VERIFICACIÓN DEL CORTE POR FLEXIÓN

Eleven of the 22 patients in whom the external sphincter had been preserved reported some deterioration of function after surgery (this was 8 of 15 patients with intersphincteric, and 3 of 7 with trans-sphincteric fistulae). By comparison, only 8 of the 15 patients who had their trans-sphincteric fistulae laid open also reported some deterioration in sphincter function postoperatively (Appendix 3.11). Eighteen of the 19 patients whose function deteriorated reported new symptoms of incontinence to flatus, soiling, or both. Three patients in addition developed an inability to withhold defaecation, including two whose external sphincters had been preserved. One patient after external sphincter division had the sole symptom of difficulty in cleaning after evacuation, but was asymptomatic once she had bathed. The levels of postoperative incontinence were not different between the two groups (Table 4.5.1). In addition, there was no change in reported functional defects at a 6 months re-interview.

Functional outcome was unrelated to gender (13 of 26 men, and 5 of 11 women had disturbed function), position of the fistula around the anal circumference, or the presence of a "gutter" (18 patients had guttering postoperatively, of whom 10 had disturbed function).

SURGERY TO SPHINCTERS FUNCTION CHANGE PRE-OP SCORE POSTOP SCORE P (W Stat) IAS- EAS+ (n=22) 11/22* 0 (0-4) 2(0-5)* 0.004 (76) IAS- EAS- (n=15) 8/15* 0 (0-4) 2(0-8)* 0.014 (36)

Table 4.5.1 Table showing the pre- and postoperative continence scores (median, range) amongst those in whom the external sphincter had been preserved (IAS-; EAS+) and those in whom it had been divided (IAS-; EAS-). External sphincter sacrifice increased neither the incidence nor the severity of incontinence. The patient with a postoperative score of 8 complained of daily incontinence to flatus, major soiling requiring gauze pads, an inability to withhold defaecation more than fifteen minutes (a symptom which she also had preoperatively), and difficulty cleaning after defaecation. She had also suffered incontinence to liquid stool in the absence of gastrointestinal upset on two occasions over the 4 months since all wounds had healed. Despite these symptoms, the patient was delighted that after 10 years and multiple unsuccessful operations, she was at last free of perineal sepsis.

* P = 0.99, comparing change in function, and <|> P = 0.78, comparing postoperative continence score, between those with and without external sphincter division.

Preoperative physiological testing revealed no significant differences between those who subsequently remained fully continent and those who had some deficit (Appendix 3.12).

Anal canal length postoperatively was not different between those who were normally continent and those who were not (Appendix 3.13), nor were there any differences in squeeze or total pressures (Appendix 3.12).

Patients with reduced continence showed lower maximum resting pressure and lower resting pressures in the distal 2cm of the anal canal (eg, resting pressure in the distal 1cm, median (interquartile range); normal continence = 55 cmHgO (39-62); impaired continence = 30 cmHgO (24-40), P=0.0002) (Appendix 3.12). Furthermore, the rise in local sensory threshold was greater in patients who had disturbed continence postoperatively (change in local sensory threshold, median (range): continent = 0.3mA (0.0-2.2); incontinent = 2.3mA (0.7-13.9), P=0.007). Patients with incontinence after surgery for trans-sphincteric fistulae (whether or not the external sphincter had been preserved) had significantly higher postoperative local sensory thresholds (postoperative threshold, median (range): 3.8mA (3.1-7.2) continent vs 8.8mA

(4.0-17.6) incontinent, P=0.011) (Appendix 3.13).

4.5.3 Discussion

In this study, some degree of disordered continence was seen in 53% of patients after surgery for intersphincteric fistulae and in 50% of patients after surgery for trans-sphincteric fistulae. Division of the external sphincter neither affected the incidence nor the severity of their incontinence. Fifty percent of those in whom the external sphincter had been preserved had some deficit in continence compared with 53% where it had been divided.

There is no standard questionnaire to assess continence (Pescatori et al 1992); and those that there are focus on gross changes and do not embrace the finer aspects of continence, which are disturbed in a high proportion of patients after minor anal surgery for haemorrhoids (Bennett et al 1963) and fissure (Khubchandani and Read 1989), and now shown in this study to be quite frequent even after fairly minor fistula surgery.

Continence is a balance between rectal pressure and the power of the anal sphincter complex to overcome this, and is modified by having adequate sensation. Most of the time the anus is closed by the involuntary action of the internal anal sphincter. At times stool descends to the sensitive transitional zone where it is sampled (Duthie and Bennett 1963; Miller et al 1988a), and the distinction is made between solid matter and flatus (Miller et al 1988a,b). Usually the external sphincter then contracts and returns the stool to the rectum to await passage at a socially convenient time.

Usually, perfect continence can be achieved through an intact internal anal sphincter which gives rise to a closed anus at rest, enough external sphincter to overcome rises in intrarectal pressure, and good sensation. In this study, incontinence was related to low postoperative resting pressures in the distal anal canal and to blunted epithelial electrosensitivity. There was no association with squeeze pressures, which is contrary to the widely held belief that preserving the external sphincter is central to a good functional outcome (Bennett 1962; Belliveau et al 1983; Pescatori et al 1989). Clearly, complete division of voluntary muscle will result in total loss of voluntary control, but equally complete division of the internal sphincter cannot be compensated for by tonic contraction of the external sphincter, which fatigues easily and cannot maintain sustained contraction.

With regard to postoperative continence, it seems that attempts to preserve as much external sphincter as possible while at the same time being prepared to sacrifice the internal sphincter may be misguided. Such a view is supported by a retrospective study of 199 patients treated for fistula (Sainio 1985), where the highest incidence of incontinence was found in patients who had high intersphincteric tracks laid open. It is further supported by the results of another study of the loose seton method (that essentially sacrifices internal sphincter while safeguarding external sphincter): of 25 patients successfully treated, all but 9 reported some alteration of continence (Kennedy and Zegarra 1990).

Surgical teaching has traditionally dictated that successful fistula surgery depends on eradicating the chronic infecting source, the diseased anal gland in the intersphincteric space (Parks 1961). Parks suggested that this was best achieved by internal sphincterectomy, which removes a segment of internal sphincter that overlies the diseased gland; but nowadays most surgeons find simple division of the internal sphincter to be sufficient.

Anal fistulae can be treated by methods that preserve both external and internal sphincter function, such as the intersphincteric approach (Matos et al 1993), core out fistulectomy (Lewis 1986) and advancement flaps (Aguilar at al 1985). The first two avoid epithelial scarring and thus preserve epithelial sensitivity. Traditionally, such techniques have been reserved for the treatment of high fistulae, but the evidence presented here suggests that functional disturbances would be reduced were these methods to be more widely applied. The drawback is that none of these methods heals the underlying fistula with such certainty as

laying it open.

This is important, because although this study has revealed a high incidence of reduced continence after fistula surgery.

much of this reduction has been relatively minor. All but two of the patients were satisfied with the results of their management. It seems that patients tolerate a reduction in function as a reasonable price to pay in order to be rid of chronic anal sepsis, which in some has been attended by years of multiple failed attempts at cure. Nevertheless, there is a functional price to pay, even for the healing of the most minor anal fistula, and this justifies continued attempts at total sphincter conservation.