Correlating femoral shape with patellar kinematics in patients with patellofemoral pain

The etiology of patellofemoral pain is likely related to pathological femoral shape and soft‐tissue restraints imbalance. These factors may result in various maltracking patterns in patients with patellofemoral pain. Thus, we hypothesized that femoral shape influences patellofemoral kinematics, but that this influence differs between kinematically unique subgroups of patients with patellofemoral pain. 3D MRIs of 30 knees with patellofemoral pain and maltracking (“maltrackers”) and 33 knees of asymptomatic subjects were evaluated, retrospectively. Dynamic MRI was acquired during a flexion‐extension task. Maltrackers were divided into two subgroups (nonlateral and lateral maltrackers) based on previously defined kinematic criteria. Nine measures of femoral trochlear shape and two measures of patellar shape were quantified. These measures were correlated with patellofemoral kinematics. Differences were found in femoral shape between the maltracking and asymptomatic cohorts. Femoral shape parameters were associated with patellar kinematics in patients with patellofemoral pain and maltracking, but the correlations were unique across subgroups within this population. The ability to better categorize patients with patellofemoral pain will likely improve treatment by providing a more specific etiology of maltracking in individual patients. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:865–872, 2010     

Sectioning the medial patellofemoral ligament alters patellofemoral joint kinematics and contact mechanics

Medial patellofemoral ligament (MPFL) disruption may alter patellofemoral joint (PFJ) kinematics and contact mechanics, potentially causing pain and joint degeneration. In this controlled laboratory study, we investigated the hypothesis that MPFL transection would change patellar tracking and PFJ contact pressures and increase the distance between the attachment points of the MPFL. Eight fresh frozen dissected cadaveric knees were mounted in a rig with the quadriceps and ITB loaded to 205 N. An optical tracking system measured joint kinematics, and pressure sensitive film between the patella and trochlea measured PFJ contact pressures. Length patterns of the distance between the femoral and patellar attachments of the MPFL were measured using a suture led to a linear displacement transducer. Measurements were repeated with the MPFL intact and following MPFL transection. A significant increase in the distance between the patellar and femoral MPFL attachment points was noted following transection (p < 0.05). MPFL transection resulted in significantly increased lateral translation and lateral tilt of the patella in early flexion (p < 0.05). Peak and mean medial PFJ contact pressures were significantly reduced and peak lateral contact pressures significantly elevated in early knee flexion following MPFL transection (p < 0.05). MPFL transection resulted in significant alterations to PFJ tracking and contact pressures, which may affect articular cartilage health. © 2013 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 31:1423–1429, 2013     

Using real‐time MRI to quantify altered joint kinematics in subjects with patellofemoral pain and to evaluate the effects of a patellar brace or sleeve on joint motion

Abnormal patellofemoral joint motion is a possible cause of patellofemoral pain, and patellar braces are thought to alleviate pain by restoring normal joint kinematics. We evaluated whether females with patellofemoral pain exhibit abnormal patellofemoral joint kinematics during dynamic, weight‐bearing knee extension and assessed the effects of knee braces on patellofemoral motion. Real‐time magnetic resonance (MR) images of the patellofemoral joints of 36 female volunteers (13 pain‐free controls, 23 patellofemoral pain) were acquired during weight‐bearing knee extension. Pain subjects were also imaged while wearing a patellar‐stabilizing brace and a patellar sleeve. We measured axial‐plane kinematics from the images. Females with patellofemoral pain exhibited increased lateral translation of the patella for knee flexion angles between 0°and 50° (p = 0.03), and increased lateral tilt for knee flexion angles between 0° and 20° (p = 0.04). The brace and sleeve reduced the lateral translation of the patella; however, the brace reduced lateral displacement more than the sleeve (p = 0.006). The brace reduced patellar tilt near full extension (p = 0.001), while the sleeve had no effect on patellar tilt. Our results indicate that some subjects with patellofemoral pain exhibit abnormal weight‐bearing joint kinematics and that braces may be effective in reducing patellar maltracking in these subjects. Published by Wiley Periodicals, Inc. J Orthop Res 27: 571–577, 2009     

