In vivo tension sustained by fascial sling in pubovaginal sling surgery for female stress urinary incontinence.
OBJECTIVE
In pubovaginal sling surgery arguments have focused on selecting stronger sling materials, better suturing methods and superior fixation techniques. However, the grounding information prerequisite for these arguments is still lacking, ie the in vivo tension sustained by the sling. We designed this study to obtain this information.


METHODS
A total of 10 female patients (mean age 65.4 years) underwent pubovaginal sling surgery while under epidural anesthesia. A strip of rectus fascia (2 x 6 cm) was isolated. Each end of the fascia was anchored with a 1-zero Prolene suture (Ethicon, Somerville, New Jersey). The fascial sling was placed over the proximal urethra. Both ends of the prolene (polypropylene) sutures were transferred to the lower abdominal incision and tied on each other. The fascial sling was adjusted just to touch the proximal urethra without elevating it. We hooked the tied polypropylene suture on a digital force gauge to measure the tension sustained by the fascial sling. Patients were instructed to cough, and the tension was measured at different bladder volumes (100, 200, 300, 400 ml) and in 2 positions (horizontal and operative table tilted head-up 20 degrees). Intravesical pressure was monitored with a pressure transducer to ensure adequate cough strength. We also investigated the in vitro length-tension relationship and tensile strength of 3 rectus fascia strips (0.5 x 6 cm) obtained from 3 of these patients.


RESULTS
Mean tension +/- SEM sustained by the fascial sling during cough in the horizontal position was 0.046 +/- 0.004, 0.043 +/- 0.006, 0.0475 +/- 0.006 and 0.0485 +/- 0.007 kg at 100, 200, 300 and 400 ml bladder volume, respectively. Bladder volume did not statistically affect the sustained tension. The 20-degree head-up position also did not statistically change the tension sustained. In vitro study showed that the fascia strip could be stretched for a mean of 0.4 cm before sling tension began to increase. A mean load of 2.4 kg broke 0.5 x 6 cm strips.


CONCLUSIONS
In the horizontal and mild tilting positions during an increase in intra-abdominal pressure, the fascial sling only sustains minor tension, which is far less than the maximal load needed to break fascial strips. The excellent elasticity of the fascia may dissipate the straining force and partly explains the measured small sustained tension.
Lin
Alex Tong Long
AT
Department of Surgery, Taipei Veterans General Hospital, National Yang-Ming University School of Medicine, Taipei, Taiwan. lintl@vghtpe.gov.tw
Wang
S J
SJ
Chen
Kuang Kuo
KK
Chang
Luke S
LS
D000368:Aged; D055592:Biophysical Phenomena; D001703:Biophysics; D005260:Female; D006801:Humans; D008875:Middle Aged; D019736:Prostheses and Implants; D014550:Urinary Incontinence, Stress / Q000601:surgery*; D013520:Urologic Surgical Procedures / Q000379:methods*