• View in gallery
    Figure 1

    Schematic depiction of the 3 experimental groups in an ex vivo study conducted to assess the biomechanical strength and incidence of gap formation among canine SDFT constructs that underwent tenorrhaphy by placement of a core LL suture only (group 1), an nES suture pattern (group 2), or a combination of the core LL suture and nES pattern (group 3). Tendons were randomly assigned to the 3 groups (18 tendons/group) and sharply transected 2.5 cm distal to the musculotendinous junction. All repairs were performed with 2-0 polypropylene suture on a swaged V-20, 26-mm, 0.5-circle tapered needle. The ovals underneath the schematic representations of the 3 constructs depict a transverse section of the tendon following application of the respective constructs. Notice that the LL sutures (blue lines) were placed in the center of the tendinous substance and the nESs (green lines) were placed approximately 3 mm apart and 1 mm deep to the tendon surface.

  • View in gallery
    Figure 2

    Photograph of the mechanical tensile testing machine used to conduct a single load-to-failure test on each construct described in Figure 1 (A) and a close-up photograph of a group 3 construct mounted in the machine (B). For each construct specimen, a 4.5-mm-diameter bolt was placed through the supratrochlear foramen of the distal aspect of the humerus to rigidly attach the bone to the custom testing jig, which was connected to a 500-N load cell mounted on the crosshead of the testing machine. The distal aspect of the manus was securely mounted in a custom bone clamp. The specimen was oriented in a vertical position to mimic the load direction of a forelimb splinted in vivo. A preload of 2 N was applied to each construct. The resulting elongation was measured and recorded as the zero point to ensure that biomechanical testing was begun under consistent conditions for all constructs. Each construct was distracted at a rate of 20 mm/min until failure. Load and displacement data were recorded at a frequency of 100 Hz by the test system software. Each test was video recorded by use of a high-definition digital camera that was synchronized with the test system software and positioned 20 cm from the tenorrhaphy site. A calibrated metric ruler was positioned parallel to the construct within the field of view for the camera to facilitate measurement of gap formation.

  • View in gallery
    Figure 3

    Box-and-whisker plots of the yield (A), peak (B), and failure (C) loads for the 3 experimental groups described in Figure 1. For each plot, the upper and lower edges of the box represent the interquartile (25th to 75th percentile) range, the horizontal line in the box represents the median, whiskers delimit the minimum and maximum values, and circles delimit outliers (values > 1.5 times the interquartile range). The mean load differed significantly (P < 0.05) between groups connected by brackets.

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Evaluation of a continuous locking novel epitendinous suture pattern with and without a core locking-loop suture on the biomechanical properties of tenorrhaphy constructs in an ex vivo model of canine superficial digital flexor tendon laceration

Daniel J. DuffyDepartment of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27607.

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Yi-Jen ChangDepartment of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27607.

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Lewis GaffneyJoint Department of Biomedical Engineering, North Carolina State University and University of North Carolina at Chapel Hill, Raleigh, NC 27695.

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Matthew B. FisherJoint Department of Biomedical Engineering, North Carolina State University and University of North Carolina at Chapel Hill, Raleigh, NC 27695.

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George E. MooreDepartment of Veterinary Administration, College of Veterinary Medicine, Purdue University, West Lafayette, IN 47906.

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Abstract

OBJECTIVE

To evaluate the effect of a continuous locking novel epitendinous suture (nES) pattern with and without a core locking-loop (LL) suture on the biomechanical properties of ex vivo canine superficial digital flexor tendon (SDFT) tenorrhaphy constructs.

SAMPLE

54 cadaveric forelimb SDFTs from 27 musculoskeletally normal adult dogs.

PROCEDURES

Tendons were assigned to 3 groups (18 SDFTs/group): sharply transected and repaired with a core LL suture alone (group 1), an nES pattern alone (group 2), or a combination of a core LL suture and nES pattern (group 3). All constructs underwent a single load-to-failure test. Yield, peak, and failure loads; gap formation incidence; and mode of failure were compared among the 3 groups.

