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Improving Outcomes in Tendon Repair: A Critical Look at the Evidence for Flexor Tendon Repair and Rehabilitation

Khor, Wee S. B.Sc., M.B.Ch.B.; Langer, Martin F. M.D., Ph.D.; Wong, Richard B.Sc., Ph.D.; Zhou, Rui M.B.Ch.B.; Peck, Fiona M.C.S.P.; Wong, Jason K. F. M.B.Ch.B., Ph.D.

doi: 10.1097/PRS.0000000000002769
CME
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Learning Objectives: After reading this article, the participant should be able to: 1. Appreciate the variation and evolution of flexor tendon management 2. Know how to assess the patient who presents with a flexor tendon laceration. 3. Understand the biology of repairing flexor tendon lacerations. 4. Appreciate the technical challenges in flexor tendon repair relating to different zones. 5. Understand the rationale of postoperative hand therapy. 6. Have an overview of the types of secondary tendon surgery.

Background: Flexor tendon injury constitutes a considerable trauma workload for hand surgeons, and a vast amount of research is dedicated toward improving outcomes in tendon repair. This Continuing Medical Education article aims to provide an up-to-date evidence-based outline of flexor tendon surgery in the hand.

Methods: The authors reviewed the literature on flexor tendon repairs to include a balanced overview of the experimental and clinical research. For each section, the best levels of evidence were assessed in the context of past research to provide a comprehensive opinion on best management.

Results: The review highlights current trends in flexor tendon surgery, clinical assessment, anesthetic technique, surgical approach, repair technique, and rehabilitation. Carefully selected illustrations, figures, tables, and video have been used to supplement the findings of the review.

Conclusions: Early active mobilization remains the only long-term proven strategy to improve outcomes. Incorporating intraoperative mobilization using “wide-awake” surgery could emerge to further improve tendon outcomes. Good surgical approach, meticulous surgery, up-to-date physiotherapy regimens, and patient education remain the cornerstone of obtaining best outcomes.

Related Video Content is Available Online.

Manchester, United Kingdom; and Münster, Germany

From the University Hospital South Manchester, Wythenhawe Hospital; Blond McIndoe Laboratories, Division of Cell Matrix Biology and Regenerative Medicine, University of Manchester; and the Klinik und Poliklinik für Unfall-, Hand- und Wiederherstellungschirurgie, Universitätsklinikum Münster.

Received for publication November 30, 2015; accepted July 18, 2016.

Disclosure: The authors have no financial interest to declare in relation to the content of this article.

Related Video content is available for this article. The videos can be found under the “Related Videos” section of the full-text article, or, for Ovid users, using the URL citations published in the article.

Jason K. F. Wong, M.B.Ch.B., Ph.D., Blond McIndoe Laboratories, 3.102 Stopford Building, Oxford Road, University of Manchester, Manchester, Greater Manchester, United Kingdom, M13 9PT, jason.k.wong@manchester.ac.uk

Flexor tendon injury is one of the most common ailments managed by hand surgeons and makes up a considerable trauma workload for plastic surgical and orthopedic trainees. It is therefore important that a good understanding of the decision-making process and evidence is presented in a comprehensive way so that the management of these cases is effective and assured. We have recently provided our own viewpoint on how to improve flexor tendon outcomes.1 This CME article aims to supplement our previous review with clinical studies and levels of evidence in areas we felt were important to highlight as must-have knowledge when managing the problem of flexor tendon injury repair and rehabilitation.

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EPIDEMIOLOGY

The incidence of flexor tendon injury in the developed world is between 30 and 42 per 100,000 per year, which appears to be gradually decreasing, with workplace injuries becoming less frequent because of safety measures.1,2 However, injuries acquired through domestic and trauma situations continue to provide us with a steady flow of work.

The choice of repair and rehabilitation varies diversely from center to center and from surgeon to surgeon. There is no Level I clinical evidence that one repair or rehabilitation regimen is truly superior to another, and it is challenging to investigate this in any meaningful way because of the sheer diversity of management protocols nationally and globally.

A number of centers around the world have seen marginal gains by systematically evolving their practice and implementing change. Notable gains have been reported by Chelmsford, Nantong, Wellington, Bern,3 and our practice (Fig. 1). Common changes in these centers include the universal adoption of multistrand repairs and early active mobilization. However, despite this trend, outcomes still vary and ruptures still occur. The evidence of how best to manage flexor tendon injuries continues to evade us.

