Hoffa's fat pad impingement treated arthroscopically: related findings on preoperative MRI in a case series of 62 patients

Predisposing factors for Hoffa's fat pad syndrome: a systematic review

BACKGROUND

Hoffa's fat pad syndrome has been defined as impingement of Hoffa's fat pad, leading to oedema and fibrosis. The primary aim of this systematic review was to identify morphological differences in Hoffa's fat pad between patients with and without Hoffa's fat pad syndrome, evaluating them as risk factors predisposing to its development. The secondary aim was to summarize and evaluate current evidence pertaining to the management of Hoffa's fat pad syndrome.

MATERIALS AND METHODS

The protocol for this review was prospectively registered (PROSPERO registration: CRD42022357036). Electronic databases, currently registered studies, conference proceedings and the reference lists of included studies were searched. All studies evaluating differences in Hoffa's fat pad anatomy under imaging between patients with and without Hoffa's fat pad syndrome were included, as well as those exploring epidemiological factors predisposing to its development (ethnicity, employment status, sex, age and BMI), and studies reporting on the effect of treatment on Hoffa's fat pad morphology.

RESULTS

A total of 3871 records were screened. Twenty one articles satisfied the inclusion criteria, evaluating 3603 knees of 3518 patients. Patella alta, increased tibial tubercle-tibial groove distance, and increased trochlear angle were found to predispose the development of Hoffa's fat pad syndrome. Trochlear inclination, sulcus angle, patient age and BMI were not associated with this condition. The link between Hoffa's fat pad syndrome and ethnicity, employment, patellar alignment, Hoffa's fat pad composition, physical activity and other pathological processes cannot be established due to lack of evidence. No studies reporting on treatment for Hoffa's fat pad syndrome were identified. Though weight loss and gene therapy may provide symptomatic relief, further research is required to corroborate these claims.

CONCLUSION

Current evidence suggests that high patellar height, TT-TG distance, and trochlear angle predispose the development of Hoffa's fat pad syndrome. In addition, trochlear inclination, sulcus angle, patient age and BMI do not seem to be associated with this condition. Further research should explore the link between Hoffa's fat pad syndrome and sport as well as other conditions pertaining to the knee. In addition, further study evaluating treatment approaches for Hoffa's fat pad syndrome is required.

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.

A comparison of anterior knee pain, kneeling pain and functional outcomes in suprapatellar versus infrapatellar tibial nailing

INTRODUCTION

Anterior knee pain and kneeling pain are some of the most common complications following intramedullary nailing of tibial shaft fractures. With the increased uptake of suprapatellar nailing at our institution, we undertook a service evaluation to assess anterior knee pain and kneeling pain in patients who underwent the suprapatellar tibial nailing technique compared with the infrapatellar approach.

METHODOLOGY

Data from all consecutive intramedullary tibial nailing operations between January 2014 and July 2017 were analysed from a prospectively collected database. All acute diaphyseal fracture nailing procedures were included. All patients were reviewed between six-month and four-year post-operation. Each patient was asked to complete a standardised questionnaire with three main outcome measures: pain on kneeling, presence of anterior knee pain and the severity of pain.

RESULTS

After exclusions, a total of 148 patients were identified. A total of 102 responses were received, 41 in the infrapatellar group (73.2%) and 61 in the suprapatellar group (66.3%). A longer time from surgery to telephone follow-up response was noted in the infrapatellar group: 32.4 months (interquartile range, 16.1) vs. 19.3 months (interquartile range, 17.4), p < 0.001. A trend towards lower reported anterior knee pain was noted in the suprapatellar group (67.9% VS 53.7%). Most patients reported mild or no pain on kneeling, with no significant difference between the two groups. There was also no significant difference in severity of knee pain between the two groups and no significant effect on the Kujala score.

CONCLUSION

With the comparable pain outcomes between the two groups, our analysis supports the continued use of the suprapatellar tibial nailing technique for tibial shaft fractures at our institution.

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.

Arthroscopic Treatment of Infrapatellar Fat Pad Impingement between the Patella and Femoral Trochlea: Comparison of the Clinical Outcomes of Partial and Subtotal Resection

Purpose

To compare the clinical outcomes of arthroscopic partial and subtotal resection of the impinged infrapatellar fat pad (IFP).