RESULTS

Mean yield, peak, and failure loads differed significantly among the 3 groups and were greatest for group 3 and lowest for group 1. Mean yield, peak, and failure loads for group 3 constructs were greater than those for group 1 constructs by 50%, 47%, and 44%, respectively. None of the group 3 constructs developed 3-mm gaps. The most common mode of failure was suture pulling through the tendon for groups 1 (12/18) and 2 (12/18) and suture breakage for group 3 (13/18).

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested augmentation of a core LL suture with an nES pattern significantly increased the strength of and prevented 3-mm gap formation at the tenorrhaphy site in ex vivo canine SDFTs. In vivo studies are necessary to assess the effectiveness and practicality of the nES pattern for SDFT repair in dogs.

Abstract

OBJECTIVE

To evaluate the effect of a continuous locking novel epitendinous suture (nES) pattern with and without a core locking-loop (LL) suture on the biomechanical properties of ex vivo canine superficial digital flexor tendon (SDFT) tenorrhaphy constructs.

SAMPLE

54 cadaveric forelimb SDFTs from 27 musculoskeletally normal adult dogs.

PROCEDURES

Tendons were assigned to 3 groups (18 SDFTs/group): sharply transected and repaired with a core LL suture alone (group 1), an nES pattern alone (group 2), or a combination of a core LL suture and nES pattern (group 3). All constructs underwent a single load-to-failure test. Yield, peak, and failure loads; gap formation incidence; and mode of failure were compared among the 3 groups.

RESULTS

Mean yield, peak, and failure loads differed significantly among the 3 groups and were greatest for group 3 and lowest for group 1. Mean yield, peak, and failure loads for group 3 constructs were greater than those for group 1 constructs by 50%, 47%, and 44%, respectively. None of the group 3 constructs developed 3-mm gaps. The most common mode of failure was suture pulling through the tendon for groups 1 (12/18) and 2 (12/18) and suture breakage for group 3 (13/18).

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested augmentation of a core LL suture with an nES pattern significantly increased the strength of and prevented 3-mm gap formation at the tenorrhaphy site in ex vivo canine SDFTs. In vivo studies are necessary to assess the effectiveness and practicality of the nES pattern for SDFT repair in dogs.

Introduction

Refinements in repair methodologies and suture material availability have significantly advanced the management of flexor tendon injuries.1,2 In human medicine, the institution of active rehabilitation protocols for patients with flexor tendon injuries has advanced the understanding of tendon physiology and the effectiveness of various suture patterns, which in turn has led to earlier accrual of repair site strength and faster recovery.3–5 In veterinary medicine, currently there is no consensus regarding the ideal suture pattern, suture material, or technique for tendon repair in dogs. The method selected for tendon repair should provide sufficient tensile strength to allow early controlled weight bearing on the repaired tendon without risk of failure. Factors associated with the initial strength of tenorrhaphy include suture size and material, knot security, number of suture strands that cross the tenorrhaphy site, length of suture purchase within the tendon substance, and augmentation of the core suture repair with ESs.1,4,6,7,8,9,10 The core suture components provide the primary resistance to gap formation and resilience to failure at the tendon repair site.11

Epitendinous sutures are peripheral circumferential sutures that penetrate the epitenon and deeper collagen fibers. In human medicine, ESs are commonly used to augment primary core tendon repairs of the hand.1,12 The use of ESs prevents fraying of the tendon ends and reduces exposure of suture material on the tendon surface.12,13 Epitendinous sutures are also used as an adjunct to commonly used core suture repair techniques in dogs.10,14,15,16 Results of an ex vivo study10 involving experimentally transected canine SDFTs indicate that augmentation of a 3LP suture pattern with an ES increases the yield force by 114% and construct strength by 133%, and augmentation of the LL suture pattern with ESs increases the yield force by 170% and construct strength by 151%. In another ex vivo study,16 the length of suture purchase within the tendon substance increased and the tissue-suture interaction was maximized as the distance at which the ESs were positioned from the transected tendon end increased from 5 to 15 mm. Increasing the ES bite depth into the tendinous core from 1 to 3 mm likewise improves the biomechanical strength of the tenorrhaphy construct.15 Epitendinous sutures represent the weakest part of tenorrhaphy constructs,11,17,18 and construct failure is initiated by the formation of progressive gaps between the tendon ends.17,18 Gaps > 3 mm at the tenorrhaphy site significantly increase the risk for reinjury and the need for corrective surgery.6 Optimal load sharing between the core suture and ES components of a tenorrhaphy should improve the strength of the repair and decrease gap formation. Given that the ESs are the weakest component of the tenorrhaphy construct, efforts to improve that aspect of the repair are warranted.

