Surgery and Rehabilitation for Primary Flexor Tendon Repair in the Digit
Linda J. Klein and Curtis A. Crimmins
Surgical Indications and Considerations
Flexor tendon injuries have a long history of challenging the hand surgeon and therapist. Surgical and rehabilitation techniques have evolved significantly since Bunnell1 suggested that tendon lacerations over the proximal phalanx not be repaired, but ultimately grafted. This basic premise went unchallenged until early mobilization techniques were developed in an attempt to prevent tendon adhesions during the healing process. In the 1960s multiple investigators were able to document that primary flexor tendon repair was superior to delayed tendon grafting.2–4
Despite dramatic improvement in outcome over the past 25 years, research has continued with both clinical and laboratory investigations at a breakneck pace. Biomechanical studies of human cadaver tendons have been extraordinarily useful. Investigators have established how much force is applied to a tendon during rehabilitation motions and during normal hand activities.5–8 The most recent repair techniques have greater tensile strength,9 which has allowed early postrepair motion to advance from passive flexion to controlled active flexion. The results are fewer adhesions, with better active motion and functional outcomes.
Tendon Healing Stages
Tendon healing occurs in three general stages. The inflammatory phase lasts about 1 week and begins with a fibrin clot at the repair site. Macrophages and other inflammatory cells begin work by removing nonviable material and attracting fibroblasts. Epitenon cells bridge the repair site to restore the gliding surface. The active repair phase lasts from 1 to 2 months. Collagen bundles form and reorient to strengthen the bond between the tendon ends. The tendon begins to revascularize primarily from the intrinsic supply of the proximal stump. The remodeling phase follows until the collagen is mature along the lines of tension and the repair site strength is maximized. The maturation phase, as with all healing tissue, lasts a number of months.10
Surgical Procedure
The principles of flexor tendon repair are well established and must be rigorously applied to achieve consistently good results. The first step is to educate the patient about the inherent complexity of the injury. The patient should not only understand the demanding technical nature of the injury but also the extraordinarily demanding rehabilitation. The patient must accept that a successful outcome will depend in large part on his or her commitment to and involvement in the rehabilitation protocol. If possible, the patient should be counseled by a hand therapist preoperatively to establish rapport and discuss the therapy protocol. Finally, every patient must be informed that a perfect outcome is unusual and multiple surgical procedures may be necessary.
Flexor tendon repairs should be done in the operating room by experienced hand surgeons within 1 week of the injury. Precise surgical technique is rewarded by better outcomes. Tendon ends usually retract after being cut, and an adequately large surgical incision is generally needed to locate and retrieve the tendon ends. Incisions require careful planning to allow adequate exposure without compromising the vascularity of the skin flaps. Zigzag or midaxial approaches are preferred to prevent scar contracture (Fig. 11-1).
The hallmark of successful flexor tendon repair surgery is atraumatic handling of the soft tissue, especially of the tendon itself. Flexor tendons almost always retract and must be retrieved and advanced back through the flexor sheath. This may well be the most difficult part of the operation. Great care must be exercised to avoid injury to the delicate synovial lining of the fibro-osseous sheath or the epitenon of the flexor tendon. Damage of one or the other may increase the probability of adhesion formation and a poor outcome.
Once the tendon ends have been located and threaded back through the sheath and pulleys as carefully as possible, the tendons are repaired through a window between the pulleys, while maintaining the anatomic relationship of the profundus and superficialis tendons. The flexor digitorum superficialis tendon divides into two slips over the proximal phalanx, then it merges again, creating a buttonhole type opening referred to as the chiasm of Camper, just before inserting into the middle phalanx. The flexor digitorum profundus (FDP), which lies deep to the superficialis until this point, emerges through the chiasm of Camper, continuing distally, to insert on the distal phalanx of the digit (Fig. 11-2). When both tendons are lacerated over the proximal phalanx, the surgeon must be certain to reestablish this special relationship. Furthermore, each divided slip of the superficialis has a tendency to derotate 180° as it retracts. This must also be corrected as the tendon is repaired. Only restoration of normal anatomic relationships will allow excellent return of function after repair of lacerated flexor tendons.
