The effect of variations in applied rehabilitation force on collagen concentration and maturation at the intrasynovial flexor tendon repair site

In Vivo Photoacoustic Ultrasound (PAUS) Assay for Monitoring Tendon Collagen Compositional Changes during Injury and Healing

Tendon injury and healing involve significant changes to tissue biology and composition. Current techniques often require animal sacrifice or tissue destruction, limiting assessment of dynamic changes in tendons, including treatment response, disease development, rupture risk, and healing progression. Changes in tendon composition, such as altered collagen content, can significantly impact tendon mechanics and function. Analyses of compositional changes typically require ex vivo techniques with animal sacrifice or destruction of the tissue. In vivo evaluation of tendons is critical for longitudinal assessment. We hypothesize that photoacoustic ultrasound detects differences in collagen concentration throughout healing. We utilized photoacoustic ultrasound, a hybrid imaging modality that combines ultrasound and laser-induced photoacoustic signals to create detailed and high-resolution images of tendons, to identify its endogenous collagen composition. We correlated the photoacoustic signal to picrosirius red staining. The results show that the photoacoustic ultrasound-estimated collagen content in tendons correlates well with picrosirius red staining. This study demonstrates that photoacoustic ultrasound can assess injury-induced compositional changes within tendons and is the first study to image these targets in rat Achilles tendon in vivo.

Longitudinal In Vivo Ultrasound Observations of the Surgically Repaired Zone II Flexor Digitorum Profundus Tendon

The link between the healing process and functional outcomes in the surgically repaired digital flexor tendon is poorly understood. This clinical note describes those gray-scale and power Doppler (PD) ultrasound parameters that can be used to document longitudinal change in the morphologic and dynamic properties of the surgically repaired zone II flexor digitorum profundus (FDP) tendon. The method is supported by ultrasound data obtained from three participants at five points in time post-surgically (two, four, six, 12 and 18 weeks). Longitudinal documentation of the ultrasound properties of echogenicity, defect size, tendon excursion and power Doppler signal is feasible and has the potential to explore the possible link between changes in the structural status of surgically repaired flexor tendons and associated clinical outcomes.

Tendon healing: an overview of physiology, biology, and pathology of tendon healing and systematic review of state of the art in tendon bioengineering

PURPOSE

Tendon injuries vary from acute rupture to chronic tendinopathy. For an optimal treatment of either condition, a profound knowledge is essential. Therefore, this article shall give an overview of physiology, biology, and pathology of tendon healing and state of the art in tendon bioengineering.

METHODS

For a preferably comprehensive survey, the current literature listed in PubMed and published in English peer-reviewed journals (March 2013) was systematically reviewed for tendon healing and tendon bioengineering including cytokine modulation, autologous sources of growth factors, biomaterials, gene therapy, and cell-based therapy. No differentiation was made between clinical and preclinical in vitro investigations.

RESULTS

Tendon healing happens in certain stadiums of inflammation, formation, and remodelling. An additional process of "collagen recycling" close to the healing site has been described recently. With increasing comprehension of physiology and pathology of tendon healing, several promising approaches in tendon bioengineering using growth factors, biomaterials, gene therapy, or cell-based therapy are described. However, only some of these are already used routinely in clinics.

CONCLUSION

Strong and resistant tendons are crucial for a healthy musculoskeletal system. The new approaches in tendon bioengineering are promising to aid physiological tendon healing and thus resulting in a stronger and more resistant tendon after injury. The growing knowledge in this field will need to be further taken into clinical studies so that especially those patients with prolonged courses, revision surgery, or chronic tendinopathy and high-demanding patients, i.e., professional athletes would benefit.

LEVEL OF EVIDENCE

II.

Rehabilitation of the upper extremity following nerve and tendon reconstruction: when and how

Following upper extremity nerve and tendon reconstruction, rehabilitation is necessary to achieve optimal function and outcome. In this review, the authors present current evidence and literature regarding the strategies and techniques of rehabilitation following peripheral nerve and tendon reconstruction.

