Comparison of modified Kessler tendon suture at different levels in the human flexor digitorum profundus tendon and porcine flexors and porcine extensors: an experimental biomechanical study

Healing strength of tendon repair with or without knots between two tendon ends and histological changes in a chicken model

We studied the healing strength and histological changes of digital flexor tendons repaired using Kessler (core suture knots placed over the tendon surface) and modified Kessler (core suture knots placed between two tendon ends) in 31 long toes of chicken. Four weeks after surgery, the healing tendons were measured in a tensile testing machine, and the adhesion formation and histological changes were observed. The strength of the Kessler repairs was significantly greater than that of the modified Kessler repairs with a 35% mean difference. No significant difference was found between the adhesion scores of the tendons repaired with both techniques. In histological sections, the arrangement of collagen fibers in the modified Kessler repair group was more disordered. We conclude that the tendons repaired with the Kessler method are stronger than those with the modified Kessler technique. The knots between tendon ends are detrimental to the early healing strength of digital flexor tendons.

The Transosseous Internal Four Strand Technique: A New All-Inside Technique for Zone 1 Flexor Tendon Repairs

BACKGROUND

Multiple techniques for the repair of flexor tendon injuries in zone 1 have been proposed over time. While pull-out suture techniques and bone anchor seem to be stronger than internal suture techniques, they are associated with a higher complication rate. We therefore developed an alternative internal suture repair with similar biomechanical stability to those of pull-out sutures and bone anchors.

METHODS

Twenty porcine distal phalanges and deep flexor tendons were randomized to 2 groups of 10 each. The tendons were transsected at the level of the distal interphalangeal joint. In group 1, repairs were performed with a well-established intraosseous suture repair and in group 2 with our new multistrand technique. The repairs were biomechanically tested with linear distraction until failure.

RESULTS

We recorded a significantly higher 2-mm gap force (2GF)-and thus higher stability-of the repairs in group 1 in comparison to group 2. With a 2GF of more than 50 N, our suture technique allows for a modern early active motion rehabilitation protocol. Breakage of the suture construct occurred at random places in the repair in both groups. No pull-outs were noted.

CONCLUSIONS

This study presents a strong transosseous multistrand repair technique for flexor tendon repair in zone 1 that is simple and fast to perform and should have enough strength to withstand early active motion rehabilitation.

Biomechanical Study of Modified Massachusetts General Hospital Flexor Tendon Repair Using Looped Sutures

Background: Massachusetts General Hospital (MGH) repair is one of the widely used 4-strand flexor tendon repair techniques. However, it uses two single strand sutures that are each passed twice across the repair site. This is time consuming and may cause imbalance of the load across the repair. We modified the MGH repair by using a looped suture and call it the looped MGH repair. The aim of this study is to compare the strength of the looped MGH repair performed with three different looped sutures against the strength of original MGH repair.

Methods: Forty porcine flexors were used for the study. The original MGH repair was performed with Prolene® 4-0. Looped MGH repair was performed with three different loop sutures, Supramid® 4-0, Tendo-Loop® 4-0 and FiberLoop® 4-0. Mechanism of failure, ultimate tensile strength, stiffness, load to 2-mm gap formation and repair time were recorded for comparison.

Results: There was no significant difference between the original MGH repair and the looped repair using Supramid® regarding their biomechanical performance. Looped MGH repair using Tendo-Loop® and FiberLoop® showed significantly higher ultimate tensile strength and FiberLoop® had highest 2-mm gap force. All looped MGH repairs required significant less time compared to original MGH repair.

Conclusions: Our modification of the MGH repair using a looped Supramid® 4-0 suture took significantly lesser time to perform while providing the same strength as the original MGH repair using Prolene® 4-0. The use of the FiberLoop® 4-0 provided significantly greater strength while taking lesser time.

Tendon grafts with preserved muscle demonstrate similar biomechanical properties to tendon grafts stripped of muscular attachments: a biomechanical evaluation in a porcine model

Purpose

(1) To evaluate the biomechanical properties of a porcine flexor digitorum superficialis tendon graft with preserved muscle fibers and (2) to compare these results with the biomechanical properties of a porcine tendon graft after removal of associated muscle.

