Cross stitch peripheral tendon repair: a mechanical comparison with core stitch techniques

The purpose of this experimental study was to compare certain mechanical properties of a true epitendineal cross stitch suture with simple and double locking core tendon repairs. Using tensile strength and tendon lengthening until gap formation as measurement parameters, these three types of repair were tested in human flexor and extensor tendons from fresh cadavers. The peripheral cross stitch and the locked core repairs were found to have a greater lengthening capacity than the simple core suture, whereas the latter significantly better withstood axial load. Our findings established that, at least when used as a true epitendinous suture, the cross stitch technique alone was not suited for the repair of severed tendons. However, its design is particularly useful in preventing the suture site from potentially restrictive bulking.     

A new core suture technique for flexor tendon repair: biomechanical analysis of tensile strength and gap formation

The purpose of this study was to test in vitro a new flexor tendon suture technique that has been developed to withstand the in vivo forces of active tendon motion. This new core suture technique involves locking loops in the form of a cross stitch. The new technique was tested for ultimate tensile strength and gap formation in cadaver human flexor tendons on a tensile testing machine. The new technique proved significantly stronger than the modified Kessler core suture.     

Comparison of postoperative early active mobilization and immobilization in vivo utilising a four-strand flexor tendon repair

We evaluated a technique of four-strand double-modified locking Kessler flexor tendon repair in healing tendons. Seventy-two canine flexor digitorum profundus tendons in Zone 2 were repaired and evaluated following either active mobilization or immobilization at 0, 7, 14, 28 and 42 days after surgery. Fifty-six tendons were examined for gap and ultimate strength using a tensile testing machine and 16 were evaluated with standard hematoxylin and eosin, and Masson's trichrome staining. All tendons healed without rupture or gap formation of more than 1 mm, thus demonstrating that this repair technique has enough tensile strength to withstand early active mobilization. The gap and ultimate strength of actively mobilized tendons did not decrease significantly during the first 7 days, and were significantly greater than those of immobilized tendons throughout the 42-day study period. Actively mobilized tendons healed without the extrinsic adhesions and large tendon calluses that were found in immobilized tendons.     

Zone II tendon repairs augmented with autogenous dorsal tendon graft: a biomechanical analysis

We investigated the biomechanical properties of a new technique for tendon repair that reinforces a standard suture with an autogenous tendon graft. A dynamic in situ testing apparatus was used to test 40 flexor digitorum profundus tendons harvested from fresh-frozen cadaver hands. The tendons were cut and repaired using 1 of 4 suture techniques: 2-strand modified Kessler, 4-strand modified Kessler, 6-strand modified Savage, and 2-strand modified Kessler augmented with autogenous dorsal tendon graft. The augmented repair uses 1 slip of the flexor digitorum superficialis tendon secured to the dorsal surface of the repair site with a continuous stitch. Ultimate tensile strength, resistance to gap formation, and work of flexion were measured simultaneously on an in situ tensile testing apparatus. No significant difference in tensile strength was found between the augmented repair and the 6-strand Savage repair. The augmented repair and the 6-strand Savage repair showed significantly greater ultimate tensile strength than the 2- and 4-strand repairs. The augmented repair had significantly greater resistance to 2 mm gap formation than the other 3 repairs. We were unable to show a significant difference in work of flexion between the repairs with the numbers tested (n = 10). Our findings suggest that the augmented repair is strong enough to tolerate the projected forces generated during active motion without dehiscence or gap formation at the repair site.     

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

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

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.     

Cyclic stress analysis of flexor tendon repair

A method of evaluating flexor tendon repair techniques with the use of cyclic testing is presented. This type of evaluation complements the presently used load-to-failure tests by providing more detailed information about gap formation at the repair site. During load-to-failure testing in this study, core sutures alone demonstrated initial gap formation at 0.85 kg tensile force or more; yet on cyclic testing all techniques demonstrated gap formation of 1.9 mm or greater at 0.5 kg tensile force. Thus cyclic testing demonstrated gap formation not readily apparent on load-to-failure testing. An epitenon stitch placed circumferentially around the laceration site added strength in both load-to-failure and cyclic tests, and significantly reduced gap formation regardless of the core suture technique.     

