Increase In Contact Pressure Research Articles

Electromagnetic noise of pantograph arc under low current conditions

With the continuous increase of electric locomotive running speed, electromagnetic noise of pantograph arc gets more and more serious and has become a kind of safety risk of electric railway's operation. With the self-developed electromagnetic noise experimental system, 66 groups of radiation elect romagnetic noise experiments were carried out by changing contact pressure, contact current and sliding speed. The experimental circuit was powered by a 220VAC low current source. The experimental materials are immersed copper-carbon slide and Cu contact wire respectively. Electromagnetic noise of pantograph arc mainly distributes in 30-570 MHz, and the noise in 30-60 MHz band is obviously higher than that of background. With the increase of frequency, the electromagnetic noise firstly decreases, then increases, and finally decreases to background noise. When the speed is lower than the critical condition of generating pantograph arc, the electromagnetic noise is independent of contact pressure and the amplitude is very small. When the speed is between 30 km/h and 40 km/h, the noise reduces with the increase of contact pressure. When the speed is higher than 50 km/h, the electromagnetic noise becomes intensive and fluctuates with the increase of contact pressure. It can be used to further research on the suppression methods of the electromagnetic noise emission.

Elastic–Plastic Sinusoidal Waviness Contact Under Combined Normal and Tangential Loading

The behavior of an elastic plastic contact between a deformable three-dimensional sinusoidal asperity and a rigid flat under combined normal and tangential loading is investigated using the finite element method. The sliding inception is determined by the maximum shear stress criterion. The resulting junction growth and static friction coefficient are investigated. It is found that for a general case, at the low dimensionless contact pressures, the static friction coefficient decreases sharply with increasing contact pressure. However, at the medium contact pressures, the static friction coefficient nearly approaches a constant value (around 0.23). Nevertheless, as the contact pressure further increases, the static friction coefficient keeps on reducing at a linear rate. The effects of material properties, geometric properties and critical shear strength on the static friction coefficient are also studied. An empirical expression for the static friction coefficient is provided.

Transtibial repair in medial meniscus root avulsions; 2 years clinical results

Introduction:Medial meniscus posterior root avulsion injuries exhibited a similar extent of increasing contact pressure and decreasing contact area, as that in the total meniscectomized knee and resulting articular cartilage loss in medial compartment of the knee joint. Although partial meniscectomy is the traditional treatment in symptomatic posterior root avulsions, this method can not restore cartilage loss. The recommended surgical treatment for posterior root avulsions is repair in non degenerated knees.Patients and methods:Arthroscopic transtibial repair was performed in 11 patients who were diagnosed as symptomatic posterior root avulsions with clinical examination and magnetic resonance imaging findings and minimum 2 years results were evaluated. There were 8 women and 3 men, and the mean age of the patients were 51 (46-58). The mean time interval between injury and surgery was 4 weeks (5 days and 8 weeks). Conservative treatment was given to all of patients except one, and surgical treatment was performed for patients whose mechanical sypmtoms and pain weren’t relieved at the end of conservative treatment. The repair method was arthroscopic pull-out technique with fixation of the posterior attachment area through a tibial tunnel. Walking 4-6 weeks non-weight bearing with two crutches and physical treatment was given that includes muscle strengthening and range of motion exercises. Patients were evaluated with preoperative and 2 years postoperative Lysholm knee scores, clinical examination and radiographic changes.Results:Mean Lysholm scores were increased preoperative from 55 to postoperative 86 that was found statictically significant. In ten patients complaints were resolved after surgical treatment and daily living began normally after surgery. In one patient arthroscopic partial meniscectomy was done due to rerupture after five months from index surgery. In two patients medial joint space narrowing was found radiologically at the end of two years but there were no clinical complaints.Conclusions:Repair must be considered in symptomatic medial meniscus posterior root avulsions also in older age if there is no degenerative osteoarthritis. The root tear that has similar effects as total meniscectomy will cause cartilage loss if not treated.

Contact size, frequency and cyclic normal force effects on Ti–6Al–4V fretting wear processes: An approach combining friction power and contact oxygenation

We present fretting wear analysis of a dry Ti-6Al-4V cylinder/plane contact, investigating sliding frequency, contact size, and cyclic normal force effects. The investigation showed that easy contact oxygenation promoted by low contact pressure, low frequency, small contact size and varying normal force favored a U-shape fretting scar morphology and high abrasive wear rates. By contrast, increasing contact pressure, frequency and contact size by reducing the contact oxygenation in the center of the contact promoted adhesive metal/metal interactions, transfers and TTS structures. This induced a W-shape fretting scar and lower wear rates. XPS analyses confirmed this description, highlighting Ti-nitriding processes in the under-oxygenated Ti transfers. A friction energy power density approach is introduced to predict wear rate and the U-to-W shape transition.

