Previously more femoral rollback has been reported in posterior-stabilized implants, but so far the kinematic change after post-cam engagement has been still unknown. The tri-condylar implants were developed to fit a life style requiring frequent deep flexion activities, which have the ball and socket third condyle as post-cam mechanism. The purpose of the current study was to examine the kinematic effects of the ball and socket third condyle during deep knee flexion.

The tri-condylar implant analyzed in the current study is the Bi-Surface Knee System developed by Kyocera Medical (Osaka, Japan). Seventeen knees implanted with a tri-condylar implant were analyzed using 3D to 2D registration approach. Each patient was asked to perform a weight-bearing deep knee bend from full extension to maximum flexion under fluoroscopic surveillance. During this activity, individual fluoroscopic video frames were digitized at 10°increments of knee flexion. A distance of less than 1 mm initially was considered to signify the ball and socket contact. The translation rate as well as the amount of translation of medial and lateral AP contact points and the axial rotation was compared before and after the ball and socket joint contact.

The average angle of ball and socket joint contact were 64.7° (SD = 8.7), in which no separation was observed after initial contact. The medial contact position stayed from full extension to ball and socket joint contact and then moved posteriorly with knee flexion. The lateral contact position showed posterior translation from full extension to ball and socket joint contact, and then greater posterior translation after contact (Figure 1). Translation and translation rate of contact positions were significantly greater at both condyles after ball and socket joint contact. The femoral component rotated externally from full extension to ball and socket joint contact, and then remained after ball and socket joint contact (Figure 2). There was no statistical significance in the angular rotation between ball and socket joint contact and maximum flexion. Translation of angular rotation was significantly greater before ball and socket joint contact, however, there was no significance in translation rate before and after ball and socket joint contact.

The ball and socket joint was proved to induce posterior rollback intensively. In terms of axial rotation, the ball and socket joint did not induce reverse rotation, but had slightly negative effects after contact. The ball and socket provided enough functions as a posterior stabilizing post-cam mechanism and did not prevent axial rotation.

Summary Statement

Tendon-bone interface becomes matured with the perforating fiber and the cells striding over the bone area. We suggest that both “perforating fiber” and “cell stride” could play a crucial role in regeneration after rotator cuff repair.

This multicentre prospective clinical trial aimed to determine whether early administration of alendronate (ALN) delays fracture healing after surgical treatment of fractures of the distal radius. The study population comprised 80 patients (four men and 76 women) with a mean age of 70 years (52 to 86) with acute fragility fractures of the distal radius requiring open reduction and internal fixation with a volar locking plate and screws. Two groups of 40 patients each were randomly allocated either to receive once weekly oral ALN administration (35 mg) within a few days after surgery and continued for six months, or oral ALN administration delayed until four months after surgery. Postero-anterior and lateral radiographs of the affected wrist were taken monthly for six months after surgery. No differences between groups was observed with regard to gender (p = 1.0), age (p = 0.916), fracture classification (p = 0.274) or bone mineral density measured at the spine (p = 0.714). The radiographs were assessed by three independent assessors. There were no significant differences in the mean time to complete cortical bridging observed between the ALN group (3.5 months (se 0.16)) and the no-ALN group (3.1 months (se 0.15)) (p = 0.068). All the fractures healed in the both groups by the last follow-up. Improvement of the Quick-Disabilities of the Arm, Shoulder and Hand (QuickDASH) score, grip strength, wrist range of movement, and tenderness over the fracture site did not differ between the groups over the six-month period. Based on our results, early administration of ALN after surgery for distal radius fracture did not appear to delay fracture healing times either radiologically or clinically.

Cite this article: Bone Joint J 2013;95-B:1544–50.

Introduction

Spinal aBMD only explains 50–80% of vertebral strength, and the application of aBMD measurements in isolation cannot accurately identify individuals who are likely to eventually experience bone fracture, due to the low sensitivity of the test. For appropriate treatment intervention, a more sensitive test of bone strength is needed. Such a test should include not only bone mineral density, but also bone quality. Quantitative computed tomography-based finite element methods (QCT/FEM) may allow structural analyses taking these factors into consideration to accurately predict bone strength (PBS). To date, however, basic data have not been reported regarding the prediction of bone strength by QCT/FEM with reference to age in a normal population. The purpose of this study was thus to create a database on PBS in a normal population as a preliminary trial. With these data, parameters that affect PBS were also analyzed.

