MR imaging of extrasynovial inflammation and impingement about the knee

Sonographic Characterization of the Pericruciate Fat Pad with the Use of Compression Elastography-A Cross-Sectional Study among Healthy and Post-Injured Patients

Background: The pericruciate fat pad (PCFP) in the knee joint is still insufficiently studied despite its potential role in knee pathologies. This is the first reported study which aimed to clarify the characteristics of the PCFP in healthy individuals and contrast them with cases of post-traumatic injuries. Methods: Conducted as a retrospective cross-sectional study (n = 110 knees each) following STROBE guidelines, it employed grayscale ultrasound with echogenicity measurement, compression elastography with elasticity measurement, and Color Doppler for blood flow assessment. Results: PCFP showed a homogenic and hyperechoic echostructure. The echogenicity of the PCFP was higher than that of the posterior cruciate ligament (PCL) (p < 0.001, z-score = 8.97) and of the medial head of gastrocnemius (MHG) (p = 0.007, z-score = 2.72) in healthy knees, but lower than subcutaneous fat (SCF) (p < 0.001, z-score = -6.52). Post-injury/surgery, PCFP echogenicity surpassed other structures (p < 0.001; z-score for PCL 12.2; for MHG 11.65 and for SCF 12.36) and notably exceeded the control group (p < 0.001, z-score = 8.78). PCFP elasticity was lower than MHG and SCF in both groups, with significantly reduced elasticity in post-traumatic knees (ratio SCF/PCFP 15.52 ± 17.87 in case group vs. 2.26 ± 2.4 in control group; p < 0.001; z-score = 9.65). Blood flow was detected in 71% of healthy PCFPs with three main patterns. Conclusions: The main findings, indicating increased echogenicity and reduced elasticity of PCFP post-trauma, potentially related to fat pad fibrosis, suggest potential applications of echogenicity and elasticity measurements in detecting and monitoring diverse knee pathologies. The description of vascularity variations supplying the PCFP adds additional value to the study by emphasizing the clinically important role of PCFP as a bridge for the middle genicular artery on its way to the inside of the knee joint.

Qualitative and Quantitative Measures in the Infrapatellar Fat Pad in Older Adults: Associations with Knee Pain, Radiographic Osteoarthritis, Kinematics, and Kinetics of the Knee

RATIONALE AND OBJECTIVES

The purpose of this study is to delineate cross-sectional associations between qualitative and quantitative measures of the infrapatellar fat pad (IPFP) and knee symptoms, structure, kinematics, and kinetics in older adults.

METHODS

Ninety eligible subjects (90 knees, mean age 54.0 years, 68.9% female) were examined at our center. We used T2-weighted fat-suppressed magnetic resonance imaging (MRI) to evaluate signal intensity alteration, maximum sagittal area, and depth of the IPFP. Symptomatic osteoarthritis (SOA) was a pain subscale score greater than 0 on the Western Ontario McMaster Osteoarthritis Index. A Kellgren-Lawrence grade ≥ 2 identified incident radiographic osteoarthritis (iROA). Three-dimensional gait data were employed to analyze knee joint kinematics and kinetics. Correlation and regression analyzes assessed associations between IPFP measurements and SOA, iROA, kinematics, and kinetics.

RESULTS

There were strong and positive associations between IPFP signal intensity alteration and both SOA and iROA in multivariable regression analyzes [OR (95% CI): 2.849 (1.440 to 5.636), 2.356 (1.236 to 4.492), respectively]. Conversely, a significant negative correlation was observed between IPFP maximum area and flexion angle [B (95%CI): - 1.557 (-2.549 to -0.564)]. Moreover, adjusting for covariates did not reveal any significant correlation between IPFP parameters and other indicators (P > 0.05, respectively).

CONCLUSION

IPFP signal intensity alteration and area were associated with knee clinical symptoms, structural abnormalities, and flexion angle in adults over 40, respectively. These findings suggest that IPFP may be a crucial imaging biomarker in early and middle knee osteoarthritis.

Abnormalities of the pericruciate fat pad: Correlations with the location and severity of chondral lesions of the knee

PURPOSE

The aim of this study was to evaluate the relationship between the grade of signal change of the pericruciate fat pad (PCFP) and the location and severity of cartilage alterations in the knee on magnetic resonance imaging (MRI).

