Effect of hyaluronic acid/chondroitin sulfate on healing of full-thickness tendon lacerations in rabbits

Fascial or Muscle Stretching? A Narrative Review

Stretching exercises are integral part of the rehabilitation and sport. Despite this, the mechanism behind its proposed effect remains ambiguous. It is assumed that flexibility increases, e.g., action on muscle and tendon, respectively, but this is not always present in the stretching protocol of the exercises used. Recently, the fasciae have increased popularity and seems that they can have a role to define the flexibility and the perception of the limitation of the maximal range of motion (ROM). Deep fascia is also considered a key element to transmit load in parallel bypassing the joints, transmitting around 30% of the force generated during a muscular contraction. So, it seems impossible dividing the action of the muscles from the fasciae, but they have to be considered as a “myofascial unit”. The purpose of this manuscript is to evaluate the mechanical behavior of muscles, tendons, and fasciae to better understand how they can interact during passive stretching. Stress-strain values of muscle, tendon and fascia demonstrate that during passive stretching, the fascia is the first tissue that limit the elongation, suggesting that fascial tissue is probably the major target of static stretching. A better understanding of myofascial force transmission, and the study of the biomechanical behavior of fasciae, with also the thixotropic effect, can help to design a correct plan of stretching.

Multi-functional electrospun antibacterial core-shell nanofibrous membranes for prolonged prevention of post-surgical tendon adhesion and inflammation

The possibility of endowing an electrospun anti-adhesive barrier membrane with multi-functionality, such as lubrication, prevention of fibroblast attachment and anti-infection and anti-inflammation properties, is highly desirable for the management of post-surgical tendon adhesion. To this end, we fabricated core-shell nanofibrous membranes (CSNMs) with embedded silver nanoparticles (Ag NPs) in the poly(ethylene glycol) (PEG)/poly(caprolactone) (PCL) shell and hyaluronic acid (HA)/ibuprofen in the core. HA imparted a lubrication effect for smooth tendon gliding and reduced fibroblast attachment, while Ag NPs and ibuprofen functioned as anti-infection and anti-inflammation agents, respectively. CSNMs with a PEG/PCL/Ag shell (PPA) and HA core containing 0% (H/PPA), 10% (HI10/PPA), 30% (HI30/PPA) and 50% (HI50/PPA) ibuprofen were fabricated through co-axial electrospinning and assessed through microscopic, spectroscopic, thermal, mechanical and drug release analyses. Considering nutrient passage through the barrier, the microporous CSNMs exerted the same barrier effect but drastically increased the mass transfer coefficients of bovine serum albumin compared with the commercial anti-adhesive membrane SurgiWrap®. Cell attachment/focal adhesion formation of fibroblasts revealed effective reduction of initial cell attachment on the CSNM surface with minimum cytotoxicity (except HI50/PPA). The anti-bacterial effect against both Gram-negative and Gram-positive bacteria was verified to be due to the Ag NPs in the membranes. In vivo studies using H/PPA and HI30/PPA CSNMs and SurgiWrap® in a rabbit flexor tendon rupture model demonstrated the improved efficacy of HI30/PPA CSNMs in reducing inflammation and tendon adhesion formation based on gross observation, histological analysis and functional assays. We conclude that HI30/PPA CSNMs can act as a multifunctional barrier membrane to prevent peritendinous adhesion after tendon surgery.

STATEMENT OF SIGNIFICANCE

A multi-functional anti-adhesion barrier membrane that could reduce fibroblasts attachment and penetration while simultaneously prevent post-surgical infection and inflammation is urgently needed. To this end, we prepared electrospun core-shell hyaluronic acid + ibuprofen/polyethylene glycol + polycaprolactone + Ag nanoparticles nanofibrous membranes by co-axial electrospinning as an ideal anti-adhesive membrane. The core-shell structure could meet the need of a desirable anti-adhesion barrier through release of ibuprofen and Ag nanoparticles to reduce infection and inflammation while hyaluronic acid can reduce fibroblasts adhesion. The superior performance of this multi-functional core-shell nanofibrous membrane in preventing peritendinous adhesion and post-surgical inflammation was demonstrated in a rabbit flexor tendon rupture model.

In Vitro Characteristics of Porcine Tendon Hydrogel for Tendon Regeneration

PURPOSE

Previous work has characterized the development of a human tendon hydrogel capable of improving mechanical strength after tendon injury. Animal tendon hydrogel has not yet been described, but would prove beneficial due to the cost and ethical concerns associated with the use of human cadaveric tendon. This study details the manufacture and assesses the biocompatibility of porcine tendon hydrogel seeded with human adipoderived stem cells (ASCs).