Flexor tendon injuries arise from a spectrum of severe to trivial injuries in patients from a diverse range of social backgrounds. Common patterns of injury at its simplest may be a single isolated zone II flexor digitorum profundus injury, and at its most extreme, multiple zone II injuries, or a “spaghetti” wrist in zone V. Work-related injuries account for approximately 25 percent of those requiring surgery in both developed and developing countries.2,4 Regarding simple zone II injuries, pooled data from two multicenter, randomized, controlled studies from Manchester and Sweden have shown the average age of patients who sustain these injuries is 35 years, with a male-to-female ratio of approximately 3:1,5,6 whereas in epidemiologic studies the ratio is between 5 and 6:1.2,4 The patient is more likely to damage either the index finger tendons or little finger in the zone II region,2,5,6 whereas in zone V, injury is more likely to occur to the middle finger tendons and involve injury of multiple tendons.2 Injuries as a result of sharp metal were more common than those from glass (69 percent versus 18 percent), and approximately two-thirds of the patients had concomitant injuries to the flexor digitorum superficialis tendon.5 Studies have shown those who sustain more violent injuries as opposed to clean cuts were more likely to encounter flexion contractures, reoperation, and poorer functional outcomes.7

The frequency of associated nerve injury has been reported at 25.4 percent,8 and associated fracture varies from 3 to 52 percent.7,9 Multiple digits are often involved and may occur in 10 to 29 percent of cases9,10; therefore, each case requires careful consideration of how to prioritize repair. For the more complex, traumatized, or contaminated digit, consideration has to be made as to how to prioritize the repair of the other damaged tissues and whether primary repair or a staged repair should be performed (Table 1). In general, a primary repair should always be attempted if the two ends of the tendon can be brought together without undue tension; otherwise, a primary repair at a later date can be challenging because of shortening from sarcomere degeneration of the muscle fibers.11

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HOW TO ASSESS THE FLEXOR TENDON–INJURED HAND

The key attributes to derive from the history are the patient’s occupation, their hand dominance, the mechanism of injury, and whether the flexors were engaged at the time of damage, as a hand grasped in flexion will dictate how far the ends have retracted from the wound edges. The finger with a divided flexor tendon usually adopts a distinct posture that can be easily assessed. A simple tenodesis test flexing and extending the wrist and looking at the tendon cascade can indicate which flexor tendon is divided (Fig. 2, above).

Global movement with an open hand to clenched fist can usually identify the injured digit(s) and indicate which tendons have been divided and also the level at which the injury is sustained. It is critical that a full neurovascular assessment is performed so that other damaged structures can be managed in the appropriate manner.

Single-digit isolation can identify whether the flexor digitorum superficialis to the digit is intact if flexion at the metacarpophalangeal joint and proximal interphalangeal joint can be performed. Isolation of the movement at the distal interphalangeal joint will indicate whether the flexor digitorum profundus is intact. (See Video, Supplemental Digital Content 1, which displays a clinical assessment for flexor tendon injury. This video is available in the “Related Videos” section of the full-text article on PRSJournal.com or at http://links.lww.com/PRS/B923.)

Pain and fear can sometimes limit the value of these tests, and are quite common in children. In these circumstances, when the patient is asleep or has a regional block, the tenodesis test along with the wrist squeeze test (Fig. 2, below) may allow one to demonstrate whether the tendons are intact. No specific studies have evaluated the sensitivity and specificity of these tests; however, the error rate for the clinical diagnosis of the volar structures damaged varies between 14 and 32 percent.12,13

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WHICH ANESTHESIA?

The vast majority of flexor tendon surgery is performed under general anesthesia, largely because of patient request and this being standard care in most centers around the world. Certainly for the novice managing tendon repairs, this is the anesthesia of choice.

Regional anesthesia allows for “fast tracking” in hand surgery, shorter periods of postoperative stay, less nausea and vomiting, and less opioid consumption than general anesthesia, but overall patient-reported outcomes are quite similar14,15 (References 14 and 15 Level of Evidence: Therapeutic, II). Successful regional anesthesia requires experienced anesthetists, as the requirement for supplemental anesthesia has been reported to be approximately 22 percent.16