In‐vivo patellar tendon kinematics during weight‐bearing deep knee flexion

This study quantified in‐vivo 3D patellar tendon kinematics during weight‐bearing deep knee bend beyond 150°. Each knee was MRI scanned to create 3D bony models of the patella, tibia, femur, and the attachment sites of the patellar tendon on the distal patella and the tibial tubercle. Each attachment site was divided into lateral, central, and medial thirds. The subjects were then imaged using a dual fluoroscopic image system while performing a deep knee bend. The knee positions were determined using the bony models and the fluoroscopic images. The patellar tendon kinematics was analyzed using the relative positions of its patellar and tibial attachment sites. The relative elongations of all three portions of the patellar tendon increased similarly up to 60°. Beyond 60°, the relative elongation of the medial portion of the patellar tendon decreased as the knee flexed from 60° to 150° while those of the lateral and central portions showed continuous increases from 120° to 150°. At 150°, the relative elongation of the medial portion was significantly lower than that of the central portion. In four of seven knees, the patellar tendon impinged on the tibial bony surface at 120° and 150° of knee flexion. These data may provide useful insight into the intrinsic patellar tendon biomechanics during a weight‐bearing deep knee bend and could provide biomechanical guidelines for future development of total knee arthroplasties that are intended to restore normal knee function. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1596–1603, 2012     

Predicting three‐dimensional patellofemoral kinematics from static imaging‐based alignment measures

Patellofemoral pain syndrome causes significant discomfort and disability among much of the general population. Despite recent breakthroughs in dynamic three‐dimensional imaging technologies to assess pathological patellofemoral motion, such tools remain costly for clinical diagnostics applications. Thus, this study investigated whether three‐dimensional patellofemoral kinematics could be predicted from routine two‐dimensional static measures of patellofemoral joint alignment quantified from magnetic resonance imaging (MRI) data acquired in full knee extension. Twenty‐six volunteers clinically diagnosed with patellofemoral pain (19 F/7 M, 25.9 ± 11.1 years) and 26 control subjects (19 F/7 M, 25.3 ± 7.7 years) were included in this IRB‐approved study. Static three‐dimensional sagittal T1‐weighted gradient recall echo and dynamic MRI scans were acquired. For the dynamic image acquisition, subjects cyclically flexed and extended their knee (at 30 cycles/min) while a full cine‐phase contrast MRI set (24 time frames of anatomic images and x‐, y‐, and z‐velocity images) was acquired. From these data, static measures of patellofemoral alignment and three‐dimensional patellofemoral kinematics were derived. Single and multiple regressions between static and kinematic variables were evaluated. Although shown reliable, the static MRI measures could only partially predict patellofemoral kinematics, with r²‐values ranging from 16% to 77%. This makes it imperitave that the current precise, accurate, 3D, dynamic imaging techniques be translated into clinical tools. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31: 441–447, 2013     

In‐vivo patellar tracking in individuals with patellofemoral pain and healthy individuals

Understanding of the exact cause of patellofemoral pain has been limited by methodological challenges to evaluate in‐vivo joint motion. This study compared six degree‐of‐freedom patellar motion during a dynamic lunge task between individuals with patellofemoral pain and healthy individuals. Knee joints of eight females with patellofemoral pain and ten healthy females were imaged using a CT scanner in supine lying position, then by a dual‐orthogonal fluoroscope while they performed a lunge. To quantify patellar motion, the three‐dimensional models of the knee bones, reconstructed from CT scans, were registered on the fluoroscopy images using the Fluomotion registration software. At full knee extension, the patella was in a significantly laterally tilted (PFP: 11.77° ± 7.58° vs. healthy: 0.86° ± 4.90°; p = 0.002) and superiorly shifted (PFP: 17.49 ± 8.44 mm vs. healthy: 9.47 ± 6.16 mm, p = 0. 033) position in the patellofemoral pain group compared with the healthy group. There were also significant differences between the groups for patellar tilt at 45°, 60°, and 75° of knee flexion, and for superior‐inferior shift of the patella at 30° flexion (p ≤ 0.031). In the non‐weight‐bearing knee extended position, the patella was in a significantly laterally tilted position in the patellofemoral pain group (7.44° ± 6.53°) compared with the healthy group (0.71° ± 4.99°). These findings suggest the critical role of passive and active patellar stabilizers as potential causative factors for patellar malalignment/maltracking. Future studies should investigate the associations between patellar kinematics with joint morphology, muscle activity, and tendon function in a same sample for a thorough understanding of the causes of patellofemoral pain. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2193–2201, 2018.

