Comparison of zone II flexor tendon repairs using an in vitro linear cyclic testing protocol

Biomechanical Evaluation of a Tubular Braided Construct for Primary Deep Flexor Tendon Surgery

PURPOSE

Immediate postoperative mobilization has been shown to avoid adhesion formation and improve range of motion after flexor tendon repair. A tubular braided construct was designed to allow for these rehabilitation protocols.

METHODS

In this ex vivo study, 92 ovine flexor tendons were divided randomly into 2 equal groups. After creating a transection, the tendons of the first group were repaired using a tubular braided construct. This construct, consisting of a tubular braid of polypropylene and polyethylene terephthalate fibers, exerts a grasping effect on the tendon ends. The control group received a multistrand modified Kessler repair with a looped polydioxanone suture (PDS) 4-0 suture and a Silfverskiöld epitendinous repair using an Ethilon 6-0 suture. After the repair, a static and an incremental cyclic tensile test was performed until failure.

RESULTS

During the static test, the tubular braid resulted in a significantly higher load at 3 mm gap formation (86.3 N ± 6.0 vs 50.1 N ± 11.6), a higher ultimate load at failure (98.3 N ± 12.7 vs 63 N ± 11.1), higher stress at ultimate load (11.8 MPa ± 1.2 vs 8.1 MPa ± 3.1), and higher stiffness (7.1 N/mm ± 2.9 vs 8.7 N/mm ± 2.2). For the cyclic tests, survival analyses for 1-, 2- and 3-mm gap formation and failure demonstrated significant differences in favor of the tubular braided construct.

CONCLUSION

The tubular braided construct withstands the required loads for immediate rehabilitation not only in static tests, but also during cyclic tests. This is in contrast with the control group, where sufficient strength is reached during static tests, but failures occur below the required loads during cyclic testing.

CLINICAL RELEVANCE

The tubular braided construct provides a larger safety margin for immediate intensive rehabilitation protocols.

A review of cyclic testing protocols for flexor tendon repairs

BACKGROUND

Cyclic testing of flexor tendons aims to simulate post-operative rehabilitation and is more rigorous than static testing. However, there are many different protocols, making comparisons difficult. We reviewed these protocols and suggested two protocols that simulate passive and active mobilization.

METHODS

Literature search was performed to look for cyclic testing protocols used to evaluate flexor tendon repairs. Preload, cyclic load, number of cycles, frequency and displacement rate were categorised.

FINDINGS

Thirty-five studies with 42 different protocols were included. Thirty-one protocols were single-staged, while 11 protocols were multiple-staged. Twenty-nine out of 42 protocols used preload, ranging from 0.2 to 5 N. Preload of 2 N was used in most protocols. The cyclic load that was most commonly used was between 11 and 20 N. Cyclic load with increment of 10 N after each stage was used in multiple-staged protocols. The most commonly used number of cycles was between 100 and 1000. Most protocols used a frequency of <1 Hz and displacement rate between 0 and 20 mm/min.

INTERPRETATION

We propose two single-staged protocols as examples. Protocol 1: cyclic load of 15 N to simulate passive mobilization with preload of 2 N and 2000 cycles at frequency of 0.2 Hz.; Protocol 2: cyclic load of 38 N to simulate active mobilization, with the same preload, number of cycles, and frequency as above. This review consolidates the current understanding of cyclic testing and may help clinicians and investigators improve the design of flexor tendon repairs, allow for comparisons of different repairs using the same protocol, and evaluate flexor tendon repairs more rigorously before clinical applications.

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

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

Cyclic Testing of the 6-Strand Tang and Modified Lim-Tsai Flexor Tendon Repair Techniques

PURPOSE

In this study, we compared the Tang repair technique with the 6-strand modified Lim-Tsai repair technique under cyclic testing conditions.

METHODS

Twenty fresh-frozen porcine flexor tendons were randomized into 2 groups for repair with either the modified Lim-Tsai or the Tang technique using Supramid 4-0 core sutures and Ethilon 6-0 epitendinous running suture. The repaired tendons were subjected to 2 stage cyclic loading. The survival rate and gap formation at the repair site were recorded.

RESULTS

Tendons repaired by the Tang technique achieved an 80% survival rate. None of the modified Lim-Tsai repairs survived. The mean gap formed at the end of 1000 cycles was 1.09 mm in the Tang repairs compared with 4.15 mm in the modified Lim-Tsai repairs.

CONCLUSIONS

The Tang repair is biomechanically stronger than the modified Lim-Tsai repair under cyclic loading.

CLINICAL RELEVANCE

The Tang repair technique may exhibit a higher tolerance for active mobilization after surgery with less propensity for gap formation.

