MR imaging of the infrapatellar fat pad of Hoffa

Association between High HbA1c Levels and Mast Cell Phenotype in the Infrapatellar Fat Pad of Patients with Knee Osteoarthritis

Diabetes mellitus (DM) has been suggested as a potential risk factor for knee osteoarthritis (KOA), and its underlying mechanisms remain unclear. The infrapatellar fat pad (IPFP) contributes to OA through inflammatory mediator secretion. Mast cells' (MCs) role in diabetic IPFP pathology is unclear. In 156 KOA patients, hemoglobin A1c (HbA1c) was stratified (HbA1c ≥ 6.5, n = 28; HbA1c < 6.5, n = 128). MC markers (TPSB2, CPA3) in IPFP were studied. Propensity-matched cohorts (n = 27 each) addressed demographic differences. MC-rich fraction (MC-RF) and MC-poor fraction (MC-PF) were isolated, comparing MC markers and genes elevated in diabetic skin-derived MC (PAXIP1, ARG1, HAS1, IL3RA). TPSB2 and CPA3 expression were significantly higher in HbA1c ≥ 6.5 vs. <6.5, both before and after matching. MC-RF showed higher TPSB2 and CPA3 expression than MC-PF in both groups. In the HbA1c ≥ 6.5 group, PAXIP1 and ARG1 expression were significantly higher in the MC-RF than MC-PF. However, no statistical difference in the evaluated genes was detected between the High and Normal groups in the MC-RF. Elevated TPSB2 and CPA3 levels in the IPFP of high HbA1c patients likely reflect higher numbers of MCs in the IPFP, though no difference was found in MC-specific markers on a cell-to-cell basis, as shown in the MC-RF comparison. These findings deepen our understanding of the intricate interplay between diabetes and KOA, guiding targeted therapeutic interventions.

The influence of inflammation on the characteristics of adipose-derived mesenchymal stem cells (ADMSCs) and tissue repair capability in a hepatic injury mouse model

BACKGROUND

Mesenchymal stem cells (MSCs) are adult stem cells with self-renewal and multi-directional differentiation potential and possess the functions of immunomodulation, regulation of cell growth, and repair of damage. Over recent years, MSCs have been found to regulate the secretion of inflammatory factors and to exert regulatory effects on various lymphocytes in inflammatory states, and on the subsequent repair of tissue damage caused by inflammation. In the present study, we analyzed the effects of tissue inflammation on the characteristics of MSCs.

METHODS

Human fat derived from the infrapatellar fat pad (IPFP) of knees with differing degrees of inflammation was extracted from specimens derived from total knee arthroplasties. HE and immunohistochemical staining was performed to directly observe the evidence and degree of inflammation in human infrapatellar fat pad tissue in order to classify MSCs cells, by their origin, into highly inflamed and lowly inflamed groups, and to study the effect of tissue inflammation on cell acquisition rates via cellular counting data. Flow cytometry assays were performed to investigate the effect of tissue inflammation on MSC surface marker expression. Trilineage differentiation, including osteogenesis, adipogenesis, and chondrogenesis, was performed to assess the effect of tissue inflammation on the ability of MSCs to undergo directed differentiation. The effect of tissue inflammation on the ability of MSCs to proliferate was investigated via clone formation studies. RNA-sequencing was performed to evaluate the transcriptomes of MSCs derived from different areas of inflammation. The effect of tissue inflammation on tissue repair capacity and safety of MSCs was investigated via a murine model of acute liver injury.

RESULTS

The results of cell count data indicate that a high degree of tissue inflammation significantly decreases the acquisition rate of MSCs, and the proportion of CD34+ and CD146+ cells. The results of our trilineage differentiation assay show that a higher degree of inflammation decreases osteogenic differentiation and enhances adipogenic and chondrogenic differentiation of MSCs. However, these differences were not statistically significant. Clone formation assays indicate that the degree of tissue inflammation at the MSC source does not significantly affect the proliferative capacity of MSCs. The transcriptomes of MSCs remain relatively stable in fat pad tissues derived from both highly and lowly inflamed samples. The results of acute liver injury investigations in mice indicate that MSCs of high and low inflammatory tissue origin have no significant difference in their tissue repair capability.

CONCLUSIONS

High tissue inflammation at the source of MSCs reduces the acquisition rate of MSCs and the percentage of CD34+ and CD146+ cells acquisition. However, source tissue inflammation may not significantly affect trilineage differentiation potential and proliferative capacity of MSCs. Also, MSCs obtained from differing source degrees of inflammation retain stable and similar transcriptomic profile and are both safe and efficacious for tissue repair/regeneration without detectable differences.

Clinical application of ultrashort echo time (UTE) and zero echo time (ZTE) magnetic resonance (MR) imaging in the evaluation of osteoarthritis

Novel compositional magnetic resonance (MR) imaging techniques have allowed for both the qualitative and quantitative assessments of tissue changes in osteoarthritis, many of which are difficult to characterize on conventional MR imaging. Ultrashort echo time (UTE) and zero echo time (ZTE) MR imaging have not been broadly implemented clinically but have several applications that leverage contrast mechanisms for morphologic evaluation of bone and soft tissue, as well as biochemical assessment in various stages of osteoarthritis progression. Many of the musculoskeletal tissues implicated in the initiation and progression of osteoarthritis are short T2 in nature, appearing dark as signal has already decayed to its minimum when image sampling starts. UTE and ZTE MR imaging allow for the qualitative and quantitative assessments of these short T2 tissues (bone, tendon, calcified cartilage, meniscus, and ligament) with both structural and functional reference standards described in the literature [1-3]. This review will describe applications of UTE and ZTE MR imaging in musculoskeletal tissues focusing on its role in knee osteoarthritis. While the review will address tissue-specific applications of these sequences, it is understood that osteoarthritis is a whole joint process with involvement and interdependence of all tissues. KEY POINTS: • UTE MR imaging allows for the qualitative and quantitative evaluation of short T2 tissues (bone, calcified cartilage, and meniscus), enabling identification of both early degenerative changes and subclinical injuries that may predispose to osteoarthritis. • ZTE MR imaging allows for the detection of signal from bone, which has some of the shortest T2 values, and generates tissue contrast similar to CT, potentially obviating the need for CT in the assessment of osseous features of osteoarthritis.

MAVRIC based T2 mapping assessment of infrapatellar fat pad scarring in patients with total knee arthroplasty

The infrapatellar fat pad (IPFP) has been implicated as a source of postoperative knee pain. Imaging the IPFP is challenging in patients with total knee arthroplasty (TKA) due to metallic susceptibility artifact. Multi-Acquisition Variable-Resonance Image Combination (MAVRIC)-based T2 Mapping has been developed to mitigate this artifact and can generate quantitative T2 data. Objectives of this study were to (1) measure T2 values of the IPFP in patients with TKAs using a MAVRIC based T2 mapping technique and (2) determine if IPFP T2 values are related to the degree of fat pad scarring or clinical magnetic resonance imaging (MRI) findings. Twenty-eight subjects (10 males, 18 females, Age: 66 + 7.2 years [Mean ± standard deviations]) undergoing clinical MRIs were sequentially recruited. Morphological imaging and quantitative T2 mapping sequences were performed on a clinical 1.5 T scanner. The morphologic images were graded for the presence and severity of fat pad scarring and clinical outcomes. T2 values were calculated in the total fat pad volume, a normal regions of interest (ROI), and an abnormal ROI. T2 values were shortened in the total IPFP volume (p = 0.001) and within abnormal regions (p = 0.003) in subjects with more severe IPFP scarring. The difference between T2 values in normal-abnormal regions was greater in subjects with severe versus no scarring (+1426.1%, p = 0.008). T2 values were elevated in patients with MRI findings of osteolysis (+32.3%, p = 0.02). These findings indicate that MAVRIC-based T2 Mapping may be used as a quantitative biomarker of postoperative IPFP scarring in individuals following TKA.

