TENS for Relief of Postoperative Pain in Orthopedic Patients

Hip fracture is most often addressed surgically (Allahabadi et al., 2022; RikshÖFt, 2020), and is commonly associated with a short-term increase in mortality, and long-term reduction in health-related quality of life (Alexiou et al., 2018; Dyer et al., 2016; Gjertsen et al., 2016; Griffin et al., 2015). A large part of this reduction in quality of life can be related to pain and mobility. According to the Swedish National Hip Fracture Registry (RikshÖFt, 2020), 5.8% of the patients registered in 2019 were experiencing severe pain either constantly or during activity at the 4-month follow-up; 42% were experiencing tolerable pain during activity, and 35% were pain-free.

In the larger context of Chronic PostOperative Pain (CPOP), severe pain on postoperative day 1 constitutes an important risk factor (Fletcher et al., 2015). A 10% increase in the amount of time spent in severe pain on postoperative day 1 has been associated with a 30% increase in the incidence of CPOP at a 12-month follow-up. Yet, a 2021 review on the prevention of CPOP (Carley et al., 2021) reported that there were no pharmaceutical pain treatments that could be universally or specifically recommended to reduce the incidence of CPOP.

To effectively manage acute and chronic pain disorders, Transcutaneous Electrical Nerve Stimulation (TENS) has been viewed a safe nonpharmacological addition to standard care (Jafra et al., 2022; Johnson et al., 2022; Vance et al., 2022). Conventional TENS with high frequency (50-100Hz) activates non-noxious afferents considered to inhibit nociceptive transmission at the spinal cord level, i.e., peripheral gate-control. Mixed-frequency TENS adds a low-frequency (mostly 2-10Hz) stimulation that activates small-diameter, high-threshold peripheral afferents considered to trigger brainstem opioid descending pain inhibitory pathways, i.e., central gate-control. Studies have indicated mixed-frequency TENS may be effective to mitigate post-operative pain (Bjordal, Johnson, \& Ljunggreen, 2003; Hamza et al., 1999).

A non-pharmacological post-operative intervention in terms of the application of transcutaneous electrical nerve stimulation (TENS), could have the potential to accelerate early mobilization and reduce the use of opioids.

A 2019 study (Elboim-Gabyzon, Najjar, \& Shtarker, 2019) demonstrated pain reduction during activity - but not at rest - following hip fracture with a 30-minute TENS intervention daily on the first 5 postoperative days. A more recent (and currently unpublished) study using TENS integrated in TENS-pants (Opolka et al., 2024) demonstrated pain reduction at rest and during activity with a single 2.5-hour intervention carried out around postoperative day 1 (POD1). However, there is there is still a lack of knowledge regarding the possible effect of a longer TENS intervention repeated over several days. Moreover, there is still a lack of statistical evidence for the opioid sparing effect of TENS following hip fracture surgery.

The primary aim of this study is to assess pain reduction and patient global impression of change following mixed-frequency TENS treatment (or placebo TENS) at rest and during activity on postoperative days 1 to 3, following hip fracture surgery. A secondary aim is to assess improvement in mobility and to test the opioid-sparing effect associated with TENS treatment. Moreover, to simplify TENS application, empower the elderly patients and improve compliance during mobilization, the authors chose to administer TENS using wearable TENS-pants with modular textile electrodes. We hypothesize that a mixed-frequency TENS intervention, carried out on POD1 to POD3, with a daily treatment duration of 3 hours, can lead to a significant opioid sparing effect, more durable pain reduction, and improve the patients' overall perception and recovery.