Keeping It Simple: The Mini-Mental State Examination and the Patient Health Questionnaire-15 Outperform Complex Psychiatric Assessments as Predictors of Postoperative Delirium Following Total Knee Arthroplasty

Postoperative delirium (POD) is defined as an “acute alteration of mental state, characterized by reduced awareness and attention, occurring up to five postoperative days after recovery from anesthesia.”1 POD is a serious, potentially preventable complication that affects up to 17% of patients following total knee arthroplasty (TKA)2. Not only is delirium disruptive and upsetting to patients and family members alike, but it also limits patients’ ability to engage in meaningful rehabilitation during the crucial early stages after surgery, with deleterious effects on surgical outcome. Patients with POD after TKA have increased rates of reoperation, readmission, and surgical and medical complications and lower patient-reported outcomes at 1 year3. The economic burden of POD after TKA is substantial and underscores its relevance as a major public health problem4. Multiple studies have identified risk factors for POD after TKA, including advanced age, cognitive impairment, a history of cerebrovascular events, blood loss, dementia, neurologic disorders, psychiatric illness, and obstructive sleep apnea2. Some studies have implicated general anesthesia as being associated with an increased risk of POD compared with spinal anesthesia, whereas other studies have suggested that only specific pharmacologic agents used in general anesthesia (including isoflurane and benzodiazepines) and the depth of sedation, rather than the type of anesthesia itself, pose a greater risk5–7. Neuroinflammatory markers, including P-tau and C-tau, have been found to have been elevated preoperatively in the cerebrospinal fluid of patients who experienced POD in comparison with those who did not8. Despite a wide range of conditions that are associated with an increased risk of POD (and somewhat unexpected protective factors such as habitual tea consumption and continuous perioperative statin use), methods to prevent POD after TKA remain poorly understood9,10. The prevention of POD is contingent upon understanding its risk factors. In the current study, Lee et al. performed a prospective cohort study of 574 patients ≥60 years of age who underwent primary TKA in 1 of 2 tertiary centers in South Korea in order to determine predictors of POD after TKA. Patients underwent a battery of cognitive tests, including the Mini-Mental State Examination (MMSE), the full Consortium to Establish a Registry for Alzheimer’s Disease (CERAD) battery, the Subjective Memory Complaints Questionnaire (SMCQ), and the Seoul Informant Report Questionnaire for Dementia (SIRQD). Psychological assessments were conducted with the Pittsburgh Sleep Quality Index (PSQI), the Patient Health Questionnaire-15 (PHQ-15), and the Hospital Anxiety and Depression Scale (HADS). POD was evaluated daily on postoperative days 1 to 5 using the 4 A’s Test (4AT) and the Confusion Assessment Method (CAM). POD was found to occur in 4.2% of patients. A multivariable logistic regression analysis was performed to identify independent risk factors for POD. Lee et al. found lower MMSE and higher PHQ-15 scores to be independent predictors of POD. Other associated factors included preoperative use of sedatives and antidepressants. Somewhat unexpectedly, patients with POD were exposed to lower in-hospital noise levels than patients without POD; however, after adjustment for covariates, noise level was not found to be independently associated with POD. This study was limited by its relatively small sample size, which may not have been powered sufficiently to identify other risk factors. Furthermore, given that patients were admitted the day prior to surgery and stayed for a minimum of 5 days postoperatively, these data may not be applicable to all patient populations, particularly those in the United States, where outpatient TKA is far more common and the mean length of stay has decreased to 0.5 day, according to the 2024 American Joint Replacement Registry Annual Report11. A prolonged length of stay, possibly related to unfamiliar perioperative surroundings, increases the risk of delirium and may have played a role in the incidence of POD in this cohort12. In summary, although Lee et al. administered a complex battery of cognitive tests, their findings revealed that simple tests, the MMSE and PHQ-15, were most predictive of POD after TKA. The role of the perioperative environment, such as noise exposure, remains unclear. Further studies are needed to develop and implement methods to prevent POD following TKA in high-risk patients.