Magnetic resonance imaging assessments for knee segmentation and their use in combination with machine/deep learning as predictors of early osteoarthritis diagnosis and prognosis

Knee osteoarthritis (OA) is a prevalent and disabling disease that can develop over decades. This disease is heterogeneous and involves structural changes in the whole joint, encompassing multiple tissue types. Detecting OA before the onset of irreversible changes is crucial for early management, and this could be achieved by allowing knee tissue visualization and quantifying their changes over time. Although some imaging modalities are available for knee structure assessment, magnetic resonance imaging (MRI) is preferred. This narrative review looks at existing literature, first on MRI-developed approaches for evaluating knee articular tissues, and second on prediction using machine/deep-learning-based methodologies and MRI as input or outcome for early OA diagnosis and prognosis. A substantial number of MRI methodologies have been developed to assess several knee tissues in a semi-quantitative and quantitative fashion using manual, semi-automated and fully automated systems. This dynamic field has grown substantially since the advent of machine/deep learning. Another active area is predictive modelling using machine/deep-learning methodologies enabling robust early OA diagnosis/prognosis. Moreover, incorporating MRI markers as input/outcome in such predictive models is important for a more accurate OA structural diagnosis/prognosis. The main limitation of their usage is the ability to move them in rheumatology practice. In conclusion, MRI knee tissue determination and quantification provide early indicators for individuals at high risk of developing this disease or for patient prognosis. Such assessment of knee tissues, combined with the development of models/tools from machine/deep learning using, in addition to other parameters, MRI markers for early diagnosis/prognosis, will maximize opportunities for individualized risk assessment for use in clinical practice permitting precision medicine. Future efforts should be made to integrate such prediction models into open access, allowing early disease management to prevent or delay the OA outcome.

Ewing sarcoma of Hoffa fat pad in the knee: a case report and review of the literature on primary intraarticular sarcomas and Hoffa fat pad masses

Primary intraarticular sarcomas are rare. We describe a unique case of intraarticular Ewing sarcoma arising in Hoffa fat pad of knee in a woman. The patient was treated successfully with chemotherapy and left knee arthroplasty; however, the tumor recurred after 3 years.We review the literature on primary intraarticular sarcomas and Hoffa fat pad masses in the knee.

Friction Syndromes of the Knee

The knee is a complex joint with many fascial and ligamentous interactions. The movement in multiple planes makes the knee a prime site for friction syndromes, especially in active individuals. The most common friction syndrome is the iliotibial band friction syndrome. This occurs commonly in runners and cyclists and can be diagnosed clinically in a patient with lateral knee pain during activity. The anterior fat pads of the knee can also be the site of friction syndromes, most often in the Hoffa fat pad. Edema here can be located in the superolateral aspect of the fat pad when associated with patellar abnormalities, or diffusely when impingement is due to other causes. Edema of the quadriceps or prefemoral fat pad may also cause anterior knee pain and may be diagnosed with magnetic resonance imaging. The posteromedial friction syndrome and medial tibial crest syndrome are rare causes of medial knee pain highly active individuals.

Effect of physical therapy on the flexibility of the infrapatellar fat pad: A single-blind randomised controlled trial

The infrapatellar fat pad plays a biomechanical role in the knee joint. After knee injury or surgery, its dynamics decrease because of an inflammatory response. Physical therapy might be one of the valuable treatments for the recovery of knee joint mobility. This study aimed to evaluate the immediate effect of physical therapy on the dynamics of the infrapatellar fat pad in healthy participants using ultrasonography. In this prospective, single-blind, randomised controlled trial, 64 healthy young participants were enrolled and randomly assigned to one of the following three interventions: manual therapy, hot pack treatment, and control. Ultrasound images of the infrapatellar fat pad were obtained before and after the intervention. The thickness change ratio of the infrapatellar fat pad was calculated to compare the changes between and within groups before and after the intervention. No significant inter-group differences were observed. The effect sizes were relatively small. Manual therapy or hot pack intervention might not have an immediate effect on infrapatellar fat pad flexibility in healthy participants. Thus, it is necessary to consider more intensive treatments to change the dynamics of the infrapatellar fat pad.

An Open Debate on the Morphological Measurement Methodologies of the Infrapatellar Fat Pad to Determine Its Association with the Osteoarthritis Process

INTRODUCTION

Knee osteoarthritis (OA) is a disease affecting all the neighboring articular tissues including the infrapatellar fat pad (IPFP). Although not yet as widely studied as other tissues in the knee, the IPFP has been recognized to have important metabolic activities and is a key player in OA.

METHODS

In this commentary, we will briefly describe the different methodologies employed for the MRI morphological measurement of this tissue and depict the findings in regard to OA.

RESULTS

The morphology of this tissue, monitored mainly with the use of magnetic resonance imaging (MRI), demonstrates changes during OA. However, studies of the IPFP morphological alterations and their association with the OA process have shown conflicting results, including a detrimental or beneficial role or no role at all. Although many reasons could explain such mixed findings, one might be the different methodologies used for the MRI measurement of area, volume, or signal intensity. In addition, several techniques are also employed for measuring the volume and signal intensity. An additional level of complexity is related to the presence within the IPFP of two different types of signal intensities, hyper-intensity, and hypo-intensity.

CONCLUSION

A consensus of a procedure to measure the morphology of the IPFP is urgently needed to fully appreciate the role of this tissue in the pathology of OA, as well as its uses for clinical decision-making.

Periarticular calcifications

Periarticular calcification and ossification is a frequent finding on imaging and may sometimes pose a diagnostic challenge. The differential diagnoses for this radiological finding are wide and can be classified into broad groups such as idiopathic, developmental, trauma, burns, infection, tumor, connective tissue disease, crystalline, metabolic, vascular, and foreign bodies. With careful consideration of the clinical and imaging findings as well as awareness of mimickers of periarticular mineralization, the list of differential diagnoses can be narrowed down. This article aims to review the clinical-radiologic findings of periarticular calcified or ossified lesions with relevant imaging illustrations.

The role of real-time elastosonography in the diagnosis of quadriceps fat pad edema

BACKGROUND

Quadriceps fat pad edema (QFPE) is one of the causes of anterior knee pain. Real-time elastosonography (RTE) has been increasingly used in musculoskeletal disorders.

PURPOSE

To evaluate the role of RTE in the diagnosis of QFPE.