An important aspect of tendon healing is anatomic alignment of the severed ends of the tendon to facilitate fibroblast migration to the center of the tendon and strengthen the repair.1,2 Identification of novel tenorrhaphy techniques that improve the biomechanical characteristics of ESs is necessary before those techniques can be recommended and implemented in clinical practice. Biomechanical testing of tenorrhaphy constructs that consist of both core suture and ES components does not allow assessment of only the ES component and its effects on load sharing and other mechanical properties of the construct.

The objective of the study reported here was to determine the effect of a continuous locking nES pattern with and without core LL suture placement on the biomechanical strength and gap formation of tenorrhaphy constructs involving cadaveric canine SDFTs. We hypothesized that the addition of nESs to a core LL repair would significantly improve the biomechanical properties and tolerable loads and minimize gap formation at the repair site in an ex vivo model of canine SDFT laceration.

Materials and Methods

Samples

This study did not involve the use of live animals; therefore, it was deemed exempt from review by the North Carolina State University Institutional Animal Care and Use Committee. Results of a sample size calculation that used information regarding failure loads for tenorrhaphy constructs of previous studies10,14 and pilot experiments conducted for this study indicated that 18 SDFTs/construct group would be sufficient to detect a mean ± SD load difference of 22 ± 5 N between groups with 95% confidence (ie, α = 0.05) and 90% power.

Fifty-four SDFTs were harvested from 27 adult (> 1-year-old) mixed-breed canine cadavers that weighed between 25 and 32 kg. All dogs were euthanized by means of an IV infusion of sodium pentobarbitala for reasons unrelated to the study at a local animal shelter. All dogs were free of gross evidence of orthopedic disease, such as angular limb deformity and osteoarthritis of the elbow and carpal joints. From each cadaver, the superficial digital flexor muscle and tendon, including the proximal origin at the medial aspect of the humeral condyle to the distal insertion sites on the manus, were harvested intact from both forelimbs as described.10,14 All other soft tissues were removed and discarded. Each SDFT specimen was labeled, wrapped in gauze soaked with saline (0.9% NaCl) solution, and stored in a sealed plastic bagb at −20°C in a thermostatically controlled environment.

Each specimen was thawed at room temperature (21°C) for 10 hours prior to testing. On the day of experimental testing, a No. 10 scalpel blade was used to transect the SDFT 2.5 cm distal to the musculotendinous junction. The cut surface of the distal end of the tendon was held parallel to a calibrated ruler and photographed with the camerac positioned 10 cm from the tenotomy. The CSA of each tendon was measured with an imaging software programd by 1 investigator (Y-JC). Briefly, the photographic images were sequentially uploaded as .jpg files into the software program. With the millimeter scale on the ruler in the photograph used as the referent, the distance in pixels and units of length (cm2) were selected and magnified. The perimeter of the tendon was manually traced, and the CSA was determined at a resolution of 12.2 megapixels by the automated software.

Experimental groups

A random number generatore was used to randomly assign each tendon specimen to 1 of 3 experimental groups (18 tendons/group), with care taken to ensure that the SDFTs from the same cadaver were not assigned to the same group. All suture patterns were performed with 2-0 polypropylene suturef on a swaged V-20, 26-mm, 0.5-circle tapered needle. All suture material was sterile, originated from the original manufacturer packaging, and was used before the expiration date stamped on the package. Each package of suture was opened immediately before use. All experimental tenorrhaphies were performed by the same board-certified veterinary surgeon (DJD) who was experienced with tendon repair. The simple continuous locking nES pattern used was specifically designed for the study by an investigator (DJD) to reduce exposure of suture material on the tendon surface and maximize the interaction between the suture and collagen fibrils within the tendon substance.