Evidence-based medicine: Flexor tendon repair

LEARNING OBJECTIVES

After studying this article, the participant should be able to: (1) Describe and apply the current evidence-based treatment of acute flexor tendon injuries. (2) Compare and contrast the current postoperative therapy regimens following repair of flexor tendons. (3) Apply an evidence-based decision-making process for suture techniques of flexor tendon injuries.

SUMMARY

Flexor tendon repair remains a challenge for hand surgeons to reliably obtain excellent results. Surgical decisions should rely on the surgeon's experience, outcome studies, and direct evidence. This review is a compilation of the evidence from the literature on optimizing outcomes for flexor tendon repair.

The role of mechanobiology in tendon healing

Mechanical cues affect tendon healing, homeostasis, and development in a variety of settings. Alterations in the mechanical environment are known to result in changes in the expression of extracellular matrix proteins, growth factors, transcription factors, and cytokines that can alter tendon structure and cell viability. Loss of muscle force in utero or in the immediate postnatal period delays tendon and enthesis development. The response of healing tendons to mechanical load varies depending on anatomic location. Flexor tendons require motion to prevent adhesion formation, yet excessive force results in gap formation and subsequent weakening of the repair. Excessive motion in the setting of anterior cruciate ligament reconstruction causes accumulation of macrophages, which are detrimental to tendon graft healing. Complete removal of load is detrimental to rotator cuff healing; yet, large forces are also harmful. Controlled loading can enhance healing in most settings; however, a fine balance must be reached between loads that are too low (leading to a catabolic state) and too high (leading to microdamage). This review will summarize existing knowledge of the mechanobiology of tendon development, homeostasis, and healing.

BIOMECHANICS AND HISTOLOGICAL ANALYSIS IN RABBIT FLEXOR TENDONS REPAIRED USING THREE SUTURE TECHNIQUES (FOUR AND SIX STRANDS) WITH EARLY ACTIVE MOBILIZATION

Objective: Analyzing suture time, biomechanics (deformity between the stumps) and the histology of three groups of tendinous surgical repair: Brazil-2 (4-strands) which the end knot (core) is located outside the tendon, Indiana (4-strands) and Tsai (6-strands) with sutures technique which the end knot (core) is inner of the tendon, associated with early active mobilization. Methods: The right calcaneal tendons (plantar flexor of the hind paw) of 36 rabbits of the New Zealand breed (Oryctolagus cuniculus) were used in the analysis. This sample presents similar size to human flexor tendon that has approximately 4.5 mm (varying from 2mm). The selected sample showed the same mass (2.5 to 3kg) and were male or female adults (from 8 ½ months). For the flexor tendons of the hind paws, sterile and driven techniques were used in accordance to the Committee on Animal Research and Ethics (CETEA) of the University of the State of Santa Catarina (UDESC), municipality of Lages, in Brazil (protocol # 1.33.09). Results: In the biomechanical analysis (deformity) carried out between tendinous stumps, there was no statistically significant difference (p>0.01). There was no statistical difference in relation to surgical time in all three suture techniques with a mean of 6.0 minutes for Tsai (6- strands), 5.7 minutes for Indiana (4-strands) and 5.6 minutes for Brazil (4-strands) (p>0.01). With the early active mobility, there was qualitative and quantitative evidence of thickening of collagen in 38.9% on the 15^th day and in 66.7% on the 30^th day, making the biological tissue stronger and more resistant (p=0.095). Conclusion: This study demonstrated that there was no histological difference between the results achieved with an inside or outside end knot with respect to the repaired tendon and the number of strands did not affect healing, vascularization or sliding of the tendon in the osteofibrous tunnel, which are associated with early active mobility, with the repair techniques applied.

The quadriga effect revisited: designing a "safety incision" to prevent tendon repair rupture and gap formation in a canine model in vitro

Loss of experimental animals due to tendon repair failure results in the need for additional animals to complete the study. We designed a relief proximal to the flexor digitorum profundus (FDP) tendon repair site to serve as a "safety incision" to prevent repair site ruptures and maximize safety incision-to-suture strength. The FDP tendons were dissected in 24 canine forepaws. The 2nd and 5th tendons were lacerated at the proximal interphalangeal joint level and sutured using a modified Kessler technique and peripheral running suture. Tendon width was measured where the FDP tendon separates into each individual digit and a safety incision, equal to the 2nd and 5th tendon widths, was performed 3, 4, or 5 mm (Groups 1, 2, and 3) proximal to the separation. The tendons were pulled at a rate of 1 mm/s until either the "safety incision" ruptured or the repair failed. There was no gap formation at the repair site in Groups 1 and 2. However, all Group 3 tendons failed by repair site rupture with the safety incision intact. An adequate safety incision to protect repair gap and rupture and maintain tendon tension for the FDP animal model should be about 4 mm from where the FDP tendon separates.