Tensile properties of suture methods for repair of partially lacerated human flexor tendon in vitro

The decision to treat zone II partially lacerated flexor tendons is challenging, because there can be justification for either repair or no repair, depending on the surgeon's assessment of the strength of the residual intact portion of the tendon. In this study tensile properties of various repair techniques were compared. Cadaveric human flexor tendons (n = 118) were lacerated to 75% of their cross-section and repaired with either a core suture method (Kessler, modified Kessler, Savage, Lee, augmented Becker, or Tsuge all finished with a circumferential running suture), an epitendinous suture alone (circumferential or partial), or the tendons were left unrepaired. Among the core suture methods there was no significant difference (p >.05) in maximum failure force (overall mean, 211.2 N; SD, 53.2) or force to produce a 1.5-mm gap (74.1 N; SD, 49.7). Likewise there was no significant difference (p >.05) in tendon stiffness (41.0 N/mm; SD, 14.0) or resistance to gap formation (52.3 N/mm; SD, 23.1). In comparison, repairs without the core suture, including unrepaired tendons, were significantly weaker (144.7 N, p <.001) and had a marginally lower stiffness (p =.04) but had a similar resistance to gap formation (43.5 N/mm).     

A biomechanical analysis of the modified Tsuge suture technique for repair of flexor tendon lacerations

Thirty-six flexor tendons from fresh frozen cadavers were randomized to three types of repairs: a Kessler-Tajima, a 4-strand modified Tsuge, and a 6-strand modified Tsuge. All repairs were accompanied by a standard epitendinous suture. The repaired tendons were then tested to initial gap and ultimate failure in an Instron machine. The average forces to ultimate failure were 31.8 N (SD, 8.8), 48.4 N (SD, 10.7), and 64.2 N (SD, 11.0) respectively. The 6-strand modified Tsuge suture was significantly stronger than the other repairs and the 4-strand modified Tsuge was significantly stronger than the 2-strand Kessler-Tajima. The 6-strand and 4-strand modified Tsuge repairs appear strong enough to withstand the forces generated during early active range of motion flexor tendon rehabilitation protocols. Clinical trials are required to evaluate the usefulness of these repairs.     

The Interlocking Modification of the Cross Locked Cruciate Tendon Repair (Modified Adelaide Repair): A Static and Dynamic Biomechanical Assessment

The 4-strand cross-locked cruciate flexor tendon repair technique (Adelaide technique) has been shown to have comparably high resistance to gap formation and ultimate tensile strength. This study aimed to determine whether an interlocking modification to the Adelaide repair would impart improved biomechanical characteristics. Twenty four sheep flexor tendons were harvested, transected and repaired using either standard or modified Adelaide techniques. Repaired tendons were cyclically loaded. Gap formation and ultimate tensile strength were measured. Additionally, suture exposure on the tendon surface was determined. There was a statistically significant increase in resistance to gap formation in the early phase of cyclic loading within the modified Adelaide group. In the later stages of testing no significant difference could be noted. The average final load to failure in the modified group was higher than the standard group but this did not achieve statistical significance. Interlocking suture techniques in four strand tendon repair constructs can improve gapping behavior in the early phase of cyclic loading.     

Effect of suture size on locking and grasping flexor tendon repair techniques

An experimental study was performed using human cadaver flexor tendons to investigate the effect of locking and grasping loop techniques on the tensile properties of repaired flexor tendons, which closely resemble the clinical model. Statistically significant improvement was observed only with the locking loop technique for ultimate and gap strength values using 2-0 core suture and ultimate strength values using 3-0 core suture. There was no statistically significant increase in tensile strength values using 4-0 core suture material. A heavier core suture used with the locking loop technique provided greater ultimate and gap strength of a repaired tendon than when used with the grasping loop technique.     

Biomechanical evaluation of flexor tendon repair techniques

Immediate active mobilization of repaired tendons is thought to be the most effective way to restore function of injured flexor tendons. Sixty human flexor digitorum profundus tendons were used to evaluate techniques for active tendon motion. The tendons were divided equally into six groups, and each group was assigned to one of the following techniques: Kessler core suture plus running peripheral suture, Kessler plus cross-stitch suture, Kessler plus Halsted suture, Tang core suture plus running peripheral suture, Tang plus cross-stitch suture, or Tang plus Halsted suture. Immediately after tendon repair, an Instron tensile testing machine was used to measure the 2-mm gap formation force, ultimate strength, elastic modulus, and energy to failure of the tendons repaired by these techniques. Ultimate strength, elastic modulus, and energy to failure were measured in load displacement curve. Results showed that the ultimate strength of the Tang plus Halsted or cross-stitch was, respectively, 116.8 +/- 9.6 N and 94.6 +/- 7.8 N; and 2-mm gap formation force was, respectively, 86.6 +/- 4.9 N and 71.9 +/- 5.1 N. The Tang plus Halsted or cross-stitch methods had a statistically significant increase in ultimate strength and 2-mm gap formation force as compared with the Kessler core suture or Tang plus running peripheral suture method. Elastic modulus and energy to failure of the Tang plus Halsted or cross-stitch suture were statistically higher than those of other techniques. The Tang plus cross-stitch or Tang plus Halsted sutures had the highest strength among the tested methods and are appropriate techniques for tendon repair in which the goal is immediate active tendon motion.     

