Chapter 29 — OPB-MOLIS: Technique, Indications, and Outcomes
This chapter opens Part III of this manual, covering the author's own techniques. It gives the full, definitive description of OPB-MOLIS, referenced throughout this manual, particularly in Chapter 11 and Chapter 18. This chapter covers the technique step by step, its indications, and the outcomes from the author's own 333-case prospective series.
29.1 What Is OPB-MOLIS
OPB-MOLIS stands for Modified Open Lateral Internal Sphincterotomy. It is commonly shortened to MOLIS in this manual and in the author's own practice.
MOLIS is the author's own technique, developed for the surgical treatment of chronic anal fissure, described in Chapter 11.
MOLIS is a modification of lateral internal sphincterotomy, the standard surgical treatment for chronic fissure. The modification addresses a specific limitation of the standard technique, described in Section 29.2.
29.2 Why MOLIS Was Developed
A standard lateral internal sphincterotomy divides the internal anal sphincter without directly seeing it. The surgeon works by feel and by positional judgement, estimating how much of the sphincter has been divided.
This creates genuine uncertainty. Dividing too little sphincter risks the fissure not healing. Dividing too much sphincter risks incontinence.
MOLIS was developed to remove this uncertainty. Instead of dividing the sphincter where it lies, the technique delivers the internal anal sphincter to the surface of the wound first. The lower one-third of the sphincter can then be identified and divided under direct vision, rather than estimated by feel alone.
29.3 Indications
The primary indication for MOLIS is chronic anal fissure that has not responded to conservative treatment, described in Chapter 11.
MOLIS is considered once conservative measures, including topical treatment, have been given a genuine trial and have failed to achieve healing.
A modification of this technique, for severe anal canal stenosis of any cause, is described fully in Chapter 18. A further modification, for fissure recurrence, is described fully in Chapter 30.
29.4 The MOLIS Technique
The patient is positioned according to the standard sequence described in Chapter 3, most often in the left lateral position.
Local, regional, or general anaesthesia is used, depending on the individual case and the surgeon's preference.
A lateral site is chosen, at the 3 o'clock or 9 o'clock position. The midline positions, at 6 o'clock and 12 o'clock, are deliberately avoided, since these sites are more prone to poor healing.
A small incision is made at the chosen lateral site.
The internal anal sphincter is then carefully delivered to the surface of the wound. This is the key step that distinguishes MOLIS from a standard lateral internal sphincterotomy, and gives the technique its name.
During this step, fibres of the corrugator cutis ani, described in Chapter 1, are commonly encountered at the wound edge. These fibres should be recognised for what they are, and gently displaced with a cotton gauze pledget, rather than divided or injured.
With the internal anal sphincter now delivered to the wound surface, the lower one-third of the sphincter is divided under direct vision. This is the standard, safe depth of division.
Haemostasis is achieved. The wound is then closed or left open, according to surgeon preference and the specific circumstances of the case.
Operative video: standard MOLIS for chronic anal fissure.
29.5 Postoperative Care
Standard wound care applies, including gentle cleaning and regular sitz baths.
Stool softeners are prescribed, to prevent straining and to protect the healing wound.
Adequate pain control is provided. Discomfort after MOLIS is typically less severe than the pain caused by the original fissure.
Follow-up is arranged to confirm wound healing, and to assess fissure resolution and continence.
29.6 The 333-Case Series — Outcomes
The author has performed and prospectively followed 333 cases of MOLIS for chronic anal fissure, between January 2016 and December 2025.
Continence was assessed at each postoperative follow-up, using the Wexner Incontinence Score. Across the full series, no case of postoperative incontinence was recorded, at any timepoint.
This series is reported here as the author's own prospectively collected clinical experience. It represents a single-surgeon series, not yet a multicentre or independently replicated trial. It is offered as a transparent account of the results achieved, rather than as a claim of universal or guaranteed outcomes for every surgeon performing this technique.
29.7 Special Situations
Severe anal canal stenosis, of any cause, is managed with a staged bilateral modification of MOLIS, described fully in Chapter 18.
Fissure recurrence, after a previous MOLIS or standard sphincterotomy, is managed with contralateral MOLIS, described fully in Chapter 30.
29.8 Complications
Bleeding or infection at the operative site, as with any anorectal surgery.
A non-healing wound, though this is uncommon with appropriate postoperative care.
Incontinence remains a theoretical risk of any sphincterotomy, though none was recorded across the author's own 333-case series, described in Section 29.6.
A keyhole deformity can result from dividing the sphincter at a midline site. This is precisely why MOLIS, like standard lateral internal sphincterotomy, deliberately avoids the midline.
29.9 Common Mistakes to Avoid
Attempting to divide the internal anal sphincter without first delivering it to the wound surface, which defeats the central purpose of this technique.
Dividing the sphincter deeper than the lower one-third, without a specific indication to do so.
Failing to recognise the corrugator cutis ani, described in Section 29.4, and injuring these fibres by mistake.
Choosing a midline site, at 6 o'clock or 12 o'clock, rather than the safer lateral position.
29.10 Recording and Follow-Up
Record the site of surgery, the depth of division, and any specific findings. For example: "MOLIS performed at the 9 o'clock position, lower one-third division under direct vision, corrugator cutis ani identified and preserved. Review in 4 weeks." Arrange follow-up to confirm wound healing, fissure resolution, and continence.
29.11 Why This Chapter Matters
MOLIS addresses a genuine limitation in the standard surgical treatment of chronic anal fissure, replacing positional judgement with direct vision. The 333-case series described in this chapter offers a transparent account of the results achieved with this technique. The next chapter turns to two further applications of MOLIS, for severe stenosis and for fissure recurrence.