6 Flexor Tendon Reconstruction (Zone 2)
Compared with primary repair, flexor tendon reconstruction poses an alternative treatment to flexor tendon injury. Termed “no man’s land,” zone 2 of the hand poses serious challenges to tendon repair. Owing to the complexity of the tendon sheaths and small margin for error, postoperative swelling, adhesion formation, or infection outcomes can be variable and the prognosis guarded. With these features in mind, one must be careful and consider the clinical picture when deciding between primary repair, single-stage, or two-stage flexor tendon reconstruction. In these instances, the entire environment must be considered so as to decrease tendon rupture, pulley failure, or adhesion formation. With close observation, the orthopaedic surgeon can utilize this information toward deciding on the most appropriate treatment as well as preoperative plan toward achieving recovery of maximum active range of motion.
Flexor tendon injuries to the hand are classified into five zones for the fingers (► Fig. 6.1).
Zone 1 is distal to the insertion of the flexor digitorum superficialis (FDS) tendon. Zone 2 is from the FDS insertion site to the distal palmar crease. Zone 3 extends from the distal palmar crease, proximally into the palm. Zone 4 consists of the carpal tunnel. Zone 5 is proximal to the carpal tunnel. Special focus will be placed on zone 2 flexor tendon reconstruction.
The flexor mechanism of each finger involves two tendons: the FDS and the flexor digitorum profundus (FDP). The FDS tendon enters the A1 pulley, then splits into two tendon slips and rotates 180 degrees in a dorsolateral direction around the FDP tendon. The FDP tendon passes through this split, also known as Camper’s chiasm. The tendinous sheath that the FDS and FDP course through begins approximately at the level of the metacarpal heads and spans to the distal phalanges.
It is important to understand the roles of the digital flexor sheath, as well as the pulley systems involved. There are three pulley systems that offer a mechanical advantage to flexion by allowing for force multiplication with less expenditure of energy. There are three pulley systems in the hand:
There are five annular and three cruciate pulleys, and the palmar aponeurosis pulley system (► Fig. 6.2). When the pulleys are damaged, bowstringing of the flexor tendons occurs, which increases work needed at the expense of reduced tendon excursion. The A2 and A4 pulleys are believed to be the most important in maintaining adequate flexor tendon function. Located over the proximal and middle phalanges, respectively, they serve primarily to anchor the tendons close to the bone. In doing so, they help translate excursion into angular motion. In addition to the pulley systems, the digital sheath helps facilitate smooth gliding of the tendons.
6.2 Key Principles
When assessing subacute or chronic flexor tendon injuries, frequent findings in flexor tendon injuries include soft tissue damage, loss of flexor function, development of adhesions, injury to one or more pulleys, joint contracture, scar tissue formation, and neurovascular injury. The Boye’s preoperative classification is frequently used to assess for probability of improved postoperative outcome. In addition to assessing degree of tendon injury, one must also identify the appropriateness of a single- or two-stage reconstruction in the setting of an inability to perform a primary repair.
6.3 Single-Stage Flexor Tendon Reconstruction
Single-stage flexor tendon reconstruction is generally appropriate in the setting of a subacute or chronic, unrepairable flexor tendons (both FDS and FDP), intact flexor tendon sheath, absence of scar tissue, and functional pulley system (► Fig. 6.3). The decision to perform a single-stage reconstruction, in the setting of an intact FDS, is controversial due to the potential for adhesion development and scarring around the FDS tendon.
Single-stage reconstruction should be avoided in patients with excessive adhesions, lack of at least one digital nerve to the digit, joint contracture, loss of multiple pulleys, and poor compliance.
6.3.3 Special Instructions, Position, and Anesthesia
The patient is generally positioned in the supine position with the afflicted arm extended on a hand table. The extremity is cleaned in a sterile fashion and remainder of the body draped. There are several methods of anesthesia that may be utilized. In certain situations, the patient may be administered general anesthesia with or without a brachial plexus block; however, recent trends have shifted toward wide-awake surgery using lidocaine and epinephrine. Benefits of local anesthetic include the ability to have the patient interact during the procedure, which is particularly helpful during tensioning of the tendon graft.
6.3.4 Surgical Technique
A midlateral or Bruner (zigzag) approach is typically utilized to gain access to the digital sheath (► Fig. 6.4). Once exposed, the damaged tendons are excised and a tendon graft is prepared. Some controversy exists as to whether to utilize intra or extrasynovial tendon grafts. Intrasynovial grafts (FDS, toe flexors) may limit adhesion formation. Extrasynovial tendon grafts (palmaris longus, plantaris) are also often used. Once harvested, the tendon graft is attached both proximally (either in the wrist or palm) to the proximal stump of the injured tendon and to the distal phalanx.
6.3.5 Postoperative Course
Postoperatively, a bulky dressing and plaster dorsal blocking splint are applied. The metacarpophalangeal (MCP) joints are ideally maintained in 90 degrees of flexion with the interphalangeal (IP) joints at neutral position. Depending on surgeon preference, the patient is seen several days after surgery and fitted for a custom dorsal blocking splint. At this time, patients begin an extensive course of both physical and occupation therapy. Rehabilitation initially consists of early passive range of motion that progresses to strengthening exercises anywhere from 6 to 10 weeks later. Depending on the stability of the distal juncture, an active range of motion may be initiated earlier.
In single-stage reconstruction, it is not uncommon for patients to develop adhesions that may require staged tenolysis. In addition, rupture of the reconstructed tendon may also be seen. Depending on the time period postoperatively, the grafted tendon may either be repaired primarily, or converted to a two-stage flexor tendon reconstruction.