Materials and Methods

This study enrolled 55 patients with IFP impingement who underwent partial resection (n=29, P group) or subtotal resection (n=26, S group). Clinical outcomes at least 2 years postoperatively were evaluated using a visual analog scale (VAS) for pain, the International Knee Documentation Committee (IKDC) 2000 subjective knee score, and the Lysholm score.

Results

In the P group, the preoperative mean VAS, IKDC 2000, and Lysholm scores were 5.6±0.61, 47.5±7.41, and 42.5±7.17, respectively, which improved significantly to 1.4±0.63, 70.9±6.15, and 82.2±7.61, respectively (all, p≤0.001). In the S group, the preoperative mean VAS, IKDC 2000, and Lysholm scores were 5.7±0.43, 47.7±9.09, and 45.2±4.18, respectively, which improved significantly to 1.8±0.77, 71.9±9.33, and 82.3±6.01, respectively (all, p≤0.001). There were no significant differences in any outcome measure between the groups at the final follow-up.

Conclusions

Arthroscopic resection of the impinged IFP between the patella and femoral trochlea resulted in favorable clinical outcomes regardless of whether the resection was partial or subtotal. Thus, partial resection can be an appropriate treatment option, considering partial resection was as effective as subtotal resection and retained more of the IFP.

Firefighters Have a Higher Incidence of Trochlear Chondral Lesions than the Normal Population

BACKGROUND

Firefighters' knees are subjected to significant dynamic and static forces, resulting in increased knee complaints and a higher relative risk of osteoarthrosis, compared with aged-matched office workers. Firefighters wear or carry a total of 80 to 100 lbs. of gear while performing intensive physical activity.

PURPOSE/QUESTION

The purpose of this study was to determine whether a central femoral trochlear lesion was observed in firefighters undergoing knee arthroscopy for other diagnoses.

METHODS

A retrospective chart review of 159 knees in 146 firefighters undergoing arthroscopy for treatment of acute meniscal injury or anterior cruciate ligament reconstruction over a 14-year period was undertaken. Patient demographics, physical examination results, trochlear lesion size and grade, and firehouse type (engine vs. ladder company) and firefighter position (seniority) were recorded. Comparisons of characteristics in those with and without trochlear lesions were performed.

RESULTS

The average patient age was 42.2 years (range, 27 to 64 years). Ninety-eight knees (62%) had trochlear lesions and 33 knees (51%) had matching patellar lesions. Patients with lesions were older (43.2 vs. 40.5 years). Mean trochlear lesion size was 19.5 ± 13.7 mm by 18.9 ± 12.4 mm. Lesion grade distribution was grade 1 or 2 in 24 knees (24%) and grade 3 or 4 in 67 knees (44%). Trochlear lesion presence was associated with a body mass index of over 30. Current engine company members had more advanced lesions.

CONCLUSIONS

A "firefighter's trochlea" was present in the majority of firefighters undergoing knee arthroscopy. Higher age and longer tenure as a firefighter prior to surgery were associated with more advanced lesions. Firefighters working in engine companies at the time of arthroscopy were at a greater risk of developing low-grade lesions but not high-grade lesions. Firefighters move between ladder and engine companies, thus a definitive association with company type cannot be reached in this retrospective study. This lesion may reflect the increase in patellofemoral biomechanical stresses secondary to the physical demands of the occupation.

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.

Nonligamentous Soft Tissue Pathology About the Knee: A Review

Knee pain is one of the most frequent complaints evaluated by orthopedic surgeons. It encompasses a broad range of pathology and can present in a variety of ways. Most of this pain can be attributed to essential structures of the knee, including the menisci, cruciate or collateral ligaments, and articular cartilage. However, there are underrecognized structures in and around the knee that can frequently be a cause of knee pathology and pain. Knee pain stemming from these structures may be missed or incorrectly diagnosed, and these patients often present for second and third opinions because of failure to diagnose and treat the underlying pathology. The synovial plica, suprapatellar pouch, lateral retinaculum, infrapatellar fat pad, and infrapatellar branch of the saphenous nerve are less common but still significant causes of knee pain. Although initial treatment involves various nonoperative modalities, operative treatment is often warranted. Operative and nonoperative management of these soft tissue structures may occur in isolation or with concomitant procedures, including knee ligament reconstruction, total knee arthroplasty, tibial tuberosity osteotomy, or lysis of adhesions. With proper recognition of the role of these structures in knee pain, the orthopedic surgeon can offer a valuable primary or adjunctive treatment option for patients with knee pain, especially those without localizing signs of meniscal, ligamentous, or cartilage damage.