Methods

Eighty-two porcine forelegs were dissected and the flexor digitorum superficialis muscle tendons were harvested. The study comprised of two groups: Group 1 (G1), harvested tendon with preserved muscle tissue; and Group 2 (G2), harvested contralateral tendon with removal of all muscle tissue. Tests in both groups were conducted using an electro-mechanical material testing machine (Instron, model 23-5S, Instron Corp., Canton, MA, USA) with a 500 N force transducer. Yield load, stiffness, and maximum load were evaluated and compared between groups.

Results

The behavior of the autografts during the tests followed the same stretching, deformation, and failure patterns as those observed in human autografts subjected to axial strain. There were no significant differences in the comparison between groups for ultimate load to failure (p = 0.105), stiffness (p = 0.097), and energy (p = 0.761).

Conclusion

In this porcine model biomechanical study, using autograft tendon with preserved muscle showed no statistically significant differences for yield load, stiffness, or maximum load compared to autograft tendon without preserved muscle. The preservation of muscle on the autograft tendon did not compromise the mechanical properties of the autograft.

Level of evidence

Level III Controlled laboratory study

Strength of side-to-side and step-cut repairs in tendon transfers: biomechanical testing of porcine flexor tendons

The aim of the study was to compare side-to-side with step-cut repairs to determine how much of the width it is possible to remove and still keep the repair strong enough to start active mobilization. Porcine flexor tendons were used to create side-to-side, one-third step-cut and half step-cut repairs. There were 15 repairs in each group. The tensile properties of the constructs were measured in a biomechanical testing machine. All repairs failed by the sutures splitting the tendon longitudinally. The maximum load and stiffness were highest in the side-to-side group. Our findings suggest that the half step-cut repair can withstand the forces exerted during active unrestricted movement of the digits in tendons of this size. The advantage of the step-cut repair is reduced bulkiness and less friction, which might compensate for the difference in strength.

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.

Strength of Pulvertaft modifications: tensile testing of porcine flexor tendons

The aim of the study was to present two new modifications of the Pulvertaft weave, allowing a higher number of weaves without the need for a longer overlap. The mechanical properties were measured and compared with the traditional technique. Forty-five pairs of porcine flexor tendons were randomized to a Pulvertaft repair with three weaves, a Double Pulvertaft and Locking Pulvertaft repairs. In the last two repairs one of the tendons in each repair was split in two before weaving. A difference in the maximum stiffness was observed between the three groups (p = 0.024). All repairs failed by the sutures being sheared through the tendons splitting the tendon fibres longitudinally. The two modifications were both stronger than the Pulvertaft weave and provide an alternative when a strong connection is needed and a longer overlap is impossible.

The elastic capacity of a tendon-repair construct influences the force necessary to induce gapping

PURPOSE

Most biomechanical investigations of tendon repairs were based on output measures from hydraulic loading machines, therefore, accounting for construct failure rather than true gapping within the rupture zone. It was hypothesized that the elastic capacity of a tendon-repair construct influences the force necessary to induce gapping.

METHODS

A tendon-repair model was created in 48 porcine lower hind limbs, which were allocated to three fixation techniques: (1) Krackow, (2) transosseous and (3) anchor fixation. Loading was performed based on a standardized phased load-to-failure protocol using a servohydraulic mechanical testing system MTS (Zwick Roell, Ulm, Germany). Rupture-zone dehiscence was measured with an external motion capture device. Factors influencing dehiscence formation was determined using a linear regression model and adjustment performed as necessary. A 3-mm gap was considered clinically relevant. Analysis of variance (ANOVA) was used for comparison between groups.

RESULTS

The elastic capacity of a tendon-repair construct influences the force necessary to induce gapping of 3 mm (F_3mm) [β = 0.6, confidence interval (CI) 0.4-1.0, p < 0.001]. Furthermore, the three methods of fixation did not differ significantly in terms of maximum force to failure (n.s) or F_3mm (n.s).