     

Measuring polyethylene wear in total knee arthroplasty by RSA: Differences between weight‐bearing and non‐weight‐bearing positioning

Measuring the minimum‐joint‐space‐width (mJSW) in total knee arthroplasty (TKA) in Roentgen stereophotogrammetric analysis (RSA) provides valuable information on polyethylene wear, a leading cause for TKA failure. Most existing studies use non‐weight‐bearing (NWB) patient positioning. The latter may compromise mJSW measurements due to knee laxity with subsequent non‐contact between the TKA components. We investigated the difference in mJSW between weight‐bearing (WB) and NWB images and the association with mediolateral (ML) knee stability. At one‐year follow‐up, 23 TKAs were included from an ongoing RSA study, and ML stability was evaluated. For each examination, the mJSW and femoral‐tibial contact locations were measured. A linear regression model was used to analyze the association between the mJSW difference (NWB–WB) with the ML stability and contact locations. The mean mJSW difference was 0.28 mm medially and 0.20 mm laterally. Four TKAs had medium (5–9°) and 19 TKAs had high (<5°) ML stability. A higher mJSW difference was found for TKAs with medium stability (0.36 mm, P = 0.01). In conclusion, mJSW measurements in existing (NWB) RSA studies are influenced by knee laxity, but may still provide information on wear progression based on TKA with high ML stability. A direct comparison of mJSW measurements from WB and NWB data is not possible. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:613–617, 2014.     

Understanding patellofemoral pain with maltracking in the presence of joint laxity: Complete 3D in vivo patellofemoral and tibiofemoral kinematics

Patellofemoral pain is widely accepted as one of the most common pathologies involving the knee, yet the etiology of this pain is still an open debate. Generalized joint laxity has been associated with patellofemoral pain, but is not often discussed as a potential source of patellar maltracking. Thus, the objective of this study was to compare the complete 6 degree of freedom patellofemoral and tibiofemoral kinematics from a group of patients diagnosed with patellofemoral pain syndrome and maltracking to those from an asymptomatic population. The following null hypotheses were tested: kinematic alterations in patellofemoral maltracking are limited to the axial plane; knee joint kinematics are the same in maltrackers with and without generalized joint laxity (defined by a clinical diagnosis of Ehlers Danlos Syndrome); and no correlations exist between tibiofemoral and patellofemoral kinematics or within patellofemoral kinematics. This study demonstrated that alterations in patellofemoral kinematics, associated with patellofemoral pain, are not limited to the axial plane, minimal correlations exist between patellofemoral and tibiofemoral kinematics, and distinct subgroups likely exist within the general population of maltrackers. Being able to identify subgroups correctly within the omnibus diagnosis of patellar maltracking is a crucial step in correctly defining the pathophysiology and the eventual treatment of these patients. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27: 561–570, 2009     

Three‐dimensional patellar motion at the natural knee during passive flexion/extension. An in vitro study