MATERIALS AND METHODS

Porcine tendon was dissected from surrounding connective and muscle tissue and decellularized via 0.2% sodium dodecyl sulfate and 0.2% sodium dodecyl sulfate/ethylenediaminetetraacetic acid wash solutions before lyophilization. Tendon was milled and reconstituted by previously described methods. Decellularization was confirmed by hematoxylin-eosin staining, SYTO Green 11 nucleic acid dye, and DNeasy assay. The protein composition of milled tendon matrix before and after digestion was identified by mass spectrometry. Rheological properties were determined using an ARG2 rheometer. Biocompatibility was assessed by live/dead assay. The proliferation of human ASCs seeded in porcine and human hydrogel was measured by MTS assay. All experimental conditions were performed in triplicate.

RESULTS

Decellularization of porcine tendon was successful. Mass spectrometry showed that collagen composes one third of milled porcine tendon before and after pepsin digestion. Rheology demonstrated that porcine hydrogel maintains a fluid consistency over a range of temperatures, unlike human hydrogel, which tends to solidify. Live/dead staining revealed that human ASCs survive in hydrogel 7 days after seeding and retain spindle-like morphology. MTS assay at day 3 and day 5 showed that human ASC proliferation was marginally greater in human hydrogel.

CONCLUSIONS

After reconstitution and digestion, porcine hydrogel was capable of supporting growth of human ASCs. The minimal difference in proliferative capacity suggests that porcine tendon hydrogel may be an effective and viable alternative to human hydrogel for the enhancement of tendon healing.

The Effect of Sodium Hyaluronate plus Sodium Chondroitin Sulfate Solution on Peritendinous Adhesion and Tendon Healing: An Experimental Study

BACKGROUND

Adhesion formation following tendon injury is a serious clinical problem.

AIMS

In this experimental study, the effects of the combination of sodium hyaluronate (HA) and chondroitin sulfate (CS) on peritendinous adhesion and tendon healing were evaluated.

STUDY DESIGN

Animal experimentation.

METHODS

Twenty-one mature Sprague Dawley male rats were randomly divided into three equal groups. The rats' Achilles tendons were cut and repaired with a modified Kessler technique. About 0.25 and 0.50 mL of the HA and CS (HA+CS) combination were injected subcutaneously into the repair site of the rats in groups 1 and 2, respectively, on days 0, 3, 7, and 10. The subjects in group 3 were used as the control group. At 6 weeks, all rats were euthanized. The tenotomy site was examined macroscopically in all animal subjects. Four samples were assigned to the histopathological examination group, and the others were assigned to the biomechanical assessment group.

RESULTS

Inflammation and adhesion in both treatment groups were observed at a lower rate than in the control group. The collagen filaments in both treatment groups were regular and the number was low when compared to the control group. However, there was no statistically significant difference between group 1 and the control group. The quantity, quality, and grade of the adhesions were statistically significantly lower in group 2 when compared with the other groups. The mean maximum stress strength in group 2 was statistically significantly higher than that in group 1 and the control group.

CONCLUSION

Local administration of the HA+CS combination solution is a valid tool for preventing peritendinous adhesion after extrasynovial tendon repair such as Achilles tendon, and is a treatment option in such cases.

PXL01 in sodium hyaluronate for improvement of hand recovery after flexor tendon repair surgery: randomized controlled trial

Background

Postoperative adhesions constitute a substantial clinical problem in hand surgery. Fexor tendon injury and repair result in adhesion formation around the tendon, which restricts the gliding function of the tendon, leading to decreased digit mobility and impaired hand recovery. This study evaluated the efficacy and safety of the peptide PXL01 in preventing adhesions, and correspondingly improving hand function, in flexor tendon repair surgery.

Methods

This prospective, randomised, double-blind trial included 138 patients admitted for flexor tendon repair surgery. PXL01 in carrier sodium hyaluronate or placebo was administered around the repaired tendon. Efficacy was assessed by total active motion of the injured finger, tip-to-crease distance, sensory function, tenolysis rate and grip strength, and safety parameters were followed, for 12 months post-surgery.

Results

The most pronounced difference between the treatment groups was observed at 6 months post-surgery. At this timepoint, the total active motion of the distal finger joint was improved in the PXL01 group (60 vs. 41 degrees for PXL01 vs. placebo group, p = 0.016 in PPAS). The proportion of patients with excellent/good digit mobility was higher in the PXL01 group (61% vs. 38%, p = 0.0499 in PPAS). Consistently, the PXL01 group presented improved tip-to-crease distance (5.0 vs. 15.5 mm for PXL01 vs. placebo group, p = 0.048 in PPAS). Sensory evaluation showed that more patients in the PXL01 group felt the thinnest monofilaments (FAS: 74% vs. 35%, p = 0.021; PPAS: 76% vs. 35%, p = 0.016). At 12 months post-surgery, more patients in the placebo group were considered to benefit from tenolysis (30% vs. 12%, p = 0.086 in PPAS). The treatment was safe, well tolerated, and did not increase the rate of tendon rupture.

Conclusions

Treatment with PXL01 in sodium hyaluronate improves hand recovery after flexor tendon repair surgery. Further clinical trials are warranted to determine the most efficient dose and health economic benefits.

