Understanding Suture Classification
Suture is classified along three axes: absorbable vs. nonabsorbable, natural vs. synthetic, and monofilament vs. multifilament (braided). The CST exam tests your ability to match a suture type to an appropriate tissue and clinical scenario, so memorize the properties, not just the names.
Absorbable Sutures
| Suture | Material | Structure | Absorption Time | Common Use |
|---|
| Plain gut | Natural (collagen) | Monofilament | 7-10 days | Mucosa, subcutaneous tissue |
| Chromic gut | Natural (collagen, chromium salt-treated) | Monofilament | 21-28 days | Oral mucosa, vaginal tissue |
| Polyglactin 910 (Vicryl) | Synthetic | Braided | 56-70 days | Fascia, subcutaneous, ligatures |
| Poliglecaprone 25 (Monocryl) | Synthetic | Monofilament | 90-120 days | Subcuticular skin closure |
| Polydioxanone (PDS) | Synthetic | Monofilament | 180-210 days | Fascia requiring extended support |
| Polyglycolic acid (Dexon) | Synthetic | Braided | 60-90 days | General soft tissue approximation |
Nonabsorbable Sutures
| Suture | Material | Structure | Common Use |
|---|
| Silk | Natural (protein filament) | Braided | Ligating vessels, securing drains |
| Nylon (Ethilon/Dermalon) | Synthetic | Monofilament | Skin closure, retention sutures |
| Polypropylene (Prolene) | Synthetic | Monofilament | Vascular anastomosis, cardiovascular |
| Polyester (Ethibond, Mersilene) | Synthetic | Braided | Tendon repair, cardiac valve annuloplasty |
| Stainless steel | Synthetic (metal) | Monofilament or twisted | Sternal closure, tendon repair |
Suture Sizing
Suture diameter is expressed on the USP (United States Pharmacopeia) scale. A higher number of zeros means a smaller, finer suture strand.
- #2, #1, 0 - Heaviest gauges, used for fascia and retention closures.
- 2-0, 3-0 - Common for subcutaneous tissue and fascia in general procedures.
- 4-0, 5-0 - Common for skin closure and subcuticular work.
- 6-0 to 11-0 - Microsurgical and ophthalmic use; the more zeros, the finer the strand.
Needle Point Types
| Needle Type | Point Description | Typical Tissue |
|---|
| Cutting | Triangular, sharp edges on the inside curve | Skin, tough fibrous tissue |
| Reverse cutting | Triangular, sharp edge on the outside curve | Skin closure with reduced tissue tear-out |
| Tapered (round) | Round body tapering to a sharp point | Bowel, fascia, peritoneum, vessels |
| Blunt | Rounded, non-cutting tip | Friable tissue such as liver or kidney |
Key Exam Points
- Monofilament sutures have a lower risk of harboring bacteria than braided sutures because they lack interstices.
- Braided sutures have higher tensile strength and better handling but carry higher infection risk (capillarity).
- Absorbable sutures are broken down by hydrolysis (synthetic) or proteolytic enzymatic action (natural, such as gut).
- The surgeon selects suture based on tissue type, healing time required, tension, and cosmetic outcome.
- Always confirm suture type and size against the surgeon's preference card before opening it to the field.