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Keywords:

  • horse;
  • laminitis;
  • transfixation pin casts;
  • support limb

Summary

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Manufacturer's address
  8. Authors' declaration of interests
  9. Source of funding
  10. Acknowledgements
  11. References

Reasons for performing study: To determine the incidence of support limb laminitis among horses treated with half limb, full limb or transfixation pin casts and determine potential risk factors.

Methods: Medical records of 113 horses treated with half limb, full limb or transfixation pin casts at an equine referral hospital from 2000 to 2009 were reviewed. Associations between potential risk factors and development of support limb laminitis were evaluated by bivariable and multivariable logistic regression analyses.

Results: Of the 113 horses that received casts, 14 (12%) developed confirmed support limb laminitis. The bodyweight of the horse and duration of casting in weeks were significantly associated with support limb laminitis. Horses requiring full limb casts or transfixation pin casts were more likely to develop this complication than horses requiring half limb casts. There were no significant associations between developing support limb laminitis and weightbearing capacity on presentation to the hospital, the limb affected (fore- or hind), whether there was a fracture present or breed of horse.

Conclusions: Support limb laminitis is a relatively common complication among horses treated with half limb, full limb and transfixation pin casts. Greater durations of casting and higher bodyweights increase the likelihood of developing this complication.

Potential relevance: Support limb laminitis may occur secondary to any painful unilateral lameness and is not necessarily more likely to develop in horses with severe orthopaedic conditions such as fractures. However, heavier horses, those requiring casts for longer periods of time and those that require a full limb or transfixation pin cast as opposed to a half limb cast should be considered to have an increased risk for developing support limb laminitis post operatively.


Introduction

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Manufacturer's address
  8. Authors' declaration of interests
  9. Source of funding
  10. Acknowledgements
  11. References

Support limb laminitis can occur with any condition resulting in excessive unilateral weightbearing in a fore- or hindlimb due to severe lameness (Baxter and Morrison 2009; Van Eps et al. 2010). Painful conditions such as complete fractures, osteoarthritis, severe wounds or sepsis of synovial structures are most often clinically associated with developing support limb laminitis, but it may also occur with any condition that causes prolonged unilateral weightbearing, including neurological deficits or mechanical lameness (Baxter and Morrison 2009). In the authors' experience, support limb laminitis occurs more frequently than previously reported (Peloso et al. 1996; Redden 2004; Richardson 2008) and is a substantial risk when managing surgical cases that develop severe unilateral lameness.

In contrast to other forms of laminitis, such as those that occur secondary to endotoxaemia or insulin resistance, little research has been performed investigating the pathological events that result in support limb laminitis. Extrapolating data from other more extensively studied forms of laminitis to support limb laminitis must be done with caution as several key differences have been noted in the literature (Baxter and Morrison 2009; Eades 2010). For instance, support limb laminitis usually occurs in only one foot and horses that develop this complication typically lack systemic abnormalities (Baxter and Morrison 2009; Eades 2010). There are currently 2 theories on the pathophysiology of support limb laminitis: the first entails a direct mechanical overload of the suspensory apparatus of the distal phalanx and the second implicates a primary hypoperfusion state resulting in tissue deficits and potentially activation of the enzymatic and chemical mediators involved in other forms of acute laminitis (Van Eps et al. 2010). Given the degree of drastic lamellar separation typically observed with support limb laminitis and weightbearing capacity of the suspensory apparatus of the distal phalanx (reportedly up to 3 times the horse's weight), some authors consider a direct mechanical overload to be an unlikely aetiology (Van Eps et al. 2010). The cyclic loading and unloading of the foot is thought to be integral in maintaining adequate perfusion to the digital lamellae and it has been proposed that the reduction in the frequency of this cyclic loading predisposes and potentially initiates, support limb laminitis (Redden 2004; Van Eps et al. 2010).

Few reports exist regarding the prevalence and associated risk factors for developing support limb laminitis. Several authors have reported anecdotally that the severity and duration of lameness are positively correlated to the risk of developing support limb laminitis (Redden 2004; Baxter and Morrison 2009; Van Eps et al. 2010). Peloso et al. (1996) confirmed in a case-control study of 20 horses that the duration of unilateral lameness was positively associated with the risk of developing laminitis but other factors including bodyweight, age, breed, limb affected, heart rate and temperature at admission, clinicopathological tests or casting were not significantly associated with a greater risk of support limb laminitis (Peloso et al. 1996). Redden suggested the 2 most important factors may be the length of time the foot remains fully loaded in weightbearing position and the structural integrity of the foot itself (Redden 2004).