Patellar maltracking may result in many patellofemoral joint (PFJ) disorders in the natural and replaced knee. The literature providing quantitative reference for normal PFJ kinematics according to which patellar maltracking could be identified is still limited. The aim of this study was to measure in vitro accurately all six‐degrees‐of‐freedom of patellar motion with respect to the femur and tibia on 20 normal specimens. A state‐of‐the‐art knee navigation system, suitably adapted for this study aim, was used. Anatomical reference frames were defined for the femur, tibia, and patella according to international recommendations. PFJ flexion, tilt, rotation, and translations were calculated in addition to standard tibiofemoral joint (TFJ) kinematics. All motion patterns were found to be generally repeatable intra‐/interspecimens. PFJ flexion was 62% of the corresponding TFJ flexion range; tilt and translations along femoral mediolateral and tibial proximodistal axes during TFJ flexion were found with medial, lateral, and distal trends and within 12°, 6 and 9 mm, respectively. No clear pattern for PFJ rotation was observed. These results concur with comparable reports from the literature and contribute to the controversial knowledge on normal PFJ kinematics. Their consistence provides fundamental information to understand orthopedic treatment of the knee and for possible relevant measurements intraoperatively. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:1426–1431, 2009     

Knee kinematics in medial osteoarthritis during in vivo weight‐bearing activities

Dynamic knee kinematics were analyzed for medial osteoarthritic (OA) knees in three activities, including two types of maximum knee flexion. Continuous x‐ray images of kneeling, squatting, and stair climbing motions were taken using a large flat panel detector. CT‐derived bone models were used for the model registration‐based 3D kinematic measurements. Three‐dimensional joint kinematics and contact locations were determined using two methods: bone‐fixed coordinate systems and by interrogation of CT‐based bone model surfaces. The femur exhibited gradual external rotation with knee flexion for kneeling and squatting activities, and gradual internal rotation with knee extension for stair climbing. From 100° to 120° flexion, contact locations showed a medial pivot pattern similar to normal knees. However, knees with medial OA displayed a femoral internal rotation bias and less posterior translation when compared with normal knees. A classic screw‐home movement was not observed in OA knees near extension. Decreased variability with both activities and methods of calculation were demonstrated for all three activities. In conclusion, the weight‐bearing kinematics of patients with medial OA differs from normal knees. Pathological changes of the articulating surfaces and the ligaments correspond to observed abnormalities in knee kinematics. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:1555–1561, 2009     

Influence of Patellar Morphology Classified by Wiberg Classification on Knee Joint Function and Patellofemoral Tracking After Total Knee Arthroplasty Without Patellar Resurfacing

BackgroundTo evaluate the influence of patellar morphology on knee joint function and patellofemoral tracking in patients with primary osteoarthritis after total knee arthroplasty (TKA) without patellar resurfacing.MethodsWe performed a retrospective study of 156 patients with primary osteoarthritis who underwent TKA without patellar resurfacing from April 2018 to July 2019. As per Wiberg classification, patients were divided into Wiberg type I (group A, n = 38), II (group B, n = 88), and III (group C, n = 30) groups. The clinical data, postoperative follow-up data, and radiological data between three groups were compared.ResultsThere was no statistically significant difference in the HSS score and Feller score between the three groups before surgery and at each follow-up point after surgery (P > .05). At the last follow-up, there were no significant differences in the height and relative thickness of the patella between the three groups (P > .05). However, the incidence of anterior knee pain was significantly higher in group C than in the group B (P < .05). The patellar tilt angle was significantly larger in group C than in the groups A and B (both P < .05). The patellar facet angle was significantly larger in group A than in group B and C, which was also significantly larger in group B than in group C (both P < .05).ConclusionPatients with three different morphologic types of the patella both exhibited improved knee joint function after TKA, however, patients with Wiberg type Ⅲ patella were more prone to have poor patellofemoral tracking and anterior knee pain after surgery.     

Patellar tilt correlates with vastus lateralis: vastus medialis activation ratio in maltracking patellofemoral pain patients

Patellofemoral (PF) pain is a common ailment of the lower extremity. A theorized cause for pain is patellar maltracking due to vasti muscle activation imbalance, represented as large vastus lateralis:vastus medialis (VL:VM) activation ratios. However, evidence relating vasti muscle activation imbalance to patellar maltracking is limited. The purpose of this study was to investigate the relationship between VL:VM activation ratio and patellar tracking measures, patellar tilt and bisect offset, in PF pain subjects and pain-free controls. We evaluated VL:VM activation ratio and VM activation delay relative to VL activation in 39 PF pain subjects and 15 pain-free controls during walking. We classified the PF pain subjects into normal tracking and maltracking groups based on patellar tilt and bisect offset measured from weight-bearing magnetic resonance imaging. Patellar tilt correlated with VL:VM activation ratio only in PF pain subjects classified as maltrackers. This suggests that a clinical intervention targeting vasti muscle activation imbalance may be effective only in PF pain subjects classified as maltrackers.     

