Biomechanical evaluation of flexor tendon graft with different repair techniques and graft surface modification

New dynamic suture material for tendon transfer surgeries in the upper extremity - a biomechanical comparative analysis

BACKGROUND

Early mobilization after tendon surgery is crucial to avoid commonly observed postoperative soft tissue adhesions. Recently, a new suture was introduced (DYNACORD; DC) with a salt-infused silicone core designed to minimize laxity and preserve consistent tissue approximation in order to avoid gap formation and allow early mobilization.

AIMS

To compare the biomechanical competence of DC against a conventional high strength suture (FiberWire; FW) in a human cadaveric tendon transfer model with an early rehabilitation protocol.

METHODS

Sixteen tendon transfers (flexor digitorum superficialis (FDS) IV to flexor pollicis longus (FPL)) were performed in 8 pairs human cadaveric forearms using either DC or FW. Markings were set 0.8 cm proximally and 0.7 cm distally to the level of the interweaving zone of the transfer. All specimens underwent repetitive thumb flexion against resistance in 9 intermittent series of 300 cycles each, simulating an aggressive postoperative rehabilitation protocol. After each series, the distance of the proximal marker to the interweaving zone (proximal), the length of the interweaving zone (intermediate) and the distance of the distal marker to the interweaving zone (distal) were measured.

RESULTS

Pooled data over all nine series, normalized to the immediate postoperative status, demonstrated no significant differences between FW and DC (p ≥ 0.355) for the proximal and distal markers. However, at the intermediate zone, DC was associated with significant length shortening (p < 0.001) compared to FW without significant length changes (p = 0.351). Load to catastrophic failure demonstrated significant higher forces in FW (p = 0.011). Nevertheless, due to failure mainly proximal or distal of the transfer zone, these loads are not informative.

CONCLUSION

From a biomechanical perspective, DC preserved tissue approximation and might be considered as a valid alternative to conventional high-strength sutures in tendon transfer surgery. DC might allow for a shorter interweaving zone and a more aggressive early postoperative rehabilitation program, possibly avoiding commonly observed postoperative soft tissue adhesions and stiffness.

Cell-based tissue engineered flexor tendon allograft: A canine in vivo study

This study aimed to compare the clinically established autologous extrasynovial tendon graft to a newly developed tissue-engineered allograft (Eng-allograft) in terms of functional outcomes following flexor tendon reconstruction in a canine model. The second and fifth flexor digitorum profundus (FDP) tendons from 16 dogs were transected and repaired in Zone II. After 6 weeks of cage activity, the repaired tendons were intentionally ruptured, creating a clinically relevant model for reconstruction. The re-ruptured FDP tendons were then reconstructed using either the clinically standard autologous extrasynovial tendon graft or the Eng-allograft, which had been revitalized with autologous bone marrow-derived mesenchymal stem cells (BMSCs) and synovialized using carbodiimide derivatized synovial fluid (cd-SYN). Following 12 weeks of postoperative rehabilitation, the functional outcomes of the surgical digits were evaluated. The Eng-allograft group exhibited improved digital function, including lower digit work of flexion and reduced adhesion status, while maintaining similar tendon gliding resistance compared to the autograft group. However, the failure load of both the distal and proximal host/graft conjunctions in the Eng-allograft group was significantly lower than that of the autograft group with higher graft rupture at the host-graft junction. In conclusion, the decellularized allogenic intrasynovial tendon, when revitalized BMSCs and synovialized with cd-SYN, demonstrates positive effects on digital function improvement and adhesion reduction. However, the healing at both proximal and distal graft/host junctions is far lower than the autograft. Further research is needed to enhance the healing capacity of allograft conjunctions, aiming to achieve a comparable level of healing seen with autografts.

Pentamidine-loaded gelatin decreases adhesion formation of flexor tendon

Background

Prevention of adhesion formation following flexor tendon repair is essential for restoration of normal finger function. Although many medications have been studied in the experimental setting to prevent adhesions, clinical application is limited due to the complexity of application and delivery in clinical translation.

Methods

In this study, optimal dosages of gelatin and pentamidine were validated by gelatin concentration test. Following cell viability, cell migration, live and dead cell, and cell adhesion assay of the Turkey tenocytes, a model of Turkey tendon repair was established to evaluate the effectiveness of the Pentamidine-Gelatin sheet.

Results

Pentamidine carried with gelatin, a Food and drug administration (FDA) approved material for drug delivery, showed good dynamic release, biocompatibility, and degradation. The optimal dose of pentamidine (25ug) was determined in the in vivo study using tenocyte viability, migration, and cell adhesion assays. Further biochemical analyses demonstrated that this positive effect may be due to pentamidine downregulating the Wnt signaling pathway without affecting collagen expression.

Conclusions

We tested a FDA-approved antibiotic, pentamidine, for reducing adhesion formation after flexor tendon repair in both in vitro and in vivo using a novel turkey animal model. Compared with the non-pentamidine treatment group, pentamidine treated turkeys had significantly reduced adhesions and improved digit function after six weeks of tendon healing.

