the initial blood sample, elevated concentrations indicate that the animal is becoming insulin resistant. Even normoglycaemic horses with pituitary tumours are usually hyperinsulinaemic Beech (1987).
No increased sex related prevalence was noted in this study and this is in agreement with the reports of Peremans et al (1991) and Hunt (1993) and contrary to the findings of Dorn et al (1975) and Amoss et al (1979).
An unexpected finding in this study was the higher failure rate in Arabs and Arab Crosses than in other breeds. Our analyses suggest that this cannot be explained by other measured factors and that it may reflect a genuine breed-related difference. Based on our clinical experience during this study we suggest that two factors may be responsible for these results. Firstly may be due in part to the shape of the feet. Most Thoroughbreds and Arabs in this study had wide flat feet with poorly developed heels and thin walls and soles. This type of foot appears to have a much narrower safety margin once the animal founders. A relatively small founder distance (e.g., 12 mm) seems to result in more damage to these cases than to animals with a more upright foot with stronger horn. In addition because the sole is thin and the heels poorly developed there is little the clinician is able to do in terms of foot treatments which do not cause the animal more pain. Secondly our experience also leads us to suspect that, these breeds Arabs and Arab Crosses may appear tend both to have a much lower pain threshold and to tend to recover less well than other breeds when give up when they do suffer the pain of founder and sinking. .
This study found that the success rate decreased with increasing Grade of lameness and this agrees with the findings of Hunt (1993). However, the Grade of lameness could not produce a useful prediction of outcome and for this reason we believe that it is risky to base prognosis on it. Without an animal with the will to live any treatment is likely to fail. For example, the difference in the pain evidenced between Welsh Section D Cobs and Arabs with similar digital pathology was remarkable. For this reason we believe that it is risky to base prognosis on the Grade of lameness.
Our results show that use of the rotation angle H as a prognostic indicator is of very limited value when the clinical Group is known and thus do not support the findings of Stick et al (1982). This is particularly true in cases of distal displacement of the distal phalanx (sinkers) when little rotation occurs. Chapman and Platt (1984), Baxter (1986), Eustace (1989; 1990) and Eustace and Caldwell (1989) have shown that such cases show little rotation of the distal phalanx as described by Stick, et al (1982): yet these cases have the most devastating foot pathology. If angles of rotation are to be quoted then the two angles H and R should be used; otherwise no information is available of the relative positions of the distal phalanx, proximal phalanges, dorsal hoof wall and the ground. Such information is important if deep digital flexor contracture is suspected. Furthermore, using Angle H as a prognostic indicator with no consideration of Group ignores the type of pathology within the foot and can only predict 4% of failures.
Comparison between the results of the normal values of D (Cripps & Eustace 1999) in which the horses were shod and those in this paper in which they were unshod may be a source of errors. However although we have not made a controlled study of any variation in D following removal of shoes it is our clinical impression that D does not alter significantly following shoe removal. The only instances when we have noted an increase in D is following division of the deep digital flexor tendon. In such circumstances a palpable increase in the depth of the coronary depression was observed as well as an increase in D measured radiologically. Additionally D was found to increase when dorsal wall resections were made too early i.e. at the acute founder stage. In these cases the distal phalanx was still partially attached to the dorsal hoof wall and receiving some suspension (Eustace and Cripps unpublished observations).
Although surgical division of the deep digital flexor tendon is often considered to be a salvage procedure for valuable breeding animals our experience (12 Successes from 20 operated cases) suggests that some animals can be returned to full ridden soundness one year following the surgery. The decision to operate is made on clinical grounds alone although an abnormally high Angle R is usually present. Cases requiring flexor surgery tend to stand and walk on their toes rather than the heels. These cases can easily be missed if they are receiving analgesic medication which masks the contracture. Some animals which are developing abscesses in the palmar/plantar parts of the foot can mimic cases of flexor contracture and we therefore prefer to postpone surgery if there is any doubt as to the diagnosis. Most cases in this study were operated on under local anaesthesia at the mid cannon site. This technique is preferred as it allows accurate realignment of the phalangeal column using check radiographs following foot dressing. All operated cases need shoes with palmar/plantar extensions. These are more easily fitted with the animal standing. Providing temporary devices, to prevent over-extension of the distal interphalangeal joint during recovery from general anaesthesia, incurs the risk of serious injury should the device be displaced during an uncoordinated recovery. Chronic founder cases with osteopaenic changes to the distal phalanx (Eustace 1992a) are unlikely to return to soundness following tenotomy as the contracture is not the only cause of pain in these cases.
It is the opinion of the authors that it is more difficult to achieve a success when treating an animal with an odd number of foundered feet than an even number. In some cases this results in a more severe founder in the originally unaffected contra-lateral foot. In others the animal tends not to bear any weight on the affected foot for long periods and the case becomes refractory with no apparent healing.
Stashak (1987b) considered that the development of solar prolapse was grounds for euthanasia. The results reported here suggest that it is the pathological mechanism causing solar prolapse that is of prognostic significance. Solar prolapse may result from slight distal displacement and considerable rotation of the distal phalanx away from the dorsal hoof wall and the line of the proximal phalanges, or to a large distal displacement of the distal phalanx with minimal rotation. The former cases have a much better prognosis than the latter.
These findings suggest that careful examination of the feet alone will allow equine practitioners to abandon the all embracing term "laminitis". Instead, cases can be given a more precise diagnosis of laminitis, acute founder, sinker or chronic founder. Use of these groupings will be of great prognostic value. Prognosis can be further refined in cases of acute founder and sinking by accurate measurement of founder distance.
Our gratitude is due to Burney Chapman who gave invaluable advice on understanding the pathological changes within the foot and the correct use of the heart bar shoe in 1987. Also to Sue Emery who gave unstinting and dedicated care to all the clinical cases.