Asymmetric six-strand core sutures enhance tendon fatigue strength and the optimal asymmetry

Effect of loading speed on gap resistance and tensile strength of flexor tendon repair under cyclic loading test

Postoperative digit motion is important for the functional recovery of injured tendons. To date, it is unknown whether the loading speed impacts the biomechanical properties of a repaired tendon. This study investigated the effect of loading speed on the gap resistance and tensile strength of tendon repairs. One hundred porcine flexor tendons were repaired with two core sutures, 4-strand modified Kessler and double Q, and cyclically loaded at the speeds of 10, 40, 80, 160, and 320 mm/min. The number of tendons that formed an initial or 2 mm gap at the repair site during cyclic loading, stiffness at the 1st and 20th loading cycles, gap size between tendon ends when cyclic loading ended, and the ultimate strength were recorded. Under the lowest loading speed, the tendons repaired with the 4-strand modified Kessler suture developed significantly larger gaps and smaller stiffness than those with a greater loading speed. The loading speed did not affect the maximum strength of both tendon repairs. The findings suggest that very slow motion promotes gap formation of tendon repair with inferior gap resistance. The rate corresponds to regular hand action or the tendon core suture possessing a strong gap resistance increases the safety margin during early active finger movement. Our findings help to guide the exercise regimens after tendon surgery.

Zone 2 flexor tendon repairs using a tensioned strong core suture, sparse peripheral stitches and early active motion: results in 60 fingers

We report the outcomes of zone 2 tendon repairs in 60 fingers using a strong core suture, sparse peripheral stitches and early active motion. From January 2014 to April 2016, we repaired 60 flexor digitorum profundus tendons with a tensioned 4-strand or 6-strand core suture and three to four peripheral stitches. The A2 or A4 pulleys were vented as necessary. Following early active flexion of the repaired tendons, no repairs ruptured and 52/60 (87%) fingers recovered to good or excellent function using the Tang criteria after follow-up of 8-33 months. We conclude that tensioned multi-strand strong core repairs only require sparse peripheral stitches and are safe for early active flexion. Standard peripheral sutures are not necessary. The core sutures should be properly tensioned to prevent gapping at tendon repair site and pulleys should be sufficiently vented to allow tendon motion. Level of evidence: IV.

Factors Accounting for Variation in the Biomechanical Properties of Flexor Tendon Repairs

PURPOSE

To investigate factors that cause variation in the mechanical properties of flexor tendon repairs.

METHODS

One surgeon repaired 50 homogeneous absorbent sticks and 40 porcine flexor tendons with a simple loop, an Adelaide repair, a peripheral over-and-over repair, or a combination of the latter 2 repairs. Ten hand surgeons repaired 1 porcine flexor tendon with the combined Adelaide core and over-and-over peripheral repair. We loaded the samples statically until failure and calculated the variations caused by the testing process, tendon substance, and surgical performance in terms of yield and ultimate load.

RESULTS

Tendon material and surgical performance both caused about half of the variation in the yield load of the combined repair. Surgical performance caused all variations observed in the ultimate load of the combined, peripheral-only, and core repairs. The effect of the tendon material was negligible in ultimate load. The intersurgeon variation was present only in yield load, and it represented one-tenth of the total variation.

CONCLUSIONS

The effect of tendon substance on variation of the ultimate load is minimal. In yield load, both tendon and surgical performance are responsible for the variation.

CLINICAL RELEVANCE

In clinical realm, variation caused by testing is not present, but intersurgeon variation may cause additional variation in yield load. A hand surgeon cannot change the variation due to tendon properties, but with a more meticulous surgical technique, the variation related to the surgical performance can probably be diminished.