Early Passive Movement in flexor tendon injuries of the hand

INTRODUCTION

Flexor tendon injuries are underestimated considering their anatomical function in the hand. According to the publications of Kleinert, Verdan and Kessler, primary suturing of the flexor tendon combined with immediate postoperative physiotherapy in terms of "Early Passive Movement" became the standard form of therapy following acute flexor tendon injuries of the hand.

MATERIALS AND METHODS

In a study between 2007 and 2009, a total of 115 flexor tendon injuries were analysed retrospectively. All patients were treated using a two-strand repair technique according to Zechner. They received physiotherapy from the first postoperative day according to the Viennese flexor tendon rehabilitation protocol. For statistical purposes, the factors: age, gender, range of motion (ROM), follow up interval, affected flexor tendon and zone were analysed. The time between injury and surgery was also determined, classified into groups and included in the study. On the basis of the range of motion AROM, the Buck-Gramcko and modified Strickland Score was calculated.

RESULTS

The mean follow-up interval was 7 months. Using the Buck-Gramcko and Strickland Score an "excellent" overall result was achieved. Complications occurred in 3.5 %, one secondary rupture (0.9 %), two tendon adhaesions requiring tenolysis (1.7 %) and one case of infection (0.9 %). The time interval between injury and operation, gender, affected zone, flexor tendon and affected finger nerve had no influence on the Buck-Gramcko and Strickland Score.

CONCLUSIONS

Using Zechner's core suture technique as the primary treatment, combined with immediate postoperative physiotherapy in terms of "Early Passive Movement" according to the Viennese flexor tendon rehabilitation programme, an excellent clinical outcome and low complication rate was acchieved.

LEVEL OF EVIDENCE

IV: case series.

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.

A systematic review of 2-strand versus multistrand core suture techniques and functional outcome after digital flexor tendon repair

PURPOSE

To determine published evidence to evaluate the hypothesis that multistrand techniques result in a poorer outcome than 2-strand techniques for digital flexor tendon repairs.

METHODS

A systematic review was undertaken to compare outcomes and rupture rates between 2-strand and multistrand core sutures in digital flexor zones 2 to 5. Outcome was measured by the American Society for Surgery of the Hand criteria, original or modified Strickland criteria, or Buck-Gramcko criteria.

RESULTS

A total of 1,878 patients (2,585 digits; 3,749 tendons) were included from the selected studies. Thirty-three studies reported 2-strand repairs and 15 reported multistrand repairs. Of the total tendon injuries, 59% were flexor digitorum profundus, 38% were flexor digitorum superficialis, and 2% were flexor pollicis longus. The pooled rupture rate was 3.9 per 100 digits. No significant difference was detected between 2-strand and multistrand repairs for outcomes by all measures or rupture rate.

CONCLUSIONS

Because of the wide variation in reporting of outcomes and study design on which this analysis was based, we cannot definitively confirm our hypothesis. We present the standards for outcomes as well as rupture rate for digital flexor tendon repair.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic III.

The search for the ideal tendon repair in zone 2: strand number, anchor points and suture thickness

This review article examines the mechanical factors involved in tendon repair by sutures. The repair strength, repair stiffness and gap resistance can be increased by increasing the number of core strands and anchor points, by increased anchor point efficiency and the use of peripheral sutures, and by using thicker sutures. In the future, laboratory tests could be standardized to a specific animal model and to a defined cyclic motion programme. Clinical studies support the use of multi-strand core and peripheral sutures, but two-strand core sutures are not adequate to ensure consistently good clinical results. Training surgeons in complex tendon repair techniques is essential.

Management of flexor tendon injuries - Part 1: Australian contributions

This review article describes the contribution of Australian authors to the basic science and clinical management of flexor tendon injuries.

Performance of a knotless four-strand flexor tendon repair with a unidirectional barbed suture device: a dynamic ex vivo comparison

With increased numbers of reports using barbed sutures for tendon repairs we felt the need to design a specific tendon repair method to draw the best utility from these materials. We split 30 sheep deep flexor tendons in two groups of 15 tendons. One group was repaired with a new four-strand barbed suture repair method without knot. The other group was repaired with a conventional four-strand cross-locked cruciate repair method (Adelaide repair) with knot. Dynamic testing (3-30 N for 250 cycles) and additional static pull to failure was performed to investigate gap formation and final failure forces. The barbed suture repair group showed higher resistance to gap formation throughout the test. Additionally final failure force was higher for the barbed suture group compared with the conventional repair group. When used appropriately, barbed suture materials could be beneficial to use in tendon surgery, especially with regard to early loading of the repair site and gap formation.

