Flexor tendon biology

[Current Trends in Flexor Tendon Surgery: Results of a National Online Survey]

Within the last 50 years, there has been a change in trend in flexor tendon surgery. After the introduction of the 2-strand technique, the 4-strand technique was propagated in the 1990s. In order to obtain a status quo of which technique is used in Germany and if the gold standard of the 4-strand suture has changed in favour of a 6-strand suture, we conducted an online survey among members of the DGH ("Deutsche Gesellschaft für Handchirurgie", German Society for Hand Surgery) on the suture technique of flexor tendon injuries zone 2.

MATERIAL AND METHODS

An online survey was conducted and sent out by email to all DGH members. The questionnaire included 7 questions. Participants accessed the survey via a link.

RESULTS

155 hand surgeons from Germany participated in the survey. All of them answered the questionnaire in full and all questionnaires were included in the evaluation. The main question of how many strands are currently used for core suturing was answered as follows: 21% (n=32) of the 155 participants (TN) stated that they use a 2-strand suture, 53% used (n=82) a 4-strand suture and 10% used a 6-strand suture. Regarding techniques, 81 TN used the Kirchmayr-Kessler technique or a modification of it, 9 TN used the M-Tang technique, and 15 TN indicated "other technique". The question about the application of an epitendinous suture was overwhelmingly answered with "yes". Here, 98.2% agreed. Only with regard to the suture material, different opinions were found. 68% (n=106) use an absorbable monofilament suture (such as PDS). Just under a quarter (23%, n=36) use a non-absorbable monofilament suture (such as Prolene).

CONCLUSION

Flexor tendon surgery has changed considerably due to intensive advances in research during the last decades. It was interesting to note in our survey that German hand surgeons have adapted their suture technique within the last years based on the results of the literature. Our results clearly show that convincing scientific data has an influence on the choice of surgical technique and that discussions about new techniques, e. g. in the context of annual meetings, may well stimulate the auditorium to rethink.

Effectiveness of Sodium Hyaluronate and ADCON-T/N for the Prevention of Adhesions in Hand Flexor Tendon Surgery: A Systematic Review and Meta-Analysis

PURPOSE

A common complication after digital flexor tendon repair in the hand is postoperative adhesions that can cause loss of motion and compromise hand function. The aim of this review of relevant published literature was to assess the effectiveness of locally administered sodium hyaluronate or ADCON-T/N for the prevention of adhesions after hand flexor tendon repair.

METHODS

A literature search was conducted in June 2020 in multiple databases for randomized controlled trials . Our primary outcome was measurement of active finger motion. Follow-up was defined as short-term (< 12 weeks), mid-term (12 weeks to 6 months) and long-term (> 6 months). Mean differences (MD) and standardized mean differences (SMD) of total active motion (TAM) of the interphalangeal joints (IPJs) and active motion of the IPJs separately were calculated where results were meta-analyzed.

RESULTS

Six randomized controlled trials were included. For ADCON-T/N, no benefits were detected for TAM of the IPJs (MD 1.71 [-21.54, 24.96]) or active motion of the IPJs separately (proximal: MD 4.77 [-4.47, 14]; distal: MD 1.17 [-10.33, 12.66]) in the short-/mid-term. The mid-term benefit in TAM of sodium hyaluronate over standard care (placebo/no treatment) did not reach statistical significance (SMD 0.31 [0, 0.63]); however, a subgroup comparison of repeated administration of sodium hyaluronate versus standard care was both statistically and clinically significant (SMD 0.55 [0.11, 0.98]).

CONCLUSIONS

Repeated administration of sodium hyaluronate at the tendon repair site may be effective in improving postoperative active finger motion after primary hand flexor tendon repair in the mid-term.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic II.

Direct Repair of Flexor Tendons Close to Bony Insertion and Ruptured Collateral Ligaments

Lacerated flexor tendons close to bony junction are commonly repaired using a pullout suture. However, these injuries very close to the tendon-bone junction can be repaired with robust direct suture repair of the proximal tendon stump with the short residual tendon stump and any local tissues such as periosteum and joint volar plate. Subacute or chronic traumatic rupture at the midpart of the collateral ligaments can also be repaired by "refreshing" the divided ligament ends and repairing the ligament stumps to local tissues with multiple sutures often combined with tightening the elongated joint capsule.

Biomechanical Analysis of Zone 2 Flexor Tendon Repair With a Coupler Device Versus Locking Cruciate Core Suture

PURPOSE

To compare flexor tendon repair strength and speed between a tendon coupler and a standard-core suture in a cadaver model.

