Patellotrochlear index: A systematic review of the first 20 years of application

To provide an update on the reliability and application of the patellotrochlear index (PTI) used to assess patellar height (PH) measurement.

A systematic literature search was conducted through PubMed registries in 2024 using the terms PTI, PH, and MRI. Inclusion criteria were original studies or review articles from 2006 onwards. All evidence levels were included. Reliability, cut-off values, statistics, and influence of muscle contraction, flexion, and weight bearing on the PTI were assessed. Comparisons with conventional radiographic measurement methods on MRI were evaluated.

Twenty-four studies met the selection criteria. These studies used a direct measure of the patellotrochlear relationship for PH on sagittal MRI, 12 used the original PTI. Five studies evaluated the effect of quadriceps contraction, weight bearing, or flexion on the PTI values. For healthy subjects, the normal PTI values varied between 31.7 % and 36.8 %, for patella alta they were <12.5 % and varied for patella infera between >50 % and 80 %. In symptomatic subjects, the normal PTI values varied between <11.9 % and 49 %, for patella alta <11.9 % and 18 %, and for patella infera >50 % and 80 % depending on the pathology. Only weak or no correlation between the PTI and measurements on conventional radiography was revealed. The statistical method influenced the PTI values.

The PTI is a reliable diagnostic tool for PH measurement on MRI. PTI values described in the studies are different for the various pathologies. Advantages and limitations exist. Radiographic measurement methods applied on MRI are not suitable.