The actual suturing of the flexor tendons has been a major focus in the evolution of stronger repairs. The current state of the art suggests that suture repair achieve adequate strength to allow early active-flexion rehabilitation protocols. To achieve this, the repair must ensure secure knots, provide a smooth juncture of tendon ends at the repair site, prevent gapping, maintain tendon vascularity, and be relatively straightforward to perform. Biomechanical studies have definitively shown that multistrand core suture techniques can withstand forces encountered during active motion protocols. In general, at least four strands of 3-0 or 4-0 sutures are needed to cross the repair site to ensure adequate strength for an early active motion protocol. Numerous suture techniques to achieve a repair of at least four strands are described in the literature. The authors prefer a double Kessler suture to produce the four strands of suture crossing the repair site, with a running epitendinous suture9 (Fig. 11-3).
During the process of repairing the flexor tendons, it is important to preserve as much of the flexor tendon sheath and pulley system as possible. The surgeon must attempt to preserve the A2 and A4 pulleys to prevent tendon bowstringing (Fig. 11-4).
A tendon injury at the level of either of these pulleys is technically demanding. Even repairs at other levels must be technically precise to allow gliding of the repair under preserved portions of the flexor sheath. Suture knots should be placed to minimize impingement of the flexor tendon repair as it passes through the pulley system. Current techniques meet these requirements, and results are expectedly good, with 75% or more tendon repairs falling consistently within the excellent to good categories.
Recent and future trends in flexor tendon surgery research include investigations of the ability of substances such as platelet-derived growth factor-BB, hyaluronic acid, and 5-flourouracil to enhance tendon healing.11–13 Polyvinyl alcohol shields and antiadhesion gels have been proposed and studied with some success to decrease adhesions.14 As these trends continue, we must stay abreast of current developments to maximize functional outcomes for patients after flexor tendon injury.
Therapy Guidelines for Rehabilitation
Flexor tendon repairs in the hand require a special rehabilitation effort. Flexor tendons will heal if positioned without tension or stress; however, adhesions to surrounding tissue will prevent tendon gliding necessary to allow active flexion once the tendon has healed. Thus the need to move a flexor tendon early in the healing process has been evident since repair of flexor tendons has begun.
After repair it takes approximately 12 weeks for a flexor tendon to regain enough tensile strength to avoid rupture with normal strong use of the hand required to grasp, hold, or lift objects during daily activities. A variety of protocols for flexor tendon rehabilitation have been developed over the past 50 years, making the choice of which protocol to use difficult. No exact method exists to determine the strength of a tendon repair during the healing process; therefore the therapist and surgeon rely on general guidelines regarding tendon healing, as well as factors that affect rate of healing to determine advancement of the patient within a flexor tendon rehabilitation protocol. The factors that are considered include the type of injury; status of the tendon, sheath, and vessels at the time of repair; injury to surrounding structures; patient health issues such as diabetes; lifestyle factors such as smoking, which decreases oxygen to the tissues; and ability to comply with the rehabilitation program. Consideration of these factors and clear communication with the surgeon are necessary to determine the most appropriate approach to choose for each particular patient. Before describing the variety of guidelines from which to choose for flexor tendon rehabilitation, it is important to understand how exercise concepts are modified for flexor tendon repair rehabilitation.
