Heel bulb lacerations

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Lacerations in the pastern are common and often result from kicks to wire fencing, ropes, or protruding objects in a stall or are self-inflicted from the contralateral or pelvic digit. These lacerations often involve the heel bulb and sometimes reach the coronary band at the level of the quarter.

These lacerations are always contaminated and may be complicated by involvement of underlying structures such as the proximal or distal interphalangeal joint; podotrochlear (navicular) bursa; digital flexor tendon sheath; superficial and deep digital flexor tendons; distal digital annular ligament; distal sesamoidean ligaments; digital vein, artery, and nerve; coronary band; and complementary cartilages of the distal phalanx. Depending on the structures involved and the degree of damage incurred, these lacerations are serious and may be life threatening. The severity of the lameness is not dependable in ascertaining the involvement of underlying deep structures. Horses that have recently sustained injury to a joint, bursa, or sheath usually bear weight on the limb, with the lameness becoming more severe only when inflammation and infection occur.

Clinical signs

The clinical signs of acute laceration depend on the underlying structure(s) involved as well as the duration of the injury. The laceration and digit must be carefully examined. Sedation and desensitization of the distal part of the limb with proximal peri­neural analgesia may be required to enable a thorough examination of the laceration. However, because weight bearing may be detrimental to the integrity of these structures1 and may worsen the prognosis, local anesthesia should be avoided until it can be ascertained that the laceration does not involve tendons or ligaments. The wound must be aseptically explored (with or without a sterile, flexible metal probe) to avoid further contamination. Radiographic assessment, with or without a probe or contrast material, is recommended to determine which structures have been affected and to detect the presence of foreign bodies; it should be kept in mind that many distal limb fractures and signs of bone sepsis may take 1 to 2 weeks to become radiographically apparent. Caution must be taken to avoid penetrating unaffected underlying structures with the probe. Radio­graphs that reveal the presence of air within the cavity may confirm lack of integrity of the underlying structures. Because wound management and the prognosis can be altered by the development of septic arthritis, bursitis, or tenosynovitis, to rule out involvement of these conditions, it is often necessary to aseptically inject a physiologic solution into the adjacent synovial cavities by inserting a needle percutaneously at a site distant to the laceration. If involvement of joints, bursae, or the digital sheath is suspected, synovial fluid should be collected from these cavities for cytologic evaluation, bacterial culture, and microbial sensitivity.

Treatment

It is best to repair heel-bulb lacerations with the patient under general anesthesia and laterally recumbent with the affected limb uppermost or lowermost, depending on the location (lateral or medial) of the laceration. This provides the opportunity to adequately clean and carefully repair underlying structures that may have been damaged. Synovial sampling should be performed if it has not already been done, followed by abundant lavage of the laceration and compromised syno­vial structures using physiologic saline solution. Sharp debridement of the laceration should proceed to render the area as surgically clean as possible and preserve vital underlying structures. When lavage and debridement have been completed, the decision to perform primary repair or delayed primary closure must be made.

In cases of synovial sepsis or severe wound contamination or when there is concern about the vascular integrity of the digit, a standard distal limb bandage should be applied before the horse recovers from anesthesia[1]. This allows easier access to the wound for reassessment, further lavage and debridement, and administration (via either intrasynovial injection or regional perfusion) of broad-spectrum antibiotics[2]. As soon as synovial sepsis has resolved and there is a good vascular supply, delayed primary closure can be attempted, followed by placement of a slipper cast. Systemic broad-spectrum antibiotics, NSAIDs, and tetanus prophylaxis should be administered immediately after synovial fluid sampling in affected horses. Systemic antibiotic therapy is then usually modified according to microbial sensitivity and should be continued for at least 3 weeks after resolution of all clinical signs of infection.

In cases of primary closure, a slipper cast should be applied immediately following lavage, debridement, and suturing to protect the suture lines from further trauma and help minimize extension of the distal limb, which may result in parting of the wound edges[3]. The deeper planes should be closed with 2-0 or 1-0 synthetic absorbable suture material to avoid dead space. The skin should be closed with large tension sutures (horizontal or vertical mattress with 0-0 or 1-0 nonabsorbable suture material with stents) and the cast applied. The horse should then be recovered from anesthesia[4]. Affected horses usually receive systemic antibiotics and NSAIDs for only 48 hours. Systemic drug therapy is not required during convalescence after simple heel-bulb lacerations. Tetanus prophylaxis is mandatory in all cases.