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.     

A biomechanical study of Tang's multiple locking techniques for flexor tendon repair

This study was designed to biomechanically compare Tang's multiple looped locking techniques with various suture techniques for flexor tendon repair in the hand. Fifty flexor digitorum profondus tendons taken from pig toes were used as models; The tendons were transected in the middle part of zone 2 defined as the area beneath bifurcation of the flexor digitorum superficialis tendons, and were repaired by five different suture methods: (1) modified Kessler, (2) Tsuge's suture, (3) double Kessler, (4) modified Kessler plus Tsuge, and (5) Tang's suture. The repaired tendons were placed in an Instron tensile testing machine to determine the tensile properties of the repair. 2 mm gap formation force and ultimate tensile strength were measured during the test. Maximal work to failure were calculated according to area under the load-displacement curve of the test. 2 mm gap formation force was 21.5 N for the Kessler, 20.6 N for the Tsuge, 31.6 N for double Kessler, 30.9 N for the Kessler plus Tsuge and 41.4 N for the Tang. Ultimate tensile strength was 23.5 N for the Kessler, 22.9 N for the Tsuge, 34.5 N for the Kessler plus Tsuge and 45.6 N for the Tang. Statistically, Tang's suture had the greatest gap formation force, ultimate strength and energy for failure among the five techniques (p < 0.01 or p < 0.001). Gap formation force, ultimate strength and energy to failure for double Kessler or the Kessler plus Tsuge were significantly greater than those for the Kessler or the Tsuge (p < 0.05 or < 0.01). The tendons repaired by Tang's method tolerated a significantly higher tensile load (133 to 198% of the other techniques) than the other methods. Among the methods tested, Tang's multiple looped locking suture provides sufficient gap resistance and tensile strength that may be able to withstand early active mobilization after primary flexor tendon repair.     

Effects of tension direction on strength of tendon repair

We investigated changes of tensile strength in tendon repair according to tension direction. Thirty-six fresh-frozen digital flexor tendons were divided into 4 groups with 9 tendons each. The tendons were repaired by the modified Kessler method. Sutured tendons were pulled against pulleys at angles of 0 degrees, 30 degrees, 60 degrees, and 90 degrees to the direction of the pull of the testing machine in the 4 groups, respectively. The repaired tendons were tested in a tensile machine to determine 2-mm gap formation force and ultimate strength of the tendons. The 2-mm gap formation force and ultimate strength in the tendons pulled at 0 degrees were statistically higher than those in the tendons pulled at 30 degrees, 60 degrees, and 90 degrees. The 2-mm gap formation force of the tendons pulled at 30 degrees, 60 degrees, and 90 degrees was 86% +/- 10%, 73% +/- 9%, and 64% +/- 8% of that at 0 degrees, respectively. Ultimate strength of tendons pulled at 30 degrees, 60 degrees, and 90 degrees was 89% +/- 9%, 82% +/- 11%, and 76% +/- 8% of that at 0 degrees, respectively. Values of the 2-mm gap formation force and ultimate strength were statistically the lowest in the group with a pulling angle of 90 degrees. There was no statistically significant difference in repair strength between tendons tested at 0 degrees and those in the model without pulleys. The strength of tendon repair changed considerably according to direction of tension added to the tendons. The gap formation force and ultimate strength decreased as angles of tension increased. The results imply that a repaired tendon will be weakened as the finger is increasingly flexed. The decrease in repair strength should therefore be considered in planning a tendon suture to tolerate active finger flexion and a tendon motion protocol after primary tendon repair.     

Effect of absorbable polydioxanone flexor tendon repair and restricted active mobilization in a canine model.

