Is the Clinician's Eye a Valid and Reproducible Tool for Diagnosing Patella Alta on a Lateral Knee Radiography?

Abstract

Introduction: Validity and reproducibility of the clinician's eye (CE) to diagnose patella alta (PA) on a lateral knee radiography (radiograph) is unknown. Methods: Cross-sectional study of 46 lateral knee x-rays. Three blind observers used CE, Insall-Salvati (IS), modified Insall-Salvati (mIS), and Caton-Deschamps (C-D) to determine patellar height. Sensitivity and specificity of each observer was compared with the musculoskeletal radiologist's C-D measurements. Intraobserver and interobserver agreement were assessed with intraclass correlation coefficient and Fleiss κ, respectively. Time needed to estimate patellar height for every method was recorded in seconds. Statistical differences between observers were calculated with a generalized estimating equation. Analysis of variance and post hoc Bonferroni test compared duration of each method ( P < 0.05). Data were analyzed using Stata 15 (StataCorp). Results: CE, IS, mIS, and C-D's sensitivity and specificity values are as follows: 77%, 92%; 94%, 52%; 67%, 58%; and 53%, 89%, respectively. Intraclass correlation coefficient and Fleiss κ of CE, IS, mIS, and C-D values are as follows: 0.66 and 0.43, 0.88 and 0.68, 0.54 and 0.09, and 0.68 and 0.59, respectively. CE was the second most sensitive and most specific method for diagnosis of PA, with moderate intraobserver and interobserver agreement. IS was the most sensitive method with good intraobserver and interobserver agreement. CE was significantly faster ( P < 0.05) than all other conventional radiographic ratios. Conclusion: CE's sensitivity increases with observer's experience and is highly specific. If normal patellar height is diagnosed, no other ratios are necessary, even in the less experienced clinician. Intraobserver and interobserver reproducibilities were moderate and only inferior to the IS ratio. In case patellar height is uncertain with the CE, the IS ratio is the most sensitive and reproducible method to confirm the diagnosis of PA.

Reply to Letter to the Editor: I Spy With My Little Clinician's Eye

“…(1) Sensitivity and specificity of the CE and the “Reference Line” (RL) 2 : As indicated in our introduction, we agree with Dr. Nizić that none of the methods used for the diagnosis of PA is considered a benchmark; therefore, reporting the sensitivity and specificity of a new reference (as the CE and the RL) might be challenging. However, as stated under the methods section of our study, the Caton-Deschamps (C-D) index has already been used to validate the commonly used modified Insall-Salvati ratio (mIS) 3 and is the preferred method of the musculoskeletal radiologist (mskR), who was considered our benchmark for comparison.…”

“…The Authors' Reply : The authors appreciate the comments of Dr. Nizić 1 in response to the publication of the above reference regarding the use of the clinician's eye (CE) as a valid method for the diagnosis of patella alta (PA) and agree with its high specificity. The authors would like to address the comments stated in his letter to the editor: (1) Sensitivity and specificity of the CE and the “Reference Line” (RL) 2 : As indicated in our introduction, we agree with Dr. Nizić that none of the methods used for the diagnosis of PA is considered a benchmark; therefore, reporting the sensitivity and specificity of a new reference (as the CE and the RL) might be challenging. However, as stated under the methods section of our study, the Caton-Deschamps (C-D) index has already been used to validate the commonly used modified Insall-Salvati ratio (mIS) 3 and is the preferred method of the musculoskeletal radiologist (mskR), who was considered our benchmark for comparison.…”

Effect of Patellofemoral Arthroplasty on Patellar Height in Patients with Patellofemoral Osteoarthritis

“…The ISR is a measurement of the patellar tendon length in relation to the patella height. [8][9][10][11] In recent comparison studies of patella alta measurements, ISR was demonstrated to be the most sensitive and reliable method for identifying patella alta. 9,10 In this study, a medical student and an attending physician working together used Vaisman et al's method to calculate ISR on X-ray by dividing the distance between the patellar tendon insertion at the tibial tuberosity and the most inferior aspect of the patella by the length between the most superior and inferior aspects of the patella (►Fig.…”

“…1 Insall-Salvati ratio (ISR) on lateral X-ray via Vaisman et al ISR is calculated A/B, where A is the distance from the inferior aspect of the patella to the insertion of the patellar tendon at the tibial tubercle and B is the length of the patella from the most superior to the most inferior aspect. 9…”

Letter to the Editor: I Spy With my Little Clinician's Eye (CE) …

“…To the Editor : I have read with pleasure an article entitled “Is the clinician's eye a valid and reproducible tool for diagnosing patella alta on a lateral knee radiography?” by Dr. Vaisman et al 1 from Chile, published this month in your journal. I hereby express my admiration for a wonderful piece of science they have produced.…”