Gliding resistance of extrasynovial and intrasynovial tendons through the A2 pulley

Cell-based tissue engineered flexor tendon allograft: A canine in vivo study

This study aimed to compare the clinically established autologous extrasynovial tendon graft to a newly developed tissue-engineered allograft (Eng-allograft) in terms of functional outcomes following flexor tendon reconstruction in a canine model. The second and fifth flexor digitorum profundus (FDP) tendons from 16 dogs were transected and repaired in Zone II. After 6 weeks of cage activity, the repaired tendons were intentionally ruptured, creating a clinically relevant model for reconstruction. The re-ruptured FDP tendons were then reconstructed using either the clinically standard autologous extrasynovial tendon graft or the Eng-allograft, which had been revitalized with autologous bone marrow-derived mesenchymal stem cells (BMSCs) and synovialized using carbodiimide derivatized synovial fluid (cd-SYN). Following 12 weeks of postoperative rehabilitation, the functional outcomes of the surgical digits were evaluated. The Eng-allograft group exhibited improved digital function, including lower digit work of flexion and reduced adhesion status, while maintaining similar tendon gliding resistance compared to the autograft group. However, the failure load of both the distal and proximal host/graft conjunctions in the Eng-allograft group was significantly lower than that of the autograft group with higher graft rupture at the host-graft junction. In conclusion, the decellularized allogenic intrasynovial tendon, when revitalized BMSCs and synovialized with cd-SYN, demonstrates positive effects on digital function improvement and adhesion reduction. However, the healing at both proximal and distal graft/host junctions is far lower than the autograft. Further research is needed to enhance the healing capacity of allograft conjunctions, aiming to achieve a comparable level of healing seen with autografts.

Anterolateral Acromioplasty Reduces Gliding Resistance Between the Supraspinatus Tendon and the Coracoacromial Arch in a Cadaveric Model

Purpose

To investigate the gliding resistance dynamics between the supraspinatus (SSP) tendon and the coracoacromial arch, both before and after subacromial decompression (anterolateral acromioplasty) and acromion resection (acromionectomy).

Methods

Using 4 fresh-frozen cadaveric shoulders, acromion shapes were classified (2 type I and 2 type III according to Bigliani). Subacromial bursa and coracoacromial ligament maintenance replicated physiologic sliding conditions. Gliding resistance was measured during glenohumeral abduction (0° to 60°) in internal rotation (IR) and external rotation (ER). Peak gliding resistance between the SSP tendon and the coracoacromial arch was determined and compared between intact, anterolateral acromioplasty, and acromionectomy.

Results

Peak SSP gliding resistance during abduction in an intact shoulder was significantly higher in IR than in ER (4.1 vs 2.1 N, P < .001). The mean peak SSP gliding resistance during 0° to 60° glenohumeral abduction in IR in the intact condition was significantly higher compared with the subacromial decompression condition (4.1 vs 2.8 N, P = .021) and with the acromionectomy condition (4.1 vs 0.9 N, P < .001). During 0° to 60° glenohumeral abduction in ER, mean peak SSP gliding resistance in the intact condition was not significantly different compared with the subacromial decompression condition (2.1 vs 2.0 N, P = .999). The 2 specimens with a hooked (i.e. type III) acromion showed significantly higher mean peak SSP gliding resistance during glenohumeral abduction in IR and ER when compared with the 2 specimens with a flat (i.e. type I) acromion (IR: 5.8 vs 3.0 N, P = .006; ER: 2.8 vs 1.4 N, P = .001).

Conclusions

In this cadaveric study, peak gliding resistance between the SSP tendon and the coracoacromial arch during combined abduction and IR was significantly reduced after anterolateral acromioplasty and was significantly higher in specimens with a hooked acromion.

Clinical Relevance

The clinical benefit of subacromial decompression remains unclear. This study suggests that anterolateral acromioplasty might reduce supraspinatus gliding resistance in those with a hooked acromion and in the typical "impingement" position.

Carbodiimide-Derivatized Synovial Fluid for Tendon Graft Coating Improves Long-Term Functional Outcomes of Flexor Tendon Reconstruction

BACKGROUND

Flexor digitorum profundus (FDP) tendon injury is common in hand trauma, and flexor tendon reconstruction is one of the most challenging procedures in hand surgery because of severe adhesion that exceeds 25% and hinders hand function. The surface properties of a graft from extrasynovial tendons are inferior to those of the native intrasynovial FDP tendons, which has been reported as one of the major causations. Improved surface gliding ability of the extrasynovial graft is needed. Thus, this study used carbodiimide-derivatized synovial fluid and gelatin (cd-SF-gel) to modify the surface of the graft, thus improving functional outcomes using a dog in vivo model.

METHODS

Forty FDP tendons from the second and fifth digits of 20 adult women underwent reconstruction with a peroneus longus (PL) autograft after creation of a tendon repair failure model for 6 weeks. Graft tendons were either coated with cd-SF-gel ( n = 20) or not. Animals were euthanized 24 weeks after reconstruction, and digits were collected after the animals were euthanized for biomechanical and histologic analyses.

RESULTS

Adhesion score (cd-SF-gel, 3.15 ± 1.53; control, 5 ± 1.26; P < 0.00017), normalized work of flexion (cd-SF-gel, 0.47 ± 0.28 N-mm/degree; control, 1.4 ± 1.45 N-mm/degree; P < 0.014), and distal interphalangeal joint motion (cd-SF-gel, 17.63 ± 6.77 degrees; control, 7.07 ± 12.99 degrees; P < 0.0015) in treated grafts all showed significant differences compared with nontreated grafts. However, there was no significant difference in repair conjunction strength between the two groups.

CONCLUSION

Autograft tendon surface modification with cd-SF-gel improves tendon gliding ability, reduces adhesion formation, and enhances digit function without interfering with graft-host healing.

CLINICAL RELEVANCE STATEMENT

The authors demonstrate a clinically relevant and translational technology by using the patient's own synovial fluid to "synovialize" an autologous extrasynovial tendon graft to improve functional outcomes following flexor tendon reconstruction.

Improving Mechanical Properties of Tendon Allograft through Rehydration Strategies: An In Vitro Study

Allogenic tendons grafts sourced from intrasynovial tendons are often used for tendon reconstruction. Processing is achieved through repetitive freeze-thaw cycles followed by lyophilization. Soaking the lyophilized tendon in saline (0.9%) for 24 h is the standard practice for rehydration. However, data supporting saline rehydration over the use of other hydrating solutions are scant. The purpose of the current study was to compare the effects of different rehydration solutions on biomechanical properties of lyophilized tendon allograft. A total of 36 canine flexor digitorum profundus tendons were collected, five freeze-thaw cycles followed by lyophilization were performed for processing, and then divided into three groups rehydrated with either saline solution (0.9%), phosphate-buffered saline (PBS), or minimum essential medium (MEM). Flexural stiffness, tensile stiffness, and gliding friction were evaluated before and after allograft processing. The flexural moduli in both fibrous and fibrocartilaginous regions of the tendons were measured. After lyophilization and reconstitution, the flexural moduli of both the fibrocartilaginous and non-fibrocartilaginous regions of the tendons increase significantly in the saline and MEM groups (p < 0.05). Compared to the saline and MEM groups, the flexural moduli of the fibrocartilaginous and non-fibrocartilaginous regions of tendons rehydrated with PBS are significantly lower (p < 0.05). Tensile moduli of rehydrated tendons are significantly lower than those of fresh tendons for all groups (p < 0.05). The gliding friction of rehydrated tendons is significantly higher than that of fresh tendons in all groups (p < 0.05). There is no significant difference in either tensile moduli or gliding friction between tendons treated with different rehydration solutions. These results demonstrate that allograft reconstitution can be optimized through careful selection of hydrating solution and that PBS could be a better choice as the impact on flexural properties is lower.