Concepts of Healing and Exercises for Flexor Tendon Repair
Role of Adhesions After Flexor Tendon Repair
Adhesions occur very early in many cases, often within 1 week after surgery, preventing gliding of the flexor tendon needed to flex the digit. The end result of dense adhesions can be a digit that does not flex any further than it did before the tendon repair was performed, but with the additional pain, discomfort, and cosmetic changes caused by extensive surgical incisions in the digit, as well as many weeks of lost use of the hand while rehabilitation is attempted. Adhesions are the most difficult to deal with in zones I and II of the hand. Zones I and II extend from the distal palmar crease of the hand to the distal phalanx, and they incorporate the area of the digit in which the flexor tendons pass under a very tight pulley system, encompassed within a tendon sheath filled with synovial fluid that allows the tendon to glide under the tight pulleys (see Fig. 11-4). When adhesions form within the sheath-pulley system in zones I and II of the digit, they are very difficult (in many cases impossible) to overcome, and the result is a digit that is limited in active flexion. Historical perspectives on tendon healing help clinicians understand the reasoning behind current approaches to flexor tendon surgery and rehabilitation. Before the 1960s, flexor tendons were allowed to heal by immobilization for the first few weeks because it was thought that the tendon could not heal without nutrition from the surrounding scar tissue.15 This immobilization for the first few weeks resulted in dense adhesions, especially with repairs in zones I and II, with the inability to actively flex the digit. These results spurred the development of immediate passive-flexion protocols. The goal was that by passively flexing the digit and allowing partial, protected extension, the flexor tendon would glide far enough under the pulley system to prevent dense restricting adhesions and allow active motion when the tendon was adequately healed. However, in many cases, tendinous adhesions still developed. Research has shown that proximal gliding of the FDP tendon is inconsistent during passive flexion.16 The flexor tendon, when the digit is passively flexed, is thought in some cases to kink, or bunch up, between the pulleys, rather than passively glide through the pulley system (Fig. 11-5). To ensure proximal gliding of the flexor tendon, an active contraction of the muscle is needed to pull the tendon proximally through the pulley system. Because research has shown that tendons do heal intrinsically without surrounding adhesions,17–19 an effort to actively flex the repaired flexor tendon immediately after repair was initiated to prevent the onset of dense adhesions. To avoid rupture of the flexor tendon with active motion immediately after surgery, however, stronger suture techniques had to be developed.
Understanding Repair Strength
Flexor tendon surgery has undergone an evolution over the past 10 to 20 years. This evolution has resulted in the development of stronger suture repair techniques that will withstand the tension placed on the repair with controlled active flexion immediately after the repair. These new and stronger tendon repair techniques, as discussed in the earlier portion of this chapter, allow immediate controlled active motion without rupture, preventing the formation of dense adhesions. In general, the more strands of suture material that cross the tendon repair, the stronger the repair (Fig. 11-6).7–9,20,21
Traditional surgical procedure, using a two-strand repair, will tolerate passive motion, but is not shown to be sufficiently strong enough to tolerate active motion immediately after repair.22 A four-strand repair will tolerate gentle active motion. An eight-strand repair will certainly tolerate active motion; however, it is technically demanding and may become so bulky as to not glide under the pulleys, creating friction, possible wearing, and eventual rupture.20 Thus a four- to six-strand repair technique is frequently chosen to apply an immediate active motion protocol.
After the traditional two-strand repair, it is safe to perform immediate passive-flexion protocols (described later in the chapter), or where necessary by patient limitation, immobilization. Immediate active-flexion protocols are generally not applied to the tendon with a traditional two-strand technique, but require a stronger four-strand technique and must be discussed with the surgeon. It is extremely important for the therapist to understand the type of suture repair that was done for a flexor tendon repair, to ensure that the protocol chosen for a particular patient stays within the tension limits of the repair.
Edema Control and Scar Management After Flexor Tendon Repair
Elevation is essential in the early phase after flexor tendon repair, because other forms of edema control are limited by the continuous splinting. Shoulder, elbow, and cervical motion exercises are performed to help with lymphatic function and circulation. In the intermediate and late phases of flexor tendon healing, use of a light compressive wrap at night is appropriate. 
This should not be used during the day because compressive wraps will increase resistance to the flexor tendon during active flexion. The therapist initiates gentle massage of the scar (for firmness) and edema massage after sutures are removed; the patient can continue this process at home when made feasible by the presence of the splint. Commercially available scar management pads may be placed or formed over the scar, applied at night only, if scars become thickened or raised. Because the splint is worn full time in the early phase of the rehabilitation programs, it is difficult for the patient to safely apply the scar management pads at night, and they are often applied beginning in the intermediate phase for this reason.