Introduction

Achieving high flexion after total knee arthroplasty is very important for patients in Asian countries where deep flexion activities are an important part of daily life. The Bi-Surface Total Knee System (Japan Medical Material, Kyoto, Japan), which has a unique ball-and-socket mechanism in the mid-posterior portion of the femoral and tibial components, was designed to improve deep knee flexion and long-term durability after total knee arthroplasty (Figure 1). The purpose of this study was to determine the in vivo three dimensional kinematics of Bi-Surface Total Knee System in order to evaluate and analyze the performance of this system with other conventional TKA designs currently available in the market today.

Introduction and aims

After internal hemipelvectomy for malignant pelvic tumors, pelvic reconstruction is necessary for eventual weight bearing and ambulation. Non-vascularised, fibular grafts (NVFG) offer fast, and stable reconstruction, post- modified Enneking's type I and I/IV resection. This study aimed to evaluate the success of graft union and patient function after NVFG reconstruction.

In Far East, including Japan and the Middle East, daily activities are frequently carried out on the floor. Deep flexion of the knee joint is therefore very important in these societies. Some patients who underwent total knee arthroplasty (TKA) in these countries often perform deep flexion activity, such as squatting, cross-leg sitting and kneeling. However it is still unknown that deep flexion activity affects long term durability after TKA. The purpose of this study was to examine the correlation between deep flexion and long term durability.

Between December 1989 and May 1997, 507 total knee arthroplasties were carried out in 371 patients using the Bi-Surface Knee System (Japan Medical Material, Osaka, Japan) at two institutions and routine rehabilitation program continued for one to two months after TKA. One patient who underwent simultaneous bilateral TKA was excluded because of pulmonary embolism within one month. The other 505 knees (370 patients) were divided into two groups according to the range of flexion after our routine rehabilitation program; one group (Group A: 207 knees) consisted of more than 135 degrees flexion knees and the other group (Group B: 298 knees) consists of less than 135 degrees flexion knees. Patients whose follow-up period was less than 10 years were excluded from this clinical evaluation. Range of flexion was measured preoperatively, at the time after routine rehabilitation program, and at the latest follow-up. Knee function was evaluated on the basis of Knee Society knee score and functional score preoperatively and at the latest follow-up. Kaplan-Meier survivorship analysis was performed with revision for any operation as the end point.

In Group A, the mean preoperative range of flexion was 133.0±16.3 degrees, and at the time after routine rehabilitation program, this improved to 139.7±5.1 degrees. This angle maintained to 136.2±14.3 at the latest follow-up. In Group B, the mean preoperative range of flexion was 111.6±20.4 degrees, and at the time after routine rehabilitation program, this improved to 114.5±13.6 degrees. This angle maintained to 118.2±17.8 at the latest follow-up. The Knee Society knee score and functional score was improved from 43.0±16.9 points and 39.0±20.2 points preoperatively to 95.1±5.8 points and 51.8±21.2 points at the latest follow-up, respectively in Group A. The Knee Society knee score and functional score was improved from 37.1±16.7 points and 31.9±18.4 points preoperatively to 92.5±8.7 points and 53.1±26.1 points at the latest follow-up, respectively in Group B. Kaplan-Meier survivorship at 10-year was 95.5% in Group A and 96.2% in Group B with any operation as the end point. The survivorship between Group A and Group B was not statistically significant.

Good range of flexion was maintained and Knee society score was excellent after a long time follow-up for the patients who achieved deep flexion after TKA. Deep flexion was proved not to affect long term durability in this Bi-Surface Knee System.

Introduction: Low-intensity pulsed ultrasound stimulation (LIPUS) can enhance bone regeneration and callus healing during fracture repair. However, whether a certain phase of the healing process in fracture repair in particular is infiuenced by LIPUS treatment remains unclear. In this investigation, the effect of LIPUS on callus remodeling in a gap healing model was evaluated by bone morphometric analyses using 3-dimensional (3D) quantitative micro computed tomography (μCT) at the healing site, providing information on the temporal sequence of mineralized remodeling events that characterize the gap healing.