Biomechanics and histology of intact and repaired digital nerves: an in vitro study

PURPOSE

To investigate the biomechanical properties of intact and repaired cadaver digital nerves.

METHODS

Ultimate tensile failure strength and stiffness were determined in 67 human cadaver digital nerves. Total nerve area, fascicular area, and nonfascicular (connective tissue) area were determined from the metacarpophalangeal to the distal interphalangeal joint in another 35 axial nerve sections to determine regional anatomic variation. Thirty-eight additional digital nerves were transected, and epineural repairs were performed using simple, interrupted sutures. Suture number (2 vs 4), gauge (8-0 vs 9-0), and purchase length (1 mm vs 2 mm) were used in various combinations, and then the repaired nerves were pulled to failure. The mechanism of repair-site failure was determined for each suture. In situ tension of the intact digital nerves was measured during passive metacarpophalangeal and proximal interphalangeal joint motion in another 19 intact digital nerves.

RESULTS

There were no significant differences in failure load or stiffness with respect to the radial or ulnar nerves within a finger or between fingers. The primary tactile side of the finger tended to have a larger diameter digital nerve. Digital nerve failure was more common proximally than distally. Intact digital nerves failed at 6 N with a stiffness of 1 N/mm. Histologic analysis showed that fascicular area and total area decreased from proximal to distal, whereas the nonfascicular-to-fascicular area ratio increased. Four epineural sutures were statistically stronger than 2 sutures. Suture purchase length and gauge did not affect repair strength. The 8-0 nylon sutures failed primarily by cut-out, whereas the 9-0 sutures failed by cut-out or breakage. Repaired nerves failed at 1 to 2 N. Maximal metacarpophalangeal joint hyperextension resulted in 4 N of digital nerve tension. When the metacarpophalangeal joint was not hyperextended, proximal interphalangeal joint motion did not generate tension.

CONCLUSIONS

Similar to flexor tendons, the number of suture strands crossing the repair site was the most important variable affecting digital nerve repair strength in this cadaveric model.

An analysis of factors associated with failure of tendon repair in the canine model

PURPOSE

The canine model is commonly used for flexor tendon repair research. The purpose of this study was to analyze the factors, including laceration mode (partial and complete), suture techniques, therapy methods, and weight-bearing status, associated with tendon repair rupture or gap formation in the canine model in vivo.

METHODS

We reviewed the factors associated with repair failure among 624 flexor tendon repairs in zone II from 242 dogs reported previously from our institution, including both partial and complete lacerations.

RESULTS

We found that weight-bearing due to failure of postoperative immobilization was the most important factor influencing tendon repair rupture or gap formation.

CONCLUSIONS

As has been noted clinically, in our canine model failure and gapping of a flexor tendon repair was primarily the result of uncontrolled loading. Rehabilitation strategies that reduce the risk of catastrophic loading of the repair are critical to reducing the experimental failure rate when using dogs for flexor tendon research. Similar strategies may also reduce such failures in humans.

Flexor tendon suture: a description of two core suture techniques and the Silfverskiöld epitendinous suture

Flexor tendon injuries are commonly treated by orthopedic, plastic, and hand surgeons. Bunnell referred to zone 2 injuries as being in "no-man's land," plagued by poor results after surgical repair. Over the last 30 years, a better understanding of the biology of flexor tendon injuries, advanced surgical techniques, and perhaps most important, improved rehabilitation protocols, have afforded consistently good to excellent results after surgical repair at all levels of injury. Complications such as restrictive adhesions, joint contracture, and repair rupture, although less frequent, can compromise functional recovery.