Passive-Flexion Exercises After Flexor Tendon Repair
Passive flexion of the digits is performed through all the phases of flexor tendon rehabilitation. Passive flexion of the digit after a flexor tendon repair places the repaired tendon on slack. Very little tension develops within the flexor tendon during passive flexion of the digit, as long as the patient is truly relaxed and not actively assisting the passive flexion.5,6 After flexor tendon repair, a finger will become stiff because of swelling, incisional scarring, and pain if passive flexion is not performed within 1 week after the procedure. If passive flexion remains limited after sutures are removed, then other therapy techniques may be used to assist in regaining passive flexion, such as heat combined with stretch into flexion before manual passive flexion within the patient’s pain tolerance.
Wrist Tenodesis Exercises After Flexor Tendon Repair
Wrist tenodesis exercises use wrist motion to assist in moving the flexor tendons. The wrist is flexed to comfortable tolerance, and the fingers allowed to gently straighten at all three joints. This will give the tendon slack at the wrist and glide the tendon distally during finger extension. Next, the fingers are relaxed, the wrist is extended to 30°, and the fingers are gently flexed. The wrist extension pulls the flexors slightly proximally and gives slack to the finger extensors, allowing the flexors to glide proximally (Fig. 11-7). The wrist tenodesis exercise is started in the intermediate phase of rehabilitation after a two-strand repair, because it creates tension in the tendon. It is started within 3 days after surgery within an immediate active-flexion approach after a four (or more) strand repair unless otherwise directed by the physician.
Active Extension of the Fingers After Flexor Tendon Repair
Full extension of all three finger joints at the same time must be limited immediately after flexor tendon repair to avoid pulling the repair apart by stretch. Extension is limited in the early phase of tendon healing by positioning within the dorsal blocking splint that places the metacarpophalangeal (MP) joints in flexion. However, interphalangeal (IP) extension is very important to obtain shortly after the repair in zones I and II because the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints contract into flexion very quickly after repairs in these zones. All flexor tendon protocols emphasize attaining full IP extension immediately after surgery, unless a digital nerve has been lacerated or another injury prevents placement of the IP joints in full extension, as directed by the surgeon. When a digital nerve has been repaired in the digit, the PIP joint is generally allowed to extend to 15° less than full extension. 
Composite extension of all three finger joints at the same time will place an adverse stretch effect on the flexor tendon repair in zone I or II initially after surgery, but it can be tolerated at 4 weeks after surgery with the wrist in flexion. Wrist and full finger extension are not performed at the same time until the late stage of tendon healing.
Passive Finger Extension After Flexor Tendon Repair
Passive extension of the fingers is potentially more dangerous than active extension, because if done overaggressively, it may stretch the tendon repair apart. It is also possible for the patient to have some tension within the flexor tendon during the passive extension, resulting in resistance to the repaired tendon and possible rupture.
In the early phase of tendon healing, passive IP extension is only performed when active IP extension is limited (in the presence of PIP or DIP joint flexion contractures). When IP joint flexion contractures appear early, passive IP joint extension can be performed carefully, with the flexor tendon in a protected position and ensuring that the patient’s hand is fully relaxed. The protected position for a flexor tendon is with all other joints supported in flexion while one joint is extended. For instance, to treat a PIP flexion contracture 3 weeks after repair, the therapist flexes the wrist and MP joints as far as can be tolerated, then passively extends the PIP joint by applying pressure under the middle phalanx into extension. The DIP joint is not passively extended at the same time as the PIP joint to avoid stressing the tendon across two joints in the early phase of tendon healing.
Active Finger Flexion After Flexor Tendon Repair
Active flexion introduces significantly increased tension in the repaired flexor tendon. Traditional approaches using immediate passive flexion or immobilization for the early phase of tendon healing introduce active flexion of the repaired digit in the intermediate phase of healing (4 weeks after surgery). An assessment of flexor tendon gliding is done to determine what type of active flexion is appropriate. To assess flexor tendon gliding, passive flexion is compared with active flexion. 
