Suture methods for flexor tendon repair. A biomechanical analysis during the first six weeks following repair

Improving results of flexor tendon repair and rehabilitation

BACKGROUND

The global time and effort attributed to improving outcomes in the management of flexor tendon injury are large, but the degree of advancement made over the past 50 years is relatively small. This review examines the current perceived wisdom in this field and aims to explore the limitations to the authors' understanding of the tendon healing process, examining how this may be a factor that has contributed to the authors' modest progress in the field.

METHODS

The authors critically evaluate the sum of laboratory and clinical literature on the topic of zone II flexor tendon management that has guided their practice and provide evidence to support their methods.

RESULTS

The review highlights some of the key developments over the years and assesses their influence on changing current practice. It also highlights recent innovations, which have the potential to influence flexor tendon outcomes by altering the surgical approach, techniques, and rehabilitation regimens. Future innovations in the field will also be discussed to examine their potential in expanding the development in the management of flexor tendon injury.

CONCLUSIONS

A better understanding of flexor tendon biology will allow progress in developing new therapies for flexor tendon injuries; however, there are as yet few real breakthroughs that will dramatically change current practice.

Development of biodegradable polycaprolactone film as an internal fixation material to enhance tendon repair: an in vitro study

Background

Current tendon repair techniques do not provide sufficient tensile strength at the repair site, and thus early active motion rehabilitation after tendon repair is discouraged. To enhance the post-operative tensile strength, we proposed and tested an internal fixation technique using a polycaprolactone (PCL) biofilm. PCL was chosen for its good biocompatibility, excellent mechanical strength, and an appropriate degradation time scale.

Methods

PCL biofilms were prepared by a modified melt-molding/leaching technique, and the physical and mechanical properties and in vitro degradation rate were assessed. The pore size distribution of the biofilm and the paratenon of native tendons were observed using scanning electron microscopy. Next, we determined whether this biofilm could enhance the tensile strength of repaired tendons. We performed tensile tests on rabbit Achilles tendons that were first lacerated and then repaired: 1) using modified Kessler suture combined with running peripheral suture (‘control’ group), or 2) using biofilm to wrap the tendon and then fixation with sutures (‘biofilm’ group). The influence of different repair techniques on tendon tensile strength was evaluated by mechanical testing.

Results

The novel biofilm had supple texture and a smooth surface. The mean thickness of the biofilm was 0.25 mm. The mean porosity of the biofilm was 45.3%. The paratenon of the rabbit Achilles tendon had pores with diameters ranging from 1 to 9 μm, which were similar to the 4–12 μm diameter pores in the biofilm cross-section. The weight loss of the biofilms at 4 weeks was only 0.07%. The molecular weight of PCL biofilms did not change after immersion in phosphate buffered saline for 4 weeks. The failure loads of the biofilm were similar before (48 ± 9 N) and after immersion (47 ± 7 N, P > 0.1). The biofilm group had ~70% higher mean failure loads and 93% higher stiffness compared with the control group.

Conclusions

We proposed and tested an internal fixation technique using a PCL biofilm to enhance tendon repair. Internal fixation with the biofilm followed by standard suturing can significantly increase the tensile strength of tendon repair sites. This technique has the potential to allow active motion rehabilitation during the early post-operative period.

Cell migration after synovium graft interposition at tendon repair site

BACKGROUND

We have recently reported that interpositional synovium grafts from tendon sheath have a potential to accelerate tendon healing when implanted at the repair site. The purpose of this study was to investigate the effect of orientation of the synovium after synovium graft transplantation, by comparing the ability of cells from the visceral and parietal surfaces to migrate into the tendon in a canine tissue culture model.

METHODS

The synovium graft was placed within a complete tendon laceration, with either the visceral or parietal surface facing the proximal end of the lacerated tendon. The number of migrating cells was quantified by a cell migration assay. Qualitative immunohistochemistry and confocal laser microscopy were also used at day 10.

RESULTS

Many labeled synovial cells were observed within the tendon to which the visceral surface of the synovium graft was facing. Migrated cells were also observed on the parietal side, but there were fewer cells compared to visceral surface cells. Migrating cells all expressed α-smooth muscle actin.

CONCLUSION

We found that graft orientation affected cell migration. Whether this finding has clinical significance awaits in vivo study.

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.

Flexor tendon repair using a new suture technique: a comparative in vitro biomechanical study

INTRODUCTION

The purpose of this experimental study was to evaluate the biomechanical characteristics of two new four-strand core suture techniques for flexor tendon repair.

