Fuji Pressure-sensitive Film Research Articles

Contact mechanics after mattress suture repair of medial meniscus vertical longitudinal tear: an in vitro study.

Most studies have concentrated on the changes in contact pressure and area on the tibiofemoral joint. This study compared the contact mechanics underneath the medial meniscus of a repaired vertical longitudinal tear with that of the intact or the torn ones. In this controlled laboratory study, a 1000 N compressive axial load was applied to eight fresh-frozen cadaveric knees at four flexion angles and four loading conditions using a custom testing apparatus attached to a material testing machine. Intact knees, knees with a medial meniscus vertical longitudinal tear, and knees after meniscal repair were tested. The peak contact pressure and area underneath the meniscus were measured using Fuji pressure-sensitive film. A medial meniscus vertical longitudinal tear significantly increased the contact pressure and decreased contact area underneath the meniscus compared with those at the intact meniscus under all tested biomechanical conditions, and repair of the tear can restore the contact pressure and area in most conditions. While the repaired group showed a significantly higher or similar contact pressure compared with the tear group at 90° neutral knee position and at 60°, 90° 5 N·m-external rotation and 134 N-anterior tibial translation, and 5 N·m-internal rotation at all flexion angles. The contact area corresponding to the aberrant result of the contact pressure in the repaired group was lower than in the intact meniscus group. The contact mechanics underneath the meniscus of the repaired medial meniscus vertical longitudinal tear were significantly improved compared with the corresponding tear conditions in most cases, while the contact pressure and area at some certain status after repair were not significantly different from those of the corresponding tear conditions.

3D-printed Talar Components for the Reconstruction of Large Osteochondral Lesions of the Talus

Category: Ankle Introduction/Purpose: The reconstruction of large osteochondral lesions of the talus (OLTs) presents a clinical challenge. In this study, a biomechanical experiment was performed using 3D-printed talar components for the reconstruction of large talar lesions, and intra-articular stress tests were conducted before and after implantation. Methods: Eight cadaveric ankle specimens were used in this study. After the specimen was fixed on an Instron mechanical testing machine, a piece of Fuji pressure-sensitive film was inserted into the articular cavity. A vertical pressure of 1500-N was applied to the ankle when it was in different positions, i.e. neutral, 10 degrees of dorsiflexion, and 14 degrees of plantar flexion. The total pressure-bearing area and the pressure intensity (MPa) on the talus were calculated to determine their changes before and after implantation. Results: The pressure-bearing area of the talus varied with the ankle position in the following order: 10 degrees of dorsiflexion > neutral position > 14 degrees of plantar flexion (P<0.05). The pressure intensity exerted on the talus varied in ascending order: 10 degrees of dorsiflexion < neutral position < 14 degrees of plantar flexion (P<0.05). However, the intensity of the pressure on the graft was insignificantly different from the overall pressure intensity on the talus (P>0.05). Conclusion: Treatment using a 3D-printed talar component can achieve precise reconstruction of a large OLT after the surgical removal of the talar lesion. The pressure intensity on the repaired site did not change before and after the operation, indicating the clinical feasibility of this approach.

Validation of a Finite Element Humeroradial Joint Model of Contact Pressure Using Fuji Pressure Sensitive Film.

A finite element (FE) elbow model was developed to predict the contact stress and contact area of the native humeroradial joint. The model was validated using Fuji pressure sensitive film with cadaveric elbows for which axial loads of 50, 100, and 200 N were applied through the radial head. Maximum contact stresses ranged from 1.7 to 4.32 MPa by FE predictions and from 1.34 to 3.84 MPa by pressure sensitive film measurement while contact areas extended from 39.33 to 77.86 mm2 and 29.73 to 83.34 mm2 by FE prediction and experimental measurement, respectively. Measurements from cadaveric testing and FE predictions showed the same patterns in both the maximum contact stress and contact area, as another demonstration of agreement. While measured contact pressures and contact areas validated the FE predictions, computed maximum stresses and contact area tended to overestimate the maximum contact stress and contact area.