The objectives of this study were to review cases in which cast immobilisation was applied to a fore- or hindlimb and 1) identify the overall incidence of support limb laminitis in the contralateral limb and 2) determine the effect of factors such as bodyweight, breed, limb affected (fore- or hind) and reason for casting (fracture, wound, arthrodesis) on the risk of developing this complication. Although an association between the type of unilateral lameness and risk of support limb laminitis has not been identified in the literature, we hypothesised that horses suffering fractures and those that are nonweightbearing on the affected limb on presentation would be at increased risk. Furthermore, we hypothesised that horses that require a full limb, half limb or transfixation pin cast have an overall incidence of support limb laminitis greater than 10% and that bodyweight and severity of disease (fracture, arthrodesis or wound) would affect the incidence of support limb laminitis. In this study, the incidence of and risk factors associated with support limb laminitis were determined in horses that received half limb, full limb or transfixation pin casts following surgical treatment. To our knowledge, there has not been a study investigating the risk factors associated with support limb laminitis in horses receiving surgical treatment and subsequent casts. This study should assist practitioners in developing a prognosis for equine surgical patients receiving casts and determining which patients may be at an increased risk for developing support limb laminitis.

Materials and methods

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Manufacturer's address
  8. Authors' declaration of interests
  9. Source of funding
  10. Acknowledgements
  11. References

Case selection

Medical records of 113 horses that received a half limb, full limb or transfixation pin cast at an equine referral hospital between 2000 and 2009 were reviewed. Cases not included were horses that received foot casts, bandage casts, bivalved casts, or splints, horses of less than one year of age or those that wore a cast for less than one week duration. Minimum follow-up was considered 3 weeks or until the time of cast removal.

Data collection

Laminitis was determined based on the presence of clinical signs and radiographic evidence of sinking and/or rotation of the third phalanx on lateromedial projections (Dyson 2003; Baxter and Morrison 2009). Sinking of the third phalanx was determined by demonstrating an increase in the distance from the extensor process of the third phalanx to the level of the coronary band observed on sequential radiographs. Rotation of the third phalanx was determined by comparing the distance from the proximal and distal dorsal parietal surface of the third phalanx to the hoof wall and measuring the angle of the solar margin of the distal phalanx to the ground (the palmar angle) as described in detail elsewhere (Belknap and Parks 2011). Cases were not included based on clinical signs alone in the absence of radiographic evidence of laminitis. All radiographs were reviewed secondarily by a diplomate of the American College of Veterinary Radiologists for evidence of laminitis. The following data were collected from the medical records: age, sex, breed, use of the horse, bodyweight, type of cast (half limb, full limb, or transfixation pin cast), limb affected (hind- vs. forelimb), development of laminitis in the contralateral limb (yes/no), cause of the unilateral lameness (fracture, pastern arthrodesis, wound repair or other), ability of the horse to bear weight on the affected limb at presentation (weightbearing or nonweightbearing), and duration of casting in weeks. Horses included in the ‘other’ category as the cause for unilateral lameness included miscellaneous procedures of which there were low case numbers such as fetlock and carpal arthrodeses and deep digital flexor tenotomies. The degree of lameness throughout hospitalisation of the horse and the prophylactic measures applied to the contralateral limb were not consistently and accurately recorded in all medical records and hence were not included.

Data analysis

An association between each potential risk factor identified in this study and development of clinical and radiographically confirmed support limb laminitis was evaluated by bivariable and multivariable logistic regressional analyses (SAS v9.2)1. The association between type of cast and support limb laminitis was evaluated using a Fisher's exact test. A P value of ≤0.05 was considered significant for all tests.

Results

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Manufacturer's address
  8. Authors' declaration of interests
  9. Source of funding
  10. Acknowledgements
  11. References

Of the 113 admissions, 67.3% (76) were Quarter Horses, 11.5% (13) Arabian, 4.4% (5) Warmbloods and the remaining 19 horses were classified as ‘other’. Bodyweights ranged from 300 to 700 kg and the mean weight of the horses that developed support limb laminitis vs. those that did not was 507 and 489 kg, respectively. Of the 105 horses for which the information was provided in the medical record, 75 horses were weightbearing and 30 nonweightbearing on the injured limb on presentation. Additionally, 46% of horses (52 of 113) had forelimb lameness and 35% (40 of 113) presented for fracture. Post operative casting was performed in 33 horses following wound repair, 53 horses following pastern arthrodesis, 18 horses following fracture repair (not including those repaired by pastern arthrodesis alone) and 9 horses following ‘other’ procedures, which included fetlock and carpal arthrodesis, deep digital flexor tenotomy and other miscellaneous procedures (Table 1). Furthermore, 14 horses were treated with transfixation pin casts, 88 with half limb casts and 11 with full limb casts.

