Dorsal-enhanced sutures improve tension resistance of tendon repair

Cyclic testing of six-strand suture techniques for zone 2 flexor tendon lacerations

BACKGROUND

Biomechanical analysis using cyclic testing for repaired flexor tendons is a clinically relevant method. The aim of this study was to evaluate the tensile properties of two six-strand suture techniques, the triple looped suture and Yoshizu #1 suture techniques using cyclic testing under simulating early active mobilization conditions.

METHODS

Twenty-five flexor digitorum profundus tendons harvested from fresh frozen human cadaver hands were repaired in zone 2 utilizing one of three repair techniques: the 2-strand modified Kessler (MK) technique as a control, the triple looped suture (TLS) and Yoshizu #1 suture (Y1) techniques. In each suture technique, 4-0 monofilament nylon sutures were used for core sutures and 6-0 monofilament nylon sutures for circumferential running sutures. Cyclic testing was performed using 20 N with 600 cycles at 1 Hz.

RESULTS

Five out of eight specimens in the MK group ruptured during cyclic testing. Thus, this group was excluded from analysis. On the other hand, all tendons in the TLS and Y1 groups tolerated cyclic testing. Average gaps of the TLS and Y1 groups were 0.5 ± 0.8 mm and 1.9 ± 2.2 mm, respectively. All tendons in the TLS group and six out of nine tendons in the Y1 group formed gaps less than 2 mm. Two tendons in the Y1 group formed a gap of 3.8 and 6.6 mm had breakage of peripheral sutures at the first cycle. Mean ultimate tensile force of the TLS and Y1 group measured after cyclic tensing, were 66.2 ± 9.0 N and 65.9 ± 13.1 N, respectively. No statistical difference between the two groups was found in gap and ultimate tensile forces.

CONCLUSIONS

This study suggested that the TLS and Y1 techniques have tensile properties to allow early active mobilization. None of tendons repaired with the TLS technique had gaps more than 2 mm.

Gap Resistance and Tensile Strength of a Q Suture Technique During Curved Loading: An Ex Vivo Porcine Flexor Tendon Study

PURPOSE

This study aimed to determine the mechanical properties of the double Q suture technique in angular motion and to compare the gap formation associated with tendon repairs during curved and linear loading.

METHODS

Eighty porcine flexor tendons were repaired with one of two 4-strand sutures: double Q suture or double modified Kessler plus peripheral running sutures. The repaired tendons were cyclically loaded sequentially against a pulley with a radius of 2.0, 1.5, and 1.0 cm or linearly without any pulleys. The number of tendons that formed an initial or 2-mm gap at the repair site during cyclic loading, the gap size between tendon ends when cyclic loading ended, and the ultimate strength were recorded.

RESULTS

The gap at the repair site formed gradually from the dorsal to volar aspect during curved loading. No double Q repairs, but half of the double Kessler plus running suture repairs, formed an initial or 2-mm gap on the volar aspect during curved loading. The double Q group had a significantly smaller gap size on the dorsal aspect than the double Kessler plus running suture group at all three radii of curvature. The ultimate strength was similar between the two groups. There were no significant differences in linear motion between these two repairs.

CONCLUSIONS

The double Q suture is superior to the conventional 4-strand tendon core suture plus running peripheral sutures in gap resistance in angular motion. This study provides insight into the formation of an unbalanced gap on the dorsal and volar aspects of tendon repair during curved loading.

CLINICAL RELEVANCE

The double Q suture provides a simple and efficient option for flexor tendon repair considering the high risk of gap formation on the dorsal aspects of the tendon repair in angular motion.

Effect of Oblique Tendon Laceration on Core Suture Strength: A Biomechanical Evaluation

BACKGROUND

The effect of obliquity of tendon laceration on repair strength is not well studied. The overwhelming majority of biomechanical studies assess repair strength following a laceration that is perpendicular to the long axis of the tendon. The aim of this study was to investigate whether the angle of tendon laceration affects the core suture strength.

METHODS

In all, 110 fresh human cadaveric flexor tendons were cut at varying angles of 15°, 30°, 45°, and 60° and the control group at 90°. All tendons were repaired with 6-strand modified Tang technique. The repair strength was tested using a custom-made tensioning machine, and the initial static gap force and the ultimate breaking force were measured.

