Suture configurations and biomechanical properties of flexor tendon repairs by 16 hand surgeons in Finland

Healing strength of tendon repair with or without knots between two tendon ends and histological changes in a chicken model

We studied the healing strength and histological changes of digital flexor tendons repaired using Kessler (core suture knots placed over the tendon surface) and modified Kessler (core suture knots placed between two tendon ends) in 31 long toes of chicken. Four weeks after surgery, the healing tendons were measured in a tensile testing machine, and the adhesion formation and histological changes were observed. The strength of the Kessler repairs was significantly greater than that of the modified Kessler repairs with a 35% mean difference. No significant difference was found between the adhesion scores of the tendons repaired with both techniques. In histological sections, the arrangement of collagen fibers in the modified Kessler repair group was more disordered. We conclude that the tendons repaired with the Kessler method are stronger than those with the modified Kessler technique. The knots between tendon ends are detrimental to the early healing strength of digital flexor tendons.

Biomechanical Study of Modified Massachusetts General Hospital Flexor Tendon Repair Using Looped Sutures

Background: Massachusetts General Hospital (MGH) repair is one of the widely used 4-strand flexor tendon repair techniques. However, it uses two single strand sutures that are each passed twice across the repair site. This is time consuming and may cause imbalance of the load across the repair. We modified the MGH repair by using a looped suture and call it the looped MGH repair. The aim of this study is to compare the strength of the looped MGH repair performed with three different looped sutures against the strength of original MGH repair.

Methods: Forty porcine flexors were used for the study. The original MGH repair was performed with Prolene® 4-0. Looped MGH repair was performed with three different loop sutures, Supramid® 4-0, Tendo-Loop® 4-0 and FiberLoop® 4-0. Mechanism of failure, ultimate tensile strength, stiffness, load to 2-mm gap formation and repair time were recorded for comparison.

Results: There was no significant difference between the original MGH repair and the looped repair using Supramid® regarding their biomechanical performance. Looped MGH repair using Tendo-Loop® and FiberLoop® showed significantly higher ultimate tensile strength and FiberLoop® had highest 2-mm gap force. All looped MGH repairs required significant less time compared to original MGH repair.

Conclusions: Our modification of the MGH repair using a looped Supramid® 4-0 suture took significantly lesser time to perform while providing the same strength as the original MGH repair using Prolene® 4-0. The use of the FiberLoop® 4-0 provided significantly greater strength while taking lesser time.

Flexor tendon repair with a polytetrafluoroethylene (PTFE) suture material

BACKGROUND

There is a consensus that after a flexor tendon repair an aggressive rehabilitation protocol with early active motion can improve functional outcome, provided that the combination of material and suturing technique can meet the higher biomechanic demands. Bearing this in mind we evaluated a polytetrafluoroethylene (PTFE) suture (SERAMON^®, Serag-Wiessner) as a possible material for flexor tendon repair.

MATERIALS AND METHODS

40 flexor tendons were harvested from fresh cadaveric upper extremities. 3-0 and 5-0 strands were used both in the polypropylene (PPL) as well as in the PTFE group. In the first phase of the study, we evaluated knotting properties and mechanical characteristics of the suture materials themselves. In the second phase, a 2-strand Kirchmayr-Kessler suture technique was applied for a core suture of a flexor tendon (n = 16). In the third phase, we performed a tendon repair including an epitendinous running suture with 5-0 PPL or 5-0 PTFE material (n = 22). One way ANOVA tests were performed.

RESULTS

The linear loading strength of single strand knotted PPL 3-0 was 19.87 ± 0.59 N. The linear loading strength of knotted PTFE 3-0 was 32.47 ± 1.67 N. For PPL 3-0 maximum linear strength was achieved with five knots, for PTFE 3-0 with eight knots. When a Kirchmayr-Kessler core-only repair was performed, then in the PPL group the loading strength of the repaired tendon was 30.74 ± 9.77 N. In the PTFE group the loading strength was 23.74 ± 5.6 N (p = 0.10). However, all repairs in the PTFE group failed due to cheese wiring. When a Kirchmayr-Kessler core and epitendinous repair technique was used, then in the PPL group the loading strength of the repaired tendon was 49.90 ± 16.05 N. In the PTFE group the loading strength was 73.41 ± 19.81 N (p = 0.006).

