Assessment of mechanical properties and dimensions of suture threads utilized in orthopedic surgeries

Avaliação das propriedades mecânicas e dimensões de fios de sutura utilizados em cirurgias ortopédicas

ORIGINAL ARTICLE

Assessment of mechanical properties and dimensions of suture threads utilized in orthopedic surgeries

Avaliação das propriedades mecânicas e dimensões de fios de sutura utilizados em cirurgias ortopédicas

Trajano Sardenberg^I; Sergio Swain Müller^II; Paulo Roberto de Almeida Silvares^II; Adriano Bovo Mendonça^III; Rafael Riscali de Lima Moraes^III

^IAssistant Professor

^IIAssistant Professor, MD

^IIIFormer Internist

^{Correspondence}

SUMMARY

Surgical materials of monofilament nylon (0, 3-0 and 4-0), braided polyester (0, 3-0 and 4-0) and monofilament polypropylene (0, 3-0 and 4-0) of 7 trademarks commercialized in Brazil, was submitted to analysis of diameter, length, enchasement resistance, tensile strength of surgery materials knotted and unknotted, according to ABNT. The results show that most of surgical materials was inside of preconizing patterns of ABNT.

Key words: Tensile strenght; Suture materials; Mechanical properties.

RESUMO

Fios de sutura de náilon (0, 3-0 e 4-0), poliéster trançado (0, 3-0 e 4-0) e polipropileno (0, 3-0 e 4-0) de 7 marcas comercializadas no Brasil, foram submetidos a análise de diâmetro, comprimento, resistência do encastoamento, resistência à tração do fio sem nó e resistência à tração do fio com nó, segundo metodologia padronizada pela Associação Brasileira de Normas Técnicas (ABNT). Os resultados obtidos indicam que a maioria dos fios testados encontra-se dentro dos valores preconizados pela ABNT.

Descritores: Resistência à tração; Material de sutura; Propriedades mecânicas; Dimensões.

INTRODUCTION

The quality of the materials forming the metallic implants used in the surgical treatment of fractures, such as intramedullar plates, screws and scapi, is fundamental to obtain bone consolidation and functionally rehabilitate the patient. The quality of the suture threads employed in surgeries is equally important. In some specific surgeries such as tenorrhaphies, miorrhaphies, ligament repairs and capsular repairs, the quality of the suture thread is a critical factor to obtain good results, as well as the surgical techniques employed. Surgeons particularly concerned with the management of tendon injuries have performed mechanical trials using the suture materials most commonly utilized in such operations ^(7,10).

The search for the ideal suture thread walks along with the history of surgery. Back in the second century b.C. Galeno was the first to use catgut in sutures and ligatures. In the nineteenth century a.C. Joseph Lister used to make his surgical threads by hand, disinfecting them with a carbolic acid solution, thus starting aseptic surgery ⁽³⁾.

Ideally, a suture thread should present features such as a safe knot, proper tensile strength, easy handling, low tissular response, lack of carcinogenic action, not being prone to cause or maintain any infection, being able to keep the injury's borders close to one another at least until the proliferation phase of the healing, and resist to the medium where it will act, besides low cost ⁽³⁾.

The global technological development during the last two decades has allowed surgeons to use suture threads that are closer and closer to an optimal thread. On the other hand, the control of the industrial production of suture threads by means of tests and constant inspection of the veracity of results is difficult, mainly due to the high operating costs. Besides, our country does not count on any agency specialized in this type of calibration. However, it is worth reminding that in 2002 ANVISA (Brazilian Health Surveillance Agency) started an administrative process of accreditation of quality control laboratories in this health area.

In spite of these drawbacks, periodically ABNT (Brazilian Association for Technical Standards), a non-profit private entity founded in 1940 that is the agency responsible for the standardization of techniques in Brazil, publishes the normative references consisting of a set of tests with standardized methodologies and recommending the minimum results to be provided by suture threads marketed in Brazil ^(1,2).

The objective of this study is to evaluate the mechanical parameters and dimensions of several suture threads marketed in Brazil and frequently used in orthopedic surgeries, having as a reference the standards recommended by ABNT.

MATERIALS AND METHOD

The suture threads analyzed in this study are included in Table 1.

The mechanical and dimensional parameters evaluated were thread length, diameter, strength, resistance to encasement, and tensile strength of knotted and non-knotted threads.

The methodology used to study the parameters is described in standard NBR 13904 of July 1997, developed and published by ABNT ⁽²⁾ that recommends the following: a) length: the thread was positioned on a flat surface and measured with no tension in it with a rigid scale (rule). The length of each thread should not show any variation greater than 5% of the length printed on the individual package; b) diameter: measured with a micrometer and using a fixed pulley system mounted on a table, in order to keep the thread tensioned. One end of the thread was fixed with a clamp, while the rest of the thread was passed through the center of the base, the free end being fixed to a weight of 1080 g for threads 0; 480 g for threads 3-0; and 300 g for threads 4-0. The diameter was measured in 3 points at distances approximately equal to ¼, ½ and ¾ of the total length of the thread (Figure 1); c) resistance to encasement: for this test, a universal tension device was used. The needle was fixed to one of the clamps of the device (which is formed by two parallel steel plates mutually compressed by 6 screws & bolts at both sides) so that the encased portion would be free and aligned with the axis of the force applied by the poppet head. The free end of the thread was fixed in the movable holder consisting of a steel cylinder around which the thread was wound 3 times; d) tensile strength of the unknotted thread: the test was performed with a universal tension device. The ends of the thread were fixed in two cylindrical holders around which the thread was wound 3 times. Then the device was actuated until the thread would break. Each time the thread broke at a point too close (up to 1.3 cm) to the cylindrical holders, the value obtained was neglected (Figure 2); e) tensile strength of the knotted thread: the tensile strength was measured on a surgically knotted thread. To make this knot, each end of the thread was held by one hand and the right-hand end of the thread was positioned over the left-hand end of the thread, forming a circle; then the superimposed end was introduced twice in the circle. The knot was fixed in the device's holder and the left-hand end of the thread was superimposed to the right-hand end of the thread, thus closing the knot. This last step was repeated for nylon monofilament threads and braided polyester threads (that is, the left-hand end was superimposed again to the right-hand end of the thread, closing the knot) (Figure 3). The thread was positioned on the test device so that the knot would be midway between the clamps.