MATERIALS AND METHODS

The two new suture techniques (Marburg 1, Marburg 2) are characterized by four longitudinal stitches which are anchored by a circular or semicircular suture. They were compared with three commonly used core suture techniques (modified Kessler, Tsuge, Bunnell). Fifty porcine flexor tendons were randomly assigned to one of the five core suture techniques. Outcome measures included ultimate tensile strength, maximum of lengthening, mode of failure and 1 mm gap formation force.

RESULTS

The highest ultimate tensile strength was found for the modified Kessler technique (115 N). Both new techniques showed an ultimate load exceeding 50 N (57 N for Marburg 1, 54 N for Marburg 2). The Marburg 1 technique showed the highest gap resistance of all tested suture techniques. The Bunnell and Tsuge core suture techniques produced the poorest mechanical performance.

CONCLUSION

From these experimental results, the new Marburg 1 core suture technique can be considered for flexor tendon repair in a clinical setting with the use of active motion protocols.

Effects of synovial interposition on healing in a canine tendon explant culture model

PURPOSE

To investigate whether synovium interposition between repaired tendon ends can integrate into the tendon repair and improve tendon healing strength in a canine tendon explant culture model.

METHODS

We used 80 flexor digitorum profundus tendons from 10 mixed-breed dogs for this study. The flexor digitorum profundus tendons were assigned to 2 groups: repaired tendons with synovium implanted between the cut tendon ends and repaired tendons without any implantation between the tendon ends. The repaired tendons were cultured for either 2 or 4 weeks and then assessed mechanically for rupture strength and histology.

RESULTS

The strength of the repaired tendons with the synovium interposition was significantly higher (p < .001) than the repaired tendons without interposition at both 2 and 4 weeks. The strength of the repaired tendons at 4 weeks was significantly higher than that at 2 weeks in both groups.

CONCLUSIONS

Interpositional synovial grafts have the potential to accelerate tendon healing when they are implanted at the repair site. The exact mechanism of this effect remains to be elucidated.

Zone 2 flexor tendon repair in young children: a comparative study of four-strand versus two-strand repair

This study compares the active ranges of finger motion and rupture rates of two-strand and four-strand repairs in zone 2 flexor tendon lacerations in young children. A total of 29 patients (under the age of 4 years) with 32 flexor tendon lacerations in zone 2 were evaluated. The injured tendons were randomly repaired with either two-strand or four-strand modified Strickland techniques. At a mean follow-up period of 11 months, the mean total active motion of interphalangeal joints was 156 degrees in the two-strand and 158 degrees in the four-strand group. According to the Strickland original method, this means an average of 89% (range 57-100%) of normal function in the two-strand and 90% (range 60-100%) in the four-strand group. There were no ruptures of the four-strand repairs, but one two-strand repair failed within 3 weeks of the repair. Statistically, we were not able to show any significant difference in the active ranges of finger motion achieved with two-strand and four-strand repairs.

A biomechanical analysis of multistrand repairs with the Silfverskiöld 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.

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

BACKGROUND

This study used in vitro cyclic testing protocol to examine the dynamic properties from a survivorship point of view for a modified Kessler core suture with a running epitenon suture, a modified Kessler core suture with a cross-stitched epitenon suture and a 4-strand Savage core suture with a running epitenon suture.

METHODS

A survivorship analysis using in vitro dynamic mechanical testing was performed using 20 N and 33 N with 500 cycles to simulate early rehabilitation. The gap formation was recorded by direct measurement with an electronic calliper every 100 cycles at the point of lowest force during the cycle at the site of greatest gap formation. Results were analysed using a log rank test for survival analysis and the relative risk of deterioration calculated.

FINDINGS

No significant increased risk of gap formation was noted for the Kessler with a cross-stitched epitenon over the standard Kessler repair. A significant decrease in the risk of significant gap formation in the Savage repair over the two Kessler repairs (>10-fold difference in the standard (P < 0.01) and > 7-fold in the cross-stitched (P < 0.05) was found.

INTERPRETATION

The survivorship testing protocol found the Savage repair to be superior to the other methods under dynamic loading. Survival curves and relative risks provide a unique way to assess the properties of different repair techniques.

Flexor tendon biology

Significant advances in the understanding of intrasynovial flexor tendon repair and rehabilitation have been made since the early 1970s. The concept of adhesion-free, or primary tendon healing--that tendons could heal intrinsically without the ingrowth of fibrous adhesions from the surrounding sheath has been validated both experimentally and clinically in studies over the past 25 years. Recent attempts to understand and improve the results of intrasynovial flexor tendon repair have focused upon restoration of the gliding surface, augmentation of early post-operative repair site biomechanical strength and on the elucidation of the molecular biology of early post-operative tendon healing. The goals of the surgical treatment of patients with intrasynovial flexor tendon lacerations remain unchanged: to achieve a primary tendon repair of sufficient tensile strength to allow application of a post-operative mobilization rehabilitation protocol. This program should inhibit the formation of intrasynovial adhesions and restore the gliding surface, while facilitating the healing of the repair site.

