Effect of Single-Injection Peripheral Nerve Block on Perioperative Myocardial Injury in Elderly Patients Undergoing Delayed Hip Fracture Surgery: A Single-Center Retrospective Cohort Study

Study Rationale and Background Hip fracture represents a major public health burden among aging populations worldwide, with rapidly rising incidence driven by global demographic shifts. In older adults, hip fracture is associated with substantially elevated morbidity and mortality, with 1-year mortality rates reaching 20-30% even after surgical treatment. Current clinical guidelines uniformly recommend surgery within 48 hours of injury as the standard of care to improve outcomes. However, delayed surgery - defined as surgery performed more than 48 hours after injury - remains highly prevalent globally, particularly in resource-limited settings, affecting up to 60-80% of patients in some regions.

Accumulating evidence demonstrates that delayed surgery is associated with a dose-dependent increase in postoperative complications and mortality, with each 24-hour delay linked to a 12% higher risk of major adverse cardiovascular events (MACE) and a 5% relative increase in 30-day mortality. A key mediator of this elevated risk is perioperative myocardial injury, also termed myocardial injury after noncardiac surgery (MINS). MINS is defined as troponin elevation above the 99th percentile upper reference limit attributable to ischemic mechanisms, and it is one of the most common serious perioperative complications in older surgical patients. In hip fracture populations, the incidence of myocardial injury is particularly high, and it is strongly associated with short- and long-term mortality. The elevated cardiac risk in delayed surgery is driven primarily by sustained severe pain leading to sympathetic overactivation, heightened systemic inflammation, hypercoagulability, and physiological stress from prolonged preoperative immobilization.

Peripheral nerve block (PNB) is the gold standard for perioperative pain management in hip fracture, strongly recommended by international anesthesiology and orthopedic guidelines. Ultrasound-guided PNB techniques, including pericapsular nerve group (PENG) block, fascia iliaca compartment block, and femoral nerve block, provide effective analgesia and reduce opioid consumption. A recent landmark two-center cohort study published in Anesthesiology in 2026 found that preoperative single-injection PNB reduced the risk of postoperative myocardial injury by 40% in high-risk older adults undergoing hip fracture surgery.

Nevertheless, critical evidence gaps remain. The prior study included a mixed population of both early and delayed surgery patients, and did not specifically evaluate the cardiac protective effect of PNB in the delayed surgery subgroup - a population at markedly higher baseline cardiac risk. It also did not distinguish preoperatively existing myocardial injury from new-onset postoperative injury, nor did it examine the potential impact of block timing or different block techniques on cardiac outcomes. It remains unknown whether PNB still confers cardiac benefit in patients who have already sustained prolonged pain and stress from delayed surgery, and whether it can attenuate progression of myocardial injury in patients with preoperatively elevated troponin.

Study Objectives This single-center retrospective cohort study aims to investigate the effect of preoperative single-injection peripheral nerve block on perioperative myocardial injury in older patients undergoing delayed hip fracture surgery (time from injury to surgery > 48 hours).