Does the angle of episiotomy affect the incidence of anal sphincter injury?

Title
Does the angle of episiotomy affect the incidence of anal sphincter injury?
Source

BJOG: An International Journal of Obstetrics & Gynaecology. 113(2):190-4, 2006 Feb.

"CONCLUSIONS: These results show that a larger angle of episiotomy is associated with a lower risk of third-degree tear and mediolateral episiotomy incisions should be made at as large an angle as possible to minimise the risk of sphincter disruption."

An episiotomy is a surgical incision, usually made with sterile scissors, in the perineum as the baby's head is being delivered. This procedure may be used if the tissue around the vaginal opening begins to tear or does not seem to be stretching enough to allow the baby to be delivered.

In most cases, the physician makes a midline incision along a straight line from the lowest edge of the vaginal opening toward the anus. In other cases, the episiotomy is performed by making a diagonal incision across the midline between the vagina and anus (called a mediolateral incision). This method is used much less often, may be more painful, and may require more healing time than the midline incision. After the baby is delivered through the extended vaginal opening, the incision is closed with stitches. A local anesthetic may be applied or injected to numb the area before it is sewn up (sutured).

Episiotomies are classified according to the depth of the incision:
*A first-degree episiotomy cuts through skin only (vaginal/lierineal).
*A second-degree episiotomy involves skin and muscle and extends midway between the vagina and the anus.
*A third-degree episiotomy cuts through skin, muscle, and the rectal sphincter.
*A fourth-degree episiotomy extends through the rectum and cuts through skin, muscle, the rectal sphincter, and anal wall.