Summary

The finding of a Hoffa’s edema in knee magnetic resonance is related with a high prevalence of abnormal patellar alignment indices such as TT-TG and Insall-Salvati, therefore further asessment for patellar malalignment is required in these cases.

Abstract

Introduction

Hoffa's edema or inflammation of the superolateral adipose fat pad of the knee is a frequent finding in magnetic resonance imaging, although its association with clinical findings is not clear. The objective of this study is to describe a series of patients with these findings and the prevalence of abnormal patellar malalignment parameters described in the literature.

Methods

90 patients (104 knees) with anterior knee pain aged between 15 and 45 years old and imaging signs suggestive of superolateral Hoffa’s fat pad edema were included. Knee MRIs were performed at Clínica Alemana de Santiago between August 2020 and August 2021. All MRIs were reported by radiologists with musculoskeletal training and more than 5 years of experience. Patients with a history of trauma, patellar dislocation, ligament injuries and incomplete records were excluded. The parameters used were TT-TG, lateral patellar displacement, Insall-Salvati index, trochlear angle and sulcus angle.

Results

70.2% are women and the mean age is 33.3 years (SD 8.6, range 15 - 45). The average BMI is 24.5 (SD 4.2, range 18.4-35.6). 51% presented a TT-TG greater than 10mm, 14.4% a lateral displacement greater than 2mm, 50% Insall-Salvati greater than 1.3, 95.2% a trochlear angle less than 11º and 12.5% a sulcus angle greater than 144º.

Discussion

In the studied subjects there is a high prevalence of abnormal trochlear angle, suggestive of trochlear dysplasia. About half of the patients studied have an abnormal TT-TG and Insall-Salvati index. The rest of the studied parameters are abnormal in less than 15% of the cases. Additional studies to standard MRI are required to evaluate and/or rule out the presence of patellar malalignment.

Conclusions

The finding of a Hoffa’s edema in knee magnetic resonance is related with a high prevalence of abnormal patellar alignment indices such as TT-TG and Insall-Salvati. Therefore, in MRIs with signs suggestive of superolateral adipose fat pad edema the presence of patellar malalignment should be evaluated.