Wide-awake local anesthesia without tourniquet for tendon repair is an emerging safe and effective modality that is gaining popularity.17,18 Wide-awake primary tendon repairs enable the surgeon (and patient) to assess the range of motion and quality of repair before skin closure. Inadequate repair (e.g., poor glide, triggering, gapping, bunching) can all be corrected immediately, and therapy regimens can be adjusted to the observed intraoperative findings. (See Video, Supplemental Digital Content 2, which displays wide-awake local anesthesia without tourniquet assessment of possible flexor tendon division. This video is available in the “Related Videos” section of the full-text article on PRSJournal.com or at http://links.lww.com/PRS/B924.) Intraoperative correction with dynamic assessment using wide-awake local anesthesia without tourniquet has acceptable low rupture rates of 3.3 percent.17,19 In addition, the overall cost of flexor tendon surgery can be reduced by removing the need for general anesthesia and its provisions.20–22 Wide-awake local anesthesia without tourniquet surgery does require the surgeon to be experienced at identifying important structures expeditiously with careful repair to maintain the confidence and comfort of the awake patient. Patient participation can be encouraged during wide-awake local anesthesia without tourniquet and good communication is essential to pacify the anxious patient.17

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HOW TO APPROACH THE TENDON

All approaches to the flexor tendon should be customized to use the existing laceration when available, and the principle should be to preserve the blood supply to the skin flaps. The two most common methods of access are the Bruner incision23 and the mid-lateral incision,24 which offer access to the flexor tendon and associated damaged structures without violating the blood supply to the finger flaps (Fig. 3). Crossing the finger creases with the incision is usually acceptable, provided that it is a staggered line.25 Variations on the incisions have been described, but no formal studies have been performed to compare the incidence of wound dehiscence or scar contractures with these techniques. We advocate limited skin incisions based on the understanding that surgical trauma increases adhesion formation.26 One can limit the incisions by appropriate tendon retrieval.

There are many different ways to retrieve the retracted flexor tendon (Table 2).27–49 Our preferred method uses a simplified pediatric feeding catheter snaring technique that greatly reduces the handling of the tendon ends26 (Fig. 4). (See Video, Supplemental Digital Content 3, which displays a multiple-digit wide-awake procedure. This video is available in the “Related Videos” section of the full-text article on PRSJournal.com or at http://links.lww.com/PRS/B925.) It is hard to demonstrate which method offers best retrieval; however, the overall aim should be to minimize damage of the tendon and surrounding soft tissue.

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WHICH REPAIR SHOULD YOU USE?

The experimental components that influence repair strength are suture material, suture gauge, the number of core strands, suture configuration, suture purchase, and the addition of an epitendinous suture.1 The uniform spread of load through a tendon repair tends to offer the best biomechanical strength and thus the configurations of the Lin modified Kessler and Adelaide repair perform well in ex vivo testing. (See Video, Supplemental Digital Content 4, which displays biomechanical evaluation of six popular tendon repairs. This video is available in the “Related Videos” section of the full-text article on PRSJournal.com or at http://links.lww.com/PRS/B926.) Despite laboratory findings, the clinical evidence to support multistrand repair is less clear.

Several systematic reviews comparing outcomes of two-strand versus multistrand repairs do not support the perceived value of multistrand repairs. The improvements in rupture rates in the past two decades of hand surgery appear to be attributable to improved quality of care and not to an increase in core strands.50 The International Federation of Societies for Surgery of the Hand committee reported a trend for later ruptures with multistrand repairs.51 Early ruptures observed in two strands (average, 18 days) are likely to relate to suture failure, whereas six-strand repairs failed on average 47 days later but are probably related to a disruption of tendon healing. This discrepancy with experimental findings and clinical observations points to other biological factors at play that warrant further research.

In vivo studies have shown that the suture repair of tendon does lead to a gradual weakening of the tendon.52 We have shown that there is a significant and persistent recruitment of inflammatory cells around a sutured tendon and the formation of acellular zones within the grasping component of the repair.53 (See Video, Supplemental Digital Content 5, which displays the effect of suturing tendon. This video is available in the “Related Videos” section of the full-text article on PRSJournal.com or at http://links.lww.com/PRS/B927.) The complex biology of suturing tendon in the context of clinical observations may, in part, explain why ruptures still occur.

It is a matter of debate whether the surgeon’s experience affects outcomes. Moriya et al. found that five of their six ruptures were performed by less experienced surgeons.54 It has been suggested that careful documentation of seniority of the surgeon is required to reflect the competency of the repair.55 Several studies relating to flexor tendon surgery did not find seniority of the surgeon to be a factor in determining outcomes or rupture rates.56,57 However, the simpler the repair, the greater the economy of movement, and less surgical trauma should be the primary repair aspiration.