RESULTS

The mean gap force and 95% confidence interval (CI) for the 15°, 30°, 45°, 60°, and 90° groups were 15.2 N (11.4-19.0 N), 15.8 N (13.6-18.1 N), 15.6 N (13.1-18.4 N), 16.6 N (13.7-19.5 N), and 22.3 N (16.6-27.9 N), respectively. In the same respective order, the break force and 95% CI were 25.9 N (21.9-29.8 N), 26.5 N (23.2-29.7 N), 31.1 N (26.1-36.1 N), 35.6 N (28.2-43.1 N), and 51.8 N (62.5-41.0), respectively. The Fisher least significant difference demonstrated significant differences between the control group and all experimental groups for both gap force and break force.

CONCLUSIONS

Obliquity of tendon laceration affects the core suture strength when compared with a transverse cut. Flexor tendons cut at 90° demonstrated a higher overall gap force and breaking strength that were statistically significant when compared with all obliquely cut groups. These findings should be considered when repairing and starting postoperative therapy for obliquely cut tendons.

Repairs of Partial Oblique Tendon Injuries: A Biomechanical Evaluation

This study evaluated the tensile properties of oblique partial tendon lacerations and the effects of peripheral sutures on their strength. Seventy-four fresh pig flexor digitorum profundus tendons were divided into eight groups and were transected across 90% of their diameter. The lacerations in the tendons of five of the groups were at 0°, 15°, 30°, 45°, and 60° to their transverse cross-section, respectively. In the other three groups the lacerations were 0°, 45°, and 60° to the cross-section and were repaired with running peripheral sutures. The tendons were subjected to load-to-failure tests in a tensile testing machine to determine the initial, 1 and 2 mm gap formation forces, and the ultimate strength. Obliquity of tendon lacerations affected the strength of partially lacerated tendons. The tendons with 45° and 60° oblique lacerations had a significantly lower ultimate strengths than those with transverse (0°), or 15° or 30° oblique lacerations. Running peripheral sutures significantly increased both the gap formation forces and the ultimate strength of the tendons with oblique partial lacerations.

Epitendinous suture techniques in extensor tendon repairs--an experimental evaluation

PURPOSE

The tension-band principle might be relevant to extensor tendon repairs, and a dorsal-only Silfverskiöld epitendinous repair is stronger and stiffer than more conventional techniques in vitro. We aimed to evaluate the strength and stiffness of the strongest epitendinous sutures described, using an in vitro model that subjects the repair to angular force over a pulley, thereby creating a tension-band model.

METHODS

Silfverskiöld dorsal-only epitendinous extensor tendon repairs in porcine foot tendons (n = 8) were compared to reverse (buried) Silfverskiöld (n = 8), Halsted (n = 8), and interrupted horizontal mattress (IHM) repairs (n = 6) in vitro with a tensiometer around a 45° pulley. Thirty tendons total were tested to assess the force required for 2-mm gapping and ultimate tensile strength.

RESULTS

The IHM repair had a significantly higher ultimate tensile strength (43 N; SD, 10 N) than the other repairs, which had strengths between 27 N (SD, 4 N) and 31 N (SD, 7 N). The IHM was also significantly more resistant to gapping than the Silfverskiöld and Halsted repairs.

CONCLUSIONS

Interlocking horizontal mattress, dorsal-only extensor tendon repairs were significantly stronger and more resistant to gapping than Silfverskiöld and Halsted repairs. Other repairs were still strong and resistant to gapping in comparison to previously published data for conventional repairs.

CLINICAL RELEVANCE

The IHM is a relatively difficult technique to perform, and it remains to be seen whether the additional strength translates to clinical benefits over the easier Silfverskiöld technique.

Biomechanical testing of a novel suture pattern for repair of equine tendon lacerations

OBJECTIVE

To compare in vitro biomechanical properties of a novel suture pattern to a current standard for primary repair of equine superficial digital flexor tendon (SDFT) laceration.

STUDY DESIGN

In vitro randomized, paired design.

ANIMALS

Cadaveric equine forelimb SDFT (n = 24).

