Chapter 14 Flexor Tendon Repairs

Kara Gallagher, MS, OTR/L, CHT

Flexor tendons are surgically corrected via a primary or secondary repair. Whether a repair is primary or secondary depends on how soon after injury that surgery occurs and the quality of the tendon.

In a primary repair, the loose ends of the injured tendon are approximated with sutures. An immediate primary repair is performed within 24 hours of injury, whereas a delayed primary repair is performed between 24 hours and 3 weeks after injury. Primary end-to-end tendon repair performed within the first few days following injury is ideal and guarantees the best outcome. Studies performed on canine and chicken tendons demonstrate that repairs performed within the first few days resulted in improved tendon excursion. It is important to be aware that delayed tendon repair increases the possibility of rupture, tendon elongation, muscle shortening, and joint contractures. A tendon injury that involves bone or neurovascular damage will complicate the rehabilitation process and possibly the outcome but does not contraindicate a primary repair.

A secondary repair is considered 3 weeks post-injury, or in situations where the quality of the tendon is beyond surgical correction. After 3 weeks, flexor tendon repair becomes more complicated because of scarring, muscle contracture, and tendon retraction. At this point, available options include a tendon graft, transfer, or two-stage tendon graft. Other situations that require a secondary repair include loss of palmar skin overlying the flexor system, flexor retinacular damage, and pulley destruction.

In a secondary repair, a tendon graft from a noninvolved tendon (often palmaris longus [PL]) is harvested to approximate the free ends of the injured tendon. If scarring or damage to adjacent tissues is severe, a conventional tendon graft is unlikely to resume adequate gliding, and staged tendon grafts are performed. Transformation of the scarred, post-injury flexor tendon and surrounding tissues to a gliding, pliable, effective system is accomplished using a two-stage tendon graft method with a silicone implant. In the first stage, a silicone implant is placed between the free ends, allowing the scar to envelope it and recreate a fibrous sheath to promote healing of the second-stage tendon graft. Tendon injuries may occur in isolation or along with fractures and neurovascular injuries.

This chapter reviews the anatomy, surgery, and rehabilitation related to a flexor tendon injury, specifically an early active mobilization protocol that is appropriate for primary tendon repairs completed with a four-strand core suture and an additional epitendinous suture augmentation crossing the repair site. Flexor tendon injuries in the forearm or hand occur when tendon continuity is disrupted by a laceration, crush, avulsion, or contusion.

Anatomic Overview

• In the distal third of the volar forearm, the flexor tendons arise from the flexor muscles.

1 The superficial group includes the wrist flexors: flexor carpi radialis, flexor carpi ulnaris, and PL.

2 The middle group consists of the four tendons of the flexor digitorum superficialis (FDS) that originate from individual muscle bundles. This allows for isolated individual flexion of each digit.

3 The deep group includes the flexor digitorum profundus (FDP) and flexor pollicis longus. The FDP tendons originate from a common muscle belly and therefore act as a group.

• Several surrounding anatomical structures are significant in flexor tendon injury.

• Flexor tendon injuries are categorized into five zones on the premises of anatomic features to systematically highlight these structures.

Zone V

• Zone V spans the distal third of the forearm to the level of the wrist and contains the musculotendinous junction of the superficial and deep flexors.

• Median and ulnar nerves, as well as the radial and ulnar arteries, course through zone V and are often associated with injury to the tendons.

• The vascular and neural structures must be protected in the early phases of rehabilitation.

• Early repair is especially recommended for tendons in this zone because of the high probability of tendon retraction with muscle contraction.

1 The tendons lie deep in the skin and subcutaneous tissue and are particularly vulnerable to adhesions.

2 Contracture and shortening of the tendons in this zone are common. Both adhesions and contracture can be reduced with a strong focus on differential tendon gliding during rehabilitation.

Zone IV

• In zone IV the flexor tendons are enclosed in synovial sheaths as they course through the carpal tunnel.

• Injuries in this zone often include more than one tendon, blood vessels, and nerves because of the close proximity of the structures to one another.

• Adhesions between the tendons are common in the postoperative phase, and differential gliding of the tendons is effective in controlling adhesion formation.

Zone III

• The lumbrical muscles originate from the flexor digitorum profundus tendon at the point where the tendons emerge from the carpal tunnel in zone III.

• Protective positioning in the lumbrical plus position (metacarpophalangeal [MP] flexion with interphalangeal [IP] extension) can lead to adhesions and contracture of the intrinsic muscles in the early weeks. Therefore, gentle, passive MP joint motion and gentle, passive intrinsic minus or hook fist (MP extension with IP flexion) early in rehabilitation are recommended for injuries in zone II.

Zone II

• Zone II begins at the distal palmar crease and includes the origin of the flexor tendon sheath. Zone II extends to the middle of the middle phalanx, just distal to where the FDP emerges from the two slips of the FDS insertion (Camper’s chiasm).

• In zone II the flexor tendons are supported by an intricate pulley system that tethers the tendons to the bones for increased mechanical advantage during flexion.

• Injured and repaired pulleys are potential sites of adhesion formation. Alternatively, unrepaired pulleys may cause “bowstringing” as the tendon pulls away from the bone in the palmar direction under muscle contraction.

