Localized nodular synovitis of the infrapatellar fat pad

We report a case of localized nodular synovitis of the infrapatellar fat pad impinging on the patellofemoral joint causing limitation of extension. Arthroscopy involved use of a superolateral portal because location of lesion hindered access via a conventional anterior portal. The infrapatellar mass impinged in the patellofemoral joint upon knee extension and retracted upon flexion. Superior-superior triangulation allowed for complete excision of the mass.     

髌下脂肪垫紊乱的研究进展

髌下脂肪垫(infrapatellar fat pad,IFP)也被称为Hoffa's脂肪垫,位于膝关节囊内,滑膜外,充填于膝关节前室内,其内有丰富的血管神经支配,参与膝关节生物力学以及损伤细胞修复中的某些过程。外伤或手术等因素会导致IFP发生纤维化、水肿、炎症等病理变化,从而发生紊乱综合征。IFP由德国外科医师Albert Hoffa在1904年发现并命名,是导致髌下膝关节疼痛的主要原因之一。临床上主要通过体检和磁共振对其进行诊断。治疗方法有物理疗法、局部麻醉阻滞和关节镜切除术等。     

Patellar tendon length after knee arthroplasty with and without preservation of the infrapatellar fat pad

Our aim was to assess whether there was any significant difference in change in patellar tendon length after knee arthroplasty, when the infrapatellar fat pad was either preserved or excised. Three-year radiographic follow-up was studied on 73 primary knee arthroplasty patients. The infrapatellar fat pad was completely preserved in 38 cases and completely excised in 35. At 3 years there was a significant patellar tendon shortening of 4.2% (P = .0004) in the fat pad excision group and no significant change in the fat pad preservation group (P = .82). The difference between the 2 groups was significant (P = .004). Our results show that patella tendon length does not always shorten after knee arthroplasty and that preservation of the infrapatellar fat pad may be a factor in preventing such shortening.     

膝关节骨性关节炎合并髌下脂肪垫劳损的B超诊断与治疗

膝关节骨性关节炎是一种常见病，是引起膝关节痛的主要原因之一。膝关节骨性关节炎与髌下脂肪垫劳损的研究甚少，我们从1995—2003年对106例膝关节骨性关节炎患者进行了髌下脂肪垫B超检查，同时与150例正常膝关节进行了对比。并对确诊为膝关节髌下脂肪垫劳损患者采用透明质酸钠关节腔注射，效果优良，现报告如下。     

The nature of anterior knee pain following injection of hypertonic saline into the infrapatellar fat pad.

The infrapatellar fat pad has been implicated as a possible source of anterior knee pain. This study examined the nature, distribution and time-course of experimentally induced pain in the infrapatellar fat pad. Hypertonic saline (5%) was injected into the medial fat pad of 11 healthy individuals with no history of knee pain. Severity of pain was assessed at rest and during activity using an 11 point numerical rating scale (NRS) at regular intervals over 15-30 min following injection. Participants described the size of the pain region from a series of different sized circles while the area and type of pain was established from a body chart and the McGill pain questionnaire. The effect of pain on temperature-pain threshold and sensory thresholds of the anterior knee was assessed. Participants generally reported a deep aching pain that peaked in severity around 3 min and gradually declined over 15 min. Pain levels were not altered by clinical manoeuvres designed to impinge the fat pad. The size of the pain region was related to pain intensity. Pain was most commonly felt in the region of the fat pad medial to the patella, although some individuals reported proximal referred pain as far as the groin region. Thermal and sensory thresholds were not altered at a region close to the injection site during the experimental pain. These results suggest that nociceptive stimulation of the infrapatellar fat pad may cause anterior knee pain that is not necessarily confined locally particularly if pain is severe. This has implications for the investigation of pathological structures in patients presenting clinically with anterior knee pain and provides an experimental model of anterior knee pain.     