We performed an experimental study to evaluate the mechanical and histologic healing process of flexor tendon repair using absorbable polydioxanone monofilament followed by active mobilization. Sixty-four canine flexor digitorum profundus tendons were repaired using polydioxanone monofilament or control braided polyester. Animals were evaluated 7, 14, 28, and 42 days after surgery with 12 day 0 control tendons. All repaired tendons healed without rupture or gap formation. Mechanically, all specimens had adequate tensile strength enabling active mobilization. The tendons that were repaired using braided polyester healed without initial tensile depression; however, the ultimate tensile strength values of polydioxanone specimens showed a significant decrease at day 14. Histologically, an inflammatory response was observed around the polydioxanone monofilament; this reaction increased from day 14 to day 42. However, the inflammatory response did not cause large adhesions or large tendon callus formation. This method of using absorbable suture material for tendon repair has the potential for use in the clinical setting.     

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.     

The effect of flexor tendon repair bulk on tendon gliding during simulated active motion: an in vitro comparison of two-strand and six-strand techniques

The gliding function of 2-strand (Tajima) and 6-strand (Savage) techniques of flexor tendon repair were compared in an in vitro biomechanical model. Stainless steel beads were inserted directly into the metacarpals, phalanges, and flexor digitorum profundus tendons of 22 human cadaver specimens. The FDP tendons were loaded from 5 to 25 N using a pneumatic actuator. The angular rotation and tendon excursion of the cadaver specimens were measured radiographically. The gliding function of the repairs was compared with core suture only, core suture plus epitenon repair, and sheath repair. There was no significant difference in angular rotation or linear excursion between the 2-strand and 6-strand techniques of flexor tendon repair. The addition of the epitendinous suture to the core suture improved the angular rotation and linear excursion for the 2-strand technique. Although the 6-strand repair tended to increase the repair site bulk more than the conventional 2-strand technique, the gliding function of the repair techniques was equivalent.     

Comparative biomechanic performances of locked cruciate four-strand flexor tendon repairs in an ex vivo porcine model

PURPOSE: To investigate the effects of 3 different locking configurations on repair strength when used in a cruciate four-strand repair. METHODS: Sixty fresh porcine flexor tendons were transected and repaired with cruciate four-strand core suture repairs with 3 different locking configurations: simple locks (a modification of the Pennigton method), circle locks, and cross locks. Half of the repairs in each locking group were reinforced with a peripheral suture. The tendon repairs were subjected to linear load-to-failure testing. Outcome measures were 2-mm gap force and ultimate tensile strength. RESULTS: The cross lock repair had significantly greater 2-mm gap force and ultimate tensile strength than the simple lock repair, both with and without a peripheral suture. The cross lock repair showed significantly greater 2-mm gap force without a peripheral suture and significantly greater ultimate tensile strength with a peripheral suture than the circle lock repair. With peripheral reinforcement, the cross lock cruciate repair had a mean 2-mm gap force of 92 N and ultimate tensile strength of 119 N. The cross lock cruciate repair consistently produced the strongest biomechanic performance in all outcome measures. CONCLUSIONS: Locking configuration influences the biomechanic performance of cruciate four-strand flexor tendon repairs. Our results suggest that the cruciate repair with cross locks is stronger than repairs with simple locks or circle locks. Whether the results of this ex vivo porcine linear model can be translated to the clinical arena is unknown, because the factors of tendon/sheath friction, tendon healing, and compromised tendon viability from the lock were not addressed.     

Repair strength of tendons of varying gliding curvature: a study in a curvilinear model

PURPOSE: This study was done to investigate changes in the strength of the repaired tendons by different curvatures of tendon motion arcs. METHOD: Forty-two fresh-frozen digital flexor tendons were divided into 4 groups and were repaired by the modified Kessler method with a running peripheral suture. The tendons were pulled over pulleys with tension at a fixed angle of 90 degrees, but radii of gliding curvature of the pulleys were set at 2.0, 1.5, and 1.0 cm in 3 groups, respectively. The tendons in the other group were subjected to linear tension. These tendons were tested in an Instron tensile machine to determine the 2-mm gap formation force and ultimate strength of the repairs. RESULTS: The 2-mm gap formation force of the tendons pulled over the curvature of a 2.0-, 1.0-, and 0.5-cm radius was, respectively, 69%, 61%, and 49% of that pulled linearly. The ultimate strength of the tendons over curvatures of 2.0-, 1.5-, and 1.0-cm radius was, respectively, 77%, 73%, and 63% of that of tendons pulled with linear tension. The gap formation force and ultimate strength were statistically the lowest in the tendons with a gliding radius of curvature of 1.0 cm. Both the gap formation force and the ultimate strength of tendon repairs decreased as the radius decreased. CONCLUSIONS: The curvature of tendon motion arcs affects the repair strength of the tendons. The findings suggest an increased likelihood of repair ruptures in the tendons that glide along curvatures over the sheaths, pulleys, or joints.