Patellar maltracking is prevalent among patellofemoral pain subjects with patella alta: An upright,weightbearing MRI study

The purpose of this study is to determine if patellar maltracking is more prevalent among patellofemoral (PF) pain subjects with patella alta compared to subjects with normal patella height. We imaged 37 PF pain and 15 pain free subjects in an open‐configuration magnetic resonance imaging scanner while they stood in a weightbearing posture. We measured patella height using the Caton–Deschamps, Blackburne–Peel, Insall–Salvati, Modified Insall–Salvati, and Patellotrochlear indices, and classified the subjects into patella alta and normal patella height groups. We measured patella tilt and bisect offset from oblique‐axial plane images, and classified the subjects into maltracking and normal tracking groups. Patellar maltracking was more prevalent among PF pain subjects with patella alta compared to PF pain subjects with normal patella height (two‐tailed Fisher's exact test, p < 0.050). Using the Caton–Deschamps index, 67% (8/12) of PF pain subjects with patella alta were maltrackers, whereas only 16% (4/25) of PF pain subjects with normal patella height were maltrackers. Patellofemoral pain subjects classified as maltrackers displayed a greater patella height compared to the pain free and PF pain subjects classified as normal trackers (two‐tailed unpaired t‐tests with Bonferroni correction, p < 0.017). This study adds to our understanding of PF pain in two ways—(1) we demonstrate that patellar maltracking is more prevalent in PF pain subjects with patella alta compared to subjects with normal patella height; and (2) we show greater patella height in PF pain subjects compared to pain free subjects using four indices commonly used in clinics. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31: 448–457, 2013     

Patients with patellofemoral pain exhibit elevated bone metabolic activity at the patellofemoral joint

Patellofemoral pain is characterized by pain behind the kneecap and is often thought to be due to high stress at the patellofemoral joint. While we cannot measure bone stress in vivo, we can visualize bone metabolic activity using ¹⁸F NaF PET/CT, which may be related to bone stress. Our goals were to use ¹⁸F NaF PET/CT to evaluate whether subjects with patellofemoral pain exhibit elevated bone metabolic activity and to determine whether bone metabolic activity correlates with pain intensity. We examined 20 subjects diagnosed with patellofemoral pain. All subjects received an ¹⁸F NaF PET/CT scan of their knees. Uptake of ¹⁸F NaF in the patella and trochlea was quantified by computing the standardized uptake value and normalizing by the background tracer uptake in bone. We detected increased tracer uptake in 85% of the painful knees examined. We found that the painful knees exhibited increased tracer uptake compared to the pain‐free knees of four subjects with unilateral pain (P = 0.0006). We also found a correlation between increasing tracer uptake and increasing pain intensity (r² = 0.55; P = 0.0005). The implication of these results is that patellofemoral pain may be related to bone metabolic activity at the patellofemoral joint. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 30:209–213, 2012     

Patellofemoral kinematics during knee flexion-extension: an in vitro study.

The purpose of this work was to obtain kinematics data for the normal human patellofemoral joint in vitro. Eight fresh-frozen cadaver knees were used. The heads of the quadriceps were separated, and the knees mounted in a kinematics rig. The femoral axis was aligned with an electromagnetic transmitter. The six heads of the quadriceps, including vasti medialis and lateralis obliquus, were loaded via cables according to their physiological cross-sectional areas and orientations. Magnetic trackers were mounted on the patella and tibia. The knee was flexed-extended against the extending muscle action, and patellar tracking was measured in six degrees of freedom. As the knee flexed, the patella flexed by 0.7 times the tibiofemoral flexion angle. It also translated medially 4 mm to engage the trochlear groove at 20 degrees knee flexion, then translated to 7 mm lateral by 90 degrees knee flexion. The patella tilted progressively to 7 degrees lateral by 90 degrees knee flexion, and patellar medial-lateral rotation was usually less than 3 degrees. This is believed to be the first set of patellar tracking data obtained in both flexion and extension motion while the patella was acted on by a full set of quadriceps muscle tensions acting in physiological directions. These data may be used in future studies of the effects of pathologies on patellar tracking.     