CONCLUSION

PTFE demonstrates superior strength properties in comparison to PPL for flexor tendon repairs. However, standard 2 strand techniques have proved inadequate to bear the higher biomechanic demands.

Comparison of the strength of two multi-strand tendon repair configurations in a chicken model

We sought to investigate the strength of two multi-strand tendon repair configurations in a chicken model. Fifty-six chicken flexor tendons were repaired with one to two different four-strand configurations: 1) a four-strand repair consisting of a two-strand core modified Kessler suture with a circle loop repair and 2) a four-strand core Kessler suture repair with three separate peripheral suture points. The strength of the repaired tendons were measured 2, 3 and 4 weeks after the surgical repair and were analyzed statistically. The strength of the two repair methods was not statistically different 2 weeks after surgery. The tendons repaired with the four-strand core Kessler suture repair and three separate peripheral suture points were significantly stronger than those repaired with a two-strand core modified Kessler suture and a circle loop repair at 3 weeks (P = 0.033) and 4 weeks (P = 0.039). The four-strand repair with three separate peripheral suture points had greater strength than a two-strand repair with one circle loop suture based on an in vivo chicken flexor tendon model.

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.

Biomechanical comparison of modified Lim/Tsai tendon repairs with intra- and extra-tendinous knots

We compared the Lim/Tsai tendon repair technique using an extra-tendinous knot with modification using an intra-tendinous knot. The ultimate tensile strength, load to 2 mm gap force, stiffness, mode of failure, location of failure, and time taken to repair each tendon were recorded during a single cycle loading test in 20 tendons with each repair method. We found that the ultimate tensile strength and 2 mm gap force of the modified Lim/Tsai repair with an extra-tendinous knot (56 SD 5 N and 14 SD 2 N, respectively) were statistically significantly higher than that of the modified Lim/Tsai repair with intra-tendinous knot (51 SD 7 N and 11 SD 2 N, respectively). We conclude that the modified Lim/Tsai repair with extra-tendinous knot is stronger, despite having the same number of core strands.

Recent evolutions in flexor tendon repairs and rehabilitation

This article reviews some recent advancements in repair and rehabilitation of the flexor tendons. These include placing sparse or no peripheral suture when the core suture is strong and sufficiently tensioned, allowing the repair site to be slightly bulky, aggressively releasing the pulleys (including the entire A2 pulley or both the A3 and A4 pulleys when necessary), placing a shorter splint with less restricted wrist positioning, and allowing out-of-splint active motion. The reported outcomes have been favourable with few or no repair ruptures and no function-disturbing tendon bowstringing. These changes favour easier surgeries. The recent reports have cause to re-evaluate long-held guidelines of a non-bulky repair site and the necessity of a standard peripheral suture. Emerging understanding posits that minor clinically noticeable tendon bowstringing does not affect hand function, and that free wrist positioning and out-of-splint motion are safe when strong surgical repairs are used and the pulleys are properly released.

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.

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.

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.

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.

Outcomes of the six-strand M-Tang repair for zone 2 primary flexor tendon repair in 54 fingers

We repaired complete divisions of flexor tendons in zone 2 in 54 fingers using a six-strand core M-Tang repair method. Partial active digital motion started with early passive digital motion carried out first in the first 3-4 weeks after surgery and full range of active motion in later weeks. The patients were followed for 4-27 months. According to Strickland criteria or Tang criteria, 24 (83%) had excellent or good, four fair and one poor results in 28 fingers with follow-up of more than one year. In the other 25 fingers which were followed for less than 12 months, 19 (76%) had excellent and good, four fair and two poor results. There were no repair ruptures. We analysed outcomes against ages, gender, pulley integrity, accompanied injuries and follow-up times. The patients younger than 37 years old, male patients and with their A2 pulley(s) vented there were significantly better outcomes. The patients with longer than one year follow-up had significantly smaller extension deficits than those with less than one year follow-up.

LEVEL OF EVIDENCE

IV.