Musculoskeletal: external fixation - casts in Horses (Equis) | Vetlexicon
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Musculoskeletal: external fixation – casts

ISSN 2398-2977


Introduction

  • To provide stabilization and immobilization of a limb following injury.

Uses

Types
  • Foot cast: for hoof wall avulsion injury External fixation: cast 02 - foot .
  • Fetlock and foot cast: heel bulb laceration External fixation: cast 01 - half limb  foot .
  • Distal or short limb cast: to cover foot up to proximal metacarpus or metatarsus.
  • Full limb cast: extends above the carpus or tarsus to proximal radius or tibia; for trauma proximal to fetlock, distal to mid-radius or mid-tibia; reduces strain deformation of the superficial and deep digital flexor tendons of the hindlimb.
  • Sleeve or tube cast: for carpus or tarsus, eg angular limb deformities; permits weightbearing on limb; from proximal radius/tibia to distal metacarpus/metatarsus.

Advantages

  • Modern materials are fast drying and lightweight.
  • Cheap alternative to surgery.
  • Enables horse to bear weight on affected limb, reducing stress and secondary complications to contralateral leg during recovery period.
  • Can be applied to the foot, lower leg or whole limb.
  • Foot casts can be applied to a compliant horse under sedation.

Disadvantages

  • Some abrasions from prolonged cast wearing are inevitable.
  • Require careful monitoring.
  • Horse may weight bear before cast has 'cured'.
  • If long-term cast - may need to replace during treatment period.
  • General anesthesia necessary for casts beyond the foot.
  • Plaster of Paris casts do not achieve full strength for 24 h.
  • Some horses will not tolerate full-limb cast.

Technical problems

  • Inaccurate placement of cast may → long bone fractures, eg radius or tibia beyond the top of a cast ending mid-diaphysis.
  • Failure to follow manufacturer's storage or preparation guidelines may → cast failure.
  • Two assistants ideal to hold limb and prepare cast material.

Alternative techniques

Decision taking

Criteria for choosing test

  • Radiographic evaluation of injury.
  • Temperament of horse.

Requirements

Personnel

Veterinarian expertise

  • Experience and competence with decision making regarding casting and the actual placement of the cast is critical

Nursing expertise

  • An assistant with comfort and experience with placing a case is important.

Materials required

Minimum equipment

  • Fiberglass tape or plaster of Paris.

Ideal equipment

Hoof preparation
  • Hoof pick.
  • Hoof knife Farriery: tools - hoof knife .
  • Hoof nippers.
  • Rasp Farriery: tools - hoof rasp .
  • Bristle brush.
Limb restraint
  • Electric drill.
  • Electric drill bit.
  • Flexible wire.

Ideal consumables

Cast padding
  • 5-10 cm stockinette, double thickness; cotton for plaster of Paris casts, polyester or polypropylene for synthetic casts; may need wider stockinette for hindlimb.
  • Adhesive tape.
  • Orthopedic felt.
  • Wound dressings or resin-impregnated foam lining.
Casting materials
  • Protective drapes.
  • Plastic bucket with liner.
  • Water of specified temperature.
  • Rubber gloves.
  • Casting materials.
Walking bars
  • 2.5 x 0.5 cm aluminum bar, 2-2.5 m long.
  • Bend to shape before beginning cast application.
Not always used - clinician preference.
Sole reinforcement
  • Acrylic resin (methylmethocrylate).
Obstetrical wire
  • Cut a length of wire twice the length of the cast plus 0.5 m; then cut it in half.
  • Insert the wire through polyethylene tubing, eg intravenous fluid giving set.
Not always used - clinician preference.

Preparation

Pre-medication

Site preparation

  • Clean and dry limb thoroughly.
  • Trim hoof level, pare out sole and scrub entire foot, particularly sulci of frog.
  • Ensure foot is dry; paint with iodine if desired.

Restraint

Technique

Approach

Step 1 - Cover wounds

  • Cover wound Coronary band: trauma 01 with a sterile non-adherent dressing Casting 01: cover wound .
  • Secure dressing with a minimal amount of gauze and tape.

Step 2 - Apply stockinette

  • Measure and cut stockinette - approximately 8 cm longer than twice the length of the cast.
  • Prepare the stockinette by rolling it - roll half of its length to the outside - the other half to the inside.
  • Apply the outward spool of stockinette to the limb beginning at the foot and rolling up Casting 02: apply stockinette .
  • Twist the stockinette below the foot and roll up the remaining spool.
  • Ensure there are no wrinkles in the stockinette.
  • Use towel clamps to secure the stockinette at the top of the limb during application of the cast.
  • Optional:
    • Secure obstetrical wires Casting 03: attach obstetrical wire on the medial and lateral side of the limb over the stockinette with adhesive tape.
    • After the cast has been applied, secure the free ends of the wire in loops with adhesive tape.

