Quadriceps Fat Pad Research Articles

Association between quadriceps fat pad edema and patellofemoral osteoarthritis: a quantitative Q-Dixon-based magnetic resonance imaging (MRI) analysis.

Anterior knee pain (AKP) is a common symptom of patellofemoral osteoarthritis (PFOA). There is limited prospective evidence supporting the relationships between patellofemoral maltracking parameters, AKP, and PFOA. Thus, this prospective cross-sectional study aimed to determine the association between quadriceps fat pad (QFP) edema and patellofemoral maltracking in patients with chronic AKP and to evaluate the feasibility and diagnostic performance of a PFOA assessment using fat fraction (FF) and T2* based on Q-Dixon. This was a cross-sectional study with prospective data collection. Patients with chronic AKP were recruited from an orthopedic outpatient magnetic resonance imaging (MRI) waiting room at Shanghai Tongren Hospital between November 1, 2022, and April, 30, 2023. Exclusion criteria included age of <18 years, knee trauma, major internal derangement, prior surgery/arthroscopy, pre-existing joint diseases, and contraindications to MRI. MRI was performed using a 3.0-T instrument, and patellofemoral maltracking parameters were measured. Patellofemoral feature-relevant items, including patellar cartilage defects, patellar bone marrow lesions (BMLs), patellar osteophytes, anterior femoral osteophytes, Hoffa synovitis, and synovitis-effusion, from the semi-quantitative MRI Osteoarthritis Knee Score (MOAKS) were measured. The Anterior Knee Pain Scale (AKPS) was used to assess pain and function. FF/T2* measurement differences between groups and their associations with maltracking metrics, osteoarthritis grading based on the Iwano grading system, MOAKS, and AKPS, were investigated. Based on Iwano grading, the participants were categorized as having no-PFOA (n=40), mild PFOA (n=40), and advanced PFOA (n=40). Chi-squared and one-way analysis of variance were used to assess potential differences between the groups. Spearman's correlation test was used to analyze the correlation between the morphological parameters, AKPS, Iwano grade, MOAKS, and MRI quantitative values. Receiver operating characteristic (ROC) curves assessed the area under the curve (AUC), sensitivity, and specificity of quantitative values for distinguishing PFOA from no-PFOA. Among the 120 included patients, those in the mild (86.2±8.5) and advanced (83.9±9.5) PFOA groups had significantly lower AKPS scores than those in the no-PFOA group (88.8±7.3) (P=0.03). The mean FF and T2* values of the QFP were significantly higher in the no-PFOA group than those in the mild and advanced PFOA groups (P<0.001 for FF and P=0.02 for T2*). Quantitative data on the QFP and patellofemoral maltracking parameters showed no association. FF (r=-0.686, P<0.001) and T2* (r=-0.314, P=0.008) showed a negative correlation with the Iwano grade. The AUCs for PFOA diagnosis were 0.906 [95% confidence interval (CI), 0.853-0.960] (FF) and 0.744 (95% CI, 0.657-0.831) (T2*). QFP FF and T2* were not associated with patellofemoral maltracking parameters but with increased PFOA in patients with AKP, suggesting that QFP abnormalities play a role in PFOA. Therefore, a quantitative QFP assessment (FF and T2*) based on Q-Dixon technology could be a convenient and reliable new imaging biomarker for PFOA severity during clinical diagnosis, treatment, and follow-up.

Patellar height: an important parameter in knee MRI associated with tendinopathy, quadriceps fat pad edema (QFPE), anterior cruciate ligament mucoid degeneration (ACL-MD), and lateral cartilage damage.