CONCLUSION

The main finding of this study demonstrated that the higher the elastic capacity of a tendon-repair construct, the higher the force necessary to induce clinically relevant gapping.

LEVEL OF EVIDENCE

Controlled biomechanical study.

An Exploratory Study Using Semi-Tabular Plate in Zone II Flexor Tendon Repair

Background: This study evaluated the feasibility of using a low-profile titanium (Ti) plate implant, also known as the Ti-button, for Zone II flexor tendon repair. We hypothesize that the use of the Ti-button can distribute the tensile force on the digital flexor tendons to achieve better biomechanical performance.

Methods: Twenty lacerated porcine flexor tendons were randomly divided into two groups and repaired using Ti-button or 6-strand modified Lim-Tsai technique. Ultimate tensile strength, load to 2 mm gap force, and mode of failure were recorded during a single cycle loading test. We also harvested twelve fingers with lacerated flexor digitorum profundus tendons from six fresh-frozen cadaver hands and repaired the tendons using either Ti-button method or modified Lim-Tsai technique. A custom-made bio-friction measurement jig was used to measure the gliding resistance and coefficient of friction of the tendon sheath interface at the A2 pulley.

Results: The ultimate tensile strength, load to 2 mm gap force, stiffness, and gliding resistance of the Ti-button repairs were 101.5 N, 25.7 N, 7.8 N/mm, and 2.2 N respectively. Ti-button repairs had significantly higher ultimate tensile strength and stiffness than the modified Lim-Tsai repair. However, Ti-button also increased the gliding resistance and coefficient of friction but there was no significant difference between the two repair techniques.

Conclusions: Ti-button repair displayed comparable mechanical properties to the traditional repair in terms of 2-mm gap formation and gliding resistance, but with a stronger repair construct. Thus, this deepened our interest to further investigate the potential of using Ti-button implant in Zone II flexor tendon repair by studying both the mechanical and biochemical (tendon healing) properties in more in-depth.

Four-Dimensional Imaging of Soft Tissue and Implanted Biomaterial Mechanics: A Barbed Suture Case Study for Tendon Repair

Timely, recent developments in X-ray microcomputed tomography (XμCT) imaging such as increased resolution and improved sample preparation enable nondestructive time-lapse imaging of polymeric biomaterials when implanted in soft tissue, which we demonstrate herein. Imaging the full three-dimensional (3D) structure of an implanted biomaterial provides new opportunities to assess the micromechanics of the interface between the implant and tissues and how this changes over time as force is applied in load-bearing musculoskeletal applications. In this paper, we present a case study demonstrating in situ XμCT and finite element analysis, using a dynamically loaded barbed suture repair for its novel use in tendon tissue. The aim of this study was to identify the distribution of stress in the suture and tendon as load is applied. The data gained demonstrate a clear 3D visualization of microscale features in both the tissue and implant in wet conditions. XμCT imaging has revealed, for the first time, pores around the suture, preventing full engagement of all the barbs with the tendon tissue. Subsequent finite element analysis reveals the localized stress and strain, which are not evenly distributed along the suture, or throughout the tissue. This case study demonstrates for the first time a powerful in situ mechanical imaging tool, which could be readily adapted by other laboratories to interrogate and optimize the interface between the implanted biomaterials and the soft tissue.

Gap Formation During Cyclic Testing of Flexor Tendon Repair

PURPOSE

Substantial gap formation of a repaired finger flexor tendon is assumed to be harmful for tendon healing. The purpose of this study was to investigate the relationship between gap formation and the failure of the repair during cyclic loading.

METHODS

Thirty-five porcine flexor tendons were repaired and tested cyclically using variable forces until failure or a maximum of 500 cycles. Depending on the biomechanical behavior during cyclic testing, specimens were divided into 3 groups: Sustained (no failure), Fatigued (failure after 50 cycles), and Disrupted (failure before 50 cycles). The relationships between the gap formations, time-extension curves, and group assignments of the samples were investigated.