Materials and Methods: The rabbit osteotomy model with 2-mm gap for the right tibia was immobilized with four pins fixed to an external fixator with double side bars. LIPUS was continued for both the treatment group (n=7/group/time point) and the control group (n=7/group/time point), for 20 min, six times/week, for 4, 6, or 8 weeks. The control group also received a sham inactive transducer under exactly the same condition as the LIPUS group. After the harvested tibia was scanned by μCT, region of interest was set at the callus healing area. It defined as a center of the osteotomy gap with a width of 1 mm. Morphometric parameters used for evaluation were mineralized callus volume (BV, cm³) and volumetric bone mineral density of mineralized tissue comprising the callus (mBMD, mBMD = BMC/ BV, mgHA/cm³). The whole ROI was measured and was subdivided into three zones. The periosteal callus zone (External), the medullary callus zone (Endosteal) and the remaining zone was the cortical gap zone (Intercortical). For each zone, BV and mBMD were measured. Data of the μCT evaluations were analyzed using a one-way ANOVA test. Statistically significant difference was set at p < 0.05.

Results: In the LIPUS groups, BV for the Endosteal zone was significantly lower for the 8-week group than for the 4-week group. Comparing results at the same time point, the LIPUS group at 8 weeks was significantly higher than that of the control group in the Intercortical zone. As for mBMD, in the LIPUS group, the 8-week group was significantly higher than the 4-week group for Total, External, Internal, and Endosteal zones, respectively. Comparing results at the same time point, mBMD was significantly higher for the LIPUS group at 8 weeks than for the control group in both External and Intercortical zones.

Discussion: The most striking finding in our study was that LIPUS accelerated bone formation in the Intercortical zone and callus resorption in the Endosteal zone. This suggests that LIPUS could shorten the time required for remodeling. However, the results of this study do not clarify whether an early phase in callus formation in particular is infiuenced by LIPUS.

Introduction: Low-intensity pulsed ultrasound stimulation (LIPUS) reportedly enhances restoration of strength at fracture healing sites. However, evaluation of strength by mechanical testing was limited to only one direction, with either bending or torsion. Quantitative micro computed tomography (μCT) scans allow us to calculate strength-related parameters such as cross-sectional moment (CSM) and cross-sectional moment of inertia (CSMI). Previous studies have performed 2-dimensional (2D) analyses, and 3-dimensional (3D) evaluations have not been described. The purpose of this study was thus to investigate the effects of LIPUS on osteotomy healing using 3D analyses of CSM and CSMI.

Materials and Methods: Bilateral, transverse, mid-tibial osteotomies with a 2-mm gap were performed in 42 rabbits. LIPUS was continued for both the treatment group (n=7/group/time point) and the control group (n=7/ group/time point), for 20 min, six times/week, for 4, 6, or 8 weeks. The control group also received a sham inactive transducer under the same condition as the LIPUS group. After the tibia was scanned by μCT, region of interest (ROI) was set at the center of the osteotomy gap with a width of 1 mm. Center of gravity for the ROI and the XYZ coordinate was calculated. An optional line (I) can be drawn in this coordinate. The angle of the Z axis (𝛉) was measured, and also the degree of angle of the X axis (φ) was measured. The 3D CSM [I (φ, 𝛉)] around this line was calculated using the following equation: I (φ, 𝛉) = ∫ r²dV (mm5), where r is the distance of a voxel to the center of gravity (mm) and dV is the area of a voxel (mm3). The axial CSM was defined as CSMx: I (0, 90), CSMy: I (90, 90), whereas the polar CSM was also defined as CSMp: I (any, 0). 3D CSMI weighted by density distribution was calculated using the following equation: I’ (φ, 𝛉) = ∫ r²dm = ∫ ρr²dV (mg.mm²), ρ is the measured volumetric callus mineral density. Likewise CSMIx, CSMIy and CSMIp were calculated. These data of the μCT evaluations were analyzed using a one-way ANOVA test (p< 0.05).

Results: When 3D CSMs at the same time point were compared, values for the LIPUS groups were significantly higher than those for control groups for CSMx at 6 weeks and CSMp at 8 weeks. As for comparison of 3D CSMIs at the same time point, values for the LIPUS groups were significantly higher than those of the control groups for CSMIx, CSMIy, and CSMIp at 6 and 8 weeks.

Discussion: Bone healing by 3D CSM and CSMI has not been described before. Our results demonstrate that these bone strength parameters improved with LIPUS during the early phases. However, whether the late phase of callus formation is infiuenced remains unclear.