Some pathologies associated with abnormal patellar height have been reported in the literature. However, its relationship with some pathologies, such as anterior cruciate ligament mucoid degeneration (ACL-MD) and focal cartilage defect, has not been investigated. To investigate the relationship between patellar height with patellar-quadriceps tendinopathy, quadriceps fat pad edema, ACL-MD, and focal cartilage defect. Magnetic resonance imaging of the knees of 261 patients were classified into three groups as normal, patella alta, and patella baja, and evaluated in terms of patellar-quadriceps tendinopathy, quadriceps fat pad edema, ACL-MD, and focal cartilage defect. There were 261 patients (140 men, 121 women; age range = 18-60 years; mean age = 30 ± 4.7 years). Of the 261 patients, 181 (69.3%) were normal, 56 (21.4%) were patella alta, and 24 were patella baja (9.1%). Patellar-quadriceps tendinopathy, quadriceps fat pad edema, and ACL-MD rates were significantly higher compared to the normal group (P <0.05). While a moderate positive correlation was found between patellar height shift and patellar-quadriceps tendinopathy and ACL-MD, there was a small correlation between patellar height shift and quadriceps fat pad edema. The rate of focal cartilage defect was significantly higher in the middle part of the lateral femoral condyle and lateral knee joint only in patella alta. The risk of patellar-quadriceps tendinopathy, quadriceps fat pad edema, ACL-MD, and lateral focal cartilage defect is higher in patients with alta-baja. The radiologist should evaluate these pathologies more carefully, especially subtle ones, in patients with abnormal patellar height.

Association among peripatellar fat pad edema and related patellofemoral maltracking parameters: a case-control magnetic resonance imaging study

BackgroundThe peripatellar fat pads are critical for protective cushioning during movement, and their endocrine function has been shown to affect osteoarthritis. Magnetic resonance imaging (MRI) is frequently used to visualize edema of the peripatellar fat pads due to injury. In this study, we aimed to assess the relationship between peripatellar fat pad edema and patellofemoral maltracking MRI parameters and investigate the association among cases of peripatellar fat pad edema.MethodsAge- and sex-matched peripatellar fat pad edema cases were identified and divided into superolateral Hoffa, quadriceps, and prefemoral groups. Images were assessed according to tibial tuberosity lateralization, trochlear dysplasia, patellar alta, patellar tilt, and bisect offset. McNemar’s test or paired t-tests and Spearman’s correlation were used for statistical analysis. Interobserver agreement was assessed with the intraclass correlation coefficient.ResultsOf 1210 MRI scans, 50, 68, and 42 cases were in the superolateral Hoffa, quadriceps, and prefemoral groups, respectively. Subjects with superolateral Hoffa fat pad edema had a lower lateral trochlear inclination (p = 0.028), higher Insall-Salvati (p < 0.001) and modified Insall-Salvati (p = 0.021) ratios, and lower patellotrochlear index (p < 0.001) than controls. The prefemoral group had a lower lateral trochlear inclination (p = 0.014) and higher Insall-Salvati (p < 0.001) and modified Insall-Salvati (p = 0.004) ratios compared with the control group. In contrast, the patellotrochlear index (p = 0.001) was lower. Mean patellar tilt angle (p = 0.019) and mean bisect offset (p = 0.005) were significantly different between cases and controls. The quadriceps group showed no association. Superolateral Hoffa was positively correlated with prefemoral (p < 0.001, r = 0.408) and negatively correlated with quadriceps (p < 0.001, r = -0.500) fat pad edema.ConclusionsSuperolateral Hoffa and prefemoral fat pad edemas were associated with patellar maltracking parameters. Quadriceps fat pad edema and maltracking parameters were not associated. Superolateral Hoffa fat pad edema was positively correlated with prefemoral and negatively correlated with quadriceps fat pad edema.

Clinical Significance of Quadriceps Fat Pad Edema: Relationship with Anterior Knee Pain and Other Patellofemoral Joint Pathologies

Clinical Significance of Quadriceps Fat Pad Edema: Relationship with Anterior Knee Pain and Other Patellofemoral Joint Pathologies

Do Patients Really Have Pain with Quadriceps Fat Pad Edema?

To determine the appropriate MRI criteria for the radiological diagnosis of significant quadriceps fat pad edema, to investigate the relationship between these criteria and anterior knee pain, and to evaluate possible structural and positional factors in the etiology. In this retrospective case-control study, individuals with and without quadriceps fat pad edema in the knee MRIs taken between May 2016 and December 2018 were determined as the case and control groups, respectively, in a ratio of 1:1. The MRI criteria for significant quadriceps fat pad edema were set as 10mm and above the anterior-posterior diameter of the quadriceps fat pad, posterior convexity, and an increased signal in the fat-suppressed proton density sequence. The groups were compared for anterior knee pain, pain characteristics, working positions (sitting and standing), and MRI findings of structural factors. P < 0.05 was considered statistically significant. A total of 108 individuals were evaluated. Anterior knee pain was more common in the case group (49/54, p < 0.001) and was highly correlated with signs of quadriceps fat pad edema (R = -0,657). Frequent pain at night (18/54, p = 0.013), increased pain when walking upstairs (40/54, p = 0.003), knees are flexed (43/54, p < 0.001), and decreased pain when knees are extended (42/54, p < 0.001) were significantly high in the case group. No significant differences were observed in working position and structural factors. Quadriceps fat pad edema is significantly associated with anterior knee pain and certain specific pain characteristics.