Table 1. Case distribution and incidence of support limb laminitis among horses treated with half limb, full limb or transfixation pin casts
Type of castPresenting conditionTotal No. horsesIncidence of support limb laminitis
  1. Miscellaneous category includes: third metacarpal bone fracture (n = 1), subluxated proximal intertarsal joint (n = 1), chronic rotational laminitis (n = 1), pastern arthrodesis repair (n = 1), septic pastern (n = 1), ulnar carpal bone fracture (n = 1), deep digital flexor tenotomy (n = 1), biaxial sesamoid fracture (n = 1), pastern arthrodesis repair (n = 1) and fetlock contracture (n = 1). DJD = degenerative joint disease. OCD = osteochondrosis.

Half limb castTotal888% (n = 7)
Proximal/distal interphalangeal joint DJD300.07% (n = 2)
Phalangeal fracture260% (n = 0)
Laceration/wound220% (n = 0)
Miscellaneous450% (n = 2)
Pastern/fetlock luxation425% (n = 1)
OCD20% (n = 0)
Full limb castTotal1130% (n = 3)
Laceration/wound520% (n = 1)
Carpal DJD250% (n = 1)
Miscellaneous420% (n = 1)
Transfixation pin castTotal1429% (n = 4)
Comminuted phalangeal fractures1242% (n = 5)
Miscellaneous250% (n = 1)

The overall incidence of support limb laminitis was 12% (n = 14). Duration of casting, horses that required transfixation pin casts and full limb casts as opposed to half limb casts and bodyweight were associated with an increased probability of support limb laminitis. In the multivariable analysis (Table 2), the probability of support limb laminitis increased for each week increase in duration of casting (P = 0.02) adjusting for weightbearing capacity on presentation, limb affected and bodyweight (kg). The probability of support limb laminitis also increased for each kg increase in bodyweight (P = 0.05) adjusting for weightbearing capacity on presentation, limb affected and duration of casting (weeks). The mean duration of casting in horses that did not develop support limb laminitis compared with those that did was 4.6 and 7.3 weeks, respectively. Additionally, of the 37 cases that had a cast applied for >4 weeks, 7 (19%) developed support limb laminitis. Overall, the association between type of cast and support limb laminitis was not significant. However, when each type of cast was compared with the other, horses that required full limb and transfixation pin casts were more likely to develop support limb laminitis when compared with the horses that required half limb casts (P = 0.04 for comparisons of both types of casts to half limb casts, Table 3). The probability of developing support limb laminitis was also lower among horses requiring a cast post operatively for pastern arthrodesis (P = 0.01) and wound repair (P = 0.01) compared with horses that required casts for ‘other’ conditions (which included fetlock and carpal arthrodesis, deep digital flexor tenotomies and other miscellaneous lameness that did not fit within any of the other categories, Table 3). Although a large percentage (50%, 7/14) of horses that had a fracture developed supporting limb laminitis, the incidence was not statistically different (P = 0.23) when compared with cases in which casts were applied for other reasons (Table 3). Breed, limb affected (hind vs. fore-) and weightbearing capacity on presentation did not differ between horses that developed support limb laminitis vs. those that did not. Of the 14 horses that developed support limb laminitis, 57% (n = 8) of horses were weightbearing on presentation.

Table 2. Results of the multivariable logistic regression analysis of risk factors associated with the development of support limb laminitis in horses treated with half limb, full limb or transfixation pin casts (controlled for weightbearing capacity on presentation, limb affected, weight [kg] and duration of casting [weeks])
Risk factorReference categoryOdds ratio95% confidence intervalP value
  1. NA = Not applicable.

