Rebecca J. Webb VetSurg, Ventura, CA, USA Tendon lacerations frequently occur secondary to penetrating wounds. The most common tendons affected are those near the metacarpal and metatarsal regions (superficial and deep digital flexor tendons [SDFTs and DDFTs]) and the common calcaneal tendon (or Achilles tendon) complex. This is due to the limited overlying soft tissue of these areas, which leaves these tendons relatively more exposed to injury. It is not uncommon for wounds in these areas to have a tendon injury that remains unrecognized until the wound is surgically explored. Early diagnosis and apposition of the severed tendon ends is important, as over time, contracture of the severed tendon ends occurs and makes the ends more difficult to appose. For this reason, it is important for clinicians exploring wounds in these areas to be evaluating thoroughly for these tendinous injuries. The clinician should either be adequately prepared to repair these tendons during wound repair themselves or plan for the case to be referred in an expedited manner upon diagnosis of a tendon laceration for repair following initial wound management. Tendons are composed of dense parallel collagen fibers, proteoglycan matrix, and fibroblasts. The structure of a tendon is similar to a rope with small collagen fibers arranged in bundles. The parallel orientation of these fibers is important for clinicians to be familiar with, as this has implications for suture pattern choice during their repair. Tendons are typically poorly vascularized, and due to this, their healing is slow. The paratenon is a loose connective tissue structure that surrounds individual tendons and is a source of blood supply to these tendons during healing. Tendons with a paratenon are classified as vascular tendons and include the common calcaneal tendon complex and triceps tendon.1 These tendons gain blood supply from both the paratenon and their intrinsic blood supply during healing. Tendons without a paratenon are classified as avascular tendons and include the digital flexor tendons. These tendons rely only on their intrinsic blood supply for healing, which can lead to more difficulties with their healing process. Maintenance of the anatomic blood supply to the tendon during repair is of vital importance for healing, and therefore, gentle tissue handling of the tendons during the repair is necessary. Apposition of the tendon ends is of paramount importance for adequate healing of a tendon laceration. When the tendon ends are apposed without a gap, the tendon ends heal together without scar tissue. However, when a gap is present, scar tissue forms between the tendon ends, which leads to a biomechanically weaker repair. Overall, the goal of surgical repair is to adequately appose the tendon ends without gap formation while maintaining the blood supply to the tendon. Initially following repair, the tendon will not be able to withstand typical forces and will need to be immobilized and supported. Following the initial recovery period, it is important to progressively allow small amounts of loading of the tendon repair, as this encourages the collagen fibers of the healing tendon to align correctly, giving it long‐term strength.1 This loading should be performed cautiously and gradually, however, as excessive premature overloading of the tendon will lead to repair failure. In uncomplicated tendon healing, a slow but gradual return of strength of the tendon following injury is expected. At six weeks post‐injury, the tendon will have approximately 56% of its original strength, and this increases to a strength of 79% at one‐year post‐injury.2 As normal forces strain tendons to 25–33% of their maximal capacity, typically, the strength obtained at six weeks post‐surgery is enough to withstand gentle activity.1 Most patients with a tendon laceration will present acutely with a laceration or wound and a minimally or non‐weight‐bearing lameness. In patients who are bearing weight at the time of presentation, characteristic hyperextension or hyperflexion of the affected joints may be noted. For patients with DDFT lacerations, a characteristic hyperextension of the affected digits is noted. Patients suffering from common calcaneal tendon lacerations can present differently depending on which components of the tendon have been affected. Laceration of the complete common calcaneal tendon complex typically presents with hyperflexion of the tarsus during stance (Figure 53.1). Given these injuries occur secondary to trauma, a full evaluation of the patient’s stability prior to anesthesia for surgical repair is indicated. During the time of patient stabilization, the wound should be covered to reduce hemorrhage and reduce the risk of a hospital‐acquired infection. Chronic, untreated tendon lacerations typically present with a chronic lameness and occasionally a palpable defect. Dependent on the tendon involved, dysfunction of the affected joints will be noted. In addition, some patients present with chronic wounds secondary to their altered weight‐bearing. Preoperative radiographs of the affected area are recommended to evaluate for both concurrent fractures and radiopaque foreign material. Ultrasound by a skilled ultrasonographer can be useful in cases of common calcaneal lacerations to determine the specific components of the tendon that are damaged and can give information about the extent of this damage. Figure 53.1 Note that even with a support bandage, the right tarsus of this patient displays a plantigrade stance, in which tarsal hyperflexion occurs with concurrent stifle extension. This stance is typically secondary to common calcaneal tendon injury. Source: © Rebecca Webb. Lacerations should be flushed with sterile isotonic fluids then filled with a sterile lubricant prior to clipping of the fur. The sterile lubricant helps trap clipped fur and prevents it from getting caught in the wound. The lubricant is flushed from the wound once clipping is complete. Dependent on the area of the laceration, the region to be clipped and prepared will vary. However, each patient should have a substantial region clipped, prepared, and draped, as extension of the laceration is commonly needed to allow enough visualization to repair the lacerated tendons. The patient should be positioned as needed to allow full access to the tendon and wound. In the case of a common calcaneal tendon laceration, this is commonly obtained with the patient in sternal recumbency with the hind limb hanging off the table (Figure 53.2). A hanging limb prep is performed in these cases, with the hind limb suspended from the ceiling or an IV pole to allow for surgical preparation of the limb (Figure 53.3). Figure 53.2 This patient with a common calcaneal tendon laceration has been positioned in the surgical suite for repair. The patient is positioned in sternal recumbency with the hind limb outstretched. Note a sterile impervious wrap (impervious drape material) has been placed over the unclipped paw and then covered with sterile Vetrap™ (3M) in this case. Source: © Rebecca Webb. In patients where the paw needs to be exposed for the surgical repair, a paw soak is performed following clipping and prior to moving the patient to the O.R., as surgical preparation of this area can prove challenging with gauze. This is performed by placing the digits and paw in an examination glove or plastic specimen bag with 4% chlorhexidine or 10% povidone‐iodine solution for three to five minutes. Porous tape or an elastic adhesive bandage (such as Vetrap™) is used to secure the top of the glove around the distal limb during soaking time to prevent spillage of scrub solution from the glove (Figure 53.4). These patients are then moved to the operating room, and the paw can be suspended for a final surgical preparation and draping using a sterile Backhaus towel clamp in the interdigital space (Figure 53.5). Figure 53.3 The limb is suspended to allow final surgical preparation using a paw wrap of Vetrap™ (3M). Once the patient is draped, the sterile assistant will grasp the paw with an impervious sterile layer (such as sterile disposable drape material or sterilized aluminum foil) and then wrap around the impervious sterile layer with sterile Vetrap™ (3M). In patients where the paw needs to be exposed for surgery, see images 53.4 and 53.5. Source: © Rebecca Webb.
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Tendon Lacerations
Introduction
Indications/Pre‐op Considerations
Surgical Procedure
General Considerations
Patient Preparation
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