MATERIALS AND METHODS

This retrospective study included 234 patients (M:F = 96:138, mean: 51 years) who underwent knee MRI. Two experienced musculoskeletal radiologists assessed any PCFP alterations (as grades 0-3) and chondral lesions using the modified Outerbridge grade (as grades 0-4). Bone marrow lesions (BMLs), meniscal status, anterior cruciate ligament alterations, and effusion-synovitis were also evaluated on the MRI. The relationships between PCFP alteration and MR findings (including the grade of chondral lesion) were evaluated.

RESULTS

Signal changes in the PCFP were detected in 150 cases by Reader 1 (grade 0, 67 cases; grade 1, 53 cases; grade 2, 21 cases; grade 3, 9 cases) and in 154 cases by Reader 2 (grade 0, 59 cases; grade 1, 61 cases; grade 2, 24 cases; grade 3, 10 cases). The grade of PCFP signal change was statistically significantly correlated with the grade of the chondral lesion of the medial femoral condyle (MFC) (p = 0.029 and p = 0.003, respectively) and the medial tibial plateau (MTP) (p = 0.045, p = 0.002, Readers 1 and 2, respectively). The grade of PCFP signal change was significantly correlated with the grade of the BMLs of the MFC, MTP, and lateral femoral condyle (p < 0.05) for both readers. PCFP alteration was related to effusion-synovitis and tears of the medial meniscus.

CONCLUSIONS

The grade of PCFP signal change was correlated with the severity of the cartilage alteration in the medial compartment of the knee joint and was also correlated with BMLs in the medial compartment, medial meniscal tears, and synovitis. Therefore, signal change in the PFCP seen on MRI can be an additional clue of the presence of osteoarthritis in the knee, particularly in the medial compartment.

Consensus Guidelines on Interventional Therapies for Knee Pain (STEP Guidelines) from the American Society of Pain and Neuroscience

Knee pain is second only to the back as the most commonly reported area of pain in the human body. With an overall prevalence of 46.2%, its impact on disability, lost productivity, and cost on healthcare cannot be overlooked. Due to the pervasiveness of knee pain in the general population, there are no shortages of treatment options available for addressing the symptoms. Ranging from physical therapy and pharmacologic agents to interventional pain procedures to surgical options, practitioners have a wide array of options to choose from – unfortunately, there is no consensus on which treatments are “better” and when they should be offered in comparison to others. While it is generally accepted that less invasive treatments should be offered before more invasive ones, there is a lack of agreement on the order in which the less invasive are to be presented. In an effort to standardize the treatment of this extremely prevalent pathology, the authors present an all-encompassing set of guidelines on the treatment of knee pain based on an extensive literature search and data grading for each of the available alternative that will allow practitioners the ability to compare and contrast each option.

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 Korean Medicine Treatments for Fat Pad Syndrome of Knee Joint: A Case Report

Fat pad syndrome is a knee joint condition/disease where acute or chronic inflammation occurs in the fat pad of the knee joint, and it is a cause of anterior knee pain. Fat pad syndrome usually occurs concurrently with other conditions/diseases to collectively cause anterior knee pain. No study to date has reported the treatment of anterior knee pain solely due to fat pad syndrome. Here, we report a case of fat pad syndrome of the knee joint as the sole cause of anterior knee pain in a 49-year-old woman who received integrated Korean medicine treatments (pharmacopuncture, acupuncture, herbal medicine, deep fascial meridian therapy, and chuna). Using patient-reported pain scale scores, the level of the patient’s pain was relieved, and her mobility improved. Integrated Korean medicine treatments could be effective for patients who have fat pad syndrome of the knee joint.

Current Clinical Concepts: Synthesizing the Available Evidence for Improved Clinical Outcomes in Iliotibial Band Impingement Syndrome

The current paradigm of insidious lateral knee pain involving the iliotibial band (ITB) in repetitive knee-flexion activities has been termed ITB friction syndrome since 1975. The original model for ITB pain was based on a limited or incorrect understanding of the relevant anatomy, biomechanics, and tissue science, which gradually led to a plethora of frustrating and ineffective interventional strategies. Mounting evidence from arthroscopic, cadaveric, and biomechanical studies, as well as from diagnostic imaging and histologic reports, has helped deconstruct this long-held paradigm for ITB-related pathology and treatment. By outlining the historical paradigm for our understanding of ITB pain and gathering newer evidence through extensive research, I will synthesize the available data in this clinical update to present an updated, more informed model for understanding insidious-onset ITB-related pathology and treating patients. The result is called ITB impingement syndrome.