The effect of partial fibulectomy on contact pressure of the knee: a cadaveric study

The fibula is a valuable source of bone graft and partial or total fibulectomy is done in some procedures, such as upper tibial osteotomy and treatment of tibial nonunion. Previous studies emphasized donor-site morbidity after fibulectomy. The aim of our study was to quantitatively survey joint reaction forces in the medial and lateral compartments of the ipsilateral knee, after partial fibulectomy. Using left knees of six cadavers, after medial and lateral arthrotomy and total meniscectomy, Fuji pressure-sensitive film was inserted to both lateral and medial knee compartments. Weight bearing was simulated using a novel device that allowed a defined axial force to be applied to the left lower limbs of supine cadavers. The axial force of half the body weight of each specimen was applied to the plantar surface of the foot. After removing the films, fibulectomy was done 12 cm proximal to lateral malleolus and 2 cm of fibula harvested. The examination was repeated again in the same manner with new films. The resulting Fuji films were scanned using HP Scanjet (G3110) with resolution of 4,800 × 9,600 dpi. Films interpreted using software for Fuji pressure-sensitive film analysis. Joint reaction force was decreased in the medial compartment (P = 0.028) and increased in the lateral compartment (P = 0.027) after partial fibulectomy. Our study also showed that pressure changes over the medial and lateral compartments of the knee were not dependent on body weight (P = 0.787 for the medial compartment and P = 0.872 for the lateral compartment) and decreasing pressure in medial compartment was not depended on increasing pressure in lateral compartment (P = 0.208 and correlation coefficient were 0.6). The current study demonstrated partial fibulectomy at 12 cm above lateral malleolus results in decreasing pressure in knee medial compartment and increasing pressure in knee lateral compartment. Further studies are needed to evaluate the clinical importance of partial fibulectomy.

The Biomechanical Effect of Increased Valgus on Total Knee Arthroplasty: A Cadaveric Study

The effects of valgus load on cadaveric knees following total knee arthroplasty (TKA) were investigated using a custom testing system. TKAs were performed on 8 cadaveric knees and tested at 0°, 30°, and 60° knee flexion in both neutral and 5° valgus. Fuji pressure sensitive film was used to quantify contact areas and pressures and MCL strain was determined using a Microscribe digitizing system. Lateral tibiofemoral pressures increased (P<0.05) at all knee flexion angles with valgus loading. Patellofemoral contact characteristics did not change significantly (P>0.05). Significant increases in strain were observed along the anterior and posterior border of the MCL at all knee flexion angles. These findings suggest that valgus loading increases TKA joint contact pressures and MCL strain with increasing knee flexion which may increase implant instability.

Changes in patellofemoral joint contact pressures caused by vastus medialis muscle weakness

BackgroundPatellofemoral joint pain is a common knee disorder, but its underlying causes remain unknown. One proposed mechanism is an imbalance in force in the knee extensor muscles. Specifically, the vastus medialis and vastus lateralis are thought to play a crucial role in proper patellar tracking, and weakness in vastus medialis is thought to lead to a lateral shift in the patella causing increased contact pressures and pain. The purpose of this study was to create an animal model of vastus medialis weakness and to test the effect of this weakness on patellofemoral contact pressures. MethodsExperiments were performed using New Zealand white rabbits (mass 4.9–7.7kg, n=12). Loading of the patellofemoral joint was produced by femoral nerve stimulation of the knee extensor muscles. Knee extensor imbalance was produced by vastus medialis ablation. Fuji pressure sensitive film was used to record contact area, shape and pressures for maximal and sub-maximal, matched-force contractions at knee angles of 30°, 60°, and 90°. FindingsPatellofemoral peak pressures, average pressures, contact areas and contact shapes were the same across all loading conditions for matched-force contractions before and after elimination of vastus medialis. InterpretationWe conclude that vastus medialis weakness does not cause changes in patellofemoral contact pressures. Since the muscular and knee joint geometry in rabbits and humans is similar, we question the idea of vastus medialis weakness as a cause of patellar mal-tracking and patellofemoral joint pain.