METHODS

The 3-loop pulley (3LP) and 6-strand Savage (SSS) suture patterns were applied to transected equine SDFT. Ultimate failure load, stiffness, mode of failure, and load required to form a 3-mm gap were obtained using a materials testing system and synchronized high-speed video analysis. Statistical comparisons were made using Student's t-test, with significance set at P < .05.

RESULTS

The SSS repair failed at a higher ultimate load (421.1 N ± 47.6) than the 3LP repair (193.7 N ± 43.0; P < .001). There was no significant difference in stiffness (P = .99). Failure mode was suture breakage for all SSS repair and suture pull through for all 3LP repair. The maximum load to create a 3-mm gap in the SSS repair (102.0 N ± 22.4) was not significantly different from the 3LP repair (109.9 N ± 16.0; P = .27).

CONCLUSIONS

SSS tenorrhaphy has improved strength and resistance to pull through compared with 3LP for equine SDFT in a single load-to-failure test. Load required to form a 3-mm gap was not significantly different between SSS and 3LP.

The tension band principle and angular testing of extensor tendon repairs

Extensor tendons in the finger are flat and not amenable to repair by core and epitendinous sutures. Mattress sutures and Kessler repairs without epitendinous stitching are often used for extensor tendon divisions in the fingers. Except when in full extension, the finger presents a series of curved surfaces (at each joint) to the tendon. It was hypothesized that extensor tendons are subject to the 'tension band' principle and that they might be amenable to repair by dorsal-only epitendinous sutures. A Silfverskiöld dorsal-only repair was compared with mattress and Kessler repairs in vitro on a curvilinear testing apparatus. The epitendinous technique was found to be significantly more resistant to gapping and rupture, as well as more resistant to deformation (i.e. stiffer) than the conventional techniques.

An inverting circumferential suture for flexor tenorraphy

Zone two flexor tendon repair remains challenging with significant outcome variation using recognised techniques. Tendon adhesion formation results in poor outcomes and rehabilitation regimes aim to limit this. Some repairs augment strength, but increasing bulk mitigates against movement. This novel epitendinous technique causes tendon inversion with potential gliding benefits and improved outcomes. 60 porcine tendons were randomised to a 2-stranded modified Kessler or a 4-stranded Adelaide repair, then sudivided into three different circumferential technique groups: locked running, Silfverskiold, or a new inverting repair. Tendon load to failure (LTF), 2 mm gap formation, bulking effect and method of failure were analysed during digital tensiometry. Four-stranded repairs demonstrated better LTF than 2-stranded techniques. The inverting epitendinous and Silfverskiold repairs showed higher LTF characteristics than the locked running suture, and better tissue holding capacity. The inverting repair has similar properties to commonly used suturing methods and the conformation creates a smooth inverted repair.

Effect of partial versus complete circumferential repair on flexor tendon strength in cadavers

PURPOSE

This study investigated the strength of epitendinous repairs covering the palmar half of the tendon circumference only.

METHODS

Two hundred porcine tendons were harvested from pig feet and separated into 2 equal groups. Group 1 tendons were sutured with a 2-strand core repair and group 2 tendons were sutured with a 4-strand core repair. Each group was then divided into 5 equal subgroups (n=20). Four of the subgroups were sutured with 1 of the following epitendinous repairs: 50% simple running (50SR), complete simple running (100SR), 50% Silfverskiold (50SK), or complete Silfverskiold (100SK). One sub-group (0C) had no epitendinous repair. The core suture material was 3-0 braided polyester (Tricon; Tyco Healthcare, Dominican Republic), and the circumferential suture material was 6-0 polypropylene (Prolene, Sumerville, NJ). The tendons were mechanically strained to failure, and force data were recorded.

RESULTS

The 50SR and 50SK repairs significantly increased the force at 1-mm and 2-mm gap formation of both core repairs. The 50SR and 50SK repairs increased the ultimate force at failure of both core repairs by approximately 20%. Both 50% circumferential (50C) repairs increased repair strength at the points of initial gap formation more than at the point of ultimate force. The 50C repairs were approximately 50% as strong as the 100% circumferential (100C) repairs at 1-mm and 2-mm gap formation and approximately 70% as strong at the ultimate force of failure.

CONCLUSIONS

The 50C repairs increased the tensile strength of 2-strand and 4-strand tendon repairs in vitro. The prevention of early gapping was more significant than the increase of strength at failure.

