The Oxford grading scale is a widely used clinical tool to assess pelvic floor muscle strength through digital vaginal examination. It grades muscle contraction from 0 (no contraction) to 5 (strong contraction), providing a standardized method to evaluate pelvic floor function. This scale is essential in diagnosing pelvic floor dysfunction and planning appropriate treatment. Other options like Pap smear, transvaginal ultrasound, and CT scan do not quantify muscle strength but serve different diagnostic purposes.

Reference: Female Pelvic Medicine and Reconstructive Surgery, Halina Zyczynski, 1st Edition.