Trial Registration

ClinicalTrials.gov NCT01022242; EU Clinical Trials 2009-012703-25.

Effect of lyophilized amniotic membrane, hyaluronic acid, and their combination in preventing adhesion after tendon repair in New Zealand white rabbits

Background: Several promising methods to reduce the peritendinous adhesion after repair include amniotic membrane and hyaluronic acid application on the repaired tendon site. This study aimed to compare the effect of lyophilized amniotic membrane, application of hyaluronic acid, and their combination in preventing peritendinous adhesion after tendon repair in New Zealand white rabbits.Methods: 64 flexor digitorum fibularis tendon from 16 rabbits were cut and then repaired by modified Kessler technique. Samples were allocated into four test groups; group I as control had simple tendon repair, group II had amniotic membrane wrapping at repair site, group III had hyaluronic acid application at repair site, and group IV had combination of amniotic membrane wrapping and hyaluronic acid application. On 6th week, 8 tendon from each group underwent macroscopic and histologic evaluation of peritendon adhesion by Tang scoring system. The rest of samples were evaluated for tendon gliding at tenth week by measuring active and passive range of motion of metatarsophalangeal joint.Results: At 6th week, macroscopic and histologic evaluation showed that groups II, III, and IV had significantly lower peritendinous adhesion compared to control group (p < 0.05). However, there was no significant difference found among groups II, III, and IV (p > 0.05). Similar results were found in tendon gliding evaluation, groups II, III, and IV had significantly better range of motion compared to control group (p < 0.05), but there was no significant difference found between these groups (p > 0.05).Conclusion: The application of lyophilized amniotic membrane, hyaluronic acid, or their combination significantly reduce the formation of peritendinous adhesion in repaired flexor digitorum fibularis tendon in rabbit model.

History and performance of implant materials applied as peritendinous antiadhesives

Peritendinous fibrotic adhesions after tendon surgery are still a problem up-to-date. Approaches to overcome or at least minimize adhesion formation include implantation of barrier materials, application of lubricants or combinations of materials and functionalized drugs that are controllably released and support the healing tendon to glide and achieve the full range of motion after regeneration. Although a huge amount of different materials have been experimentally tested, the optimal strategy with respect to material and method has not yet been determined. In this review, we present a historical overview of physical barriers as well as liquid agents that have been used in order to prevent peritendinous adhesion formation. The materials are divided according to their first publication into two time frames; before and after 1980. There is no claim to include all materials tested neither will the "best" material be chosen; however, we present several materials that were experimentally tested in different animal trials as well as in clinical trials in contrast to other materials that were only tested once and disappeared from the assortment of anti-adhesives; which as such is a valuable information about its applicability for this purpose.

ROLE OF THE HYALURONAN-PRODUCING TENOSYNOVIUM IN PREVENTING ADHESION FORMATION DURING HEALING OF FLEXOR TENDON INJURIES

Flexor tendons of white Leghorn chickens (n = 25) were used for this study. One chicken was used as a normal control (no surgery), and the remaining 24 were used for experiments. After partial tendon-severing in both legs of 24 chickens, the right and the left leg were treated differently, thereby creating two groups: Group I, in which the tenosynovium was preserved, and Group II, in which the tenosynovium was removed. Hematoxylin-eosin staining was performed to observe adhesions; immunohistochemical analysis was used to localize HA. HA production was noted in granulation tissue invading between the tendon stumps in both groups; however, HA expression in the tenosynovium was observed only in Group I where adhesion formation was minimal. The HA-producing tenosynovium plays a crucial role in preventing adhesion formation in this model of flexor tendon injuries.

Hyaluronan modulates proliferation and migration of rabbit fibroblasts derived from flexor tendon epitenon and endotenon

PURPOSE

There is a growing body of evidence supporting the use of hyaluronan (HA) for treatment of injured tendons, although the mechanism of the healing effect has not yet been clarified. We therefore investigated the effects of HA on the proliferation and migration of tendon fibroblasts derived from rabbit flexor tendon epitenon and endotenon.

METHODS

From explanted rabbit intrasynovial flexor tendons (n = 5), we cultured tendon fibroblasts derived from the epitenon and endotenon. CD44 expression on the tendon fibroblasts was detected by flow cytometric analysis. Various concentrations of HA (0.1-5.0 mg/mL) were added to monolayer-cultured tendon fibroblasts. We evaluated cell proliferation by recording changes in cell number, and measured cell migration by wound-healing assay.

RESULTS

Flow cytometric analysis detected CD44 expression on the tendon fibroblasts. Treatment with HA at various concentrations notably and dose dependently inhibited cell proliferation and promoted cell migration.

CONCLUSIONS

Hyaluronan modulates the proliferation and migration of rabbit fibroblasts derived from the flexor tendon epitenon and endotenon.