Short-term assessment of optimal timing for postoperative rehabilitation after flexor digitorum profundus tendon repair in a canine model

Abstract The purpose of this study was to compare the short-term outcome following flexor tendon repair for postoperative rehabilitation commencing on day 1 (a common clinical choice) versus day 5 (the day on which, with postoperative immobilization, the initial gliding resistance is least in this model) in an in vivo canine model. Work of flexion (WOF) and tendon strength were evaluated following tendon laceration and repair in 24 dogs sacrificed 10 days postoperatively. Starting postoperative mobilization at day 5 resulted in no tendon ruptures compared with tendon ruptures in four of the dogs (33%) in the group subjected to mobilization starting at day 1. While there was no statistically significant difference in WOF between groups at day 10, there was a trend toward lower resistance favoring the day 5 start group, and the statistical power to detect a difference in WOF was diminished by the ruptures in the day 1 group. We conclude that starting rehabilitation on day 5, when initial gliding resistance is lower, may have an advantage over earlier starting times, when surgical edema and other factors increase the initial force requirements to initiate tendon gliding. We plan further studies to evaluate the longer-term benefits of this rehabilitation program.

Functional efficacy of tendon repair processes

Despite various attempts to repair and replace injured tendon, an understanding of the repair processes and a systematic approach to achieving functional efficacy remain elusive. In this review the epidemiology of tendon injury and repair is first examined. Using a traditional paradigm for repair assessment, the biology and biomechanics of normal tendon, natural healing, and repair are then explored. New treatment strategies such as functional tissue engineering are discussed, including a functional approach to treatment that involves the development of in vivo functional design parameters to judge the acceptability of a repair outcome. The paper concludes with future directions.

Biomechanics of tendon injury and repair

Many clinical and experimental studies have investigated how tendons repair in response to an injury. This body of work has led to a greater understanding of tendon healing mechanisms and subsequently to an improvement in their treatment. In this review paper, characterization of normal and healing tendons is first covered. In addition, the debate between intrinsic and extrinsic healing is examined, and the cellular and extracellular matrix response following a tendon injury is detailed. Next, clinical and experimental injury and repair methods utilizing animal models are discussed. Animal models have been utilized to study the effect of various activity levels, motions, injury methods, and injury locations on tendon injury and repair. Finally, current and future treatment modalities for improving tendon healing, such as tissue engineering, cell therapy, and gene therapy, are reviewed.

A new testing device for measuring gliding resistance and work of flexion in a digit

In order to move the finger the tendon force must overcome the gliding resistance of the tendon as well as the forces to move the joints, finger inertias, and external load. These sources, combined, make up the work of flexion (WOF) which has been experimentally used to evaluate the finger function. In this study, we have designed a new device, which can measure the forces at the proximal and distal end of the tendon during finger flexion, so that gliding resistance can be isolated from the WOF. Two index fingers from a pair of human cadaver hands were used for testing this device. Preliminary data showed that internal resistance occupied about 10% of WOF with an intact tendon. However, after tendon repair, the gliding resistance increased 31% of WOF for a modified Kessler repair and 50% of WOF for a Becker repair compared to intact tendon. We simulated joint stiffness by injection of saline solution into the proximal interphalangeal joint. This increased the overall WOF but not the gliding resistance. We believe that this testing device provides a useful tool to evaluate finger function after tendon repair in an experimental model.

The effect of suture technique on adhesion formation after flexor tendon repair for partial lacerations in a canine model

BACKGROUND

Adhesion formation is a serious problem after flexor tendon repair. Many repair techniques have been developed to increase the suture strength after tendon repair surgery. The purpose of this study was to assess adhesion formation with different suture techniques in an in vivo canine model.

METHODS

Sixty flexor digitorum profundus tendons were partially lacerated (80%) and repaired with either a modified Kessler (MK) or Becker (MGH) suture technique and supplemented with a simple running suture. The dogs were sacrificed at 1 week, 3 weeks, or 6 weeks after surgery and the repaired tendons were evaluated for adhesion breaking strength.

RESULTS

At 1 week there was no significant difference between the two repair groups (p > 0.05). At 3 and 6 weeks, the adhesion breaking strength in the MK suture group was significantly less than that of the MGH suture group (p < 0.05).

CONCLUSION

High friction suture techniques may cause more adhesion formation than the lower friction suture techniques under passive postoperative therapy.