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Osteonecrosis, also known as avascular necrosis or AVN, is characterized by a stereotypical pattern of cell death and a complex repair process of bone resorption and formation. It is not the necrosis itself but rather the resorptive component of the repair process that results in loss of structural integrity and subchondral fracture. Most likely, a common pathophysiological pathway exists involving compromised subchondral microcirculation. Decreased femoral head blood flow can occur through three mechanisms: vascular interruption by fractures or dislocation, intravascular occlusion from thrombi or embolic fat, or intraosseous extravascular compression from lipocyte hypertrophy or Gaucher cells. In this review, we emphasize etiologic relationships derived mostly from longitudinal cohort studies or meta-analyses whose causal relationships to osteonecrosis can be estimated with confidence. Understanding risk factors and pathophysiology has therapeutic implications since several treatment regimens are available to optimize femoral head circulation, interrupt bone resorption, and preserve the subchondral bone.

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Background: Since 2016, over half of the states in the United States have passed mandatory limits on opioid prescriptions, with limited evidence of effectiveness. In this study, we evaluated postoperative opioid prescriptions following orthopaedic surgery before and after the implementation of one of the earliest such laws. Methods: Following the implementation of state legislation limiting opioid prescriptions for opioid-naïve patients, 2 patient cohorts (pre-law and post-law) were compared. Both opioid-tolerant and opioid-naïve patients undergoing 6 common orthopaedic procedures (total knee arthroplasty, rotator cuff repair, anterior cruciate ligament reconstruction, open reduction and internal fixation for a distal radial fracture, open reduction and internal fixation for an ankle fracture, and lumbar discectomy) met inclusion criteria. Patients undergoing >1 primary procedure in the same operative session were excluded. All benzodiazepine and opioid prescriptions from 30 days before to 90 days after the surgical procedure were recorded. Logistic regression was performed to determine risk factors for prolonged postoperative opioid use. Results: In this study, 836 pre-law patients were compared with 940 post-law patients. The 2 groups were similar with regard to demographic variables, baseline opioid tolerance, and recent benzodiazepine use (all p > 0.05). Post-law, for all patients, there were decreases in the initial prescription pill quantity (49.65 pills pre-law and 22.08 pills post-law; p < 0.001) and the total morphine milligram equivalents (MMEs) (417.67 MMEs pre-law and 173.86 MMEs post-law; p < 0.001), regardless of patient preoperative opioid exposure (all p < 0.001). Additionally, there were decreases in the mean cumulative 30-day MMEs (790.01 MMEs pre-law and 524.61 MMEs post-law; p < 0.001) and the 30 to 90-day MMEs (243.51 MMEs pre-law and 208.54 MMEs post-law; p = 0.008). Despite being specifically exempted from the legislation, opioid-tolerant patients likewise experienced a significant decrease in cumulative 30-day MMEs (1,304.08 MMEs pre-law and 1,015.19 MMEs post-law; p = 0.0016). Opioid-tolerant patients required more postoperative opioids at all time points and had an increased likelihood of prolonged opioid use compared with those who were opioid-naïve preoperatively (odds ratio, 8.73 [95% confidence interval, 6.21 to 12.29]). Conclusions: A clinically important and significant reduction in opioid utilization after orthopaedic surgery was observed following the implementation of statewide mandatory opioid prescription limits. Clinical Relevance: After implementation of mandatory opioid prescription regulations, a clinically important and significant decline in the volume of opioids dispensed in the short term and intermediate term following orthopaedic surgery was observed. Furthermore, important clinical predictors of prolonged postoperative opioid use, including preoperative opioid use and preoperative benzodiazepine use, were identified. These findings have important implications for public health, as well as the potential to influence policymakers and to change practice among orthopaedic surgeons.