METHODS

In 5 matched-pair fresh cadaver hands, we cut the flexor digitorum profundus tendon of each finger in zone 2 and assigned 20 tendons to both the coupler and the suture groups. Coupler repair was with low-profile stainless steel staple plates in each tendon stump, bridged by polyethylene thread. Suture repair was performed using an 8-strand locking-cruciate technique with 4-0 looped, multifilament, polyamide suture. One surgeon with the Subspecialty Certificate in Surgery of the Hand performed all repairs. Via a load generator, each flexor digitorum profundus was loaded at 5 to 10 N and cycled through flexion just short of tip-to-palm and full extension at 0.2 Hz for 2,000 cycles to simulate 6 weeks of rehabilitation. We recorded repair gapping at predetermined cycle intervals. Our primary outcome was repair gapping at 2,000 cycles. Tendons that had not catastrophically failed by 2,000 cycles were loaded to failure on a servohydraulic frame at 1 mm/s.

RESULTS

Tendon repair gapping was similar between coupled and sutured tendons at 2,000 cycles. Tendons repaired with the coupler had higher residual load to failure than sutured tendons. Mean coupler repair time was 4 times faster than suture repair.

CONCLUSIONS

Zone 2 flexor repair with a coupler withstood simulated early active motion in fresh cadavers. Residual load to failure and repair speed were better with the coupler.

CLINICAL RELEVANCE

This tendon coupler may eventually be an option for strong, reproducible, rapid flexor tendon repair.

Improved tendon healing by a combination of Tanshinone IIA and miR-29b inhibitor treatment through preventing tendon adhesion and enhancing tendon strength

Background: Despite significant advances in the materials and methods development used in surgical repair and postoperative rehabilitation, the adhesion formation remains the most common clinical problem in tendon injuries. Therefore, the development of novel therapies is necessary for targeting at preventing tendon adhesion formation and improving tendon strength. Methods: We used rat fibroblasts for in vitro experiments to determine the optimal concentration of TSA in rats, and then set up negative control group, TSA intervention group, mir-29b interference adenovirus intervention group and TSA and mir-29b interference adenovirus co-intervention group. By comparing cell proliferation and protein expression in different group, we verified the effect and mechanism of drugs on fibroblast function. At the same time, the Sprague-Dawley rat Achilles tendon model in vivo was established in this study, which was divided into sham operation group and operation group. Afterwards in the operation group, mir-29b inhibitor and placebo were injected every 3 days respectively. Then the injection inhibitor group was divided into 5 groups which mean TSA was injected into the marked area at 0, 6, 24 and 72 hours after operation for 1 week, finally all of the rats were died at 3 weeks after operation. Through the observation of general properties, histological observation of Achilles tendon injury, biomechanical test and cell and protein expression in rats' tendon cell, the effect of drugs on tendon adhesion formation was analyzed. Results: We demonstrated that the combination of miR-29b inhibitor and tanshinone IIA(TSA) could prevent tendon adhesion and also enhance tendon strength. Mechanically, the miR-29b inhibitor could activate the TGF-β/Smad3 pathway to trigger endogenous pathways and induce a high proliferation of fibroblast. Subsequently, we also found adding TSA after 6 hours of miR-29b treatment gave less cell cytotoxicity in our rat model with better outcome of less tendon adhesion and enhanced strength. Conclusion: We conclude that the use of miR-29b inhibitor at the end of the tendon break could initiate endogenous repair mechanism and subsequently use of TSA should be able to inhibit the exogenous repair mechanism. Therefore, the combination of both treatments could prevent tendon adhesion and ensure tendon strength. Our findings suggested that this approach would be a feasible approach for tendon repair.

Electrospun Water-Borne Polyurethane Nanofibrous Membrane as a Barrier for Preventing Postoperative Peritendinous Adhesion

Peritendinous adhesion is a major complication after tendon injury and the subsequent repairs or reconstructions. The degree of adhesion can be reduced by the interposition of a membranous barrier between the traumatized tendon and the surrounding tissue. In the present study, electrospun water-borne polyurethane (WPU) nanofibrous membranes (NFMs) were created for use after the reparation or reconstruction of tendons to reduce adhesion. In the electrospinning process, water was employed as the solvent for WPU, and this solvent was ecofriendly and nontoxic. The nanofibrous architecture and pore size of the WPU NFMs were analyzed. Their microporosity (0.78⁻1.05 µm) blocked the penetration of fibroblasts, which could result in adhesion and scarring around the tendon during healing. The release of WPU mimicked the lubrication effect of the synovial fluid produced by the synovium around the tendon. In vitro cell studies revealed that the WPU NFMs effectively reduced the number of fibroblasts that became attached and that there was no significant cytotoxicity. In vivo studies with the rabbit flexor tendon repair model revealed that WPU NFMs reduced the degree of peritendinous adhesion, as determined using a gross examination; a histological cross section evaluation; and measurements of the range of motion of interphalangeal joints (97.1 ± 14.7 and 79.0 ± 12.4 degrees in proximal and distal interphalangeal joints respectively), of the length of tendon excursion (11.6 ± 1.9 cm), and of the biomechanical properties.

