Tendon repair using flexor tendon splints: An experimental study

Mechanical strength of tendon repair using Dacron tendon splints across the laceration site were evaluated in human cadaver profundus tendons; the splints were placed both on the dorsal surface and internally within the tendon substance. Comparison was made to modified Kessler, Becker, and Savage repair techniques. Ultimate tensile strength was 2.55 kgf for the Kessler, 3.00 kgf for the Becker, 8.29 kgf for the Savage, 8.46 kgf for the internal tendon splint, and 8.10 kgf for the dorsal tendon splint; the Savage and both Tendon Splints techniques had significant higher tensile strength than the Kessler and Becker. Gap strength was 1.44 kgf for the Kessler, 2.22 kgf for the Becker, 2.45 kgf for the Savage, 2.05 kgf for internal tendon splint, and 3.15 kgf for the dorsal tendon splint. The dorsal tendon splint technique showed significant greater gap strength than the other four techniques. There was no significant difference in the magnitude of the gap during cyclic testing of these techniques; however, three of seven Kessler repairs failed and one of six Becker repairs failed. The results of these cadaver studies suggest that both tendon splint repair techniques are comparable to the Savage and may have sufficient strength to allow postoperative active motion against minimal resistance. Further in vivo testing is in order.     

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.     

Strength analysis and comparison of the Teno Fix Tendon Repair System with the two-strand modified Kessler repair in the Achilles tendon

BACKGROUND: Various options exist for repair of Achilles tendon ruptures, yet a method that consistently provides sufficient gap resistance to allow early mobilization remains elusive. This study compares the mechanical performance of a modified Kessler repair with that of the Teno Fix Tendon Repair System (Ortheon Medical, LLC) in matched pairs of cadaver Achilles tendons. METHODS: The two-strand modified Kessler repair was selected as the control construct on the basis of literature review and physician interviews which identified it among the many options as a popular method for repair of acutely ruptured Achilles tendons. Test specimens were harvested from matched pairs of cadaver ankles. The tendons were transected 3.5 cm proximal to the calcaneal insertion and repaired with either the two-strand modified Kessler suture construct or the Teno Fix Tendon Repair System. Assignment to the modified Kessler or Teno Fix group was done randomly for the first member of each pair. All test and control repairs were performed by the same author to reduce variability. Evaluation of the repairs consisted of tensile strength testing and measurement of the gap formation and peak stresses. RESULTS: Gap and peak stress for the two-strand modified Kessler repair were 0.30 +/- 0.15 N/mm2 and 1.03 +/- 0.51 N/mm2, respectively. For the Teno Fix repairs the mean gap and peak stress values were 0.80 +/- 0.46 N/mm2 and 1.19 +/- 0.12 N/mm2, respectively. The mean gap formation stress was significantly higher in the Teno Fix repairs than in the control repairs (p < .0005). There was no significant difference in peak strength between the repairs (p < .10). CONCLUSIONS: The Teno Fix repair was superior to the modified Kessler repair. In the Teno Fix repairs, the gap formation stress was 67% of the peak tensile stress. In comparison, in the modified Kessler repairs, the gap formation stress was 29% of the peak stress. This can be correlated to the elastic property of the modified Kessler suture and the initial tightening of the suture around the tendon fibers. The Teno Fix system is nonelastic and is fully tensioned during installation. This lends to a more gap resistant repair.     

Biomechanical assessment of a new type of flexor tendon repair

A four-strand adaptation of the Kessler repair is described and the results of biomechanical testing in pig tendons are reported. The strength of our repair was compared against standard Kessler repairs using Ethibond or Ti.cron as the core sutures. The average tensile strength for the Ethibond Kessler repair was 33 Newtons and that of the Ti.cron Kessler repair was 31 Newtons. The average tensile strength for the Evans repair was 52 Newtons. This new method of flexor tendon repair is significantly stronger than the modified Kessler repair and is simpler to use than other multi-strand repair techniques.     