New Developments Are Improving Flexor Tendon Repair

New developments in primary tendon repair in recent decades include stronger core tendon repair techniques, judicious and adequate venting of critical pulleys, followed by a combination of passive and active digital flexion and extension. During repair, core sutures over the tendon should have sufficient suture purchase (no shorter than 0.7 to 1 cm) in each tendon end and must be sufficiently tensioned to resist loosening and gap formation between tendon ends. Slight or even modest bulkiness in the tendon substance at the repair site is not harmful, although marked bulkiness should always be avoided. To expose the tendon ends and reduce restriction to tendon gliding, the longest annular pulley in the fingers (i.e., the A2 pulley) can be vented partially with an incision over its distal or proximal sheath no longer than 1.5 to 2 cm; the annular pulley over the middle phalanx (i.e., the A4 pulley) can be vented entirely. Surgeons have not observed adverse effects on hand function after judicious and limited venting. The digital extension-flexion test to check the quality of the repair during surgery has become increasingly routine. A wide-awake surgical setting allows patient to actively move the digits. After surgery, surgeons and therapists protect patients with a short splint and flexible wrist positioning, and are now moving toward out-of-splint freer early active motion. Improved outcomes have been reported over the past decade with minimal or no rupture during postoperative active motion, along with lower rates of tenolysis.

Gap Formation During Cyclic Testing of Flexor Tendon Repair

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

CLINICAL RELEVANCE

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

Localized delivery of miRNAs targets cyclooxygenases and reduces flexor tendon adhesions

The formation of adhesions during healing of an injured tendon remains a difficult problem in clinical practice. Local anti-inflammation gene delivery provides high local gene concentration, reduces the inflammatory response of the injured tendon microenvironment, and decreases systemic side effects to enhance in vivo efficacy. In this study, we designed a novel local sustained gene delivery system by using cyclooxygenase (COX-1 and COX-2)-engineered miRNA plasmid/nanoparticles embedded in hyaluronic acid (HA) hydrogel to reduce flexor tendon adhesions. The local sustained gene delivery system significantly downregulates COX-1 and COX-2 expression in the tendon tissue and the surrounding subcutaneous tissue. More importantly, this plasmid/nanoparticle hydrogel system significantly reduced tissue adhesion formation. This approach offers an effective therapeutic strategy to reduce tendon adhesions by directly targeting the down-regulation of COX-1 and COX-2 expression within the microenvironment of the injured tendon.

STATEMENT OF SIGNIFICANCE

A local sustained gene delivery system was developed to regulate the expression of targeted genes in the specific time and location for tendon adhesion treatment. The engineered miRNA plasmid/nanoparticles embedded in hyaluronic acid hydrogel were synthesized to downregulate the expression of cyclooxygenases in the tendon tissue during the early stage of tendon healing with inflammatory response. This plasmid/nanoparticle hydrogel system offers an effective therapeutic strategy to attenuate the formation of tendon adhesion through direct downregulation of COX-1 and COX-2 expression within the microenvironment of the injured tendon.

A Biomechanical Comparison Between Asymmetric Pennington Technique and Conventional Core Suture Techniques: 6-Strand Flexor Tendon Repair

PURPOSE

To evaluate the fatigue strength and gap sizes of the asymmetric Pennington technique compared with 2 conventional 6-strand core suture techniques: the triple-looped suture and the Yoshizu #1.

METHODS

We recorded the fatigue strength (forces × cycles) and gap sizes of a 6-strand flexor tendon repair with different core suture techniques under cyclic loading in 30 porcine tendons. The asymmetric Pennington technique was performed with a Pennington repair of equal suture purchase in the 2 tendon stumps, with the 2 other Pennington repairs shifted by 3 mm, respectively, along the longitudinal axis of the tendon in relation to the first Pennington repair. The triple-looped suture technique was made with triple Tsuge sutures. The Yoshizu #1 technique was performed with a combined Pennington repair (using a double strand) and Tsuge suture.

RESULTS

The asymmetric Pennington technique showed significantly greater fatigue strength and significantly smaller gaps in comparison to the triple-looped suture and Yoshizu #1 techniques.

CONCLUSIONS

This study demonstrated that the asymmetric Pennington technique generated increased fatigue strength and reduced gap sizes compared with 2 conventional 6-strand core suture techniques, the triple-looped suture and Yoshizu #1.

CLINICAL RELEVANCE

The asymmetric Pennington technique may permit an early active motion rehabilitation protocol similar to the triple-looped suture and Yoshizu #1 techniques.