Introduction: There is a clear need for the development of more sensitive risk assessment tools for clinical predictors of fractures. Bone densitometries are limited in the ability to account for complex geometry, architecture, and heterogeneity of bone. Quantitative computed tomography (QCT)-based finite element (FE) Methods: (QCT/FEM) are able to perform structural analyses taking these factors into consideration to accurately predict bone strength. However, no basic data have been available regarding predicted strength (PS) of the proximal femur by QCT/FEM with reference to age in a normal population. The purpose of this study was thus to create a database on PS in a normal population as a preliminary trial. With these data, parameters that affect PS were also analyzed.

Methods: Participants in this study comprised individuals who participated in a health checkup program with computed tomography (CT) at our hospital in 2008. Participants included 487 men and 237 women (age range, 40–87 years). Exclusion criteria were provided. Scan data of the proximal femur were isolated and taken from overall data from CT of each participant with simultaneous scans of a calibration phantom containing hydroxyapatite rods. A FE model was constructed from the isolated data using Mechanical Finder software. For each of the FE models, loading and boundary conditions as well as the definition of PS were exactly the same as described by Bessho et al. (Bone 2009). For each participant, height, weight, and abdominal circumference (AC) were measured. The analyses included linear regression analysis relating age and PS, one-way analysis of variance to compare average PS among the groups of participants who were divided into 5-year age brackets, and multiple regression analysis to determine how PS was affected by age, height, weight, and AC. Differences were considered significant for values of p< 0.05.

Result: The following results were obtained. First, average PS was lower in women than in men for all age ranges. Second, PS in men under stance configuration, and those in women under stance and fall configurations significantly decreased with age. Third, weight positively affected PS in both men and women.

Discussion: This was the first study to investigate changes in PS with age in a normal population. Whether PS by QCT/FEM correlates more closely with fracture risk for osteoporotic patients in comparison to other bone densitometries remains unclear, but the our results did not contradict any existing concept of risk factors for fragility fracture. More baseline data for PS in normal populations need to be accumulated by increasing the number of participants in studies like this.

We evaluated the effect of low-intensity pulsed ultrasound stimulation (LIPUS) on the remodelling of callus in a rabbit gap-healing model by bone morphometric analyses using three-dimensional quantitative micro-CT. A tibial osteotomy with a 2 mm gap was immobilised by rigid external fixation and LIPUS was applied using active translucent devices. A control group had sham inactive transducers applied. A region of interest of micro-CT was set at the centre of the osteotomy gap with a width of 1 mm. The morphometric parameters used for evaluation were the volume of mineralised callus (BV) and the volumetric bone mineral density of mineralised tissue (mBMD). The whole region of interest was measured and subdivided into three zones as follows: the periosteal callus zone (external), the medullary callus zone (endosteal) and the cortical gap zone (intercortical). The BV and mBMD were measured for each zone.

In the endosteal area, there was a significant increase in the density of newly formed callus which was subsequently diminished by bone resorption that overwhelmed bone formation in this area as the intramedullary canal was restored. In the intercortical area, LIPUS was considered to enhance bone formation throughout the period of observation. These findings indicate that LIPUS could shorten the time required for remodelling and enhance the mineralisation of callus.

Introduction: Since 2004, in addition to the original curved varus osteotomy for osteonecrosis of the femoral head, we have intentionally performed anterior or posterior rotation without incising the articular capsule to obtain a more extensive viable area in the loaded portion. We investigated the extent of viable area on the loaded portion after this modified operation.

Materials and Methods: Subjects included 11 patients (13 joints: anterior, 12 joints; posterior, 1 joint) who underwent a modified curved varus osteotomy and anterior or posterior rotation. We investigated the percent of viable area in the preoperative vs. the postoperative weighted portion. In addition, we measured the extent of viable area in the loaded portion when the extent of curved varus osteotomy without rotation was performed based on a schematic drawing.

Results: In this study, the combination of transtrochanteric curved varus osteotomy and anterior or posterior rotation significantly increased the percent viable area from 66% to 85%.

Discussion: The extent of postoperative viable area on the loaded portion might have been increased more than in the original procedure.

Introduction: We studied resphericity of the collapsed femoral head moved medially after posterior rotational osteotomy for osteonecrosis at a mean of 8.5 years follow-up.