RESULTS

The time-extension curves of the Fatigued specimens showed a sudden onset of repair elongation-a fatigue point-which preluded the subsequent failure of the repair. This point coincides with the start of plastic deformation and, thereafter, cumulative injury of the repair consistently led to failure of the repair during subsequent cycles. None of the sustained repairs showed a fatigue point or substantial gapping during loading.

CONCLUSIONS

We conclude that the emergence of a fatigue point and subsequent gap formation during loading will lead to failure of the repair if loading is continued.

CLINICAL RELEVANCE

The results of this experimental study imply that an inadequate flexor tendon repair that is susceptible to gap formation is under risk of failure.

A cyclic testing comparison of two flexor tendon repairs: asymmetric and modified Lim-Tsai techniques

This study compared the biomechanical performance of a novel 6-strand asymmetric flexor tendon repair with the modified Lim-Tsai technique using cyclic testing. Two groups of ten porcine tendons each were repaired and tested. Gap formation at every 100 cycles was measured. Survival was defined as maximum gap formation below 2 mm. All the repairs survived Stage I. With increased cyclic load in Stage II, the mean gap formation of modified Lim-Tsai repairs exceeded 2 mm at the 600th cycle and reached 4.2 mm (SD 1.93) at the end of Stage II, resulting in 0% survival. The mean gap formation of asymmetric repairs reached 2.0 mm (SD 1.43) at the 800th cycle and was 2.4 mm (SD 1.52) at the end of Stage II, with 60% survival. The asymmetric repair has better biomechanical performance under cyclic testing as compared with the modified Lim-Tsai repair.

The impact of different peripheral suture techniques on the biomechanical stability in flexor tendon repair

PURPOSE

Flexor tendon repair consists of circumferential peripheral sutures in combination with core sutures to avoid fraying and reduces the exposure of suture material on tendon surface. The peripheral suture adds up to a tenfold increase of the biomechanical stability compared to the core suture alone. The purpose of our study was to determine the most favourable peripheral repair technique for tendon repair.

METHODS

Seventy-two porcine flexor tendons underwent standardized tenotomy and repair using one of the following six methods (n = 12): simple-running (SR), simple-locking (SL), Halsted-mattress (HM), lin-locking (LL), Lembert-mattress (LM), and Silfverskiöld cross-stich (SCS) suture technique. The SL- suture was placed 2 mm; the HM, LM, SC, and LL suture were placed 5 mm from the tendon gap. The SR suture was placed 1, 2, and 3 mm from tendon ends; no additional core suture was applied. For cyclic testing (1000 cycles), elongation was calculated; for load to failure construct stiffness, yield load and maximum load were determined.

RESULTS

The mean cyclic elongation for all tested suture techniques was less than 2 mm; there was no significant difference between the groups regarding elongation as well as yield load. The HM, LM, SCS, and LL suture techniques presented significantly higher maximum loads compared to the SR- and SL-sutures. The 3 mm SR showed significantly higher maximum loads compared to the 2 and 1 mm SR.

CONCLUSIONS

Beside the distance from tendon gap, the type of linkage of the suture material across and beneath the epitendineum is important for biomechanical stability. Simple-running suture is easy to use, even with a slight increase of the distance from tendon gap significantly increases biomechanical strength. For future repairs of flexor tendon injuries, 3 mm stitch length is highly recommended for simple peripheral suture, while the Halsted-mattress suture unites the most important qualities: biomechanically strong, most part of suture material placed epitendinous, and not too complicated to perform.

A Biomechanical Study of a Novel Asymmetric 6-Strand Flexor Tendon Repair Using Porcine Tendons

BACKGROUND

This study evaluated the biomechanical performance of a novel asymmetric 6-strand flexor tendon repair technique without locking loops.

METHODS

Twenty porcine flexor tendons were equally repaired by using the asymmetric technique and compared with the modified Lim-Tsai repair technique. The ultimate tensile strength, load to 1-mm gap force, stiffness, and mechanism of failure were measured.

RESULTS

The asymmetric repair technique had significantly higher tensile strength (63.3 ± 3.7 N) than the modified Lim-Tsai repairs (46.7 ± 8.3 N).