Biomechanical comparison of the Lim/Tsai tendon repair with a modified method using a single looped suture

The Lim/Tsai tendon repair technique has been modified clinically to achieve a 6-strand repair using a single looped suture with one extratendinous knot. We compared biomechanical performance of the original and modified methods using 20 porcine flexor digitorum profundus tendons. The ultimate tensile strength, load to 2 mm gap force, mode of failure, and time taken to repair each tendon were recorded during a single cycle loading test in 10 tendons with each repair method. We found that despite having the same number of core strands, the single looped suture modified Lim/Tsai technique possessed significantly greater ultimate tensile strength and load to 2 mm gap force. Also, less repair time was required. We conclude that the modified 6-strand repair using a single looped suture has better mechanical performance than the original method. The difference likely was due to the changes in locations of the knots and subsequent load distribution during tendon loading.

Robust thumb flexor tendon repairs with a six-strand M-Tang method, pulley venting, and early active motion

We present the outcomes of flexor pollicis longus tendon repairs in 34 thumbs using a six-strand M-Tang repair with venting of one or two pulleys according to site of tendon laceration. The A2 pulley was vented in all three thumbs with zone 1 injury. In 31 thumbs with zone 2 injuries, the oblique pulley was vented partially or entirely. Twenty-two thumbs had both the A1 and oblique pulleys vented. Six to 46 months post-surgery, 14 thumbs with zone 2 injuries were rated excellent, 13 good, three fair and one failure according to Tang criteria. No tendon ruptures or bowstringing occurred. Fourteen of 34 thumbs had deficits in interphalangeal joint extension averaging 13°. We conclude that venting of one or two pulleys may ensure recovery of thumb function without risking tendon bowstringing and that early active thumb motion is safe with a robust tendon repair.

LEVEL OF EVIDENCE

IV.

Primary Flexor Tendon Repair with Early Active Motion: Experience in Europe

The protocol for primary flexor tendon repair in zones 1 and 2 of the hand is changing. This article discusses recent changes. Immediate repair within 48 hours is performed whenever possible. A 6-strand core suture is performed using the M modification of Tang's technique. The pulleys are divided to allow free excursion of the repaired tendon within the tendon sheath. To avoid repaired structures within the sheath being too bulky, the authors generally repair only half of the flexor digitorum superficialis. In some cases, the flexor digitorum superficialis is excised completely. Rehabilitation remains based on controlled active motion.

Strong Digital Flexor Tendon Repair, Extension-Flexion Test, and Early Active Flexion: Experience in 300 Tendons

Over the past 2 decades, repair and rehabilitation methods of primary repair of the digital flexor tendon have changed. In this article, we outline interim results from ongoing investigations in several units. Surgeons in these units now perform digital flexor tendon repairs according to a treatment protocol. Before adopting the protocol, they had no history of tendon-related research; they had not used any of the repair and rehabilitation methods described in the protocol. The surgeons involved are junior or midlevel attending surgeons. At the end of this article, we outline current practice of digital flexor tendon repair in Asian countries.

Effect of the Optimal Asymmetry on the Strength of Six-Strand Tendon Repair: An Ex Vivo Biomechanical Study

PURPOSE

To evaluate the mechanical properties of a 6-strand core suture repair with asymmetric purchase in the 2 tendon ends, in comparison with a repair with symmetric suture purchases.

METHODS

Under cyclic loading of the tendons, we recorded the fatigue strength (Forces × Cycles) of a 6-strand flexor tendon repair with different symmetry in the lengths of suture purchase in 60 porcine tendons. The symmetric repair was made with 3 groups of parallel Kessler repairs of equal suture purchase (10 mm from the cut end) in the 2 tendon stumps. The asymmetric core suture repairs were then made with a Kessler repair of equal suture purchase (10 mm from the cut end) in the 2 tendon stumps, and shifting 2 other Kessler repairs by 1, 2, 3, 4, or 5 mm, respectively, along the longitudinal axis of the tendon in relation to the first (symmetric) Kessler repair.

RESULTS

The core repairs with 2 mm or more asymmetry in suture purchases in 2 tendon ends showed significantly greater fatigue strength compared with those with symmetric suture placement. The core repairs with 3 mm or more asymmetry in suture purchases in 2 tendon ends showed significantly smaller gaps compared with those with symmetric suture placement.

CONCLUSIONS

The core repairs with 3 mm or more asymmetry in suture purchases in 2 tendon ends generated increased fatigue strength and reduced gap sizes compared with those with symmetric suture placement in an ex vivo porcine model.

CLINICAL RELEVANCE

An asymmetric core suture repair with 3 mm or more difference in purchase length may allow for earlier rehabilitation and reduce the risk of postoperative complications.