Materials and Methods: Twenty-eight hips in 24 patients with osteonecrosis with apparent collapse treated by this operation were studied. All hips had no recollapse at final follow-up. The mean age of patients was 26 years. Twenty-two hips were non-traumatic, 6 were traumatic. The resphericity was studied by ratio (%, medial area of collapse/hip center to superior viable joint surface) at less than 6 months, 3years, and at final follow-up on postoperative antero-posterior radiographs. Disappearance of the subchondral fracture was also observed.

Results and Discussion: The mean ratio of the medial collapse area was 18.4% at less than 6 months, 8.3% at 3years, and 3.4% at final follow-up. Subchondral fracture was seen in 25 of 28 hips at less than 6 months, subchondral fractures disappeared in 17 hips at 3 years, and in 23 hips at final follow-up. We thought that remodeling of the postoperative medial collapsed lesion occurred after this operation.

Introduction: To investigate the presence or absence of osteonecrosis of femoral head (ONFH) in patients undergoing massive corticosteroid therapy, we have performed magnetic resonance imaging (MRI) early after administration. In some patients, MRI revealed an increase in hip fluid. In this study, we evaluated retention of hip fluid early after massive steroid therapy by MRI.

Materials and Methods: The subjects were 14 patients (28 joints) in whom oral administration of prednisolone at an initial dose of 40 mg/day or more or pulse therapy was performed. They consisted of 3 men (6 joints) and 11 women (22 joints). Ages ranged from 17 to 72 years, with a mean of 38.2 years. We evaluated retention of hip fluid in T2-weighted MRI images or T2 fat-suppressed images within 3 months after massive steroid therapy according to the joint fluid grading established by Mitchell et al and evaluated volume of hip fluid by integrating an area (by using Mac scope ver 2.58).

Results: Average volume of all joints was 7.18 cm³. Eleven joints were evaluated as Grade 1, in which a small amount of joint fluid is noted, and their average volume was 3.98 cm³. Fifteen joints were evaluated as Grade 2, in which retention involves the entire femoral neck, and their average volume was 8.96 cm³. Two joints were evaluated as Grade 3, in which marked retention involves the excavation of the cupsula articularis, and their average volume was 11.45 cm³. No joint was evaluated as Grade 0, in which no joint fluid is detected.

Discussion: The pathogenesis of corticosteroid-related ONFH is multifactorial; various hypotheses have been proposed, suggesting the involvement of arteriosclerosis, thrombosis, fat embolization, vascular endothelial disorder, venous return disorder, enhanced blood coagulation, fibrinolytic abnormalities, and bone tissue apoptosis. However the detailed mechanism remains to be clarified. In this survey, when regarding Grade 2 or higher joints as showing a significant increase in hip fluid, the increase was noted in 17 joints (60.7%). We understood objectively by an increase in hip fluid by estimating its volume. An increase in hip fluid early after massive steroid therapy may persistently increase intraarticular pressure, affecting influx of nutrient vessels in the femoral neck or venous return, which is considered to be a tamponade effect. This may be an etiological factor involved in ONFH.

Ring frames have the advantage of allowing progressive correction. However, the available frames for complex deformities are heavy and bulky leading to poor compliance by patients. Also, the mounting procedure requires considerable expertise and skill. On the other hand, a unilateral external fixator has the advantages of less bulk and a lighter weight. Thus, it causes less disability and can achieve better patient compliance even with bilateral application. However, previous unilateral fixators have had various limitations with respect to deformity correction, such as restricted placement of hinges, restricted correction planes, and a limited range of correction angles. In addition, it was impossible to achieve progressive correction while fixation was maintained. To overcome these disadvantages of existing unilateral fixators, we developed a new fixator for gradual correction of multi-plane deformities including translational and rotation deformities. This unilateral external fixator is equipped with a universal bar link system. The link is constructed from three dials and two splines that are connecting the dials. The pin clamps are able to vary the direction of a pin cluster in the three dimensional planes. The system allows us to correct angulation, translation, rotation, and the combination of the above. In addition, open or closed hinge technique is available because the correction hinge can be placed right on the center of rotational angulation (CORA), or at any desired location, by adjusting the length of the link spline. By increasing the spline length, the virtual hinge can also be set far from the fixator. Gradual correction can be performed by rotating the three dials using a worm gear goniometer that is temporarily attached. A 3D reconstructed image of the bone is generated preoperatively. Preoperative planning can be done using this image. Mounting parameters are determined by postoperative AP and lateral computed radiography images. These postoperative images are matched with the pre-operative 3D CT image by 2D and 3D image registration. Then, the fixator can be virtually fixed to the bone. By performing virtual correction, it is possible to plan the correction procedure. The fixator is manipulated by rotating each of the three dials to the predetermined angles calculated by the software. Static load testing disclosed that the fixator could bear a load of 1700 N. No breakage or deformation of the fixator itself was recognized. Mechanical testing demonstrated that this new fixator has sufficient strength for full weight bearing, as well as sufficient fatigue resistance for repeated or prolonged use. The results of clinical application in patients with multi-plane femoral deformities were excellent, and correction with very small residual deformity was achieved in each plane.