兔髌下脂肪垫损伤动物模型的制备和组织病理变化

目的;制备髌下脂肪垫损伤的动物模型,观察其病理变化。方法：损伤组应用水囊在膝关节前方压迫髌下脂肪垫,对所压迫的膝关节进行屈伸运动,取下脂肪垫与滑膜,进行ＨＥ染色。结果：损伤后的指肪垫及滑膜可见脂肪垫内小血管扩张,血管内充血,及小片状出血,脂肪间质水肿,淋巴细胞,浆细胞肥大细胞和巨噬细胞浸润,可风脂肪垫表面滑膜细胞增生,及滑膜绒毛状增生。结论：脂肪垫及滑膜符合急性挤压伤的表现,并出现一些慢性损伤的变     

Distribution of substance-P nerves inside the infrapatellar fat pad and the adjacent synovial tissue: a neurohistological approach to anterior knee pain syndrome

Introduction The purpose of the study was to determine the distribution and number of nerves inside the infrapatellar fat pad and the adjacent synovium, in particular with regards to nociceptive substance-P nerves.Materials and methods The infrapatellar fat pad of the knee was resected from 21 patients (4 male, 17 female, mean age 69 years) during the course of standard total knee arthroplasty operations performed in our clinic. The fat pad was dissected into five standardized segments, fixed in formalin and embedded in paraffin. Immunohistochemical techniques using antibodies against S-100 protein and substance-P (SP) were employed to determine and specify the nerves.Results Studying all the detectable nerves present in 50 observation fields (200-fold magnification), we found an average of 106 S-100 versus 25 SP nerves (24%) in the synovium and 27 S-100- versus 7 SP nerves (26%) in the interior of the fat pad. The total nerve count was significantly ( P <0.001) higher in the synovium than in the fat pad for both marker types. The number of S-100 nerves was significantly ( P <0.05) higher in the central and lateral segments of the fat pad, while SP nerves were equally distributed throughout all segments of the fat-pad. SP nerves were significantly more frequently associated with blood vessels inside the fat pad (43%, P <0.05) than in the synovial tissue (28%).Conclusion The occurrence and distribution of SP nerves inside the infrapatellar fat pad suggest a nociceptive function and a neurohistological role in anterior knee pain syndrome. The data support the hypothesis that a neurogenous infection of the infrapatellar fat pad could contribute to anterior knee pain syndrome.     

Influence of an infrapatellar fat pad edema on patellofemoral biomechanics and knee kinematics: a possible relation to the anterior knee pain syndrome

Introduction  An edema of the infrapatellar fat pad following knee arthroscopy or in case of chronic anterior knee pain syndrome is suspected to increase the patellofemoral pressure by a modification of the patellofemoral glide mechanism. The study was performed to evaluate this hypothesis. Materials and methods  Isokinetic knee extension from 120° of flexion to full extension was simulated on 10 human knee cadaver specimens (six males, four females, average age at death 42 years) using a knee kinemator. Joint kinematics was evaluated by ultrasound sensors (CMS 100^TM, Zebris, Isny, Germany), and retro-patellar contact pressure was measured using a thin-film resistive ink pressure system (K-Scan^TM 4000, Tekscan, Boston). Infrapatellar tissue pressure was analyzed using a closed sensor cell which was implanted inside the fat pad (GISMA, Buggingen, Germany). An inflatable fluid cell was implanted by ultrasound control in the center of the infrapatellar fat pad and filled subsequently with water to simulate a fat pad edema. All parameters were recorded and analyzed from 0 to 5 ml volume of the fluid cell. Results  Simulating a fat pad edema resulted in a significant (P < 0.01) increase of the infrapatellar fat pad pressure (247 mbar at 0 ml to 615 mbar at 5 ml volume). In knee extension and flexion the patella flexion (sagittal plane) was decreased while we did not find any other significant influence of the edema on knee kinematics. During the analysis of the patellofemoral biomechanics, a simulated fat pad edema resulted in a significant (P < 0.05) decrease of the patellofemoral force between 120° of knee flexion and full extension. The contact area was reduced significantly near extension (0°–30°) by an average of 10% while the contact pressure was reduced at the entire range of motion up to 20%. Conclusion  An edema of the infrapatellar fat pad does not cause an increase of the patellofemoral pressure or a significant alteration of the patellofemoral glide mechanism. Anterior knee pain in case of a fat pad edema may be related to a significant increase of the tissue pressure and possible histochemical reactions. The study was funded by the German Speaking Association of Artroscopy (AGA).     