External Support: Slipper Cast

Although several reports describe application of slipper casts to standing, sedated horses,5,6 we prefer to apply them with patients under general anesthesia because:

  • General anesthesia is usually required for initial laceration management.
  • It is extremely difficult to obtain adequate digit extension for correct cast application in a conscious horse.
  • Movement or weight bearing before "curing" of the cast material usually results in stretched, misfitted casts, predisposing patients to pressure sores and complications necessitating early cast removal[5].

Before applying the fiberglass cast (3M Animal Care Products, Saint Paul, MN), padded support is recommended. A double layer of casting stockinette (Smith & Nephew, Inc., Lachine, Quebec, Canada) should be placed over the foot and carefully rolled up above the fetlock to prevent disruption of the wound dressing. Next, a 5- to 7-cm-wide strip of orthopedic felt should be placed in the pastern around the first phalanx, just below the proximal sesamoid bones, and a 2- to 4-cm-wide strip should be placed on the coronary band. Foam padding (3M Animal Care Products) should be applied in a spiral fashion over the stockinette and felt, from just below the coronary band to the top of the proximal felt, and covered with casting tape. Acrylic (Heraeus Kulzer GmbH & Co KG, Wehrheim, Germany) should be added to the solar margin once the cast is dry. Excess stockinette should be removed and folded down over the top of the cast and secured to the cast with adhesive tape or casting tape. An adhesive tape (BSN Medical Ltd, Pinetown, South Africa) should then be wrapped around the cast all the way onto the exposed leg to prevent debris from entering the cast. Horses usually walk extremely well with this type of external support and without apparent discomfort.

Care must be taken to apply the slipper cast just below the fetlock or just proximal to the coronary band but never to end it in the midpastern because this may result in deep horizontal skin erosions at the dorsoproximal and palmaroproximal borders of the cast.

In the absence of serious cast-related complications, the most frequent being the aforementioned pressure sores in the midpastern, the slipper cast is usually left on for 2 to 3 weeks and removed while the horse is sedated and standing. The functional and cosmetic outcome is usually excellent.

The key to success of using slipper casts lies in appropriate case selection, meticulous application, and vigilant postoperative monitoring.

Special cases

  • Involvement of the Coronary Band

Wounds that interrupt the coronary band present a distinct challenge because hoof regeneration may be compromised after surgery. The coronary band must be repaired because treatment with bandages or casts alone often leads to poor functional results, including the development of horny spurs or permanent cracks or deformation of the hoof wall. In addition to suturing of the heel-bulb laceration as already described, the coronary band should be sutured (with 2-0 or 1-0 nonabsorbable suture material) and the hoof wall stabilized with wire sutures before the slipper cast is applied. The hoof can be expected to grow with a permanent defect associated with the coronary band scar. Proper shoeing for the patient's lifetime usually allows the hoof to remain sound and functional.

  • Chronic Laceration with Excessive Granulation Tissue

Uncomplicated or superficial lacerations sometimes go unnoticed by owners and then heal by second intention without complications. However, deep or complicated lacerations that are not managed as already described often become chronically infected and develop exuberant granulation tissue, causing delayed closure. Wound contamination, high mechanical loads, and the low temperature of the distal limb can prevent routine bandaging from adequately immobilizing and protecting the damaged area[6]. Chronic infection, the development of exuberant granulation tissue, and delayed closure often ensue. To decrease bacterial population and allow good apposition of the wound edges, the laceration must be lavaged, debrided, and debulked as soon as a sound granulation bed has developed. The rest of the procedure should be identical to delayed primary closure using a slipper cast, as already described.

References

  1. Booth TM, Knottenbelt DC (1999) Distal limb casts in equine wound management. Equine Vet Educ 11(5):273-280
  2. Murphey ED, Santschi EM, Papich MG (1994) Local antibiotic perfusion of the distal limb of horses. Proc AAEP 40:141
  3. Theoret C (2004) How I treat heel bulb lacerations. Proc NAVC pp:226
  4. Booth TM, Dart AJ, Watkins JP (2003) Equine limb casts: Classification and indications. Compend Contin Educ Pract Vet 25:701-706
  5. Blackford JT, Latimer FG, Wan PY (1994) Treating pastern and foot lacerations with a phalangeal cast. Proc AAEP 40:97-98
  6. Schwartz AJ, Wilson DA, Keegan KG, et al (2002) Factors regulating collagen synthesis and degradation during second-intention healing of wounds in the thoracic region and the distal aspect of the forelimb of horses. Am J Vet Res 63:1564-1570
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