The Facet Joint Loading Profile of a Cervical Intervertebral Disc Replacement Incorporating a Novel Saddle-shaped Articulation

Biomechanical study. To evaluate the cervical facet loading profile of an intervertebral cervical disc prosthesis incorporating a unique saddle-shaped articulation and to determine the effect of implantation of the prosthesis on both the loading curve and area distribution of facet loading, when compared with that of an intact specimen. This is the first study that examines the effect of implantation of a cervical disc replacement on the loading of the facet joints. Fresh-frozen ovine cervical spine specimens were used. Specimens were prepared and disarticulated to yield 6 functional spinal units, which were secured and mounted in a custom fixture on a material testing apparatus. A novel pressure sensor was constructed by combining a resistive ink thin film sensor with Fuji pressure-sensitive film. The sensor was calibrated before unilateral insertion into the cervical facet joint via a small arthrotomy. Specimens were tested in both intact condition and after surgical intervention consisting of discectomy and implantation of an intervertebral cervical disc prosthesis (CerviCore, Stryker Spine, Allendale, NJ). Specimens were tested in flexion, extension, and lateral bending to 3 Nm and in torsion to 2.5 Nm. At the termination of each loading profile, the load was maintained for 30 seconds to permit full exposure of the Fuji film. For each configuration, the maximum resultant load, load rate, and contact area pressure at the endpoint of the loading profile were determined. A paired Student t test was used to determine the differences between the intact specimen and the specimen with an implanted intervertebral disc prosthesis. There were no statistically significant differences in mean or maximum pressures between the intact specimen and the specimen with an intervertebral disc in all loading configurations. Similarly, there was no significant difference in the total measured force between the groups in all loading configurations. There was no significant difference in contact areas between the groups in flexion, lateral bending, and torsion. When evaluated in extension, the intact specimen had a mean contact area of 0.8 cm compared with 0.5 cm for the intervertebral disc (P<0.02). Biomechanical testing in an ovine model demonstrated no significant difference in measured facet pressures and forces between an intact native cervical disc specimen and a cervical intervertebral disc prosthesis using a saddle-shaped articulation. Peak and mean pressures were not demonstrated to be significantly different between the implanted and intact disc conditions. Implantation of the prosthesis resulted in a significant reduction of contact area under extension moments.

Biomechanical Consequences of a Tear of the Posterior Root of the Medial Meniscus

Tears of the posterior root of the medial meniscus are becoming increasingly recognized. They can cause rapidly progressive arthritis, yet their biomechanical effects are not understood. The goal of this study was to determine the effects of posterior root tears of the medial meniscus and their repairs on tibiofemoral joint contact pressure and kinematics. Nine fresh-frozen cadaver knees were used. An axial load of 1000 N was applied with a custom testing jig at each of four knee-flexion angles: 0 degrees , 30 degrees , 60 degrees , and 90 degrees . The knees were otherwise unconstrained. Four conditions were tested: (1) intact, (2) a posterior root tear of the medial meniscus, (3) a repaired posterior root tear, and (4) a total medial meniscectomy. Fuji pressure-sensitive film was used to record the contact pressure and area for each testing condition. Kinematic data were obtained by using a robotic arm to record the position of the knees for each loading condition. Three-dimensional knee kinematics were analyzed with custom programs with use of previously described transformations. The measured variables were axial rotation, varus angulation, lateral translation, and anterior translation. In the medial compartment, a posterior root tear of the medial meniscus caused a 25% increase in peak contact pressure compared with that found in the intact condition (p < 0.001). Repair restored the peak contact pressure to normal. No difference was detected between the peak contact pressure after the total medial meniscectomy and that associated with the root tear. The peak contact pressure in the lateral compartment after the total medial meniscectomy was up to 13% greater than that for all other conditions (p = 0.026). Significant increases in external rotation and lateral tibial translation, compared with the values in the intact knee, were observed in association with the posterior root tear (2.98 degrees and 0.84 mm, respectively) and the meniscectomy (4.45 degrees and 0.80 mm, respectively), and these increases were corrected by the repair. This study demonstrated significant changes in contact pressure and knee joint kinematics due to a posterior root tear of the medial meniscus. Root repair was successful in restoring joint biomechanics to within normal conditions.