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

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. To evaluate the role of RTE in the diagnosis of QFPE. 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. 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). RTE may be an effective imaging method for evaluating QFPE.

Quadriceps fat pad edema in MR imaging: Association with quadriceps tendon alterations in a retrospective analysis

PurposeEdema of the quadriceps fat pad (QFP) in MR imaging has been described as a distinct finding associated with anterior knee pain, its etiology, however, remains under debate. The aim of this study was to investigate a potential relationship between QFP edema, alterations of the quadriceps tendon (QT) and other anterior knee structures. Method800 consecutive, clinically indicated MRI exams of the knee at 3T were retrospectively analyzed for the absence or presence of QFP edema. If present, QFP edema was determined visually by three independent readers and classified into 3 grades (A to C); concomitant alterations of the QT were classified into 5 grades (1 to 5). Furthermore, QT thickness, femoropatellar cartilage degeneration and parameters of patellar instability were determined. 20 MRI studies of healthy individuals served as control group. For statistical analysis Kruskal-Wallis test, one-way ANOVA and Fleiss kappa were used. Results153 of 800 patients (19%) presented with various degrees of QFP edema. Analysis showed significantly higher grades of QT alterations in patients with intermediate (grade B) and intensive (grade C) QFP edema (p < .001) compared to controls and also significantly different grades of QT alterations in patients with mild and intermediate compared to those with intensive QFP edema (p < .001). Increased mean QT thickness was found in patients with intermediate and intensive QFP edema compared to controls (p < .05). ConclusionsOur study suggests that QFP edema shows an association with QT alterations and QT thickness.

The relationship between quadriceps fat pad syndrome and patellofemoral morphology: a case\u2013control study

BackgroundThe purpose of this prospective case–control study is to investigate the relationship between quadriceps fat pad syndrome (QFPS) and patellofemoral morphology.Materials and methodsTwenty-two patients with QFPS and 22 age- and gender-matched healthy volunteers were included. The diagnosis of QFPS was supported both clinically and radiologically. On magnetic resonance imaging (MRI), patellofemoral morphology was evaluated with 13 radiological measurements including trochlear sulcus angle, trochlear sulcus depth, trochlear facet asymmetry, trochlear condyle asymmetry, lateral trochlear inclination angle, patellar translation, tibial tubercle–trochlear groove (TT–TG) distance, Insall–Salvati ratio, patellotrochlear index, patellar tilt, the ratio between lateral and medial facet lengths, interfacet angle, and quadriceps tendon thickness. The mean of measurements was compared between groups using the Mann–Whitney U test.ResultsThere were 22 patients (12 male, 10 female) with mean age of 30.81 ± 1.41 (range 19–38) years in group I and 22 patients (12 male, 10 female) with mean age of 31.13 ± 1.31 (range 19–39) years in group II. The mean age and the gender distribution were statistically similar between groups (p = 0.845, p = 1, respectively). All measured values except for patellar tilt (p = 0.038) and TT–TG distance (p = 0.004) were similar (p > 0.05 for the other variables). However, all of the measured variables were within the normal range.ConclusionsQFPS may not be associated with anatomical variations of the patellofemoral joint. Further studies are required to understand the etiology and risk factors.Level of evidenceLevel III, prospective case–control study

Qualitative and quantitative measures of prefemoral fat pad and quadriceps fat pad predict incident radiographic osteoarthritis

Purpose: To determine if qualitative and quantitative measures of prefemoral fat pad (PFP) and quadriceps fat pad (QFP) are predictive of incident radiographic osteoarthritis (iROA) over 4 years in the Osteoarthritis Initiative (OAI) study.