Utility of early active motion for flexor tendon repair with concomitant injuries: A multivariate analysis

INTRODUCTION

Flexor tendon injury often occurs with concomitant injuries such as fracture, vascular injury, and extensor tendon injury. These injuries are repaired independently, without a comprehensive strategy. We aimed to identify the effect of concomitant injuries and treatment choice on the outcome of flexor tendon repair.

PATIENTS AND METHODS

We evaluated 118 fingers of 102 adult patients with zone 1-3 flexor digitorum profundus (FDP) tendon injuries who underwent primary surgery at our hospital between April 2009 and December 2017. The 2-strand pull-out, 4-strand Tsuge, 6-strand Lim & Tsai, and 8-strand cross-locked cruciate suturing techniques were used. We performed multivariate analyses, with the active range of motion (AROM) of the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints as dependent variables, and age, existence of concomitant injuries, and their treatment as independent variables.

RESULTS

The average AROM of the PIP + DIP joints was 130° at the last follow-up, and 'excellent' or 'good' function was obtained in 74 (63%) of 118 fingers by using the Strickland criteria. Old age, concomitant diaphyseal fractures, and specific methods of osteosynthesis, such as pinning, flexor digitorum superficialis injury, and immobilisation for 3 weeks, significantly worsened the results. However, wiring for osteosynthesis and early active motion protocol improved postoperative functional outcome. Although the outcome did not differ among the suture techniques, the 4-strand Tsuge procedure was performed for the two surgically confirmed ruptures of repair that occurred in our series.

DISCUSSION

We clarified the superiority of early mobilisation protocols with rigid osteosynthesis procedure, other than pinning. To minimise tendon adhesion or joint stiffness, surgeons should repair the tendon and fractured bone appropriately, to ensure early mobilisation without serious complications.

Fabrication of novel tubular scaffold for tendon repair from chitosan in combination with zinc oxide nanoparticles

Chitosan bears numerous properties, such as biocompatibility, biodegradability and non-toxicity making it suitable for use in different biomedical fields. Zinc (Zn) is required for fibroblasts proliferation and collagen synthesis as essential elements of wound healing. Its nanoparticles are well known for their capability to enhance wound healing by cell adhesion and migration improvement through growth factors-mediated mechanisms. Poor blood supply and unique histological characteristics of tendon make its regeneration always slow. Also, adhesion formation between tendon and its surrounding tissues is another problem for neotendon to return to its normal structure and functional activities. In this study, a novel tubular scaffold of zinc oxide (ZnO) nanoparticles loaded chitosan has been fabricated for tendon repair. Experimental complete tenotomy of deep digital flexor tendon in a rabbit model was done and scaffolds were placed in the transected area after two ends suturing. After four and eight weeks, adhesion formation around the tendons and tissue reaction to the scaffolds were evaluated macroscopically. Inflammation, angiogenesis and collagen fibers arrangement were also analyzed in histopathological evaluations. After eight weeks, the scaffolds were absorbed completely, adhesions around the tendon were decreased and there was no sign of significant tissue reaction and/or infection in histopathological analyses. The reduced adhesion formation, improved gliding function and better histopathological characteristics suggest this scaffold application as a potential therapy in treatment of tendon acute injuries.

Tendon injury and repair - A perspective on the basic mechanisms of tendon disease and future clinical therapy

Tendon is an intricately organized connective tissue that efficiently transfers muscle force to the bony skeleton. Its structure, function, and physiology reflect the extreme, repetitive mechanical stresses that tendon tissues bear. These mechanical demands also lie beneath high clinical rates of tendon disorders, and present daunting challenges for clinical treatment of these ailments. This article aims to provide perspective on the most urgent frontiers of tendon research and therapeutic development. We start by broadly introducing essential elements of current understanding about tendon structure, function, physiology, damage, and repair. We then introduce and describe a novel paradigm explaining tendon disease progression from initial accumulation of damage in the tendon core to eventual vascular recruitment from the surrounding synovial tissues. We conclude with a perspective on the important role that biomaterials will play in translating research discoveries to the patient.

STATEMENT OF SIGNIFICANCE

Tendon and ligament problems represent the most frequent musculoskeletal complaints for which patients seek medical attention. Current therapeutic options for addressing tendon disorders are often ineffective, and the need for improved understanding of tendon physiology is urgent. This perspective article summarizes essential elements of our current knowledge on tendon structure, function, physiology, damage, and repair. It also describes a novel framework to understand tendon physiology and pathophysiology that may be useful in pushing the field forward.

Early Passive Movement in flexor tendon injuries of the hand

INTRODUCTION

Flexor tendon injuries are underestimated considering their anatomical function in the hand. According to the publications of Kleinert, Verdan and Kessler, primary suturing of the flexor tendon combined with immediate postoperative physiotherapy in terms of "Early Passive Movement" became the standard form of therapy following acute flexor tendon injuries of the hand.