Magnetic resonance imaging of Hoffa's fat pad and relevance for osteoarthritis research: a narrative review

OBJECTIVE

To give an illustrative overview of Hoffa's fat pad pathology with a radiologic emphasis on the anatomy, on technical considerations, and on imaging differential diagnoses in the context of osteoarthritis (OA) imaging research.

DESIGN

A PubMed database search including only English literature and covering a 20 year period was performed. The search was based on but no limited to the query terms "Hoffa", "Hoffa's fat pad" or "infrapatellar fat pad (IPFP)" in combination with "synovitis", "OA", and "magnetic resonance imaging (MRI)". The literature search yielded 289 publications that were screened for relevance; additional references were included when these were considered of importance.

RESULTS

Several anatomic variants and pathologic conditions may be encountered when assessing Hoffa's fat pad including tumors and tumor-like lesions such as osteochondroma, tenosynovial giant cell tumor (TGCT) (and pigmented nodular synovitis) and arthrofibrosis, traumatic changes including contusions and anatomic variants such as recesses. The latter may be accountable for differences in cross-sectional area or volume changes over time. Signal changes are commonly used in OA research as surrogate markers for synovitis but are non-specific findings.

CONCLUSIONS

Quantitative approaches to evaluate 3D parameters of Hoffa's fat pad are increasingly applied and their role in regard to structural progression and clinical manifestations of disease needs to be further elucidated. In applying such approaches, knowledge of the detailed anatomy and potential pitfalls that may be a result of anatomical variants, inflammatory disease manifestations and additional diverse pathologies encountered seems to be paramount.

Character, Incidence, and Predictors of Knee Pain and Activity After Infrapatellar Intramedullary Nailing of an Isolated Tibia Fracture

OBJECTIVE

To study the activity and incidence of knee pain after sustaining an isolated tibia fracture treated with an infrapatellar intramedullary nail at 1 year.

DESIGN

Retrospective review of prospective cohort.

SETTING

Multicenter Academic and Community hospitals.

PATIENTS

Four hundred thirty-seven patients with an isolated tibia fracture completed a 12-month assessment on pain and self-reported activity.

INTERVENTION

Infrapatellar intramedullary nail.

OUTCOMES

Demographic information, comorbid conditions, injury characteristics, and surgical technique were recorded. Knee pain was defined on a 1-7 scale with 1 being "no pain" and 7 being a "very great deal of pain." Knee pain >4 was considered clinically significant. Patients reported if they were "able," "able with difficulty," or "unable" to perform the following activities: kneel, run, climb stairs, and walk prolonged. Variables were tested in multilevel multivariable regression analyses.

RESULTS

In knee pain, 11% of patients reported a "good deal" to a "very great deal" of pain (>4), and 52% of patients reported "no" or "very little" pain at 12 months. In activity at 12 months, 26% and 29% of patients were unable to kneel or run, respectively, and 31% and 35% of patients, respectively, stated they were able with difficulty or unable to use stairs or walk.

CONCLUSIONS

Clinically significant knee pain (>4/7) was present in 11% of patients 1 year after a tibia fracture. Of note, 31%-71% of patients had difficulty performing or were unable to perform routine daily activities of kneeling, running, and stair climbing, or walking prolonged distances.

LEVEL OF EVIDENCE

Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.

