Le corps adipeux infra-patellaire : carrefour antérieur du genou

Dimensional changes of Hoffa’s fat pad related to aging: evaluation by MRI

Background

Hoffa's fat pad is an intra-capsular extra-sinovial structure of the knee joint that has a significant biomechanical and metabolic role, minimizing the influence of stresses created by loading and generating cytokines. Changes in its size can lead to variations in the homeostasis of the knee in elderly patients. This work intends to assess the dimensional variations of Hoffa's fat pad associated to aging in both sexes, using MRI sagittal sequences acquired from the OAI (Osteoarthritis Initiative) database.

Methods

We examined the Hoffa's fat pad sagittal thickness in 217 men and women with knee osteoarthritis who were grouped into four age groups for the study: 40–49; 50–59; 60–69; and 70–80. 3T sagittal IW 2D TSE Fat-suppressed MRI sequences, taken from the OAI (Osteoarthritis Initiative) database, were examined.

Results

Hoffa’s fat pad thickness was shown to differ significantly between groups in both men and women, decreasing in the older individuals' groups (R = − 0.46; p 0.0001). By dividing the patients into ten-year age groups and by sex, the thickness of both the right knee and the left knee was examined. In fact, the average thickness of Hoffa's fat pad of the right knee was reported to be, in males, 33.6+/− 3 mm in subjects aged between 40 and 49 years, 31+/− 2.4 mm for patients aged between 50 and 59, 30.3 ± 1.8 mm in the group between 60 and 69 years and 28.7+/− 1.8 mm between 70 and 80 years. In women the values obtained were the following: 29+/− 1.6 mm between 40 and 49 years; 28.9+/− 2.6 mm in the group between 50 and 59 years, 25.3+/− 1.9 mm for patients aged 60 and 69 years and 26+/− 2 mm between 70 and 80 years. Similar results were obtained for the left knee.

Conclusions

Hoffa’s fat pad gradually thins with aging in both male and female patients with knee osteoarthritis, and this can be detected by evaluating the thickness of the fat pad on sagittal MRI sequences.

Hyaluronic acid sheet transplantation attenuates infrapatellar fat pad fibrosis and pain in a rat arthritis model

Fibrosis of the infrapatellar fat pad (IFP) occurs after knee joint surgery or during knee osteoarthritis (KOA) and causes persistent pain and limited mobility. Previous studies demonstrated that treating IFP fibrosis alleviated pain in animal models. In this study, we examined the effects of hyaluronic acid (HA) sheet transplantation on IFP fibrosis and articular cartilage degeneration in a monoiodoacetic acid (MIA) rat arthritis model (95 male rats). Rats received bilateral intra-articular MIA injections (1.0 mg/30 μL) and underwent surgery 4 days later. HA sheets were transplanted on the right knee of each rat (HA group), with the left knee receiving sham surgery (sham group). Incapacitance tests were performed at multiple time points up to 28 days after MIA injection. Macroscopic, histological, and immunohistochemical analyzes were performed 14 and 28 days after injection. The concentrations of HA and interleukin-1β (IL-1β) in the synovial fluid were measured using ELISA. Transplantation of HA sheets could alleviate persistent pain 10-28 days after injection. The HA sheets inhibited articular cartilage degeneration at 14 days. Fibrosis and the invasion of calcitonin gene-related peptide-positive nerve fiber endings in the IFP were inhibited at both 14 and 28 days. Moreover, the HA sheets remained histologically until 10 days after transplantation. The concentration of HA reached its peak on Day 10 after transplantation; the concentration of IL-1β in the sham group was significantly higher than that in the HA group on Day 7. Therefore, HA sheets could be a promising option to treat IFP fibrosis occurring in KOA and after knee joint surgery.

Effect of Infrapatellar Fat Pad Preservation vs Resection on Clinical Outcomes After Total Knee Arthroplasty in Patient with End-Stage Osteoarthritis

Purpose

The management of infrapatellar fat pad (IPFP) during total knee arthroplasty (TKA) is the subject of ongoing debate. There is conflicting evidence whether IPFP should be preserved or resected during TKA to improve clinical outcomes. This study sought to establish if there is a benefit of one over another in terms of clinical function & patient satisfaction.