Step 3 - Place padding

  • Cut a piece of orthopedic felt 5 cm wide and 0.5 cm thick to wrap around the proximal margin of the cast Casting 04: place orthopedic padding .
  • Secure it in place with tape.
  • Ensure there are no wrinkles.
  • Place padding over anatomical prominences if necessary, eg proximal sesamoid bones, accessory carpal bone, calcaneal tuberosity, styloid processes, tibial malleoli, coronary band.

Step 4 - Place traction wires (optional)

  • Drill two holes in the hoof wall (insensitive laminae) at similar angle to shoe nails.
  • Pass wire through each hole to create a loop that can be held by an assistant.

Step 5 - Position limb for cast application

  • Place limb in an anatomically correct position.
  • It may be a flexed, extended or neutral position depending on injury.

Core procedure

Step 1 - Apply contouring plaster cast

  • If desired apply 2-3 rolls of plaster cast before fiberglass to improve contouring of the cast on the limb.

Allow plaster to dry thoroughly (10-20 min) before applying fiberglass.

  • Alternatively, apply resin-impregnated foam lining - extra padding is only required at the proximal extent of the cast.

Step 2 - Apply fiberglass tape

  • Wear gloves.
  • Free up the end of the first roll of tape.
  • Dip tape in water and handle according to manufacturer's instructions.

Use water that is slightly below recommended temperature rather than too hot, to avoid rapid curing of the tape.

  • Apply the first layer firmly but without tension beginning either at the proximal padding or from the foot Casting 05: apply casting material.
  • Ensure there are no wrinkles or tucks in the tape Casting 06: apply cast material.
  • Use narrower tape for the first few rolls, particularly for contouring.
  • Each spiral wrap of tape should cover half of the previous spiral.
  • If the sole is not flat incorporate a heel support Casting 07: heel supportCasting 08: incorporate heel support, eg wooden block or roll of casting tape.
  • Cover limb in 4-8 layers.
  • Reinforce at the toe and at any bends in the cast.
  • Apply walking bar if desired after about 6 rolls of tape have been applied.

Step 3 - Protect the cast

  • Turn over the stockinette and wrap the proximal end of the cast in elastic adhesive tape  Casting 09: apply elastic tapeto prevent debris entering between limb and cast.
  • Reinforce the sole with acrylic resin if desired to protect the cast from wearing.

Apply elastic tape over this to improve traction.

Exit

Step 1 - Allow time for cast to cure

  • Ensure the horse will remain recumbent for at least 20 min before weightbearing.

Step 2 - Recovery if anesthetized

  • Ensure horse is lying with cast limb uppermost during recovery from anesthesia.
  • Use tail and head ropes if necessary to provide additional support during recovery.

Aftercare

Immediate Aftercare

Monitoring

  • Monitor the patient's ability to ambulate and use the cast properly.
Ill-fitting casts will lead to complications and should be replaced.
  • Additionally, patients that are not using the affected limb as well as expected need a re-evaluation of the injury.

Analgesia

  • Caution with use of anti-inflammatories as may mask early signs of cast complications. However, comfort and even weight-bearing are vital in these patients.

Antimicrobial therapy

  • Based on primary injury.

Other medication

  • Confine horse to clean stall.
  • Observe regularly:
    • Check that horse is weight bearing and not lame.
    • Monitor vital signs regularly - increased temperature, pulse or respiration may indicate pain, inflammation or infection under the cast.
    • Check cast for breaks, cracks or other signs of wear and tear, especially at the toe.
    • Palpate for increased local temperature and looseness.
    • Check for exudate, foul odor, swelling, sores - change the elastic adhesive tape at the top of the cast regularly.
    • The accumulation of flies are an early sig of cast sores or problems with the cast.
    • Check digital pulse on contralateral limb for possible laminitis Foot: laminitis.

Special precautions

Cast removal
  • Sedate horse if cast is not being replaced and horse is amenable to the noise and handling that removal involves.
  • General anesthesia Anesthesia: general - overview if cast might be replaced - if the cast is not replaced, protect the limb during anesthetic recovery with a heavy bandage Musculoskeletal: Robert Jones bandage or splint Musculoskeletal: fracture - first aid .
  • Powered cast cutter:
    • Wear surgical mask.
    • Cut a groove into the cast surface along the full medial and lateral length of the cast, joining these cuts under the foot.
    • Embed the cast cutter the full thickness of the cast gently at multiple sites, separated by the width of the cast cutter.

    Sedated or anesthetized horses may not react to laceration by the cast cutter - take great care when penetrating the full depth of the cast.

    • Use the obstetrical wire to cut through the cast.
    • If obstetrical wire was not embedded in cast, begin the full thickness cut at the top of the cast, using thumb as a depth gauge and make intermittent vertical cuts along the line marked. Do not move cast cutter parallel (proximal to distal) to skin, but rather in and out (superficial to deep), to avoid cutting the limb.
  • Cast spreader:
    • Used to separate the two halves of the cast.

