Summary

This systematic review underscores the critical need for standardization in the measurement of patellar height and the definition of patella baja (PB) in total knee arthroplasty (TKA).

Abstract

Background

The lack of consensus on patellar height measurement and the definition of patella baja (PB) following total knee arthroplasty (TKA) has led to inconsistent clinical evaluations and varied outcomes. Divergent interpretations arising from different measurement techniques can impact clinical decision-making and patient recovery. This systematic review aims to identify and synthesize the methods used to measure patellar height, evaluate the definitions of PB, and propose evidence-based recommendations to standardize these practices.

Methods

A systematic review was conducted in accordance with PRISMA guidelines, analyzing 53 studies involving 13,476 patients who underwent TKA. The review focused on the prevalence and application of various patellar height measurement methods, including the Insall-Salvati Index (IS), Modified Insall-Salvati Index (mIS), Blackburne-Peel Index (BP), and Caton-Deschamps Index (CD). Data were extracted on patient demographics, the methods used, and the definitions of PB. Descriptive statistics summarized the findings, and the consistency of PB definitions across different methods was assessed.

Results

The IS and its modified version (mIS) were the most commonly utilized methods, with IS used in 67% and mIS in 15% of the studies. The mIS was particularly favored in cases involving prosthetic components that alter knee anatomy, demonstrating improved accuracy in these contexts. The BP and CD indices were used in 10% and 8% of studies, respectively, often selected for their relative independence from patellar morphology. The differences between original and modified methods were more pronounced in studies involving complex TKA cases, such as knee revisions or TKA in knees with severe deformities. PB was consistently defined within each method (e.g., IS/mIS ≤ 0.8, BP < 0.54), but significant variability was observed between methods, leading to potential differences in clinical interpretation. The systematic review highlights that the mISR is particularly recommended for contexts where precise patellar height evaluation is critical to prevent postoperative PB, especially in patients with large polyethylene spacers or voluminous femoral components. The Modified Caton-Deschamps Index is valuable for evaluating patients where accurate patellofemoral relationship assessment is necessary, especially when the patella is retained without resurfacing.

Conclusion

This systematic review underscores the critical need for standardization in the measurement of patellar height and the definition of patella baja (PB) in total knee arthroplasty (TKA). Given the improved correlation with postoperative outcomes, particularly in the presence of prosthetic components that alter knee anatomy, we recommend adopting the Modified Insall-Salvati Index (mIS) as the primary standard for evaluating patellar height postoperatively. The Blackburne-Peel Index (BP) should be used as a supplementary method in cases involving atypical patellar anatomy. Standardizing these methods can significantly reduce diagnostic variability, enhance surgical outcomes, and ensure more consistent reporting in clinical studies. Implementing these recommendations is essential for advancing orthopedic practice and improving patient outcomes following TKA.