The mid urethral sling (MUS) procedure is a common and generally successful surgical treatment for women experiencing stress urinary incontinence (SUI). SUI involves involuntary urine leakage caused by physical activities like coughing, sneezing, or exercising, which increase abdominal pressure. The MUS involves placing a narrow ribbon of synthetic mesh, typically monofilament polypropylene, under the middle of the urethra to provide support and prevent leakage. While the procedure is considered the standard of care for SUI and has high success rates, like any surgery, it carries a possibility of complications. These potential negative outcomes can range from issues that resolve shortly after the operation to complex problems that develop years later.
Immediate Post-Operative Issues
Complications occurring during or immediately following the mid urethral sling placement are generally related to the surgical process itself. One significant risk is intraoperative injury to nearby structures, such as bladder perforation, which occurs more often with the retropubic sling approach than the transobturator approach. Severe injuries to major blood vessels, bowel, or nerves can also occur, particularly during the blind passage of the instruments used to position the sling.
Significant bleeding is a potential complication, sometimes resulting in a hematoma, which is a collection of blood that can form in the retropubic space or groin area. Hematomas usually resolve on their own, though they may cause swelling and discomfort. Transient urinary retention, or the temporary inability to urinate spontaneously, is a common early issue that can affect up to 17% of patients. This temporary retention is often due to swelling and local irritation and is typically managed with temporary catheterization until normal function returns.
Long-Term Material and Tissue Interaction Complications
Long-term issues often arise from the body’s interaction with the synthetic mesh material over months or years. Mesh erosion, sometimes called extrusion or exposure, is a situation where the polypropylene material wears through the vaginal wall or the lining of the urethra or bladder. The average rate of mesh erosion into the vagina is approximately 1.9% to 2.5% following SUI surgery, which is considerably lower than with mesh used for pelvic organ prolapse repair.
When the mesh erodes into the vagina, it can cause symptoms such as vaginal discharge, bleeding, and pain during sexual intercourse (dyspareunia). Erosion into the urinary tract is a more severe complication that can lead to recurrent urinary tract infections, chronic pelvic pain, and bladder stones forming on the exposed mesh.
Chronic pain is another long-term complication often linked to the presence of the foreign material or nerve irritation. This pain can manifest as persistent pelvic, groin, or inner thigh pain, with the transobturator approach having a higher association with groin pain. The pain can sometimes be neuropathic, resulting from irritation or entrapment of the nerves near the mesh placement. Chronic infection or inflammation related to the foreign material can also contribute to persistent discomfort.
Impact on Bladder Function and Urination
Functional complications relate to how the sling affects the mechanics of bladder emptying and storage. Persistent or delayed urinary retention occurs when the sling is placed too tightly, creating an obstruction to the outflow of urine. While transient retention is expected immediately after surgery, obstruction that lasts longer than a few weeks or requires intervention is more concerning, with reported rates ranging from 2% to 7%.
This functional obstruction can cause a slow or weak urinary stream, the need to strain to empty the bladder, or a feeling of incomplete bladder emptying. If the obstruction is not addressed, it can lead to recurrent urinary tract infections or the eventual development of de novo urgency symptoms.
De novo urgency refers to the new onset of overactive bladder symptoms, such as a sudden, compelling need to urinate, or even urge incontinence, in a patient who did not have these symptoms before the procedure. This functional change is often attributed to the irritative or obstructive effect of the sling on the urethra and surrounding tissues. Painful urination, known as dysuria, can also be a long-term symptom caused by chronic irritation or scarring around the sling material.
Evaluation and Treatment of Complications
The identification of a mid urethral sling complication requires a thorough evaluation, starting with a detailed physical examination and medical history. The physician will often perform a pelvic exam to check for mesh exposure in the vagina and assess for areas of tenderness or pain.
Diagnostic tests are frequently employed to understand the nature of the issue and may include cystoscopy, which involves inserting a small camera into the urethra and bladder. Cystoscopy allows the surgeon to directly visualize the inside of the bladder and urethra to check for mesh erosion or perforation into the urinary tract. Urodynamic testing measures bladder function, pressure, and flow to determine if there is an obstruction or a new overactive bladder component.
Management strategies vary depending on the type and severity of the complication. Non-surgical treatment is often the first step for functional issues like de novo urgency, which may involve medications to calm the bladder or physical therapy. Small, asymptomatic mesh erosions may sometimes be managed conservatively with topical estrogen creams. Symptomatic or extensive complications usually require surgical intervention, ranging from a simple sling incision or lysis to reduce tension for obstruction, to a partial or complete removal of the mesh. Complex mesh removal and reconstruction are reserved for cases involving mesh erosion into the bladder or urethra, or for refractory chronic pain.