Biomechanical assessment of a novel tendon junction

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.

The Effect of an Additional Core Suture During Pulvertaft Tendon Repair: A Fresh-Frozen Cadaver Study

PURPOSE

Pulvertaft tendon repair is a strong suture technique; however, proper tendon tension is impaired by repair site elongation. Therefore, methods to reduce postoperative elongation are warranted. This study aimed to determine the effects of additional core sutures during Pulvertaft tendon repair on repair site elongation and rupture strength.

METHODS

A total of 48 finger extensor tendons were harvested from fresh-frozen cadavers, and tendons with similar diameters were paired. The 24 pairs of tendons were divided into the following 4 groups: group I, 3 interlaced weaves only; group II, 3 interlaced weaves and 2 core suture strands with 4-0 nylon; group III, 3 interlaced weaves and 2 core suture strands with 4-0 FiberWire; and group IV, 4 interlaced weaves only. Each sutured tendon was placed in a Universal Testing Machine, and repair site elongation after repeated traction loads and rupture strength were measured.

RESULTS

The mean elongation values were 2.74 ± 0.84 mm, 1.80 ± 0.16 mm, 1.60 ± 0.18 mm, and 1.92 ± 0.18 mm for groups I, II, III, and IV, respectively. The elongation values were significantly lower in groups II, III, and IV than in group I. The mean rupture strengths were 64.9 ± 16.0 N, 94.8 ± 17.2 N, 110.9 ± 21.3 N, and 104.9 ± 17.5 N for groups I, II, III, and IV, respectively. Rupture strengths were significantly higher for groups III and IV than for group I.

CONCLUSIONS

After adding core sutures during Pulvertaft tendon repair, the elongation amount decreased, and the rupture strength improved.

CLINICAL RELEVANCE

The study showed the effect of additional core sutures during Pulvertaft tendon repair, suggesting that it could be useful in reducing postoperative tendon elongation when extensor tendon transfers are performed.

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.

Transfer of the Posterior Tibial Tendon for Chronic Peroneal Nerve Palsy

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The common peroneal nerve (CPN) is one of the most frequently injured nerves of the lower extremity.

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One-third of patients who develop CPN palsy proceed to chronic impairment without signs of recovery.

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Ankle-foot orthoses can provide improvement with respect to gait dysfunction and are useful as a nonsurgical treatment option.

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Severe cases of CPN palsy demonstrating no signs of recovery may require operative intervention with tendon transfer.

The strengths of one-, two-, and three-weave Pulvertaft tendon repairs

We tested the tensile strength of the proximal juncture of tendon grafts with Pulvertaft tendon repairs in 18 cadaveric digital flexor tendons. These tendons were divided into three groups of six: single, two, or three weaves. Each of the interlacing weaves was secured with eight anchoring sutures. The specimens were loaded in a biomechanical tester until failure. The ultimate tensile strength did not show any significant differences across all three groups with statistical power of 0.77. The mean tendon elongation before repair failure showed significant difference at 10 mm (standard deviation (SD) 2), 16 mm (SD 3), and 15 mm (SD 3), respectively. All specimens failed by intra-tendinous pull-out of the weaves. We conclude that the two-weave Pulvertaft construct demonstrated comparable tensile strength to three weaves and tendon elongation was similar when two or three weaves were used.

Biomechanical and Dimensional Measurements of the Pulvertaft Weave Versus the Cow-Hitch Technique

Background: In this study, biomechanical strength and bulkiness of the cow-hitch technique and Pulvertaft weave were compared. Our goal was to investigate whether the cow hitch can withstand equal strength in comparison with the Pulvertaft and to see if there is a difference in bulk, which could enhance gliding function and reduce friction and adhesion formation. Methods: Sheep tendons were used to perform 10 cow-hitch and 10 Pulvertaft repairs. Tensile strength was obtained with a cyclic loading tensile testing machine and tendon width and height measurements were obtained through digital analysis by photographs of the repairs. Results: The cow hitch showed significantly better ultimate strength and had less bulk. There was no statistical difference in displacement, defined as gain in total length of the tendon. Conclusions: The results in this study show that the cow hitch outperforms the Pulvertaft weave in both ultimate strength and bulk.

Side-to-Side Versus Pulvertaft Extensor Tenorrhaphy-A Biomechanical Study

PURPOSE

We hypothesized that a side-to-side (STS) tendon repair has biomechanical characteristics that match those of a Pulvertaft (PT) weave.

METHODS

Thirty extensor tendons were harvested (4 extensor digitorum communis and 1 extensor indicis proprius from 6 cadaver arms). Three hand surgery fellows with similar backgrounds of training under the same conditions and precise standardized technique performed the repairs (5 PT and 5 STS per surgeon). After the repairs, the tendons were passed through a graft-sizing guide to determine bulk and results were expressed as a repaired versus native diameter ratio. The specimens were then tested for ultimate strength and fatigue properties. Failure type and mechanical properties were recorded and compared with those of the native tendon.

RESULTS

The average peak force to failure was 93 ± 20 N for the STS and 62 ± 32 N for PT group. Relative strength ratio (repair strength compared with native tendon strength) was 37% ± 21% for the STS and 22% ± 11% for the PT group. In the STS group, all failures occurred as a result of tissue failure; however, in the PT, suture failures occurred in 3 tendons before tissue failure. The mean bulk ratio of the repaired site versus native proximal tendon was 37 ± 14% and 40% ± 22% more for the STS and PT groups, respectively. These values for native distal tendon were 28% ± 9.9% and 26% ±24 %, respectively for STS and PT repair. Furthermore, the bulk of the repaired site for the STS and PT groups was 4.2 ± 0.50 and 4.7 ± 1.2 mm, respectively.

CONCLUSIONS

Side-to-side repair technique showed superior biomechanical properties while demonstrating comparable repair bulk of the tendon coaptation compared with the Pulvertaft weave.

CLINICAL RELEVANCE

The results of this study may help guide a surgeon's choice of repair technique when addressing tendon injuries or tendon transfers.

Tendon grafts: their natural history, biology and future development

The use of tendon grafts has diminished as regimes of primary repairs and rehabilitation have improved, but they remain important in secondary reconstruction. Relatively little is known about the cellular biology of grafts, and the general perception is that they have little biological activity. The reality is that there is a wealth of cellular and molecular changes occurring with the process of engraftment that affect the quality of the repair. This review highlights the historical perspectives and modern concepts of graft take, reviews the different attachment techniques and revisits the biology of pseudosheath formation. In addition, we discuss some of the future directions in tendon reconstruction by grafting, which include surface modification, vascularized tendon transfer, allografts, biomaterials and cell-based therapies.

Recent developments in flexor tendon repair techniques and factors influencing strength of the tendon repair

Over the last decade, both basic researchers and surgeons have sought to identify the most appropriate techniques to be applied in flexor tendon repairs. Recent developments in experimental tendon repairs and clinical outcomes of newer repair techniques have been reviewed in an attempt to comprehensively summarize the most critical mechanical factors affecting the performance of tendon repairs and the surgical factors influencing clinical outcomes. Among them, attention to annular pulleys, the purchase and tension of the core suture, and the direction and curvature of the path of tendon motion have been found to be determining factors in the results of tendon repair.