The effect of surface treatment using hyaluronic acid and lubricin on the gliding resistance of human extrasynovial tendons in vitro

PURPOSE

To investigate the effects of tendon surface treatment using hyaluronic acid (HA) and lubricin on the gliding resistance of human extrasynovial palmaris longus (PL) tendon in vitro.

METHODS

Thirty-two fresh-frozen cadaver human fingers and 16 ipsilateral PL tendons were used. Each PL tendon was divided into 2 pieces, which were randomly assigned into 4 experimental groups. After the gliding resistance of the normal PL tendon segments were measured, the tendons were treated with either saline, carbodiimide derivatized (cd) gelatin and HA (cd-HA gelatin), cd gelatin with lubricin added (cd gelatin plus lubricin), or cd-HA gelatin plus lubricin. After treatment, tendon gliding resistance was measured during up to 1000 cycles of simulated flexion and extension motion.

RESULTS

The gliding resistance of the PL tendons in the cd-HA gelatin, cd gelatin plus lubricin, and cd-HA gelatin plus lubricin groups was significantly lower than that of the saline-treated control after 1000 cycles. The gliding resistance in these treatment groups decreased within the first 50 cycles and then increased at a much more gradual rate over the 1000 cycles, with the cd-HA gelatin plus lubricin group being most stable.

CONCLUSIONS

The results suggest that tendon surface treatment using HA and lubricin can improve the gliding of human PL tendon in vitro. If validated in vivo, tendon surface treatment has the potential to improve the gliding ability of tendon grafts clinically.

Auto-crosslinked hyaluronic acid gel accelerates healing of rabbit flexor tendons in vivo

This study's purpose was to assess the in vivo effect of auto-crosslinked hyaluronic acid (HA) gel, a natural HA derivative with increased viscosity and tissue residence time, on adhesions and healing of injured and surgically repaired rabbit digital flexor tendons. The second and third right deep digital flexor tendons from 48 rabbits (n = 96 tendons) were cut and repaired with a modified Kessler and running peripheral suture. Animals were randomized to two groups, receiving either HA gel or saline injected around both freshly repaired tendons. After 2, 3, 6, and 12 weeks, six rabbits in each group were euthanized. Tendon pull-out force and breaking strength were measured as a value for adhesion formation and tendon healing, respectively. A histological assessment of adhesions and healing was related to the mechanical results. A significantly faster increase in breaking strength was found in HA gel-treated compared to saline-treated tendons; this coincided with a significantly accelerated tissue repair response after injury. No significant difference in adhesion formation was found between the two groups at any time. Our results indicate a significant acceleration of in vivo healing of tendons treated with HA gel. Adhesion formation was unaffected. These results could have important clinical value in promoting rehabilitation after tendon injury.

Lubricin surface modification improves tendon gliding after tendon repair in a canine model in vitro

This study investigated the effects of lubricin on the gliding of repaired flexor digitorum profundus (FDP) tendons in vitro. Canine FDP tendons were completely lacerated, repaired with a modified Pennington technique, and treated with one of the following solutions: saline, carbodiimide derivatized gelatin/hyaluronic acid (cd-HA-gelatin), carbodiimide derivatized gelatin to which lubricin was added in a second step (cd-gelatin + lubricin), or carbodiimide derivatized gelatin/HA + lubricin (cd-HA-gelatin + lubricin). After treatment, gliding resistance was measured up to 1,000 cycles of simulated flexion/extension motion. The increase in average and peak gliding resistance in cd-HA-gelatin, cd-gelatin + lubricin, and cd-HA-gelatin + lubricin tendons was less than the control tendons after 1,000 cycles (p < 0.05). The increase in average gliding resistance of cd-HA-gelatin + lubricin treated tendons was also less than that of the cd-HA-gelatin treated tendons (p < 0.05). The surfaces of the repaired tendons and associated pulleys were assessed qualitatively with scanning electron microscopy and appeared smooth after 1,000 cycles of tendon motion for the cd-HA-gelatin, cd-gelatin + lubricin, and cd-HA-gelatin + lubricin treated tendons, while that of the saline control appeared roughened. These results suggest that tendon surface modification can improve tendon gliding ability, with a trend suggesting that lubricin fixed on the repaired tendon may provide additional improvement over that provided by HA and gelatin alone.

The effect of carbodiimide-derivatized hyaluronic acid and gelatin surface modification on peroneus longus tendon graft in a short-term canine model in vivo

PURPOSE

We have recently reported that application of carbodiimide-derivatized hyaluronic acid and gelatin (cd-HA gelatin) to a peroneus longus tendon graft increased tendon graft gliding ability and decreased work of flexion compared with untreated grafts in a canine model in vivo. In this study, we investigated the effect of this modification on adhesions, stiffness, strength of the distal attachment, and fibroblast count.

METHODS

A total of 24 dogs were used for this study. The peroneus longus tendons of each hind leg were grafted into the 2nd and 5th digits of one forepaw in each dog. One peroneus longus tendon was treated with cd-HA gelatin prior to grafting, and the other one was immersed in 0.9% saline solution as a control. Animals were killed 1, 3, or 6 weeks postoperatively.