The Achillon achilles tendon repair: is it strong enough?

BACKGROUND: Open repair of the Achilles tendon is associated with wound breakdown, infection and percutaneous methods risk sural nerve injury. The Achillon mini-incision technique can reduce these risks and may provide the opportunity for early active rehabilitation. The aim of this study was to compare the strength of the Achillon method with the commonly used Kessler method and to assess whether the strength of the repair was related to tendon diameter. MATERIALS AND METHODS: Simulated ruptures in sheep Achilles tendons were repaired using either the Achillon method or a two-strand Kessler technique with a No. 2 Ticron suture (Tyco Healthcare, UK). Each tendon diameter was measured, and matched for both groups. Specimens were loaded to failure using an Instron tensile testing machine (Instron Limited, UK). RESULTS: Mean load to failure for the Achillon repair was 153 N+/-60 (range, 65 to 270), and the mean load to failure for the Kessler Repair was 123 N+/-24 (range, 75 to 150). This difference was not statistically significant (p=0.21). There was a statistically significant higher mean load to failure for wider tendons repaired by the Achillon method (p=0.05), however mean load to failure was not related to tendon width in Kessler repairs (p=0.23). CONCLUSION: This is the first study to compare these two methods of repair. The Achillon repair has comparable tensile strength to the Kessler Repair. CLINICAL RELEVANCE: The Achillon repair appears to be a biomechanically sound method of repair for the acutely ruptured Achilles tendon.     

The influence of cross-sectional area on the tensile properties of flexor tendons

Clinicians have long noted substantial variation in the cross-sectional size of flexor tendons in the hand; however, data indicating that surgical repair techniques of lacerated flexor tendons should be altered according to size are unavailable. Our objectives were to evaluate the cross-sectional size differences among tendons within the same hand and to correlate tendon size with tensile mechanical properties after suture repair. Fifty human cadaver flexor digitorum profundus tendons were measured with digital calipers to determine radioulnar and volardorsal diameters. Twenty tendons were used to measure resistance to suture pull-through; tendons were transected at the A2 pulley, and a transverse double-stranded 4-0 Supramid suture (S. Jackson, Inc, Alexandria, VA) was passed through the radioulnar plane of the tendon 1 cm from the transection site. The remaining tendons were transected and repaired by using a modified Kessler repair with double-stranded 4-0 Supramid suture. Both tendon repairs and tendon-suture pull-through specimens were tested to failure in tension by using a material testing machine. Dorsovolar tendon height and tendon cross-sectional area varied significantly between digits, with an average difference of approximately 40% between the values of the smallest (fifth) and largest (third) fingers. Yield and ultimate force determined by pull-through tests of the simple transverse suture correlated positively with tendon radioulnar width. Tensile properties of tendons repaired with a double-stranded modified Kessler repair, however, did not depend significantly on tendon size. These results indicate that the strength of the commonly used Kessler suture technique is not dependent on tendon cross-sectional size within the clinically relevant range of tendons evaluated.     

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.     

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.     

Total and intrasynovial work of flexion of human cadaver flexor digitorum profundus tendons after modified Kessler and MGH repair techniques

PURPOSE: The purpose of this study was to compare directly the total work of flexion (TWOF) and the intrasynovial work of flexion (IWOF) of human flexor digitorum profundus tendons and to analyze the ratio of the IWOF to the TWOF of human flexor digitorum profundus tendons. These factors may be important clinically in understanding the role of different methods of postoperative tendon rehabilitation for different types of tendon repairs, especially at the early stage after tendon repair. METHODS: Two different tendon repairs, the modified Kessler and the Massachusetts General Hospital, were used in 18 digits from 6 freshly frozen human cadaver hands. The TWOF and the IWOF were tested by using a digit-resistance testing device. RESULTS: After tendon repair the TWOF increased 11.2% and 26.9% for the modified Kessler and MGH groups, respectively. The differences in increase between the 2 groups were significant. The IWOF increased 126.8% and 308.8% for the modified Kessler and Massachusetts General Hospital groups, respectively. The IWOF accounted for 16.4% of the TWOF for the intact tendon; this percentage was 28.6% and 45.0% for the modified Kessler and Massachusetts General Hospital groups, respectively. CONCLUSIONS: The IWOF accounts for 16% of the TWOF of normal human cadaver digits but it accounts for a much higher fraction after tendon repair. The ratio of the work of flexion within the synovial sheath to the TWOF varies depending on the type of repair chosen.     