MATERIAL AND METHODS

A total of 23 patients with QFPE on magnetic resonance imaging (MRI) (study group) were prospectively compared with 29 patients with normal MRI findings (control group) using RTE. On MRI, the thickness of the quadriceps fat pad (QFP), and on RTE, strain ratio (SR) of QFP were measured and compared between the two groups.

RESULTS

The study group contained 23 patients (12 men, 11 women; mean age = 41.6 ± 7.0 years) and the control group contained 29 patients (14 men, 15 women; mean age = 42.3 ± 6.1 years). No significant differences were found in terms of mean age and sex between the two groups (P = 0.70, P = 0.78, respectively). The median thicknesses of the QFPs were 8.10 mm and 6.75 mm in the study and control groups, respectively (P < 0.001). The median SR values of the study group and control group were found to be 63.20 and 6.24, respectively. The SR values were significantly higher in patients with QFPE (P < 0.001).

CONCLUSION

RTE may be an effective imaging method for evaluating QFPE.

Fat Chance for Hidden Lesions: Pictorial Review of Hoffa's Fat Pad Lesions

Hoffa's fat pad (HFP) is the most commonly afflicted among all the knee fat pads. Anterior knee pain is common in various pathologies of HFP, as it is richly innervated. A potpourri of the intrinsic and extrinsic pathologies and the tumors and tumor-like conditions affect HFP, and MRI remains the fundamental modality to assess them and provide a specific diagnosis.

Hypoperfusion of the infrapatellar fat pad and its relationship to MRI T2* relaxation time changes in a 5/6 nephrectomy model

The purpose of present study was to longitudinally investigate the alterations in infrapatellar fat pad (IPFP) vascularity in 5/6 nephrectomized rats by using dynamic contrast enhanced (DCE) MRI and IPFP degeneration by using MRI T2* relaxation time. Twelve male Sprague–Dawley rats were assigned to a control group and a 5/6 nephrectomy CKD group. The right knees of all rats were longitudinally scanned by 4.7 T MRI, and serial changes in the IPFP were assessed at 0, 8, 16, 30, and 44 weeks by DCE-MRI (parameters A, k_el and k_ep) and MRI T2* mapping. After MRI measurements, knee specimens were obtained and evaluated histologically. The CKD group had IPFPs with lower blood volume A and lower permeability k_ep values from 16 weeks (p < 0.05), lower venous washout k_el value from 30 weeks (p < 0.001), and significantly higher T2* values reflecting adipocyte degeneration beginning at 16 weeks (p < 0.05). The histopathological results confirmed the MRI findings. Hypoperfusion and adipocytes degeneration related to CKD were demonstrated in a rodent 5/6 nephrectomy model. DCE parameters and MRI T2* can serve as imaging biomarkers of fat pad degeneration during CKD progression.

Hoffa's fat pad thickness: a measurement method with sagittal MRI sequences

Background

Hoffa’s fat pad is a structure located within the fibrous joint capsule of the knee joint, but outside the synovial cavity. It plays an important biomechanical and metabolic role in knee joint, reducing the impact of forces generated by loading and producing cytokines. Changes in its size can induce modifications in the knee homeostasis. However, a great variability exists regarding its measurements. This work aims to evaluate the reliability of a measurement method of Hoffa’s fat pad dimensions through MRI.

Methods

3T sagittal IW 2D TSE fat-suppressed MRI sequences, taken from the OAI (Osteoarthritis initiative) database, of 191 male and female patients, aged between 40 and 80 years, were analysed; a manual measurement of the thickness of Hoffa’s fat pad of each subject was then performed by two different readers. The interobserver reliability and intraobserver reliability of the measurements were described by coefficient of variation (CV), Pearson correlation and Bland–Altman plots.

Results

All statistical analyses have shown that not significant intra- or interobservers differences were evident (intraobserver CV % for the first observer was 2.17% for the right knee and 2.24% for the left knee, while for the second observer 2.31% for the right knee and 2.24% for the left knee; linear correlation was for the first observer r = 0.96 for the right knee and r = 0.96 for the left knee, while for the second observer r = 0.97 for the right knee and r = 0.96 for the left knee; in addition, the interobserver CV % was 1.25% for the right knee and 1.21% for the left knee and a high interobserver linear correlation was found: r = 0.97 for the right knee and r = 0.96 for the left knee).

All results suggest that this manual measurement method of Hoffa’s fat pad thickness can be performed with satisfactory intra- and interobserver reliability.

Conclusions

Hoffa’s fat pad thickness can be measured, using sagittal MRI images, with this manual method that represents, for his high reliability, an effective means for the study of this anatomical structure.

Hyperechoic and Low Morphological Changes in the Prefemoral Fat Pad in Individuals with Knee Osteoarthritis Based on Ultrasonographic Findings

Background:

To clarify the changes in the echo intensity (EI) in the prefemoral fat pad (PFP) and identify the relationship between the PFP and clinical features of knee osteoarthritis (OA).

Methods:

Twenty-six women with knee OA (mean age: 76 years) and 17 healthy women (mean age: 73 years) were enrolled. The Kellgren and Lawrence grading scale was used for the radiographic evaluation of knee OA. The EI of the PFP was measured as grayscale values. The change ratio of the anteroposterior PFP length during quadriceps contraction was measured. Knee range of motion and pain (100-mm visual analog scale) were evaluated.

Results:

The EI was significantly higher in the OA group than in the healthy group (P < 0.001). The change ratio of the PFP in the OA group was significantly lower than that in the healthy group (P < 0.001). The ranges of knee flexion and extension were correlated with the EI of the PFP (both P < 0.01) and the change ratio of the PFP (both P < 0.01). There was no significant correlation observed with knee pain.

Conclusion:

Hyperechoic changes and a decreased change ratio of the PFP were observed in the patients with knee OA. High EI and decreased morphological PFP changes were associated with decreased ranges of motion.

Dynamic changes in the infrapatellar knee structures with quadriceps muscle contraction. An in vivo study

OBJECTIVE

To determine the effect of knee flexion and submaximal isometric quadriceps muscle (Q) contraction on the patellar tendon (PT), the infrapatellar fat pad (IPFP), and the deep infrapatellar bursa (IPB) from extension to full flexion.

METHODS

In Study 1, the dominant knee of seven healthy subjects was studied in full extension and at 60° flexion during relaxation and Q contraction. Each knee was inspected and palpated, the transverse infrapatellar diameter was measured by plicometry, and measurements of the anteroposterior (AP) thickness of the IPFP were made by ultrasound (US). In Study 2, the dominant knee of seven healthy subjects was studied by US in full flexion, and then, at 15° decrements, down to 60° flexion during relaxation and Q contraction. Both studies had IRB approval. Results were analyzed with the Wilcoxon test and descriptive statistics.

RESULTS

In Study 1, Q contraction caused straightening of the patellar tendon (PT), a statistically significant widening of the IPFP by plicometry, and an increased AP thickness of the IPFP by US, in both knee positions. In Study 2, in full knee flexion, the PT contacted the tibial cortex in all seven subjects. Upon increasing extension, the PT-tibial cortex contact was lost in all subjects nearing 90° flexion. The contraction of the Q made the concave PT straight, grew the width of the underlying IPFP, and the apron of the IPFP moved distally within the IPB in all knee positions. A small amount of bursal fluid was present in all seven subjects.

