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Patellar instability following total knee arthroplasty (TKA) is a rare, yet serious complication, potentially requiring revision surgery or resulting in chronic dysfunction. When encountered, it is paramount to understand the etiologies, diagnostic approaches, treatment options, and outcomes of the selected treatment. The most common cause of patella instability is improper positioning of components, leading to lateral maltracking of the patella. Factors such as internal rotation and/or medialization of femoral or tibial components and lateralization of the patellar button have been identified as factors that contribute to instability. Additionally, a longstanding valgus deformity of the knee may exacerbate patella maltracking. Patients typically present with anterior knee pain, worsened by activities like stair climbing, and may report sensations of giving way. Radiographs and computed tomography scans aid in evaluating component positioning and rotation. Operative intervention is often necessary, with options ranging from soft-tissue realignment to component revision. Lateral retinacular release is a common approach, although it is associated with complications such as osteonecrosis of the patella. Proximal or distal realignment procedures may be required if instability persists. Some recent case reports have also described medial patello-femoral ligament (MPFL) reconstruction as a treatment modality, but more investigation on the topic is still pending. It is important that the treatment strategy address the underlying cause, as failure to do so may result in recurrent instability. The best way to avoid patella instability is to pay attention to all the details of component position and soft-tissue balance during the index procedure., Competing Interests: Michael Mont: 3M: Paid consultant American Association of Hip and Knee Surgeons: Board or committee member CERAS Health: Stock or stock Options Exactech, Inc: Paid consultant Hip Society: Board or committee member Johnson & Johnson: Paid consultant; Research support Journal of Arthroplasty: Editorial or governing board Journal of Knee Surgery: Editorial or governing board Knee Society: Board or committee member Kolon TissueGene: Paid consultant Medicus Works LLC: Publishing royalties, financial or material support Medtronic: Research support MirrorAR: Stock or stock Options National Institutes of Health (NIAMS & NICHD): Research support Next Science: Paid consultant Organogenesis: Research support Orthofix, Inc.: Research support Pacira: Paid consultant Patient-Centered Outcomes Research Institute (PCORI): Research support Peerwell: Stock or stock Options Smith & Nephew: Paid consultant Stryker: IP royalties; Paid consultant; Research support Surgical Techniques International: Editorial or governing board Up-to Date: Publishing royalties, financial or material support USMI: Stock or stock Options Wolters Kluwer Health - Lippincott Williams & Wilkins: Publishing royalties, financial or material support Sumon Nandi: American Association of Hip and Knee Surgeons: Board or committee member American Orthopaedic Association: Board or committee member Arthroplasty: Editorial or governing board Journal of Arthroplasty: Editorial or governing board Journal of Bone and Joint Surgery - American: Editorial or governing board Maryland Orthopaedic Association: Board or committee member Springer: Publishing royalties, financial or material support Giles Scuderi: 3M: Paid consultant; Paid presenter or speaker; Research support Biomet: IP royalties; Paid consultant; Paid presenter or speaker Enhanced Medical Nutrition: Stock or stock Options Force Therapeutics: Stock or stock Options Journal of Arthroplasty: Editorial or governing board Journal of Knee Surgery: Editorial or governing board KCI: Paid consultant Next Science: Research support Operation Walk USA: Board or committee member ROM Tech: Stock or stock Options SpringerElsevierThiemeWorld Scientific: Publishing royalties, financial or material support Zimmer: IP royalties; Paid consultant; Paid presenter or speaker Ronald Delanois: Baltimore City Medical Society.: Board or committee member DePuy Synthes Product, Inc.: Research support Orthofix, Inc.: Research support Smith & Nephew: Research support Stryker: Research support Tissue Gene: Research support, (Thieme. All rights reserved.)

Background: With the expansion of the Affordable Care Act in 2014, there has been a growing interest in how the Medicaid population will affect postoperative outcomes following total knee arthroplasty (TKA). Studies have shown that lower socioeconomic status, non-Caucasian race, women, cardiac and renal disorders, and younger age have been associated with increased lengths of stay (LOS) after TKA. The primary purpose of our study was to compare the total complications and LOS among patients undergoing TKA who have cash, commercial, government, Medicaid, and Medicare insurances., Methods: We queried a national, all-payer administrative claims database from 2016 to 2022 among patients undergoing TKA who had cash (n = 3,923), commercial (n = 966,169), government (n = 25,644), Medicaid (n = 56,184), and Medicare (n = 524,034) insurances. We compared and analyzed various baseline demographics, total complications, and LOS (<1 day, 1 to 2 days, 3 to 4 days, and >4 days), between the insurance types., Results: Medicaid and Medicaid insurance types had patients who had the most comorbidities at baseline, including a comorbidity index >3 (P < 0.0001), women, alcohol abuse, diabetes, obesity, tobacco use, chronic kidney disease, and congestive heart disease (all P < 0.0001). In accounting for comorbidities, Medicaid was the biggest risk factor for total complications (P < 0.001) as well as increased LOS after TKA at 4 to 6 days, 7 to 9 days, and >9 days (P < 0.0001)., Conclusions: Medicaid insurance is a risk factor for increased total complications and LOS following TKA. Appropriate preoperative and perioperative management of these patients is essential in order to mitigate the risk and burden on the health care system in this population., (Copyright © 2024 Elsevier Inc. All rights reserved.)