RESULTS

The adhesion score of cd-HA gelatin-treated tendons was significantly less than that in the saline-treated tendons at all time points. There was no significant difference in the indentation stiffness between HA- and saline-treated grafts at any time point. For the ultimate force at the distal attachment, there was a significant difference among the time points, with a steady increase over time, but no significant difference between treated and control tendons at any time point. There was no significant difference in fibroblast count between treated and control tendons at any time point.

CONCLUSIONS

Although gross adhesion formation was less, there was no significant difference in strength at the distal tendon-bone interface, cellularity, or tendon graft stiffness when comparing saline-treated and cd-HA gelatin-treated tendon grafts in vivo.

Surface treatment of flexor tendon autografts with carbodiimide-derivatized hyaluronic Acid. An in vivo canine model

BACKGROUND

Clinical and experimental studies have demonstrated that restrictive adhesions and poor digital motion are common complications after extrasynovial tendon grafting in an intrasynovial environment. The purpose of this study was to test the hypothesis that surface modification of an extrasynovial tendon with use of a carbodiimide-derivatized hyaluronic acid-gelatin polymer (cd-HA) improves gliding ability and digital function after tendon grafting in a canine model in vivo.

METHODS

The peroneus longus tendons from both hindpaws of twenty-four dogs were harvested and transplanted to replace the flexor digitorum profundus tendons in the second and fifth digits of one forepaw. Prior to grafting, one of the peroneus longus tendons was coated with cd-HA, which consists of 1% hyaluronic acid, 10% gelatin, 0.25% 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC), and 0.25% N-hydroxysuccinimide (NHS), while the other was immersed in saline solution only. Eight dogs were killed at one, three, and six weeks. Digital normalized work of flexion, tendon gliding resistance, and hyaluronic acid quantification (with the hyaluronic acid-binding-protein staining technique) were the outcome measures.

RESULTS

The normalized work of flexion of the tendons treated with cd-HA was significantly lower than that of the saline-solution-treated controls at each time-point (p < 0.05). The gliding resistance of the cd-HA group was significantly lower than that of the saline-solution group at three and six weeks (p < 0.05). The ratio between the intensity of staining of the cd-HA-treated tendons with that of the saline-solution-treated controls was significantly greater at time-0 than at three or six weeks (p < 0.05), but there was no significant difference between time-0 and one-week values.

CONCLUSIONS

Treating the surface of an extrasynovial tendon autograft with a carbodiimide-derivatized hyaluronic acid-gelatin polymer decreases digital work of flexion and tendon gliding resistance in this flexor tendon graft model in vivo.

CLINICAL RELEVANCE

cd-HA gelatin may provide surgeons with a new and useful method to improve the quality of tendon graft surgery.

Optimization of surface modifications of extrasynovial tendon to improve its gliding ability in a canine model in vitro

Previous studies have shown that the carboxyl groups in hyaluronic acid (HA) could be activated by 1-ethy 1-3-[3-dimethylaminopropyl] carbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS) to form intermediate O-acylisoureas, which can chemically bind to exposed amino groups on the tendon surface, leading to improved gliding ability. However, the optimal ratio and concentrations of the components in this chemical mixture were not investigated. The purpose of this study was to optimize the constituents of this tissue engineering approach to tendon surface modification, to reduce friction and improve durability. Peroneus longus (PL) tendons (n=40) were harvested from adult mongrel dogs along with the A2 pulley obtained from the ipsilateral hind paw. After the gliding resistance of the normal PL tendon was measured, the tendons were treated under varying concentrations of HA (0.5, 1, and 2%) and EDC/NHS (0.05, 0.25, and 1%) mixed with a 10% gelatin. Tendon friction was measured for 1000 cycles of simulated flexion/extension motion. Following testing, the residual HA on the tendon surface was evaluated by immunohistochemisty. The gliding resistance of the untreated PL tendons had a mean value of 0.087+/-0.021 N. After surface treatment, there was no significant difference in friction due to HA concentration alone, but the concentration of EDC/NHS and the interaction between HA concentration and EDC/NHS concentration had a significant effect on friction. Regardless of HA concentration, the friction after 1000 cycles was significantly decreased in preparations which included a 1% concentration of EDC/NHS. The tendons with lower gliding resistance presented a smoother surface on light microscopy and maintained more residual HA on the tendon surface. By varying the relative concentrations of HA, EDC, and NHS it is possible to optimize the effect of surface treatment on friction and durability in a canine extrasynovial tendon in vitro.

