Evaluation of Central Sensitization, Fear-Avoidance, and Pain-Pressure Threshold With Chronic Pain After Hysterectomy

Assessment via the validated Central Sensitization Inventory (CSI) questionnaire prior to hysterectomy. Central sensitization is defined as an increased responsiveness of nociceptive neurons in the central nervous system to normal or sub-threshold afferent stimuli. The CSI a 25-item questionnaire, with each item rated 0 to 4. A higher value indicates greater central sensitization, and a threshold score of 40 was shown to be associated with increased risk of chronic pain.

Assessment via the validated Fear Avoidance Components Scale (FACS) questionnaire prior to hysterectomy. Fear-avoidance is defined as the negative emotional perception of pain as terrorizing, which can generate catastrophic thoughts and vigilance. Pain fear-avoidance behavior can be assessed with the FACS, a 20-item questionnaire, with each item rated 0 to 5.

Assessment via the validated Hospital Anxiety and Depression Scale (HADS) questionnaire prior to hysterectomy. Anxiety and depression are known risk factors associated with CPHP. HADS is a combination test for both anxiety and depression, is a 14-item questionnaire, with each item rated 0 to 3. HADS > 8 has been associated specifically with increased CPHP.

Assessment via the validated Pain Catastrophizing Scale (PCS) questionnaire prior to hysterectomy. Pain catastrophizing refers to the negative thought processes patients have when they are exposed to pain or painful experiences. The PCS is a 13-item scale, with each item rated on a 5-point scale: 0 (Not at all) to 4 (all the time). It is broken into three subscales being magnification (0-12), rumination (0-16), and helplessness (0-24). A higher value in each subscale indicates a higher tendency to that subscale (worse outcome).

Assessment via the validated EQ-5D questionnaire prior to hysterectomy. Lower preoperative quality of life has been associated with CPHP. EQ-5D is a validated questionnaire to assess generic health-related quality of life, consisting of two components: health state description and evaluation.

The description component measures health status via five dimensions: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression, with each dimension rated according to severity using a three-level scale.

The evaluation component assesses overall health status using the visual analogue scale (EQ-VAS).

Assessment via Mechanical Temporal Summation before hysterectomy. A 180 gram von Frey filament is applied on the subject's forearm. Patient will then be asked to rate the pinprick pain score on a verbal rating scale, 0-100. Following this, 10 consecutive touches at random locations are applied with a 1 second interstimulus interval and within a 1 cm diameter circle. The patient will then be asked to rate the 10th pain score (0-100). The Mechanical Temporal Summation Score is obtained by the difference between the 11th pain score and the 1st pain score. If the score is greater than zero, the patient is implied to have presence of Mechanical Temporal Summation.

Assessment of Pain-pressure threshold (PPT) prior to hysterectomy. PPT is measured via an algometer in both groups. Pressure is applied 90 degree straight down force on the subject's right/left centre of the trapezius muscle using an algometer, with a speed of pressure ~ 1kgf/s. The above procedure is then repeated 3 times at each site (left/right) which is indicated on the pressure mark with each time having the reading recorded. When patient shows no response ≥ 6kgf, the threshold is recorded as 6kgf. The patient upon feeling pain will say stop or raise the hand to terminate the test. The mean value is obtained by averaging the readings and will then be recorded as the threshold estimate.

The primary outcome measure is the development of chronic post-hysterectomy pain, which is defined as pain that lasts for at least 3 months around the surgical site, lower abdominal, or pelvic region. This will be determined by phone or online assessment at 6 months after surgery, based on the protocol used by Brandsborg et al and the investigators' previous study.

Heart rate variability will be determined from the R-to-R intervals obtained from a 5 minute ECG recording with the patient supine.

Patients will be asked to rate, using a 0-100 mm visual analog scale (VAS), their surgical anxiety level ("On a scale of 0-100, with 0 being not anxious at all through 100 being extremely anxious, how anxious are you about your upcoming surgery?")

Assessment via State-Trait Anxiety Inventory questionnaire prior to hysterectomy, a standardized assessment of anxiety. This is a validated 40-item questionnaire, each item scored using a categorical scale from 1-4, with total score from 40 to 160.

Assessment via Beck's Depression Inventory questionnaire prior to hysterectomy, a standardized assessment of depressive symptoms.This is a validated 21-item questionnaire, each item scored using a categorical scale from 0-3, with total score from 0 to 63.

Patients will be asked to rate, using a 0-100 mm visual analog scale (VAS), their anticipated pain ("On a scale of 0-100, with 0 being no pain at all and 100 being pain as bad as you can imagine, how much pain do you anticipate experiencing after your upcoming surgery?")

Patients will be asked to rate, using a categorical scale, their anticipated pain medication need ("On a scale of 0-5, with 0 being none at all, 1 being much less than average, 2 being less than average, 3 being average, 4 being more than average, and 5 being much more than average, how much pain medication do you anticipate needing after your upcoming surgery?")