Holistic approach to understanding anterior knee pain. Clinical implications

Anterior knee pain is one of the most frequent reasons for consultation within knee conditions. The aetiology is not well known, which explains the sometimes unpredictable results of its treatment. Normally, when we see a patient in the office with anterior knee pain, we only study and focus on the knee. If we do this, we are making a big mistake. We must not forget to evaluate the pelvis and proximal femur, as well as the psychological factors that modulate the course of the illness. Both the pelvifemoral dysfunction as well as the psychological factors (anxiety, depression, catastrophization and kinesiophobia) must be included in our therapeutic targets of the multidisciplinary treatment of anterior knee pain. We must not only focus on the knee, we must remember to "look up" to fully understand what is happening and be able to solve this difficult problem. The aetiology of anterior knee pain is multifactorial. Therefore, diagnosis and treatment of patellofemoral disorders must be individualized. Our findings stress the importance of tailoring physiotherapy, surgery and psycho-educational interventions to each patient.

Arthroscopic resection of fat pad lesions and infrapatellar contractures

The infrapatellar fat pad (IFP), also known as Hoffa's fat pad, may be a common site of pain in the knee because of its susceptibility to injury and its vast innervation and vascular supply. Patients who have trauma to the IFP may undergo a process of hemorrhage, inflammation, and fibrosis that may become painful. Patients with Hoffa's disease in whom conservative treatment with medications, physical therapy, and injections has failed may receive significant pain relief and benefit from undergoing arthroscopic subtotal removal of the IFP. We describe a safe and effective way to perform this procedure allowing excellent visualization through the use of a superolateral viewing portal.

T2 relaxometry of the infrapatellar fat pad after arthroscopic surgery

OBJECTIVE

To investigate the T2 relaxation values of the infrapatellar fat pad (IFP) after arthroscopic surgery.

MATERIALS AND METHODS

This study was approved by the institutional review board; all individuals signed informed consent. We performed MRI in 16 knees from 8 subjects. Prior to imaging, each subject had unilateral arthroscopic knee surgery and an asymptomatic non-operated contralateral knee. We used a 10-echo multiple-TE fast-spin echo pulse sequence for creation of T2 relaxation time maps. Two musculoskeletal radiologists independently placed regions of interest in the IFP, suprapatellar subcutaneous and deep intermuscular adipose tissue. Qualitative assessments were performed to assess fibrotic changes affecting patellar retinaculum and IFP. Statistical analyses of T2 values determined differences between groups, correlation with time after surgery, and cut-off values to differentiate groups.

RESULTS

The average time between arthroscopy and imaging was 3.5 ± 0.4 years. IFP of knees with prior surgery had significantly shorter mean T2 values (133 ± 14 ms) compared with control knees (147 ± 8 ms, P = 0.03). There was no significant difference between operated and control knees regarding T2 values of suprapatellar subcutaneous (P = 0.3) or deep intermuscular adipose tissue (P = 0.2). There was no correlation between IFP T2 values and time after surgery (P > 0.2). IFP T2 values ≤ 139 ms had 75 % sensitivity and 88 % specificity in identifying prior arthroscopy.

CONCLUSION

Shortening of T2 relaxation values is present in IFP chronically after arthroscopic surgery and may be an indicator of adipose tissue fibrosis.

Fat pad entrapment at the hip: a new diagnosis

PURPOSE

To establish if a positive impingement sign in femoroacetabular impingement (FAI) may result from entrapment of the fat pad located at the anterior head-neck junction of the upper femur. This fat pad is routinely removed before any cam lesion excision.

METHODS

We report a prospective study of 142 consecutive hip arthroscopies for symptomatic FAI where the aim was to remove the arthroscopically identified area of impingement, not necessarily to create a spherical femoral head. Patients were divided into two groups. Group 1 (n = 92; 34 females, 58 males), where a cam-type bony FAI lesion was identified and excised in addition to the fat pad which overlay it, and Group 2 (n = 50; 29 females, 21 males) where the only identified point of impingement was a prominent fat pad. In this situation the fat pad was excised in isolation and the underlying bone preserved. Patients were assessed preoperatively, at six weeks, six months, one year and two years with a modified Harris hip score (mHHS).

RESULTS

Both groups were comparable preoperatively for mean age, mean alpha angle and mean anterior offset ratio. Both groups improved significantly after surgery at all time points. However, Group 1 (fat pad and bone resection) demonstrated 16.0% improvement in mHHS by two years while for Group 2 (fat pad resection only) the improvement was 18.9% (p = 0.628).