Potential complications

  • Cast sores:
    • Due to movement beneath the cast - may occur if limb was swollen at time of cast application (if limb is swollen, replace cast when inflammation has settled, eg 48 h later).
    • Decubital sores Elbow: wound - pressure sore - usually develop on the dorsal aspect of proximal metacarpus or metatarsus, palmar or plantar surfaces of the proximal sesamoid bones, the heel bulbs.
    • Suspect if there is decreased weight bearing, focal local heat, exudate or odor, moisture at the top of the cast.
  • Gangrene Forelimb: casting sore - gangrene .
  • Cast cracks or breakage:
    • Insufficient cast material.
    • Inadequate cast bonding.
    • Stress on cast before it has cured.
    • Repair is not feasible - must replace.
  • Long bone fracture:
  • Peroneus tertius rupture Peroneus tertius: rupture:
    • Due to struggle with full limb, hindlimb cast - tarsus is fixed but stifle able to flex.
  • Sequelae of immobilization:
    • Muscle atrophy.
    • Joint laxity.
    • Joint stiffness.
    • Disuse osteopenia.

Outcomes

Complications

  • Cast sores.
  • Fracture.
  • Support limb laminitis.
  • Cellulitis.
  • Swelling and compression of soft tissues and/or vasculature.
  • Ischemic necrosis.

Reasons for treatment failure

  • Excessive movement of patient.
  • Cast too loose/too tight.
  • Ill-fitting cast.
  • Cast not made strong enough.
  • Cast and patient not monitored closely enough.
  • Injury not amenable to treatment choice.

Prognosis

  • Duration of cast application depends on injury.
  • Phalangeal or metacarpal or metatarsal III fractures MC / MT 3: fracture - recovery only if cast.
  • Heel bulb lacerations , joint wounds, tendon lacerations Flexor tendon: trauma - 2-3 weeks immobilization. See picture series of laceration Coronary band: trauma 01, two weeks after cast removal Coronary band: trauma 02 - 2 weeks post-cast and four weeks after cast removal Coronary band: trauma 03 - 4 weeks post-cast.
  • Primary means of fracture immobilization - leave on until fracture has healed, replacing at monthly intervals or sooner if required.
  • Foals - replace cast at 10-14 day intervals.

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Stewart H L, Werpy N M, McIlwraith C W & Kawcak C E (2020) Physiologic effects of long-term immobilization of the equine distal limb. Vet Surg 49 (5), 840-851 WileyOnline.
  • Eggleston R B (2018). Equine Wound Management: Bandages, Casts, and External Support. Vet Clin North Am Equine Pract 34 (3), 557-574 PubMed.
  • Pérez-Nogués M, Dechant J E, Garcia-Nolen T & Stover S M (2018) Evaluation of the effects of initial water temperature and curing time on fiberglass cast strengthVet Surg 47 (6), 809-816 PubMed.
  • Janicek J C, McClure S R, Lescun T B et al (2013) Risk factors associated with cast complications in horses: 398 cases (1997-2006)J Am Vet Med Assoc 242 (1), 93-98 PubMed.
  • David F, Cadby J, Bosch G et al (2012) Short-term cast immobilisation is effective in reducing lesion propagation in a surgical model of equine superficial digital flexor tendon injury. Equine Vet J 44 (5), 570-575 WileyOnline.
  • Virgin J E, Goodrich L R, Baxter G M & Rao S (2011) Incidence of support limb laminitis in horses treated with half limb, full limb or transfixation pin casts: a retrospective study of 113 horses (2000-2009). Equine Vet J Suppl (40), 7-11 PubMed.
  • Milner P (2009) Application of a distal limb (foot) cast. UK Vet 14 (1), 15-18 VetMedResource.
  • S A Hopper, R K Schneider, M H Ratzlaff et al (1998) Effect of different full-limb casts on in vitro bone strain in the distal portion of the equine forelimb. Am J Vet Res 59 (2), 197-200 VetMedResource.
  • Riggs C M (1997) Indications for an application of limb casts in the mature horse. Equine Vet Educ 9 (4), 190-197 WileyOnline.
  • Wilson D G & Vanderby R (1995) An evaluation of fiberglass cast application techniques. Vet Surg 24, 118-121 PubMed.
  • McClure S R, Watkins J P, Bronson D G & Ashman R B (1994) In vitro comparison of the standard short limb cast and three configurations of short limb transfixation casts in equine forelimbs. Am J Vet Res 55 (9), 1331-1334 PubMed.

Other sources of information

  • Nixon A J (2020) Ed. Equine Fracture Repair. 2nd edn. Wiley-Blackwell, USA. ISBN: 978-0-813-81586-2.
  • Auer J A & Stick J (2019) Equine Surgery. 5th edn. W B Saunders, USA.