The initial assessment of active flexion is done cautiously, with the wrist in 20° to 30° of extension (Fig. 11-8). When a difference exists in the repaired digit between passive and active flexion of 15° or more,23 it indicates the presence of adhesions, limiting tendon gliding. When flexor tendon adhesions limit active more than passive flexion 3 to 4 weeks after surgery, active tendon-gliding exercises are initiated. Tendon gliding can be achieved by performing a sequence of three fists: hook fist, straight fist, and composite fist (Fig. 11-9). A hook fist is similar to a claw position, flexing the PIP and DIP joints with the MPs extended. This type of fist results in the largest differential gliding of the FDP and flexor digitorum superficialis. A straight fist results in the most excursion of the flexor digitorum superficialis. A composite fist results in the most excursion of the FDP tendon.
Active flexion is begun in the early phase of tendon healing when the patient is placed in an immediate active motion flexor tendon rehabilitation approach. At the first postoperative physician or therapy visit 2 to 3 days after surgery, a controlled method of active flexion termed place-hold is begun. Place-hold flexion uses the therapist’s or patient’s other hand to passively place the fingers into a light fist; then the patient holds the fingers actively in the light-fist position as the other hand is removed. This requires an active muscle contraction and flexor tendon gliding in a proximal direction to keep the finger in a flexed position actively. The place-hold exercise is believed to result in less tension on the repaired tendon than if the finger were actively flexed without the assistance of the patient’s opposite hand or the therapist’s hand. 
Within an immediate active motion approach, the three types of fists described earlier are not performed until the intermediate phase of tendon healing if flexor tendon adhesions develop in spite of early active motion attempts.
Postoperative Guidelines
In general, three types of flexor tendon rehabilitation guidelines exist. These are (1) immobilization, (2) immediate passive flexion, and (3) immediate active-flexion approaches. The reasoning for choosing one approach over another is based on the complexity of injury, the age of the patient, patient compliance, patient health factors, and the suture repair technique. The choice of which set of guidelines within which to place a patient is best determined in conjunction with the referring surgeon, with the final decision resting with the surgeon.
Within each approach the patient progresses through three general levels or phases: early, intermediate, and late phases. The decision of when to advance a patient to the next level within each approach is determined by the amount of flexor tendon adhesion that limits the tendon gliding and the amount of time after repair. To determine the level of flexor tendon adhesion, the therapist compares passive flexion with active flexion. When a large discrepancy exists between passive and active flexion, with passive flexion 15° or more better than active flexion, it signifies the presence of flexor tendon adhesions. When adhesions limit gliding of the flexor tendon, and the time period after repair is adequate to allow increased tension on the tendon, the patient is progressed to the next level of the rehabilitation approach. 
The tendon that does not have limiting adhesions is more at risk for rupture than the tendon with strong adhesions that surround the tendon repair site. When tendon adhesions limit active flexion more than passive flexion, the tendon can tolerate more tension before rupture, and thus can be advanced to the next level sooner than the tendon without limiting adhesions.23 Flexor tendon adhesions are assessed on a continual basis to determine the level of the rehabilitation program that is appropriate for the patient at that time. The time after surgery, combined with the level of flexor tendon adhesion, determines the placement of the patient in the program.23 When adhesions prevent gliding of the flexor tendon, it is appropriate to advance the patient to the next phase of rehabilitation to encourage tendon gliding, with surgeon approval. When flexor tendon gliding is adequate, the patient is kept in the current level of the program until the number of weeks after surgery dictates that the repair is strong enough to tolerate the increased tension of the next phase of the treatment protocol.
The appropriate choice of which guideline to use and advancement of the patient within the chosen guideline require in-depth knowledge of flexor tendon healing and tensile strength guidelines at various times after repair, awareness of the type of repair, and the patient’s compliance level, as well as communication with the referring surgeon.