3-D computer modelling of malunited posterior malleolar fractures: effect of fragment size and offset on ankle stability, contact pressure and pattern

BackgroundThe positioning of the fracture fragment of a posterior malleolus fracture is critical to healing and a successful outcome as malunion of a posterior malleolar fracture, a condition seen in clinical practice, can affect the dynamics of the ankle joint, cause posterolateral rotational subluxation of the talus and ultimately lead to destruction of the joint. Current consensus is to employ anatomic reduction with internal fixation when the fragment size is larger than 25 to 33% of the tibial plafond.MethodsA 3-dimensional finite element (FE) model of ankle was developed in order to investigate the effect of fragment size (6–15 mm) and offset (1–4 mm) of a malunited posterior malleolus on tibiotalar joint contact area, pressure, motion of joint and ligament forces. Three positions of the joint were simulated; neutral position, 20° dorsiflexion and 30° plantarflexion.ResultsCompared to the intact joint our model predicted that contact area was greater in all malunion scenarios considered. In general, the joint contact area was affected more by section length than section offset. In addition fibula contact area played a role in all the malunion cases.ConclusionsWe found no evidence to support the current consensus of fixing posterior malleolus fractures of greater than 25% of the tibial plafond. Our model predicted joint instability only with the highest level of fracture in a loaded limb at an extreme position of dorsiflexion. No increase of peak contact pressure as a result of malunion was predicted but contact pattern was modified. The results of our study support the view that in cases of posterior malleolar fracture, posttraumatic osteoarthritis occurs as a result of load on areas of cartilage not used to loading rather than an increase in contact pressure. Ankle repositioning resulted in increased force in two ankle ligaments. Our finding could explain commonly reported clinical observations.

Rapid Analyses of Polyetheretherketone Wear Characteristics by Accelerated Wear Testing with Microfabricated Surfaces for Artificial Joint Systems

Wear particle-induced biological responses are the major factors resulting in the loosening and then failure of total joint arthroplasties. It is feasible to improve the lubrication and reduce the wear of artificial joint system. Polyetheretherketone (PEEK) is considered as a potential bearing material due to its mechanical characteristics of resistance to fatigue strain. The PEEK wear particles have been indicated to be involved in biological responses in vitro, and further studies regarding the wear phenomena and wear particle generation are needed. In this study, we have established an accelerated wear testing system with microfabricated surfaces. Various contact pressures and lubricants have been utilized in the accelerated wear tests. Our results showed that increasing contact pressure resulted in an increase of wear particle sizes and wear rate, and the size of PEEK wear particles can be controlled by the feature size of microfabricated surfaces. These results provided the information rapidly about factors that affect the morphology and amount of PEEK wear particles and can be applied in the future for application of PEEK on the biological articulation system.

Numerical analyses of stress induced damage during a reciprocating lubricated test of fecmo sps sintered alloy

Contact-induced stresses during reciprocating movement may lead to surface/subsurface damage. Sintering processes may be used to produce advanced materials with improved wear and friction behavior, but the volume fraction of pores may compromise structural integrity under high loads or fatigue conditions. In this work, the Finite Element Method (FEM) is applied to analyze contact-induced stress distributions produced by surface and inner pores on boundary lubrication condition during reciprocating tests. Material microstructure and mechanical properties are based on sintered FeCMo produced by Spark Plasma Sintering (SPS) process. Results indicate different behavior of surface pores with the increase of contact pressure. It was also observed that pores close to the surface promote a shift of high stress towards the surface, which may improve pitting resistance.