Knotless Tendon Repair with a Resorbable Barbed Suture: An In-vivo Comparison in the Turkey Foot

Background: Un-knotted barbed suture constructs are postulated to decrease repair bulk and improve tension loading along the entire repair site resulting in beneficial biomechanical repair properties. Applying this repair technique to tendons has shown good results in ex-vivo experiments previously but thus far no in-vivo study could confirm these. Therefore, this current study was conducted to assess the value of un-knotted barbed suture repairs in the primary repair of flexor tendons in an in-vivo setting. Methods: Two groups of 10 turkeys (Meleagris gallapovos) were used. All turkeys underwent surgical zone II flexor tendon laceration repairs. In group one, tendons were repaired using a traditional four-strand cross-locked cruciate (Adelaide) repair, while in group two, a four-strand knotless barbed suture 3D repair was used. Postoperatively repaired digits were casted in functional position, and animals were left free to mobilise and full weight bear, resembling a high-tension post-op rehabilitation protocol. Surgeries and rehabilitations went uneventful and no major complications were noted. The turkeys were monitored for 6 weeks before the repairs were re-examined and assessed against several outcomes, such as failure rate, repair bulk, range of motion, adhesion formation and biomechanical stability. Results: In this high-tension in-vivo tendon repair experiment, traditionally repaired tendons performed significantly better when comparing absolute failure rates and repair stability after 6 weeks. Nevertheless, the knotless barbed suture repairs that remained intact demonstrated benefits in all other outcome measures, including repair bulk, range of motion, adhesion formation and operating time. Conclusions: Previously demonstrated ex-vivo benefits of flexor tendon repairs with resorbable barbed sutures may not be applicable in an in-vivo setting due to significant difference in repair stability and failure rates. Level of Evidence: Level IV (Therapeutic).

The Effects of the TSOL Knot on the Repair Strength and Gliding Resistance Following Flexor Tendon Repair

BACKGROUND

The stability of a suture knot construct has been realized as an important parameter that affects the strength of flexor tendon repairs. A novel 2-strand-overhand-locking (TSOL) knot, which is not commonly used in the clinical setting, recently was reported to increase repair strength and to decrease tendon gliding resistance in a 2-strand repair technique. The purpose of the present study was to investigate the effect of the TSOL knot on tendon repair strength and gliding resistance compared with a typical surgical knot in both 2-strand and 4-strand repair techniques using an in vitro turkey flexor tendon model.

METHODS

Sixty flexor digitorum profundus tendons from the long digit of the turkey foot were divided evenly into 4 groups and repaired with the following techniques: (1) a 2-strand modified Pennington repair with a square knot, (2) a 2-strand modified Pennington repair with a TSOL knot, (3) a 4-strand grasping cruciate repair with a square knot, and (4) a 4-strand grasping cruciate repair with a TSOL knot. Repaired tendons were tested for failure mode, gliding resistance, and repair strength at failure.

RESULTS

The repair strength and stiffness of the 4-strand repairs were significantly higher than those of the 2-strand repairs, regardless of knot type (p < 0.05). The repair strength at failure of the TSOL knot was significantly greater than that of the square knot in 2-strand repairs (p < 0.05) but not in 4-strand repairs. The gliding resistance of the TSOL knot was significantly decreased compared with that of the square knot in both 2-strand and 4-stand repairs (p < 0.05). With regard to failure mode, the TSOL knot was less likely to fail due to knot unravelling.

CONCLUSIONS

In this in vitro biomechanical study involving the use of turkey flexor tendons to compare gliding resistance and repair strength characteristics for knot-inside 2 and 4-strand repairs, the TSOL knot was associated with decreased repaired tendon gliding resistance, regardless of the number of strands used. Although the TSOL knot also increased the repair strength, the difference was only significant when 2-strand repairs were used. The results of our study support the use of the TSOL knot in the clinical setting of flexor tendon repair using 2 or 4-strand, knot-inside methods.

CLINICAL RELEVANCE

In surgical repair of flexor tendons, there is substantial interest in maximizing strength while minimizing friction. This study shows the potential utility of the TSOL knot to increase repair strength while decreasing gliding resistance, particularly in 2-strand repairs.

Secondary Flexor Tendon Reconstruction: Protocol for a Systematic Review and Meta-Analysis

Introduction:

Flexor tendon injuries of the hand and wrist involve complete or partial severance of the tendon, and primary repair is standard treatment. In cases of significantly delayed presentation, rupture of the repair or segmental tendon loss may require 1- or 2-stage secondary tendon reconstruction where a tendon graft is used. There is a risk of poor functional outcome due to stiffness and reduced range of motion which may affect patient’s employment and activities of daily living. This study seeks to systematically evaluate the current evidence to determine outcomes of secondary flexor tendon reconstruction in terms of functional outcomes, complications, patient-reported outcome measures (PROMS) and costs.

Methods:

This is a PROSPERO registered study protocol for systematic review and meta-analysis of comparative and non-comparative studies. Outcomes of intrasynovial versus extrasynovial tendon grafting and seniority of the surgeon will be analysed in addition to comparing graft weaving at the wrist and palm for both single- and two-stage tendon reconstruction. The primary outcome is functional active range of motion. Secondary outcomes are complications, PROMs and resource use. A comprehensive literature search will be conducted from 2000 to present. All studies involving secondary flexor tendon repairs will be involved, without limitation on language, and will be screened by two independent reviewers. Tools to appraise the quality of study methodology and/or bias will be used (e.g., Cochrane Collaborative Risk of Bias tool) and if feasible, a random effects meta-analysis will be conducted.

Ethics and dissemination:

Ethical approval was not required for this study. The results of this systematic review and meta-analysis will be published in a peer-reviewed journal, and presented at both national and international conferences involving hand surgeons. The data collected will allow patients to be counselled more accurately by clinicians and may suggest areas where further research could be undertaken.

Systematic review registration:

PROSPERO CRD42021296009.

Highlights

Secondary Procedures following Flexor Tendon Reconstruction

LEARNING OBJECTIVES

After studying this article, the participant should be able to: 1. Understand the indications and management options for secondary flexor tendon reconstruction, including tenolysis, tendon grafting, and tendon transfers. 2. Understand the reconstructive options for pulley reconstruction. 3. Understand the options for management of isolated flexor digitorum profundus injuries.

SUMMARY

Despite current advances in flexor tendon repair, complications can still occur following surgery. This article presents the spectrum of treatment options for secondary flexor tendon reconstruction ranging from tenolysis to one- and two-stage tendon grafting, and tendon transfers. In addition, an overview of pulley reconstruction and the treatment of isolated flexor digitorum profundus injuries are discussed. A management algorithm for secondary flexor tendon reconstruction is provided.

Relationships and Mechanisms Between Occupational Risk Factors and Distal Upper Extremity Disorders

OBJECTIVE

The relationships between workplace risk factors and upper extremity injuries from epidemiological and laboratory studies were examined.

BACKGROUND

Epidemiological studies are associated with several limitations, affecting the strength of association between risk factors and the development of injuries.

METHOD

In this narrative review, we identified epidemiological and laboratory studies (published primarily since 1997) investigating exposure to workplace risk factors (force, repetition, posture, vibration) and risk of hand/wrist tendon-related disorders, epicondylitis, and carpal tunnel syndrome (CTS).

