Patellar height assessment in total knee arthroplasty: a new method

Area of Science:

• Orthopedics
• Radiology
• Biomedical Engineering

Background:

• The original patellar height index (AT/AP ratio) is valuable for assessing knee conditions but is unsuitable after total knee arthroplasty (TKA).
• Accurate patellar height measurement is crucial for evaluating surgical outcomes and planning approaches.

Purpose of the Study:

• To introduce and validate a modified patellar height index (AT’/AP ratio) applicable before and after TKA.
• To establish a reliable method for comparing patellar height changes following TKA.

Main Methods:

• A new landmark (T') was defined on the tibial plateau, identifiable both pre- and post-TKA.
• The modified index (AT’/AP ratio) was developed using this new landmark.
• Reproducibility and repeatability of the modified index were assessed using intra-class correlation coefficients (ICCs).

Main Results:

• The modified AT’/AP index demonstrated good intra-observer (ICCs 0.58–0.75) and inter-observer (ICCs 0.64–0.72) reliability.
• The new landmark (T') is identifiable before and after TKA, enabling consistent measurements.
• This method facilitates the comparison of patellar height before and after TKA.

Conclusions:

• The modified patellar height index (AT’/AP ratio) is a reliable and reproducible tool for assessing patellar height after TKA.
• This modified index allows for the evaluation of patellar height changes and their correlation with functional results post-TKA.
• The original AT/AP index should still be used to detect patella infera influencing surgical approach.