A systematic review of tibial stem extensions in patients with obesity undergoing total knee arthroplasty

Background: Patients with higher body mass index (BMI) are becoming the main cohort undergoing total knee arthroplasty (TKA). This demographic may be at greater risk of aseptic tibial loosening than patients in the normal BMI range, necessitating interventions to improve outcomes. Stem extensions in tibial components have emerged as a potential solution, however no consensus or protocol currently exist to guide clinicians. Methods: A systematic review was conducted to assess the protective role of stem extensions against aseptic tibial loosening in primary TKAs for patients with obesity. Medline, Embase, and Central databases were searched as per the PRISMA process. Data analysis included quality assessment of our selection with the NHLBI tool for controlled intervention studies and the MINORS tool for non-randomized studies. Additionally, the analysis scrutinized the performance of stem extensions based on the various suggested lengths and combinations with different BMI cut-offs. Results: Twelve studies met eligibility criteria, comprising a total of 42,547 TKAs. Stem extensions showed favourable or equivalent outcomes compared with non-stemmed tibial components, with no inferior performance observed. The most utilized stem lengths were 30 and 100 mm with BMI cut-offs of 30, 35 and 40 kg/m2. Some evidence of superior results of the 30-mm stems was also obtained. The study quality check derived fair to good results. Conclusion: The findings supported the use of stem extensions in primary TKAs of patients with obesity as a safe and effective means to mitigate aseptic tibial loosening. The recommendations made here include employing a 30-mm extension stem and ensuring adequate metaphyseal fixation based on the zonal fixation concept. The use of standard terms is also suggested, due to high variability in terminology. Limitations involved heterogeneity of stem lengths and BMI thresholds along with marginal follow up. Nevertheless, the selection contained good quality data, proposing a specific protocol or guidelines for optimizing outcomes in TKAs of patients with obesity.