RESULTS

Forceful exertions are strongly associated with hand/wrist tendon-related disorders, epicondylitis, and CTS. Dose-response relationships were found for epicondylitis (repetition) and CTS (posture). Interactions demonstrate multiplicative effects of risk factors for injury risk. Laboratory studies display clear associations between task demands and biomechanical measures linked to mechanisms for upper extremity injuries with animal models providing further evidence of a dose-response between risk factors and injury.

CONCLUSION

Forceful, repetitive work requiring non-neutral postures are associated with increasing risk of hand/wrist tendon-related disorders, epicondylitis, and CTS as evidenced by epidemiology studies and laboratory-based investigations of humans and animals.

APPLICATION

Understanding the relationship between exposure levels of workplace risk factors and upper extremity disorders can improve injury prevention and rehabilitation strategies.

Differentially Expressed Proteins in Intra Synovial Compared to Extra Synovial Flexor Tendon Grafts in a Rabbit Tendon Transplantation Model

&nbsp;Uncomplicated healing of grafts for tendon reconstruction remains an unsolved problem in hand surgery. Results are limited by adhesion formation and decreased strength properties, especially within the tight fibro-osseous sheath of the digits. This is especially problematic when an extra synovial tendon graft is used to replace an intra synovial flexor tendon. Compositional differences are likely to play an important role in these processes. The aim of this study was, therefore, to compare protein expression in pair-matched intra synovial tendon grafts with extra synovial tendon grafts, using a rabbit tendon injury model. We hypothesized that there would be significant differences in proteins critical for response to tensile loading and adhesion formation between the two groups. Using mass spectrometry and multivariate statistical data analysis, we found tissue-specific differences in 22 proteins, where 7 explained 93% (R2) of the variation, with a prediction of 81% (Q2). Among the highest discriminating proteins were Galectin, Histone H2A, and Periostin, which were found in a substantially larger amount in the extra synovial tendons compared to the intra synovial tendons. These findings may contribute to improved understanding of the differences in outcome seen after tendon reconstruction using tendon grafts with intra synovial and extra synovial grafts.

[Tenolysis of extensor and flexor tendons of the hand]

BACKGROUND

Unrestricted gliding of extensor and flexor tendons is essential for normal functioning of the hand. If tendon gliding is impaired, a restricted range of motion of finger joints and, finally, joint stiffness result.

OBJECTIVES

To answer the questions about the causes of tenodesis in the hand, which examinations are most informative, how tenolysis is technically performed, and what results can be expected.

METHODS

The reasons, examinations, surgical technique, and results of extensor and flexor tendon tenolysis are presented.

RESULTS

Based on the data in the literature tenolysis of flexor tendons leads to range of motion that is only 50-60% of the preoperative range of motion. In about 20% of patients, deterioration as serious as secondary tendon rupture is observed. Meaningful results of extensor tendon tenolysis have not yet been published.

CONCLUSIONS

Tenolysis of extensor and flexor tendons in the hand is a demanding surgical procedure, and in addition to detailed knowledge of anatomy and biomechanics, it requires sufficient experience-especially following the primary repair of tendon injuries. The earliest indication for tenolysis can occur at about 3 months, usually after 6 months, if continuous intensive hand therapy and splinting have not been successful. General and individual benefits and risks must be carefully weighed. The key to successful tenolysis is the patient's access to and unrestricted participation in competent postoperative treatment, ideally performed by a specialist in hand therapy, which may last for weeks or months.

Tendon With Z-Lengthening Technique and Construct Assessment: A Biomechanical Study for Use in Tendon Reconstructions

PURPOSE

Tendon reconstruction is frequently required under conditions of tendon deficiency. The authors sought a technique that could obviate the need for tendon harvest yet meet the minimum load of 45 N required for an early active motion protocol. This study was designed to determine the ideal suture construct utilizing the tendon with Z-lengthening (TWZL) technique.

METHODS

Sixty fresh-frozen cadaveric flexor digitorum profundus tendons of the index, middle, and ring fingers were randomized into 5 different TWZL construct designs using 3-0 braided polyethylene suture. Constructs were tested on an electromechanical actuator until failure was observed on the load-elongation recording. Data points on maximum yield and load at 8% strain were recorded for each construct.

RESULTS

The maximum yield data revealed the construct with a 4-core suture type configuration (construct #4) had the highest overall mean load to failure at 150 N compared with all other constructs. The construct with the highest mean load at 8% strain was that with a 4-core type repair (construct #4) at 59 N. The constructs with Krackow locking sutures (constructs #2, #3, and #4 were found to withstand a significantly higher mean load at 8% strain than those without Krackow sutures (#0 and #1). Comparison among constructs with Krackow locking sutures #2 (56 N), #3 (48 N), and #4 (59 N) did not show a significant difference in mean load at 8% strain. Construct #3, however, had an SD and 95% confidence interval that fell below the 45 N early active motion threshold, whereas both #2 and #4 had 95% confidence intervals that fell no lower than 50 N.

CONCLUSIONS

This study provides evidence that the TWZL technique utilizing either construct #2 or #4 could provide sufficient strength and reproducibility for tendon reconstruction.

CLINICAL RELEVANCE

The study describes the application of the TWZL technique for utilization in tendon reconstruction and quantifies differences in the yield strengths of the 5 proposed constructs.

Flexor tendon grafts for pulley reconstruction - Morphological aspects

BACKGROUND

Pulleys are crucial to convert flexor tendon excursion into angular motion at the metacarpophalangeal and interphalangeal joints. Loss of pulley function can lead to significant impairment of hand function and may require surgical reconstruction. This reconstruction can be achieved using different flexor tendons grafts, such as the intrasynovial flexor digitorum superficialis (FDS) or the extrasynovial palmaris longus (PL). However, there is limited knowledge on the micromorphology of human pulleys and the suitability of flexor tendon grafts for their reconstruction remains elusive.

METHODS

In the present cadaver study A2 and A4 pulleys were compared with FDS and PL tendons by means of scanning electron microscopy (SEM), histology and immunohistochemistry. Surface morphology, core structure and vascularization of the specimens were analyzed.

RESULTS

SEM imaging of the gliding surfaces revealed morphological differences between tendons and pulleys. Moreover, the core structure of FDS samples was characterized by bundles of individual collagen fibrils whereas PL tendons exhibited a less hierarchical microstructure. In contrast, pulleys consisted of lamellar sheets of densely packed collagen fibrils. Finally, immunohistochemical analyses revealed that the flexor tendons and pulleys contain similar numbers of CD31⁺ microvessels, indicating a comparable tissue vascularization.

CONCLUSION

This study provides novel SEM and immunohistochemical insights into the micromorphology of human pulleys and flexor tendon grafts. Intrasynovial flexor tendons may be particularly suitable for pulley reconstruction and preserving the paratenon may be crucial for graft revascularization.

Flexor Tendon Grafting Using Extrasynovial Tendons Followed by Early Active Mobilization

Purpose

This study evaluated the outcomes of early active mobilization after flexor tendon grafts using extrasynovial tendons with a novel distal fixation technique.

Methods

This study was a retrospective case series. The flexor digitorum profundus (FDP) tendons of 7 digits in 7 patients were reconstructed with extrasynovial tendons, which included the palmaris longs, plantaris, and extensor digitorum longus, in a single- or 2-stage procedure between 2008 and 2017. Of the 7 patients, 6 were male and the average patient age was 48 years. The injuries involved 2 middle, 2 ring, and 3 little fingers. The tendons were sutured into the appropriate FDP tendon proximally using end-weave anastomosis; the distal end of the graft was fixed to the distal stump of the FDP using an interlacing suture or a small bone anchor combined with the pull-through technique. The digits were mobilized with a combination of active extension and passive and active flexion in a protective orthosis during the first 6 weeks after surgery. Average follow-up was 18 months. We measured active and passive digit motion both before tendon grafting and at the final evaluation. Outcomes were graded by the LaSalle formula to assess staged flexor tendon reconstruction.

