Subcuticular Running Suture Technique: Step-by-Step Guide

The skin has three main layers: epidermis (outermost, dead layer), dermis (middle, living tissue), and subcutaneous layer (bottom, fat). The epidermis contains five layers from deepest to outermost: stratum germinativum/basal cell layer (new cell birth and melanin production via melanocytes), stratum spinosum/spiny layer (shedding begins and keratinization starts), stratum granulosum/granular layer (fully dead cells with visible keratin), stratum lucidum/clear layer (only on palms and soles), and stratum corneum/horny layer (outermost, water-resistant). The dermis (cutis/chorium) is 25 times thicker than the epidermis and contains two layers: papillary (top, near epidermis) and reticular (bottom). It houses sebaceous glands, sweat glands, nerves, blood vessels, lymph vessels, hair follicles, and erector pili muscles (causing goosebumps). The subcutaneous layer (adipose tissue/fat) provides cushioning, shape, and insulation beneath the dermis.

The skin comprises three main layers: epidermis (stratified squamous epithelium with basal, spinous, granular, and stratum corneum layers), dermis (papillary and reticular zones with collagen and appendages), and subcutis (adipose tissue). The epidermis contains melanocytes (producing melanin via dendrites for UV protection), Langerhans cells (antigen-presenting cells in mid-spinous layer), and Merkel cells. The dermis has rete ridges with dermal papillae containing capillaries supplying oxygen to the avascular epidermis. White spaces on histology slides represent lymphovascular channels, glandular spaces, or processing artifacts. Appendages include sebaceous glands (sebocytes with lipid vacuoles draining into follicles), eccrine sweat glands (coiled secretory portions with double-layered ducts), and hair follicles with bulbs containing dividing matrical cells. The triad of pink spindle bundles includes dense regular connective tissue (collagen), nerve tissue, and smooth muscle, each identifiable by characteristic features.

The skin consists of three main layers: epidermis (superficial), dermis (middle), and subcutaneous tissue (deepest). The epidermis has 4-5 layers: stratum basale, spinosum, granulosum, lucidum (thick skin only), and corneum. Thick skin (palms, soles) has 5 layers while thin skin has 4. The dermis has papillary and reticular layers connected by dermal papillae. The epidermis contains four cell types: keratinocytes (most abundant, forming the barrier), melanocytes (produce melanin, 1 per 10 keratinocytes), Merkel cells (tactile receptors), and Langerhans cells (antigen-presenting cells). The basement membrane zone connects epidermis to dermis and consists of hemidesmosomes, lamina lucida, lamina densa, and reticular lamina. Defects cause blistering diseases. The dermis contains fibroblasts (producing collagen, elastin, ground substance), immune cells, adipocytes, and nerve cells. Collagen (80% of dermal weight): type I provides tensile strength, type III provides elasticity, type IV is in basement membrane. Elastic fibers (2-4% of weight) enable skin recoil. Cutaneous appendages include hair follicles (bulb, isthmus, infundibulum), sebaceous glands (holocrine secretion), eccrine and apocrine sweat glands, and arrector pili muscles. The hair growth cycle has three phases: anagen (growth, 85% of hairs, 4-6 years), catagen (transition, 12%, 2-3 weeks), and telogen (resting, 13%, 3-4 months).

The skin has three layers: epidermis (outer layer of tough, flattened cells protecting against environment), dermis (middle layer containing blood vessels, sensory neurons, hair follicles, and connective tissue), and subcutaneous tissue (below dermis, composed mainly of adipose/fat cells for insulation and energy storage).

This section provides a comprehensive overview of the skin's three main layers. The hypodermis (subcutaneous layer) is composed of loose connective tissue or adipose tissue, about 80% fat, creating a protective cushion that gives contour and smoothness to the body and serves as an energy source. It contains vessels, nerves, fibers, adipose cells, and fibroblasts, and decreases with age. Fat storage is influenced by hormones and may be reflected by acne, hair growth, oiliness, or dryness. The dermis is the support layer of connective tissues, about 25 times thicker than the epidermis, consisting of the reticular layer (denser, deeper) and papillary layer (connects to epidermis). It comprises collagen (70% of dermis, provides strength and wound healing) and elastin (1/15 of collagen, provides elasticity). Glycosaminoglycans like hyaluronic acid maintain moisture and support collagen/elastin. The dermis supplies oxygen and nutrients through blood vessels and lymphatic channels. The epidermis is the outermost epithelial tissue, a thin protective covering with many nerve endings, composed of five layers: stratum germinativum (basal cell layer), stratum spinosum (spiny layer), stratum granulosum (granular layer), stratum lucidum (clear layer), and stratum corneum (horny layer).