Hyaluronic acid diminishes the resistance to excursion after flexor tendon repair: An in vitro biomechanical study

Adhesion between the tendon and tendon sheath after primary flexor tendon repair is seen frequently, and postoperative finger function is occasionally unsatisfactory. A reduction of the friction may facilitate tendon mobilization, which in turn may reduce the risk of the adhesion and restriction of range of motion. We considered the possibility of utilizing the hyaluronic acid (HA) as a lubricant. To evaluate the effect of HA, the gliding resistance between the canine flexor digitorum profundus tendon repaired by a modified Kessler suture technique with running epitendinous suture and the annular pulley located on the proximal phalanx (corresponding to the A2 pulley in humans) was evaluated and compared before and after administration of HA. The HA solution measurement groups were identified as follows; intact tendon as a control; repaired tendon; tendon soaked in 0.1, 1, and 10 mg/ml HA. The resistance increased after repairing, then it decreased after soaking in 10 mg/ml HA solution. The results of this study revealed that HA diminishes the excursion resistance after flexor tendon repair. We believe that some style of administration of the HA might reduce the excursion resistance and prevent adhesion until the synovial surface is fully developed.

Friction of the gliding surface. Implications for tendon surgery and rehabilitation

Finger flexor tendon rehabilitation has come a long way, but further advances are possible. Ideally, a healing tendon should move, but under the minimum load necessary to achieve motion. It is possible to design suture repairs that minimize the friction between tendon and sheath while simultaneously maintaining adequate strength to provide a wide margin of safety during therapy. A looped, four-strand modified Kessler repair is a good example of this type of high-strength, low-friction repair. At the same time, rehabilitation methods can also be optimized. A new modified synergistic motion protocol is described in which wrist flexion and finger extension is alternated with wrist and metacarpophalangeal joint extension and finger interphalangeal joint flexion. Based on evidence from basic science studies, the authors hypothesize that this new protocol will deliver more effective proximal tension on the tendon repair than either passive flexion/active extension or synergistic protocols, and may be useful in patients who are not ready for, or are not reliable with, active motion or place and hold protocols. The scientific basis for these new methods is reviewed, and the concept of the "safe zone" for tendon loading, in which tendon motion occurs without gapping of the repair site, is developed.

Effect of hylan G-F 20 in achilles’ tendonitis: An experimental study in rats11No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated

OBJECTIVE

To investigate the local effects of hylan G-F 20 on locally administered corticosteroid-induced experimental Achilles' tendonitis.

DESIGN

Before-after trial.

SETTING

Institutional practice.

ANIMALS

Convenience sample of 18 male Wistar white rats (weight range, 322-375 g).

INTERVENTIONS

After performing Achilles' degeneration with local corticosteroid injections, the rats were divided into 4 groups. The right Achilles' tendon of the rats served as the hylan injection group and the left tendon as the control group, which was injected with saline at 5-day intervals. The tendons and paratenons were excised at the end of 60 or 75 days and evaluated histopathologically and statistically.

MAIN OUTCOME MEASURE

Histopathologic changes, including staining affinity, nuclear appearance, fibrillar appearance for tendon and thickness, occurrence of fibrosis and edema, capillary changes, and inflammation for paratenon, were assessed according to a semiquantitative scoring system. The Mann-Whitney U test was used for statistical analysis, with a P value of.05 or less considered statistically significant.

RESULTS

Semiquantitative scoring of histopathologic changes showed that histologic appearances differed between the hylan and saline groups and between 2 hylan groups. Hylan-injected tendons and paratenons demonstrated significantly lower scores, especially after 75 days.

CONCLUSIONS

Hylan G-F 20 has a promising curative effect on the tendon and paratenon and can be used in Achilles' tendonitis. This finding should be supported by biomechanical and biochemical studies.

Tendon surface modification by chemically modified HA coating after flexor digitorum profundus tendon repair

Carbodiimide derivatized HA (cd-HA) is less soluble in water than normal HA, and therefore has an increased tissue residence time. The purpose of this study was to study the effect of cd-HA gel on gliding and repair integrity during simulated repetitive motion of a repaired tendon in vitro. A total of 36 flexor digitorum profundus (FDP) tendons from six adult mongrel dogs were used and divided into three groups of control, simple HA, and cd-HA. The gliding resistance between the FDP and the proximal pulley, FDS, and bone was measured before laceration and after modified Kessler technique repair at 1, 5, 10, 50, 100, 200, 300, 400, and 500 cycles. After gliding testing, failure load, tendon stiffness, and resistance to gap formation were measured. The results showed from the first cycle to the 10th cycle, there were no significant differences in gliding resistance between the three testing groups (p > 0.05). From the 50th cycle onwards, the friction was significantly lower in the cd-HA gel group than in the control group (p < 0.05). Neither breaking strength, nor tendon stiffness, nor resistance to gap formation of the repairs were significantly different between the three groups (p > 0.05).

