Mitsuhiko Ikebuchi

Comparison of Bone Mineral Density Between Porous Tantalum and Cemented Tibial Total Knee Arthroplasty Components

BACKGROUND Porous tantalum was recently introduced as a metallic implant material for total knee arthroplasty. Its porosity, low modulus of elasticity, and high frictional characteristics were expected to provide physiologic load transfer and relative preservation of bone stock. However, to our knowledge, the effect of a Trabecular Metal tibial component on bone mineral density has not been reported. The purpose of the present study was to compare the periprosthetic bone mineral density between patients managed with uncemented Trabecular Metal and cemented tibial components. METHODS Twenty-eight knees receiving a Trabecular Metal tibial component and twenty-eight knees receiving a cemented cobalt-chromium tibial component had dual x-ray absorptiometry scans at two weeks preoperatively and at two weeks and six, twelve, eighteen, and twenty-four months postoperatively, to assess periprosthetic bone mineral density. All of the operations were performed by one surgeon through a medial parapatellar approach. RESULTS None of the differences between the two groups in terms of preoperative bone mineral density in the femoral neck, wrist, lumbar spine, or knee were significant. In both groups, the bone mineral density in the tibia decreased postoperatively. However, the postoperative decrease in bone mineral density in the lateral aspect of the tibia was significantly less in knees with Trabecular Metal components than in knees with cemented tibial components at twenty-four months (mean and standard deviation, -6.7% +/- 22.9% compared with -36.8% +/- 24.2%; p = 0.002). At twenty-four months postoperatively, there was no significant difference between the two groups in terms of the Knee Society score, range of motion of the knee, or bone mineral density in the lumbar spine. No prosthetic migration or periprosthetic fracture was detected in either group. CONCLUSIONS The decrease in bone mineral density of the lateral tibial plateau was less in knees with a Trabecular Metal tibial component following total knee arthroplasty than in knees with a cemented tibial component. Additional research is needed to determine whether long-term clinical benefits are realized with the use of porous tantalum tibial components for total knee arthroplasty.

In Vivo Analysis of Polyethylene Wear Particles After Total Knee Arthroplasty: The Influence of Improved Materials and Designs

Polyethylene wear particles induce macrophages to release cytokines, which can lead to osteolysis and aseptic loosening of total joint prostheses1. The generation of polyethylene wear particles is one of the most important factors that affects the midterm and long-term clinical results associated with total knee arthroplasty2,3. The generation of polyethylene wear particles is correlated with the activity level of the patient4, and greater demands are placed on a total knee prosthesis when it is implanted in a younger, more active patient5. Therefore, to achieve better long-term results for patients who have higher activity levels, modifications of materials (i.e., highly cross-linked polyethylene and alumina ceramic) and design (i.e., mobile bearing and medial pivot) have been developed to reduce polyethylene wear after total knee arthroplasty. It takes decades to evaluate the long-term results of newly introduced total knee prostheses. Thus, it is particularly important to examine in vivo polyethylene wear generation in new prostheses before they come into widespread use. It is difficult to determine the in vivo polyethylene wear of total joint prostheses (with the exception of total hips) with use of postoperative radiographs. To measure polyethylene wear in vivo, we developed and employed a method in which we isolated and analyzed polyethylene wear particles in the synovial fluid of knees that had a well-functioning total knee prosthesis6-9. The number, size, and shape of polyethylene wear particles have been reported to be critical factors in the development of osteolysis. Greater volume, submicrometer size, and an elongated shape of polyethylene wear particles all stimulate an increased macrophage response10-12. Our hypothesis was that modification of total knee arthroplasty materials and designs can influence the generation of polyethylene wear particles in vivo. In the present study, …

A cemented mobile-bearing total knee replacement prevents periprosthetic loss of bone mineral density around the femoral component: A MATCHED COHORT STUDY

Bone mineral density (BMD) around the femoral component has been reported to decrease after total knee replacement (TKR) because of stress shielding. Our aim was to determine whether a cemented mobile-bearing component reduced the post-operative loss of BMD. In our study 28 knees receiving a cemented fixed-bearing TKR were matched with 28 receiving a cemented mobile-bearing TKR. They underwent dual-energy x-ray absorptiometry, pre-operatively and at three weeks and at three, six, 12, 18 and 24 months post-operatively. The patients were not taking medication to improve the BMD. The pre-operative differences in the BMD of the femoral neck, wrist, lumbar spine and knee in the two groups were not significant. The BMD of the femur decreased postoperatively in the fixed-bearing group, but not the mobile-bearing group. The difference in the post-operative change in the BMD in the two groups was statistically significant (p < 0.05) at 18 and 24 months. Our findings show that a cemented mobile-bearing TKR has a favourable effect on the BMD of the distal femur after TKR in the short term. Further study is required to determine the long-term effects.