Contact stress distributions on the femoral head of the emu ( Dromaius novaehollandiae)

Osteonecrosis of the femoral head remains a challenging orthopaedic problem. The disease frequently progresses to femoral head collapse, leading to debilitating osteoarthritis in the affected hip(s). Since a major goal of pre-collapse interventions is to forestall the need for hip arthroplasty, it is important that any animal models used to develop or study such interventions also have a natural history of progression to femoral head collapse. The emu ( Dromaius novaehollandiae), a large flightless bird native to Australia, consistently progresses to femoral head collapse when osteonecrosis is experimentally induced cryogenically. Full biomechanical characterization of the demands this animal places on its hip is an important consideration in future usage of this model. This study reports in vitro measurement of the contact stress distributions on the emu femoral head during stance phase of the gait cycle, using Fuji pressure-sensitive film. Applied hip loadings were based upon ground reaction forces and hip flexion angles recorded in vivo. The contact stress data showed reasonable homology with the human hip, both in terms of stress magnitude and sites of habitual loading on the femoral head.

Biomechanical Consequences of a Tear of the Posterior Root of the Medial Meniscus

Tears of the posterior root of the medial meniscus are becoming increasingly recognized. They can cause rapidly progressive arthritis, yet their biomechanical effects are not understood. The goal of this study was to determine the effects of posterior root tears of the medial meniscus and their repairs on tibiofemoral joint contact pressure and kinematics. Nine fresh-frozen cadaver knees were used. An axial load of 1000 N was applied with a custom testing jig at each of four knee-flexion angles: 0 degrees, 30 degrees, 60 degrees, and 90 degrees. The knees were otherwise unconstrained. Four conditions were tested: (1) intact, (2) a posterior root tear of the medial meniscus, (3) a repaired posterior root tear, and (4) a total medial meniscectomy. Fuji pressure-sensitive film was used to record the contact pressure and area for each testing condition. Kinematic data were obtained by using a robotic arm to record the position of the knees for each loading condition. Three-dimensional knee kinematics were analyzed with custom programs with use of previously described transformations. The measured variables were axial rotation, varus angulation, lateral translation, and anterior translation. In the medial compartment, a posterior root tear of the medial meniscus caused a 25% increase in peak contact pressure compared with that found in the intact condition (p < 0.001). Repair restored the peak contact pressure to normal. No difference was detected between the peak contact pressure after the total medial meniscectomy and that associated with the root tear. The peak contact pressure in the lateral compartment after the total medial meniscectomy was up to 13% greater than that for all other conditions (p = 0.026). Significant increases in external rotation and lateral tibial translation, compared with the values in the intact knee, were observed in association with the posterior root tear (2.98 degrees and 0.84 mm, respectively) and the meniscectomy (4.45 degrees and 0.80 mm, respectively), and these increases were corrected by the repair. This study demonstrated significant changes in contact pressure and knee joint kinematics due to a posterior root tear of the medial meniscus. Root repair was successful in restoring joint biomechanics to within normal conditions.