Material & Methods

Total of 67 patients (96 knees), 11 males & 56 females with a mean age of 66.29 years, who underwent TKA between 2016 and 2020 were included in the study. The planning for IPFP preservation (IPFP-P) on right side (50 knees) & IPFP resection (IPFP-R) on left side (46 knees) was done prospectively. We prospectively evaluated clinical outcomes post-TKA, comparing the right knee to the left knee in terms of IPFP-P vs IPFP-R using the oxford knee scoring (OKS) system. The SF-12 was used to evaluate and compare patient satisfaction between the two groups.

Results

The mean OKS in the IPFP-P group was 42.86 ± 2.63 & in the IPFP-R group was 44.22 ± 2.40. The OKS differed significantly between the two groups (p < 0.05). Patient with IPFP-R group had significantly better OKS. The mean Sf-12 (physical & mental component) in the IPFP-P was 51.05 ± 4.15 & 59.29 ± 2.53 & in IPFP-R was 51.23 ± 4.74 & 59.24 ± 2.78, showing no significant differences.

Conclusion

Our study shows that IPFP-R gave marginally better patient-reported functional outcome scores (OKS), but there was no difference in patient satisfaction (SF-12 scores) between the two groups.

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.

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.

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.

Inflammation of the infrapatellar fat pad

The infrapatellar fat pad (IFP) of Hoffa's fat pad is the main adipose structure within the knee joint. It is located between the joint capsule and the synovial membrane, which lines its posterior aspect. The IFP is composed chiefly of adipocytes and receives an abundant supply of blood vessels and nerves. Immune cells can infiltrate the IFP, which can become a major source of numerous proinflammatory mediators (cytokines and adipokines). The physiological role for the IFP remains unclear but may involve shock absorption and the protection of adjacent tissues. Hoffa's disease is characterized by inflammation, hypertrophy, and fibrosis of the pad in response to repetitive trauma. Anterior knee pain is the most common symptom. In advanced forms, metaplasia of the IFP may result in the development of a sometimes sizable osteochondroma. The IFP may also contribute to the pathophysiology of knee osteoarthritis, in particular via procatabolic and proinflammatory effects on its synovial lining. Finally, in patients with knee osteoarthritis, inflammation of the IFP may be a source of pain.

Hoffa's fat pad abnormalities, knee pain and magnetic resonance imaging in daily practice

Hoffa's (infrapatellar) fat pad (HFP) is one of the knee fat pads interposed between the joint capsule and the synovium. Located posterior to patellar tendon and anterior to the capsule, the HFP is richly innervated and, therefore, one of the sources of anterior knee pain. Repetitive local microtraumas, impingement, and surgery causing local bleeding and inflammation are the most frequent causes of HFP pain and can lead to a variety of arthrofibrotic lesions. In addition, the HFP may be secondarily involved to menisci and ligaments disorders, injuries of the patellar tendon and synovial disorders. Patients with oedema or abnormalities of the HFP on magnetic resonance imaging (MRI) are often symptomatic; however, these changes can also be seen in asymptomatic patients. Radiologists should be cautious in emphasising abnormalities of HFP since they do not always cause pain and/or difficulty in walking and, therefore, do not require therapy. Teaching Points • Hoffa's fat pad (HFP) is richly innervated and, therefore, a source of anterior knee pain. • HFP disorders are related to traumas, involvement from adjacent disorders and masses. • Patients with abnormalities of the HFP on MRI are often but not always symptomatic. • Radiologists should be cautious in emphasising abnormalities of HFP.

Induction of an inflammatory and prodegradative phenotype in autologous fibroblast-like synoviocytes by the infrapatellar fat pad from patients with knee osteoarthritis

OBJECTIVE

The infrapatellar fat pad (IFP) of the knee joint has an inflammatory phenotype in osteoarthritis (OA). Its close proximity to the synovial membrane suggests that the IFP could be involved in the induction of OA synovitis. This study was undertaken to investigate the response of fibroblast-like synoviocytes (FLS) to autologous IFP and subcutaneous adipose tissue (SCAT) from patients with severe knee OA.