Tendon specimens assigned to group 1 underwent tenorrhaphy by means of the LL suture technique as described.19 Briefly, a continuous strand of suture was placed through the center of the tendinous substance. The first suture bite was initiated 15 mm from the transected end of the proximal tendon segment and passed longitudinally through the center of the tendinous substance into the center of the tendinous substance of the distal tendon segment to exit 15 mm from the transected end of that segment. The second bite was started 5 mm toward (ie, 10 mm from) the transected end of the tendon from of the first bite and passed laterally through the tendon to exit on the opposite side. The third and fourth bites were the same as the first and second bites except the longitudinal suture loop passed from the distal to the proximal tendon segment (Figure 1).

Figure 1
Figure 1

Schematic depiction of the 3 experimental groups in an ex vivo study conducted to assess the biomechanical strength and incidence of gap formation among canine SDFT constructs that underwent tenorrhaphy by placement of a core LL suture only (group 1), an nES suture pattern (group 2), or a combination of the core LL suture and nES pattern (group 3). Tendons were randomly assigned to the 3 groups (18 tendons/group) and sharply transected 2.5 cm distal to the musculotendinous junction. All repairs were performed with 2-0 polypropylene suture on a swaged V-20, 26-mm, 0.5-circle tapered needle. The ovals underneath the schematic representations of the 3 constructs depict a transverse section of the tendon following application of the respective constructs. Notice that the LL sutures (blue lines) were placed in the center of the tendinous substance and the nESs (green lines) were placed approximately 3 mm apart and 1 mm deep to the tendon surface.

Citation: American Journal of Veterinary Research 82, 4; 10.2460/ajvr.82.4.302

Tendon specimens assigned to group 2 were repaired with only a peripheral circumferential continuous locking nES pattern. The first suture bite was initiated 10 mm from the transected end of the proximal tendon segment. The needle was passed through the segment in a transverse manner so that the suture exited on the palmarolateral surface of the tendon. Then, a longitudinal bite was taken 1 mm deep to the periphery of the tendon surface beginning 12 mm from the transected end of the proximal tendon segment (thereby creating a loop to lock the suture in place), crossing the gap, and exiting 12 mm from the transected end of the distal tendon segment. A transverse bite was taken 10 mm from the transected end of the distal tendon segment to create a loop to lock the suture in place. The pattern was then continued such that longitudinal loops were placed 3 mm apart around the circumference of the tendon. Constant tension was maintained to remove slack from the construct prior to the knot being tied at pattern completion (Figure 1). The tendon specimens assigned to group 3 were repaired with a core LL suture as described for group 1 specimens, followed by a peripheral nES pattern as described for group 2 specimens.

A calibrated surgical ruler and fine-tip markerg were used to mark the tendons prior to construct application to ensure consistent exit and entry points for the suture needle relative to the transected ends of the specimens. For all constructs, the transected ends of the tendon were brought together in close apposition without tissue plication at the tenotomy site. All suture pattens were ended with a square knot followed by 3 additional throws, and all suture tags were cut to a length of 4 mm. All tendon specimens were kept moist by use of physiologic saline solution, which was applied with a spray bottle as necessary throughout construct application and biomechanical testing.

Biomechanical testing

All biomechanical tests were performed at room temperature (21°C) with a mechanical tensile testing machine.h For each construct specimen, a 4.5-mm-diameter bolt was placed through the supratrochlear foramen of the distal aspect of the humerus to rigidly attach the bone to a custom testing jig, which was connected to a 500-N load cell mounted on the crosshead of the testing machine. The distal aspect of the manus was securely mounted in a custom bone clamp.i The construct was vertically aligned in the machine to mimic the direction of acute force applied to a forelimb in the immediate postoperative period and simulate clinical repair failure (Figure 2). A ruler was positioned adjacent and parallel to the construct to facilitate measurement of gap formation during experimental testing. A high-definition cameraj was positioned at the level of and 20 cm from the tendon repair site to record each test.