Results

Average passive range of motion (ROM) of the proximal and distal interphalangeal joints before flexor tendon grafting was 146° (SD, 22°). Mean active ROM of these joints at the final evaluation was 123° (SD, 34°). Using the LaSalle formula, mean recovery of active motion was 83%. We encountered no grafted tendon rupture and no finger required tenolysis.

Conclusions

Our proximal and distal fixation techniques allowed the autologous extrasynovial tendon grafts to withstand the stress encountered during early active mobilization with good postoperative ROM and minimal complications.

Type of study/level of evidence

Therapeutic I.

Evaluation of hollow mesh augmentation on the biomechanical properties of the flexor tendon repaired with modified Kessler technique

Purpose

The aim of the study was to test flexor tendon repair with a novel hollow mesh suture augmentation served as a centre core cable [Triple-C (Tri-C)] in an in vitro study using a turkey model.

Methods

Forty long digits from white turkey feet were divided into the following four groups based on repair techniques: Group 0, intact tendon without repair; Group 1, modified Kessler (MK) repair only (MKo); Group 2, MK repair plus Tri-C (MK ​+ ​Tri-C); and Group 3, MK repair plus an additional outside knot plus Tri-C (MK-2knots ​+ ​Tri-C). Mechanical evaluations were performed for all groups.

Results

The frictions of the two groups with Tri-C were not significantly different than those of the MKo group. The ultimate tensile strength of the MK ​+ ​Tri-C group was not significantly different from that of the MKo group or the MK-2knots ​+ ​Tri-C group. In contrast, the MK-2knots ​+ ​Tri-C group had a significantly greater ultimate tensile strength compared with that of the MKo group. Forces at 2-mm gap formation in the groups with Tri-C were significantly stronger than that of MK alone.

Conclusion

Our data have demonstrated that MK repair augmented with the centre hollow mesh suture increased failure strength without inducing increased friction.

The translational potential of this article

Our study elucidates that a Tri-C augmentation designed in this study can achieve mechanical enhancements without increasing the repaired tendon friction. Hence, this novel technique has potential biological validity and clinical application.

Lipid-hyaluronan synergy strongly reduces intrasynovial tissue boundary friction

Hyaluronan (HA)-lipid layers on model (mica) surfaces massively reduce friction as the surfaces slide past each other, and have been proposed, together with lubricin, as the boundary layers accounting for the extreme lubrication of articular cartilage. The ability of such HA-lipid complexes to lubricate sliding biological tissues has not however been demonstrated. Here we show that HA-lipid layers on the surface of an intrasynovial tendon can strongly reduce the friction as the tendon slides within its sheath. We find a marked lubrication synergy when combining both HA and lipids at the tendon surface, relative to each component alone, further enhanced when the polysaccharide is functionalized to attach specifically to the tissue. Our results shed light on the lubricity of sliding biological tissues, and indicate a novel approach for lubricating surfaces such as tendons and, possibly, articular cartilage, important, respectively, for alleviating function impairment following tendon injury and repair, or in the context of osteoarthritis. STATEMENT OF SIGNIFICANCE: Lubrication breakdown between sliding biological tissues is responsible for pathologies ranging from dry eye syndrome to tendon-injury repair impairment and osteoarthritis. These are increasing with human longevity and impose a huge economic and societal burden. Here we show that synergy of hyaluronan and lipids, molecules which are central components of synovial joints and of the tendon/sheath system, can strongly reduce friction between sliding biological tissues (the extrasynovial tendon sliding in its sheath), relative to untreated tissue or to either component on its own. Our results point to the molecular origins of the very low friction in healthy tendons and synovial joints, as well as to novel treatments of lubrication breakdown in these organs.

The effects of lyophilization on flexural stiffness of extrasynovial and intrasynovial tendon

Tendon or ligament reconstructions often use autologous or allogenic tendons from either extrasynovial or intrasynovial sources. Allograft tendons must be lyophilized for preservation before transplantation, a process which can impact mechanical properties of the graft. Reconstituted graft properties that are similar to native tendon are desirable. Although tensile and compressive properties of tendons have been investigated, there is a paucity of information describing flexural properties of tendon, which can impact the gliding resistance. This study aims to design a testing method to quantify tendon flexural modulus, and investigate the effects of lyophilization/rehydration procedures on tendon flexibility. A total of 20 peroneus longus tendons (extrasynovial) and 20 flexor digitorum profundus tendons (intrasynovial) were collected. Ten of each tendon were processed with 5 freeze-thaw cycles followed by lyophilization and rehydration with saline solution (0.9%). Bend testing was conducted on tendons to quantify the flexural modulus with and without processing. As canine FDP tendons contain fibrous and fibrocartilaginous tissue regions, the flexural moduli were measured in both regions. Flexural modulus of rehydrated, lyophilized extrasynovial PL tendon was significantly lower than that of similarly processed intrasynovial FDP tendon (p < 0.001). Flexural moduli of both the fibrocartilaginous and non-fibrocartilaginous regions of intrasynovial tendon significantly increased after lyophilization (p < 0.001). The flexural modulus of the fibrocartilaginous region was significantly higher than that of the non-fibrocartilaginous region in intrasynovial tendon (p < 0.001). Lyophilization significantly increases the flexural modulus of extrasynovial and intrasynovial tendons, and flexural modulus differs significantly between these two tendon types. Increases in stiffness caused by lyophilization may impact the mechanical performance of the allograft in vivo.

Comprehensive simulation on morphological and mechanical properties of trigger finger - A cadaveric model

Trigger finger has long been a common disorder in hand orthopedics. To clarify the unknown causative factors regarding the disease, numerous experiments were done on human cadavers, including tendon forces, tendon moment arm, mechanical properties of the pulley, gliding resistance, etc. However, most of these studies were conducted on normal fingers. As the etiology of trigger finger is still controversial on whether it is an outcome of tendon nodule or pulley scarring, in this study, a trigger finger model was built combining both the nodule created by silicone gel injection and pulley constriction by external compression. Indentation and gliding resistance tests were performed on cadaveric specimens to verify the model. Results showed that after silicone gel injection into the tendon, a significant increase in thickness was found. In addition, no significant difference was found in the toe region compressive modulus of the tendon after injection. Moreover, maximum, drop of gliding resistance and work of extension were all found to be significantly larger as the severity of triggering increased. Our results indicated we have developed a feasible cadaver model simulating trigger finger nodule which could be utilized for further experiments to elucidate other causative factors and biomechanical features of trigger finger in the future.

Comparison of Autograft and Allograft with Surface Modification for Flexor Tendon Reconstruction: A Canine in Vivo Model

BACKGROUND

Flexor tendon injury is common, and tendon reconstruction is indicated clinically if the primary repair fails or cannot be performed immediately after tendon injury. The purpose of the current study was to compare clinically standard extrasynovial autologous graft (EAG) tendon and intrasynovial allogeneic graft (IAG) that had both undergone biolubricant surface modification in a canine in vivo model.

METHODS

Twenty-four flexor digitorum profundus (FDP) tendons from the second and fifth digits of 12 dogs were used for this study. In the first phase, a model of failed FDP tendon repair was created. After 6 weeks, the ruptured FDP tendons with a scarred digit were reconstructed with the use of either EAG or IAG tendons treated with carbodiimide-derivatized hyaluronic acid and lubricin. At 12 weeks after tendon reconstruction, the digits were harvested for functional, biomechanical, and histologic evaluations.