MATERIALS AND METHODS

In a study between 2007 and 2009, a total of 115 flexor tendon injuries were analysed retrospectively. All patients were treated using a two-strand repair technique according to Zechner. They received physiotherapy from the first postoperative day according to the Viennese flexor tendon rehabilitation protocol. For statistical purposes, the factors: age, gender, range of motion (ROM), follow up interval, affected flexor tendon and zone were analysed. The time between injury and surgery was also determined, classified into groups and included in the study. On the basis of the range of motion AROM, the Buck-Gramcko and modified Strickland Score was calculated.

RESULTS

The mean follow-up interval was 7 months. Using the Buck-Gramcko and Strickland Score an "excellent" overall result was achieved. Complications occurred in 3.5 %, one secondary rupture (0.9 %), two tendon adhaesions requiring tenolysis (1.7 %) and one case of infection (0.9 %). The time interval between injury and operation, gender, affected zone, flexor tendon and affected finger nerve had no influence on the Buck-Gramcko and Strickland Score.

CONCLUSIONS

Using Zechner's core suture technique as the primary treatment, combined with immediate postoperative physiotherapy in terms of "Early Passive Movement" according to the Viennese flexor tendon rehabilitation programme, an excellent clinical outcome and low complication rate was acchieved.

LEVEL OF EVIDENCE

IV: case series.

A Review of Current Concepts in Flexor Tendon Repair: Physiology, Biomechanics, Surgical Technique and Rehabilitation

Historically, the surgical treatment of flexor tendon injuries has always been associated with controversy. It was not until 1967, when the paper entitled Primary repair of flexor tendons in no man’s land was presented at the American Society of Hand Surgery, which reported excellent results and catalyzed the implementation of this technique into worldwide practice. We present an up to date literature review using PubMed and Google Scholar where the terms flexor tendon, repair and rehabilitation were used. Topics covered included functional anatomy, nutrition, biome-chanics, suture repair, repair site gapping, and rehabilitation. This article aims to provide a comprehensive and complete overview of flexor tendon repairs.

Prevention of peritendinous adhesions with electrospun chitosan-grafted polycaprolactone nanofibrous membranes

As one of the common complications after tendon injury and subsequent surgery, peritendinous adhesions could be minimized by directly placing a physical barrier between the injured site and the surrounding tissue. With the aim of solving the shortcomings of current biodegradable anti-adhesion barrier membranes, we propose the use of an electrospun chitosan-grafted polycaprolactone (PCL-g-CS) nanofibrous membrane (NFM) to prevent peritendinous adhesions. After introducing carboxyl groups on the surface by oxygen plasma treatment, the polycaprolactone (PCL) NFM was covalently grafted with chitosan (CS) molecules, with carbodiimide as the coupling agent. Compared with PCL NFM, PCL-g-CS NFM showed a similar fiber diameter, permeation coefficient for bovine serum albumin, ultimate tensile strain, reduced pore diameter, lower water contact angle, increased water sorption and tensile strength. With its submicrometer pore diameter (0.6-0.9μm), both NFMs could allow the diffusion of nutrients and waste while blocking fibroblast penetration to prevent adhesion formation after tendon surgery. Cell culture experiments verified that PCL-g-CS NFM can reduce fibroblast attachment while maintaining the biocompatibility of PCL NFM, implicating a synergistic anti-adhesion effect to raise the anti-adhesion efficacy. In vivo studies with a rabbit flexor digitorum profundus tendon surgery model confirmed that PCL-g-CS NFM effectively reduced peritendinous adhesion from gross observation, histology, joint flexion angle, gliding excursion and biomechanical evaluation. An injured tendon wrapped with PCL-g-CS NFM showed the same tensile strength as the naturally healed tendon, indicating that the anti-adhesion NFM will not compromise tendon healing.

Preparation and characterization of antiadhesion barrier film from hyaluronic acid-grafted electrospun poly(caprolactone) nanofibrous membranes for prevention of flexor tendon postoperative peritendinous adhesion

Peritendinous adhesion is one of the common complications encountered after tendon injury and subsequent surgery, and it can be minimized by introducing a physical barrier between the injured site and the surrounding tissue. An electrospun hyaluronic acid-grafted poly(caprolactone) (PCL-g-HA) nanofibrous membrane (NFM) is proposed as an alternative to current antiadhesion barrier films. HA is covalently grafted to surface-aminolyzed PCL nanofibers, using carbodiimide as the coupling agent. Pristine PCL and PCL-g-HA NFMs were characterized by scanning electron microscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and mechanical testing. In vitro cell culture with fibroblasts showed that PCL-g-HA NFMs reduced cellular adhesion on the membrane surface while maintaining cell proliferation. Animal experiments using a rabbit flexor digitorum profundus tendon model confirmed the efficacy of PCL-g-HA in reducing peritendinous adhesion, based on gross observation, histology, joint flexion-angle measurements, gliding tests, and biomechanical evaluation.