CONCLUSION

Q contraction makes the IPFP bulge anteriorly, on both sides of the PT, and distally into the IPB, with possible biomechanical implications. In full knee flexion, the PT contacted the tibia, confirming a fulcrum at this site.

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.

Partial resection of the infrapatellar fat pad during anterior cruciate ligament reconstruction has no effect on clinical outcomes including anterior knee pain

BACKGROUND

Anterior knee pain (AKP) is a major complication that occurs after anterior cruciate ligament reconstruction (ACLR), even when hamstring tendon (HT) grafts are used. Damage to the infrapatellar fat pad (IPFP) during arthroscopy can cause AKP. The purpose of this study was to evaluate the influence of IPFP preservation on clinical outcomes, including AKP, in patients who underwent ACLR with HT autografts using the inside-out technique.

METHODS

Forty-two patients who underwent primary ACLR with HT autografts were prospectively assessed for 2 years after surgery. They were randomly selected to undergo treatment with as much intercondylar IPFP preservation as possible or with intercondylar IPFP resection to confirm the ACL origin on the femoral and tibial sides, especially the femoral footprint in deep flexion of the knee joint. The total IPFP volume was calculated using sagittal MR images before and 6 months after surgery. The patients completed a subjective knee score questionnaire and were assessed for patellar tendon tenderness and pain with the half-squat test or single-leg hop test at 6 months and 2 years postoperatively.

RESULTS

There were no differences in the patient characteristics, including age, sex, BMI, time from injury to surgery, and meniscus tear. The difference in the total size of the IPFP preserved was significant (P = 0.004). However, there were no significant differences in the subjective knee scores. Moreover, there were no differences in the clinical assessment parameters between the IPFP preservation and resection groups.

CONCLUSIONS

The size of the IPFP decreased more in the resection group than in the preservation group at 6 months after surgery. However, partial IPFP resection, which was used to better visualize the origin of the ACL, had no effect on the clinical outcomes, including AKP.

LEVEL OF EVIDENCE

Level II.

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.

A numerical investigation of the infrapatellar fat pad

The infrapatellar fat pad is an adipose tissue in the knee that facilitates the distribution of synovial fluid and absorbs impulsive actions generated through the joint. The correlation between morphological configuration and mechanical properties is analyzed by a computational approach. The microscopic anatomy of the infrapatellar fat pad is studied aiming to measure the dimension of adipose lobules and the thickness of connective septa. Results from histomorphometric investigations show that the infrapatellar fat pad is an inhomogeneous tissue, constituted by large lobules in the superficial part and smaller lobules in the deepest one. Finite element models of the infrapatellar fat pad are developed. The first model considers the inhomogeneous conformation of the infrapatellar fat pad, composed of micro- and macro-chambers, while the second model considers a homogeneous distribution of adipose lobules with similar dimensions. Computational analyses are performed considering the static standing configuration and the passive flexion-extension movement. The computational results allow us to identify the different stress and strain fields within the tissue and to appreciate the variation of the mechanical performance of the overall system considering the distribution of adipose lobules. Results show that the distribution of adipose lobules in macro- and micro-chambers allows major deformation of the infrapatellar fat pad, decreasing the stress inside the tissues.

Magnetic resonance imaging of impingement and friction syndromes around the knee

The knee is a complex joint with its function dependent on a combination of osseous and soft tissue structures. Alteration in the relationship of these tissues, due to either acute or chronic repetitive injury with possible underlying congenital predisposing factors, can result in impingement between the structures resulting in pain, particularly on activity. The purpose of this article is to provide a comprehensive review of the MRI features of various impingement syndromes around the knee.

Fibrotic changes in the infrapatellar fat pad induce new vessel formation and sensory nerve fiber endings that associate prolonged pain

The infrapatellar fat pad (IFP) contains nerve fiber endings and is considered to play an important role in the perception of knee pain. However, it is unclear whether and to what degree prolonged pain influences the nociceptive role of the IFP. To answer this question, we established a novel rat model of knee pain in which inflammation is restricted to the IFP. Rats received a single intra-IFP injection of monoiodoacetic acid (MIA) (0.2 mg/10 µL or 1.0 mg/10 µL) in the left knee and a phosphate-buffered saline (10 µL) injection in the right knee as a control. Pain-avoidance behavior and histological changes of the knee joint were measured at multiple time points up to 28 days after MIA injection. Histological analysis showed a transient inflammatory response in the IFP body in the 0.2-mg model, whereas prolonged inflammation followed by fibrotic changes was observed in the 1.0-mg model. Subtle histological alterations were observed in the articular cartilage and IFP surface regardless of the dose. The pain-avoidance behavior test indicated the development of prolonged knee pain throughout the experimental period in the 1.0-mg group. Histological assessments showed a significant increase in calcitonin gene-related peptide (CGRP)-positive nerve fiber endings inside IFPs with fibrosis in newly vascularized surrounding regions. These data suggest that irreversible fibrotic changes in the IFP induce the formation of new vessels and CGRP-positive nerve fiber endings that associate prolonged pain in the joint.

An update on the association between metabolic syndrome and osteoarthritis and on the potential role of leptin in osteoarthritis

Metabolic syndrome (MetS) has been associated with osteoarthritis (OA). Leptin, which is one of the markers of MetS, has been associated with OA pathophysiology. This study aimed to provide an update on the association between MetS and OA and on the potential role of leptin in OA. In this review, we summarized the current knowledge of the association between MetS and OA and updated the evidence on the potential role of leptin in OA. Clinical studies have investigated the epidemiologic association between MetS or its components and OA. Results suggested strong epidemiologic associations between MetS and OA, especially in the Asian population. Animal studies also indicated that metabolic dysregulation may lead to OA pathogenesis. The systemic role of MetS in OA pathophysiology is associated with obesity-related inflammation, the beneficial role of n-3 polyunsaturated fatty acids and deleterious role of cholesterol, physical inactivity, hypertension-induced subchondral ischemia, dyslipidemia-induced ectopic lipid deposition in chondrocytes, hyperglycemia-induced local effects of oxidative stress and advanced glycation end-products, low-grade systemic inflammation, and obesity-related adipokines by inducing the expression of proinflammtory factors. Leptin levels in serum/plasma and synovial fluid were associated with joint pain, radiographic progression, bone formation biomarkers, cartilage volume, knee OA incidence, and total joint arthroplasty in OA patients. Elevated leptin expression and increased effect of leptin on infrapatellar fat pad, synovium, articular cartilage, and bone were also involved in the pathogenesis of OA. Current knowledge indicates a convincing epidemiologic association between MetS and OA, especially in the Asian population. Animal studies have also shown that metabolic dysregulation may lead to OA pathogenesis. Accumulating evidence suggests that leptin may play a potential role in OA pathogenesis. Therefore, leptin and its receptor may be an emerging target for intervention in metabolic-associated OA.

Movement and volume of infrapatellar fat pad and knee kinematics during quasi-static knee extension at 30 and 0° flexion in young healthy individuals

INTRODUCTION

The purpose of this study was to determine the changes in the shape and volume of the infrapatellar fat pad (IPFP) associated with knee flexion angle in young healthy individuals.