The effects of freezing on the tensile properties of repaired porcine flexor tendon

PURPOSE

When conducting complex testing of tendon repairs, it is essential that the samples are adequately preserved to prevent degradation. Freezing of samples is the most convenient method of preservation; however, there is no evidence in the literature to prove that freezing tendon before or after repair is acceptable. We aimed to prove that freezing tendons does not significantly alter the results of linear load-to-failure testing of tendon repairs.

METHODS

After a power study, 150 tendons were harvested from porcine forelimbs and randomized into 5 groups of 30 tendons. After division, tendons were repaired using a Pennington modified core technique with a Silfverskiöld peripheral cross-stitch. Tendons in group 1 were divided, repaired, and tested within 3 hours postmortem. Tendons in group 2 were refrigerated at 4 degrees C for 24 hours prior to repair and testing. Tendons in group 3 were frozen at -25 degrees C for 3 months prior to repair and testing. Tendons in group 4 were frozen at -25 degrees C for 6 months prior to repair and testing. Tendons in group 5 were frozen at -25 degrees C for 6 months, repaired, refrozen for 1 month, and then tested. All repairs were linear load tested to ascertain the ultimate strength and force to produce 3-mm gap in the repair.

RESULTS

Analysis of variance analysis of the results did not demonstrate any significant differences between groups.

CONCLUSIONS

Freezing tendons both before and after suture repair is an acceptable method of preservation when investigating the force to produce 3-mm gap and ultimate strength of tendon repairs.

Influence of core suture purchase length on strength of four-strand tendon repairs

PURPOSE

Recently the length of core suture purchase has been identified as a variable affecting the strength of tendon repairs. The influence of the length of the core suture purchase on the strength of multistrand locking and grasping suture repairs, however, has not been studied extensively in transversely lacerated tendons. We assessed the effects of the length of the core suture purchase on the strength of three 4-strand grasping or locking repair techniques.

METHODS

Seventy-four fresh adult pig flexor tendons were cut transversely and repaired with 1 of 3 methods: double-modified Kessler, locking cruciate, and modified Savage. Each method was assessed using 2 different lengths of core suture purchase (1.0 and 0.4 cm). The tendons were subjected to a linear noncyclic load-to-failure test in a tensile testing machine. We recorded the forces required for gap formation, ultimate strength, stiffness of the tendon, and the mode of repair failure.

RESULTS

The resistance to gap formation, the ultimate strength of all 3 repairs, and the stiffness of the tendons with the double-modified Kessler and modified Savage repairs decreased significantly as the length of core sutures decreased from 1.0 to 0.4 cm. Locking and grasping repairs had a similar decrease in strength when the purchase was decreased from 1.0 to 0.4 cm. All tendons with modified Savage repairs with 1.0-cm purchase failed by suture breakage and tendons with 0.4-cm purchase failed predominantly by pullout.

CONCLUSIONS

The length of core suture purchase significantly affects the strength of these 4-strand tendon repairs. The forces required for gap formation and the ultimate failure of repairs with 0.4-cm purchase were 20% to 45% lower than those of the repairs with 1.0-cm purchase. Locking repairs did not show a greater capacity to offset the decrease in strength than grasping repairs when the length of core suture purchase was decreased from 1.0 to 0.4 cm. Our study indicates that the length of suture purchase directly influences the strength of both locking and grasping core tendon repair methods.

Biomechanical evaluation of a four-strand modification of the Tang method of tendon repair

We report a four-strand modification of the Tang technique of tendon repair that uses fewer sutures and fewer knots on the tendon surface. This repair consists of four longitudinal and two horizontal strands that form a "U" configuration within the tendon made with a single looped suture. Thirty-four fresh pig flexor tendons were divided into 3 groups and repaired with the four-strand modified Tang method, a double-looped four-strand method or a double Kessler repair (four-strand). The tendons were subjected to a single cycle of load-to-failure test in a tensile testing machine. The initial force, 2-mm gap formation force and ultimate strength of the four-strand modified Tang repair were statistically identical to those of the double looped suture and were superior to those of the double Kessler repair. Ultimate strength was 43.4+/-4.3N for the four-strand modified Tang method, 45.2+/-4.0N for the double-looped method and 39.1+/-4.0N for the double Kessler repair. The four-strand modification of the Tang method appears to have strength sufficient for protected active finger motion. Given our preliminary clinical experience with this method, we recommend this new and simplified technique for clinical flexor tendon repairs.