• Zone II also includes the viniculae, which provide vascularity and nutrition to the tendons.

• Laceration in zone II often involves both FDS and FDP, in addition to the supporting structures.

• Historically, this region has been referred to as “no man’s land” because of the complicated system of synovial sheaths, pulleys, and viniculae supporting the flexor tendons.

• In the past, poor results were expected with tendon injury in zone II because of the combination of intertendinous adhesions as well as the effects of injury to the sheath, viniculae, pulleys, and other surrounding structures.

• During the last 10 years, advances in suture technique, strength, and early postoperative active mobilization protocols have improved the ability to obtain better results.

Zone I

• Zone I, the most distal zone, spans from the insertion of the FDS on the middle phalanx to the insertion of the FDP on the distal phalanx.

• Zone I includes only the FDP tendon as it emerges from the flexor sheath.

• This is a common site for FDP rupture, where the terminal tendon is avulsed with or without a bony component, at its insertion on the distal phalanx.

• Complications following tendon repair in zone I include development of distal interphalangeal (DIP) joint flexion contracture or poor gliding through the A-4 and A-5 pulleys.

Surgical Overview

• Surgical repair of flexor tendons has evolved over the years. For many years, two-strand repairs were performed. In the past decade, four-strand repairs have become more common.

• The strength of a tendon repair is roughly proportional to the number of strands that cross the repair. The number of strands in a repair refers to the number of times the suture material crosses the repair site.

• Today, the most common primary repair is accomplished with a four-strand core suture plus an epitendinous suture crossing the repair site to strengthen the procedure.

• Many core suture designs have been described in the literature, ranging from four to eight strands. These designs include the Bunnell, modified Kessler, Tajima, locking running epitendinous, and double-grasping techniques.

• The surgeons at the Hospital for Special Surgery (HSS) typically use a four-strand modified Kessler core suture with a reinforcing epitendinous suture. Like other early active mobilization programs, this guideline requires a four-strand core repair and an epitendinous suture at the repair site. Therefore, motion can be initiated within the first 3 days post-surgery.

• Early active mobilization requires adequate tensile strength of the suture material and appropriate design of the suture so that the tendon can withstand active muscle pull without rupture or gapping.

Rehabilitation Overview

• There are three approaches to rehabilitating a flexor tendon after surgical repair. They include immobilization, early passive mobilization, and early active mobilization.

1 Passive mobilization programs, such as those described by Kleinert et al. and Duran and Houser, involve gentle passive flexion and active extension exercises that are performed in a dorsal block splint, with or without rubber band traction that assists the digits into flexion.

2 Early active mobilization consists of active hold or active place-hold programs.

– Active place-hold indicates that the therapist passively places the digits into flexion and then directs the patient to actively maintain the position with a gentle muscle contraction.

– This guideline details an active hold/place-hold mobilization program that the authors have found to be most successful. Their version has been modified from protocols designed by Strickland, Cannon, and Silfverskiold and May.

– The goal of rehabilitation following flexor tendon repair is to promote an opportune environment for a strong repair to support normal forces acting on the tendon in everyday functional use.

1 Research demonstrates that stressing a repaired tendon with early mobilization facilitates healing, tensile strength, excursion, and minimizes adhesion formation.

2 This protocol offers a method to encourage a durable tendon repair that glides freely.

• Passive mobilization techniques based on principles from the Controlled Passive Mobilization Technique by Duran and Houser and the method by Kleinert et al. are also incorporated into this guideline.

1 The passive mobilization techniques are included to preserve joint motion.

2 Like most early active mobilization protocols, this guideline was developed for flexor tendon injuries in zone II. However, the principles can be applied to injuries in all zones.

Active Mobilization

• The active mobilization protocol must begin within 1 to 2 days of surgery, when the repair is physiologically strong.

1 The tensile strength of the immobilized tendon diminishes 3 to 5 days postoperatively because of softening of the tendon ends.

2 A study by Hitchcock et al. determined that the ends of flexor profundus tendons in chickens softened during the inflammatory phase of wound healing. The same study compared the immobilized group to a group that was mobilized 1 to 2 days after repair. The study found that the mobilized group did not encounter a notable inflammatory phase, and rather the repair gained strength, appearing to heal through intrinsic means, with less adhesion formation.

• Active mobilization of the repaired tendon begins with place-hold positions protected by tenodesis (wrist extension with digit flexion/wrist flexion with digit extension).

• Active mobilization progresses toward active flexion along the following ladder: place-hold tenodesis, active tenodesis, differential tendon gliding, blocking, and strengthening.

• Strengthening begins with blocking with resistance, progressing toward isometric grip, and, finally, isotonic strengthening of grip and pinch.

CRITERIA FOR ADVANCEMENT

• Rehabilitation of the repaired flexor tendon progresses through four phases of therapy that can last up to 16 weeks postoperatively.

• The phases of this protocol reflect the three stages of wound healing: inflammation, fibroplasia, and scar maturation.

• Advancement of the patient depends upon the stage of wound healing, excursion of the flexor tendon, and opinions of the surgeon and therapist.

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