Appraisal and summary of patellofemoral pain clinical practice guideline

ObjectiveThe purpose of this commentary was to critically appraise the patellofemoral pain clinical practice guideline published by the Academy of Orthopaedic Physical Therapy in 2019 and to summarize their recommendations for chiropractic practice.MethodsQuality and reporting of this guideline was assessed with the Appraisal of Guidelines for Research and Evaluation II (AGREE II) instrument. Three reviewers independently scored between 1–7 (strongly disagree-strongly agree) for 23 items organized into six quality domains.ResultsAGREE II quality domain scores ranged between 57%–98%, with overall quality of the recommendation rated 89%. The guideline contained evidence summaries and/or recommendations for three topics: impairment/function-based diagnosis; examination; and interventions.ConclusionBased on its methodological quality, we recommend the use of this guideline for the examination, diagnosis, and management of patellofemoral pain in chiropractic practice. A summary of recommendations from this guideline is presented for use within the scope of chiropractic practice in Canada.     

髌内外侧稳定结构与髌股关节稳定性实验研究

目的 :了解髌内外侧稳定结构对髌骨的稳定作用,探讨临床中松解髌外侧支持带的治疗作用及效果,为临床治疗髌骨不稳提供生物力学依据。方法:6例新鲜膝关节标本,对股四头肌进行加载(模拟肌力正常的情况),在不同屈曲度,对髌骨施加外侧方移位载荷,使髌骨外侧半脱位,读取记录载荷大小。干预1:松解髌内侧支持带(模拟病理状态),重复上述操作,读取记录载荷大小;干预2:在干预1的基础上进一步松解外侧支持带(模拟手术治疗),重复上述操作,读取记录载荷大小。结果:松解髌内侧支持带后,使髌骨半脱位的载荷比支持带完整时减小,差异有统计学意义(P0.05)。进一步松解外侧支持带,半脱位载荷进一步减小,但与干预1差异无统计学意义(P0.05)。结论:髌内侧支持带在维持髌骨稳定及髌股关节正常运动轨迹中有重要作用,在临床治疗复发性髌骨脱位或半脱位时,应该重视髌内侧支持带的修复重建,单纯松解外侧支持带的方法并非最佳选择。     

Simulation of patella alta and the implications for in vitro patellar tracking in the ovine stifle joint

Patella alta is associated with adverse cartilage adaptations, patellofemoral pain, and instability. It is defined by a relatively long patellar tendon and patella positioned in a more proximal location within the patellar groove of the femur. This study used the ovine stifle joint model to investigate the effect of patellar tendon lengthening on the 3D passive kinematics of the patellofemoral and tibiofemoral joints. Eight patellar tendons were lengthened in 2 mm increments up to a maximum of 12 mm (20%) using a device placed in series with the transected patellar tendon. Three‐dimensional kinematics were measured in the intact joint and at each increment of patellar tendon length (L_T) during passively induced tibiofemoral flexion. Patellar flexion angle was linearly correlated with tibial flexion angle in the intact joint, and this correlation persisted after tendon lengthening (R = 0.897–0.965, p < 0.01). Patellofemoral kinematics expressed as a function of tibial flexion angle were significantly altered by L_T increases >9%. In contrast, when patellofemoral kinematics were expressed as a function of patellar flexion angle they were not significantly altered by increases in L_T. Tibiofemoral kinematics were not affected by the L_T increases. These results demonstrate that for a given tibial flexion angle, patellar tendon lengthening alters the patellar flexion angle. However, for a given patellar flexion angle, the orientation of the patella in the remaining five degrees of freedom is unchanged, implying a repeatable path of patellar motion. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1789–1797, 2012     

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).