The comparison of macroscopic and histologic healing of side-to-side (SS) tenorrhaphy technique and primer tendon repair in a rabbit model

INTRODUCTION

The side-to-side (SS) tenorrhaphy technique has been used in tendon transfer surgery. The mechanical properties of SS tendon suture have been studied previously. However, the histo-pathological healing of the SS tenorrhaphy of the tendons is unknown. The aim of this study was to assess the gross and histological effects of SS tenorrhaphy in a rabbit model.

MATERIALS AND METHODS

Twenty New Zealand rabbits were used. The extensor hallucis longus and tibialis anterior tendon were sewed SS at the level distal to the ankle joint. The patellar tendon (PT) at the same side was used as control group. A unilateral midline incision was made and repaired with a single suture. The animals were killed at the 12th week postoperatively. The histological sections were obtained from the side of surgery from each group. Each sample was stained with hematoxylene and eosin (H&E). Gross and microscopic healing was compared between the two groups.

RESULTS

Gross examination of the control group showed complete healing with a thin peri-tendinous sheath formation around the suture site, whereas in the study group, a thick peri-tendinous sheath was formed around the area of the tendon-tendon anastomosis. In the control group, at the 12th week after surgery, the healing was almost completed in all samples. In the study group, a thick fibro vascular sheath has formed around the side of anastomosis. In all specimens few inter-digitations were observed between the tendons;however, the trough was still present.

CONCLUSION

The result of the current study showed that histological healing and union of SS tenorrhaphy differ from that in primary tendon injury and healing. Further studies are required to clarify the healing stages at the tenorrhaphy site.

A nitinol based flexor tendon fixation device: gapping and tensile strength measurements in cadaver flexor tendon

In this study, a new nitinol based fixation device was investigated for use in repairing severed digital flexor tendons. The device, composed of superelastic nitinol, is tubular in shape with inward facing tines for gripping tissue. Its cellular structure was designed such that it has a large effective Poisson's ratio, which facilitates a “finger trap” effect. This allows for reduced tendon compression during a resting state (to permit vascular perfusion) and increased compression during loading (to drive the tines into the tissue for gripping). To test the feasibility of using this device for flexor tendon repair, it was tested on cadaver flexor digitorum profundus tendons. The tendons were excised, cut in the region corresponding to a zone II laceration, and repaired using the device. The device was easy to install and did not prevent the tendon from bending. Constant strain rate tensile testing revealed a mean tensile strength of 57.6 ± 7.7 N, with a force of 53.2 ± 7.8 N at a 2 mm gap. This exceeds the suggested primary repair strength of 45 N, which has been proposed as the necessary strength for enabling early mobilization. Although considerable future studies will be needed to determine the suitability of the new repair device for clinical use, this study demonstrates the feasibility of utilizing a tubular, nitinol repair device for flexor tendon fixation.

Musculoskeletal regeneration and its implications for the treatment of tendinopathy

Tendinopathies are common muskoloskeletal injuries that lead to pain and disability. Development and pathogenesis of tendinopathy is attributed to progressive pathological changes to the structure, function, and biology of tendon. The nature of this disease state, whether acquired by acute or chronic injury, is being actively investigated. Scarring, disorganized tissue, and loss of function characterize adult tendon healing. Recent work from animal models has begun to reveal the potential for adult mammalian tendon regeneration, the replacement of diseased with innate tissue. This review discusses what is known about musculoskeletal regeneration from a molecular perspective and how these findings can be applied to tendinopathy. Non-mammalian and mammalian models are discussed with emphasis on the potential of Murphy Roths Large mice to serve as a model of adult tendon regeneration. Comparison of regeneration in non-mammals, foetal mammals and adult mammals emphasizes distinctly different contributing factors to effective regeneration.

Cellular distribution and gene expression profile during flexor tendon graft repair: A novel tissue engineering approach(*)

To understand scar and adhesion formation during postsurgical period of intrasynovial tendon graft healing, a murine model of flexor digitorum longus tendon graft repair was developed, by utilizing flexor digitorum longus tendon allograft from donor Rosa26/+ mouse, and the healing process at days 3, 7, 14, 21, 28, and 35 post surgery of host wild-type mouse was followed. Using X-gal staining, β-galactosidase positive cells of allograft origin were detectable in tissue sections of grafted tendon post surgery. Graft healing was assessed for the cellular density, scar and adhesion formation, and their interaction with surrounding tissue. From histological analysis, it was evident that the healing of intrasynovial flexor digitorum longus tendon graft takes place in an interactive environment of donor graft, host tendon, and host surrounding tissue. A total of 32 genes, analyzed by RNA analysis, expressed during healing process. Particularly, Alk1, Postn, Tnc, Tppp3, and Mkx will be further investigated for therapeutical value in reducing scars and adhesions.