Qualitative and quantitative measures of prefemoral and quadriceps fat pads are associated with incident radiographic osteoarthritis: data from the Osteoarthritis Initiative

To determine if qualitative and quantitative measures of prefemoral fat pad (PFP) and quadriceps fat pad (QFP) are associated with incident radiographic osteoarthritis (iROA) over 4 years in the Osteoarthritis Initiative (OAI) study. Participants in this nested case-control study were selected from the OAI study with knees that had Kellgren Lawrence grades (KLG)of 0 or 1at baseline. Case knees were defined by iROA (KLG≥ 2) over 4 years. Control knees without iROA were matched 1:1 with case knees. Magnetic resonance images (MRIs) were read at P0 (time of onset of iROA), P-1 (1 year prior to P0) and baseline, and used to assess PFP (i.e., prefemoral hyperintensity alteration, patellofemoral hyperintensity alteration, maximum axial area) and QFP (i.e., hyperintensity alteration, mass effect, maximum axial area). Conditional logistic regression analyses were performed to study the associations between PFP/QFP measures and iROA, after adjustment for covariates. 354 case knees with iROA were matched to 354 control knees. 66.9% of the participants were female, with an average age of 60.1 years. PFP prefemoral hyperintensity alteration measured at three time points (OR [95%CI]: 1.46 [1.18-1.82], 1.50 [1.20-1.88], 1.52 [1.22-1.89] respectively), PFP maximum axial area (OR [95%CI]: 1.07 [1.01-1.14], 1.08 [1.01-1.15], 1.08 [1.02-1.15] respectively) and QFP hyperintensity alteration (OR [95%CI]: 1.59 [1.27-2.00], 1.44 [1.13-1.82], 1.38 [1.09-1.73] respectively) were significantly associated with iROA in multivariable conditional logistic analyses. QFP mass effect measured at BL and P-1 (OR [95%CI]: 1.42 [1.11-1.82], 1.33 [1.01-1.73] respectively) were significantly associated with iROA. Qualitative and quantitative measures of PFP and QFP are associated with increased iROA over 4 years.

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

PurposeQuadriceps 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 methodsSixty-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.ResultsThere 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.ConclusionsQuadriceps fat pad oedema detected in MRI examinations should warn the radiologist against the presence of various pathologies related to the patellofemoral joint.

Ultrasonography-Guided Injection for Quadriceps Fat Pad Edema: Preliminary Report of a Six-Month Clinical and Radiological Follow-Up.

Purpose:To investigate efficacy and safety of ultrasonography-guided local corticosteroid and anesthetic injection followed by physical therapy for the management of quadriceps fat pad (QFP) edema.Materials and Methods:We prospectively evaluated 1671 knee MRI examinations in 1542 patients for QFP edema with mass effect, which was present in 109 (6.5%) knees. Participants were assigned into injection and therapy groups (both received the same physical therapy program). Injection group was first treated with ultrasonography-guided QFP injection of 1 mL corticosteroid and 1 mL local anesthetic agent. Patients were evaluated at baseline and 1-, 2-, 6-month follow-up for pain using static and dynamic visual analogue scale (VAS), suprapatellar tenderness, and QFP edema on MRI.Results:Final sample size consisted of 19 knees (injection group, 10; therapy group, 9) in 17 patients. An overall improvement was detected in both groups between baseline and final assessments. The injection group fared better than the therapy group in static VAS scores (3.33 ± 1.70 versus 0.56 ± 1.33), while there was no such difference for dynamic VAS. Incidence of suprapatellar tenderness decreased in both groups, statistically significantly in the injection group (from 100% to 0%). Pain reduction was greater in the injection group at the first month (88.9% – 90% good response versus 50% – 66.7% good response, static-dynamic VAS scoring, respectively), whereas there was no such superiority at the sixth month. No severe adverse events were identified.Conclusion:Ultrasonography-guided local injection followed by physical therapy is safe in the management of QFP edema; however, it is not superior to stand-alone physical therapy program in the long term.

