Radiographic patellar height assessment of knee osteoarthritis

Abnormal patellar height can lead to patellar instability and can contribute to the development of knee osteoarthritis. Currently, there are no standardized normal values or protocols of the imaging techniques to provide a robust assessment or to define the correct patellar height with a high rate of inter observer and intra-observer agreements. Also, investigating patellar height of different knee compartments is scarce. Therefore, the purposes of this study are evaluating patellar height using different radiographic imaging measurement methods such as Insall-Salvati Index, comparing their correlations and inter observer measurement reliability, and investigating their association with different compartmental knee osteoarthritis.

A retrospective cross-sectional imaging study was performed, involving individuals who had knee X-rays between January 2022 and December 2023. The images were collected and independently evaluated by two radiologists. Four measurement methods including Insall-Salvati Index, Modified Insall-Salvati Index, Caton-Deschamps Index, and Blackburne-Peel Index were used to evaluate the patellar height on the X-ray images.

This study included 362 subjects. Most of the patellar height measurement methods of the osteoarthritic group demonstrated lower mean values than the normal group (P value < 0.05). The Caton-Deschamps Index was the only measurement that had a good inter-observer reliability based on the intra-class correlation coefficient value of 85 %. The strongest correlation (r = 0.69) was found between Insall-Salvati Index and Modified Insall-Salvati methods.

Patellar height indices are associated with osteoarthritis severity in this cohort. Caton-Deschamps method showed the highest inter-observer reliability.

Patellar height measurement using radiographic images can support KL grading system for knee osteoarthritis severity staging.