Core suture purchase affects strength of tendon repairs

PURPOSE

It generally is considered that a certain distance should be maintained between the site of the tendon-suture junction and the laceration level of the tendon. In this study we assessed how the length of core suture purchase may affect the repair strength of transversely cut tendons using a 2-strand modified Kessler method and a 4-strand circle-locking method.

METHODS

Seventy-four fresh pig flexor tendons were transected. Fifty-eight tendons were divided into 4 groups and repaired with a 2-strand grasping repair technique with the core suture purchase in the tendon stump ranging from 0.4 to 1.2 cm. Sixteen tendons were repaired with a 4-strand circle-locking tendon-suture repair technique. The core suture purchase of these tendons was 0.4 and 1.0 cm, respectively. The tendons were subjected to a linear, noncyclic, load-to-failure test in a tensile testing machine. The forces measured for initial gap formation, 2-mm gap formation, and ultimate strength were recorded for each repair.

RESULTS

The resistance to gap formation and ultimate strength of 2-strand grasping technique repairs increased significantly as the suture purchase increased from 0.4 to 0.7, 1.0, and 1.2 cm although strength remained constant from 0.7 to 1.2 cm. The strength of 4-strand circle-locking repairs with a suture purchase of 1.0 cm was statistically greater than that of the repairs with a suture purchase of 0.4 cm.

CONCLUSIONS

For both the 2-strand grasping and 4-strand circle-locking repair methods, the length of core suture purchase significantly influences the resistance to 2-mm gap formation and the ultimate strength of repairs in transversely lacerated flexor tendons. We determined that the optimal length of purchase is between 0.7 and 1.0 cm and that increased length of purchase from 0.7 to 1.2 cm does not increase the strength of the repair. Core suture purchase length of 0.4 cm or less results in significantly weaker repairs.

Investigation of locking configurations for tendon repair

PURPOSE

Locking sutures have proven beneficial to the strength of the repaired tendon. In this study we investigated the effects of 3 locks in the tendon-suture junction and their effect on repair strength.

METHODS

Forty-seven fresh pig flexor tendons were transected and repaired using 4-strand repairs with 3 different configurations of locks in each tendon-suture junction: 1 exposed cross-lock, 1 embedded cross-lock, and 1 circle lock. The tendons were subjected to a linear noncyclic load-to-failure test using a tensile testing machine. The initial gap, the 2-mm gap force, and the ultimate strength were measured to compare the biomechanical performance for each repair.

RESULTS

Despite noticeable differences in the configurations of locks the gap formation force and ultimate strength were not significantly different among the 3 tested locking configurations.

CONCLUSIONS

An exposed cross-lock, an embedded cross-lock, and a circle lock at tendon-suture junctions had similar locking power. Circle-lock repairs without cross-locking components produce tensile strength similar to cross-locking repairs. The findings of this study suggest that the creation of cross-configurations in locking repairs used conventionally by many surgeons is not essential to repair strength and that circle locking is as efficient as cross-locking in the repair of lacerated flexor tendons.

Effects of locking area on strength of 2- and 4-strand locking tendon repairs

PURPOSE

The area of the tendon within the locking suture configuration of the modified Pennington repair is an important determinant of eventual tendon strength. This 2-strand repair's loop configurations encompass a large cross-sectional area of the tendon. Many recently proposed repairs, however, consist of locks in a number of narrow sites on the tendon surface and most are multistranded. It is not clear how the area within the locks affects tendon strength and whether the effects of locking areas change according to the number of repair strands. In this study we investigate the effects of locking area on repair strength of 2- and 4-strand tendon repairs.

METHODS

Sixty-five fresh pig flexor tendons were divided equally into 6 groups and were transected completely. They were repaired with 2- or 4-strand techniques. The tendon-suture interface was a circle-locking junction and diameters of the locks were 1, 2, or 3 mm. The tendons were pulled in a tensile testing machine until failure of the repair and the mode of failure, 2-mm gap force, and ultimate strength were measured.

