Microsurgical Techniques for Digital Nerve Injuries and Vascular Injuries.

Background: Tension-free end-to-end digital nerve repair or reconstruction under loupe or microscope magnification are surgical treatment options for lacerated digital nerves in patients with multiple injured digits, injuries to the border digits, or injuries to the thumb, with the goal of improved or restored sensation and a decreased risk of painful traumatic neuroma formation. Different techniques for primary repair have been described and include epineurial sutures, nerve "glues" including fibrin-based gels^1,2, biologic or synthetic absorbable or nonabsorbable nerve wraps or conduits, or a combination of these materials. Nerve "glues" have demonstrated decreased initial gapping at the repair site³ and an increased tensile load to failure when utilized with a nerve wrap or conduit^4,5. When there is a gap or defect in the nerve and primary repair is not feasible, nerve allograft and autograft provide similar results and are both better options than conduit reconstruction⁶. Concomitant or isolated digital vascular injuries may also be surgically treated with end-to-end repair in a dysvascular digit, with the goal of digit and function preservation. In the absence of complete circumferential injury or complete amputation, redundant or collateral flow may be present. Single digital artery injuries often do not need to be repaired because of the collateral flow from the other digital artery.

Description: Digital nerve and vascular injuries are often found in the context of traumatic wounds. In such cases, surgical exploration is often required, with possible surgical extension of the wounds to facilitate identification of the neurovascular bundles. The proximal and distal ends of the transected nerve and/or artery are identified, and the traumatized ends are incised sharply, maintaining as much length as possible to facilitate end-to-end repair, interposition of a graft, and the use of a conduit. The proximal and distal aspects of the nerve and/or artery are appropriately mobilized by dissecting or releasing any scar tissue or soft tissue that may be tethering the structure. The defect is measured in the natural resting position of the digit. Gentle flexion of the digit may be performed to facilitate a primary repair in the setting of very small defects. Primary repair or reconstruction is selected, and an 8-0 or 9-0 nonabsorbable monofilament suture is utilized to anastomose the appropriate structures under magnification with use of a single or double stitch⁶. A tubular nerve conduit is placed prior to epineurial suturing, or a nerve conduit wrap is applied circumferentially around the repair site and augmented with a fibrin glue. The wound is then irrigated and closed in a standard fashion, as determined by the presence of any soft-tissue or structural injury.

Alternatives: Alternatives to primary repair include the use of conduits or autologous or allogenic grafting. Factors that necessitate reconstruction include gapping and poor soft-tissue integrity, which can be related to the mechanism of injury. Alternatives to repair or reconstruction include treatment of the-soft tissue or structural injury without concomitant repair or reconstruction of the damaged digital nerves or vessels.

Rationale: Primary end-to-end repair and reconstruction of digital nerves increases a patient's likelihood of sensation recovery, and arterial repair can preserve a digit and avoid the need for amputation. Sensation in the digits is very important for fine motor skills and interaction with the environment, and it is particularly important for patients who rely on their hands for work and/or recreation. For these reasons, the digital nerves to the border digits, such as the ulnar aspect of the small finger, radial aspect of the index finger, and both digital nerves to the thumb, are given particular attention.

Expected outcomes: Surgical intervention to repair or reconstruct the digital nerves increases the likelihood of recovering pre-injury sensation; however, the chance of complete recovery remains low. A systematic review of the outcomes of digital nerve repair in adults published in 2019 showed that the average percentage of patients who had undergone repair and reported a recovery to Highet grade 4 was 24% (range, 6% to 60%)⁸. The rate of adverse events was comparable between the operatively and nonoperatively treated patients, with complications including neuromas, hyperesthesia, and infection.

Important tips: The use of a microvascular background material can provide better visualization of the proximal and distal ends while performing the repair.It is important to sharply guillotine the ends of the nerve to freshen up the laceration and provide healthy nerve ends for repair.Repair sutures need to be passed through the epineurium, with care taken not to pass through the nerve fascicles.

Acronyms and abbreviations: OR = operating roomPIP = proximal interphalangealPT = prothrombin timePTT = partial thromboplastin time.