METHODS

Young, healthy individuals without a history of knee injuries participated in this cross-sectional study. Behavior of the IPFP was quantified using three-dimensional (3D) models of the IPFP, patella, patellar tendon, femur, and tibia obtained from MRI taken at 0° and 30° flexion. The outcomes were movement and volume change of the IPFP, movement of the patella and the tibia, and change of the patellar tendon angle and length.

RESULTS

The anterior surface of the IPFP significantly moved anteriorly by 5.23 mm (p = .003) between 30° and 0°. Change in the volume of the IPFP was significantly increased or decreased in eight hyperoctants defined by the tibial coordinate system. The IPFP moved from the postero-supero hyperoctants to anterior hyperoctants. Significant correlations were observed between the IPFP and mobility of the patella, patellar tendon or tibia.

CONCLUSION

The IPFP moves antero-inferiorly during quasi-static knee extension from 30 to 0° in young healthy individuals. Comparisons of IPFP behavior between the healthy and pathological knees may help us understand the role of IPFP and problems caused by IPFP contracture in future studies.

Clinics in diagnostic imaging (202). Osgood-Schlatter disease (OSD)

A 14-year-old boy presented with left anterior knee pain, which was aggravated by exercise and relieved by rest. On clinical examination, there was tenderness at the tibial tuberosity with reproducible pain on resisted active extension of the knee. Radiographs showed heterotopic ossification of the patellar tendon with irregularity and fragmentation of the tibial tubercle. Clinical and radiological findings were consistent with Osgood-Schlatter disease, which is a traction apophysitis of the tibial tubercle commonly occurring in adolescents. The clinical presentation and imaging features are discussed.

Endoscopic Resection of Localized Pigmented Villonodular Synovitis in the Hoffa Fat Pad

Pathologies within the fat pad can have either intrinsic or extrinsic causes. Most of them are the consequences of trauma and degeneration, but inflammatory and neoplastic diseases can arise in the fat pad. Pigmented villonodular synovitis is the most common space-occupying lesion of the Hoffa fat pad, followed by ganglion. The purpose of this Technical Note is to describe the details of endoscopic resection of localized pigmented villonodular synovitis in the Hoffa fat pad. Hopefully, this can allow complete resection of the lesion with minimal surgical trauma and scar tissue formation.

Magnetic resonance imaging of the quadriceps fat pad oedema pattern in relation to patellofemoral joint pathologies

Purpose

Quadriceps fat pad is located posterior to the quadriceps tendon. Increased signal intensity of this fat pad is seen on routine knee magnetic resonance imaging (MRI) examinations, but the exact mechanism and related pathologies are not clear. In this study we aimed to evaluate the relationship between MRI signal intensity and morphological features of quadriceps fat pad, as well as various pathologies of the patellofemoral joint.

Material and methods

Sixty-one knees with quadriceps fat pad oedema out of 457 knee MRI examinations were included. Quadriceps fat pad signal intensity, dimensions, posterior indentation, and various parameters related to patellofemoral joint such as trochlear facet asymmetry, trochlear depth and sulcus angle, and the Insall-Salvati ratio were evaluated.

Results

There was no statistically significant correlation between quadriceps fat pad oedema intensity and its dimensions, but it was significant when compared to posterior indentation. There was no correlation between fat pad oedema and each of the pathologies. However, there was a significant correlation between the presence of fat pad oedema and the presence of at least one of the pathologies related to patellofemoral joint.

Conclusions

Quadriceps fat pad oedema detected in MRI examinations should warn the radiologist against the presence of various pathologies related to the patellofemoral joint.

Intra-articular fibroma-like perivascular epithelioid tumor (PEComa) mimicking tenosynovial giant cell tumor, diffuse type

Perivascular epithelioid cell tumors (PEComas) are rare mesenchymal neoplasms composed of perivascular epithelioid cells that are immunoreactive for both melanocytic and myogenic markers. Recently, a fibroma-like PEComa associated with tuberous sclerosis complex (TSC) has been identified. We describe the first intra-articular case of a fibroma-like PEComa in a 44-year-old man who presented with a hypointense intra-articular knee mass, which was mistaken for tenosynovial giant cell tumor, diffuse type. This case report demonstrates that fibroma-like PEComa should be included in the extended differential diagnosis of intra-articular soft tissue masses. In addition, given their strong association with TSC mutations, a diagnosis of fibroma-like PEComa should trigger an evaluation for TSC.

Contribution of Infrapatellar Fat Pad and Synovial Membrane to Knee Osteoarthritis Pain

Osteoarthritis (OA) is the most common form of joint disease and a major cause of pain and disability in the adult population. Interestingly, there are patients with symptomatic OA displaying pain, while patients with asymptomatic OA that do not experience pain but show radiographic signs of joint damage. Pain is a complex experience integrating sensory, affective, and cognitive processes related to several peripheral and central nociceptive factors besides inflammation. During the last years, the role of infrapatellar fat pad (IFP), other than the synovial membrane, has been investigated as a potential source of pain in OA. Interestingly, new findings suggest that IFP and synovial membrane might act as a functional unit in OA pathogenesis and pain. The present review discuss the role of IFP and synovial membrane in the development of OA, with a particular focus on pain onset and the possible involved mediators that may play a role in OA pathology and pain mechanisms. Inflammation of IFP and synovial membrane may drive peripheral and central sensitization in KOA. Since sensitization is associated with pain severity in knee OA and may potentially contribute to the transition from acute to chronic, persistent pain in knee OA, preventing sensitization would be a potentially effective and novel means of preventing worsening of pain in knee OA.

A Case of Prefemoral Fat Pad Impingement Syndrome Caused by Hyperplastic Fat Pad

Case

We report a rare case of prefemoral fat pad impingement syndrome that was caused by a hyperplasia of the normal suprapatellar fat pad. Pain and catching were observed in the proximal-lateral patellofemoral joint, and MRI imaging confirmed a hyperplasic mass in the same area. Although conservative treatment showed no signs of improvement, symptoms improved after an arthroscopic excision of the mass.

Conclusion

Prefemoral fat pad impingement syndrome is related to patellar motion and should be considered as one of the underlying causes of anterior knee pain (AKP). Surgeons should recognize that a small hyperplasia composed of normal adipose tissue can cause AKP.

Calcified or ossified benign soft tissue lesions that may simulate malignancy

The purpose of this article is to review calcified or ossified benign soft tissue lesions that may simulate malignancy. We review the clinical presentations, locations, imaging characteristics, and differential diagnostic considerations of myositis ossificans, tophaceous gout, benign vascular lesions, calcific tendinopathy with osseous involvement, periosteal chondroma, primary synovial chondromatosis, Hoffa's disease, tumoral calcinosis, lipoma with metaplasia, calcifying aponeurotic fibroma, calcific myonecrosis, ancient schwannoma, and Castleman disease.