RESULTS

In the tendons with either 2- or 4-strand repairs locks with a diameter of 2 or 3 mm had significantly greater gap formation force and ultimate strength than those of 1 mm. The gap formation and ultimate forces were not statistically different between tendons with locks of 2 or 3 mm in diameter.

CONCLUSIONS

In both the 2- and 4-strand tendon repairs tested in this study repair strength increased as the diameter of locks of the repair increased from 1 mm to 2 or 3 mm. An increase in the diameter from 2 mm to 3 mm, however, did not increase the gap force and ultimate strength. These findings indicate that the cross-sectional area within the locks affects repair strength when the diameter of the locks is within a certain range (2 mm) and that further enlargement of the locking area does not increase strength.

Locking repairs for obliquely cut tendons: Effects of suture purchase and directions of locking circles

PURPOSE

Oblique cuts in tendons weaken conventional repairs but locking sutures improve the repair strength of the tendon. In this study we assessed how suture purchase and direction (or type) of locking sutures affect the repair strength.

METHODS

Ninety-three fresh pig flexor tendons were transected obliquely (45 degrees to the long axis of the tendon) and repaired with either a locking Kessler repair (with perpendicular or horizontal locking circles) or a locking cruciate method (with oblique locking or perpendicular locking circles). The suture purchase in the short side of the tendon stump with a perpendicular locking Kessler repair ranged from 0.3 to 1.2 cm. The gap formation and ultimate strength were measured to compare the biomechanical performance for each repair.

RESULTS

The repair strength increased significantly as the suture purchase increased from 0.3 to 1.0 cm in oblique tendon lacerations, with a suture span of 1.0 cm being the strongest. The strength decreased significantly when the span was 1.2 cm. The repairs with horizontal locking sutures were significantly weaker than those with perpendicular locking sutures. The locking cruciate repair with the perpendicular locking circles had strength identical to that of the cruciate with oblique locking circles.

CONCLUSIONS

Both suture purchase and the direction of locking circles affect the repair strength remarkably. For locking repairs the suture purchase of 1.0 cm in an obliquely cut tendon produced the highest strength; the repairs with a purchase less than 0.4 cm had significantly reduced strength. The strength of the repairs with locking circles perpendicular to the long axis of the tendon was significantly greater than that of the repairs with locking circles parallel to the long axis of the tendon.

Changes in tendon strength after partial cut and effects of running peripheral sutures

We performed a study to evaluate the tensile properties of partial tendon lacerations and the effects of peripheral sutures on the tendon strength. Seventy-two fresh pig flexor digitorum profundus tendons were divided equally into eight groups. Tendons in four of the groups were subjected to partial lacerations (60%, 70%, 80%, and 90%) and were not repaired. In the other four similar groups partial lacerations were repaired with running peripheral sutures. The tendons were subjected to load-to-failure tests in an Instron tensile machine to determine the initial, 1mm, 2mm gap formation forces and the ultimate strength. The tendons with lacerations of 80% and 90% had a remarkably lower tensile strength than those 60% and 70% lacerations. Running peripheral sutures increased the gap formation forces and the ultimate strength of all the tendons, though particularly those with 80% and 90% lacerations.

Embedded cross-stitch suture: an alternative to current cross-stitch peripheral suture

The cross-stitch peripheral suture has good strength, but the large amount of exposed suture on the tendon surface has restricted its clinical usage. We report a method of embedded cross-stitch that incorporates cross-stitches into peripheral sutures and reduces the amount of exposed suture on the tendon surface. Thirty-three fresh pig flexor tendons were divided equally into three groups and repaired with cross-stitch, embedded cross-stitch, or modified Halsted sutures. The tendons were tested in an Instron tensile machine to assess the mechanical performance of these repairs. With an identical number of strands across the repair site, the gap formation and ultimate forces of the embedded cross-stitch method were statistically greater than those of the cross-stitch and modified Halsted methods. The embedded cross-stitch method also had significantly greater stiffness and energy to failure than the cross-stitch method. The embedded cross-stitch method, with little suture exposure on the tendon and sufficient strength, presents an alternative to the current cross-stitch peripheral repair.