Changes in Contact Area in Meniscus Horizontal Cleavage Tears Subjected to Repair and Resection

To assess the changes in tibiofemoral contact pressure and contact area in human knees with a horizontal cleavage tear before and after treatment. Ten human cadaveric knees were tested. Pressure sensors were placed under the medial meniscus and the knees were loaded at twice the body weight for 20 cycles at 0°, 10°, and 20° of flexion. Contact area and pressure were recorded for the intact meniscus, the meniscus with a horizontal cleavage tear, after meniscal repair, after partial meniscectomy (single leaflet), and after subtotal meniscectomy (double leaflet). The presence of a horizontal cleavage tear significantly increased average peak contact pressure and reduced effective average tibiofemoral contact area at all flexion angles tested compared with the intact state (P < .03). There was approximately a 70% increase in contact pressure after creation of the horizontal cleavage tear. Repairing the horizontal cleavage tear restored peak contact pressures and areas to within 15% of baseline, statistically similar to the intact state atall angles tested (P < .05). Partial meniscectomy and subtotal meniscectomy significantly increased average peak contactpressure and reduced average contact area at all degrees of flexion compared with the intact state (P < .05). The presence of a horizontal cleavage tear in the medial meniscus causes a significant reduction in contact area and a significant elevation in contact pressure. These changes may accelerate joint degeneration. A suture-based repair of these horizontal cleavage tears returns the contact area and contact pressure to nearly normal, whereas both partial and subtotal meniscectomy lead to significant reductions in contact area and significant elevations in contact pressure within the knee. Repairing horizontal cleavage tears may lead to improved clinical outcomes by preserving meniscal tissue and the meniscal function. Understanding contact area and peak contact pressure resulting from differing strategies for treating horizontal cleavage tears will allow the surgeon to evaluate the best strategy for treating his or her patients who present with this meniscal pathology.

Fretting Fatigue Experiment and Analysis of AlSi9Cu2Mg Alloy.

An investigation was carried out in order to study the fretting fatigue behavior of an AlSi9Cu2Mg aluminum alloy. The fretting fatigue tests of AlSi9Cu2Mg were performed using a specially designed testing machine. The failure mechanism of fretting fatigue was explored by studying the fracture surfaces, fretting scars, fretting debris, and micro-hardness of fretting fatigue specimens using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and micro Vickers hardness test techniques. The experimental results show that the fretting fatigue limit (42 MPa) is significantly reduced to approximately 47% of the plain fatigue limit (89 MPa) under 62.5 MPa contact pressure. Furthermore, the fretting fatigue life decreases with increasing alternating stress and increasing contact pressure. The examination results suggest that the stress concentrates induced by oxidation-assisted wear on the contact interface led to the earlier initiation and propagation of crack under the fretting condition.

Effect of lingual gauze swab placement on pulse oximeter readings in anaesthetised dogs and cats

This study aimed to evaluate the effect of lingual gauze swab placement on pulse oximeter readings in anaesthetised dogs and cats. Following anaesthetic induction, the following pulse oximeter probe configurations...

Tibiofemoral Contact Mechanics with Horizontal Cleavage Tear and Resection of the Medial Meniscus in the Human Knee.

The meniscus is known to increase the contact area and decrease contact pressure in the tibiofemoral compartments of the knee. Radial tears of the meniscal root attachment along with partial resections of the torn meniscal tissue decrease the contact area and increase pressure; however, there is a lack of information on the effects of a horizontal cleavage tear (HCT) and partial leaf meniscectomy of such tears on tibiofemoral contact pressure and contact area. Twelve fresh-frozen human cadaveric knees were tested under 10 conditions: 5 serial conditions of posterior medial meniscectomy (intact meniscus, HCT, repaired HCT, inferior leaf resection, and resection of both inferior and superior leaves), each at 2 knee flexion angles (0° and 60°) under an 800-N axial load. Tekscan sensors (model 4000) were used to measure the contact pressure and contact area. HCT and HCT repair resulted in small changes in the contact area and an increase in contact pressure compared with the intact condition. Resection of the inferior leaf resulted in significantly decreased contact area (to a mean 82.3% of the intact condition at 0° of flexion and 81.8% at 60° of flexion; p < 0.05) and increased peak contact pressure (a mean 36.3% increase at 0° flexion and 43.2% increase at 60° flexion; p < 0.05) in the medial compartment. Further resection of the remaining superior leaf resulted in additional significant decreases in contact area (to a mean 60.1% of the intact condition at 0° of flexion and 49.7% at 60° of flexion; p < 0.05) and increases in peak contact pressure (a mean 79.2% increase at 0° of flexion and 74.9% increase at 60° of flexion; p < 0.05). Resection of meniscal tissue forming the inferior leaf of an HCT resulted in substantially decreased contact area and increased contact pressure. Additional resection of the superior leaf resulted in a further significant decrease in contact area and increase in contact pressure in the medial compartment. Repair or minimal resection of meniscal tissue of an HCT may be preferred to complete leaf resection to maintain knee tibiofemoral contact mechanics.