The most important issue in the assessment of fracture healing is to acquire information on the restoration of mechanical integrity of the bone. To measure bending stiffness at the healing fracture site, we focused on the use of echo tracking (ET) that was a technique measuring minute displacement of bone surface by detecting a wave pattern in a radiofrequency echo signal with an accuracy of 2.6 μ. The purpose of this study was to assure that the ET system could quantitatively assess the progress, retardation or arrest of healing by detecting bending stiffness at the fracture site.

With the ET system, eight tibial fractures in 7 patients with an average age of 37 years (range: 24–69) were measured. Two tibiae in 2 patients were treated conservatively with a cast, and 6 tibiae in 5 patients were treated with internal fixation (intramedullary nailing: 4, plating: 1, screw 1). Patients assumed supine position, and the affected lower leg was held horizontally with the antero-medial aspect faced upwards. The fibula head and the lateral malleolus were supported and held tight by a Vacufix ®. A 7.5 Hz ultrasound probe was placed on each antero-medial aspect of the proximal and distal fragments along its long axis. Each probe was equipped with a multi-ET system with 5 tracking points with each span of 10 mm. A load of 25 N was applied at a rate of 5 N/second using a force gauge parallel to the direction of the probe and these probes detected the bending angle between the proximal and distal fragments. An ET angle was defined as the sum of the inclinations of both fragments. In the patients treated with a cast, the contralateral side was also measured and served as a control. Fracture healing was assessed time sequentially with an interval of 2 or 3 weeks during the treatment.

None of the patients complained of pain, or no other complication related to this measurement occurred. In the patient (patient:M) treated with a cast, the ET angle exponentially decreased as time elapsed (y = 1.4035e-0.1053x, R = 0.9754) and the radiographic appearance showed normal healing. Including this case, in all patients with radiographic normal healing, the ET angle exponentially decreased. However, in patients with retarded healing (patient:N), the decrease of the angle was extremely slow(y = 0.2769e-0.0096x, R = 0.815). In patients with non union (patient:T), the angle stayed at the same level.

With this method, noninvasive assessment of bending stiffness at the healing site was achieved. Bending angle measured by ET diminished over time exponentially in patients with normal healing. On the contrary, in patients with healing arrest, no significant decrease of the bending angle was recognized. It was demonstrated that the echo tracking method could be applicable clinically to evaluate fracture healing as a versatile, quantitative and noninvasive technique.

Despite improvements in techniques and materials, aseptic loosening of artificial hip joints remains as the most serious problem. This study investigated mechanical and biological effects of biocompatible 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer on prevention of aseptic loosening.

To examine mechanical effects of MPC grafting, we performed hip simulator tests (3million cycles) using cross-linked polyethylene (CL-PE) liners with or without nano-grafting of MPC onto articulating surface (MPC liner/CL-PE liner) and PE liner against CoCrMo heads. To examine biological responses of macrophages and osteoblasts, we prepared MPC nanoparticles (500nm). Using in vitro/vivo murine particle-induced osteolysis model, we examined biological effects of MPC nanoparticles on osteoclastogenesis.

The friction torque was about 90% lower in MPC liners than control liners. Total amounts of wear produced from MPC liner was about 1/5and 1/30 of those from CL-PE and PE liners, respectively. Three-dimensional analysis and SEM analysis of MPC liners revealed no or little wear. The effect of MPC nanografting was maintained even after the test, because XPS analysis confirmed the remainder of specific spectra of MPC on the liner surface. When nanoparticles were exposed to cultured mouse macrophages, MPC nano particles were hardly phagocytosed by macrophages and did not enhance the concentration of bone resorptive cytokines and PGE2. Furthermore, culture medium of macrophages exposed to MPC nanoparticles did not induce RANKL expression in osteoblasts and osteoclastogenesis from bone marrow cells. In vivo murine osteolysis model, particle-induced bone resorption was hardly observed in mice implanted MPC nanoparticles.