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CONSIDERATIONS IN DIFFERENT ZONES

In each of the flexor zones (Fig. 5, above), the strategy for repair follows similar principles, but each has its own unique anatomical considerations. De Jong et al. found the relative distribution of flexor tendon injuries seen in zones I, II, III, IV, and V to be 12.7, 59.1, 6.8, 0.6, and 20.7 percent, respectively, for the fingers; and 18.6, 55.9, 10.2, 5, and 6.7 percent, respectively, for the thumb.2

Division of the flexor digitorum profundus at zone I with the distal stump greater than 1 cm is usually amenable to primary repair (zone 1b and 1c). A short distal stump length (<1 cm in zone 1a) may require tendon repair to or through the bone to ensure adequate repair strength. Many different techniques, which include external fixation, internal fixation with sutures or wires, and bone anchors, have been described (reviewed by Huq et al.58). Where anchorage to the bone is necessary, there are no clinical studies that demonstrate clear superiority of one technique to another. Clinical outcomes of suture anchors are comparable to pullout button techniques but do have a quicker return-to-work time.59

The technical challenges are performing a repair that has sufficient distal and proximal tendon purchase while preserving the A4 pulley and achieving good tendon glide. Often, the window of repair is very small because of the distal interphalangeal joint being flexed, and the repair may impinge on the A4 pulley. This zone Ic/II region historically has been associated with poor outcomes because of repairs impinging on the pulleys or two tendons healing within a narrow sheath space where space is limited and inelastic because of fibro-osseous pulleys. It is also important to realize that within zones I and II, the vincula are prone to injury, and in cases where a tourniquet is used, occult bleeding into the sheath may contribute to adhesion formation (Fig. 5, right). Biomechanical and clinical research has seen perceptions change, from A2 and A4 pulley being critical,60 to seeing any pulley being partially vented in preference of adequate excursion and glide.61 There is Level IV evidence that this is the acceptable practice.62 It is almost impossible to repair a vented pulley without impinging on glide; thus, careful consideration has to be made to which part of the pulley to vent.

In zone II, the decision to repair one or two strands or no strands of flexor digitorum superficialis depends largely on gliding function on the table. We advocate venting enough pulley to allow adequate excursion without resistance. Even slight resistance can give rise to a stuck repair and subsequent rupture, especially at the A4 pulley in the days immediately after surgery. In zones III, IV, and V, tendons move in a more spacious environment without the confines of the fibro-osseous sheath and generally have better outcomes.

Operating in zone III comes with its own challenges, as often injuries to the tendon have associated injuries to the nerves and the palmar arch that require repair (Fig. 5, below). Not infrequently, zone III injuries can result in hidden retracted tendon ends in the carpal tunnel that require exploration and retrieval. In Al-Qattan’s series, 80 percent of zone III tendon injuries required decompression of the carpal tunnel to retrieve tendon ends.63

Zone IV injuries are rare because of protection by the carpal tunnel. Operating in zone V can be a complicated task because of retraction of the tendons into the muscle bellies and the challenge of matching up the correct tendon ends to each other when multiple tendons are divided.64 The close proximity of divided tendons in the zone V region often gives rise to dramatic tendon adhesion. Thus, after repair, early protected active mobilization is critical to maintaining differential glide.65 The aim of any repair performed in any zone would be a strong repair, avoidance of gapping, intraoperative stress testing, appropriate management of the pulleys to ensure glide, and protection of the repair with an appropriate splint that avoids overstressing the repair with active motion.

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SPLINTS

There remains much controversy on how best to functionally splint the hand following injury, although it is generally accepted that some form of protection is required. Follow-up for hand therapy and splint compliance is often a problem, with one study showing two-thirds of patients removing their splints when they were still at risk of rupture.66

There has been no direct comparison between a Kleinert dynamic traction splint and the newer short splints to clearly identify which is superior, but the simplicity offered by the short splint seems to be attractive to therapists and patients (Fig. 6). The Manchester short splint was introduced to liberate the wrist, increase patient freedom, and improve compliance with splinting.67 The new short splint extends from the dorsal proximal wrist crease to the fingertips. When compared with the traditional dorsal splint, early results at 12 weeks show improved distal interphalangeal joint motion without affecting rupture rates.67

This is now combined with instructions in the safe light use of the hand excluding the injured digit, which helps prevent inappropriate activity and makes the patient aware of how to protect the repair.65 This illustrates the importance of patient education in the safe use of the hand and enhances patient compliance.