Preponderance of sensory versus sympathetic nerve fibers and increased cellularity in the infrapatellar fat pad in anterior knee pain patients after primary arthroplasty

Sensory nerve fibers transmit pain perception and secrete pro‐inflammatory substance P (SP). Sympathetic nerve fibers secrete anti‐inflammatory norepinephrine and endogenous opioids, which inhibit pain perception in a bidirectional crosstalk with sensory fibers. In patients with anterior knee pain after primary arthroplasty of the knee (AKP), this study investigated in parallel the innervation of the infrapatellar fat pad by sensory and sympathetic nerve fibers. A total of 32 patients with osteoarthritis (OA) of the knee (n = 10), AKP after primary knee joint replacement (n = 7), and OA of the hip (n = 15) were included. Sensory nerve fibers were semiquantitatively detected by immunohistochemistry against SP, and sympathetic nerve fibers were stained with an antibody against tyrosine hydroxylase. Cellular density of the tissue was investigated by counting cell nuclei. The density of sympathetic nerve fibers in the fat tissue was similar in knee OA as compared to AKP. In the fat tissue, density of sensory substance P–positive nerve fibers was higher in AKP than in knee OA, which was not observed in the fibrosis capsule of the fat pad. The preponderance of sensory over sympathetic nerve fibers was accompanied by an increased cellular density in fat tissue in patients with AKP compared to knee OA. A positive correlation existed between cellularity and sensory nerve fiber density in fat tissue. This study revealed a preponderance of sensory over sympathetic innervation in the infrapatellar fat pad in AKP after primary arthroplasty of the knee, which possibly leads to aggravation and continuation of AKP and local inflammation. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:342–350, 2008     

髌下脂肪垫对全膝关节置换术后患者膝关节功能恢复影响的meta分析

目的通过meta分析评价髌下脂肪垫对全膝关节置换患者术后功能恢复的影响。 方法检索Cochrane Library、Embase、PubMed英文数据库和万方数据库、维普数据库以及中国知网数据库有关于髌下脂肪垫对全膝关节置换术后影响的临床随机对照试验（RCTs）和回顾性队列研究实验（RCSs）,使用Revman5.3软件进行meta分析。 结果最终共纳入8篇文献,其中英文文献4篇,中文文献4篇,共纳入全膝关节置换术病例1 474例,其中髌下脂肪垫切除术696例,髌下脂肪垫保留组778例。与髌下脂肪垫切除相比,髌下脂肪垫保留组可降低术后髌韧挛缩（MD=-2.34,95% CI：-3.38~-1.31,P<0.05）,麦克马斯特骨关节炎指数（WOMAC）评分（MD=2.34,95% CI：2.04~2.65,P<0.05）;提高膝关节功能评分（MD=-0.77,95% CI：-1.02~-0.52,P<0.05）,降低术后膝关节前侧疼痛发生率（RR=12.58,95% CI：3.24~48.75,P<0.05）。两组患者在术后膝关节活动度（MD=-7.53,95% CI：-20.27~5.21,P>0.05）,髌腱长度与髌骨最大长轴比值（Insall-Savatict）评分法（MD=-0.04,95% CI：-0.09~0.01,P>0.05）;术后膝关节返修率：（RD=0.01,95% CI：-0.01~0.02,P>0.05）方面无明显差异。 结论与髌下脂肪垫去除组相比,全膝关节置换术后髌下脂肪垫保留可以降低髌韧带痉挛程度,提高膝关节功能评分,同时可降低膝关节前侧疼痛。     

Age‐associated increases in the size of the infrapatellar fat pad in knee osteoarthritis as measured by 3T MRI

Obesity, as a primary risk factor for osteoarthritis (OA), has been shown to alter joint loading, but may also result in metabolic changes characterized by chronic, low‐level inflammation due to increased circulating levels of adipose‐derived cytokines, or “adipokines.” The presence of the infrapatellar fat pad in the knee suggests that local changes in adipokine concentrations may influence knee OA. This study examined the hypotheses that the volume of the infrapatellar fat pad is correlated to the body mass index (BMI) of OA patients, and that fat pad volume is greater in subjects with OA. Fat pad volume was measured in sequential magnetic resonance (MR) images taken over one year in a cohort of 15 control and 15 knee OA subjects. No differences were observed in the fat pad volume between the two groups at baseline, 3, 6, or 12 months. In control subjects, no significant correlations were present between any parameters (age, BMI, weight, volume of fat pad at any time point). However, in the osteoarthritic group, fat pad volume was correlated with age at every time point. One possible explanation is that local factors related to knee OA may also induce enlargement of the fat pad with age. Alternatively, subjects who are prone to growth or enlargement of the fat pad may also be more prone to symptomatic OA. These findings provide intriguing preliminary data on the potential role of the infrapatellar fat pad in OA, although additional study is required to better understand the mechanisms of this relationship. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:1149–1154, 2010     

