History has shown that injuries located in zone II of the hand, classified between the distal palmar crease and the flexor digitorum superficialis (FDS) insertion, have been particularly challenging to repair. This is due to the fact that tendon gliding must be restored within a tight sheath while minimizing the adhesions in surrounding tissues. At one point surgery in this area was deemed “no man’s land”. However, there have been remarkable advances in the understanding of healing characteristics, both mechanically and histologically of tendons. Over time, there has been a shift toward surgical repair of finger flexor tendon injuries, including in the area or zone II. While injuries to the flexor tendons are relatively rare among acute hand injuries (less than one percent) there has been extensive research into the injury and subsequent repair.
The FDS and the flexor digitorum profundus FDP originate from the elbow and proximal ulna and interosseous membrane respectively. The muscles divide into tendons in the mid forearm and travel through the carpal tunnel toward each of the fingers. In zone II the FDS tendon splits with each slip traveling laterally and dorsally to the FDP tendon. The FDS slips attach separately along the palmar aspect of the middle phalanx bone while the FDP tendons further attach along the base of the last or distal phalanx. The finger possesses a series of flexor pulleys that allow for maximal mechanical efficiency of the flexor system. Tendon healing occurs through a combined extrinsic cellular response and intrinsic ability that the flexor tendons posses to heal themselves after injury. It has been shown that early mobilization of a repaired tendon shifts the healing process to an intrinsic mechanism to allow for collagen to be laid down in a pattern that closely replicates the native tendon and results in diminished amount of adhesions forming.
Evaluation of the patient with a flexor tendon injury should include a thorough history and physical examination to identify the type and extent of the injury. This should also include a neurovascular examination to identify if there was additionally any injury to the nerves or blood supply to the area. Within zone II, the FDP tendon is the more commonly injured of the two tendons. With a FDP repair, recent studies have suggested that there be partial excision of up to 50 per cent into the A2 pulley and complete division of the A4 pulley to allow for increased tendon gliding. Whereas, traditionally, many surgeons would have deemed these pulley inviolable. There have been many suture configurations described, the author of this review stresses that the treating surgeon us a technique that allows for properly coapted repair in the absence of gapping and minimal trauma to the tendon edges. It was also recommended that at least four core suture strands are used in surgical repair to minimize the risk of rupture. The senior author of this review paper’s preferred technique is a modified Kessler suture configuration that adds a separate cross-locked cruciate technique especially if there is an increased risk for adhesions anticipated. Mechanical testing demonstrated that ideal placement of the core suture was seven to ten mm from the repair site. Gapping or elongation of the repair site must be avoided as they can affect the strength of the repaired tendon thus the use of peripheral suture in addition to the core suture are important. The peripheral suture both minimizes the bulk of the repair and can help prevent elongation of the tendon or gapping. Whether to pursue repairing a FDS tendon in zone II depends on the exact location of the injury. If warranted, to limit bulk of the repaired tendon under the A2 pulley, surgeons will excise one of the slips of the FDS and repair the other to allow for improved gliding of the repaired tendons.
Postoperative rehabilitation is a very important process of the flexor tendon repair. Like mentioned previously early mobilization enhances the strength of the repair site and decreases possible adhesions. It is the discretion of the surgeon to chose either early passive or early active motion protocol. It is recommended that range of motion exercises are not initiated until at minimum four days post surgery but not later than seven days post surgery. A systematic review of the literature demonstrated that both early passive and early active mobilization protocols deliver adequate motion. In the only randomized controlled trial that compared the two protocols it was found that patients who underwent an active place-and-hold protocol showed greater ROM, less flexion contractures and greater patient satisfaction. It was noted that it’s important for the surgeon to select a rehabilitation protocol that best matches the patients ability to comply with the protocol’s restrictions.
It is difficult to draw conclusions on the reported outcomes of flexor tendon repairs due to the heterogeneity of the the rehabilitation protocols and studies on flexor tendon repairs, the variability in reporting of the finger motion and the lack of use of patient-reported outcome measures. Patients with multiple finger involvement, have additional nerve injury and those who smoke were found to more likely have poor outcomes.