Biomechanical effects of glenoid retroversion in total shoulder arthroplasty

The purpose of this study was to evaluate the effects of glenoid retroversion after total shoulder arthroplasty on glenohumeral joint contact pressures, contact areas, and forces. We studied 8 cadaveric shoulders with a custom shoulder testing system that permits anatomic loading of the rotator cuff and the humerothoracic muscles. Each shoulder was tested intact and after total shoulder arthroplasty with the glenoid component in a neutral position and with the glenoid component retroverted 15 degrees . Glenohumeral contact pressures and areas were measured with Fuji pressure-sensitive film, and the glenohumeral forces were measured with a 6-df load cell. Glenohumeral contact areas decreased significantly, and contact pressures increased after total shoulder arthroplasty with both neutral glenoid components and retroverted glenoid components (P < .0002 to .04). Inferior forces decreased significantly after total shoulder arthroplasty with the retroverted glenoid components when compared with the intact, native shoulder (P < .02). Posterior forces also decreased significantly with the retroverted glenoid when compared with the neutral glenoid (P < .03). Placement of the glenoid in 15 degrees of retroversion significantly decreased glenohumeral contact area, increased contact pressure, and decreased inferior and posterior glenohumeral forces. Glenoid component retroversion may result in eccentric loading of the glenoid component and possibly lead to wear and loosening, signifying the importance of correct anatomic placement during total shoulder arthroplasty.

Positional-dependent changes in glenohumeral joint contact pressure and force: Possible biomechanical etiology of posterior glenoid wear

The purpose of this study was to simulate the forces in the individual periscapular muscles and investigate the possible biomechanical etiology of posterior erosion of the glenoid. Twelve fresh-frozen human cadaveric shoulders were used with a custom shoulder jig that uses independently controlled pneumatic cylinders to apply forces across the tendon of each muscle. The simulated muscle forces included the rotator cuff, the deltoid, the latissimus dorsi, and the pectoralis major. The shoulders were tested in 12 overhead activity positions. A 6-degree-of-freedom load cell was used to measure the glenohumeral joint forces, and the glenohumeral contact pressures and areas were measured by use of Fuji pressure-sensitive film. There were no significant differences in glenohumeral joint forces between 60 degrees and 90 degrees of vertical abduction or between 60 degrees and 90 degrees of external rotation. At 70 degrees of horizontal adduction from the scapular plane, there was a significant decrease in superior force, a significant increase in posteriorly directed force, and a significant decrease in compression when compared with 30 degrees and 50 degrees of horizontal adduction ( P < .05). Similar statistical trends were seen for 60 degrees of vertical adduction. For the glenohumeral contact area and pressure, a significant decrease in contact area was seen between 30 degrees of horizontal adduction and 70 degrees of horizontal adduction for both 60 degrees and 90 degrees of vertical adduction ( P < .05). A significant increase in contact pressure was seen at 70 degrees of horizontal adduction compared with 50 degrees and 30 degrees ( P < .05). The contribution of the humerothoracic muscles is significant and should be considered for proper restoration of glenohumeral joint biomechanics. Furthermore, asymmetric loading with excessive or repetitive overhead activities may eventually lead to posterior glenoid erosion.

Paper #188 Stress distributions in mobile bearing knees

Wear of polyethylene (PE) and the development of subsequent osteolysis remains a problem in total knee arthroplasty. The proximal femoral-PE insert articulation is known to be the primary producer of PE wear particles in conventional fixed bearing modular knee designs. Secondary production of PE wear occurs at the fixed insert-tibial interface due to relative micromotion between the components. Retrieval analyses of fixed bearing knees demonstrate a number of wear mechanisms that, in part, reflect the low conformity and high contact stress at the articulations and kinematics. Mobile bearing knees have been designed with increased conformity to decrease the contact stress and minimise the constraint to the PE insert with the hope of more natural kinematics. An increase in contact area has been hypothesized to produce lower wear rates. Experimental techniques have been reported to evaluate the contact stress and area footprints but are limited in that only the surface stresses can be examined. Subsurface stress distributions in PE insert may play an important role in the fatigue related wear mechanisms. This study explored subsurface stress distributions in PE using Finite element modeling (FEM) and an electronic pressure sensor or Fuji pressure sensitive film.