Signal intensity alteration and maximal area of pericruciate fat pad are associated with incident radiographic osteoarthritis: data from the Osteoarthritis Initiative

OBJECTIVE

To determine whether pericruciate fat pad (PCFP) signal intensity alteration and maximal area are associated with incident radiographic osteoarthritis (ROA) over 4 years in the Osteoarthritis Initiative (OAI) study.

METHODS

Participants were from the Osteoarthritis Initiative (OAI) study. Case knees (n = 355) were defined by incident ROA between 12 and 48 months visits and were matched by sex, age, and radiographic status with control knees (n = 355). Magnetic resonance images (MRIs) were used to assess PCFP signal intensity alteration and PCFP maximal area at P0 (time of onset of ROA), P-1 (1 year prior to P0), and baseline. Conditional logistic regression analyses were applied to assess associations between PCFP measures and the risk of incident ROA.

RESULTS

The mean age of participants was 60.1 years and 66.9% were women. In multivariable analyses, PCFP signal intensity alteration measured at three time points (OR [95%CI]: 1.28 [1.10-1.50], 1.52 [1.30-1.78], 1.50 [1.27-1.76], respectively) and PCFP maximal area (OR [95%CI]: 1.21 [1.03-1.42], 1.27 [1.07-1.52], 1.37 [1.15-1.62], respectively) were significantly associated with incident ROA.

CONCLUSIONS

PCFP signal intensity alteration and maximal area were associated with incident ROA over 4 years, implying that they may have roles to play in ROA.

KEY POINTS

• Pericruciate fat pad signal intensity alteration and maximal area were associated with incident ROA, implying that they may have roles to play in ROA.

Prevalence of lateral patellofemoral maltracking and associated complications in patients with Osgood Schlatter disease

OBJECTIVE

To evaluate adults with history of Osgood Schlatter disease (OSD) for imaging features of lateral patellofemoral maltracking.

METHODS

In a span of four years, 10,181 unique non-contrast knee MRIs were performed on patients aged 20-50. Patients with acute trauma, prior surgery, and synovial pathologies were excluded. 171 exams had imaging findings of OSD, and an age-matched control group of 342 patients without OSD was randomly selected. Two radiologists retrospectively reviewed MRIs for features of lateral patellofemoral maltracking. Maltracking was defined as edema in superolateral Hoffa's fat or a tibial tuberosity-trochlear groove (TT-TG) distance ≥20 mm with either patellar tilt/translation. Binomial logistic regression identified predictors of maltracking in OSD. Optimal TT-TG distance to indicate maltracking was determined by receiver operating characteristic curve.

RESULTS

59% (101/171) of the knees with OSD showed findings of maltracking, with patella alta, trochlear dysplasia, and quadriceps tendinosis as significant predictors of maltracking (p < 0.001). Patellofemoral chondrosis was present in 63% (107/171), with maltracking contributing to higher grade chondrosis more so than increasing age (OR 8.4 versus 1.07). 13 mm was the optimal cut-off TT-TG distance to indicate maltracking (sensitivity 83%, specificity 80%). The prevalence of maltracking in the control group was 15% (p < 0.001 compared with the OSD group).

CONCLUSION

Adults with sequelae of OSD are at high risk of maltracking and are likely to develop patellofemoral chondrosis. A lower threshold for identifying maltracking patients, including a lower cut-off TT-TG distance can help identify those at risk. Radiologists should maintain a high index of suspicion for maltracking in adults with OSD to guide clinical intervention.

The relationship between quadriceps fat pad syndrome and patellofemoral morphology: a case-control study

Background

The purpose of this prospective case–control study is to investigate the relationship between quadriceps fat pad syndrome (QFPS) and patellofemoral morphology.

Materials and methods

Twenty-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.

Results

There 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.

Conclusions

QFPS may not be associated with anatomical variations of the patellofemoral joint. Further studies are required to understand the etiology and risk factors.

Level of evidence

Level III, prospective case–control study

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.

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.

MRI Findings Consistent with Peripatellar Fat Pad Impingement: How Much Related to Patellofemoral Maltracking?

Peripatellar fat pads are intracapsular extrasynovial adipose cushions that accommodate the changing shape and volume of articular spaces during movement. Variations in bone geometry, passive and active stabilization mechanisms and/or functional demands may lead to peripatellar fat pad abnormalities. While peripatellar fat pads may be affected a variety of conditions such as synovial inflammation, tumor and fibrosis, a mechanical origin should also be considered. Commonly, the clinical term "impingement" is used synonymously in the radiological literature to refer to three distinct entities of structural peripatellar fat pad abnormalities: superolateral the infrapatellar fat pad (Hoffa fat pad) edema, suprapatellar fat pad edema, and prepatellar fat pad edema, implying a mechanical origin of these conditions. The aim of this pictorial review is to describe the normal anatomy of the extensor mechanism of the knee, and discuss the relation of patellofemoral maltracking to the above-mentioned peripatellar fat pad conditions based on current evidence.

