Ambient PM₂.₅, residential greenspace, and household healthcare expenditure in Shandong, China.

According to the World Health Organization (WHO), the population aged 60 years and over will increase from 1 billion in 2020 to 1.4 billion by 2030, with a particularly rapid increase in older adults at risk for hip joint pathology due to reduced physical function and osteoporosis [, ]. Hip fracture incidence will increase at a rate of 2.4% per year, and by 2050 it is projected that twice as many people will suffer from hip fractures as in 2015 []. With the increasing incidence of femoral neck fracture and femoral head necrosis, total hip arthroplasty (THA) is currently the ideal treatment method due to its advantages of less damage, faster recovery, and shorter hospitalization [, ]. It can effectively relieve patients’ pain, improve joint function, improve quality of life, and reduce the burden on the family [–], and the medium- and long- term therapeutic effects are satisfactory []. Nevertheless, even with improvements in surgical techniques and approaches to pain control, pain in elderly patients is often under-treated []. The final recovery outcome of joint replacement surgery depends on early, active post-surgical rehabilitation, and because the procedure is so invasive, it is difficult to ensure active early post-surgical functional exercise if severe pain during rehabilitation training cannot be effectively managed []. Several pharmacologic strategies are available for analgesia after THA, but each presents particular challenges for elderly patients []. Acetaminophen has minimal analgesic effects []. Nonselective NSAIDs carry risks of gastric, bleeding, and renal complications []. While COX-2-selective NSAIDs have a better gastrointestinal safety profile, concerns regarding renal impairment persist [–]. Opioids, though effective [, ], are associated with side effects like constipation, nausea, sedation, and respiratory depression [–]. Continuous femoral nerve block (CFNB) with local anesthetics techniques could provide superior analgesia and fewer side effects compared with systemic opioids. However, studies have demonstrated that it causes muscle weakness, increases fall risk, and may hinder active rehabilitation and delay functional recovery in total knee replacement []. These challenges are especially pertinent for managing pain specifically elicited by rehabilitation training. Rehabilitation-induced pain is physiologically and clinically distinct from postoperative resting pain. While resting pain is relatively constant and can be managed with around-the-clock systemic analgesics, pain during rehabilitation is transient, movement-evoked, and requires rapid-onset, short-duration analgesia that does not impair motor function or cognition. Current systemic analgesic regimens often fail to provide adequate, timely relief for these transient pain flares, creating a significant barrier to optimal recovery. Effective management of this procedure-related pain is critical for enabling active participation in rehabilitation and achieving optimal functional recovery. Hence, the exploration of safer and more effective analgesics for pain induced by rehabilitation training after THA should be a priority.