CONCLUSIONS

The fat pad found at the anterior head/neck junction of the hip joint can be a source of pain and we propose fat pad entrapment as a new, previously undescribed diagnosis. Our findings also suggest that a large number of cam lesions are being excised unnecessarily and that further efforts should be made to understand the role of the fat pad as a source of groin discomfort.

LEVEL OF EVIDENCE

Level IV, case series.

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.

Is there an association between superolateral Hoffa fat pad edema on MRI and clinical evidence of fat pad impingement?

OBJECTIVE

Patients with symptomatic Hoffa fat pad impingement often exhibit fat pad edema on MRI. We studied two patient groups to determine the association between MRI fat pad edema and clinical symptoms of Hoffa fat pad impingement.

MATERIALS AND METHODS

We studied 34 consecutive patients with an MRI diagnosis of fat pad edema and no injury in the prior year (group 1) and 47 consecutive patients with a knee MRI examination and no injury in the prior year (group 2). Two sports medicine physicians reviewed the clinical records to confirm or exclude symptomatic fat pad impingement. Two musculoskeletal radiologists independently scored 12 Hoffa fat pad locations for the presence of edema, noting the epicenter.

RESULTS

Seventeen of the 34 patients in group 1 had clinical symptoms of fat pad impingement, with all 34 having fat pad edema. There was no association between clinical fat pad impingement and fat pad edema in any specific location (p > 0.183), but patients with fat pad impingement had a greater number of regions of edema (p = 0.005, 0.026 for two observers). In group 2, all four patients with clinical fat pad impingement had MRI fat pad edema, but 38 of the 43 patients without clinical impingement had MRI fat edema; 11 of the 38 had edema centered in the superolateral fat pad.

CONCLUSION

Edema is present on MRI in the superolateral region of Hoffa fat pad in patients with clinical fat pad impingement. However, such edema can also be present in patients without symptoms of fat pad impingement.

Evaluation and treatment of disorders of the infrapatellar fat pad

The infrapatellar fat pad (IFP), also known as Hoffa's fat pad, is an intracapsular, extrasynovial structure that fills the anterior knee compartment, and is richly vascularized and innervated. Its degree of innervation, the proportion of substance-P-containing fibres and close relationship to its posterior synovial lining implicates IFP pathologies as a source of infrapatellar knee pain. Though the precise function of the IFP is unknown, studies have shown that it may play a role in the biomechanics of the knee or act as a store for reparative cells after injury. Inflammation and fibrosis within the IFP, caused by trauma and/or surgery can lead to a variety of arthrofibrotic lesions including Hoffa's disease, anterior interval scarring and infrapatellar contracture syndrome. Lesions or mass-like abnormalities rarely occur within the IFP, but their classification can be narrowed down by radiographical appearance. Clinically, patients with IFP pathology present with burning or aching infrapatellar anterior knee pain that can often be reproduced on physical exam with manoeuvres designed to produce impingement. Sagittal MRI is the most common imaging technique used to assess IFP pathology including fibrosis, inflammation, oedema, and mass-like lesions. IFP pathology is often successfully managed with physical therapy. Passive taping is used to unload or shorten an inflamed IFP, and closed chain quadriceps exercises can improve lower limb control and patellar congruence. Training of the gluteus medius and stretching the anterior hip may help to decrease internal rotation of the hip and valgus force at the knee. Gait training and avoiding hyperextension can also be used for long-term management. Injections within the IFP of local anaesthetic plus corticosteroids and IFP ablation with ultrasound guided alcohol injections have been successfully explored as treatments for IFP pain. IFP pathology refractory to physical therapy can be approached through a variety of operative treatments. Arthroscopic partial resection for IFP impingement and Hoffa's disease has showed favourable results; however, total excision of the IFP performed concomitantly with total knee arthroplasty (TKA) resulted in worse results when compared with TKA alone. Arthroscopic debridement of IFP fibrosis has been successfully used to treat extension block following anterior cruciate ligament reconstruction, and arthroscopic anterior interval release has been an effective treatment for pain associated with anterior interval scarring. Arthroscopic resection of infrapatellar plicae and denervation of the inferior pole of the patella have also been shown to be effective treatments for refractory infrapatellar pain.