Figure 2
Figure 2

Photograph of the mechanical tensile testing machine used to conduct a single load-to-failure test on each construct described in Figure 1 (A) and a close-up photograph of a group 3 construct mounted in the machine (B). For each construct specimen, a 4.5-mm-diameter bolt was placed through the supratrochlear foramen of the distal aspect of the humerus to rigidly attach the bone to the custom testing jig, which was connected to a 500-N load cell mounted on the crosshead of the testing machine. The distal aspect of the manus was securely mounted in a custom bone clamp. The specimen was oriented in a vertical position to mimic the load direction of a forelimb splinted in vivo. A preload of 2 N was applied to each construct. The resulting elongation was measured and recorded as the zero point to ensure that biomechanical testing was begun under consistent conditions for all constructs. Each construct was distracted at a rate of 20 mm/min until failure. Load and displacement data were recorded at a frequency of 100 Hz by the test system software. Each test was video recorded by use of a high-definition digital camera that was synchronized with the test system software and positioned 20 cm from the tenorrhaphy site. A calibrated metric ruler was positioned parallel to the construct within the field of view for the camera to facilitate measurement of gap formation.

Citation: American Journal of Veterinary Research 82, 4; 10.2460/ajvr.82.4.302

A preload of 2 N was applied to each construct. The resulting elongation was measured and recorded as the zero point to ensure that biomechanical testing was begun under consistent conditions for all constructs. Each specimen was distracted until failure at an extension rate of 20 mm/min. Load and displacement data were recorded at a frequency of 100 Hz by the test system software.k An automated triggering system linked the camera footage and biomechanical testing data such that there was synchronization of the 2 systems during each test after the construct was preloaded at 2 N. Yield load was defined as the greatest force achieved prior to any initial sharp decrease in the load-displacement curve. Peak load was defined as the maximum force measured during each test. Failure load was defined as the force at which the suture broke or pulled through the tendinous tissue or when there was a sharp decrease in the load-displacement curve. Failure method was documented on the basis of visual assessment at the time of testing and review of the video recording by 1 investigator (Y-JC).

Load-displacement curves generated by the test system software were used to determine load at yield, peak, and failure for each specimen. A custom programl developed by one of the investigators (LG) was used to facilitate accurate selection of yield, peak, and failure loads. From each load-displacement curve, data points were manually selected to determine the yield, peak, and failure loads and the exact times when those loads occurred. During review of the video recording of each test, digital calipers within an imaging software programd were used to determine the time and load when 1- and 3-mm gaps formed prior to construct failure. If construct failure occurred prior to the formation of an identifiable gap, the construct was recorded as having no gaps.

Statistical analysis

For each continuous variable (loads at yield, peak, and failure and loads required to create 1- and 3-mm gaps), the data distribution was assessed for normality by means of the Shapiro-Wilk test. All continuous variables were normally distributed. Mixed linear models were used to assess factors associated with each continuous variable of interest. Each model included fixed effects for tendon CSA and experimental group and a random effect to account for the evaluation of SDFTs from both forelimbs of each cadaver (ie, repeated measures). The Bonferroni adjustment was used for post hoc pairwise comparisons when necessary. Pearson χ2 tests of association were used to compare the proportion of constructs that developed 1- and 3-mm gaps prior to failure and the mode of failure (suture breakage or tissue failure [sutures pulled through the tissue]) among experimental groups. All analyses were performed with a commercially available statistical software program,m and values of P < 0.05 were considered significant.

Results

Experimental constructs

All SDFTs were successfully transected and sutured for biomechanical testing, and all 54 constructs were included in all analyses. The distribution of left and right forelimb SDFTs did not differ significantly among the 3 experimental groups. The mean ± SD CSA was 0.25 ± 0.05 cm2 for all SDFTs and did not differ significantly (P = 0.706) among the 3 groups.

Biomechanical testing

Box-and-whisker plots of yield, peak, and failure loads were created for each experimental group (Figure 3). The same trend was observed for yield, peak, and failure loads among the experimental groups. Briefly, all 3 loads differed significantly among the 3 groups and were consistently greatest for group 3 (core LL suture in combination with nES pattern) and lowest for group 1 (core LL suture only).