CONCLUSIONS

A novel flexor tendon repair technique with improved biomechanical performance may be available for use in flexor tendon repairs.

Biomechanical investigation of uneven load bearing in six-strand Lim-Tsai flexor tendon repair using FiberLoop®

We hypothesized that, in providing biomechanical strength, at least one of the two middle strands in a modified six-strand Lim-Tsai flexor tendon repair could be divided without obvious reduction in repair strength owing to uneven load bearing. A total of 40 porcine flexor digitorum profundus tendons were repaired using the six-strand Lim-Tsai technique with a 4-0 FiberLoop^® suture and then divided into four equal groups. (no cut, one middle strand cut, both middle strand cut, one side strand cut). The biomechanical performance of repaired tendons was tested and found to vary according to the location of the cuts.

Suture configurations and biomechanical properties of flexor tendon repairs by 16 hand surgeons in Finland

The aim of this study was to find out how common it is to modify standard core suture configurations in flexor tendon repair and whether the use of standard core suture configurations gives a stronger repair. A total of 16 hand surgeons or residents participated in a workshop, in which they were asked to draw the suture configurations they used and to repair a porcine tendon. The properties of the repaired tendons were measured. Seven participants used a standard core suture configuration, and nine used a modified core suture. The biomechanical properties of the repairs were not affected by modifications to the core suture. However, they were affected by the number and lengths of peripheral suture bites, type of peripheral suture and the location of the core suture knot.

Direct Radiological Visualization of Loading on Four Flexor Tendon Repair Suture Configurations

PURPOSE

To study the deformation of 4 suture configurations used in flexor tendon repair using fluoroscopy.

METHODS

All flexor tendon repair techniques have a longitudinal component, a link component, and/or a transverse component. We had previously described 4 types of link components, namely an arc (grasping loop), a simple loop (locking loop), a complex loop, and a knot. The effect of loading on suture configurations using each of these link components was tested in flexor tendon from the first ray of porcine feet. Forty flexor tendons were divided into 4 groups of 10 each, and one-half of a tendon repair was simulated on each group using 0.5 mm stainless steel wire. The tendons were mounted on a materials testing machine, and tensile force was applied until failure. The deformation of the suture within the tendon substance was observed using an image intensifier, and the maximal load to failure was measured.

RESULTS

The loading of the suture led to unraveling of the suture in an arc, constriction and unraveling in a simple loop, and initial constriction with no further change of the construct in the complex loop with no change in the knot design. The mean pullout strength of the complex loop was statistically greater than all the other 3 designs.

CONCLUSIONS

Each of the link component designs demonstrated unique deformation characteristics. The complex loop design had the strongest grasping ability.

CLINICAL RELEVANCE

This study identified the differences in the deformation characteristics of the 4 types of link components used in flexor tendon repair. This knowledge may allow for the development of better flexor tendon repair techniques and the adoption of a more precise classification of flexor tendon repair techniques.

Comparison of Flexor Tendon Repair Between 6-Strand Lim-Tsai With 4-Strand Cruciate and Becker Technique

PURPOSE

To compare the strength of 6-strand Lim-Tsai repair with 4-strand cruciate and Becker repair, which were done using braided polyblend. We hypothesized that the biomechanical strength of 4-strand repair could be as strong as 6-strand repair because of different flexor tendon repair configurations and uneven load bearing.

METHODS

We harvested 60 porcine flexor tendons. A transverse cut at the middle of the tendons was made to perform tendon repair. Six-strand Lim-Tsai repair (consisting of 2 Lim-Tsai locking loops), 4-strand cruciate repair (with 3 cross-stitch loops), and 4-strand Becker repair (with 2 double cross-stitch locking loops) were used for the repairs. The repaired tendons were pulled until failure using a mechanical tester. We recorded ultimate tensile strength, load to 2-mm gap force, stiffness, and mechanism of failure.

RESULTS

The Becker repairs had significantly greater tensile strength than the cruciate and Lim-Tsai repairs. The load to 2-mm gap force and stiffness were significantly greater for cruciate repairs and Becker repairs than Lim-Tsai repairs.