Simple interrupted suturing is a fundamental wound closure technique where individual stitches are tied separately; the procedure involves grasping the needle 2/3 back, entering skin at 90 degrees with one or two bites, creating a surgeon's knot for the first throw, then tying subsequent throws with mirror-image technique while maintaining even tension to approximate wound edges; optimal spacing is 2mm minimum with finer sutures requiring closer placement, and knots should be positioned above the laceration to prevent blood accumulation.

The simple interrupted stitch is a fundamental suturing technique performed by going deep to superficial within the wound, pulling the thread almost all the way through with minimal tail, creating a surgeon's knot with two overhand wraps, adding one additional wrap, and dressing the knot by pulling the thread to the side.

This section teaches fundamental suturing skills including proper forceps selection (Adson forceps with teeth vs skin forceps with single rat tooth), correct needle loading at the inflection point, and the basic suturing motion where the needle enters about an eighth inch from the skin edge at a perpendicular angle. The section also introduces the instrument tie technique, which uses only surgical instruments to create knots without hand tying. Key elements include maintaining the needle holder above the suture throughout the tying process, making two initial wraps, crossing hands, and pulling the short end through. Different sutures require different knot counts: silk needs three knots while Vicryl requires approximately seven.

This section introduces the six fundamental suturing techniques used in practical examinations: simple interrupted, simple continuous, continuous locking, vertical mattress, horizontal mattress, and figure of eight. The most commonly used techniques in clinical practice are simple interrupted and figure of eight. Essential instruments include needle holder, silk suture, scissors, and tissue forceps. The needle should be held at one-third distance from the eye. The simple interrupted suture technique involves entering tissues perpendicular to the incision, passing the needle along its curve at equal depth on both sides, and tying knots in a clockwise-anti-clockwise-clockwise sequence. Key principles include approximating tissues without blanching and avoiding placing knots on the incision line.

The simple interrupted suture is the most common technique: needle enters one wound side at consistent distance and depth, exits opposite side at same measurements, then repeats adjacent. Symmetry is critical—both sides must match to prevent tissue misalignment and poor healing. Knots use two initial throws then simple knots; tight enough to approximate tissue but not so tight as to compromise blood supply. The subcuticular inverted suture enters subcutaneously and exits below skin surface, creating invisible line. Performed entirely beneath skin using absorbable material. Knot must be buried deep to prevent visible lumping. This technique provides hemostasis, reduces tension, and approximates tissue planes. Knots should be minimal to reduce foreign body reaction. Both techniques require consistent depth and distance throughout.

Absorbable sutures are degraded by the body through proteolysis (natural sutures) or hydrolysis (synthetic sutures). Examples include Vicryl (14-90 days absorption), PGA (200 days), and PDS (14-56 days). They are useful in hard-to-reach areas and for intradermal sutures where removal is not possible. Non-absorbable sutures are not degraded by the body and must be manually removed. They reduce rejection risk and allow wound inspection during removal but require removal regardless of access difficulty. Factors like fever, infection, and oral cavity moisture can accelerate absorbable suture degradation.

Sutures are classified as absorbable or non-absorbable. Absorbable sutures lose 50% of tensile strength at absorption time and are completely degraded at dissolution time. Non-absorbable sutures like chromic silk braided coated silk remain in place until manually removed. Each material has different half-life and degradation times.

Absorbable sutures have different absorption rates depending on their composition: (1) Chromic suture - absorbs relatively quickly but can cause tissue reaction; (2) Polyglycolic acid (Vicryl 910) - absorbs over 1-2 months; (3) Polyglactin 910 (Vicryl) - absorbs over 1-2 months; (4) Polydioxanone (PDS) - absorbs over 6-8 months; (5) Polypropylene (Prolene) - non-absorbable; (6) Nylon - non-absorbable. The absorption rate is an important consideration when selecting sutures, as it affects how long the wound will be supported and the risk of premature wound dehiscence.