Chondroitin sulfate-coated polyhydroxyethyl methacrylate membrane prevents adhesion in full-thickness tendon tears of rabbits

Polyhydroxyethyl methacrylate (pHEMA) membranes coated on one side with chondroitin sulfate (CS) were used to block adhesion physically and to reduce friction between healing flexor tendons and the surrounding tissue in rabbit forepaws after surgical repair. Digits with pHEMA-only, standard tendon sheath repair, and with no sheath repair were the controls. Over 12 weeks the CS-coated membranes were evaluated for joint flexion, adhesion limitation, and tendon healing progress. The membranes initially allowed for better flexion (ie, for 6 weeks), but their relative superior effectiveness faded afterward. Histology showed that adhesions were less severe and healing was better in the CS-pHEMA membranes at 3 and 6 weeks. If further studies determine precise amounts or thicknesses of CS coats that will maximize its healing properties, CS-pHEMA should prove useful in clinical settings in which restoration of tendon sheath integrity with a minimum of adhesions is not possible.

Mixture of hyaluronic acid and phospholipid prevents adhesion formation on the injured flexor tendon in rabbits

Dipalmitoyl phosphatidylcholine, a highly surface-active polar lipid, has been implicated as a potential boundary lubricant for synovial joints. We examined the effects of dipalmitoyl phosphatidylcholine on the flexor tendon and its protective effect against postoperative adhesion in two experimental steps. First, the flexor digitorum fibularis and the distal pulley of rabbits were set for a friction test. The test was performed with saline solution, sodium hyaluronate, or a mixture of dipalmitoyl phosphatidylcholine and sodium hyaluronate as the lubricant. The friction coefficient was significantly lower with the mixture of dipalmitoyl phosphatidylcholine and sodium hyaluronate than with saline solution or sodium hyaluronate. We concluded that the decreased friction coefficient indicates that dipalmitoyl phosphatidylcholine could complement the boundary-lubricating ability of the tendon. In the second experiment, we used an experimental adhesion model of the flexor digitorum fibularis in the rabbit. During the operation, either saline solution, sodium hyaluronate, or a mixture of dipalmitoyl phosphatidylcholine and sodium hyaluronate was injected into the tendon sheath. The specimen was sent to another tester, and the work required to tear off the adhesion was measured. The work required was significantly greater for the tendons that had been injected with saline solution than for those given injections of dipalmitoyl phosphatidylcholine and sodium hyaluronate. Our findings suggest that dipalmitoyl phosphatidylcholine plays an important role in the boundary lubrication of the tendon and that after tendon injury, the administration of a mixture of dipalmitoyl phosphatidylcholine and sodium hyaluronate may improve tendon lubrication and prevent adhesion formation.

Hyaluronic acid modulates cell proliferation unequally in intrasynovial and extrasynovial rabbit tendons in vitro

As tendons differ in biochemical composition and cellular capacities, we have compared dose response effects of hyaluronic acid on cell proliferation and synthesis of matrix components in intermediate and proximal segments of intrasynovial deep flexor tendons and extrasynovial peroneus rabbit tendons in vitro. Compared with matched control tendons, hyaluronic acid inhibited cell proliferation in intermediate and proximal intrasynovial flexor tendon segments at the concentrations of 0.1-2.0 mg/ml and 0.5-2.0 mg/ml respectively, but in extrasynovial tendon segments only at the concentration of 0.5 mg/ml. Hyaluronic acid did not affect synthesis of proteoglycan, collagen and non-collagen protein in either type of tendon. These results show that hyaluronic acid modulates cell proliferation unequally in intra- and extrasynovial tendons without affecting the synthesis of matrix components in the two types of tendons, indicating differential hyaluronic acid sensitivity and a possible mechanism of action.

Tendon repair--cellular activities in rabbit deep flexor tendons and surrounding synovial sheaths and the effects of hyaluronan: an experimental study in vivo and in vitro

One deep flexor tendon and its surrounding sheath of each hindpaw of 48 rabbits were transected and repaired in order to investigate the abilities of rabbit flexor tendons and synovial sheaths to synthesize DNA and matrix components during healing and to study the effects of hyaluronan (HA). After repair, HA or saline was injected between the tendon and the sheath. Short-term culture and labeling in vitro were used up to 6 weeks after surgery to determine synthesis of DNA, proteoglycan, collagen, and noncollagen protein. Within tendon repair sites, the rate of cell proliferation increased and reached a maximum 5 days after surgery; within repaired synovial sheaths, the rate immediately decreased. In the healing tendons, the rate of collagen synthesis decreased and the rate of noncollagen protein synthesis remained unchanged. The opposite results were found within the healing synovial sheaths. HA did not affect the rate of cell proliferation or matrix synthesis in healing tendons or surrounding sheaths. These results show that cellular activities differ between tendons and synovial sheaths during healing and that those activities may not be affected by HA.