RESULTS

The tendon failure model was a clinically relevant and reproducible model for tendon reconstruction. The IAG group demonstrated improved digit function with decreased adhesion formation, lower digit work of flexion, and improved graft gliding ability compared with the EAG group. However, the IAG group had decreased healing at the distal tendon-bone junction. Our histologic findings verified the biomechanical evaluations and, further, showed that cellular repopulation of allograft at 12 weeks after reconstruction is still challenging.

CONCLUSIONS

FDP tendon reconstruction using IAG with surface modification has some beneficial effects for reducing adhesions but demonstrated inferior healing at the distal tendon-bone junction compared with EAG. These mixed results indicate that vitalization and turnover acceleration are crucial to reducing failure of reconstruction with allograft.

CLINICAL RELEVANCE

Flexor tendon reconstruction is a common surgical procedure. However, postoperative adhesion formation may lead to unsatisfactory clinical outcomes. In this study, we developed a potential flexor tendon allograft using chemical and tissue-engineering approaches. This technology could improve function following tendon reconstruction.

Gliding Resistance After Epitendinous-First Repair of Flexor Digitorum Profundus in Zone II

PURPOSE

The importance of flexor tendon repair with both core and epitendinous suture placement has been well established. The objective of this study was to determine whether suture placement order affects gliding resistance and bunching in flexor digitorum profundus tendons in a human ex vivo model.

METHODS

The flexor digitorum profundus tendons of the index, middle, ring, and little fingers of paired cadaver forearms were tested intact for excursion and mean gliding resistance in flexion and extension across the A2 pulley. Tendons were subsequently transected and repaired with either an epitendinous-first (n = 12) or a control (n = 12) repair. Gliding resistance of pair-matched tendons were analyzed at cycle 1 and during the steady state of tendon motion. The tendon repair breaking strength was also measured.

RESULTS

The mean steady state gliding resistance was less for the epitendinous-first repair than for the control repair in flexion (0.61 N vs 0.72 N) and significantly less in extension (0.68 N vs 0.85 N). Similar results were seen for cycle 1. None of the repairs demonstrated gap formation; however, control repairs exhibited increased bunching. Load to failure was similar for both groups.

CONCLUSIONS

The order of suture placement for flexor tendon repair is important. Epitendinous-first repair significantly decreased mean gliding resistance, allowed for easier placement of core sutures, and resulted in decreased bunching.

CLINICAL RELEVANCE

Epitendinous-first flexor tendon repairs may contribute to improved clinical outcomes compared with control repairs by decreasing gliding resistance and bunching.

Outcomes of grafting intrasynovial tendons of the toes to the hands in 10 patients: a preliminary report

Ten patients had intrasynovial tendon grafting harvested from the toes for secondary flexor tendon reconstruction in nine fingers and one thumb in our institutes from 2009 to 2014. These patients were followed for a mean of 15 (range: 8-36) months. The ranges of total active motion of the proximal and distal interphalangeal joints of these nine fingers were 143° (range: 108-175°) and of the metacarpophalangeal and interphalangeal joints of one thumb were 110°. In conclusion, this technique is feasible and gives a good result when successful but with a high complication rate. Level of Evidence IV.

Turkey model for flexor tendon research: in vitro comparison of human, canine, turkey, and chicken tendons

BACKGROUND

Flexor tendon injuries are one of the most common hand injuries and remain clinically challenging for functional restoration. Canine and chicken have been the most commonly used animal models for flexor tendon-related research but possess several disadvantages. The purpose of this study was to explore a potential turkey model for flexor tendon research.

METHODS

The third digit from human cadaveric hands, canine forepaws, turkey foot, and chicken foot were used for this study. Six digits in each of four species were studied in detail, comparing anatomy of the flexor apparatus, joint range of motioņ tendon excursion, tendon cross-sectional area, work of flexion, gliding resistance at the level of the A2 pulley, modulus of elasticity, suture retention strength, and histology across species.

RESULTS

Anatomically, the third digit in the four species displayed structural similarities; however, the tendon cross-sectional area of the turkey and human were similar and larger than canine and chicken. Furthermore, the turkey digit resembles the human's finger with the lack of webbing between digits, similar vascularization, tendon excursion, work of flexion, gliding resistance, mechanical properties, and suture holding strength. More importantly, human and turkey tendons were most similar in histological appearance.

CONCLUSIONS

Turkey flexor tendons have many properties that are comparable to human flexor tendons which would provide a clinically relevant, economical, nonhuman companion large animal model for flexor tendon research.

Delineation of the mechanisms of tendon gliding resistance within the carpal tunnel

BACKGROUND

Forceful, high-velocity, and repetitive manual hand tasks contribute to the onset of carpal tunnel syndrome. This study aimed to isolate and identify mechanisms that contribute to tendon gliding resistance in the carpal tunnel.

METHODS

Eight human cadaver hands (four pairs) were used. Tendon gliding resistance (force, energy, and stiffness) was measured under different conditions: with intact and with divided subsynovial connective tissue, at 2mm/s and 60mm/s tendon excursion velocity, and with and without relaxation time before tendon excursion.

RESULTS

Subsynovial connective tissue stretching substantially contributed to increased gliding resistance force and energy during higher tendon excursion velocities, and subsynovial connective tissue stiffening was observed. Poroelastic properties of the tendon (and possibly the subsynovial connective tissue) also appear to be involved because relaxation time significantly increased gliding resistance force and energy (P<0.01), and the difference in energy and force between high- and low-velocity tendon excursions increased with relaxation time (P=0.01 and P<0.01). Lastly, without relaxation time, no difference in force and energy was observed (P=0.06 and P=0.60), suggesting contact friction.

INTERPRETATION

These findings are consistent with the hypothesis that the mechanics of tendon motion within the carpal tunnel are affected by the integrity of the subsynovial connective tissue. While not tested here, in carpal tunnel syndrome this tissue is known to be the fibrotic, thickened, and less-fluid-permeable. An extrapolation of our findings suggests that these changes in the subsynovial connective tissue of carpal tunnel syndrome patients could increase contact friction and carpal tunnel pressure.

Effects of lubricant and autologous bone marrow stromal cell augmentation on immobilized flexor tendon repairs

The purpose of the study was to test a novel treatment that carbodiimide-derivatized-hyaluronic acid-lubricin (cd-HA-lubricin) combined cell-based therapy in an immobilized flexor tendon repair in a canine model. Seventy-eight flexor tendons from 39 dogs were transected. One tendon was treated with cd-HA-lubricin plus an interpositional graft of 8 × 10(5) BMSCs and GDF-5. The other tendon was repaired without treatment. After 21 day of immobilization, 19 dogs were sacrificed; the remaining 20 dogs underwent a 21-day rehabilitation protocol before euthanasia. The work of flexion, tendon gliding resistance, and adhesion score in treated tendons were significantly less than the untreated tendons (p < 0.05). The failure strength of the untreated tendons was higher than the treated tendons at 21 and 42 days (p < 0.05). However, there is no significant difference in stiffness between two groups at day 42. Histologic analysis of treated tendons showed a smooth surface and viable transplanted cells 42 days after the repair, whereas untreated tendons showed severe adhesion formation around the repair site. The combination of lubricant and cell treatment resulted in significantly improved digit function, reduced adhesion formation. This novel treatment can address the unmet needs of patients who are unable to commence an early mobilization protocol after flexor tendon repair.

Surface Modification with Chemically Modified Synovial Fluid for Flexor Tendon Reconstruction in a Canine Model in Vivo

BACKGROUND

Functional restoration is the major concern after flexor tendon reconstruction in the hand. The purpose of the present study was to investigate the effects of modifying the surface of extrasynovial tendon autografts with carbodiimide-derivatized synovial fluid with gelatin (cd-SF-G) on functional outcomes of flexor tendon reconstruction using a canine model.