NonweightbearingWeightbearing on presentation2.00.57–7.140.28
Forelimb lamenessHindlimb lameness2.010.59–6.810.26
Duration of casting (weeks)NA1.181.02–1.350.02
Weight (kg)NA1.011–1.010.05
Table 3. Results of bivariable logistic regression analysis for risk factors associated with development of support limb laminitis in horses treated with half limb, full limb or transfixation pin casts
Risk factorReference categoryOdds ratio95% confidence intervalP value
Presence of fractureNo fracture2.000.65–6.170.23
BodyweightBaseline weight in nonlaminitis horses1.001.00–1.010.17
Forelimb lamenessHindlimb lameness2.080.20–1.900.39
Arabian breed‘other breed’1.550.19–12.830.69
Warmblood breed‘other breed’2.130.15–29.660.58
Quarter Horse breed‘other breed’1.140.23–5.780.87
Quarter Horse breedArabian breed0.740.14–3.960.72
Warmblood breedArabian breed1.380.10–19.880.82
Warmblood breedQuarter Horse breed1.860.19–18.550.60
Duration of cast in weeksBaseline duration in nonlaminitic horses1.181.039–1.3420.011*
Nonweightbearing on presentationWeightbearing on presentation2.080.65–6.670.21
Fracture repairHorses casted for ‘other’ conditions0.360.06–2.000.2411
Pastern arthrodesisHorses casted for ‘other’ conditions0.130.03–0.650.013*
Pastern arthrodesisFracture repair0.360.09–1.540.17
Wound repairHorses casted for ‘other’ conditions0.040.00–0.430.008*
Wound repairFracture repair0.110.01–1.070.057
Wound repairPastern arthrodesis0.300.03–2.690.28
Full limb castHalf limb cast4.961.04–23.560.044
Transfixation pin castHalf limb cast4.631.15–18.660.031
Transfixation pin castFull limb cast0.930.16–5.540.94

Discussion

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Manufacturer's address
  8. Authors' declaration of interests
  9. Source of funding
  10. Acknowledgements
  11. References

There are few reports in the literature regarding the incidence of support limb laminitis in horses. Levine and Richardson (2007) reported a 16% incidence of this complication in 31 horses that had a fracture repaired or a joint arthrodesis using locking compression plates (Levine and Richardson 2007). Another retrospective review investigating the efficacy of a contralateral limb support device among horses with unilateral lameness reported a 2.3% incidence among 86 horses (Redden 2004).

Among the horses included in this study, 12% developed support limb laminitis. Although the presence of a fracture was not significant in this study, it is of clinical importance to note that in the present study as well as that performed by Levine and Richardson (2007), the incidence of support limb laminitis was higher among horses with fractures. In the present study, 17.5% (7/40) of horses with a fracture developed supporting limb laminitis and 7 of the 14 total support limb laminitis cases (50%) had fractures. Levine and Richardson (2007) reported a 27% (4 of 15 horses) incidence of this complication among horses with fractures. The incidence of support limb laminitis in the present study may have been lower than that reported by these authors due to the greater severity of orthopaedic conditions included in previous study (i.e. highly comminuted phalangeal fractures, luxations, suspensory apparatus breakdowns and condylar fractures), a marked difference in breed distributions between the 2 studies and potentially the larger sample size included in the present study. The present study also included horses treated with half limb, full limb or transfixation pin casts subsequent to various surgical procedures because in the authors' opinions, horses requiring a cast post operatively typically have more severe unilateral lameness as a group compared with horses that do not require casts post operatively and thus are considered to be at a greater risk of developing support limb laminitis. Additionally, the populations of horses that require casts are an easily identifiable group with unilateral lameness among medical record searches. Consequently, our study covered a wide breadth of lameness types, from fractures to severe wounds, which would be expected to vary in degree of post operative pain and weightbearing capacity and hence affect the probability of support limb laminitis.

The incidence of support limb laminitis varies with the severity and duration of lameness (Peloso et al. 1996) and thus can be expected to be heavily influenced by the case population and quality of post operative analgesia. The results of this study could have been improved by including the severity of lameness recorded on a grading scale (both on presentation and post cast application), the form of prophylactic shoeing or wedging of the contralateral limb and the type and amounts of analgesics administered to each case. Due to the subjectivity and lack of consistent documentation in the medical record, however, retrieval of this data was not possible. In addition, clinical opinion and hence case management regarding treatment of the contralateral limb and analgesic modalities undoubtedly varied over the 10 year period this study was performed. These factors likely have a significant impact on the incidence of support limb laminitis.

Similar to other authors' findings that the duration of lameness is an important risk factor for support limb laminitis, support limb laminitis (Peloso et al. 1996), the results of this study showed that duration of casting is also positively associated with an increased likelihood of developing this complication. For each week increase in duration of casting, the likelihood of support limb laminitis increased by 20% (odds ratio = 1.2) in the horses included in this study. This finding was not unexpected and it can be reasoned that more painful conditions that required longer durations of casting were more likely to develop support limb laminitis in the contralateral limb.