The translational potential of this article

This study for the first time showed that a common clinical drug, pentamidine, has a potential for clinical application to reduce tendon adhesions and improve tendon gliding function without interfering with tendon healing.

Carbodiimide-Derivatized Synovial Fluid for Tendon Graft Coating Improves Long-Term Functional Outcomes of Flexor Tendon Reconstruction

BACKGROUND

Flexor digitorum profundus (FDP) tendon injury is common in hand trauma, and flexor tendon reconstruction is one of the most challenging procedures in hand surgery because of severe adhesion that exceeds 25% and hinders hand function. The surface properties of a graft from extrasynovial tendons are inferior to those of the native intrasynovial FDP tendons, which has been reported as one of the major causations. Improved surface gliding ability of the extrasynovial graft is needed. Thus, this study used carbodiimide-derivatized synovial fluid and gelatin (cd-SF-gel) to modify the surface of the graft, thus improving functional outcomes using a dog in vivo model.

METHODS

Forty FDP tendons from the second and fifth digits of 20 adult women underwent reconstruction with a peroneus longus (PL) autograft after creation of a tendon repair failure model for 6 weeks. Graft tendons were either coated with cd-SF-gel ( n = 20) or not. Animals were euthanized 24 weeks after reconstruction, and digits were collected after the animals were euthanized for biomechanical and histologic analyses.

RESULTS

Adhesion score (cd-SF-gel, 3.15 ± 1.53; control, 5 ± 1.26; P < 0.00017), normalized work of flexion (cd-SF-gel, 0.47 ± 0.28 N-mm/degree; control, 1.4 ± 1.45 N-mm/degree; P < 0.014), and distal interphalangeal joint motion (cd-SF-gel, 17.63 ± 6.77 degrees; control, 7.07 ± 12.99 degrees; P < 0.0015) in treated grafts all showed significant differences compared with nontreated grafts. However, there was no significant difference in repair conjunction strength between the two groups.

CONCLUSION

Autograft tendon surface modification with cd-SF-gel improves tendon gliding ability, reduces adhesion formation, and enhances digit function without interfering with graft-host healing.

CLINICAL RELEVANCE STATEMENT

The authors demonstrate a clinically relevant and translational technology by using the patient's own synovial fluid to "synovialize" an autologous extrasynovial tendon graft to improve functional outcomes following flexor tendon reconstruction.

Alternative Tendon Coaptations to the Pulvertaft Weave Technique: A Systematic Review and Meta-Analysis of Biomechanical Studies

BACKGROUND

The Pulvertaft weave technique (PT) is frequently used during tendon repairs and transfers. However, this technique is associated with limitations. In this systematic review and meta-analysis, quantitative and qualitative analyses were performed on in vitro, biomechanical studies that compared the PT with alternative techniques.

METHODS

Articles included for qualitative and/or qualitative analysis were identified following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Studies included in the meta-analysis were analyzed either as continuous data with inverse variance and random effects or as dichotomous data using a Mantel-Haenszel analysis assuming random effects to calculate an odds ratio.

RESULTS

A comprehensive electronic search yielded 8 studies meeting inclusion criteria for meta-analysis. Two studies with a total of 65 tendon coaptations demonstrated no significant difference in strength between the PT and traditional side-to-side (STS) techniques (P = .92). Two studies with a total of 43 tendon coaptations showed that the STS with 1 weave has a higher yield strength than the PT (P = .03). Two studies with a total of 62 tendon repairs demonstrated no significant difference in strength between the PT and the step-cut (SC) techniques (P = .70). The final 2 studies included 46 tendon repairs and demonstrated that the wrap around (WA) technique has a higher yield strength than the PT (P < .001).

CONCLUSIONS

The STS, SC, and WA techniques are preferred for improving tendon form. The STS and WA techniques have superior yield strengths than the PT, and the SC technique withstands similar stress to failure as the PT.

Optimizing the Pulvertaft Weave Technique: A Comprehensive Systematic Review of Comparative Biomechanical Studies

PURPOSE

The Pulvertaft weave continues as a staple technique for tendon coaptations. Many have proposed minor alterations to the original technique to improve its strength, though a lack of consensus exists. Our aim was to explore how the number of weaves and suture characteristics contribute to the overall strength of the coaptation.

METHODS

A comprehensive electronic search was conducted using PubMed, Cochrane Library, and Scopus. Criteria for inclusion consisted of cadaveric human or animal biomechanical studies evaluating ultimate failure load (Newtons, N) as well as number of weaves, suture characteristics, tendon source, and number of coaptations. Weaves with minimum averages of 75 N were deemed successful, and those with >120 N were considered high performing.

RESULTS

A total of 347 tendon transfers from 15 studies met inclusion criteria. Average strength by number of weaves was 36.4 N (n=52) for 1 weave; 54.2 N (n=58) for 2 weaves; 115.9 N (n=174) for 3 weaves; and 81.7 N (n=63) for 4 weaves. Statistical differences were observed between 1 and 2 weaves (p<0.0001); 2 and 3 weaves (p<0.0001); 3 and 4 weaves (p<0.003); and 2 and 4 weaves (p<0.0001). High performing tendon transfers utilized 3 weaves, 3-0 or 4-0 braided sutures, and figure-of-eight or mattress core sutures.