The mechanical interaction between three geometric types of nylon core suture and a running epitenon suture in repair of porcine flexor tendons

The effect of core suture geometry on the mechanical interaction with the epitenon suture in terms of gap prevention, failure strength and mode of failure was investigated in a flexor tendon repair model. A total of 48 porcine flexor tendons were repaired using three techniques with distinct core suture geometry: single Kessler; double Kessler; and cruciate repair. Cyclic linear testing was carried out with and without a simple running epitenon suture. At failure load the epitenon suture reduced gapping by 87% in the double Kessler, 42% in the single Kessler and 15% in cruciate repairs. It increased the strengths of the repairs by 58%, 33% and 24%, respectively. Kessler repairs failed mainly by suture rupture, with and without epitenon suture, but cruciate repairs failed mainly by suture pull-out. The epitenon suture did not have a significant mechanical effect on the three repairs. Rather, its effect varied with the core suture geometry. The greatest effect occurred with double Kessler repairs.

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.

A biomechanical assessment of repair versus nonrepair of sheep flexor tendons lacerated to 75 percent

PURPOSE

The benefit of repairing a 75% partial flexor tendon laceration remains controversial. The purpose of this study was to assess the degree of gap formation with and without repair when the 75% lacerated tendon is subjected to cyclic loading. Repair with only a peripheral suture was compared to that using a core and peripheral repair technique.

METHODS

Sixteen deep flexor tendons from sheep hind limbs were lacerated to 75% of the tendon diameter. The cut tendons were loaded for 100 cycles from 3 N up to 30 N and then back to 3 N, at a rate of 0.2 Hz. Gap formation was measured at 0 and 100 cycles. Tendons were then randomized into 2 repair groups of 8 each: group 1 was repaired with only a simple, running peripheral suture (6-0 polypropylene monofilament), whereas group 2 was repaired with a modified Kessler core suture (4-0 silicone-coated braided polyester) plus a peripheral suture (6-0 polypropylene monofilament). Repaired tendons were tested for 500 cycles, and the gap was measured at 0, 100, and 500 cycles. After cycling, gap was measured at 100 N load, and the peak loads were determined on static failure testing.

RESULTS

The 75% partially lacerated tendons had >2 mm gap at 100 cycles. This gap was significantly reduced by peripheral or peripheral plus core repairs (p < .001). There was no difference in gap formation between tendons with peripheral repair only and those with both peripheral and core repairs. Gap formation in repaired tendons remained <or=1 mm at 500 cycles. After cycling, neither gap formation at 100 N load or the peak loads on failure testing differed between the 2 repair groups.

CONCLUSIONS

There is a large gap when an unrepaired 75% partial laceration is cyclically loaded. This gap is significantly reduced with a peripheral repair whether or not a core suture is used.

Flexor tenorrhaphy tensile strength: reduction by cyclic loading: in vitro and ex vivo porcine study

The integrity of the repair is critical to maintain coaptation of the severed flexor tendon end until healing has advanced sufficiently. In our hospital, we use a modified Savage repair (four-strand Adelaide technique) using 3-0 Ethibond (Ethicon, Somerville, NJ, USA) for acute flexor tenorrhaphy and an active postrepair mobilization protocol. To explain the apparent differences between the theoretical and actual repair strength of a multistrand repair in a single tension test and the reduced strength of a repair subjected to cyclic loading, we compared single and cyclical tensile loading with different suture in vitro configurations of 3-0 Ethibond (Ethicon, Somerville, NJ, USA; one, two, and four strands) and an ex vivo four-strand repair of freshly divided porcine tendon to calculate the ultimate tensile strength (UTS). Mechanical testing was repeated 15 times with both single tensile and cyclical loading for each suture configuration and porcine repair. In the in vitro model, the presence of a knot in a single strand reduced the UTS by 50%. The stiffness of a knotted strand was substantially less than the unknotted strand but became identical after cyclical loading. There was no statistical significance of the UTS between single and cyclical loading with different numbers of strands in this model. In the ex vivo four-strand porcine repair model, there was a significant reduction in UTS with cyclical loading, which equated to the number of strands times the strength of the knotted strand. This discrepancy can be explained by the change in stiffness of the knotted strand after cyclical loading and has important implications for previous studies of suture tendon repair using single tensile loading where the UTS may have been overestimated. We believe that cyclical loading is more representative of physiological loading after acute flexor tendon repair and should be the testing model of choice in suture tenorrhaphy studies.