A biomechanical analysis of multistrand repairs with the Silfverskiold peripheral cross-stitch

We compared the bulking and tensile strength of the Pennington modified Kessler, Cruciate and the Savage repairs in an ex vivo model. A total of 60 porcine tendons were randomised to three groups, half repaired using a core suture alone and the remainder employing a core and peripheral technique. The tendons were distracted to failure. The force required to produce a 3 mm gap, the ultimate strength, the mode of failure and bulking for each repair were assessed. We found that there was a significant increase in strength without an increase in bulk as the number of strands increased. The Cruciate repair was significantly more likely to fail by suture pullout than the Pennington modified Kessler or Savage repairs. We advise the use of the Savage repair, especially in the thumb, and a Cruciate when a Savage is not possible. The Pennington modified Kessler repair should be reserved for multiple tendon injuries.     

A biomechanical comparison of multistrand flexor tendon repairs using an in situ testing model

An in situ testing model was used to evaluate the performance of zone II flexor tendon repairs and to compare the biomechanical properties of 4-strand repairs with 2- and 6-strand repairs. Fifty digits from human cadaveric hands were mounted in a custom apparatus for in situ tensile testing. Intratendinous metallic markers were placed so that gap formation could be determined by fluoroscopy during tensile testing. Three 4-strand repairs (the 4-strand Kessler, the cruciate, and a locked modification of the cruciate repair) were compared with the 2-strand Kessler and the 6-strand Savage repairs. Ultimate tensile strength, load at 2-, 3-, and 4-mm gap formation, and work of flexion were determined. Work of flexion, while increased for the multistrand repairs, did not show a statistically significant correlation with the number of strands crossing the repair site. The tensile strength of the 6-strand repair was significantly greater than each of the 2- or 4-strand repairs. The tensile strength of all 4-strand repairs was significantly greater than the 2-strand repair. The 6-strand repair and the 2 cruciate repairs demonstrated a statistically increased resistance to gap formation compared with the 2-strand Kessler repair, but notably there was no statistically significant difference in gap resistance between the 2and 4-strand Kessler repairs. This in situ tensiletesting protocol demonstrated that 4- and 6-strand repairs have adequate initial strength to withstand the projected forces of early active motion protocols. Three of the 4 multistrand repairs demonstrated improved gap resistance compared with the 2-strand repair. The presence of the second suture in the Kessler configuration significantly increases its strength but not its gap resistance.     

Simplifying four-strand flexor tendon repair using double-stranded suture: a comparative ex vivo study on tensile strength and bulking

We have compared a simple four-strand flexor tendon repair, the single cross-stitch locked repair using a double-stranded suture (dsSCL) against two other four-strand repairs: the Pennington modified Kessler with double-stranded suture (dsPMK); and the cruciate cross-stitch locked repair with single-stranded suture (Modified Sandow). Thirty fresh frozen cadaveric flexor digitorum profundus tendons were transected and repaired with one of the core repair techniques using identical suture material and reinforced with identical peripheral sutures. Bulking at the repair site and tendon-suture junctions was measured. The tendons were subjected to linear load-to-failure testing. Results showed no significant difference in ultimate tensile strength between the Modified Sandow (36.8 N) and dsSCL (32.6 N) whereas the dsPMK was significantly weaker (26.8 N). There were no significant differences in 2 mm gap force, stiffness or bulk between the three repairs. We concluded that the simpler dsSCL repair is comparable to the modified Sandow repair in tensile strength, stiffness and bulking.     