Imaging of traumatic injury and impingement of anterior knee fat

Fat is not just used by the body as bulk tissue. In addition to its role in storing energy and regulating hormone action, fat is used in some parts of the body for its mechanical properties. The anatomy of anterior knee fat is more complex than it appears at first sight and is capable of withstanding considerable compressive and shear stress. Specific lesions occur when such mechanical stress exceeds the physiological limits and are yet little known. Superficial fat can be the site of either acute injury by closed degloving called the Morel-Lavallée lesion or chronic injury, when subject to repeat excessive shear forces, due to more complex and less well-defined disruptions that result in pseudo-bursitis. There are three main anterior, intracapsular and extrasynovial fat pads in the knee joint, which are the infrapatellar fat pad (IFP) or Hoffa's fat pad, the quadriceps fat pad and the prefemoral fat pad. The IFP plays an important role as a mechanical shock absorber and guides the patella tendon and even the patella itself during flexion-extension movements. In response to repeated excessive stress, an inflammatory reaction and swelling of the IFP is first observed, followed by a fibrotic reaction with metaplastic transformation into fibrous, cartilaginous or bone tissue. More rarely, the two other deep fat pads (quadriceps and prefemoral) can, if subject to repeated stress, undergo similar restructuring inflammatory reactions with metaplasia resulting in tissue hardening, anterior pain and partial loss of function.

Unusual Symptomatic Multipartite Patella Associated with Quadriceps Fat Pad Edema.

Partite patella is a known cause of anterior knee pain, especially in adolescents and young males, although most patients are asymptomatic. Symptomatic partite patella is usually revealed on magnetic resonance imaging (MRI) as bone marrow edema within the opposing bone fragments. We present a case of unusual bilateral symptomatic multipartite patella in an adult who presented with quadriceps fat pad edema and mass effect as well as slightly edematous signal changes within the bone fragments on MRI. This case indicates that symptomatic partite patella can also present with edema-like imaging findings in the adjacent soft tissue due to chronic mechanical irritation.

Quadriceps Fat Pad Edema

The fat pad is the normal fat pad between the suprapatellar recess posteriorly and tendon anteriorly. The term quadriceps fat pad has been used to describe an inflammatory process within the suprapatellar fat, manifested on magnetic resonance imaging (MRI) as high T2 signal, low T2 signal, and mass effect on the tendon. 1 To our knowledge, there are no reports of fat pad edema as shown on sonography. We report a case in which fat pad edema seen on MRI in a patient with anterior knee pain was demonstrable on sonography and was treated with steroid and local anesthetic injection under sonographic guidance with symptomatic relief.

Quadriceps fat pad edema: significance on magnetic resonance images of the knee

While clinically reading magnetic resonance (MR) images of the knees we have occasionally noted edema within the suprapatellar fat pad, with mass effect both on the suprapatellar joint recess posteriorly, and on the quadriceps tendon anteriorly. This MR appearance is analogous to Hoffa's disease described in the infrapatellar fat pad. We sought to evaluate the frequency and pattern of this finding and to provide clinical and histological correlation. The suprapatellar (quadriceps) fat pad was evaluated in 770 consecutive MR examinations (on 1.5 T and 0.3 T) in 736 patients (353 females and 383 males, age range 5-86 years, mean 44.3 years). The MR images were retrospectively evaluated by two observers in consensus for the presence of quadriceps fat pad edema with mass effect. In 46 patients who had intravenous administration of gadolinium, the presence of enhancement was also evaluated. Clinical correlation was performed in abnormal cases; in one patient, 1-year follow-up MRI was evaluated and in one patient a percutaneous biopsy as well as 2-year clinical follow-up was performed. Thirty-two (4.2%) knees in 29 patients showed quadriceps fat pad edema and mass effect. In five of these patients imaging of the contralateral knee was also performed and four of these showed symmetric edema. Another five cases had gadolinium-enhanced images with prominent enhancement. Most patients had clinical symptoms of meniscal tears (n=16, 55%) or anterior knee pain (n=8, 27.6%). The remainder had nonspecific pain (n=4, 13.8%) or suspected avascular necrosis (n=1, 3.4%). In the case with 1-year follow-up MRI, improvement was seen. Biopsy in another patient revealed vasculitis with obliteration of the small vessels. Resection of the fat pad in this patient led to complete resolution of the symptoms. Suprapatellar fat pad edema may be analogous to Hoffa's disease, is rare, and may be a cause of anterior knee pain. However, this finding is not infrequent and its precise association with symptoms remains unclear.

Quadriceps fat pad signal intensity and enlargement on MRI: prevalence and associated findings.

