Ultrasound evaluation of infrapatellar fat pad impingement: An exploratory prospective study

Ultrasound assessment of the infrapatellar fat pad can detect Hoffa-synovitis in patients following anterior cruciate ligament reconstruction: A pilot study

Introduction

Osteoarthritis (OA) commonly occurs following anterior cruciate ligament reconstruction (ACLR), affecting over 50 % of patients within 10-15 years post-ACLR. The Hoffa-synovitis of the infrapatellar fat pad (IPFP) has been implicated as a major contributor to OA pathogenesis. While MRI is typically used to evaluate the IPFP, it is cost-prohibitive for routine screening. This study aimed to validate ultrasound as an alternative for detecting IPFP Hoffa-synovitis in participants post-ACLR.

Methods

In this cross-sectional study, 15 participants (18-35 years, 1-5 years post-ACLR) underwent two imaging sessions separated by one week. First, a standardized bilateral anterior knee ultrasound assessment was used to examine IPFP echo-intensity. Second, MRI scans of both knees were graded by a board-certified musculoskeletal radiologist for Hoffa-synovitis according to the Anterior Cruciate Ligament Osteoarthritis Score grading system. IPFP echo-intensity were quantified on each ultrasound image, and a limb symmetry index (LSI) was calculated to assess between-limb differences. We used an independent t-test and Cohen's d effect sizes to compare IPFP echo-intensity LSI between people with and without MRI-confirmed Hoffa-synovitis.

Results

Four of the 15 participants (27 %) exhibited MRI-confirmed Hoffa-synovitis. Significantly higher IPFP echo-intensity LSI values were found in participants with Hoffa-synovitis (32.1 ± 12.1 %) compared to those without (10.5 ± 10.4 %), confirming the ultrasound's ability to distinguish between the two groups (t = -3.44; p = 0.004; d = 2.01).

Discussion

Ultrasound detects bilateral IPFP signal intensity alterations in participants post-ACLR with MRI-confirmed Hoffa-synovitis. This work should be seen as a proof-of-concept, and further validation in a larger, more diverse sample is essential for verifying these results.

Ultrasound imaging in professional soccer: when is it adequate?

Ultrasound imaging plays an important role in the diagnosis, monitoring and treatment of injuries in professional soccer players. With the rapid increase in the availability of hand-held portable ultrasound devices and the pressure to make timely and accurate diagnosis in professional soccer where return to play time is crucial, ultrasound imaging is an essential diagnostic tool. In this article, we discuss examples of injuries that can be adequately assessed by ultrasound imaging alone and injuries where ultrasound imaging provides a useful first step to guide further investigation and management.

Predisposing factors for Hoffa's fat pad syndrome: a systematic review

BACKGROUND

Hoffa's fat pad syndrome has been defined as impingement of Hoffa's fat pad, leading to oedema and fibrosis. The primary aim of this systematic review was to identify morphological differences in Hoffa's fat pad between patients with and without Hoffa's fat pad syndrome, evaluating them as risk factors predisposing to its development. The secondary aim was to summarize and evaluate current evidence pertaining to the management of Hoffa's fat pad syndrome.

MATERIALS AND METHODS

The protocol for this review was prospectively registered (PROSPERO registration: CRD42022357036). Electronic databases, currently registered studies, conference proceedings and the reference lists of included studies were searched. All studies evaluating differences in Hoffa's fat pad anatomy under imaging between patients with and without Hoffa's fat pad syndrome were included, as well as those exploring epidemiological factors predisposing to its development (ethnicity, employment status, sex, age and BMI), and studies reporting on the effect of treatment on Hoffa's fat pad morphology.

RESULTS

A total of 3871 records were screened. Twenty one articles satisfied the inclusion criteria, evaluating 3603 knees of 3518 patients. Patella alta, increased tibial tubercle-tibial groove distance, and increased trochlear angle were found to predispose the development of Hoffa's fat pad syndrome. Trochlear inclination, sulcus angle, patient age and BMI were not associated with this condition. The link between Hoffa's fat pad syndrome and ethnicity, employment, patellar alignment, Hoffa's fat pad composition, physical activity and other pathological processes cannot be established due to lack of evidence. No studies reporting on treatment for Hoffa's fat pad syndrome were identified. Though weight loss and gene therapy may provide symptomatic relief, further research is required to corroborate these claims.