Zone I flexor tendon rehabilitation with limited extension and active flexion

This article describes an immediate active motion protocol for primary repair of zone I flexor tendons treated with tendon to tendon, or tendon to bone repair, and reviews clinical results. A rehabilitation protocol is proposed that will limit excursion of the zone I repair by blocking full distal interphalangeal (DIP) extension and by applying controlled active tension to both the unrepaired flexor digitorum superficialis (FDS) and the repaired flexor digitorum profundus (FDP). The rehabilitation technique utilized a dorsal protective splint with a relaxed position of immobilization with 30 degrees of wrist flexion, 40 degrees of metacarpophalangeal (MP) joint flexion, and a neutral position for the proximal interphalangeal (PIP) joints without dynamic traction. In addition, within the confines of the dorsal splint, the involved DIP joint was splinted at 40-45 degrees to prevent DIP joint extension during the early wound healing phases. Relaxed composite flexion was used to apply active tension to both the uninjured FDS, and the repaired FDP. This technique applies excursion of approximately 3 mm to the zone I tendon in a limited arc (45-75 degrees). The modified position of active flexion applies low loads of force (< 500 g), even with drag considered. This technique is supported by previous mathematical studies of excursion and internal tendon force, and clinical experience. Forty nine cases treated over a 10-year period were reviewed, and eight were excluded for incomplete follow-up. The use of this protocol for 41 zone I flexor digitorum profundus repairs by 12 different surgeons using varied surgical techniques was evaluated. None of the tendon to tendon repairs used more than two suture strands for the core repairs. Mean total active range of motion was 142 degrees (PIP 95 degrees plus DIP 47 degrees), or 81% of normal. Three tendons ruptured in non-protocol-related incidents and were excluded from the study. Results from this clinical study support the use of limited DIP extension combined with active tension with conventional repair in zone I.

The evolution of early mobilization of the repaired flexor tendon

The most important difference between the various approaches to postoperative digital flexor tendon rehabilitation is how the repaired tendon is treated during the first three to six weeks, in the earliest stages of healing. Early mobilization is the most commonly reported method of managing the healing flexor tendon. There are many different protocols and abundant research to support published approaches to tendon management. With so many choices, today's hand therapist must understand not only what those choices are, but also why and when to use them. There is no one correct way to manage a repaired flexor tendon; the specialist who does not understand how current techniques evolved is ill-equipped to design the appropriate treatment for a given patient. This article presents an overview of management options and how they have been developed over time, with special attention to changes in splint and exercise design in the crucial first few weeks after repair.

Clinical outcomes associated with flexor tendon repair

Review of the outcomes of clinical flexor tendon repairs reported over the past 15 years showed advances in the outcomes with excellent or good functional return in more than three fourths of primary tendon repairs following a variety of postoperative passive/active mobilization treatments. Strickland and Glogovac criteria are the most commonly adopted methods to assess function. Repair ruptures (4%-10% for zone II finger flexors and 3%-17% for the FPL tendon), adhesion formations, and stiffness of finger joints remain frustrating problems in flexor tendon repairs and rehabilitation. Four approaches are suggested to improve outcomes of the repairs and to solve these difficult problems,which include stronger surgical repairs, appropriate pulleys or sheath management, optimization of rehabilitation regimens, and modern biologic approaches.

Flexor tendon biology

Significant advances in the understanding of intrasynovial flexor tendon repair and rehabilitation have been made since the early 1970s. The concept of adhesion-free, or primary tendon healing--that tendons could heal intrinsically without the ingrowth of fibrous adhesions from the surrounding sheath has been validated both experimentally and clinically in studies over the past 25 years. Recent attempts to understand and improve the results of intrasynovial flexor tendon repair have focused upon restoration of the gliding surface, augmentation of early post-operative repair site biomechanical strength and on the elucidation of the molecular biology of early post-operative tendon healing. The goals of the surgical treatment of patients with intrasynovial flexor tendon lacerations remain unchanged: to achieve a primary tendon repair of sufficient tensile strength to allow application of a post-operative mobilization rehabilitation protocol. This program should inhibit the formation of intrasynovial adhesions and restore the gliding surface, while facilitating the healing of the repair site.