Radiocapitellar contact characteristics during prosthetic radial head subluxation

Metallic radial head prostheses are often used in the management of comminuted radial head fractures and elbow instability. We hypothesized that during radiocapitellar subluxation, the contact pressure characteristics of an anatomic radial head prosthesis will more closely mimic those of the native radial head compared with a monopolar circular or a bipolar circular radial head design. With use of 6 fresh frozen cadaver elbows, mean radiocapitellar contact pressures, contact areas, and peak pressures of the native radial head were assessed at 0, 2, 4, and 6 mm of posterior subluxation. These assessments were repeated after the native radial head was replaced with anatomic, monopolar circular and bipolar circular prostheses. The joint contact pressures increased with the native and the prosthetic radial head subluxation. The mean contact pressures for the native radial head and anatomic prosthesis increased progressively and significantly from 0 to 6 mm of subluxation (native, 0.6 ± 0.0 MPa to 1.9 ± 0.2 MPa; anatomic, 0.7 ± 0.0 MPa to 2.1 ± 0.3 MPa; P < .0001). The contact pressures with the monopolar and bipolar prostheses were significantly higher at baseline and did not change significantly further with subluxation (monopolar, 2.0 ± 0.1 MPa to 2.2 ± 0.2 MPa [P = .31]; bipolar, 1.7 ± 0.1 MPa to 1.9 ± 0.1 MPa [P = .12]). The pattern of increase in contact pressures with the anatomic prosthesis mimicked that of the native radial head. Conversely, the circular prostheses started out with higher contact pressures that stayed elevated. The articular surface design of a radial head prosthesis is an important determinant of joint contact pressures.

Research on Sealing Properties and its Influence Factors of Spherical Mechanical Seal Based on ANSYS

When a marine stern shaft is bent with shafting misalignment and stern bearing wear factors, etc., the sealing properties of a plane mechanical seal is declined with the increase of both contact pressure and temperature of sealing surface, so a spherical mechanical seal which can automatically adjust the contact state of sealing surfaces is proposed to replace the plane mechanical seal in order to solve the aforementioned problems. The sealing properties of a spherical mechanical seal is directly influenced by the sealing structure size such as sealing spherical radius, the distance between stator and rotary ring seats, inner and outer diameters of stator ring. The thermal-structure coupling model of the spherical mechanical seal in underwater vehicles is built with ANSYS finite element method, and the influence of structure size on the sealing performances of the spherical mechanical seal is discussed. The study results show that as spherical radius is increased, the contact region of spherical sealing surfaces is decreased and the opening region is expanded, and the highest temperature and maximum contact pressure on the spherical sealing surfaces are raised. As inner or outer diameter of stator ring is increased, the maximum contact pressure of the former is raised, and one of the latter is declined, but the highest temperatures of both on sealing surfaces are enhanced linearly. When the distance between static and rotary ring seats is increased, the highest temperature of sealing surface and maximum contact pressure are increased in a nonlinear way. These conclusions are of important theoretical significance and engineering application value for the structure optimization of spherical mechanical seals in vessels, particularly underwater vehicles.

ВЛИЯНИЕ ПРОТИВОИЗНОСНЫХ ПРИСАДОК НА ПАРАМЕТРЫ ГИДРОДИНАМИЧЕСКОГО РЕЖИМА ТРЕНИЯ В ПОДШИПНИКАХ ДВС

An essential condition to ensure an engine life having 300,000 – 1 000,000 km according to race consists in assurance of a minimum wear rate of crankshaft bearings. For such units as connectingrod bearings a maximum allowable value of bearing brass wear makes 100 mkm which corresponds to an integral linear wear intensity of 10-14 …10-13 that is possible only at a hydrodynamic mode of friction actually at all modes of engines operations. Ensuring liquid friction in all range of contact pressures is achieved both through design methods, and technological ones. To the latter belongs first of all the application of lubricants with high wearresistant properties. In this connection arises a problem to reveal a mechanism and degree of the effect of lubricant components upon a range of contact pressure where liquid friction is realized. This paper reports the experimental evidences of the increase of contact pressures at which is achieved a minimum value of a constant of friction at the introduction in lubricant a standard wear-resistant additive – dialkyldithiophosphate of zinc (ZDDP). So, at the introduction in coal oil without additives I-20A (viscosity type ISO 32) 1.25 and 2.5% ZGGP maxi-mum contact pressure at which is realized a hydrody-namic mode of friction increases by 1.8 and 2 times accordingly. Because of impossibility to explain experimental data by a chemical interaction of ZDDP with surface material of tribo-coupling there is offered and substantiated a mechanism of ZDDP influence upon rheological parameters of lubricant in a separation layer. A rheological model allowing the computation of the wearresistant additives influence upon a value of hydrodynamic pressures in a lubrication layer is of-fered. The idea of the initiation by a wearresistant additive of multimolecular adsorption of lubricant on the surface of tribocoupling may be used for the optimization of ZDDP structure and also for the prognostication of changes in pressure coefficient of viscosity in a lubrication layer.