Resurfacing with chemically modified hyaluronic acid and lubricin for flexor tendon reconstruction

We assessed surface coating with carbodiimide derivatized hyaluronic acid combined with lubricin (cd-HA-Lubricin) as a way to improve extrasynovial tendon surface quality and, consequently, the functional results in flexor tendon reconstruction, using a canine in vivo model. The second and fifth flexor digitorum profundus tendons from 14 dogs were reconstructed with autologs peroneus longus (PL) tendons 6 weeks after a failed primary repair. One digit was treated with cd-HA-Lubricin, and the other was treated with saline as the control. Six weeks following grafting, the digits and graft tendons were functionally and histologically evaluated. Adhesion score, normalized work of flexion, graft friction in zone II, and adhesion breaking strength at the proximal repair site in zone III were all lower in the cd-HA-Lubricin treated group compared to the control group. The strength at the distal tendon/bone interface was decreased in the cd-HA-Lubricin treated grafts compared to the control grafts. Histology showed inferior healing in the cd-HA-Lubricin group at both proximal and distal repair sites. However, cd-HA-Lubricin treatment did not result in any gap or rupture at either the proximal or distal repair sites. These results demonstrate that cd-HA-Lubricin can eliminate graft adhesions and improve digit function, but that treatment may have an adverse effect on tendon healing.

Surface modification counteracts adverse effects associated with immobilization after flexor tendon repair

Although post-rehabilitation is routinely performed following flexor tendon repair, in some clinical scenarios post-rehabilitation must be delayed. We investigated modification of the tendon surface using carbodiimide derivatized hyaluronic acid and lubricin (cd-HA-Lub) to maintain gliding function following flexor tendon repair with postoperative immobilization in a in vivo canine model. Flexor digitorum profundus tendons from the 2nd and 5th digits of one forepaw of six dogs were transected and repaired. One tendon in each paw was treated with cd-HA-Lub; the other repaired tendon was not treated. Following tendon repair, a forearm cast was applied to fully immobilize the operated forelimb for 10 days, after which the animals were euthanized. Digit normalized work of flexion (nWOF) and tendon gliding resistance were assessed. The nWOF of the FDP tendons treated with cd-HA-Lub was significantly lower than the nWOF of the untreated tendons (p < 0.01). The gliding resistance of cd-HA-Lub treated tendons was also significantly lower than that of the untreated tendons (p < 0.05). Surface treatment with cd-HA-Lub following flexor tendon repair provides an opportunity to improve outcomes for patients in whom the post-operative therapy must be delayed after flexor tendon repair.

Rehabilitation regimens following surgical repair of extensor tendon injuries of the hand-a systematic review of controlled trials

There is no consensus on the most effective rehabilitation regimen following extensor tendon repair of the hand. This systematic review evaluates the outcomes of the various regimens. The Cochrane, MEDLINE, EMBASE, CINAHL, AMED, PEDro, OTseeker databases were searched for any prospective randomised clinical trials comparing rehabilitation regimens for acute extensor tendon injuries in adults. Five papers met the inclusion criteria. The regimens were static immobilisation, dynamic splinting and early active motion (EAM). There was no standard format of reporting. The sample size ranged from 27 to 100 patients. The duration of follow-up ranged from 8 to 24 weeks. Overall, patients' total active motion improved with time. Early mobilisation regimens (active and passive) achieve quicker recovery of motion than static immobilisation but the long-term outcome appears similar. Given the comparable outcomes between dynamic splinting and EAM, we therefore favour EAM which is simpler and more convenient.

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.

What we should know before using tissue engineering techniques to repair injured tendons: a developmental biology perspective

Tendons connect muscles to bones, and serve as the transmitters of force that allow all the movements of the body. Tenocytes are the basic cellular units of tendons, and produce the collagens that form the hierarchical fiber system of the tendon. Tendon injuries are common, and difficult to repair, particularly in the case of the insertion of tendon into bone. Successful attempts at cell-based repair therapies will require an understanding of the normal development of tendon tissues, including their differentiated regions such as the fibrous mid-section and fibrocartilaginous insertion site. Many genes are known to be involved in the formation of tendon. However, their functional roles in tendon development have not been fully characterized. Tissue engineers have attempted to generate functional tendon tissue in vitro. However, a lack of knowledge of normal tendon development has hampered these efforts. Here we review studies focusing on the developmental mechanisms of tendon development, and discuss the potential applications of a molecular understanding of tendon development to the treatment of tendon injuries.

Quantification of partial or complete A4 pulley release with FDP repair in cadaveric tendons

PURPOSE

Repair of a lacerated flexor digitorum profundus (FDP) tendon underneath or just distal to the A4 pulley can be technically challenging, and success can be confounded by tendon triggering and scarring to the pulley. The purpose of this study was to quantify the effect of partial and complete A4 pulley release in the context of a lacerated and repaired FDP tendon just distal to the A4 pulley.