Figure 3
Figure 3

Box-and-whisker plots of the yield (A), peak (B), and failure (C) loads for the 3 experimental groups described in Figure 1. For each plot, the upper and lower edges of the box represent the interquartile (25th to 75th percentile) range, the horizontal line in the box represents the median, whiskers delimit the minimum and maximum values, and circles delimit outliers (values > 1.5 times the interquartile range). The mean load differed significantly (P < 0.05) between groups connected by brackets.

Citation: American Journal of Veterinary Research 82, 4; 10.2460/ajvr.82.4.302

The proportion of group 1 constructs that developed 1-mm gaps (18/18) was significantly (P < 0.001) greater than the proportion of group 2 (11/18) and group 3 (13/18) constructs that developed 1-mm gaps. The mean load required to create a 1-mm gap also differed significantly (P < 0.01 for all comparisons) among the 3 groups. Likewise, the proportion of group 1 constructs that developed 3-mm gaps (14/18) was significantly (P < 0.001) greater than the proportion of group 2 (1/18) and 3 (0/18) constructs that developed 3-mm gaps.

The mode of construct failure differed significantly (P < 0.014 for all comparisons) among the 3 experimental groups. The most common mode of construct failure was the suture pulling through the tendinous tissue for groups 1 (12/18) and 2 (13/18) and suture breakage for group 3 (13/18).

Discussion

In the present ex vivo study, the biomechanical properties of a core LL suture alone (group 1), an nES pattern alone (group 2), and a core LL suture in combination with an nES pattern (group 3) for repair of experimentally induced SDFT rupture in dogs were assessed and compared. Results indicated that the mean yield, peak, and failure loads for the group 3 constructs were significantly greater than those for the group 1 constructs by 50%, 47%, and 44%, respectively. Moreover, the group 3 construct successfully prevented the formation of 3-mm gaps in all 18 SDFT specimens evaluated. Thus, the findings of this study supported our hypothesis that the addition of an nES pattern to a core LL suture would significantly improve the biomechanical and tolerable loads and minimize gap formation at the SDFT repair site.

Results of the present study corroborated the findings of other studies1,2 that ESs provide additional strength and decrease gap formation at tenorrhaphy sites and represent an important structural component of SDFT repair constructs in dogs. Ideal characteristics for any tenorrhaphy repair technique include repeatability, secure fixation, provision of adequate tensile strength to allow weight bearing on the limb, excellent apposition and alignment of tendon segments, and preservation of the peritendinous blood supply.6,18,20,21 Tenorrhaphy constructs involving ESs have been proven to have many of those characteristics in multiple studies involving human1,2,11 and veterinary10,14,15,16 subjects.

The force borne by the musculotendinous structures of the forelimbs of dogs is currently unknown. In dogs, the ground reaction force of a forelimb when the animal is walking is assumed to be equal to 30% of its body weight22; thus, for a 30-kg dog, the estimated ground reaction force sustained by a forelimb when the animal is walking is 90 N. In the present study, the mean loads for the group 3 constructs exceeded the estimated ground reaction force those tendons would sustain in vivo when the animal was walking. That finding supported use of the nES pattern to improve the strength of a core LL suture for SDFT repair in dogs. Improving the strength of the tenorrhaphy should translate clinically to a decrease in the risk for repair failure. The ES pattern and core LL suture share the load applied to the tendon; thus, the tendon can sustain a greater load than it could if only a core LL suture was used for the repair.23 Epitendinous sutures also provide resistance to deformation at the tenorrhaphy site. Improved mechanical strength and resistance to deformation are clinically beneficial because they facilitate early and rapid recovery of tensile strength by the tendon, decrease peritendinous adhesion formation, and improve tendon excursion.24–26