Measurements of interfacial thermal contact conductance between pressed alloys at low temperatures

Interfacial thermal contact conductance is the primary factor limiting the heat transfer in many cryogenic engineering applications. This paper presents an experimental apparatus to measure interfacial thermal contact conductance between pressed alloys in a vacuum environment at low temperatures. The measurements of thermal contact conductance between pressed alloys are conducted by using the developed apparatus. The results show that the contact conductance increases with the decrease of surface roughness, the increase of interface temperature and contact pressure. The temperature dependence of thermal conductivity and mechanical properties is analyzed to explain the results. Thermal contact conductance of a pair of stainless steel specimens is obtained in the interface temperature range of 135–245K and in the contact pressure range of 1–9MPa. The results are regressed as a power function of temperature and load. Thermal conductance is also obtained between aluminums as well as between stainless steel and aluminum. The load exponents of the regressed relations for different contacts are compared. Existing theoretical models (the Cooper-Mikic-Yovanovich plastic model, the Mikic elastic model and the improved Kimura model) are reviewed and compared with the experimental results. The Cooper-Mikic-Yovanovich model predictions are found to be in good agreement with experimental results, especially with measurements between aluminums.

Three-dimensional finite analysis of acetabular contact pressure and contact area during normal walking

This study aims to analyze the contact areas and pressure distributions between the femoral head and mortar during normal walking using a three-dimensional finite element model (3D-FEM). Computed tomography (CT) scanning technology and a computer image processing system were used to establish the 3D-FEM. The acetabular mortar model was used to simulate the pressures during 32 consecutive normal walking phases and the contact areas at different phases were calculated. The distribution of the pressure peak values during the 32 consecutive normal walking phases was bimodal, which reached the peak (4.2 Mpa) at the initial phase where the contact area was significantly higher than that at the stepping phase. The sites that always kept contact were concentrated on the acetabular top and leaned inwards, while the anterior and posterior acetabular horns had no pressure concentration. The pressure distributions of acetabular cartilage at different phases were significantly different, the zone of increased pressure at the support phase distributed at the acetabular top area, while that at the stepping phase distributed in the inside of acetabular cartilage. The zones of increased contact pressure and the distributions of acetabular contact areas had important significance towards clinical researches, and could indicate the inductive factors of acetabular osteoarthritis.

Effects of Contact Pressure and Sliding Speed on the Unlubricated Friction and Wear Properties of Zn-15Al-3Cu-1Si Alloy

ABSTRACTThe unlubricated friction and wear properties of Zn-15Al-3Cu-1Si alloy were studied over a range of contact pressure (1–5 MPa) and sliding speed (0.5–2.5 ms−1) for a sliding distance of 2,500 m using a block-on-disc type test machine. It was observed that as the contact pressure increased, the friction coefficient of the alloy decreased but its working temperature, surface roughness, and wear volume increased. Sliding speed had no significant effect on the friction coefficient of the alloy but increased its working temperature, surface roughness, and wear volume. It was also observed that the formation of a hard and brittle surface layer had a great influence on the wear behavior of the experimental alloy. The hardness and thickness of this layer increased with increasing contact pressure and sliding speed. However, contact pressure was found to be much more effective on the hardness of the surface layer of this alloy. Both adhesion and abrasion were observed to be the dominant wear mechanisms for the alloy under the given sliding conditions. The results obtained from the friction and wear tests are discussed in terms of the test conditions and microstructural changes that take place during sliding.