CONCLUSIONS

The biomechanical strength of 4-strand and Becker repairs could be as strong as 6-strand Lim-Tsai repairs. This study implies that the number of strands crossing the repair site of tendons may not be proportional to the biomechanical strength of flexor tendon repair.

CLINICAL RELEVANCE

Hand surgeons are urged to be aware of the biomechanic characteristics of different flexor tendon repair techniques used in the clinical setting.

Barbed suture vs conventional tenorrhaphy: biomechanical analysis in an animal model

Background

The advantages of barbed suture for tendon repair could be to eliminate the need for a knot and to better distribute the load throughout the tendon so as to reduce the deformation at the repair site. The purpose of this study was to evaluate the breaking force and the repair site deformation of a new barbed tenorrhaphy technique in an animal model.

Materials and methods

Sixty porcine flexor tendons were divided randomly into three groups and repaired with one of the following techniques: a new 4-strand barbed technique using 2/0 polypropylene Quill™ SRS or 2/0 polydioxanone Quill™ SRS and a modified Kessler technique using 3/0 prolene. All tendons underwent mechanical testing to assess the 2-mm gap formation force, the breaking force and the mode of failure. The percentage change in tendon cross-sectional area before and after repair was calculated.

Results

The two-sample Student t-test demonstrated a significant increase in 2-mm gap formation force and in breaking force with barbed sutures, independently from suture material, when compared to traditional Kessler suture. Concerning the tendon profile, we registered less bunching at the repair site in the two barbed groups compared with the Kessler group.

Conclusions

This study confirms the promising results achieved in previous ex vivo studies about the use of barbed suture in flexor tendon repair. In our animal model, tenorrhaphy with Quill™ SRS suture guarantees a breaking force of repair that exceeds the 40–50 N suggested as sufficient to initiate early active motion, and a smoother profile at the repair site.

Level of evidence Not applicable.

Sutured tendon repair; a multi-scale finite element model

Following rupture, tendons are sutured to reapproximate the severed ends and permit healing. Several repair techniques are employed clinically, with recent focus towards high-strength sutures, permitting early active mobilisation thus improving resultant joint mobility. However, the arrangement of suture repairs locally alters the loading environment experienced by the tendon. The extent of the augmented stress distribution and its effect on the tissue is unknown. Stress distribution cannot be established using traditional tensile testing, in vivo, or ex vivo study of suture repairs. We have developed a 3D finite element model of a Kessler suture repair employing multiscale modelling to represent tendon microstructure and incorporate its highly orthotropic behaviour into the tissue description. This was informed by ex vivo tensile testing of porcine flexor digitorum profundus tendon. The transverse modulus of the tendon was 0.2551 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pm $$\end{document}± 0.0818 MPa and 0.1035 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pm $$\end{document}± 0.0454 MPa in proximal and distal tendon samples, respectively, and the interfibrillar tissue modulus ranged from 0.1021 to 0.0416 MPa. We observed an elliptically shaped region of high stress around the suture anchor, consistent with a known region of acellularity which develop 72 h post-operatively and remain for at least a year. We also observed a stress shielded region close to the severed tendon ends, which may impair collagen fibre realignment during the remodelling stage of repair due to the lack of tensile stress.

The suture loop holding capacity of flexor digitorum profundus tendon within and outside the digital tendon sheath

In a previous study we found that the strength of a Kessler core suture in the flexor tendon was greater in flexor zone 2 than in zone 3. To further investigate the material properties of the flexor tendon without the influence of a locking suture configuration, we measured the ultimate strength of a simple loop suture in the flexor digitorum profundus tendon in zones 1, 2, and 3. Eight cadaver flexor digitorum profundus tendons were tested in 10 mm increments with a 3-0 polyester suture loop pull-out test in the mid-substance of the tendon. The mean strength in zones 1 and 2 (26.7 N, SD 5.6) was significantly higher than the mean strength in zone 3 (17.7 N, SD 5.4). We conclude that the difference is owing to variations of the structure of the flexor tendon in different sections of the tendon, as the suture configuration was a simple loop without a locking or grasping component.