Perineal Tears and Grading
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Direct answer
Perineal tears are graded by the structures divided: first degree involves skin and vaginal epithelium only; second degree adds the perineal muscles but leaves the anal sphincter intact (this grade includes periurethral tears); third degree involves the anal sphincter complex, subclassified as 3a (less than half of the external sphincter thickness), 3b (more than half), 3c (external plus internal sphincter); and fourth degree extends through the sphincters into the anal epithelium. First and second degree tears are repaired with continuous or interrupted 2-0 polyglactin sutures; third and fourth degree tears need theatre, good light and assistance, repair of the internal sphincter with interrupted 3-0 polydioxanone or polyglactin, the external sphincter by end-to-end or overlapping technique, antibiotics (co-amoxiclav or metronidazole-covering regimen) and laxatives for the postpartum period, and follow-up for anal incontinence.
What you must remember
- Grading ladder: 1 — perineal skin and vaginal mucosa; 2 — perineal body muscles (bulbospongiosus, superficial transverse perineal); 3a — external anal sphincter less than 50 per cent torn; 3b — more than 50 per cent; 3c — internal sphincter also torn; 4 — anal epithelium breached.
- Risk factors: first birth, macrosomia (above 4 kg), instrumental delivery especially forceps, occipitoposterior position, midline episiotomy, shoulder dystocia, prolonged second stage and a short perineum — the exam lists these as a set.
- Repair material: sphincter repair with 3-0 polydioxanone or polyglactin; muscle and vaginal mucosa with 2-0; skin usually subcuticular; the knot burying technique reduces pain and granuloma.
- Third/fourth degree bundle: repair in theatre under regional or general anaesthesia (a sphincter cannot be sutured properly on the labour table), broad-spectrum antibiotics, stool-softening regimen (lactulose with ispaghula for about 7-10 days), analgesia and physiotherapy referral.
- Examination rule: every vaginal delivery needs a systematic inspection and, if any tear is suspected beyond second degree, a digital rectal examination — a missed third degree tear is the commonest litigation and recall item here.
- Complications of poorly repaired OASIS: faecal incontinence (flatus first), urgency, perineal pain, dyspareunia, fistula; secondary repair success is worse than primary, hence the primary repair doctrine.
- Future birth counselling: after one sphincter injury with continence, a vaginal birth may be offered; after a fourth degree tear, symptomatic sphincter defect or abnormal endoanal ultrasound, elective caesarean is advised.
Repairing a tear, step by step
A primigravida delivers a 3.8 kg baby after a forceps lift-out, the right mediolateral episiotomy extended. First, assess: the tear reaches the anal margin, and on rectal examination the sphincter is torn with anal epithelium intact — a 3c injury. In theatre: spinal anaesthesia, lithotomy, antiseptic cleaning. The internal sphincter is repaired first — with interrupted 3-0 sutures; the external sphincter follows, overlap (Osman-Peacock) with 3-0 polydioxanone for a complete tear with retracted ends, end-to-end apposition for partial ones. Then perineal muscles with 2-0, vaginal mucosa continuous, skin subcuticular. Antibiotics — co-amoxiclav or a cephalosporin plus metronidazole where penicillin-allergic — and a laxative plan for ten days.
Contrast a straightforward second degree extension: repair on the labour table under local infiltration (lignocaine 1 per cent up to 20 mL, or topping up the epidural), identical layer logic minus the sphincter. The difference in outcome is almost entirely the care of the sphincter, which is why grading is examined so heavily.
Where students slip
The 3a/3b/3c subdivision is where marks leak: candidates call every sphincter tear "third degree" and lose the one-best-answer. The second slip is mistaking a buttonhole tear of the rectal mucosa (intact sphincter, mucosal defect) as fourth degree — the repair differs, and diagnosis requires the rectal examination. Third is a vaginal wall tear beyond the hymen without perineal skin involvement — still second degree-equivalent, repaired by the same principles. And in counselling, quoting "all third degree tears need caesarean next time" is wrong: only symptomatic, complex, or sonographically disrupted sphincters dictate elective caesarean.
Frequently asked questions
What defines a third degree perineal tear?
Any injury involving the anal sphincter complex, subclassified 3a (under half of external sphincter), 3b (over half), 3c (external plus internal sphincter); breach into anal epithelium makes it fourth degree.
Which suture material repairs the anal sphincter?
3-0 polydioxanone or polyglactin, with the internal sphincter repaired separately by interrupted sutures and the external sphincter by end-to-end or overlap technique in theatre.
What post-repair bundle follows a third or fourth degree tear?
Broad-spectrum antibiotics, laxatives such as lactulose with ispaghula for 7-10 days, adequate analgesia, pelvic floor physiotherapy, and scheduled follow-up for continence assessment.
How is a missed sphincter injury prevented?
Systematic inspection of vagina, perineum and a digital rectal examination after every birth, with theatre repair when the sphincter is involved — the inspection is the step most often skipped.
Can a woman with a previous third degree tear deliver vaginally again?
Yes, if she is continent and the sphincter appears intact; elective caesarean is advised after fourth degree tears, symptomatic injuries, or abnormal endoanal ultrasound or manometry.