The usefulness of ultrasound and the posterior fat pad sign in pulled elbow

IntroductionA pulled elbow is a common cause of acute elbow pain that is generally managed by a reduction maneuver without radiographic examination. However, children with atypical presentation with no history of abrupt longitudinal traction should undergo elbow imaging. This study aimed to investigate plain radiography findings and determine the usefulness of ultrasonography (US) in atypical pulled elbow.Materials and methodsWe retrospectively reviewed the medical records and images of 37 (22 males) consecutive patients with pulled elbow who presented with an atypical history or failed reduction between April 2015 and September 2018. Mean age at presentation was 4.34 years (range, 1.25–9.5 years). Of the 37 elbows, 20 were left elbows. The injury mechanism, incidence of the posterior fat pad sign on plain radiographs, and characteristic US findings, pre- and post- reduction, were investigated.ResultsThe original mechanisms of injury included slipping (n = 14), rolling over the arm (n = 7), vague history (n = 6), falling down (n = 6), abrupt longitudinal traction (n = 2), and direct injury (n = 2). On plain radiographs, six of the 37 elbows (16%) showed the posterior fat pad sign. Before the reduction, an entrapped supinator, a pathognomonic sign of pulled elbow, was identified on US in all cases. After reduction, the characteristic US findings showed a disentangled and swollen supinator (100%) and restored annular ligament (100%) in all successful cases. Although a click was not felt in three cases, the reductions were considered successful because the annular ligament was restored on US with free elbow motion.ConclusionPulled elbow may be caused by atypical mechanisms of injury, such as slipping and rolling over the arm. Clinicians should be aware of the possibility of the posterior fat pad sign on plain radiographs of pulled elbow to prevent unnecessary immobilization. In such circumstances, US is a useful method for detecting an entrapped supinator and confirming adequate reduction via restoration of the annular ligament in children with atypical pulled elbow.     

Infrapatellar fat pad volume and Hoffa-synovitis after ACL reconstruction: Association with early osteoarthritis features and pain over 5 years

Infrapatellar fat pad (IPFP) morphology and Hoffa-synovitis may be relevant to the development and progression of post-traumatic osteoarthritis (OA). We aimed to compare IPFP volume and Hoffa-synovitis in participants with anterior cruciate ligament reconstruction (ACLR) and uninjured controls, and to determine their association with prevalent and worsening early knee OA features and pain in participants post-ACLR. We assessed IPFP volume and Hoffa-synovitis from magnetic resonance imaging (MRI) in 111 participants 1-year post-ACLR and 20 uninjured controls. Patellofemoral and tibiofemoral cartilage and bone marrow lesions (BMLs) were assessed from MRIs at 1 and 5 years post-ACLR, and worsening defined as any longitudinal increase in lesion size/severity. IPFP volume and Hoffa-synovitis prevalence were compared between groups with analysis of covariance and χ ² tests, respectively. Generalized linear models assessed the relation of IPFP volume and Hoffa-synovitis to prevalent and worsening features of OA and knee pain (Knee injury and Osteoarthritis Outcome Score—Pain Subscale, Anterior Knee Pain Scale). No significant between-group differences were observed in IPFP volume (ACLR 34.39 ± 7.29cm³, Control 34.27 ± 7.56cm³) and Hoffa-synovitis (ACLR 61%, Control 80%). Greater IPFP volume at 1-year post-ACLR was associated with greater odds of patellofemoral BMLs at 1-year (odds ratio [OR] [95% confidence intervals]: 1.104 [1.016, 1.200]) and worsening tibiofemoral cartilage lesions at 5-year post-ACLR (OR: 1.234 [1.026, 1.483]). Hoffa-synovitis at 1-year post-ACLR was associated with greater odds of worsening patellofemoral BMLs at 5-year post-ACLR (OR: 7.465 [1.291, 43.169]). In conclusion, IPFP volume and Hoffa-synovitis prevalence are similar between individuals 1-year post-ACLR and controls. Greater IPFP volume and Hoffa-synovitis appear to be associated with the presence and worsening of some early OA features in those post-ACLR, but not pain.