This article sought to evaluate the available in vivo instrumented-assisted patellofemoral evaluation methods for quantifying the patellar mobility in response to an external force. Often times in the clinical setting, we struggle for objective data in the context of patellofemoral instability or pain. Our current grading system of patellar quadrants (1+, 2+ or 3+) may show good intra-observer reliability, but often times fails in the hope of communicating specific values across physicians that would help for a more precise and accurate diagnosis of patellar instability or pain.

The authors did an excellent job of defining their study parameters for the systematic review, despite much variability in study designs. Out of 1,952 relevant studies, 21 full-text articles met the eligibility criteria and only nine studies met the final inclusion criteria. The authors found that there was profound heterogeneity in patellar displacement measured by in vivo instrumentation. Due to this heterogeneity, it was not possible to achieve pooled medial and lateral translations for PF instability patients. They could also not statistically compare the patellar translations between the asymptomatic group, the PF pain group and the PF instability group. Having said that, the overall summary of the data shows the knees with PF instability are more likely to show greater patellar displacement than asymptomatic knees. 

The study was well done, and the limitations of the study show that we need a more standardized method of evaluating patellar mobility. I believe that in an era where research funding can be scarce and many attempted iterations of projects have been done, we can use this study to look back and see what should have been done in each of the prior studies to start definitively moving toward an acceptable method of patellar mobility quantification.