Composition
Surgical silk is a widely used natural non-absorbable suture material, may be plain or braided/twisted and capillary in nature. It is composed of a natural organic protein Fibrion (composed of 70% protein fibers and 30% extraneous material like gum) which is obtained from the cocoon of silk worm (domesticated Bombyx mori), processed to remove its natural waxes and gums, and dyed black with a vegetable dye (also available in undyed form or virgin silk). De-gumming process helps in compact braiding and retention of their natural body and elasticity.
Its natural capillarity is decreased by treating/coating it with oil, pure bee wax or silicone (mainly coated with silicone). Coating also decreases tissue drag and facilitates easy passage through tissue.
Virgin silk is undyed form in white colour and comes with sericin gum which holds the filaments together.
Tensile strength & Absportion
It has excellent handling characteristics, tensile strength and good knot security (additional throws are required).
Silk stitches are not degraded of weakened by the action of enzymes. It loses tensile strength slowly over the period of 6 months and complete absorption may take up to 2 years (proteolysis). It is gradually encapsulated by the fibrous connective tissue.
(*non-absorbable strictly doesn’t mean they really don’t get absorbed like metal or stainless steel sutures but sometimes they take more time to get absorbed than defined period for absorbable suture materials)
Silk suture material is sterilised by ethylene oxide. It can be sterilized by autoclaving. Silk can be boiled repeatedly without impairing its tensile strength.
Tissue reaction
The main disadvantage earlier was the moderate to high degree of tissue reaction caused. The material binds with gamma globulins which eventually lead to acute inflammation.
With modern technology and more purified protein does not cause severe tissue reaction (grade 0) / sometimes minimal inflammatory reactions are seen at the site of implantation.
It is effective as a pull out suture and lacks adherence to tissue.
If permanent tensile strength is required then stainless steel sutures should be preferred rather than silk sutures because silk loses its tensile strength over the period of time.
Indications
It is used in the general soft tissue approximation, skin approximation, oral surgical procedures, gastrointestinal surgeries, cardiovascular surgeries (for vascular grafts), caesarean section, thyrodectomy, ophthalmic surgeries, dental surgeries, tendon repairs, episiotomy, muscle approximation, opthalmic and neurological procedures. It is most widely used as ligature or skin closure.
In ophthalmic procedures non-coated silk sutures are usually preferred.
Fig: Sutura – Braided Silk suture by dolphin sutures
Contraindications
Silk suture is contraindicated in patients with known history of the sensitivity or allergy to silk. The ends of the suture material, if protruding into the lumen, may cause ulceration in the gastrointestinal tract and may act as a nidus for calculus formation in the urinary bladder and gall bladder.
The material should not be used to close contaminated / infected wounds as the fibers will hold blood which is an excellent medium for bacterial proliferation. It also have poor microbe resistance characteristics. It harbours bacteria within the braid and causes persistent infection.
Sizes
It is available in different gauze sizes ranging from USP 8-0 to 14 (different sizes are available with different manufacturers) with different kind of swaged needles (taper point, cutting edge, round bodied, straight, blunt point etc.) or needle less and suture length.
Storage
It is economical. Storage is recommended below 25 ºC in dry condtions. It can be stored up to 5 years after manufacturing/harvesting. In modern practice silk is being replaced by synthetic monofilament sutures.
Fig: Perma – Hand Silk Suture USP 4-0 by Ethicon
FAQs
Silk suture is indicated for variety of surgical procedures like skin and general soft tissue approximation and/or ligation. It is popularly used in cardiovascular, gynaecological, ophthalmic, and neurological procedures.
No. Silk sutures are non-absrobable like prolene, nylon etc. They lose tensile strength in 6 – 12 months and take more than 2 years to get absorbed.
Silk is a natural, braided multifilament non-absorbable suture material.
Silk suture loses tensile strength in 6-12 months and gets absorbed in 2 years if they are implanted in the internal organs.