CONCLUSION

Current evidence suggests that high patellar height, TT-TG distance, and trochlear angle predispose the development of Hoffa's fat pad syndrome. In addition, trochlear inclination, sulcus angle, patient age and BMI do not seem to be associated with this condition. Further research should explore the link between Hoffa's fat pad syndrome and sport as well as other conditions pertaining to the knee. In addition, further study evaluating treatment approaches for Hoffa's fat pad syndrome is required.

Difference in Movement between Superficial and Deep Parts of the Infrapatellar Fat Pad during Knee Extension

(1): The superficial and deep parts of the infrapatellar fat pat (IFP) have different morphological and functional characteristics. Knee pain often occurs during movement, and it is important to clarify the movement of the IFP during knee joint movement. The purpose of this study is to clarify that the movement of the superficial and deep parts of the IFP are different during knee extension in vivo using ultrasonography (US). (2): US was performed on 15 knees of 15 healthy adults. The probe was placed longitudinally at the center of the patellar tendon and the IFP was imaged. Measurements were taken during active extension of the knee from 90 degrees to 10 degrees of knee flexion at a rate of 30 times/min. The captured US videos were analyzed using Flow particle image velocimetry (Flow PIV) fluid measurement software. The region-of-interest (ROI) was set at the superficial part and the deep part of the IFP, and the flow velocity was calculated for each. (3): The flow velocity of the deep part (1.37 ± 0.13 cm/s) of the IFP was significantly faster than that of the superficial part (0.80 ± 0.23 cm/s). (4): Our results show that the flow velocity of the IFP is different between the superficial and deep parts and that US may be a better assessment tool for the movement of the IFP.

Flexibility of infrapatellar fat pad affecting anterior knee pain 6 months after anterior cruciate ligament reconstruction with hamstring autograft

This study aimed to identify factors affecting anterior knee pain (AKP) after anterior cruciate ligament reconstruction (ACLR) with hamstring tendon autograft using ultrasonography. Forty-two patients were evaluated by ultrasound, 6 months after ACLR. The thickness of the superficial part of the infrapatellar fat pad was measured, as well as the thickness change ratio between the two angles. Color Doppler evaluated the rate of blood flow in the fat pad. AKP was assessed with the Kujala Scale. The correlations between AKP and age, body mass index, the thickness change ratio, and the grade of increased blood flow were examined. Independent variables showing significant correlations with AKP were used for multiple linear regression analysis. There were significant correlations between AKP and age (r = − 0.68), body mass index (r = − 0.37), the thickness change ratio of the fat pad (r = 0.73) and the grade of increased blood flow (r = − 0.42), respectively. Age and the thickness change ratio of the fat pad affected the AKP score (R² = 0.56). After ACLR, older age and a decrease in the thickness change ratio of the superficial area of the infrapatellar fat pad appear to affect post-operative AKP after 6 months.

Diagnostic accuracy of ultrasonography in the assessment of anterior knee pain

Background

Anterior knee pain (AKP) is a problematic complaint, considered to be the most frequent cause of orthopedic consultancy for knee problems. This study aimed to highlight diagnostic accuracy of ultrasonography as a fast imaging technique in assessment of patients with AKP.

Methods and results

A prospective study was conducted on 143 patients with clinically confirmed AKP. All patients underwent ultrasonography and MRI examinations of the knee. The diagnostic accuracy of ultrasonography compared to MRI for evaluating different findings of possible causes of AKP were analyzed using receiver operating characteristic (ROC) curve and judged by area under curve (AUC). A total of 155 knees were included in the study; 26 knees showed no abnormalities, 19 knees showed positive MRI only, and 110 knees showed positive ultrasonography and MRI. Ultrasonography and MRI reported 11 different findings of possible causes of AKP or related to it. Joint effusion was the most common finding (38%) followed by trochlear cartilage defect (20.6%) and superficial infrapatellar subcutaneous edema (20%). The overall accuracy of ultrasonography was 85.3% sensitivity and 100% specificity. The ultrasonography provided the highest sensitivity (100%) in detecting bipartite patella, followed by 91.5% for joint effusion, and 87.5% for quadriceps tendinopathy. The ROC curve analysis of overall accuracy of ultrasonography showed an AUC of 0.93. The overall Kappa agreement between ultrasonography and MRI was good (k = 0.66).

