Debridement and exploration of the involved area are carried out. Adjacent nerves and vessels are identified and retracted. If possible, the tendon ends are located in the wound and gently grasped with forceps (Figure 3). Gentle tissue handling is of utmost importance, as crush injury to the tendon can lead to poor healing, gapping of the repair, and eventual failure. Lacerations that involve less than 60% of the cross-section of the tendon do not need to be repaired. The loose fibers should only be trimmed to prevent catching of the tendon on the flexor pulleys. Complete transections and those greater than 60% require repair. Depending on the location of the laceration, the proximal tendon stump may retract and require maneuvers to retrieve it. Retrieval should be atraumatic and under direct visualization if possible. Flexing the wrist and elbow and squeezing the muscles of the forearm can help deliver the proximal stump to the incision. Sometimes counter incisions proximal in the palm or forearm need to be performed to identify the tendon. Generally, the distal segment is identified easily with finger flexion. In multiple tendon injury cases, care must be taken to confirm the anatomy and orientation of the proximal and distal tendons. General principles of tendon suturing have evolved over time, with both multi-strand core sutures and epitendinous sutures proving their benefit. A running, epitendinous suture line of 6-0 permanent monofilament suture provides both strength and a smooth gliding surface. Frequently the “back wall” epitendinous repair will be performed first, followed by a multi-strand core suture repair with 3-0 or 4-0 permanent suture, finished by epitendinous repair of the “front wall” to complete the repair. For both epitendinous and core suturing, there are several methods described (Figures 4 and 5). The most reliable core sutures are performed with locking four-strand repair techniques and most epitendinous repairs are performed in a running fashion (simple, locking, horizontal mattress).
Zone I injuries (distal to the insertion of the flexor digitorum superficialis tendon on the middle phalanx) usually require percutaneous button suturing of the proximal tendon to the distal phalanx due to the frequent shortage of distal tendon available (Figure 6). Zone II injuries (within the flexor sheath) are the most difficult cases and should only be attempted by a surgeon experienced with these injuries. Both the flexor digitorum superficialis and profundus tendons (FDS and FDP, respectively) should be repaired. Zone III injuries (in the palm) are generally more straightforward and heal well. Zone IV injuries (within the carpal tunnel under the transverse carpal ligament) are rare and are frequently associated with injuries to the median nerve. Zone V injuries (in the forearm) can be complicated if the injury occurs at the musculotendinous junction, as muscle does not hold sutures securely. Potential injury to the arteries and nerves of the forearm need to be evaluated.
Once all repairs have been completed, the tourniquet is released and meticulous hemostasis is achieved. The field must be dry before closure is attempted.