Unlike the results of Peloso et al. (1996), the present study showed a statistically significant association between greater body weights and likelihood of support limb laminitis. For every kilogram increase in bodyweight, the likelihood of support limb laminitis increased by 1% (P = 0.05, odds ratio = 1.01). A greater odds ratio and stronger association between bodyweight and support limb laminitis may have been observed if our study had included a greater variety of breeds including more draught breeds and Warmbloods, as well as documented differences in body condition scores. Given that body composition may also predispose horses to developing ‘endocrinopathic’ forms of laminitis subsequent to insulin resistance and impaired glucose metabolism (Eades 2010), obese or overweight horses may be inherently more prone to developing support limb laminitis. Furthermore, certain foot conformations, such as low heels and long toes (Redden 2004) have been suggested to predispose some horses to developing support limb laminitis, which could result in breed predilections for this complication. Further studies involving various populations of horses are needed to clarify the significance of bodyweight, body composition and breed on the risk of support limb laminitis.

An increased incidence of support limb laminitis was not related to the degree of lameness on presentation (weightbearing vs. nonweightbearing) in this study. However, horses that were nonweightbearing at presentation had a greater incidence of support limb laminitis than those that were weightbearing (23 vs. 11%). Despite the lack of statistical significance, this finding may be of clinical significance. Other limitations of this study include a small sample size, potential human errors in medical record interpretation and follow-up, and limited variation in case population. Most horses included in this study were western performance horses of Quarter Horse breed. Phalangeal fractures and pastern osteoarthritis were overrepresented, hence, pastern arthrodesis was the most common surgical procedure performed. A higher incidence of support limb laminitis may have been observed if a more varied case population was included.

This study should provide guidance regarding how commonly support limb laminitis develops in surgical cases requiring a cast as well as the risk factors that are important in the development of this disease. Support limb laminitis should be considered a risk in any horse with a painful unilateral lameness but especially those requiring a full limb or transfixation pin cast and those casted for several weeks' duration. The results of this study also imply that heavier horses may indeed be at an increased risk for developing this complication, although further research is needed to clarify the role of breed, bodyweight, foot conformation and body composition in the pathophysiology of support limb laminitis. As suggested by other authors, aggressive pain management and timely treatment of painful unilateral conditions remains critical in minimising the risk of developing support limb laminitis among hospitalised patients (Goodrich 2009).

References

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Manufacturer's address
  8. Authors' declaration of interests
  9. Source of funding
  10. Acknowledgements
  11. References
  • Baxter, G.M. and Morrison, S. (2009) Complications of unilateral weight bearing. Vet. Clin. N. Am.: Equine Pract. 24, 621-642.
  • Belknap, J.K. and Parks, A. (2011) Laminitis. In: Adam's and Stashak's Lameness in the Horse, Ed: G.M. Baxter, Wiley-Blackwell, Philadelphia. pp 535-558.
  • Dyson, S.J. (2003) Diagnosis of laminitis. In: Diagnosis and Management of Lameness in the Horse, Eds: M.W. Ross and S.J. Dyson, WB Saunders Co, St Louis. pp 329-332.
  • Eades, S.C. (2010) Overview of current laminitis research. Vet. Clin. N. Am.: Equine. Pract. 26, 51-63.
  • Goodrich, L.R. (2009) Strategies for reducing the complication of orthopedic pain postoperatively. Vet. Clin. N. Am.: Equine Pract. 24, 611-620.
  • Levine, D.G. and Richardson, D.W. (2007) Clinical use of the locking compression plate (LCP) in horses: a retrospective study of 31 cases (2004–2006). Equine vet. J. 39, 401-406.
  • Peloso, J.G., Cohen, N.D., Walker, M.A., Watkins, J.P., Gayle, J.M., Moyer, W. (1996) Case-control study of risk factors for the development of laminitis in the contralateral limb in Equidae with unilateral lameness. J. Am. vet. med. Ass. 209, 1746-1749.
  • Redden, R.F. (2004) Preventing laminitis in the contralateral limb of horses with non-weightbearing lameness. Clin. Tech. Equine Pract. 3, 57-63.
  • Richardson, D.W. (2008) Complications of orthopaedic surgery in horses. Vet. Clin. N. Am.: Equine Pract. 24, 591-610.
  • Van Eps, A., Collins, S.N. and Pollitt, C.C. (2010) Supporting limb laminitis. Vet. Clin. N. Am.: Equine Pract. 26, 287-302.