Analytical Modelling of Elastic-Plastic Interference Fit Joints

The interference fit is a widely process, used to produce a joint assembly of two parts achieved by friction. It is a popular type of joint in machine elements and it is found in many field applications related to the automotive, aerospace, oil and gas and shipbuilding industries. Consequently, a better understanding of its limit behavior together with an accurate evaluation of the residual stresses generated by this process are very important for the design of mechanical components requiring high optimized performance. This work focuses on the analytical development of the residual stresses when the two assembled parts are circular cylinders and deform elasto-plastically under plane strain condition. The constitutive law that governs their material strain hardening behavior is assumed to follow a general power law which also covers the particular cases of elastic perfectly plastic and bilinear hardening. To validate the developed analytical model (AM), the finite element method (FEM) was used and the results showed good agreement between the two approaches. The obtained results show that the stresses increase when the interference value increases causing maximum stress intensity at the inner surface of the two assembled parts to exceed their material yield stress. After hollow shaft plastic collapse, any increase in interference results in a small increase in residual contact pressure with a large increase of the equivalent stresses localized at the hollow shaft inner surface. The method could be used to determine the maximum value of the interference in order to prevent assembly failure.

A finite element model to investigate the effect of ulnar variance on distal radioulnar joint mechanics.

Ulnocarpal impaction syndrome involves excessive loading of the ulnocarpal joint. Ulnar shortening osteotomies are an effective way to reduce ulnocarpal loading but alter contact mechanics at the distal radioulnar joint (DRUJ). This study used a computational model to investigate the relationship between ulnar length and DRUJ mechanics. Detailed, finite element models of the radius and ulna bones were constructed from magnetic resonance imaging data. The length of the ulna bone model was increased and decreased up to 5 mm in 1 mm increments. A computational model was used to predict joint contact at the DRUJ for each ulnar length. Lengthening the ulna caused a slight decrease in DRUJ contact pressure, with a more substantial decrease in contact area. Shortening the ulna caused a substantial increase in contact area, with a smaller increase in DRUJ contact pressure. The location of contact on the radial sigmoid notch changed with 2 mm lengthening and 3 mm shortening. The results of this study demonstrate the sensitivity of DRUJ contact to ulnar length changes, which may explain the DRUJ cartilage degeneration that often follows ulnar osteotomies. The joint contact model implemented in this study allowed the relationship between ulnar length and DRUJ contact to be examined systematically, in a way that is difficult to achieve through cadaveric experimentation. The results confirmed published experimental data showing an increased DRUJ contact pressure with ulnar shortening. It is important that clinicians consider the influence of ulnar osteotomies, not only on ulnocarpal loading but also on DRUJ mechanics. Copyright © 2016 John Wiley & Sons, Ltd.

Biomechanical Consequences of Excessive Patellar Distalization

Iatrogenic patellar baja can be a result of excessive tibial tubercle distalization or overtightented patellar tendon repair. Tubercle distalization is increasing in popularity for the treatment of recurrent patella instability. Clinically, patellar baja can present as a debilitating problem with motion loss, increased pain, and arthrosis progression. However, previous biomechanical studies have not shown an increase in patellofemoral joint contact pressures. The purpose of this study is to examine the patellofemoral contact pressure after a tibial tubercle distalization osteotomy. Ten matched pair fresh-frozen cadaveric knees were studied. Average Blackburne-Peel ratio of the native knees was 0.91. The knees were placed on a testing rig, with a fixed femur and tibia mobile through 90° of flexion. Individual quadriceps heads and the iliotibial band were separated and loaded with 205 N in anatomic directions using a weighted pulley system. A straight tubercle distalization osteotomy of 1 cm was performed and fixed with screws, with and without a lateral release. Patellofemoral contact pressures were measured at 0°, 10°, 20°, 30°, 45°, 60°, and 90° of flexion using pressure-sensitive films on the medial and lateral trochlea. The contact force, area and pressure were measured at the following states: (1) native knee, (2) with distalization and (3) distalization with lateral release. Average Blackburne-Peel ratio after distalization was 0.64. Tibial tubercle distalization resulted in a six fold increase in mean contact pressures at 0° (0.15 versus 0.90 MPa, p<0.001), and a 55% increase at 10° of flexion (0.70 versus 1.09 MPa, p=0.02). After distalization, total contact area was significantly higher at 0° of flexion (17.7 mm2 versus 58.4 mm2, p=0.02). Lateral release after distalization did not significantly change contact pressure (p>0.21). Our results suggest that patellar baja, as a result of excessive patellar distalization, can cause increased patellofemoral contact pressures during early flexion.