Knee Fat Pad Volumes in Patients with Hemophilia and Their Relationship with Osteoarthritis

Hemophilic arthropathy is a progressive, disabling condition with poorly understood pathobiology. Since there is an emerging interest to study the role of intra-articular fat pad size and biology in arthritic conditions, we explored fat pad volume changes in hemophilic arthropathy and to what extent they differed from osteoarthritis. We matched a cohort of 13 adult patients with hemophilic arthropathy of the knee with age- and gender-matched cohorts without osteoarthritis ("control cohort") and with the same degree of radiographic osteoarthritis ("OA cohort") in 1 : 2 fashion. Infrapatellar fat pad (IPFP) and suprapatellar fat pad (SPFP) volumes were calculated based on magnetic resonance imaging and differences in fat pad volumes, demographics, height, weight, and osteoarthritis scores were evaluated. Fat pad volumes were positively associated with body size parameters in all three cohorts but were unaffected by the degree of osteoarthritis. While IPFP volumes did not differ between cohorts, SPFP volumes expanded disproportionally with weight in hemophilia patients. Our observations indicate that IPFPs and SPFPs behave biologically differently in response to different arthritic stimuli. The exaggerated expansion of the SPFP in hemophilia patients highlights the importance of further studying the implications of fat pad biology for progression of hemophilic arthropathy.

Magnetic Resonance Signal Abnormalities within the Pericruciate Fat Pad: A Possible Secondary Sign for Acute Anterior Cruciate Ligament Tears

Purpose

The study sought to investigate the presence of magnetic resonance (MR) signal alterations within the pericruciate fat pad in patients with an acute anterior cruciate ligament (ACL) tear as well as evaluate its diagnostic value in comparison with the main secondary signs of ACL tears.

Methods

Two musculoskeletal radiologists retrospectively reviewed knee MR examinations performed from May to October 2015. The ACL was considered as torn or intact based on either previous arthroscopic findings or unequivocal MR imaging interpretation if arthroscopic correlation was unavailable. Abnormalities of the pericruciate fat pad were evaluated as increased signal on the fluid-sensitive sequences; the main secondary signs of ACL tears were identified. Sensitivity and specificity were calculated for each sign.

Results

A total of 182 patients entered this study: 22 with an acute ACL tear, 160 with intact ACL. Signal hyperintensity of the pericruciate fat pad was demonstrated in all patients with an acutely torn ACL, resulting significantly different between individuals with intact ACL and those with ligament tear ( P < .0001). This sign was much more sensitive (100%) but less specific (72.5%-75%) than other secondary signs.

Conclusions

Signal hyperintensity of the pericruciate fat pad on the fluid-sensitive sequences is associated with acute ACL tears and could be considered as a possible indicator of these injuries.

The iliotibial tract: imaging, anatomy, injuries, and other pathology

The iliotibial tract, also known as Maissiat's band or the iliotibial band, and its associated muscles function to extend, abduct, and laterally rotate the hip, as well as aid in the stabilization of the knee. A select group of associated injuries and pathologies of the iliotibial tract are seen as sequela of repetitive stress and direct trauma. This article intends to educate the radiologist, orthopedist, and other clinicians about iliotibial tract anatomy and function and the clinical presentation, pathophysiology, and imaging findings of associated pathologies. Specifically, this article will review proximal iliotibial band syndrome, Morel-Lavallée lesions, external snapping hip syndrome, iliotibial band syndrome and bursitis, traumatic tears, iliotibial insertional tendinosis and peritendonitis, avulsion fractures at Gerdy's tubercle, and Segond fractures. The clinical management of these pathologies will also be discussed in brief.

[Chronic sports injuries of the knee joint]

Chronic sports injuries of the knee joint are common and mainly caused by repetitive (micro) trauma and exertion. Chronic insertion tendinopathies and avulsion fractures and symptoms related to entrapment, friction and impingement can be pathophysiologically distinguished in athletes. In this review, we depict the characteristic magnetic resonance imaging (MRI) findings of the most commonly occurring pathologies.

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.