Suture materials are the most critical component in tissue approximation, directly impacting surgical prognosis. An ideal suture must have appropriate tensile strength, good knot security, flexibility, visibility when wet, tissue inertness, and minimal bacterial accumulation. Materials are classified by diameter (higher numbers = thinner), structure (monofilament vs multifilament), and absorbability. Absorbable sutures include animal-based types (Catgut Simple: 3-5 days absorption, loses 50% strength in 24 hours; Chromic Catgut: 7-10 days absorption with chromium coating) and synthetic types (Polyglycolic Acid: 180-210 days absorption, monofilament; Polydioxanone/PDS: 180 days absorption, difficult handling; Polyglactin 910/Vicryl: 56-70 days absorption with triclosan coating; Polyglactin: 90 days absorption). All synthetic sutures absorb through hydrolysis rather than enzymatic digestion.

Absorbable sutures break down through enzymatic or hydrolytic processes, with absorption rates influenced by material composition, tissue location, and patient factors. Common absorbable materials include Vicryl (40-60 days), PDS II (up to 200 days), and chromic catgut (14 days). Non-absorbable sutures persist until manual removal and provide long-term support for slow-healing tissues like fascia, tendons, and hernia repairs. Natural sutures (collagen-based) provoke greater tissue reactions and carry infection risks, while synthetic alternatives offer more predictable performance. Color coding aids rapid identification: yellow=polypropylene, brown=chromic catgut, black=silk, white=polyester. Selection depends on healing time requirements, tissue type, and infection risk considerations.

The three main types of wound closure are: primary closure (closure with local tissues), local tissue flap closure, and free skin flap closure. The main principles for choosing closure methods are minimal tension and color/structure matching. Primary closure without tension is always the best option when possible. Local tissue flaps are preferred over free skin flaps because free skin flaps often have less aesthetic appearance.

Primary intention healing involves approximating wound edges so they heal directly into each other. The process requires wound assessment to confirm cleanliness, absence of foreign bodies, and no infection or necrotic tissue. Methods to facilitate healing include sutures, super glue, or steri-strips. Advantages include rapid healing (sutures removed after 7-10 days), small scars with good functional and cosmetic results. However, primary closure is contraindicated when there is infection risk, foreign material, or necrotic tissue, as closing such wounds promotes anaerobic conditions that allow bacterial growth and can lead to abscess formation.

Initial wound management follows ATLS principles - address life-threatening injuries first. Examine wound characteristics and connect appearance to mechanism of injury. Before numbing, perform neurovascular assessment. Debridement removes dead tissue (bacterial food source) through surgical excision, autolytic methods, enzymatic agents, or biological debridement (maggots). The second-look operation is vital for contaminated wounds. Closure must be tension-free - if edges must be pulled hard, sutures cut through and wounds break down. Layered closure with absorbable deep sutures and non-absorbable skin sutures achieves tension-free approximation.

Wound closure should never be performed blindly without proper assessment. Primary closure should be avoided when it would result in excessive tension, as this can lead to wound dehiscence or pathological scarring. Flap reconstruction is indicated when primary closure would result in excessive tension or when there is a need for tissue reconstruction beyond simple coverage. Examples include exposed fractures requiring bone reconstruction. The key principle is to ensure wounds are closed with appropriate tension to promote healing while minimizing complications.

Wound closure techniques include primary closure with sutures for wounds with good tissue approximation, secondary closure with strips or adhesive dressings for small wounds without active bleeding, tissue adhesive (glue) for wounds with good approximation, and stapling for rapid closure. Acute wound care principles include assessing for active bleeding and controlling hemorrhage, preventing infection through aseptic technique, creating optimal moisture balance (not too dry, not too wet), protecting the wound from trauma, and promoting healing through appropriate dressing selection. Wound assessment includes evaluating location, depth, presence of foreign bodies, duration, signs of infection, and underlying cause. Debridement removes necrotic tissue through autolytic, enzymatic, mechanical, or surgical methods. Complications include primary hemorrhage, secondary hemorrhage, dehiscence, evisceration, and hypertrophic scarring.