Biomechanical analysis of a modification of Tang method of tendon repair

We report a modification of the original Tang technique of tendon repair which uses fewer sutures and has fewer knots on the tendon surface. The modified method consists of six longitudinal and two horizontal strands that form an "M" configuration within the tendon and four dorsal longitudinal strands made with a single looped suture. Thirty-six fresh pig flexor tendons were divided and repaired with either the modified Tang or the Tang method. The tendons were subjected to linear or 90 degrees angular loading in an Instron tensile machine. The gap formation strength and ultimate strength of the modified Tang repair was statistically identical to those of the Tang method under linear tension. Under angular tension, the ultimate strength of the modified Tang method was greater than that of the Tang method.

Effects of direction of tendon lacerations on strength of tendon repairs

PURPOSE

We compared the tensile strength of different repair configurations on tendons with oblique and transverse lacerations.

METHOD

Seventy-two fresh pig flexor tendons were divided randomly and repaired using the modified Kessler, the cruciate, or the 4-strand Massachusetts General Hospital (MGH) repair methods. The tendons were lacerated either transversely or obliquely. They were repaired with conventional and oblique suture repairs. The 2-mm gap formation force and ultimate strength were determined as biomechanical performance for each repair.

RESULTS

The gap formation and ultimate strength of the tendons vary with orientations of tendon lacerations and suture methods. In the tendons repaired with the modified Kessler or the cruciate methods, the 2-mm gap formation and ultimate strength of obliquely cut tendons were significantly lower than those of transversely cut tendons. The obliquely placed modified Kessler or cruciate sutures significantly improved the repair strength in the tendons with an oblique laceration. In the tendons repaired with the MGH method, no statistical differences were found in the repair strength of obliquely and transversely lacerated tendons.

CONCLUSIONS

The direction of tendon lacerations affects strength of certain repair configurations. The nonlocking modified Kessler or the cruciate tendon repairs are weakened considerably when the tendon laceration is oblique but their mechanical performance is strengthened by re-orienting the repair strands to lie parallel to the laceration. The cross-locked configuration of the MGH repair is not affected by the obliquity of the tendon laceration.

Increased suture embedment in tendons: an effective method to improve repair strength

We evaluated the effect of length of suture embedment within tendons on the tensile strength of repaired tendons. Thirty fresh pig flexor tendons were divided into three groups and subjected to repairs with the Halsted tendon sutures in which 1/3, 1/2, and 2/3 of the length of the longitudinal sutures was embedded within the tendons. The repaired tendons were pulled to complete failure by an Instron tensile testing machine. The 2 mm gap-formation force, ultimate strength, stiffness, and energy to failure were greatest when 2/3 of the suture length was embedded within the tendon. The results indicate that suture embedment is an important contributor to the tensile properties of the repair, and that increase in length of suture embedment is an effective way to strengthen tendon repairs.

Biomechanical studies of 3 different 6-strand flexor tendon repair techniques

We investigated the gap formation and ultimate strength, energy to failure, and patterns of failure of tendon repairs with the modified Savage, Lim, and Tang methods. Fifty-four fresh-frozen flexor digitorum profundus tendons were assigned to 3 groups and repaired with one of the previously mentioned methods. Nine tendons from each group were pulled to failure in a tensile testing machine when they were subjected to a linear load. The 2-mm gap formation force of the tendons was 37.4 N for the modified Savage, 44.5 N for the Tang, and 40.2 N for the Lim method. Ultimate strength was 57.8 N for the modified Savage, 60.2 N for the Tang, and 51.3 N for the Lim method. Statistically, the gap formation force was significantly higher in the Tang method than in the modified Savage and the Lim methods. Ultimate strength of the modified Savage and Tang methods was similar and significantly higher than that of the Lim method. The rest of the tendons were subjected to angular tension by placement of the tendons against a pulley. The tests show that resistance of the modified Savage and Tang methods to angular tension was significantly greater than that of the Lim method. The results indicate that the resistance to failure and failure modes of the repairs vary according to number of locking junctions with the tendon, location, and orientation of the sutures regardless of an equal number of strands across the repair site. We conclude that the modified Savage and Tang methods have greater tensile strength than the Lim method and may more effectively resist linear and angular tension generated by postoperative tendon motion.