The purpose of this investigation was to characterize the MRI appearance of the quadriceps fat pad and to correlate the findings with other knee abnormalities, anatomic measurements of the extensor mechanism, and findings from history and at physical examination. Ninety-two consecutive knee MRI examinations from 84 patients were retrospectively reviewed by two musculoskeletal radiologists for quadriceps fat pad enlargement and signal intensity. Other data from the retrospective review included infrapatellar and prefemoral fat pad signal intensity, quadriceps and patellar tendon abnormalities, joint effusion, medial plica, chondromalacia, articular muscle thickness, and prepatellar edema. The patellar length, patellar articular length, patellar tendon length, and femoral sulcus angle were measured. MRI reports were reviewed for meniscal and ligament abnormalities. Clinical data were reviewed for findings of anterior knee pain in the history and at physical examination. The chi-square and Student's t tests were used to determine significant associations. Twelve percent (11/92) of MRI examinations showed quadriceps fat pad mass effect on the suprapatellar recess, which was associated with intermediate or fluid signal intensity of the quadriceps fat pad (chi(2) = 7.19, p = 0.0274) but with no other findings on knee MRI. Anterior knee pain at physical examination was associated with quadriceps fat pad mass effect (chi(2) = 8.76, p = 0.0031), medial collateral ligament abnormality (chi(2) = 4.83, p = 0.0031), and history of anterior knee pain (chi (2) = 22.76, p < 0.0001). Enlargement of the quadriceps fat pad on MRI has a prevalence of 12% and is significantly associated with intermediate or fluid signal intensity of the quadriceps fat pad and anterior knee pain.

Clinical Features of Diffuse Pigmented Villonodular Synovitis in the Knee Joint

Purpose : Diffuse pigmented villonodular synovitis (PVNS) is a rare benign disorder characterized by an exuberant inflammation on synovial membrane. The purpose of this study was to report clinical manifestations and the results of treatment in eight cases of PVNS. Materials and Methods : Eight patients presenting with PVNS were analyzed from the patient records and the pathologic records. The seven of the patients had been managed with arthroscopic synovectomy and one patient underwent open synovec-tomy and total joint replacement. Four of the eight patients had magnetic resonance imagings (MRI). Recurrence after synovecto-my was considered to have occurred, if there were noteworthy clinical symptoms and signs. Results : The average age of the eight patients with PVNS was thirty years-old. They complained of nonspecific pain and discom-fort. Four knees on MRI scans had irregularity with loss and deformity of the intracapsular fat pad (infrapatellar, the suprapatellar and the quadriceps fat pad). Recurrence occurred in three of the eight patients (one total synovectomy, two partial synovectomy). Conclusion : We observed characteristic changes in the intracapsular fat pads on the MR images of patients with PVNS. The recurrence rate was high after arthroscopic synovectomy.

MR imaging of the knee: can changes in the intracapsular fat pads be used as a sign of synovial proliferation in the presence of an effusion?

Synovial proliferation is difficult to detect on MR images when joint effusions are present. The objective of this study was to assess the efficacy of MR changes in intracapsular fat pads (prefemoral, quadriceps, Hoffa's) as a sign of synovial proliferation in patients with knee effusions. MR images were obtained in 70 patients with knee effusions. An effusion was considered present if the suprapatellar bursa was distended 1 cm in anterior to posterior diameter on T2-weighted sagittal images. The experimental group consisted of 32 patients with proliferative effusions (effusions associated with synovial proliferation) diagnosed on the basis of histologic or microbiologic data or strict rheumatologic criteria. This group comprised 11 patients with pigmented villonodular synovitis, six with rheumatoid arthritis, one with psoriatic arthritis, three with hemosideric arthritis, and 11 with septic arthritis. The control group comprised 38 subjects with knee effusions who had no arthroscopic evidence of synovial proliferation. After determining the MR criteria of proliferative effusion, two observers who had no knowledge of these cases evaluated abnormalities of the intracapsular fat pads seen on sagittal intermediate-weighted midline MR images. Characteristic changes in the fat pads were noted on MR images in patients with proliferative synovial effusions. Scalloping or truncation of the prefemoral fat pad was 77% sensitive and 95% specific as a predictor of proliferative effusion. Defects and displacement of Hoffa's fat pad had a sensitivity of 57% and a specificity of 99%, and nonvisualization or irregular margins of the quadriceps fat pad had a sensitivity of 61% and a specificity of 100%. Characteristic changes in intracapsular fat pads seen on MR images of patients with proliferative effusions can help distinguish these patients from those with effusions without synovial proliferation.