Conclusion

Ultrasonography can be used to make a swift screening and assessment of painful anterior knee and as an alternative to MRI when it is unavailable or contraindicated.

Diagnostic accuracy of ultrasonography in the assessment of anterior knee pain

Background

Anterior knee pain (AKP) is a problematic complaint, considered to be the most frequent cause of orthopedic consultancy for knee problems. This study aimed to highlight diagnostic accuracy of ultrasonography as a fast imaging technique in assessment of patients with AKP.

Methods and results

A prospective study was conducted on 143 patients with clinically confirmed AKP. All patients underwent ultrasonography and MRI examinations of the knee. The diagnostic accuracy of ultrasonography compared to MRI for evaluating different findings of possible causes of AKP were analyzed using receiver operating characteristic (ROC) curve and judged by area under curve (AUC). A total of 155 knees were included in the study; 26 knees showed no abnormalities, 19 knees showed positive MRI only, and 110 knees showed positive ultrasonography and MRI. Ultrasonography and MRI reported 11 different findings of possible causes of AKP or related to it. Joint effusion was the most common finding (38%) followed by trochlear cartilage defect (20.6%) and superficial infrapatellar subcutaneous edema (20%). The overall accuracy of ultrasonography was 85.3% sensitivity and 100% specificity. The ultrasonography provided the highest sensitivity (100%) in detecting bipartite patella, followed by 91.5% for joint effusion, and 87.5% for quadriceps tendinopathy. The ROC curve analysis of overall accuracy of ultrasonography showed an AUC of 0.93. The overall Kappa agreement between ultrasonography and MRI was good (k = 0.66).

Conclusion

Ultrasonography can be used to make a swift screening and assessment of painful anterior knee and as an alternative to MRI when it is unavailable or contraindicated.

The characteristics of the lobular arrangement indicate the dynamic role played by the infrapatellar fat pad in knee kinematics

The infrapatellar fat pad (IFP) is an intracapsular but extrasynovial structure, located between the patellar tendon, the femoral condyles and the tibial plateau. It consists of white adipose tissue, organised in lobules defined by thin connective septa. The aim of this study is the morphometric and ultrasonographic analysis of IFP in subjects without knee pathology during flexion-extension movements. The morphometric study was conducted on 20 cadavers (15M, 5F, mean age 80.2 years). Ultrasound was performed on 24 volunteers with no history of knee diseases (5M, 19F, mean age: 45 years). The characteristics of the adipose lobules near the patellar tendon and in the deep portion of the IFP were evaluated. Numerical models were provided, according to the size of the lobules. At histological examination, the adipose lobules located near the patellar tendon were larger (mean area 12.2 mm²  ± 5.3) than those at a deeper level (mean area 1.34 mm²  ± 0.7, P < 0.001) and the thickness of the septa of the deepest adipose lobules (mean value 0.35 mm ± 0.32) was greater than that of the superficial one (mean value 0.29 mm ± 0.25, P < 0.001). At ultrasound, the IFP was seen to be composed of very large lobules in the superficial part (mean area 0.29 cm²  ± 0.17 in extension), with a significant reduction in flexion (mean area 0.12 cm²  ± 0.07, P < 0.01). The deep lobules were smaller (mean area 0.11 cm²  ± 0.08 in extension) and did not change their values (mean area 0.19 cm²  ± 0.52 in flexion, P > 0.05). In the sagittal plane, the reduction of thickness of the superficial layer (with large adipose lobules) during flexion was 20.6%, whereas that of the deep layer (with small adipose lobules) was 1.3%. Numerical simulation of vertical loads, corresponding to flexion of the knee, showed that stress mainly developed within the interlobular septa and opposed bulging of the lobules. The characteristics of the lobular arrangement of the IFP (large lobules with superficial septa in the superficial part and small lobules with thick septa in the deep one), significant changes in the areas and perimeters of the superficial lobules, and the reduced thickness of the superficial layer during flexion all indicate the dynamic role played by the IFP in knee kinematics.