Porous Tantalum Tibial Component Prevents Periprosthetic Loss of Bone Mineral Density After Total Knee Arthroplasty for Five Years—A Matched Cohort Study

In 21 knees receiving porous tantalum tibial component and 21 knees receiving a cemented cobalt-chromium tibial component, dual x-ray absorptiometry scans were performed for five years post-operatively. The postoperative decrease in the bone mineral density in the lateral aspect of the tibia was significantly less in knees with porous tantalum tibial components (11.6%) than in knees with cemented cobalt-chromium tibial components (29.6%) at five years (p < 0.05). No prosthetic migration or periprosthetic fracture was detected in either group. The present study is one of the studies with the longest follow-up period on bone mineral density after total knee arthroplasty. Porous tantalum tibial component has a favorable effect on the bone mineral density of the proximal tibia after total knee arthroplasty up to five years.

The flexion gap preparation does not disturb the modified gap technique in posterior stabilized total knee arthroplasty

PURPOSE Preparation of the flexion gap (resection of the posterior femoral condyle and removal of the osteophytes on the posterior aspect of the femur to re-establish the posterior capsular recess) during modified gap technique might change the soft-tissue balancing and disturb the preparation of equal and rectangular extension and flexion joint gaps. The purpose of this study was to measure the change in the extension and flexion gaps using tension device during posterior stabilized TKA with modified gap technique. METHODS We examined changes in the extension gap and flexion gap during posterior stabilized TKA using modified gap technique in 100 consecutive varus osteoarthritis knees. The extension gap was first prepared and then the distance and angle of both extension and flexion gaps were measured before and after preparation of the flexion gap using a tension device. RESULTS Although both the extension and flexion gaps significantly increased during the operation, the amount of the increase was very small, and the difference between the increase in the extension gap (0.9 ± 0.1mm [mean ± SE]) and that in the flexion gap (0.7 ± 0.1mm) was not statistically significant. Mean angular changes in extension and flexion gaps during the operation were less than 1°. CONCLUSIONS The preparation of the flexion gap in posterior stabilized TKA did not disturb the modified gap technique in terms of equal and rectangular extension and flexion gaps.

Advantages of externally powered prosthesis with feedback system using pseudo-cineplasty

Externally powered upper-limb prostheses are difficult to use because of the lack of sensory feedback. Neuroprostheses have recently been developed for people with upper-limb amputation but are complicated, expensive, and still developing. We therefore designed a simple system by combining pseudo-cineplasty with extended physiological proprioception to provide sensory feedback to the body. We penetrated the palmaris longus tendon percutaneously with a metal ring, similar to that used in body piercing, in a nondisabled subject as a pseudo-cineplasty. The tendon and ring were connected to the system, and a sensory feedback experiment was performed. We investigated the ability of the user to determine the size of an object grasped by the prosthetic hand without visual information. The subject could distinguish between large and small objects with 100% accuracy and between small, medium, and large objects with 80% accuracy. In pseudo-cineplasty, control and sensory feedback are natural because the prosthetic hand is controlled by muscle contraction. Tension transmitted from the prosthetic hand is sensed via muscle spindles and skin sensors. This technique allows only partial sensory feedback but appears to offer several advantages over other human-machine interfaces.

Impingement of the patellar component against the tibial post depends on the design of the post-cam mechanism: Comparison between 12 posterior stabilized total knee prostheses