METHODS

The second and fifth flexor digitorum profundus tendons from eleven dogs were transected and repaired in zone II. The dogs then had six weeks of free activity leading to tendon rupture and scar formation (the repair-failure phase). In the reconstruction phase, two autologous peroneus longus tendons from each dog were harvested; one tendon was coated with cd-SF-G and the other, with saline solution, as a control. A non-weight-bearing rehabilitation protocol was followed for six weeks after reconstruction. The digits were then harvested and evaluations of function, adhesion status, gliding resistance, attachment strength, cell viability, and histology were performed.

RESULTS

The tendons coated with cd-SF-G demonstrated significantly lower values (mean and standard deviation) compared with the saline-solution group for work of flexion (0.63 ± 0.24 versus 1.34 ± 0.42 N-mm/deg), adhesion score (3.5 ± 1.6 versus 6.1 ± 1.3), proximal adhesion breaking force (8.6 ± 3.2 versus 20.2 ± 10.2 N), and gliding resistance (0.26 ± 0.08 versus 0.46 ± 0.22 N) (p < 0.05). There was no significant difference between the cd-SF-G and saline-solution groups (p > 0.05) in distal attachment-site strength (56.9 ± 28.4 versus 77.2 ± 36.2 N), stiffness (19 ± 7.5 versus 24.5 ± 14.5 N/mm), and compressive modulus from indentation testing (4.37 ± 1.26 versus 3.98 ± 1.24 N/mm). Histological analysis showed that tendons coated with cd-SF-G had smoother surfaces and demonstrated tendon-to-bone and tendon-to-tendon incorporation. No significant difference in viable cell count between the two groups was observed on tendon culture.

CONCLUSIONS

Modification of the flexor tendon surface with cd-SF-G significantly improved digital function and reduced adhesion formation without affecting graft healing and stiffness.

CLINICAL RELEVANCE

This study used native synovial fluid as a basic lubricating reagent to treat a tendon graft in vivo, a novel avenue for improving clinical outcomes of flexor tendon reconstruction. This methodology may also apply to other surgical procedures where postoperative adhesions impair function.

Evidence-based flexor tendon repair

The goal of flexor tendon repair is to achieve normal range of motion of the finger or thumb. The surgical approach depends on the level of injury. Multistrand core suture repairs are recommended for primary flexor tendon repair. It is evident that at least 4 strands are required to an initiate and active range of motion protocol. The epitendinous suture can also increase the strength of the repair. Careful attention to the post-operative therapy regiment is critical to a successful repair.

[Use of tissue engineering in the reconstruction of flexor tendon injuries of the hand]

In his literary analysis, the author describes a novel method applied in the reconstruction of flexor tendon injuries of the hand. This procedure is named tissue engineering, and it is examined mainly under experimental circumstances. After definition of the method and descriptions of literary preliminaries the author discusses the healing process of the normal tendon tissue, then development of the scaffold, an important step of tissue engineering is described. After these topics the introduction of the pluripotent mesenchymal stem cells into the scaffold, and proliferation of these cells and development of the sliding systems are presented. The mechanical resisting ability of the formed tendon tissue is also discussed. Finally, the author concludes that as long as results of experimental research cannot be successfully applied into clinical practice, well-tried tendon reconstruction operations and high quality postoperative rehabilitation are needed.

Effect of triggering and entrapment on tendon gliding properties following digital flexor tendon laceration: in vitro study on turkey tendon

The optimal management of partial flexor tendon laceration is controversial and remains a clinical challenge. Abnormal tendon gliding (triggering and entrapment) was assessed at the A2 pulley in 40 turkey tendons in three groups: intact, partially divided (palmar or lateral), and trimmed. Testing was of gliding resistance and friction coefficient at 30° and 70° of flexion, loaded with 2 and 4 N. We observed for triggering and entrapment. The changes in gliding properties were compared and analysed using Wilcoxon matched pair testing. A significant difference was found in the change in gliding properties of intact to lacerated and lacerated to trimmed tendons and between tendons that glided normally compared with those exhibiting triggering or entrapment. This suggests that palmar and lateral lacerations which, through clinical examination and visualization, are found to glide normally should be treated with early mobilization. However, partial lacerations that exhibit triggering or entrapment should be trimmed.

The effects of biological lubricating molecules on flexor tendon reconstruction in a canine allograft model in vivo

BACKGROUND

Using allograft is an attractive alternative for flexor tendon reconstruction because of the lack of donor-site morbidity, and better matching to the intrasynovial environment. The purpose of this study was to use biological lubricant molecules to modify the graft surface to decrease adhesions and improve digit function.

METHODS

Twenty-eight flexor digitorum profundus tendons from the second and fifth digits of 14 dogs were lacerated and repaired to create a model with repair failure and scar digit for tendon reconstruction. Six weeks after the initial operation, the tendons were reconstructed with flexor digitorum profundus allograft tendons obtained from canine cadavers. One graft tendon in each dog was treated with saline as a control and the other was treated with carbodiimide-derivatized hyaluronic acid and gelatin plus lubricin. Six weeks postoperatively, digit function, graft mechanics, and biology were analyzed.

RESULTS

Allograft tendons treated with carbodiimide-derivatized hyaluronic acid-lubricin had decreased adhesions at the proximal tendon/graft repair and within the flexor sheath, improved digit function, and increased graft gliding ability. The treatment also reduced the strength at the distal tendon-to-bone repair, but the distal attachment rupture rate was similar for both graft types. Histologic evaluation showed that viable cells migrated to the allograft, but these were limited to the tendon surface.

CONCLUSIONS

Carbodiimide-derivatized hyaluronic acid-lubricin treatment of tendon allograft improves digit functional outcomes after flexor tendon reconstruction. However, delayed bone-to-tendon healing should be a caution. Furthermore, the cell infiltration into the allograft tendon substance should be a target for future studies, to shorten the allograft self-regeneration period.

Tissue engineering in flexor tendon surgery: current state and future advances

Tissue engineering of flexor tendons addresses a challenge often faced by hand surgeons: the restoration of function and improvement of healing with a limited supply of donor tendons. Creating an engineered tendon construct is dependent upon understanding the normal healing mechanisms of the tendon and tendon sheath. The production of a tendon construct includes: creating a three-dimensional scaffold; seeding cells within the scaffold; encouraging cellular growth within the scaffold while maintaining a gliding surface; and finally ensuring mechanical strength. An effective construct incorporates these factors in its design, with the ultimate goal of creating tendon substitutes that are readily available to the reconstructive hand surgeon.

Intrasynovial tendon graft for chronic flexor tendon laceration of the finger: a case report

We present the case of a patient with flexor digitorum profundus tendon laceration at the A2 pulley level caused by an injury to the base of the right ring finger by a knife. The patient was treated by flexor tendon reconstruction from the palm to the fingertip by using the left second toe flexor tendon as a graft, which improved the active range of motion. Further improvement was achieved by subsequent tenolysis, which eventually restored nearly normal function. Our experience with this case indicates that the intrasynovial tendon is a reasonable graft source for the synovial space in fingers and may enable restoration of excellent postoperative function.

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.

Gliding resistance and modifications of gliding surface of tendon: clinical perspectives

The smooth gliding of the normal human digital flexor is maintained by synovial fluid lubrication and lubricants bound to the tendon surface. This system can be disrupted by degenerative conditions such as trigger finger, or by trauma. The resistance to tendon gliding after surgical repair of the lacerated digital flexor tendon relates to location of suture knots, exposure of suture materials, and type of surgical repair and materials. Restoration of a functioning gliding surface after injury can be helped by using low-friction, high-strength suture designs, therapy that enables gliding, and the addition of lubricants to the tendon surface.