METHODS

Tendon biomechanics were tested in 6 cadaveric hands secured to a rigid frame, permitting measurement of tendon excursion, tendon force, and finger range of motion. After control testing, each finger had laceration and repair of the FDP tendon at the distal margin of the A4 pulley using a 6-strand core suture technique and epitendinous repair. Testing was then repeated after the following interventions: (1) intact A4 pulley, (2) release of the distal half of the A4 pulley, (3) complete release of the A4 pulley, and (4) continued proximal release of the sheath to the distal edge of A2 (release of C2, A3, and C1 pulleys). Release of the pulleys was performed by incision; no tissue was removed from the specimens.

RESULTS

From full extension to full flexion, average FDP tendon excursion for all intact digits was 37.9 ± 1.5 mm, and tendon repair resulted in average tendon shortening of 1.6 ± 0.4 mm. Flexion lag increased from <1 mm to >4 mm with venting of the A4 pulley, complete A4 release, and proximal sheath release, respectively. Compared to the intact state, repair of the tendon with an intact A4 pulley, release of half the A4 pulley, complete A4 release, and proximal sheath release resulted in percentage increases in work of flexion of 11.5 ± 3.1%, 0.83 ± 2.8%, 2.6 ± 2.4%, and 3.25 ± 2.2%, respectively.

CONCLUSIONS

After FDP laceration and repair in the region of the A4 pulley, work of flexion did not increase by more than 3% from control conditions after partial or complete A4 pulley release, and work of flexion was significantly less than that achieved by performing a repair and leaving the A4 pulley intact.

Gliding resistance and strength of composite sutures in human flexor digitorum profundus tendon repair: an in vitro biomechanical study

PURPOSE

Although the strength of a tendon repair is clearly important, the friction of the repair is also a relevant consideration. The purpose of this study was to characterize the frictional coefficient, gliding resistance, and breaking strength of suture materials and a suture construct commonly used for flexor tendon repair.

METHODS

We measured the friction coefficients of 3-0 braided nylon enclosed in a smooth nylon outer shell (Supramid, S. Jackson, Alexandria, VA), 3-0 braided polyester coated with polybutilate (Ethibond, Ethicon, Somerville, NJ), and 3-0 braided polyester/monofilament polyethylene composite (FiberWire, Arthrex, Naples, FL) sutures. We also measured the gliding resistance, linear breaking strength, and resistance to gapping of zone 2 modified Pennington tendon repairs with the 2 lowest-friction sutures in 20 human cadaveric flexor digitorum profundus tendons.

RESULTS

The braided polyester/monofilament polyethylene composite had a significantly lower friction coefficient (0.054) than either the coated polyester (0.076) or nylon (0.130) sutures. The gliding resistances of the repaired tendons with braided/monofilament polyethylene composite suture and those of coated, braided polyester were similar. The strength of the 2 repairs (force to produce a 2 mm gap) and resistance to gap formation were also not significantly different.

CONCLUSIONS

Braided polyester composite is a low-friction suture material. However, when this suture was used for tendon repair with a locking suture technique, it did not show a significant effect on the gliding resistance and repair strength compared with the same repair using a coated polyester suture.

Adhesions in a murine flexor tendon graft model: autograft versus allograft reconstruction

Reconstruction of flexor tendons often results in adhesions that compromise joint flexion. Little is known about the factors involved in the formation of flexor tendon graft adhesions. In this study, we developed and characterized a novel mouse model of flexor digitorum longus (FDL) tendon reconstruction with live autografts or reconstituted freeze-dried allografts. Grafted tendons were evaluated at multiple time points up to 84 days post-reconstruction. To assess the flexion range of the metatarsophalangeal joint, we developed a quantitative outcome measure proportional to the resistance to tendon gliding due to adhesions, which we termed the Gliding Coefficient. At 14 days post-grafting, the Gliding Coefficient was 29- and 26-fold greater than normal FDL tendon for both autografts and allografts, respectively (p < 0.001), and subsequently doubled for 28-day autografts. Interestingly, there were no significant differences in maximum tensile force or stiffness between live autograft and freeze-dried allograft repairs over time. Histologically, autograft healing was characterized by extensive remodeling and exuberant scarring around both the ends and the body of the graft, whereas allograft scarring was abundant only near the graft-host junctions. Gene expression of GDF-5 and VEGF were significantly increased in 28-day autografts compared to allografts and to normal tendons. These results suggest that the biomechanical advantages for tendon reconstruction using live autografts over devitalized allografts are minimal. This mouse model can be useful in elucidating the molecular mechanisms in tendon repair and can aid in preliminary screening of molecular treatments of flexor tendon adhesions.