The tensile strength and encasement tests were performed using a universal device for mechanical tests (EMIC Curitiba, PR) model DL 10000, at a speed of 30 mm/min with a 50 N cell load for threads 3-0 and 4-0 and 1000 N for threads 0.

The diameter was measured using a 0.001-mm accuracy, 0-25 mm range Mitutoyo micrometer caliper model 102-119. The length was measured with a metal rule.

Each parameter was measured 5 times for each sample. A comparison was made between the values obtained and the values mentioned in ABNT's NBR 13904 standard ⁽²⁾.

RESULTS

The results obtained are included in Tables 2 to 10.

DISCUSSION

The features of the suture threads are grouped by their physical properties, handling properties, and tissular response properties ⁽⁴⁾. The present study is limited to physical properties, particularly dimensions, resistance to encasement and tensile strength of the unknotted thread and knotted thread.

The comparison between the dimensions (length and diameter) observed in the present sample and the standards of ABNT's NBR 13904 ⁽²⁾ is only relatively important in the practical use of suture threads, being more relevant for the quality control in the manufacturing and marketing of the threads.

The features regarding mechanical properties, more specifically the resistance to encasement and tensile strength of both the unknotted and knotted thread are fundamental in orthopedic surgeries. The resistance to encasement, that is, the thread's strength as regards its fastening to the needle, is important when surgical knots are made, since it can be easily understood that a thread that separates from its needle while passing through a tendon will impair the whole surgical technique. Post-operative protocols that recommend early articular mobilization demand that the suture immediately show the proper strength that, until the proliferative phase of the healing is reached, will depend on the type of the suture thread employed, as well as on the type of stitch and the number of knots employed.

The need to test the strength of the unknotted thread and knotted thread is based on the fact that, as the surgeon tightens the suture's knot, it is expected that the stitch will not loosen until the proliferative phase of the tissular healing is reached ^(5,6,8,10). The analysis of the mechanical test results underlines such importance, since the maximum strength of the knotted thread was significantly lower than that of the unknotted thread, in all samples investigated in this study.

The tensile strength characteristics of suture threads have been studied viewing to guide surgeons in the selection of the optimal thread by comparing several suture materials ^(5,8,10,11). In the present study comparisons were made with the standards recommended by ABNT's NBR 13904 ⁽²⁾ within the objectives of the study, which consists of analyzing suture threads marketed in Brazil as compared to the recommended Brazilian standard.

ABNT's NBR 13904 standard ⁽²⁾ does not specify the speed of load charge in mechanical tests for strength. In this study, the speed used was 30 mm/min, which is considered an average value ⁽⁹⁾.

The braided polyester- and nylon threads were tested with a type of knot recommended by ABNT's NBR 13904 standard ⁽²⁾, although with an extra loop (Figure 3B) to avoid sliding as noticed in the previous pilot study and also observed by Trail et al ⁽¹⁰⁾.

The analysis of the results of tensile strength of the unknotted thread and knotted thread with the sample of this study for nylon 4-0 threads, polyester 4-0 threads and polypropylene 4-0 threads showed that such results are similar to the ones reported by Trail et al ⁽¹⁰⁾.

A comparative analysis of the results from the present study and ABNT's NBR 13904 ⁽²⁾ standards indicates that:

a) regarding nylon 0 thread: all samples meet the standard;

b) regarding nylon 3-0 thread: Point Suture and Ethicon have diameters that is larger than the recommended value;

c) regarding nylon 4-0 thread: Point Suture and Ethicon have diameters larger than the recommended value;

d) regarding polyester 0 thread: all samples meet the standard;

e) regarding polyester 3-0 thread: B/Braun Synthofil showed a length that is shorter than the recommended value;

f) regarding polyester 4-0 thread: B/Braun Synthofil showed a length that is shorter than the recommended value;

g) regarding polypropylene 0 thread: JP showed a resistance with the knotted thread that is lower than the recommended value;

h) regarding polypropylene 3-0 thread: all samples meet the standard;

i) regarding polypropylene 4-0 thread: all samples meet the standard.

CONCLUSIONS

The analysis of the mechanical and dimensional parameters of 31 types of suture threads from 7 brands marketed in Brazil indicated that 77.42% of the samples meet the standard recommended by ABNT ⁽²⁾.

ACKNOWLEDGEMENTS

The authors wish to thank Mr. Luis Carlos Edevalter Bardella for his help in performing the tests; to Mr. Marcos Eduardo Barreiros Aloise for the illustrations; to Mr. Carlos Luis Miguel for editing the texts and tables; to Engineer Manoel Alvaro Guimaraes and Mr. Jose Vicente Fortes for setting up the calibration methods for the measurement of the dimensions of the materials investigated.

Work performed at the Departamento de Cirurgia e Ortopedia da Faculdade de Medicina de Botucatu da Universidade Estadual Paulista Júlio de Mesquita Filho (FMB-UNESP)

Trabalho recebido em 31/01/2002

Aprovado em 14/03/2003

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Publication Dates

• Publication in this collection
  03 June 2003
• Date of issue
  Apr 2003

History

• Received
  31 Jan 2002
• Accepted
  14 Mar 2003