The influence of surgical malalignment on the contact pressures of fixed and mobile bearing knee prostheses––a biomechanical study

Objective. To investigate the effect of surgical malalignment on contact pressures of fixed and mobile bearing knee prostheses. Design. An experimental set-up was used to measure contact pressure on the tibial component of fixed and mobile bearing knee prostheses subjected to a compression load and surgical malalignment situations were simulated. Background. Mobile bearing knee prostheses were designed to decrease tibiofemoral contact pressure by providing both high congruity and mobility. It was also assumed to accommodate surgical malalignment. However, few studies have reported the effect of malalignment of the tibiofemoral joint on contact pressure of fixed and mobile bearing knee prostheses. Methods. Surgical malalignment situations were simulated to evaluate contact characteristics of tibial component of fixed and mobile bearing knee prostheses. The simulated malalignment conditions include the medial–lateral translation (0.5 and 1 mm), anterior–posterior translation (2 and 4 mm) and internal–external rotation (1°, 3°, 5° and 10°) of the femoral component relative to the tibial component. Fuji pressure sensitive film was used to measure the contact pressure. Results. The greatest increase of maximum contact pressure in the anterior–posterior maltranslation was 7.63% and 7.62% relative to the neutral contact situation in the fixed and mobile bearing designs respectively. In the medial–lateral maltranslation, there was 23.3% in the fixed bearing design and was 22.0% in the mobile bearing design. In the internal/external malrotation, the greatest increase of maximum contact pressure in the fixed bearing design was 27.1%, which was much higher than the mobile bearing design (22.4%). Conclusions. The mobile bearing design can reduce maximum contact pressure more significantly than the fixed bearing design when malalignment conditions of the tibiofemoral joint occurs, especially in the internal/external malrotation. The mobile bearing design offers the advantage of self-adjusting over the fixed bearing design to accommodate surgical malalignment. Relevance This study revealed that the mobile bearing design has smaller maximum contact pressures than the fixed bearing design in knee prosthesis under malalignment biomechanical tests. This result indicates that there is an advantage for a mobile bearing design over a fixed bearing design to accommodate malalignment conditions caused by surgical technique or soft tissues imbalance in total knee arthroplasty.

Effect of Fuji pressure sensitive film on actual contact characteristics of artificial tibiofemoral joint

Objective. To investigate the effect of inserting a Fuji pressure sensitive film into an artificial tibiofemoral joint on the actual contact mechanics. Design. The experimental measurement and finite element analysis were used. Background. Although Fuji pressure sensitive film was widespread used for measuring the contact characteristics of artificial joint, how this measurement approaches actual contact characteristics has not yet been studied extensively. Method. Two three-dimensional finite element models of an artificial tibiofemoral joint were constructed. The with-film-model was used to mimic the experimental setup and was verified by comparing the contact area and pressure on the simulated film calculated from finite element analysis to the measured one from the Fuji film (ultra-super low and medium grades) in the experimental test. Then the with-film-model was modified to the without-film-model in which the simulated film was removed. The contact characteristics on the film calculated from the with-film-model were represented to the measured one and the contact characteristics on the tibial component calculated from the without-film-model were represented to the actual one. The measured and actual contact characteristics were studied to investigate the effects of Fuji film on the actual contact characteristics in the tibiofemoral joint of knee prosthesis. Results. The contact characteristics calculated from with-film-model was reasonable agreement with measured one by Fuji film in the experimental test. The maximum difference is 13% in maximum contact pressure under a load of 3000 N. The maximum difference of contact area and pressure between the model simulating actual contact circumstance and the model with inserting a Fuji film between contacting surface are 2.4% and 14% respectively. Conclusion. This study revealed that contact area and pressure of the tibiofemoral joint of knee prosthesis measured by Fuji pressure sensitive film could be simulated by finite element analysis. The measurement of contact area in the artificial joint by using ultra-super low grade Fuji film is overestimated its actual contact area by 1.2–2.4%, but the measurement of contact pressure by using medium grade Fuji film is underestimated its actual contact pressure by 8–14%. Relevance This study revealed that the ultra-super low grade Fuji film is a reliable sensor to measure the contact area and the medium grade film would underestimate its actual contact pressure in the artificial tibiofemoral joint. This finding can provide a better understanding of the reliability of Fuji film to measure the contact characteristics of artificial joint in the experimental test.