In the present study, the mean yield, peak, and failure loads for the group 2 constructs were significantly greater than those for the group 1 constructs by 45%, 50%, and 50%, respectively, which suggested that the nES pattern was biomechanically superior to the LL suture. This was likely because the circumferential nature of the nES pattern resulted in a greater number of suture strands crossing the tenotomy site, compared with the core LL suture in which only 2 strands of suture crossed the tenotomy site. Construct strength at the tenorrhaphy site is positively correlated with the number of suture strands that cross the repair site.21 Augmentation of the LL suture with the nES pattern (group 3) increased the loads sustained by the constructs by approximately 50%, compared with the loads sustained by the group 1 constructs, which was similar to results of other studies10,14 in which core LL sutures were augmented with various ES patterns for SDFT repair. The nES pattern described in the present study engages a greater number of collagen fibrils around the periphery of the repair than does the core LL suture, which facilitates load sharing and distribution among the nES, core suture, and tendon substance.10,14,27 Evaluation of the LL suture and nES pattern alone and in combination allowed us to assess the additive effects the 2 combined patterns had on the biomechanical strength and resistance to gap formation for tenorrhaphy constructs.

Successful repair of tendon injuries in dogs can be challenging for veterinary surgeons, especially when recommended postoperative restrictions regarding exercise and activity are not strictly enforced by owners. Implementation of rigid fixation techniques, such as external skeletal fixators, limits tendon strain associated with continued muscle contraction and can mitigate overuse of the limb.28 However, the application of some stress to the tendon substance following tenorrhaphy is necessary to enhance collagen production and fibril alignment, thereby increasing the tensile strength of the repair.29 The formation of gaps > 3 mm wide at the tenorrhaphy site significantly decreases the stiffness and ultimate force that can be sustained by the repair,6,30 decreases the accrual of strength at the repair site, and increases the risk for rerupture of the tendon within the first 4 to 6 weeks after the tenorrhaphy.2,6,30 During that protracted period of tendon healing, the tenorrhaphy suture is solely responsible for construct strength.2,6 Gapping at a tenorrhaphy site occurs when the force applied to the construct during ambulation or unrestricted motion by the patient exceeds that tolerated by the primary repair.2,6,30 In the present study, the mean loads required to create a 1-mm gap for groups 2 and 3 were 1.7 and 2.4 times, respectively, the mean load required to create a 1-mm gap for group 1. The tensile strength of a tenorrhaphy is positively associated with the number and size (diameter) of the suture strands that cross the repair site and whether the suture pattern is locking or grasping.5,20,27,31 Results of multiple studies2,5,9 indicate that the increase in tensile strength of a tenorrhaphy afforded by ESs outweighs any potential drawbacks associated with the increased amount of suture used and the greater number of needle punctures made in the tendon for suture placement. Although other ex vivo studies19,22,32 involving canine tendons indicate that the 3LP pattern is superior to a core LL suture for tensile strength and resistance to gap formation, we chose to use the core LL suture in the present study owing to its superior apposition of the tendon ends and subsequent ease of nES placement relative to the 3LP pattern. Further modifications of the nES pattern described in the present report are necessary to assess the effects of suture penetration depth into the tendon substance, suture bite distance from the repair site, increasing the suture caliber used for the repair, and the use of barbed suture so as to avoid the need for tying knots.

Previous studies1,5,27 indicate that ES patterns generally fail as a result of the suture material pulling through the tendon substance or suture breakage. Suture knotting causes tensile weakness in flexor tendon repairs.33 However, in the present study, the constructs of groups 1 and 2 failed predominantly owing to the suture pulling through the tendon substance rather than suture breakage or unraveling at the knot, whereas most constructs of group 3 failed because of suture breakage. We believe that these findings might be reflective of the force required to overcome the interaction between collagen fibrils and suture strands as well as the load sharing between the core and peripheral components of the repair. The peripheral continuous locking nES pattern evaluated in the present study was purposefully developed on the basis of findings in previous studies.1,2,11 The nES pattern, with its locking and continuous nature at the periphery of the tendon repair, incorporates and interacts with a much greater number of collagen fibrils, compared with traditional single-strand suture repairs, such as the 3LP and LL sutures. Results of translational research models34,35 indicate that tenorrhaphy constructs involving locked suture patterns are superior to those involving nonlocking suture patterns. Extraneous sutures produce higher surface friction and increase the risk for adhesion development at the repair site, which may impair subsequent function.12,36,37 The nES pattern described in the present study was designed to reduce suture exposure on the tendon surface, which will improve tendon glide function and reduce suture catching on tissue surrounding the repair site.12,36 Further investigation to evaluate the effect of the nES pattern on tendon glide function is necessary to inform modifications to the technique.