Comparative advantages of infrapatellar fat pad: an emerging stem cell source for regenerative medicine

Growing evidence indicates that infrapatellar fat pad (IPFP)-derived stem cells (IPFSCs) exert robust proliferation capacities and multilineage differentiation potentials. However, few papers summarize the advantages that the IPFP and IPFSCs have in regenerative medicine. In this review we delineate the development and anatomy of the IPFP by comparing it with an adjacent fibrous tissue, synovium, and a more frequently harvested fat depot, subcutaneous adipose tissue. Furthermore, we explore the similarities and differences of stem cells from these three tissues in terms of IPFSCs, synovium-derived stem cells and subcutaneous adipose tissue-derived stem cells in proliferation capacity and tri-lineage differentiation potentials, including chondrogenesis, osteogenesis and adipogenesis. Finally, we highlight the advantages of IPFSCs in regenerative medicine, such as the abundant accessibility and the ability to resist inflammation and senescence, two hurdles for cell-based tissue regeneration. Considering the comparative advantages of IPFSCs, the IPFP can serve as an excellent stem cell source for regenerative medicine, particularly for cartilage regeneration.

The infrapatellar fat pad is a dynamic and mobile structure, which deforms during knee motion, and has proximal extensions which wrap around the patella

PURPOSE

The infrapatellar fat pad (IFP) is a common cause of knee pain and loss of knee flexion and extension. However, its anatomy and behavior are not consistently defined.

METHODS

Thirty-six unpaired fresh frozen knees (median age 34 years, range 21-68) were dissected, and IFP attachments and volume measured. The rectus femoris was elevated, suprapatellar pouch opened and videos recorded looking inferiorly along the femoral shaft at the IFP as the knee was flexed. The patellar retinacula were incised and the patella reflected distally. The attachment of the ligamentum mucosum (LMuc) to the intercondylar notch was released from the anterior cruciate ligament (ACL), both menisci and to the tibia via meniscotibial ligaments. IFP strands projecting along both sides of the patella were elevated and the IFP dissected from the inferior patellar pole. Magnetic resonance imaging (MRI) of one knee at ten flexion angles was performed and the IFP, patella, tibia and femur segmented.

RESULTS

In all specimens the IFP attached to the inferior patellar pole, femoral intercondylar notch (via the LMuc), proximal patellar tendon, intermeniscal ligament, both menisci and the anterior tibia via the meniscotibial ligaments. In 30 specimens the IFP attached to the anterior ACL fibers via the LMuc, and in 29 specimens it attached directly to the central anterior tibia. Proximal IFP extensions were identified alongside the patella in all specimens and visible on MRI [medially (100% of specimens), mean length 56.2 ± 8.9 mm, laterally (83%), mean length 23.9 ± 6.2 mm]. Mean IFP volume was 29.2 ± 6.1 ml. The LMuc, attached near the base of the middle IFP lobe, acting as a 'tether' drawing it superiorly during knee extension. The medial lobe consistently had a pedicle superomedially, positioned between the patella and medial trochlea. MRI scans demonstrated how the space between the anterior tibia and patellar tendon ('the anterior interval') narrowed during knee flexion, displacing the IFP superiorly and posteriorly as it conformed to the trochlear and intercondylar notch surfaces.

CONCLUSION

Proximal IFP extensions are a novel description. The IFP is a dynamic structure, displacing significantly during knee motion, which is, therefore, vulnerable to interference from trauma or repetitive overload. Given that this trauma is often surgical, it may be appropriate that surgeons learn to minimize injury to the fat pad at surgery.

Regulation of calcitonin gene-related peptide expression through the COX-2/mPGES-1/PGE2 pathway in the infrapatellar fat pad in knee osteoarthritis

BACKGROUND

The infrapatellar fat pad (IFP) is implicated in knee osteoarthritis (KOA). Calcitonin gene-related peptide (CGRP), a vasoactive neuropeptide expressed in joint tissues and synovial tissues (ST), was recently found to be associated with KOA progression and pain. CGRP is expressed in the IFPs of human KOA patients; however, its regulation has not been elucidated.

METHODS

IFPs and STs were harvested from 138 KOA patients during total knee replacement (TKR) and analyzed for CGRP, cycloxygenase-2 (COX-2), and microsomal prostaglandin E synthase-1 (mPGES-1) expression using real-time polymerase chain reaction (PCR). To investigate CGRP regulation by prostaglandin E2 (PGE2), adipocytes (Ad) and the stromal vascular fraction (SVF) were harvested from IFPs using collagenase. Synovial cells (SYC) were also harvested from ST and stimulated with vehicle (serum-free culture medium), PGE2, or CGRP.

RESULTS

CGRP, COX-2, and mPGES-1 expression levels were significantly higher in IFPs than STs. PGE2 stimulation increased CGRP expression in Ad, the SVF, and SYC; however, CGRP expression was significantly higher in PGE2-stimulated SVF than PGE2-stimulated SYC. CGRP stimulation had no effect on COX-2 or mPGES-1 expression.

CONCLUSIONS

CGRP expression in the IFP of KOA patients is regulated by the COX-2/mPGES-1/PGE2 pathway.

Systemic and local adipose tissue in knee osteoarthritis

Knee osteoarthritis (OA) is the most common joint disease. Body adipose tissue has been shown to be related to the development and progression of knee OA. Among systemic adipose tissues, subcutaneous adipose tissue is significantly and negatively associated with muscle mass and forces, and could be related to the presence and progression of knee OA. Visceral adipose tissue is associated with increased cartilage loss and production of pro-inflammatory cytokines. Intra-muscular adipose tissue is associated with knee osteoarthritic changes, but it remains controversial if inter-muscular adipose tissue has a role to play in the pathogenesis for knee OA. Knee local adipose tissue such as infrapatellar fat pad (IPFP) can interact with neighbouring tissues, and may have a biphasic effect in knee OA. The underlying mechanisms for the roles of the systemic and local fat in knee OA could be related to biomechanical, metabolic, inflammatory factors and fat fibrosis, which may have a separated or combined effect on OA. Tissue engineering from systemic or local adipose tissue is a new research direction, and adipose tissue-derived stem cells from systemic or local adipose tissue may be beneficial for OA cartilage repair. Research on systemic and local adipose tissue would provide novel approaches for prevention and treatment of knee OA, but further studies are required to explore the roles of different adipose tissues in knee OA and the effects of stem cells derived from different adipose tissues on knee OA.

Ultrasonographic Morphological Changes in the Prefemoral Fat Pad Associated with Knee Osteoarthritis

Background

In normal knees, quadriceps contraction changes the shape of the prefemoral fat pad (PFP). However, in persons with knee osteoarthritis (OA), the functional or morphological changes of the PFP are unclear. This study aimed to clarify the morphological changes in the PFP in individuals with knee OA through ultrasonography.

Materials and Methods

Participants were divided into the OA (36 knees; mean age, 74 years), elderly (31 knees; mean age, 70 years), and young (26 knees; mean age, 21 years) groups. The anteroposterior (AP) length of the PFP before and during isometric quadriceps contraction at 0°, 30°, 60°, and 90° knee flexion was measured ultrasonographically. The difference between the maximum and minimum length values, change in length, was also measured. These parameters were compared among the three groups. In the OA group, correlations between the parameters and clinical features (knee pain; visual analog scale, knee range of motion [ROM], Kellgren and Lawrence (K/L) grade, and intercondylar distance) were examined by Spearman and Pearson's correlation coefficient tests.

