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

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

Background

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.

Methods

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.

Results

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*).

Conclusions

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.

The suprapatellar fat pad: A histotopographic comparative study

The suprapatellar fat pad is an adipose tissue located in the anterior knee whose role in osteoarthritis is still debated. Considering that anatomy drives function, the aim of this histotopographic study was to investigate the specific morphological features of the suprapatellar fat pad versus the infrapatellar fat pad in the absence of osteoarthritis, for a broad comparative analysis. Suprapatellar fat pad and infrapatellar fat pad tissue samples (n = 10/group) underwent microscopical/immunohistochemical staining and transmission electron microscopy analysis; thus, tissue-specific characteristics (i.e., vessels and nerve endings presence, lobuli, adipocytes features, septa), including extracellular matrix proteins prevalence (collagens, elastic fibers), were focused. Multiphoton microscopy was also adopted to evaluate collagen fiber orientation within the samples by Fast Fourier Transform (coherency calculation). The absence of inflammation was confirmed, and comparable counted vessels and nerve endings were shown. Like the infrapatellar fat pad, the suprapatellar fat pad appeared as a white adipose tissue with lobuli and septa of comparable diameter and thickness, respectively. Tissue main characteristics were also proved by both semithin sections and transmission electron microscopy analysis. The suprapatellar fat pad adipocytes were roundish and with a smaller area, perimeter, and major axis than that of the infrapatellar fat pad. The collagen fibers surrounding them showed no significant difference in collagen type I and significantly higher values for collagen type III in the infrapatellar fat pad group. Regarding the septa, elastic fiber content was statistically comparable between the two groups, even though more represented by the suprapatellar fat pad. Total collagen was significantly higher in the infrapatellar fat pad and comparing collagen type I and type III they were similarly represented in the whole cohort despite collagen type I appearing to be higher in the infrapatellar fat pad than in the suprapatellar fat pad and vice versa for collagen type III. Second harmonic generation microscopy confirmed through coherency calculation an anisotropic distribution of septa collagen fibers. From a mechanical point of view, the different morphological characteristics determined a major stiffness for the infrapatellar fat pad with respect to the suprapatellar fat pad. This study provides, for the first time, a topographic description of the suprapatellar fat pad compared to the infrapatellar fat pad; differences between the two groups may be attributed to a different anatomical location within the knee; the results gathered here may be useful for a more complete interpretation of osteoarthritis disease, involving not only cartilage but the whole joint.

Patellar Lateralization, Absence of Joint Hypermobility, and the Mechanism of Injury Are Associated With Osteochondral Fracture After First-time Acute Lateral Patellar Dislocation in Adolescents: An MRI-based Evaluation

BACKGROUND

Although the risk factors for patellofemoral dislocation are clearly defined, risk factors for osteochondral fracture (OCF) after patellar dislocation are not as well defined. The aim of this study was to investigate the risk factors for OCF by evaluating patients with and without OCF after first-time acute patellar dislocation.

METHODS

This multicenter study was conducted as a retrospective examination of the radiologic measurements on the magnetic resonance imaging of 306 patients. The patients were divided into the OCF group and non-OCF group, and OCFs were grouped according to whether the fracture was in the patella or femur. Patellar height, patellar lateralization, trochlear morphology, patellofemoral matching, and patella types were evaluated on patient magnetic resonance imaging. The presence of joint hypermobility in the patients was determined according to the Beighton scale score. The injury mechanisms of the patients were grouped as sports-related injuries, injuries resulting from simple falls, and injuries during daily activities.

RESULTS

A total of 120 OCFs were detected in 108 (35.2%) patients, of which 96 (80%) were in the patella and 24 (20%) in the femur. The rate of OCF after sports-related injuries was found to be significantly higher than in other injury mechanisms ( P =0.001). More joint hypermobility was detected in patients without OCF ( P =0.041). The measurements of tibial tubercle-trochlear groove, tibial tubercle-posterior cruciate ligament distance and lateral patellar displacement were statistically higher in cases with OCF ( P =0.001). In patients with normal joint mobility, the rate of OCF localization in the patella was significantly higher ( P =0.035). No correlation was found between any other parameters and OCF ( P >0.05). The absence of joint hypermobility and the measurements of tibial tubercle-trochlear groove distance, tibial tubercle-posterior cruciate ligament distance, and lateral patellar displacement were independent risk factors for the incidence of OCF according to the logistic regression analysis.

CONCLUSIONS

The absence of joint hypermobility and patellar lateralization are independent risk factors for the occurrence of OCF after first-time patellar dislocation. Sports-related injury is a nonindependent risk factor for the presence of OCF. In patients with normal joint mobility, the incidence of OCF in the patella is higher than in the femur. These important factors should be considered when evaluating patients and starting their treatment.

LEVEL OF EVIDENCE

Level III-retrospective cohort study.

Anatomic Risk Factors for Osteochondral Fracture of Acute First-Time Patellar Dislocation in Adolescents: A Retrospective Magnetic Resonance Imaging Study

Objective

To analyze the risk factors for osteochondral fracture (OCF) of first-time acute patellar dislocation (APD) through measurements of patellofemoral anatomy in adolescents.

Methods

In this prospective study, all patients were divided into two groups according to whether OCF was detected on magnetic resonance imaging (MRI): Group A (associated with OCF) and Group B (without OCF). Patellofemoral anatomy was evaluated with four aspects including trochlear/patellar dysplasia, patella location, patellofemoral matching, and morphologic classification. On MRI scans, trochlear facet asymmetry ratio (TFAR), lateral trochlear inclination (LTI), sulcus angle (SA), trochlear depth (TD), and patellar depth (PD) were measured to assess trochlear/patellar dysplasia. Insall–Salvati index (ISI), Caton–Deschamps index (CDI), Blackburne–Peel index (BPI), lateral patellofemoral angle (LPFA), patellar tilt angle (PTA), and lateral patellar displacement (LPD) were measured to show the location of patella. Patellofemoral matching was analyzed through the measurements of patellofemoral congruence angle (PFCA), patellofemoral index (PFI), and patellotrochlear index (PTI).

Results

A total of ninety-four adolescents from 49 boys and 45 girls (mean age, 15 years; range, 10–18 years) with first-time APD were recruited and included in Group A (65) and Group B (29). The PFI (2.62 ± 0.51 vs. 2.10 ± 0.44) and PTI (0.28 ± 0.05 vs. 0.22 ± 0.07) were significantly higher in Group B than Group A (P < 0.05). There were no significant differences in other quantitative outcomes of the two groups (P > 0.05). The distribution of Dejour/Wiberg classification was statistically similar between the two groups (P > 0.05).

Conclusions

Adolescent patients with first-time APD complicating OCF have closer morphologic features of patellofemoral dysplasia and patella location when compared to adolescents without OCF. Abnormal patellofemoral matching increases the risk of OCF after first-time APD in adolescents.

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.