The present study had some inherent limitations owing to its ex vivo nature. Biological factors, such as tissue ischemia, edema, and adhesion formation during the healing process, could not be evaluated. The tendon constructs of the present study were tested to failure by means of linear distraction to simulate acute construct failure; however, cyclic testing would have been more representative of the loading forces sustained in vivo.24 Additionally, the straight-line testing method used in the present study did not accurately mimic normal tendon alignment, geometry, or loading in vivo. The size of the suture material used for the constructs of this study was larger than that typically used for flexor tendon repair in human patients, which may have contributed to increased failure loads observed in this study relative to those reported for ex vivo constructs involving human flexor tendons.38 The caliber of suture used in the present study was selected on the basis of SDFT tendon size, assumed lack of compliance with exercise restriction by canine patients, and clinical relevance.20 The SDFTs of the present study were experimentally transected with a scalpel, which led to a sharp and precise tenotomy. That is in contrast to clinical flexor tendon rupture in which fraying and degeneration of the ruptured tendon ends impair their capacity to hold suture. It is also important to note that we did not evaluate the glide function of the constructs in this study. In human patients, a paramount concern during repair of zone II tendon injuries is achieving smooth gliding,2,5,12,36 which is generally accomplished by ensuring that no foreign material protrudes from the tendon surface to catch on or impede movement of surrounding soft tissue structures. Achieving smooth gliding of the SDFT following tenorrhaphy is not as critical in dogs as it is in humans because functional union of the tendon ends is of greater concern than is fine motor control of the manus.

Results of the present study indicated that the addition of a peripheral continuous locking nES pattern to a core LL suture tenorrhaphy significantly increased the yield, peak, and failure loads and reduced the incidence of gap formation between the tendon ends of canine SDFT constructs. Use of the nES pattern in combination with core suture tenorrhaphy may decrease the reliance on other concurrent fixation techniques, such as external skeletal fixators, to augment, protect, and strengthen the primary repair. The success of any tendon repair method is dependent on patient compliance with postoperative restrictions on activity and the implementation of controlled rehabilitation soon after surgery. Therefore, adjunctive stabilization of core tendon repair techniques is still recommended for veterinary patients.

Acknowledgments

All suture material used in this study was provided by Medtronic Incorporated, Mansfield, Mass. No other financial support was received for this study.

The authors declare that there were no conflicts of interest.

The authors thank Dr. Adam Eby, North Carolina State University, for the photograph used in Figure 2B.

Abbreviations

3LP

Three-loop pulley

CSA

Cross-sectional area

ES

Epitendinous suture

LL

Locking loop

nES

Novel epitendinous suture

SDFT

Superficial digital flexor tendon

Footnotes

a.

Euthasol, Virbac AH Inc, Fort Worth, Tex.

b.

Ziplock 1-gallon bags, SC Johnson & Son Inc, Racine, Wis.

c.

iPhone XR, Apple Inc, Cupertino, Calif.

d.

ImageJ, NIH, Bethesda, Md.

e.

Research Randomizer, version 4.0, Geoffrey C. Urbaniak and Scott Plous. Available at: www.randomizer.org. Accessed Oct 20, 2020.

f.

Surgipro, Covidien Ltd, Dublin, Ireland.

g.

Medline Industries Inc, Northfield, Ill.

h.

5944 Universal Testing System, Instron Inc, Norwood, Mass.

i.

Sawbones, Vashon Island, Wash.

j.

Brio 4k Webcam, Logitech, Silicon Valley, Calif.

k.

Bluehill 3, Instron Inc, Norwood, Mass.

l.

Matlab R2018b, Mathworks Inc, Natick, Mass.

m.

SAS, version 9.4, SAS Institute Inc, Cary, NC.

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Contributor Notes

Address correspondence to Dr. Duffy (djduffy@ncsu.edu).