CONCLUSIONS

Contrary to the current dogma of 'the more the better', our findings show that Pulvertaft weave strength is optimized when 3 weaves are used to combine donor and recipient tendons. Braided sutures with either figure-of-eight or mattress sutures were associated with highest strength of repair.

Biomechanical Study Comparing Pulvertaft, Double Side-to-Side, and Locking Side-to-Side Tendon Suture Techniques

PURPOSE

In this study, we present a single-sided locking side-to-side (STS) suture technique as a possible alternative for the Pulvertaft weave in tendon transfers. The aim of the study was to compare the biomechanical characteristics of the single-sided locking STS reconstruction with Pulvertaft and double-sided nonlocking STS reconstructions.

METHODS

Twenty-four human cadaveric extensor digitorum communis tendons and 24 flexor digitorum superficialis tendons were randomly assigned to 1 of 3 groups, resulting in a total of 8 flexor tendons and 8 extensor tendons per group: Pulvertaft, double-sided nonlocking STS, and single-sided locking STS reconstructions. Load to failure was measured with a tensile testing machine. Increase in cross-sectional area was used as a measure of bulkiness at the reconstruction site.

RESULTS

In extensor tendons, single-sided locking STS reconstructions showed a higher load to failure than Pulvertaft reconstructions, whereas no difference was found in load to failure between single-sided locking and double-sided nonlocking STS reconstructions. In flexor tendons, single-sided locking STS reconstructions showed a higher load to failure than Pulvertaft reconstructions. However, load to failure of single-sided locking STS reconstructions was less than double-sided nonlocking STS reconstructions. In both extensor and flexor tendons, the percent increase in cross-sectional area at the reconstruction site was higher in Pulvertaft reconstructions than single-sided locking STS reconstructions, whereas no difference was found between single-sided locking STS and double-sided nonlocking STS reconstructions.

CONCLUSIONS

Single-sided locking and double-sided nonlocking STS reconstructions are suitable alternatives to the Pulvertaft technique for tendon transfers owing to a higher strength and less bulkiness. Because load to failure of both STS reconstructions did not differ in extensor tendon transfers, the single-sided locking STS reconstruction seems especially suitable for extensor tendon transfers.

CLINICAL RELEVANCE

This study provides anatomical evidence that the single-sided locking STS reconstruction yields a higher strength and is less bulky than the Pulvertaft reconstruction in tendon transfers.

Clinical Characteristics Associated with the Prognosis of One-Stage Grafting for Flexor Digitorum Profundus Reconstruction in Zones I and II

BACKGROUND

The authors aimed to identify clinical characteristics related to the prognosis after one-stage grafting for flexor digitorum profundus reconstruction in zones I and II.

METHODS

A total of 401 patients who underwent one-stage flexor digitorum profundus reconstruction after injuries in zones I and II, between January 1, 2006, and June 1, 2016, were included for analysis. The authors recorded the following clinical characteristics: duration from injury to reconstruction, graft type and length, handling (preservation or removal) of flexor digitorum superficialis, tenorrhaphy technique, and duration of postoperative immobilization.

RESULTS

There was no significant difference in age, sex, duration between injury and reconstruction, graft type, and handling of flexor digitorum superficialis between subjects who underwent successful reconstruction and those who did not. Univariate and multivariate analyses revealed that end-to-end tenorrhaphy, immediate controlled motion, and immobilization for less than 2 weeks all independently were related to improved final outcomes. Grafting within zones I and II contributed to increased incidence of failure. In a subgroup having an injury-reconstruction duration of less than 2 weeks, the authors observed that grafting from zone III to zones I and II tended to result in better outcomes compared with grafting from zone III to the flexor digitorum profundus insertion. This, however, was not statistically significant (p = 0.11).

CONCLUSIONS

The authors recommend end-to-end tenorrhaphy, reducing immobilization to less than 2 weeks, and avoiding grafting within zones I and II. In addition, further studies are still needed to clarify the optimal length of grafting.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, III.

Kinetic analysis of canine gait on the effect of failure tendon repair and tendon graft

Kinetic analysis of canine gait has been extensively studied, including normal and abnormal gait. However, no research has looked into how flexor tendon injury and further treatment would affect the walking pattern comparing to the uninjured state. Therefore, this study was aimed to utilize a portable pressure walkway system, which has been commonly used for pedobarographic and kinetic analysis in the veterinary field, to examine the effect of a failed tendon repair and tendon graft reconstruction on canine digit kinetics during gait. 12 mixed breed (mongrel) hound-type female dogs were included in this study and 2^nd and 5^th digits were chosen to undergo flexor tendon repair and graft surgeries. Kinetic parameters from the surgery leg in stance phase were calculated. From the results, after tendon failure repair, decrease of weight bearing was seen in the affected digits and weight bearing was shifted to the metacarpal pad. After tendon graft reconstruction, weight bearing returned to the affected digits and metacarpal pads. Slight alteration in peak pressure and instant of peak force were identified, but it was estimated to have little influence on post-reconstruction gait. This study could serve as a reference in evaluating canine digit function in flexor tendon injury for future studies.