The exception to the use of a shorter splint is in less compliant patients, where a traditional long splint with a cage can be used as an alternative. This works especially well in children, who are unable to follow strict instructions to protect the hand, and simultaneously allows sufficient room for unrestricted movement.9,68 In general, children fair better after flexor tendon injury, where good or excellent outcomes can be expected in 80 to 100 percent of patients, whether they have two- or four-core repairs.69–73

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REHABILITATION

Over the years, the change from clinician- to hand therapist–delivered rehabilitation regimens has probably been the single most influential factor on improving results in hand surgery.74 The importance of the dedicated hand therapist, independent of any particular regimen, is essential to achieving any positive outcomes from a tendon repair. To prevent adhesions from forming, it is essential that sufficient “excursion” can be achieved and that, when tendons are in close proximity, they can obtain “differential glide.” It is critical that the repair must move freely through a full range of normal active motion that can then be maintained by one’s favored rehabilitation regimens. Rehabilitation has evolved from passive motion protocols,75 to active extension and passive flexion,76,77 to a combination of these regimens, to early active motion.78 The evolution of these regimens simply relates to active mobilization providing more excursion and differential glide with controlled joint isolation than passive regimens. The move away from the Kleinert dynamic splint to the dorsal blocking splint is attributable largely to simplifying rehabilitation for the patient and its risk of developing flexion contractures in non-compliant patients. A careful balance of active motion78–80 against the tendon repair strength is offered by modern multistrand repairs.81

Two recent meta-analyses generally acknowledge that early active mobilization regimens give better functional outcomes with the trade-off for slightly increased rupture rates.50,82 A randomized controlled study comparing early active mobilization and passive mobilization supports early active mobilization regimens, although universal adoption remains patchy.83

The timing of when best to start rehabilitation remains debatable. Wide-awake local anesthesia without tourniquet surgery commences early active mobilization at the time of surgery and ensures the repair moves freely. Full movement and force should be avoided, as high strain across the repair is unlikely to be helpful for healing.84 Results from in vivo experiments suggest that between 3 and 7 days is the optimal time to commence early active mobilization, when the postoperative swelling has subsided and fibrosis has yet to set in.85 Simple elevation of the operated hand is essential to achieve this.

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SECONDARY FLEXOR TENDON SURGERY

An 8-year retrospective analysis of 5229 patients revealed a reoperation rate of 6 percent. Of these reoperations, 58 percent constituted tenolysis alone, 38 percent required repeated repair alone, and the remaining 4 percent required tenolysis and repeated repair.8 These cases are relatively rare; thus, evidence for best practice in reoperations is limited. One would expect primary ruptures to fare worse after repeated repair, but reported outcomes suggest that appropriate surgery can achieve acceptable results.86

Tenolysis requires the surgeon to have a good strategy to liberate the tendon from the surrounding scarred tissue, which can often be difficult to assess. Once again, the wide-awake local anesthesia without tourniquet technique is particularly good for this procedure, as it allows one to assess for any mechanical obstacles before closure of the wound. (See Video, Supplemental Digital Content 6, which displays tenolysis and Bunnell A2 pulley reconstruction with the flexor digitorum superficialis under wide-awake anesthesia. This video is available in the “Related Videos” section of the full-text article on PRSJournal.com or at http://links.lww.com/PRS/B928.)

A recent study of 40 patients who underwent tenolysis saw marginal gains from 128 degrees to 192 degrees at 3 months, with a rupture rate of 17.5 percent.87 Strategies to reduce the rupture rate in this cohort would be particularly valuable.

Tendon reconstruction may take the form of a primary graft approach or a more classic two-stage approach using a silicone rod.88 Other methods to reconstruct the flexor tendon include the Paneva-Holevich technique or vascularized tendon transfers (reviewed by Wong et al.89).

In conjunction with these secondary procedures, pulley reconstruction is sometimes required, and many different methods have been described (Fig. 7). Evidence of the superiority of any one method is lacking, but small cases series do report favorable results.90

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CONCLUSIONS

It is truly remarkable how much experimental and clinical research has been devoted to the area of flexor tendon repair and rehabilitation. Our evolving views of how tendons heal informed by basic science and better clinical data collection are allowing us to develop less invasive and more innovative ways to conduct our flexor tendon management. The levels of evidence in flexor tendon surgery remain poor. Future research should focus on answering key questions with well-designed clinical studies to advance the field. The combination of fundamentals of good surgical approach and meticulous surgery coordinated with up-to-date physiotherapy regimens, patient education, and patient ownership remains the cornerstone of obtaining good outcomes.

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ACKNOWLEDGMENTS

The authors thank Alison Roe for help with hand assessment and Andrea Fotticchia for help with the biomechanics video. Richard Wong, B.Sc., Ph.D., and Jason K. F. Wong, M.B.Ch.B., Ph.D., would also like to thank the Medical Research Council for previous and continuing support (G1000788 and MR/M007642/1) on tendon research.

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