Some medical devices grafted MPC onto itssurface have been already used under authorization of the FDA. This study demonstrated that MPC grafting markedly decreases wear production. In addition, even if wear particles are produced, they are biologically inert in respect to phagocytosis by macrophages and subsequent resorptive actions, suggesting an epochal improvement of artificial hip joints preventing aseptic loosening.

Introduction: In cases of small and middle size osteonecrosis on conventional antero-posterior (AP) radiographs, we studied the extent of the lesion on AP radiographs at the 45 degrees flexion position for lesions of the anterior area of the femoral head.

Materials and Methods: Classification of Japanese organizing committee was applied for the extent of the lesion on joint surface. Type A lesions occupy the medial one-third or less; Type B, the medial two-thirds or less; Type C-1 occupies more than the medial two-thirds; and Type C-2 extends laterally to the acetabular edge at the neutral position on conventional AP radiographs. Thirty-three hips (25 patients) with small or middle size lesions (Type A;11, Type B;22) were studied. On AP radiographs taken at the 45 degrees flexion position, the extent of the lesion was studied in 33 hips.

Results: Seven of 11 hips of Type A on neutral position showed Type A lesions. For the remaining 4 hips, 2 were Type B, 2 were on Type C-1 at 45 degrees flexion position. For 22 hips with Type B on neutral position, 6 were Type B, 12 were Type C-1, 4 were Type C-2 found at the 45 degrees flexion position.

Discussion: AP radiographs at the 45 degrees flexion position revealed more extensive necrotic area in cases of small and middle size lesions comparing with the neutral position. This finding may be related to progression of the disease.

Aims: The purpose of this study was to clarify how the mechanical characteristics of the lengthened bone changes with time by means of the analyses using the CT based finite element method. Methods: CT images were obtained from the bilateral tibiae of five patients who had undergone unilateral tibia. The average time interval from completion of lengthening to CT scanning was 30 months. There were two patients had CT examinations twice. The analyses were made using the Mechanical Finder®(Mitsubishi Space Software, Osaka, Japan). 3-D finite element models were made from axial CT images of the whole tibiae. The models were 3mm tetrahedron elements for a cancellous bone and 3 nodal-points shell elements with a thickness of 0.3 mm for a cortical bone. The uni-axial compressive load was applied on the tibial plateau, while the distal part of the tibia was fully restrained. The elastic moduli at the middle of the lengthened bones and the maximum principal strains were calculated using the elastic analysis. Results: The elastic moduli of the lengthened bones were significantly smaller than those of the contra-lateral bones, while the maximum principal strains of the lengthened bones tended to be larger. The ratios of the elastic modulus disparity between the lengthened bone and the paired contra-lateral bone to the elastic modulus of the contra-lateral bone decreased significantly with time. Likewise, the ratios of the maximum principal strains calculated as above decreased identically. Conclusions: The results indicated that the stiffness of the lengthened bone got closer to that of the contra-lateral with time, which means the lengthened bones were in the process of modeling during these follow up time intervals.

Axial radiographs were obtained under valgus and external rotation stress at 45° of knee flexion with and without contraction of the quadriceps muscle in order to assess the dynamics of patellar subluxation or dislocation. The radiography was performed on 82 knees in 61 patients with patellofemoral instability, and on 44 normal knees. The lateral patellofemoral angle and the congruence angle were measured and compared with the conventional Merchant views. Both parameters showed greater differences between symptomatic and normal knees on the stress radiographs obtained without quadriceps contraction. There was a major difference in the lateral patellofemoral angles between the groups, which clearly distinguished symptomatic knees from normal controls. Congruence angles on stress radiography had a significant correlation with the functional scores obtained after a period of conservative treatment and a positive correlation with the frequency of patellar subluxation.

When the quadriceps contracted, two patterns of patellar shift were observed. While the patella reduced into the trochlear groove in all normal knees and about 70% of the symptomatic knees, contraction of the quadriceps caused further subluxation of the patella in the remaining symptomatic knees. All the knee joints which showed this displacement failed to respond to conservative treatment and eventually required surgical treatment. Thus, this technique of stress radiography is a simple, cost-effective and useful method of evaluating patellar instability and predicting the prognosis.