Keiji Iwamoto

Significant effect of the posterior tibial slope on the weight-bearing, midflexion in vivo kinematics after cruciate-retaining total knee arthroplasty.

The purpose of the present study was to compare weight bearing (WB) and non-WB conditions, and to evaluate the effect of the posterior tibial slope (PTS) on the in vivo kinematics of 21 knees after posterior cruciate ligament-retaining total knee arthroplasty during midflexion using 2-dimensional/3-dimensional registration. During WB, medial pivot and bicondylar rollback were observed. During non-WB, both the medial and lateral condyles moved significantly more anteriorly as compared to the WB state. These patients were divided into 2 groups according to their PTS. The large PTS group showed a significant posterior displacement of the medial femoral condyle as compared with the small PTS group, but no significant difference was observed at the lateral femoral condyle during both WB and non-WB. The PTS influenced knee kinematics through gravity (124/125).

Carbonyllithium chemistry. Intramolecular conversion of an acyllithium via the utilization of an anionic 1,2-stannyl rearrangement☆

Abstract The reaction of α-stannylmethyllithium with CO (1 atm) generates the acyllithium that smoothly undergoes anionic 1,2-stannyl rearrangement at −78°C to give the enolate derivative of acyltin. The rearrangement of the stannyl group is much faster than that of the silyl group.

In vivo kinematic analysis of posterior-stabilized total knee arthroplasty for the valgus knee operated by the gap-balancing technique.

BACKGROUND Most in vivo kinematic studies of total knee arthroplasty (TKA) report on the varus knee. The objective of the present study was to evaluate in vivo kinematics of a posterior-stabilized fixed-bearing TKA operated on a valgus knee during knee bending in weight-bearing (WB) and non-weight-bearing (NWB). METHODS A total of sixteen valgus knees in 12 cases that underwent TKA with Scorpio NRG PS knee prosthesis and that were operated on using the gap balancing technique were evaluated. We evaluated the in vivo kinematics of the knee using fluoroscopy and femorotibial translation relative to the tibial tray using a 2-dimensional to 3-dimensional registration technique. RESULTS The average flexion angle was 111.3°±7.5° in WB and 114.9° ± 8.4° in NWB. The femoral component demonstrated a mean external rotation of 5.9° ± 5.8° in WB and 7.4° ± 5.2° in NWB. In WB and NWB, the femoral component showed a medial pivot pattern from 0° to midflexion and a bicondylar rollback pattern from midflexion to full flexion. The medial condyle moved similarly in the WB condition and in the NWB condition. The lateral condyle moved posteriorly at a slightly earlier angle during the WB condition than during the NWB condition. CONCLUSIONS We conclude that similar kinematics after TKA can be obtained with the gap balancing technique for the preoperative valgus deformity when compared to the kinematics of a normal knee, even though the magnitude of external rotation was small. LEVEL OF EVIDENCE IV.

In vivo kinematics of three-component mobile-bearing total ankle replacement in rheumatoid ankle with talocalcaneal arthrodesis and spontaneous talocalcaneal fusion

Abstract Objective. It is often that patients with rheumatoid arthritis (RA) who require ankle surgeries already have the degeneration of talocalcaneal joints. When talocalcaneal joint was fused, whether operatively or spontaneously, ankle kinematics would be affected. The purpose of this paper was to study in vivo kinematics of mobile-bearing total ankle replacement (TAR) in rheumatoid ankle with concomitant talocalcaneal arthrodesis or with preexisting spontaneous talocalcaneal fusion. Methods. Thirteen TARs in ten patients with RA, in whom talocalcaneal joints had already been fused spontaneously or surgically, were studied. Fluoroscopic images were obtained while each patient was walking with full weightbearing on the implanted ankle. Thereafter tibio–talar motion was analyzed by 2D/3D registration technique. Results. Average tibio–talar motion was 4.0 ± 5.3° for plantarflexion and 6.6 ± 0.3° for dorsiflexion. Average range of internal/external rotation, inversion/eversion and AP translation was 3.8 ± 1.3°, 2.7 ± 1.0° and 1.6 ± 0.6 mm, respectively. Conclusions. Mobility of mobile-bearing TAR with talocalcaneal fusion was small during the stance phase of gait, but clinically measured ROM was mostly preserved. The movements of internal/external rotation and AP translation were allowed to a certain degree, but not of inversion/eversion. Even though the movement of inversion/eversion is limited, talocalcaneal arthrodesis could be accompanied with mobile-bearing TAR in rheumatoid ankles.

Primary and Revision Total Ankle Arthroplasty in Japan

Ankle arthrodesis is still performed more frequently than total ankle replacement for treatment of painful degenerative changes about the ankle joint. However, total ankle replacement has advanced during the last few decades and the clinical results have been improved substantially. Prosthesis design, preoperative planning, operative techniques to balance the joint, and postoperative evaluation of outcomes have made progress and have allowed surgeons to achieve good clinical results reliably. Since 2003, we started to use the three-component total ankle prosthesis with a mobile-bearing polyethylene insert. As a result, the FINE Total Ankle System is the most frequently employed ankle prosthesis in Japan today. It was designed to allow not only dorsiflexion and plantar flexion but also ±10° of internal and external rotation and ±3-mm anterior–posterior sliding along the mobile-bearing mechanism. We have investigated the in vivo kinematics of this three-component total ankle replacement. The preliminary results are promising and the prosthesis mimics the normal ankle kinematics during gait. Since 2006, the sliding medial malleolar osteotomy technique to balance varus malalignment, the use of a preoperative three-dimensional preoperative bone model based upon DICOM data obtained from a preoperative computed tomography scan, and dedicated patient-specific surgical instruments have played important roles in total ankle replacement surgery precision. However, we previously have limited the indication for total ankle replacement to only inflammatory arthritis due to low-demand physical activities, but more recently, we started expanding our indications to include osteoarthritis patients with higher daily activities. Even with the limited clinical experiences, the midterm results may be promising.