Results

The AP lengths of the PFP before contraction were significantly lower in the OA group than in elderly group and young group at 30° (6.9 ± 2.5 vs. 12.0 ± 3.6 or 11.1 ± 2.7 mm, respectively; in order P = 0.014, P = 0.006) and 60° (6.5 ± 2.0 vs. 9.7 ± 2.5 or 9.1 ± 2.7 mm, respectively; both P < 0.001). The AP lengths of the PFP during contraction were significantly lower in the OA group than in elderly group and young group at 0° (6.7 ± 2.3 vs. 8.8 ± 3.7 or 9.1 ± 1.6 mm, respectively; both P < 0.001), 30° (7.9 ± 2.6 vs. 12.9 ± 3.7 or 13.0 ± 2.6 mm, respectively; both P < 0.001), and 60° (7.1 ± 2.5 vs. 13.5 ± 2.6 or 13.6 ± 3.0 mm, respectively; both P < 0.001). The change in length before maximum isometric quadriceps contraction was significantly lower in the knee OA group than in both elderly and young groups (3.3 ± 1.9 vs. 8.4 ± 2.5 or 6.8 ± 3.0 mm, respectively; both P < 0.001). The change in length during contraction was also significantly lower in the knee OA group than in both the elderly and young groups (3.9 ± 2.3 vs. 8.7 ± 2.3 or 8.9 ± 2.0 mm, respectively; both P < 0.001). In the OA group, change in length during contraction was significantly associated with knee pain (r = -0.476, P = 0.007), knee ROM (r = 0.388, P = 0.019), and Kellgren and Lawrence grade (r = -0.357, P = 0.045).

Conclusions

In knee OA, movement of PFP was decreased more than healthy participants. In the knee OA group, the decrease of the morphological change of the PFP showed the relationship between VAS score, knee extension ROM, intercondylar distance (ICD), and K/L grade. An evaluation to the PFP may be required in individuals with knee OA.

Clinics in diagnostic imaging (185)

A 20-year-old National Serviceman presented with left knee pain and swelling after training for his physical fitness test. Lateral knee radiography and magnetic resonance (MR) imaging showed patellar tendon-lateral femoral condyle friction syndrome (PT-LFCFS), on a background of patella alta and patellar malalignment. The patient was treated non-operatively with a course of physiotherapy and given advice on rest and activity modification. PT-LFCFS is a less well-recognised but important cause of anterior knee pain and represents an entity in a spectrum of disorders related to patellofemoral instability. We herein discuss the MR imaging findings specific to and associated with this condition, as well as briefly describing treatment options. In addition, we showcase a range of commonly encountered abnormalities that affect the infrapatellar fat pad and briefly discuss their specific MR imaging findings.

Amendment of the OMERACT ultrasound definitions of joints' features in healthy children when using the DOPPLER technique

BACKGROUND

Recently preliminary ultrasonography (US) definitions, in B mode, for normal components of pediatric joints have been developed by the OMERACT US group. The aim of the current study was to include Doppler findings in the evaluation and definition of normal joint features that can be visualized in healthy children at different age groups.

METHODS

A multistep approach was used. Firstly, new additional definitions of joint components were proposed during an expert meeting. In the second step, these definitions, along with the preliminary B-mode-US definitions, were tested for feasibility in an exercise in healthy children at different age groups. In the last step, a larger panel of US experts were invited to join a web-based consensus process in order to approve the developed definitions using the Delphi methodology. A Likert scale of 1-5 was used to assess agreement.

RESULTS

Physiological vascularity and fat pad tissue were identified and tested as two additional joint components in healthy children. Since physiological vascularity changes over the time in the growing skeleton, the final definition of Doppler findings comprised separate statements instead of a single full definition. A total of seven statements was developed and included in a written Delphi questionnaire to define and validate the new components. The final definitions for fat pad and physiological vascularity agreed by the group of experts reached 92.9% and 100% agreement respectively in a web survey.

CONCLUSION

The inclusion of these two additional joints components which are linked to detection of Doppler signal in pediatric healthy joints will improve the identification of abnormalities in children with joint pathologies.

Hyperintense signal alteration in the suprapatellar fat pad on MRI is associated with degeneration of the patellofemoral joint over 48 months: data from the Osteoarthritis Initiative

OBJECTIVE

To analyze associations of suprapatellar fat pad (SPFP) hyperintense signal alterations and mass effect with progression of patellofemoral osteoarthritis (OA) and clinical symptoms over 48 months.

MATERIALS AND METHODS

Subjects from the Osteoarthritis Initiative (n = 426; 51.8 ± 3.8 years; 49.8% women) without radiographic tibiofemoral OA underwent 3T-MRI of their right knees and clinical evaluation using the Knee Injury and Osteoarthritis Outcome Score at baseline and at 48 months. Elevated SPFP signal was assessed on intermediate-weighted, fat-saturated turbo spin-echo (TSE) images. Mass effect was defined as a convex posterior contour. Patellofemoral cartilage, bone marrow lesions (BML), and subchondral cysts were assessed using the Whole-Organ Magnetic Resonance Imaging Score (WORMS). Associations of SPFP imaging findings with MRI and clinical progression were assessed using general linear models and logistic regressions.

RESULTS

Baseline SPFP signal alterations were found in 51% of the subjects (n = 217), of whom 11% (n = 23) additionally had a mass effect. Progression of cartilage lesions was significantly higher in subjects with signal alteration versus without (adjusted mean increases, 95% CI; patella: 0.29, -0.07 to 0.64 vs -0.04, -0.40 to 0.31; p < 0.001; trochlea: 0.47, 0.16 to 0.77 vs 0.31, 0.01 to 0.61; p = 0.007). BML progression was also more likely in subjects with signal alteration (OR 1.75, 95% CI 1.09 to 2.82; p = 0.021). Mass effect was not associated with joint degeneration and SPFP findings were not associated with clinical worsening (p > 0.18 for all).

CONCLUSION

Patellofemoral joint degeneration over 48 months was significantly increased in subjects with SPFP signal alteration, suggesting an association between SPFP abnormalities and the progression of patellofemoral OA.

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

BACKGROUND

We sought to determine whether there are ultrasound parameters that differ between knees with symptomatic fat pad synovial impingement and asymptomatic knees.

METHODS

A prospective study was performed in patients with clinical signs and symptoms of fat pad synovial impingement and asymptomatic controls. Eleven symptomatic knees and 10 asymptomatic controls were evaluated. Ultrasound imaging was performed before and after exercise. Evaluated parameters included largest fat lobule compressibility, subjective assessment of vascularity, largest vessel diameter, and subjective assessment of dynamic fat pad motion during flexion and extension. Receiver operating characteristic (ROC) curve analysis was used to assess whether changes in these parameters were different between symptomatic and asymptomatic knees.

RESULTS

Change in the largest vessel diameter was greater and trended toward dilation in asymptomatic knees compared to symptomatic knees (mean: 0.83 vs. -0.02; P<0.001). No significant differences were observed between symptomatic and asymptomatic knees with respect to pre-exercise versus post-exercise states in subjective assessment of vascularity (P=0.131), fat pad motion (P=0.115), or percent change of the largest fat lobule (P=0.241). However, overall compressibility of the fat pad lobule was significantly diminished in the pre-exercise state in symptomatic knees compared to asymptomatic controls.