Immobilization Approach
Indications for Immobilization
Immobilization is rarely used after a flexor tendon repair; however, some situations call for its application. Immobilization is used for young children, who are unable to adhere to a motion protocol with its specific precautions. Children younger than age 12 are most often placed in immobilization for the first 3 to 4 weeks, but each child should be evaluated related to his or her maturity level. Other population types that may be placed in immobilization after a flexor tendon repair would be those that have cognitive limitations (e.g., Alzheimer disease, noncompliant patients). It is sometimes difficult to know the patient’s compliance ability at the first therapy session. When a patient demonstrates inability to appropriately comply with the precautions and exercises within a certain approach, it may become necessary to change the rehabilitation approach to one with less early motion, or a cast may be needed instead of a removable splint in the first 4 to 5 weeks after surgery. When a concomitant fracture or significant loss of skin requiring a skin graft occurs, a period of immobilization may be necessary to allow the bone or skin to heal adequately before beginning motion. Not all fractures require immobilization. Stable fractures or those that have had open reduction internal fixation may tolerate immediate controlled motion, as determined by the surgeon. Few sets of guidelines exist for therapy after immobilization of the repaired flexor tendon because of dense adhesion formation. The most frequently sited guideline, described as follows, encourages motion and light resistance to facilitate tendon gliding after the initial phase of tendon healing.24,25
Immobilization Guidelines
Phase I (Early)
TIME: 0 to 4 weeks
GOALS: Prevent joint stiffness, avoid tension on tendon repair, prevent flexion contractures, patient and family education regarding tendon protection, manage edema, full active range of motion (AROM) of upper extremity (UE) joints proximal to the wrist (Table 11-1)
TABLE 11-1
Flexor Tendon Repair in the Digit (Immobilization Approach)
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AROM, Active range of motion; IP, interphalangeal; MP, metacarpophalangeal; ROM, range of motion.
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Splinting.
When used, the immobilization approach will place the patient’s hand in a dorsal blocking cast (or in a dorsal blocking splint wrapped securely in place, with instructions not to remove the splint at home). The position of the cast or splint in the early phase of immobilization is 20° to 30° of wrist flexion, and 40° to 50° of MP flexion, with IP extension. This position keeps the flexor tendons on slack, yet prevents the most difficult joint problems (e.g., PIP flexion contractures). The cast or splint will stay in place for 3 to 4 weeks.
Exercises.
Within phase I (zero to 3 or 4 weeks after surgery) the patient generally remains immobilized in the dorsal blocking splint or cast. When referred to therapy during the early phase, the therapist may perform passive flexion to prevent joint stiffness and a significant other, such as a parent, may be taught to perform passive flexion at home if he or she is reliable. Goals in the early phase of the immobilization approach include protecting the repaired flexor tendon(s) from rupture with full time splinting and patient education, obtaining passive flexion when allowed, edema control, and obtaining full active motion of the UE proximal to the wrist.
Phase II (Intermediate)
TIME: 3 or 4 weeks to 6 weeks
GOALS: Improve joint mobility (full flexion passive range of motion [PROM], partial flexion AROM, full IP extension), patient and family education, scar management, splinting to prevent tendon repair rupture between exercises (Table 11-2)
TABLE 11-2
Flexor Tendon Repair in the Digit (Immobilization Approach)
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| Rehabilitation Phase | Criteria to Progress to This Phase | Anticipated Impairments and Functional Limitations | Intervention | Goal | Rationale |
| Phase II 3/4-6 wk |
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Exercises.
With phase II exercises, the splint position is adjusted to bring the wrist to neutral. The splint is removed for exercises hourly. Passive flexion is initiated first, to loosen stiff joints created by immobilization, swelling, and scarring. After passive flexion, wrist tenodesis is initiated as described previously, to begin gentle tendon gliding (see Fig. 11-7). Tendon-gliding exercises are initiated, with three types of fisting exercises (i.e., straight fist, hook fist, and composite fist; see Fig. 11-9