[The influence of duration of Kleinert immobilization on the functional recovery of primarly reconstructed flexor tendons in children and adult patients]

Flexor tendon repair in the hand is very often complicated by the formation of peritendinous adhesions that result in loss of normal tendon gliding, digital stiffnes and functional disability. While stability is critical for a successful tendon repair, mobility is also important, as motion of the repaired tendon decreases the formation of postoperative adhesions and increases the strength of the repair. Immobilization and its duration, can ensure the integrity of the repair but can also lead to scaring, stiffness, and joint contractures. This study included 20 children and 39 adult patients, in the period from January 2000 to April 2003., with flexor tendon ruptures of the hand. Tendons were primary repaired using direct tennoraphy, and postoperately patients were treated with Kleinert dynamic imobilization. The aim of this study was to investigate the influence of the duration of the dynamic immobilization on successful postoperative functional recovery, separately in children and adult patients. Research in this area has been directed at achieving the optimal balance between stability and mobility, without compromising one for the other.

Bone marrow-derived mesenchymal stem cells influence early tendon-healing in a rabbit achilles tendon model

BACKGROUND

A repaired tendon needs to be protected for weeks until it has accrued enough strength to handle physiological loads. Tissue-engineering techniques have shown promise in the treatment of tendon and ligament defects. The present study tested the hypothesis that bone marrow-derived mesenchymal stem cells can accelerate tendon-healing after primary repair of a tendon injury in a rabbit model.

METHODS

Fifty-seven New Zealand White rabbits were used as the experimental animals, and seven others were used as the source of bone marrow-derived mesenchymal stem cells. The injury model was a sharp complete transection through the midsubstance of the Achilles tendon. The transected tendon was immediately repaired with use of a modified Kessler suture and a running epitendinous suture. Both limbs were used, and each side was randomized to receive either bone marrow-derived mesenchymal stem cells in a fibrin carrier or fibrin carrier alone (control). Postoperatively, the rabbits were not immobilized. Specimens were harvested at one, three, six, and twelve weeks for analysis, which included evaluation of gross morphology (sixty-two specimens), cell tracing (twelve specimens), histological assessment (forty specimens), immunohistochemistry studies (thirty specimens), morphometric analysis (forty specimens), and mechanical testing (sixty-two specimens).

RESULTS

There were no differences between the two groups with regard to the gross morphology of the tendons. The fibrin had degraded by three weeks. Cell tracing showed that labeled bone marrow-derived mesenchymal stem cells remained viable and present in the intratendinous region for at least six weeks, becoming more diffuse at later time-periods. At three weeks, collagen fibers appeared more organized and there were better morphometric nuclear parameters in the treatment group (p < 0.05). At six and twelve weeks, there were no differences between the groups with regard to morphometric nuclear parameters. Biomechanical testing showed improved modulus in the treatment group as compared with the control group at three weeks (p < 0.05) but not at subsequent time-periods.

CONCLUSIONS

Intratendinous cell therapy with bone marrow-derived mesenchymal stem cells following primary tendon repair can improve histological and biomechanical parameters in the early stages of tendon-healing.

Tendon Healing In Vitro: Adeno-Associated Virus-2 Effectively Transduces Intrasynovial Tenocytes with Persistent Expression of the Transgene, but Other Serotypes Do Not

BACKGROUND

Transfer of exogenous growth factor genes to injured tendons offers a promising method for strengthening tendon repairs. Adeno-associated virus vectors have advantages of being both nonpathogenic and nontoxic. The authors explored the efficiency of transduction of intrasynovial tenocytes with different serotypes of adeno-associated virus (AAV) and the persistency of its expression of a growth factor transgene.

METHODS

Tenocytes were obtained from cultures of rat intrasynovial tendons and distributed to 82 wells in eight culture plates and to 30 culture dishes. The tenocytes in the wells were treated with AAV1, AAV2, AAV3, AAV4, AAV5, AAV7, and AAV8 vectors containing the lacZ gene, and plasmid vectors (pCMVbeta-lacZ). The tenocytes were stained with in situ beta-galactosidase 5 days later. The basic fibroblast growth factor (bFGF) gene was cloned to the AAV2 vector to construct the AAV2-bFGF vector, which transduced tenocytes in culture dishes. Expression of the transgene was measured over 3 weeks and analyzed statistically.

RESULTS

AAV2 effectively delivered exogenous genes to proliferating intrasynovial tenocytes. In contrast, other tested adeno-associated viruses transduced tenocytes minimally or not at all. The efficiency of gene transfer by AAV2, indicated by the percentage of cells with positive beta-galactosidase staining, was significantly greater than that by a plasmid vector (p = 0.001). Expression of the bFGF gene in tenocytes transduced with the AAV2-bFGF was significantly higher than that in the control over the 3-week period (p < 0.01).

CONCLUSIONS

Gene transfer to tenocytes by AAV2 is more efficient than that by a plasmid vector. However, other adeno-associated virus serotypes cannot effectively transduce tenocytes. The bFGF gene can be delivered to intrasynovial tenocytes by the AAV2 vector effectively, and the gene transfer significantly increases expression of bFGF gene over 3 weeks.