Biomechanical consequences of secondary congruence after both-column acetabular fracture.

To create a both-column acetabular fracture model with secondary congruence and to determine the intraarticular loading characteristics present in simulated single-leg stance. The normal contact pressures on the weight-bearing portion of the acetabulum in simulated single-leg stance are different from those present in a both-column fracture model exhibiting secondary congruence. Cadaveric Biomechanical model. Biomechanical testing laboratory. Nine fresh frozen cadaveric hemipelves. Both-column fracture model with secondary congruence of the acetabular articular surface with respect to the femoral head was created and tested using Materials Testing Machine (MTS Systems Corp., Minneapolis, MN) and Fuji pressure-sensitive film (Sensor Products, Inc., East Hanover, NJ). Testing data recorded and analyzed comparing the fractured and unfractured states. With respect to the intact specimen, the contact area, mean pressure, and peak pressure in the dome region all increased (p < 0.003) in the both-column model. The contact area in the anterior articular region decreased (p < 0.02) as did the mean pressure (p < 0.032). The posterior articular region demonstrated a trend toward decreased contact area and increased mean and peak pressures. Descriptively, the stress concentration shifted toward the fracture in all cases with the most anterior and most posterior articular regions having little contact in the fracture model. In the authors' both-column model of secondary congruence, the stress concentration during simulated single-leg stance was increased significantly in the dome of the acetabulum adjacent to the fracture line.

Distribution of patellofemoral joint pressures after femoral trochlear osteotomy.

Anterior osteotomy of the lateral femoral condyle was designed for the treatment of recurrent patellar dislocations. This study examined whether anterior femoral trochlear osteotomy significantly elevates contact pressures in the patellofemoral joint. Static intrajoint loads and contact area determination were recorded using prescale Fuji pressure-sensitive film under static loading. Peak pressures, average pressures and contact areas of the patellofemoral joint were calculated on intact specimens and after anterior osteotomy of the lateral condyle. Our results indicate that a 6-mm or 10-mm anterior osteotomy of the lateral condyle significantly elevates patellofemoral contact pressures.

The influence of inserting a Fuji pressure sensitive film between the tibiofemoral joint of knee prosthesis on actual contact characteristics

Objective. To investigate the influence of inserting a Fuji pressure sensitive film between the tibiofemoral joint of knee prosthesis on actual contact characteristics. Design. A finite element analysis was used to investigate the alteration of contact characteristics of the tibiofemoral joint due to inserting a pressure sensitive film between the contacting surfaces. Background. The discrepancy between actual contact behaviors of tibiofemoral joint of knee prosthesis and the measurement using Fuji pressure sensitive film was not discussed extensively. The change of direct contact circumstance of the tibiofemoral joint due to inserting a pressure sensitive film was not well reported. Method. A two-dimensional finite element model of the tibiofemoral joint of knee prosthesis in the sagittal plane was constructed. Four different radii of the femoral component were used to investigate the conformity effect. Two-layers of plane strain element were used to model the pressure sensitive film. The influence of inserting a pressure sensitive film on the actual contact characteristics was analyzed by comparing the results of the change in contact radius. Results. Inserting a pressure sensitive film between contacting surfaces would disturb the original contact behaviors, especially in the lowest conformity design. The maximum difference of contact radius between the model simulating actual contact circumstance and the model with inserting a pressure sensitive film between contacting surface was 77% in the lowest conformity condition at the smallest load. Conclusions. This study proposes a quantitative analysis of contact characteristics in the tibiofemoral joint of knee prosthesis between the models with and without inserting a pressure sensitive film into the contact surface. The measurement of contact area in artificial tibiofemoral joints by using Fuji pressure sensitive film is always overestimated its true contact area by 14–77%. Relevance This study revealed the measurement of contact characteristics of artificial tibiofemoral joints by using Fuji pressure sensitive film which depends on not only the applied load, but also the conformity and material properties of the contact surface. Therefore, the information of the conformity and material properties of the contact surface should be provided as well as the applied load wherever a measurement of contact characteristics using Fuji pressure sensitive film is analyzed and interpreted.