Influence of core suture geometry on tendon deformation and gap formation in porcine flexor tendons

The effects of core suture geometry on the mechanics of failure in flexor tendon surgery are investigated. Forty porcine flexor tendons were repaired using a Kessler; a Kessler-Pennington; a double Kessler; a continuous Kessler; and a cruciate repair. At maximum breaking strength, the cruciate repair gapped more then the double Kessler (12.8 mm vs 9.1 mm), but the double Kessler was less strong (37N vs 45 N). Transverse narrowing was 22% and 24% for the Kessler and the Kessler-Pennington, 11% for the double Kessler, and 0% for the continuous Kessler and the cruciate repair. Kessler-type sutures failed by suture breakage and the cruciate repair by pull-out. Under load, the transverse part of the Kessler sutures narrows, allowing longitudinal parts to lengthen, leading to gapping. The double Kessler shortened transverse segment decreases gapping. Eliminating a transverse component (the cruciate repair) decreased gapping, but the cruciate failed at higher loads by suture pull-out.

Biomechanical comparison of modified Kessler and running suture repair in 3 different animal tendons and in human flexor tendons

PURPOSE

To establish the animal flexor tendon that best mimics the biomechanical performance of human flexor tendons. We investigated the biomechanical behavior of core and running sutures in 3 different animal flexor tendons and in human flexor tendons. Additionally, we attempted to help standardize future flexor tendon studies. To that purpose, nearly all variables occurring in the test setup have been highlighted.

METHODS

The species selected were pig, calf, sheep, and human. Two groups were formed. In the first group we tested 3-0 core sutures (Ticron; Tyco Healthcare, Vienna, Austria), and in the second group we tested 5-0 running sutures (Ethilon; Ethicon, Vienna, Austria). In each group, 10 tendons of each specimen were tested, which yielded a total of 80 tendons. In each group, the repaired tendons were subjected to 3,000 linear load cycles at a load of 15 N. At the end of this procedure, final gap values were recorded. In the next step, ultimate load-to-failure data were obtained from each specimen.

RESULTS

Core sutures behaved similarly in the human, sheep, and pig tendons with respect to ultimate loads. With respect to gap formation, core sutures behaved similarly in the human, sheep, and calf tendons. Deep running sutures behaved similarly in the human, sheep, and pig tendons in terms of ultimate load to failure.

CONCLUSIONS

In this study, sheep tendons were found to best mimic the biomechanical behavior of human tendons. Calf tendons seem to be unsuitable. There is a strong need for consistency in biomechanical test setups.

Flexor tendon repair using the two-strand side-locking loop technique to tolerate aggressive active mobilization immediately after surgery

BACKGROUND

Early mobilization after tendon repair decreases adhesion formation and improves repair-site strength. We investigated whether the two-strand side-locking loop technique would tolerate aggressive active mobilization immediately after surgery.

METHODS

Twelve flexor digitorum profundus tendons of the porcine forelimbs were sutured by the two-strand side-locking loop technique with a cross-stitch epitendinous repair (Group A), and by the 8-strand repair method with a simple running suture (Group B). Gaps and residual tensile strength after cyclic loadings of 3-50 N (for 10,000 rounds) were measured.

FINDINGS

Gaps after cyclic loading in Group A were 0.5+/-0.3 and 1.2+/-0.8 mm while those in Group B were 3.5+/-0.8 and 5.2+/-1.2 mm at 3 and 50 N, respectively. In addition, the respective residual tensile strength of Groups A and B were 207.1+/-15.2 and 84.2+/-18.3N.

INTERPRETATION

A combination of the two-strand side-locking loop technique with cross-stitch epitendinous repair served as the optimum suture method in establishing safe and early active mobilization without the aid of a specialized rehabilitation staff.

Optimum location of knot for tendon surgery in side-locking loop technique

BACKGROUND

Although various tendon repair techniques have been reported to achieve stronger repair, suture failures tend to occur near the knot. We experimentally investigated whether the location of a single core suture knot affects the biomechanical properties of the repair.

METHODS

Transected bovine tendons (male Japanese black cattle, 24 months old) of the medial gastrocnemius (9-11 x 14-16 mm in diameter) were sutured with the side-locking loop technique using a USP2-sized polyethylene and polyester multifilament suture or polyester multifilament suture. The knot was made using 7 simple square ties (a surgeon's knot plus 5 ties) at three locations; on the loop, between the tendon stumps, or between the loops burying the knot in a tendon slit using a scalpel. A cyclical loading protocol from 10N to 100N was used and the loading was repeated 10,000 times.

FINDINGS

The gap was most decreased and the ultimate strength was most increased when the knot was located between the loops when using a polyethylene and polyester multifilament suture. Cross-sectional area of the tendon showed the ratio of the buried knot relative to the tendon was only 1.6-2.3%, and the polyethylene and polyester multifilament suture was very durable against frictional abrasion.

INTERPRETATION

We found that the knot between the loops, buried in the bovine tendon provided the optimum results.