What is neuromuscular injury following hemorrhoidectomy?

Neuromuscular Injury from Hemorrhoidectomy

Neuromuscular injury from hemorrhoidectomy refers to inadvertent damage to the internal anal sphincter (smooth muscle) or external anal sphincter (striated muscle) during surgical excision of hemorrhoids, occurring in up to 15.8% of cases based on histopathologic examination of resected specimens. 1

Incidence and Types of Sphincter Injury

• Smooth muscle (internal anal sphincter) injury is the most common type, found in approximately 12.7% of hemorrhoidectomy specimens (80.5% of all muscle injuries detected). 1
• Striated muscle (external anal sphincter) injury occurs less frequently, identified in approximately 3.1% of cases (19.5% of all muscle injuries). 1
• Up to 12% of patients demonstrate sphincter defects on postoperative ultrasonography and anorectal manometry, even when not clinically apparent. 2, 3

Mechanism of Injury

The primary mechanisms leading to neuromuscular injury during hemorrhoidectomy include:

• Excessive retraction with extensive dilation of the anal canal during surgery is the principal cause of sphincter injury and subsequent incontinence. 3
• Inadvertent excision of muscle fibers during dissection of hemorrhoidal tissue, particularly when the surgical plane extends too deeply into the sphincter complex. 1, 4
• Aggressive sphincter manipulation or adjunctive procedures like lateral internal sphincterotomy actually increase incontinence rates rather than reducing them. 3

Clinical Consequences

Immediate Complications

• Urinary retention (2-36% incidence) results from reflex inhibition of detrusor contraction caused by anal pain and sphincter spasm. 3, 5
• Postoperative pain requiring narcotic analgesics, with most patients unable to return to work for 2-4 weeks. 2, 3

Long-Term Functional Impairment

• Fecal incontinence develops in 2-12% of patients after hemorrhoidectomy, with sphincter defects documented by objective testing. 2, 3
• Anal dilatation as an adjunctive procedure causes a 52% incontinence rate at 17-year follow-up and should never be performed. 2, 3
• The presence of muscle fibers in hemorrhoidectomy specimens is considered a "normal feature" by some authors, but this finding raises concerns about effects on postoperative anorectal function. 1, 4

Risk Factors for Neuromuscular Injury

• Surgical technique: Open (Milligan-Morgan) hemorrhoidectomy may carry higher risk than closed (Ferguson) technique, though both can cause sphincter injury. 1
• Extent of disease: Grade III-IV hemorrhoids requiring more extensive excision increase injury risk. 1
• Concomitant procedures: Adding sphincterotomy or performing aggressive anal dilation significantly elevates complication rates. 3
• Surgeon experience: Inadequate submucosal dissection or failure to maintain proper surgical planes. 4

Prevention Strategies

The most critical preventive measure is avoiding excessive retraction and dilation of the anal canal during surgery. 3

• Maintain the surgical plane in the submucosa, avoiding deep dissection into the sphincter complex. 4, 6
• Perform hemorrhoidectomy under adequate local anesthesia to minimize sphincter spasm and allow precise dissection. 6
• Never add lateral internal sphincterotomy as an adjunct to hemorrhoidectomy, as this increases rather than decreases incontinence rates. 3
• Avoid anal dilatation entirely due to its association with 52% long-term incontinence. 2, 3

Diagnostic Evaluation

• Anorectal manometry can detect changes in maximal resting pressure (MRP) and maximal squeeze pressure (MSP), though these may normalize over 6-12 months in many patients. 7, 8
• Three-dimensional transanal ultrasonography identifies structural sphincter defects in up to 12% of patients postoperatively. 2, 7
• Clinical assessment of continence function should be performed preoperatively and at 6-month follow-up. 6, 7

Recovery Timeline

• Immediate postoperative period (5 days): Maximal resting pressure may be significantly elevated due to pain and spasm. 8
• 30 days: MRP values typically return to preoperative levels but remain elevated compared to healthy controls. 8
• 6-12 months: Most manometric alterations resolve completely, with MRP values comparable to healthy subjects. 8
• However, structural sphincter defects documented on ultrasonography may persist despite functional recovery. 2, 7

Critical Pitfalls to Avoid

• Never perform anal dilatation as it causes irreversible sphincter damage with 52% long-term incontinence. 2, 3
• Do not add lateral sphincterotomy to hemorrhoidectomy, as this increases incontinence rates. 3
• Avoid excessive retraction and dilation during surgery—this is the primary preventable cause of sphincter injury. 3
• Do not dismiss the finding of muscle fibers in hemorrhoidectomy specimens as "normal"—this represents inadvertent sphincter injury. 1, 4