Pyramid of progressive force exercises to the injured flexor tendon

Postoperative rehabilitation for patients who have sustained a laceration to their flexor tendon apparatus is an important factor in maximizing functional outcome. Quality rehabilitation is characterized by the development of a tailored exercise regimen. There is currently no model available to tailor an exercise regimen for a person with an atypical physiologic response pattern. If rehabilitation protocols were classified according to the criteria of forces applied across a tendon juncture and/or excursion, and a clinical method were available to assist in the identification of optimal tendon loading and/or excursion application, then those individuals with atypical response patterns could be treated more efficiently and effectively. The author conducted a literature review and case study. A model for systematic application of progressive loading exercises to the intrasynovial flexor tendon injury and repair is conceptually developed. The model consists of a pyramidal series of eight specific rehabilitation exercises in the following sequence: passive protected extension, place and hold, active composite fist, hook and straight fist, isolated joint motion, resistive composite fist, resistive hook and straight fist, and resistive isolated joint motion. Concepts are developed to implement a three-point clinical adhesion-grading system. Clinical application of the system is highlighted. An excellent outcome was considered 112% total active motion. A model for systematic application of progressive loading exercises has been conceptually developed in concert with a method for determination of optimal tendon loading. Further substantiation is necessary to validate the proposed theory.

Gene intervention in ligament and tendon: current status, challenges, future directions

Ligament and tendon injuries are common clinical problems. Healing of these tissues occurs, but their properties do not return to normal. This predisposes to recurrent injuries, instability and arthritis, loss of motion and weakness. Gene therapy offers a novel approach to the repair of ligaments and tendons. Introduction of genes into ligaments and tendons using vectors has been successful. Marker genes and therapeutic genes have been introduced into both tissues with evidence of corresponding functional alterations. In addition, gene transfer has been used to manipulate the healing environment, opening the possibility of gene transfer to investigate ligament and tendon development and homeostasis, in addition to using this technology therapeutically. Several factors modulate the 'success' of gene transfer in these tissues.

Early active motion flexor tendon protocol using one splint

This article describes an early active motion protocol for use after a four-strand flexor tendon repair. The protocol uses a simple dorsal blocking splint with the wrist in neutral and four fingers in rubber band traction for the first five weeks, then gradually advances the patient over the next seven weeks. The patient is able to perform the exercises without changing the splint at home during the first five weeks of the protocol. The results of the retrospective chart review are promising. Of 40 digits, 95% experienced excellent and good results in zone II, and 87.5% experienced excellent and good results in zones I, II, and III. One rupture (2.5%) occurred in a noncompliant patient. The DASH scale was used to determine functional outcome, with results of 7.82 on the physical function/symptoms category, 16.07 in sports/ performing arts, and 10.23 in the work category.

The insertion site of the canine flexor digitorum profundus tendon heals slowly following injury and suture repair

Treatment of injuries of the flexor digitorum profundus (FDP) tendon insertion site has changed little during the past 50 years, in part because there are no reports describing flexor tendon insertion site healing. Our objective was to assess the effects of repair technique and post-operative time on tendon-bone healing using a canine model of injury and repair. We transected 48 FDP tendons from 24 dogs at their insertions and repaired them using either a four- or eight-strand suture technique. We assessed the mechanical properties of the repaired tendon-bone construct, tendon collagen biochemistry, and distal phalanx bone mineral density (BMD) at 0, 10, 21 and 42 days. Suture method had no significant effect on any outcome (p > 0.05). In particular, use of an eight-strand double modified Kessler technique did not result in increased stiffness or strength compared to a four-strand technique. With time, the repair site became stiffer, as demonstrated by a 230% increase in rigidity and a 50% decrease in strain from 0 to 42 days. However, from 0 to 42 days the ultimate force of the insertion site did not increase. This lack of increase in ultimate force was consistent with decreases in collagen content, non-reducible crosslinks and distal phalanx BMD. Taken together, our results indicate that the canine FDP tendon heals slowly after it is injured at its insertion site and sutured onto the distal phalanx. While these findings may be limited to the particular repair method we used, they demonstrate a need for devising new treatment strategies to improve healing of flexor tendon insertion site injuries.