CONCLUSIONS

This study demonstrated a statistically significant change in the largest vessel diameter from pre- to post-exercise states between symptomatic and asymptomatic knees, as well as abnormal pre-exercise fat lobule compressibility in symptomatic knees. These findings show promise that with further research, ultrasound could have clinical utility in diagnosing infrapatellar fat pad impingement.

The association of patellar maltracking with infrapatellar fat pad edema and chondromalacia patella: A quantitative morphological magnetic resonance imaging analysis

Objectives

This study aims to investigate the relationship of patellofemoral joint morphology with infrapatellar fat pad edema and chondromalacia patella (CP) using patellar maltracking parameters on magnetic resonance imaging (MRI).

Patients and methods

Between January 2010 and January 2013, 50 patients with edema in the superolateral portion of the infrapatellar fat pad (the study group) and control group (n=50) with a normal infrapatellar fat pad were identified on MRI to compare with regard to five patellar maltracking parameters retrospectively. These parameters were trochlear depth, the trochlear sulcus angle (TSA), patellar translation, the lateral patellofemoral angle (PFA), and the Insall-Salvati ratio. The relationship between patellar maltracking and the CP was also evaluated using the same parameters.

Results

In the study group, the Insall-Salvati index and TSA were significantly higher (p=0.001), and the trochlear depth and PFA were low (p=0.001, p=0.01), while patellar translation showed no difference (p=0.957). In the CP group, the Insall-Salvati index and TSA were significantly high (p=0.001), the trochlear depth was low (p=0.001). No statistically significant difference was found in PFA and patellar translation (p=0.292, p=0.446).

Conclusion

Our study results suggest that edema in the superolateral portion of infrapatellar fat pad and CP are associated with patellar maltracking.

Validity of Radiograph-Based Infrapatellar Fat Pad Opacity Grading for Assessing Knee Synovitis: Correlation With Contrast-Enhanced MRI

OBJECTIVE

The purpose of this study was to determine the validity of infrapatellar fat pad (IPFP) opacity grading based on lateral knee radiography for assessing knee synovitis using correlation with contrast-enhanced (CE) MRI.

MATERIALS AND METHODS

Retrospective reviews of radiographs and CE knee MR images from 79 patients were independently performed by two radiologists. They evaluated IPFP opacity alteration (IPFP_CR) and joint effusion grades on lateral knee conventional radiographs, IPFP signal intensity alteration (IPFP_MR) and joint effusion grades on CE MR images, and synovitis (SYN_MR) grade in nine divided regions, three compartments (parapatellar, periligamentous, perimeniscal), and the whole knee on CE MR images. Correlations between radiographic grades and MRI assessments were evaluated using Spearman correlation tests, and the correlation coefficients (ρ) were compared. Interobserver agreement was evaluated using weighted kappa values.

RESULTS

The IPFP_CR grade was very highly correlated with the IPFP_MR grade (ρ = 0.906, p < 0.001) and highly correlated with SYN_MR grades from four regions (suprapatellar, infrapatellar, intercondylar, lateral parapatellar recess), the parapatellar compartment, and the whole knee (ρ = 0.614-0.740, all p < 0.001). The IPFP_CR grade was moderately correlated with the SYN_MR grades of the remaining five regions and two compartments (ρ = 0.457-0.547, all p < 0.001). The differences between correlation coefficients for SYN_MR grades and the IPFP_CR and IPFP_MR grades were not statistically significant (p = 0.290-1.0). Interobserver reliabilities were excellent or good for IPFP_CR, IPFP_MR, and SYN_MR grades (κ = 0.661-1.000).

CONCLUSION

IPFP_CR grade assessment enables valid evaluation and reporting of knee synovitis, especially in the parapatellar compartment and the whole knee.

Giant Cell Tumor of the Patellar Tendon Sheath: A Rare Case of Anterior Knee Pain

Giant cell tumor of the tendon sheath (GCTTS) is a benign, proliferative lesion of the synovium of the joint, the bursa, and the tendon sheath. We report a case of intra-articular, localized GCTTS arising from the patellar tendon, which is a rare cause of anterior knee pain. The diagnosis may be delayed due to non-specific symptoms and normal plain radiographic findings. Magnetic resonance imaging (MRI) is diagnostic to detect the lesion, but several other clinical entities and lesions should be evaluated in the differential diagnosis. The treatment of choice is a total excision of the lesion without leaving residual tumor tissue, in order to reduce the risk of recurrence. We present a patient with GCTTS of the patellar tendon and discuss its clinical and radiographic characteristics, differential diagnosis, pathology, and treatment.

Biographical background and origin of common eponymous terms in orthopedic surgery: anatomy and fractures in knee surgery

An eponym is a person after whom an eponymous term is named. These eponymous terms are easy shorthand in communication between surgeons. Therefore, they are often used and hard to eradicate. We discuss eponymous terms that describe anatomical features and fracture types in the knee. With these terms, an overview of the historical background of the eponym and its current clinical implication is discussed. The eponymous terms discussed are Gerdy tubercle, Pellegrini-Stieda lesion, Segond fracture, Hoffa fracture and fat pad. The meaning of the eponymous term is clarified, the biography of the namegiver given and its contemporary clinical implication discussed. Since eponymous terms are used frequently in inter-collegial discussion and literature, the meaning should be clear for everyone, since otherwise it might give room for misunderstanding.

Expression of calcitonin gene-related peptide in the infrapatellar fat pad in knee osteoarthritis patients

Background

The infrapatellar fat pad (IPFP) has been implicated as a possible source of osteoarthritis (OA) development and knee pain due to the production of inflammatory mediators and the existence of nerve fibers within this structure. Calcitonin gene-related peptide (CGRP) is a vasodilatory neuropeptide that is localized to joint tissues and has recently been implicated in the development of knee OA and OA pain. To date, however, the expression levels of CGRP in the IPFP of human knee OA patients have not been examined.

Methods

IFFP and synovial (SYN) tissues were harvested from 100 individuals with radiographic knee OA (unilateral Kellgren/Lawrence [K/L] grades 2–4) during total knee arthroplasty and subjected to immunohistochemical analysis for CGRP localization. In addition, the messenger RNA (mRNA) expression levels of CGRP and cyclooxygenase-2 (COX-2) in the collected tissues were evaluated and compared using real-time PCR analysis of total RNA extracts. CGRP and COX-2 mRNA expression were also compared among individuals with K/L grades 2–4.

Results

CGRP-positive cells were detected in the capillaries within the IPFP and lining layer of SYN tissue. The expression levels of CGRP in the IPFP were positively correlated with COX-2 and were significantly higher than those in SYN tissue. CGRP expression in tissue from the KL4 group was twofold higher than that from the KL2 group.

Conclusions

The IPFP of knee OA patients produces relatively high levels of CGRP, which may be regulated by COX-2 at the transcriptional level. Further studies are needed to determine if CGRP levels are directly linked to OA pathology.