Effects of hyaluronan on cell proliferation and collagen synthesis: a study of rabbit flexor tendons in vitro

Hyaluronan (HA), a high-molecular-weight polysaccharide, has been suggested to play a possible role during the early stages of healing of a variety of connective tissues and when topically applied to decrease the formation of adhesions following tendon surgery. As the mechanisms of HA actions are still being discussed, this study was designed to assess the effects of HA on cell proliferation and synthesis of matrix components of deep flexor tendons in a well-defined culture system. Cell proliferation, measured as the radioactive 3H-thymidine uptake by cultured segments of rabbit flexor tendons, was inhibited by the addition of HA to the culture medium. HA of molecular weight 0.5 x 10(6) inhibited the uptake significantly at concentrations within the range of 0.1-2.0 mg/mL, HA of molecular weight 1.6 x 10(6) at 0.5-2.0 mg/mL, and HA of molecular weight 3.6 x 10(6) at 1.0-2.0 mg/mL, as compared to matched control groups. At the concentration of 2 mg/mL, HA of the molecular weights of 0.5, 0.8, 1.6, and 3.6 x 10(6) equally inhibited cell proliferation. No effect on synthesis of matrix components, measured as the radioactive incorporation of 35S-sulfate, 3H-hydroxyproline, and 3H-proline by cultured segments of rabbit flexor tendons, was observed. These findings show that exogenously applied HA may act as a modulator of flexor tendon fibroblast proliferation, indicating a possible mechanism for antiadhesive effects following administration after flexor tendon surgery.

Fibrin glue reduces the dissolution rate of sodium hyaluronate

Sodium hyaluronate (HA) is known to modulate wound healing and interact with inflammatory reactions. High concentrations of extracellular HA are for example correlated to scarless wound healing. Topical treatment with HA has, however, limited effect due to the rapid clearance of HA in the tissue. In an effort to prolong the dissolution rate and enhance the effect of topically administered HA, HA was incorporated in a cross linked fibrin clot and placed in NaCl. The concentration of HA in the NaCl solution was analysed after 30', 60', 4h, 8h, and 24h. It was found that the dissolution rate of HA incorporated in cross linked fibrin was dramatically decreased in vitro, especially when the HA-fibrin mixture was put at rest and not exposed to a mechanical stress. The findings indicate a new possibility for slow release of HA after topical administration.

Sodium hyaluronate as an adjunct in adhesion prevention after flexor tendon surgery in rabbits

Topical application of sodium-hyaluronate (NaHe) has been proposed to decrease the formation of adhesions after tendon surgery, but reports published thus far have been contradictory. A new test instrument capable of simultaneous registration of tensile load, tendon excursion, and joint motion was therefore developed and used to evaluate the effect of locally administered NaHe of different concentrations and molecular weights on the outcome after tenorrhaphy of rabbit hindlimb flexor tendons. Immediately after tenorrhaphy, NaHe or saline solution was deposited into the tendon sheath. The functional characteristics of the digits were evaluated 15 days after surgery. NaHe with a concentration of 19 mg/ml and a molecular weight of 6 x 10(6) significantly limited the strength of the adhesions formed without impairment of tensile strength. These results suggest that the efficacy of NaHe is affected by both the concentration and the molecular weight of the NaHe preparation used.

Exogenous hyaluronate as an adjunct in the prevention of adhesions after flexor tendon surgery: a controlled clinical trial

Postoperative adhesions that restrict tendon gliding are a major cause of failure after tendon repair and grafting in zone II. Several experimental reports have claimed that exogenously administered sodium hyaluronate helps to prevent the formation of such adhesions. In a prospective double-blind, randomized, clinical study with open therapeutic control sodium hyaluronate or physiologic saline solution was injected into the tendon sheath after completion of tenorrhaphy or tendon grafting in 120 digits. Sodium hyaluronate had no statistically significant effect as evaluated on total active motion at follow-up.

Elimination of exogenously injected sodium-hyaluronate from rabbit flexor tendon sheaths

To obtain information about the elimination of Na hyaluronate (NaHe) deposited in flexor tendon sheaths in rabbits, two flexor tendon sheaths from each hind limb were operatively exposed in 15 animals and each filled with one of four different NaHe preparations, namely: 10 mg/ml, MW 2.6 x 10(6); 10 mg/ml, MW 6.3 x 10(6); 19 mg/ml, MW 3.0 x 10(6); and 19 mg/ml, MW 6.5 x 10(6). One, 3, and 7 days after surgery, the NaHe concentration was measured in frozen specimens from the tendon sheaths. One day after surgery, NaHe concentration in the tendon sheath fluid was close to 10 mg/ml in all groups. Three and 7 days after surgery it was higher in tendon sheaths in which NaHe preparations with a high (19 mg/ml) rather than with a low concentration (10 mg/ml) had been deposited. At 3 days, NaHe concentration was also higher in sheaths that had received a preparation with a high MW (6.5 x 10(6)) than those with a lower MW (2.6 or 3.0 x 10(6)). The findings suggest that within the first 24 h, a dilution of concentrated NaHe preparations takes place, probably as a result of their hyperoncotic properties. After 24 h, there was a slower decline in NaHe concentration when more concentrated solutions (19 mg/ml) and solutions with high MWs (6.5 x 10(6)) were administered. Development of pharmaceutical NaHe preparations with slow elimination from tendon sheaths should reasonably be focused on a solution with a high MW and high concentration.