BACKGROUND Patella-post impingement (PPI), contact of the patellar component with the tibial post, occurs during deep knee flexion after posterior stabilized total knee arthroplasty (TKA). In a previous pilot study, only two product lines were investigated. The aim of this study was to compare PPI between 12 contemporary posterior stabilized knee prostheses. METHODS Twelve posterior stabilized knee prostheses were implanted in full-length sawbone models of the femur and tibia using a navigation system. The distance between the lower edge of the patellar component and the cut surface of the tibia was defined as the tibial-patellar clearance (TPC), which represents the length of the patellar tendon. The TPC was set from 20 to 40 mm and the knee was moved from full extension to deep flexion while the knee angle at which PPI occurred (PPI angle) was recorded. RESULTS The PPI angle differed between prostheses (P < 0.05). Shorter TPCs resulted in smaller PPI angles and longer TPCs resulted in larger PPI angles (P < 0.05). To achieve more than 130° of flexion without PPI, the TPC should be prepared at a minimum of 20 mm for the NexGen LPS-Flex, Persona PS, Legion PS, and Evolution PS, 22 mm for the Attune RP and Journey II, 24 mm for the Triathlon PS, PFC Sigma PS, and Attune PS, and 26 mm for the NRG PS, Vanguard PS, and Vanguard RP. CONCLUSIONS The design of the tibial post significantly affects the PPI angle. To avoid PPI during deep flexion, appropriate TPC should be prepared during surgery.

Asymmetric Tibial Component Improved the Coverage and Rotation of the Tibial Component in a Medial Pivot Total Knee Prosthesis

Abstract Malrotation of tibial components is one of the important causes of failure in total knee arthroplasty. The aim of this study is to determine the relationship between tibial rotational positioning and coverage of the tibial surface during the operation, using a symmetric and newly introduced asymmetric medial pivot tibial components. The coverage and overhang were compared between a symmetric component (Advance medial pivot) and a newly introduced asymmetric medial pivot tibial component (Evolution medial pivot) in 31 knees during the operation. When the tibial component was placed parallel to the anteroposterior (AP) axis, the uncovered width in the posteromedial part using a symmetric design was larger than that using an asymmetric design (p < 0.01). Overhang in the posterolateral part was observed in 42% for a symmetric design and 3% for an asymmetric design (p < 0.01). When the component was placed in malrotation (10 degrees internal to the AP axis), overhang in the posteromedial part was observed in 6% for a symmetric design and in 71% for an asymmetric design (p < 0.01). The tibial rotation parallel to the AP axis and maximizing coverage of the tibial surface conflict in a symmetric design, but are compatible in an asymmetric design. An asymmetric tibial component is expected to improve the coverage and the rotational positioning of medial pivot total knee prosthesis.

Anatomical landmarks of the distal femoral condyles are not always parallel to the tibial bone cut surface in flexion during total knee arthroplasty

BACKGROUND Soft tissue balancing is crucial to the success of total knee arthroplasty (TKA). To create a rectangular flexion joint gap, the rotation of the femoral component is important. The purpose of this study is to determine whether or not anatomical landmarks of the distal femoral condyles are parallel to the tibial bone cut surface in flexion. METHODS Forty-eight patients (three male and 45 female) with a mean age of 74years were examined. During the operation, we estimated the flexion joint gap with the following three techniques. 1) a three degree external cut to the posterior condylar line (MR1), 2) a parallel cut to the surgical transepicondylar axis (MR2), and 3) a parallel cut to the anatomical transepicondylar axis (MR3). RESULTS The flexion joint gap was 1.1±3.0° (mean±standard deviation (SD)) in internal rotation in the case of MR1, 0.9±3.4° in internal rotation in the case of MR2, and 2.1±3.4° in external rotation in the case of MR3. An outlier (flexion joint gap >3.0°) was observed in 12 cases (25%) in MR1, 13 cases (27%) in MR2, and 15 cases (31%) in MR3. CONCLUSIONS The anatomical landmarks of the distal femoral condyles are not always parallel to the tibial bone cut surface in flexion. To create a rectangular flexion joint gap, the rotation of the femoral component rotation is based not only on the anatomical landmarks but also on the ligament balance.

Measurement of 3D Distance between Artificial Cement-Type Cup and Head After THR

The purpose of our study is a measurement of 3D (three dimensional) distance between an artificial cement-type cup and a artificial femoral head in a living patients body after THR(total hip replacement) from an AP(anterior-posterior) Roentgen image and a lateral image, when the angle between the two images is unknown. Recently we proposed a measurement method for non-cement-type cup. We modified the 3D measurement method for a non-cement cup with evolutionary computation(EC) and extend the framework for a cement-type cup. Our method needs only two times of shots using an ordinary Roentgen equipment without measurement the angle of the two images. So our method is superior to Martells Method. And it needs no metal balls in a patient body unlike RSA (Roentgen stereophotogrammetric analysis). We show the result of a computer simulation with CG (computer graphics) image we made and the result in vitro with Roentgen images of artificial cup and head moved by a micro-manipulator.