METHODS

Samples of IFP, SCAT, and autologous synovial membrane tissue close to the IFP were harvested during surgery from 28 patients with end-stage knee OA. FLS from 14 patients were stimulated with autologous IFP- or SCAT-conditioned medium, and levels of messenger RNA (mRNA) expression and protein release of interleukin-6 (IL-6), IL-8, secretory phospholipase A2 (sPLA2 ), cytosolic PLA2 , cyclooxygenase 2 (COX-2), microsomal prostaglandin E synthase, prostaglandin E2 (PGE2 ), and matrix metalloproteinases (MMPs) 1, 3, 9, and 13 were evaluated. Both IFP- and SCAT-conditioned medium were evaluated by enzyme-linked immunosorbent assay for secretion of IL-6, soluble IL-6 receptor (sIL-6R), IL-8, tumor necrosis factor α (TNFα), PGE2 , IL-1β, and interferon-γ. In addition, OA FLS were treated with PGE2 receptor antagonists to evaluate the contribution of IFP-derived PGE2 to the inflammatory response of FLS to the IFP.

RESULTS

Stimulation of OA FLS with IFP-conditioned medium induced the mRNA expression and protein release of IL-6, IL-8, sPLA2 , COX-2, PGE2 , and MMPs 1, 3, 9, and 13. The extent of stimulation was consistently stronger with IFP-conditioned medium than with SCAT-conditioned medium. Moreover, secretion of IL-6, sIL-6R, IL-8, TNFα, and PGE2 was greater in IFP-conditioned medium than in SCAT-conditioned medium, especially PGE2 , whose secretion was 75-fold stronger in IFP-conditioned medium (P < 0.0001). PGE2 receptor antagonists dose-dependently inhibited the release of IL-6, IL-8, and PGE2 by IFP-stimulated FLS.

CONCLUSION

This study showed that the IFP has a potential role in the induction of synovial inflammation in patients with severe knee OA. Furthermore, secretion of PGE2 by the IFP may be involved in the OA inflammatory process.

MRI characteristics of cysts and "cyst-like" lesions in and around the knee: what the radiologist needs to know

Objectives and Methods

A variety of benign cystic or “cyst-like” lesions may be encountered during a routine magnetic resonance imaging (MRI) of the knee. These lesions comprise a diverse group of entities from benign cysts to complications of underlying diseases. In addition, normal anatomic bursae and recesses may be misdiagnosed as an intra-articular cystic lesion when they are distended. However, the majority of the aforementioned lesions have characteristic MR appearances that allow a confident diagnosis, thus obviating the need for additional imaging or interventional procedures.

Results

This article includes a comprehensive pictorial essay of the characteristic MRI features of common and uncommon benign cysts and “cyst-like” lesions in and around the knee joint.

Discussion

For accurate assessment of the “cystic structure”, a radiologist should be able to identify typical MRI patterns that contribute in establishing the correct diagnosis and thus guiding specific therapy and avoiding unwarranted interventional procedures such as biopsy or arthroscopy.

Teaching points

• Cystic lesions are common in knee MRI and the commonest, the Baker’s cyst, has an incidence of 38 %.

• Synovial cysts, meniscal cysts, normal knee bursae and recesses have characteristic MR appearances.

• Miscellaneous “cyst-like” lesions may require a more dedicated MR protocol for a correct diagnosis.

MR imaging of anterior knee pain: a pictorial essay

Anterior knee pathology is a frequent cause of joint pain and limitation of function and mobility among patients presenting to an orthopaedic department. Proper recognition and treatment of pathologic conditions depend on the knowledge of normal anatomy and of the various abnormalities, which affect this area of the knee and may present with anterior knee pain. A broad array of benign and malignant processes may be manifested as anterior knee discomfort, and this common clinical entity is among the most frequent indications for MR imaging of the lower extremities. Clinical history and physical examination are also of paramount importance. The disorders can be categorized and differentiated primarily according to their location. Traumatic or non-traumatic disorders of the patella, patellar retinacula, quadriceps and patellar tendons and supra or infrapatellar fat pad can be the source of symptoms. This article includes a comprehensive pictorial essay of the characteristic MR features of common and uncommon disorders causing anterior knee pain. For accurate assessment of the aforementioned clinical problem, a radiologist should be able to identify typical MR imaging patterns that contribute in establishing the correct diagnosis and thus tailoring the appropriate therapy. Level of evidence IV.