Effects of stress deprivation on lubricin synthesis and gliding of flexor tendons in a canine model in vivo

BACKGROUND

Lubricin facilitates boundary lubrication of cartilage. The synthesis of lubricin in cartilage is regulated by mechanical stimuli, especially shear force. Lubricin is also found in flexor tendons. However, little is known about the effect of mechanical loading on lubricin synthesis in tendons or about the function of lubricin in flexor tendons. The purpose of this study was to investigate the relationship of mechanical loading to lubricin expression and gliding resistance of flexor tendons.

METHODS

Flexor tendons were harvested from canine forepaws that had been suspended without weight-bearing for twenty-one days and from the contralateral forepaws that had been allowed free motion. Lubricin expression in each flexor tendon was investigated with real-time RT-PCR (reverse transcription polymerase chain reaction) and immunohistochemistry. Lubricin in the flexor tendon was extracted and quantified with ELISA (enzyme-linked immunosorbent assay). The friction between the flexor tendon and the proximal pulley was measured.

RESULTS

The non-weight-bearing flexor tendons had a 40% reduction of lubricin expression (p < 0.01) and content (p < 0.01) compared with the flexor tendons in the contralateral limb. However, the gliding resistance of the tendons in the non-weight-bearing limb was the same as that of the tendons on the contralateral, weight-bearing side.

CONCLUSIONS

Mechanical loading affected lubricin expression in flexor tendons, resulting in a 40% reduction of lubricin content, but these changes did not affect the gliding resistance of the flexor tendons.

The effects of hylan g-f 20 surface modification on gliding of extrasynovial canine tendon grafts in vitro

PURPOSE

Studies have shown that a lubricant exogenously applied on extrasynovial tendon surfaces can reduce the gliding resistance after flexor tendon repair; however, the reagents that have been tested are solely for experimental testing and are not available for clinical use. The purpose of this study was to investigate the effect of exogenously applied hylan G-F 20, a U.S. Food and Drug Administration-approved hyaluronic acid for the treatment of osteoarthritis, on extrasynovial tendon gliding resistance in an in vitro canine model.

METHODS

Twenty-four canine peroneus longus (PL) tendons and proximal pulleys of the ipsilateral paws were treated with 1 of 3 solutions: saline, carbodiimide derivatized hylan G-F 20, or unmodified hylan G-F 20. The gliding resistance of each tendon preparation was then measured over 1000 cycles in a saline bath.

RESULTS

After 1,000 cycles, the gliding resistance of the PL tendons treated with unmodified hylan G-F 20 decreased significantly compared with the saline-treated tendons. The gliding resistance of the PL tendons treated with modified hylan G-F 20 increased significantly compared with the saline group.

CONCLUSIONS

The PL tendons treated with pure hylan G-F 20 showed a positive effect on the gliding resistance.

CLINICAL RELEVANCE

The results of this in vitro canine study suggest that exogenously applied hylan G-F 20 improves gliding of the extrasynovial tendon graft. This material may be capable of reducing friction over flexor tendon repair sites and flexor tendon grafts.

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.

Surface treatment of flexor tendon autograft and allograft decreases adhesion without an effect of graft cellularity: a pilot study

BACKGROUND

Flexor tendon grafting is often required to reconstruct a failed tendon repair. Previous reports have demonstrated flexor grafts coated with lubricants such as carbodiimide derivatized hyaluronic acid (cd-HA) decrease adhesion formation and improve digit function. However, whether this surface modification would affect graft adhesion and cellularity is unknown.

QUESTIONS/PURPOSES

Adhesion score and the cellularity of the graft of untreated and cd-HA surface-modified autograft and allograft tendons were studied using a canine forepaw in vivo model.

METHODS

The peroneus longus tendons (n = 6) and flexor digitorum profundus tendons (n = 8) were used as extrasynovial autograft and intrasynovial allograft, respectively. The flexor digitorum profundus (FDP) tendons in the second and fifth digits in each dog were reconstructed with one digit treated with cd-HA and the other treated with saline as a control. Six weeks after surgery, the grafted tendons were harvested for histological evaluation with hematoxylin and eosin staining. During dissection, the adhesions were observed and scored.

RESULTS

The adhesion score was greatest in the extrasynovial autograft without surface modification and the least in the intrasynovial allograft with surface modification. Autograft tendons had a higher cell density than the allografts regardless of surface treatment. Cd-HA graft treatment did not affect cellularity when compared with controls.

CONCLUSIONS

Our observations suggest surface modification of a tendon graft with cd-HA decreased the adhesion formation without altering the cellularity in either autologous or allograft tendon. We therefore presume this surface modification would not adversely affect graft healing.

The effects of oblique or transverse partial excision of the A2 pulley on gliding resistance during cyclic motion following zone II flexor digitorum profundus repair in a cadaveric model

PURPOSE

To compare the gliding resistance of flexor tendons after oblique versus transverse partial excision of the A2 pulley in a human cadaveric model, to determine the effect of the angle of pulley trimming.

METHODS

We obtained 36 human flexor digitorum profundus tendons from the index through the little finger and repaired them with a modified Massachusetts General Hospital suture using 4-0 FiberWire. We repaired all tendons with a similar epitendinous stitch. We randomly assigned the tendons to 1 of 3 groups: intact pulley, transverse partial excision, or oblique partial excision. We measured peak and normalized peak gliding resistance between the repairs and the A2 pulley during 1,000 cycles of simulated motion.

RESULTS

There was no significant difference in the peak or normalized peak gliding resistance at any cycle among the 3 groups.

CONCLUSIONS

Both transverse and oblique trimming of the A2 pulley had similar effects on the peak and normalized gliding resistance after flexor tendon repair.

CLINICAL RELEVANCE

When partial pulley resection is needed after flexor tendon repair, the transverse or oblique trimming of pulley edge does not affect repaired tendon gliding resistance.

Tendon injuries of the hand

Tendon injuries are the second most common injuries of the hand and therefore an important topic in trauma and orthopedic patients. Most injuries are open injuries to the flexor or extensor tendons, but less frequent injuries, e.g., damage to the functional system tendon sheath and pulley or dull avulsions, also need to be considered. After clinical examination, ultrasound and magnetic resonance imaging have proved to be important diagnostic tools. Tendon injuries mostly require surgical repair, dull avulsions of the distal phalanges extensor tendon can receive conservative therapy. Injuries of the flexor tendon sheath or single pulley injuries are treated conservatively and multiple pulley injuries receive surgical repair. In the postoperative course of flexor tendon injuries, the principle of early passive movement is important to trigger an “intrinsic” tendon healing to guarantee a good outcome. Many substances were evaluated to see if they improved tendon healing; however, little evidence was found. Nevertheless, hyaluronic acid may improve intrinsic tendon healing.

The effect of core suture flexor tendon repair techniques on gliding resistance during static cycle motion and load to failure: a human cadaver study

The purpose of this study was to describe a modification of the Massachusetts General Hospital (MMGH) tendon repair and to compare it with three other suture techniques. Twenty human flexor digitorum profundus (FDP) tendons were randomly assigned to the modified Pennington (MP) suture and the MMGH suture. These were compared to the modified Kessler (MK) and Massachusetts General Hospital (MGH) sutures, using data from a previous study. All tendons were repaired with a similar epitendinous stitch and core sutures of 4-0 FiberWire. There was no significant difference in the normalized gliding resistance within the two-strand or four-strand core repair groups. The MP suture had significantly higher 2 mm gap force and ultimate load to failure than the MK suture. The MMGH suture had significantly higher 2 mm gap force and maximum failure ultimate load than the MGH suture. All repairs failed by knot unravelling.