Tensile strength of a new suture for fixation of tendon grafts when using a weave technique

PURPOSE: To evaluate a new corner stitch construct for tendon graft or tendon transfer fixation and compare the tensile strength with a conventional central cross-suture design in human cadaver tendons. METHODS: Flexor digitorum profundus tendons of the index, middle, and ring fingers (48 total) were used as recipients and palmaris longus, extensor indicis proprius, and extensor digitorum communis tendons of the index finger (48 total) were used as grafts from 16 fresh-frozen human cadaver hands. We compared the cross-stitch technique with a new corner stitch technique in tendon repairs made with 1, 2, or 3 weaves (8 per group). Tendons were sutured at each weave with either 2 full-thickness cross-stitches or 4 partial-thickness corner stitches of 4-0 nylon. Mattress sutures also were placed through the free tendon end for each repair type. The tensile strength of the tendon-graft composite was measured with a materials testing machine. RESULTS: The tensile strength of the repairs increased significantly with the number of weaves. When 2 or 3 weaves were used with the corner stitch or when 3 weaves were used with the cross-stitch, the repairs were significantly stronger. Although no significant difference in strength to failure was noted when comparing cross and corner stitches with equivalent numbers of weaves, qualitatively there was a difference in mode of failure with the 3-weave corner stitches failing primarily by intrasubstance tendon failure and the 3-weave cross-stitch repairs failing by tendon pullout. CONCLUSIONS: The corner stitch is as strong as conventional cross-stitch repairs and its superficial placement may be more favorable to tendon blood supply. This repair may be advantageous for clinical applications.     

Biomechanical analysis of the cruciate four-strand flexor tendon repair

The purpose of this study was to develop and test in vitro a new flexor tendon suture technique that was simple and easy to perform, yet strong enough to withstand the projected forces of an in vivo active motion rehabilitation protocol. Forty human cadaveric flexor digitorum profundus tendons were divided and repaired using 1 of 4 suture techniques (the modified Kessler, the Strickland, the modified 4-strand Savage, and the Cruciate 4-strand repairs). Each repair was tested using a slow-test machine and displacement control at 2 mm/s. Force applied, the resultant gap, and ultimate tensile strength were recorded and statistical comparisons were performed using a two-tailed Student's t-test with level of significance set at p = .05. The Cruciate suture technique was demonstrated to be nearly twice as strong to 2-mm gap formation (44 N) compared with the Kessler, Strickland, and Savage repairs. Ultimate tensile strength was also significantly stronger for the Cruciate technique (56 N) than the Kessler, Strickland, or Savage repairs. The technique was significantly faster to perform than the Savage or Strickland repairs and was comparable in repair time to the 2-stranded Kessler repair. The design of the new suture technique allowed the tendon repair to be completed with the ease and speed of a 2-strand technique, but bestowed on the repair strength that exceeded current 4-strand techniques.     

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.     

Does Strand Configuration and Number of Purchase Points Affect the Biomechanical Behavior of a Tendon Repair? A Biomechanical Evaluation Using Different Kessler Methods of Flexor Tendon Repair