Removal of the lateral or medial third of patellar tendon alters the patellofemoral contact pressure and area: an in vitro experimental study in dogs

Objectives. To compare patellofemoral contact pressure and areas after immediate removal of the lateral, central, or medial third of patellar tendon. Design. In vitro experiment in 12 dogs. Background. Alteration of the vector sum of the quadriceps muscle contraction after removal of partial patellar tendon might result in changes of patellar tracking in the trochlea. Methods. Patellofemoral contact pressure and areas were recorded using Fuji pressure-sensitive film at 45°, 60°, and 90° of knee flexion under an isometric quadriceps force of 100% body weight. The patellofemoral contact imprint from the intact knees were obtained as control, and the lateral ( n=4), central ( n=4), and medial ( n=4) third of the patellar tendon were subsequently removed and the patellofemoral contact imprint was recorded. Results. The patellofemoral contact area was found to increase with increasing knee flexion angles. No change in patellofemoral contact pressure and areas was found after removal of the central third patellar tendon. However, after removal of either lateral or medial third of patellar tendon, the patellofemoral contact was rotated with increasing knee flexion angles. This was due to the altered vector sum of the quadriceps force, resulting in significantly decreased patellofemoral contact areas and simultaneously a significantly increased contact pressure, characterized with concentration of patellofemoral contact pressure on both lateral and medial facets of the patellofemoral joint. Conclusions. The results suggest that removal of the central third of patellar tendon may not alter the patellofemoral contact pressure and areas as compared with removal of either lateral or medial third of patellar tendon that may result in an altered postoperative tracking mechanism of the patellofemoral joint immediately after operation. Relevance Findings of this in vitro animal study supports the use of central third of patellar tendon as autograft for anterior cruciate ligament reconstruction. However, further experimental studies are needed to investigate how the postoperative healing of the host patellar tendon will influence the findings obtained from this in vitro study.

Endurance sports after total knee replacement: a biomechanical investigation.

No biomechanical evaluation of total knee designs exists for loads occurring during sports activities. It was the purpose of the present study to evaluate the contact stress distribution and contact area of different knee joint designs for loads that occur during four common recreational endurance activities. Three different total knee designs were evaluated for loads occurring during cycling (1.2 body weight (BW) at 80 degrees of knee flexion), power walking (4 BW at 20 degrees), hiking (8 BW at 40 degrees), and jogging (9 BW at 50 degrees) using Fuji pressure-sensitive film. The designs consisted of a flat tibial inlay, a curved inlay, and an inlay with mobile bearings. Five measurements were conducted for each load. The pressure sensitive films were scanned and analyzed using an image analysis program. During cycling, the area with stress levels above the yield point of polyethylene (overloaded area) was below 15 mm2 for each design. During power walking, the mobile bearing design showed no overloaded area, whereas it was below 50 mm2 for the flat and curved design. During downhill walking and jogging, more than 140 mm2 were overloaded for each design. It was concluded that patients after total knee replacement should alternate activities such as power walking and cycling. For mountain hiking, patients are advised to avoid descents or at least use ski poles. Jogging or sports involving running should be discouraged after total knee replacement.