The Reliability and Reproducibility of Patellotrochlear Index as a Measure of Patellar Instability in Indian Population

Abstract

Introduction: The knee joint is one of the most used and abused joint of the body and hence knee discomfort and pain is one of the primary complaint of patients presenting to the orthopaedic out-patient department. There is a long list of conditions affecting the knee joint of which patellar instability and patellofemoral pain is a significant component; however often the most difficult to diagnose. There are numerous ratios, angles and measurements available to quantify the instability but they lack standardization. Mostly these ratios are based on the bony outlines of the joints and do not consider the actual articular surfaces. Patellotrochlear index (PTI) is unique in this regard as this index quantifies and depicts the relation and congruency of the patellar and femoral trochlear articular cartilages. Aim: To establish normal values of patellotrochlear index in an Indian population. Materials and Methods: A prospective study was conducted on 100 patients who presented to the orthopaedic out-patient department with knee complaints other than anterior knee pain. All these patients were subjected to MRI and sagittal T2 WI and proton density images and were evaluated for the PTI. The images were evaluated by a musculoskeletal radiologist and an orthopaedic surgeon to look for reliability and reproducibility of the index. Results: The mean PTI was 0.35 when measured by the radiologist and 0.36 when measured by the orthopaedic surgeon with a standard deviation of 0.13 and 0.14 respectively. A high degree of correlation was noted between these groups, hence establishing its reliability and reproducibility. Conclusion: PTI is an easy, reliable and reproducible index for the quantification of patellar instability which can be used by the radiologist and orthopaedic surgeon.

Keywords

• articular cartilages
• knee joint
• patellofemoral joint