This study compares the mechanical properties of modified Kessler and double-modified Kessler flexor tendon repair techniques and evaluates simple modifications on both methods. Forty fresh sheep flexor tendons were divided equally into four groups. A transverse sharp cut was done in the middle of each tendon and then repaired with modified Kessler technique, modified Kessler with additional purchase point in the midpoint of each longitudinal strand, double-modified Kessler technique, or a combination of outer Kessler and inner cruciate configuration based on double-modified Kessler technique. The tendons were tested in a tensile testing machine to assess the mechanical performance of the repairs. Outcome measures included gap formation and ultimate forces. The gap strengths of the double-modified Kessler technique (30.85 N, SD 1.90) and double-modified Kessler technique with inner cruciate configuration (33.60 N, SD 4.64) were statistically significantly greater than that of the two-strand modified Kessler (22.56 N, SD 3.44) and modified Kessler with additional purchase configuration (21.75 N, SD 4.03; Tukey honestly significant difference test, P < 0.000). There were statistically significant differences in failure strengths of the all groups (analysis of variance, P < 0.000). With an identical number of strands, the gap formation and ultimate forces of the repairs were not changed by additional locking purchase point in modified Kessler repair or changing the inner strand configuration in double-modified Kessler repair. The results of this study show that the number of strands across the repair site together with the number of locking loops clearly affects the strength of the repair; meanwhile, the longitudinal strand orientation and number of purchase points in a single loop did not affect its strength.     

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

This study compared the biomechanical behaviour of repairs in the human flexor digitorum profundus tendon in zones I, II and III with repairs of different segments of the porcine flexor tendon of the second digit and the extensor digiti quarti proprius tendon, in order to assess the validity of porcine tendons as models for human flexor tendon repairs. These porcine tendons were selected after comparing their size with the human flexor digitorum profundus tendon. The tendon repairs were done in three segments of each porcine tendon and repairs in the human tendons were done in zones I,II and III. Ten tendons in each group yielded a total of 90 specimens. A modified Kessler repair was done with 3-0 coated braided polyester suture and subjected to uniaxial tensile testing. In human flexor tendons, the ultimate force was higher in zones I and II than in zone III. The porcine flexor digitorum profundus tendon from the second digit and the proximal segment of the extensor digiti quarti proprius tendon behaved similarly to the human flexor tendon in zone III and can be considered as surrogates for the human flexor tendon.     

Gliding resistance after FDP and FDS tendon repair in zone II

Many suture techniques have been described for flexor tendon repair. While many of these sutures have been tested and used clinically, the interaction between repairs of the flexor digitorum profundus (FDP) and flexor digitorum superficialis (FDS) in the same digit has not been rigorously examined. Moreover, while much data are available on the mechanical properties of various suture techniques for FDP repair, much less is known about the mechanical performance of FDS repairs during motion of tendons.

To make up for this lack of information, we measured the gliding resistance of the repaired FDP tendon, as compared to different FDS tendon repairs in a human cadaver model. The FDP tendon was repaired with a modified Kessler technique, while the FDS was repaired with a modified Kessler (n = 10), Becker (n = 10), or a new double running zig-zag suture (n = 10). The modified Kessler repair had a threefold increase from normal gliding resistance, the Becker repair increased twofold, and the zig-zag repair increased twofold. The peak gliding resistance increased twofold with a modified Kessler repair, 2.5-fold with a Becker repair, and 2.5-fold with a zig-zag repair.     

Gliding resistance after FDP and FDS tendon repair in zone II: an in vitro study

Many suture techniques have been described for flexor tendon repair. While many of these sutures have been tested and used clinically, the interaction between repairs of the flexor digitorum profundus (FDP) and flexor digitorum superficialis (FDS) in the same digit has not been rigorously examined. Moreover, while much data are available on the mechanical properties of various suture techniques for FDP repair, much less is known about the mechanical performance of FDS repairs during motion of tendons. To make up for this lack of information, we measured the gliding resistance of the repaired FDP tendon, as compared to different FDS tendon repairs in a human cadaver model. The FDP tendon was repaired with a modified Kessler technique, while the FDS was repaired with a modified Kessler (n = 10), Becker (n = 10), or a new double running zig-zag suture (n = 10). The modified Kessler repair had a threefold increase from normal gliding resistance, the Becker repair increased twofold, and the zig-zag repair increased twofold. The peak gliding resistance increased twofold with a modified Kessler repair, 2.5-fold with a Becker repair, and 2.5-fold with a zig-zag repair.     

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.