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.

Compressive properties of cd-HA-gelatin modified intrasynovial tendon allograft in canine model in vivo

Although we sometimes use the intrasynovial tendon allograft as a donor, the gliding ability of allograft prepared by lyophilization is significantly decreased. The gliding ability of the grafted tendon after tendon reconstruction is very important because the high gliding resistance causes more adhesion and leads to poor clinical results. We recently revealed that tendon surface treatment with a carbodiimide derivatized HA (cd-HA)-gelatin mixture for intrasynovial tendon allograft significantly improved its gliding ability. The purpose of this study was to investigate whether this cd-HA-gelatin treatment affects the tendon mechanical property or not. A total of 40 flexor digitorum profundus (FDP) tendons from canines were evaluated for compressive property by using indentation test. Indentation stiffness was measured for normal tendon, rehydrated tendon after lyophilization, rehydrated tendon after lyophilization that was implanted 6 weeks in vivo, and cd-HA treated rehydrated tendon after lyophilization that was implanted 6 weeks in vivo. The results for all groups showed no significant difference in the tendon compressive properties. The findings of these results demonstrate that cd-HA treatment for intrasynovial tendon allograft is an excellent method to improve the tendon gliding ability after lyophilization without changing the compressive property of donor tendon.

Application of carbodiimide derivatized synovial fluid to enhance extrasynovial tendon gliding ability

PURPOSE

To investigate the effects of surface modification of extrasynovial tendon with a carbodiimide derivatized synovial fluid (SF) on the gliding ability of extrasynovial tendon for a possible tendon graft application.

METHODS

We used 63 peroneus longus tendons from canine hind legs. We immediately assessed 3 tendons morphologically using a scanning electron microscope (SEM); these served as the normal tendon group. The other 60 tendons were randomly assigned to each of 6 experimental groups treated with (1) control (saline); (2) 1% 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) plus 1% N-hydroxysuccinimide (NHS) (cd only); (3) 1% EDC/NHS plus 10% gelatin (cd-G); (4) SF plus 1% EDC/NHS plus 10% gelatin (cd-SF-G); (5) SF only; or (6) SF plus 1% EDC/NHS (cd-SF). We measured the gliding resistance for 1,000 cycles of simulated flexion-extension motion. We also observed the tendon surface smoothness by SEM.

RESULTS

Compared with the first cycle in each group, the gliding resistance after 1,000 cycles of tendon motion was significantly increased in the control, cd only, cd-gelatin, SF only, and cd-SF groups (p<.05). In contrast, we found no significant difference in gliding resistance between the first cycle and 1,000 cycles for the cd-SF-G-treated group. In addition, the gliding resistance in the cd-SF, cd-G, and cd-SF-G groups was significantly lower than the control group after 1,000 cycles of tendon motion (p<.05) and the gliding resistance of the cd-SF-G group was significantly lower than both the cd-G and cd-SF groups (p<.05). On SEM, the surface treated with cd-SF-G was smooth after 1,000 cycles, whereas the other surfaces were rough.

CONCLUSIONS

Surface modification of extrasynovial tendon with cd-SF-G improves tendon gliding ability. This treatment may be useful clinically in improving the outcomes of tendon autografts.

Effects of different temperatures, velocities and loads on the gliding resistance of flexor digitorum profundus tendons in a human cadaver model

The purpose of this study was to investigate the effects of temperature, velocity and load on the gliding resistance (GR) of flexor digitorum profundus (FDP) tendons in a human cadaver model. A total of 40 FDP tendons from the index through small digits of ten human cadavers were tested to assess the effect of temperature (4, 23 or 36 °C), velocity (2, 4, 6, 8, 10 or 12 mm/s) and load (250, 500, 750, 1000, 1250 and 1500 g) on GR. The mean GR at 4 °C was significantly higher than the mean GR at 36 °C (p<0.0066). There was no significant difference in the mean GR of the tested velocities. The mean GR was proportional to load, with each successive load having significantly higher GR than the loads before it (all p<0.001). There was no significant difference in the mean GR by digit. In this in vitro model, we have demonstrated that tendon gliding resistance is proportional to load, independent of velocity and somewhat affected by temperature. We conclude that it is important to specify these conditions when reporting gliding resistance, especially load and temperature.

Effect of core suture technique and type on the gliding resistance during cyclic motion following flexor tendon repair: a cadaveric study

We investigated the effects of two suture techniques using three suture types in a human model in vitro. We obtained 60 flexor digitorum profundus (FDP) tendons from cadavers and measured the gliding resistance during 1,000 cycles of simulated flexion-extension motion and load to failure of six groups: the modified Kessler (MK) repair using 3-0 coated, braided polyester (Ethibond, Ethicon, Somerville, NJ), 3-0 coated, braided polyester/monofilament polyethylene composite (FiberWire®; Arthrex, Naples, FL), or 4-0 FiberWire; and the Massachusetts General Hospital (MGH) repair using 3-0 Ethibond, 3-0 FiberWire, or 4-0 FiberWire. The 3-0 Ethibond MGH suture had significantly higher ultimate load to failure than the 3-0 or 4-0 FiberWire MK suture. The 3-0 and 4-0 FiberWire MGH sutures had significantly higher load to failure than the three MK groups. The gliding resistances of the three MGH groups were significantly higher than that of the three corresponding MK groups. The MGH repair had more gliding resistance than an MK repair, even when comparing large diameter suture in the MK repair with smaller diameter suture in the MGH repair. In this study, suture technique was more important in predicting repair load to failure and gliding resistance than the nature or caliber of the suture material that was used.

The effect of epitendinous suture technique on gliding resistance during cyclic motion after flexor tendon repair: a cadaveric study

PURPOSE

To investigate the effects of motion following repair with a modified Kessler core suture and 5 different epitendinous suture designs on the gliding resistance, breaking strength, 2-mm gap force, and stiffness of flexor digitorum profundus tendons in a human in vitro model.

METHODS

The flexor digitorum profundus tendons of the index, middle, ring, and little fingers of 50 human cadavers were transected and repaired with a 2-strand modified Kessler suture and assigned to 5 groups based on type of epitendinous suture design. The 5 epitendinous designs tested were a simple, running epitendinous suture whose knot was outside the repair (simple running KO); a simple, running epitendinous suture whose knot was inside the repair (simple running KI); a cross-stitch epitendinous suture; an interlocking, horizontal mattress (IHM) epitendinous suture; and a running-locking epitendinous suture. The tendon repair strength and 2-mm gap force were measured after 1,000 cycles of tendon motion. The resistance to gap formation, a measure of repair stiffness, was obtained from the force versus gap data.

RESULTS

None of the repairs showed any gap formation after 1,000 cycles of tendon motion. The cross-stitch epitendinous suture, IHM epitendinous suture, and running-locking epitendinous suture all had significantly lower gliding resistance than the simple running KO epitendinous suture after 1 cycle. The simple running KI epitendinous suture had significantly lower gliding resistance than the simple running KO epitendinous suture after 100 cycles and 1,000 cycles. The differences for gap force at 2 mm and stiffness of the repaired tendon evaluation were not statistically significant. The cross-stitch epitendinous suture, IHM epitendinous suture, and running-locking epitendinous suture all had significantly higher maximal failure strength after 1,000 cycles than the simple running KI epitendinous suture.

CONCLUSIONS

The cross-stitch, IHM, and running-locking epitendinous sutures had the best combination of higher strength and lower gliding resistance in this study. Although these findings suggest a potential for these suture types to be preferred as epitendinous sutures, these repairs should first be investigated in vivo to address their effect on tendon healing and adhesion formation.