Tamotsu Tamaki

MECHANICAL STABILITY OF THE PEDICLE SCREW FIXATION SYSTEMS FOR THE LUMBAR SPINE

Five different pedicle screw systems: AO Fixator Interne, VSP Steffee plate, Luque ISF, modified Zielke, and Chibatype plate screw system (experimental device), were evaluated for biomechanical strength. A fatigue test for the screw, compressive, and torsional tests for the pedicle screw systems and a pull-out test of the pedicle screw were done. Even the Schanz screw, which showed the highest endurance limit, may be broken under the continuous loading condition in the body. The AO Fixator Interne and Steffee plate system themselves are rigid and are indicated for injuries that need reduction. The Luque ISF, modified Zielke, and Chiba-type plate screw systems, however, are indicated for degenerative lumbar disease requiring in situ fusion. There was a linear positive correlation between the bone mineral density of the vertebral body and the pull-out strength of the pedicle screw (correlation coefficient, 0.68). The fixation strength of the pedicle screw to the bone decreased remarkably in osteoporosis.

Three-dimensional motion analysis of the cervical spine with special reference to the axial rotation.

The purpose of this study is to obtain basic data on the rotational motion of the cervical spine. Twenty normal men aged 25 to 31 years were investigated. Biplanar roentgenograms of the neck with the head held in neutral and maximally rotated positions were taken in a reference frame. Three sets of x-ray films were measured using a three-dimensional analysis system composed of a digitizer and a personal computer. Total axial rotation was 105° on an average between the occiput and the C7 vertebra. Seventy percent of the total axial rotation occurred between the occiput and the C2 vertebra. Each motion segment between the C2 and C7 vertebrae showed from 4° to 8° rotation on an average. When the head was rotated, lateral bending occurred by coupling in the same direction as rotation at each segment below the C3-C4 level, and in the opposite direction above the C2-C3 level. At the same time, flexion took place by coupling at each segment below the C5-C6 level, and extension above the C4-C5 level.

Using cineradiography for continuous dynamic-motion analysis of the lumbar spine.

Study Design. Cineradiography was used to analyze continuous dynamic motion in the lumbar spine. Objectives. To identify motion patterns of the lumbar spine in asymptomatic volunteers and symptomatic patients with L4 degenerative spondylolisthesis, and to use the findings to discuss segmental instability in this disorder. Summary of Background Data. The use of radiographic findings to assess lumbar spine instability remains controversial. Although some studies have reported on lumbar kinematics during actual movement, the motion patterns in asymptomatic volunteers and symptomatic patients with L4 degenerative spondylolisthesis have not been fully clarified. Methods. While asymptomatic volunteers (n=20; mean age, 27; control group) and symptomatic patients with L4 degenerative spondylolisthesis (n=41; mean age, 63; degenerative spondylolisthesis [DS] group) flexed from a sitting neutral position and back to the neutral position (flexion course), cineradiography was used to record lateral segmental lumbar motions. Twelve frames were selected during the flexion course, and flexion-extension angle (f-e angle) and translation in the sagittal plane were measured at each motion segment (L2–L3, L3–L4, L4–L5, and L5–S1). The DS group was classified into 2 subgroups according to percentage of slip: DS group I, with a slip equal to or less than 15%; and DS group II, with a slip of more than 15%. The motion pattern was compared between the groups. Results. In the control group, f-e angle and translation at the L2–L3, L3–L4, and L4–L5 segments moved simultaneously, although the L5–S1 segment showed an initial delay. The amount of f-e angle and translation changed almost symmetrically. In both f-e angle and translation, the L4–L5 segment showed a large motion pattern. In DS group I (n=21), the L4–L5 segment showed a large motion pattern in f-e angle and an intermediate motion pattern in translation. In DS group II (n=20), the L4–L5 segment showed an intermediate motion pattern in f-e angle, and a small motion pattern in translation. The relative range of f-e angle at the L4–L5 segment had the largest range in DS group I, and the relative translation showed a serial decrease from the control group through DS group II. A significant correlation between f-e angle and translation (harmonious motion pattern) was noted at the L2–L3, L3–L4, and L4–L5 segments in the control group. The harmonious motion pattern at the L4–L5 segment was significantly less in the DS group than in the control group. The loss of harmonious motion pattern (disordered motion pattern) at L4–L5 was well-revealed in the DS group II. Conclusions. Motion analyses using cineradiography helped to explain the phenomena of lumbar spine kinematics. Based on continuous dynamic-motion analysis with cineradiography, large f-e angle and disordered motion pattern during the flexion-backward course in the DS group I was considered to be caused by segmental instability. The decreased translation and disordered motion pattern throughout the flexion course in the DS group II was considered to be caused by restabilization.

The effect of striking angle on the buckling mechanism in blowout fracture.

Background: The buckling mechanism is widely accepted as a mechanism of blowout fractures, along with the hydraulic mechanism. Although many studies have been performed related to the buckling mechanism, none of them have taken the direction of the striking force into consideration. As the orbital floor is not parallel to the horizontal plane, a difference in the striking force direction might affect resultant fracture patterns. The present study aims to investigate whether fracture patterns in the orbital floor were influenced by the striking force direction in terms of the buckling mechanism. Methods: The authors produced three-dimensional models on a workstation simulating eight dry skulls and applied striking forces on the orbital rim of each model from three different angles (0, 15, and 30 degrees in the upward direction). Using finite element analysis, the authors calculated the width of the area where the resultant stresses exceed the bones yielding criterion. The width was termed the “theoretical fracture width” because, theoretically, fracture was expected to occur in the area. Then, the authors compared the theoretical fracture width in groups with the three different striking force angles. Finally, the validity of the theoretical width was verified with an experiment on actual skull models. Results: The theoretical fracture width was the greatest when the striking force was directed at 30 degrees in the upward direction. Conclusions: For the buckling mechanism, fracture would occur in a wider area of the orbital floor when striking force was directed upward than when the force was horizontally directed. This finding would be helpful in predicting fracture width in blowout fractures.

Experimental Study on External Tibial Rotation of the Knee

Using biplanar roentgenographic photogrammetry, we investigated posterolateral rotatory instability of the knee joint both before and after sectioning of postero lateral structures, the posterior cruciate ligament, and the lateral collateral ligament. Fifteen fresh-frozen ca daveric knees were used. Compared with the intact state, sectioning of the posterior cruciate ligament alone did not increase the amount of external tibial rotation, but the axis of external tibial rotation shifted when the anterolateral bundle of the posterior cruciate ligament was cut. When the posterior cruciate ligament was cut after sectioning of the posterolateral structures and the lateral collateral ligament, external tibial rota tion increased and the axis of external rotation shifted. The results demonstrated that sectioning of the antero lateral bundle of the posterior cruciate ligament is as sociated with a change in the location of the axis of tibial rotation. Therefore an isolated posterior cruciate ligament injury can alter the kinematics of the knee joint by changing the axis of external tibial rotation. The present results also demonstrate that the posterior cruciate ligament serves as a kind of secondary re straint to posterolateral rotatory instability in knees with injured posterolateral structures. Helical motion analy sis using biplanar roentgenographic photogrammetry is a useful method for evaluating knee kinematics.

Influence of the Interosseous Talocalcaneal Ligament Injury on Stability of the Ankle-Subtalar Joint Complex — a Cadaveric Experimental Study

The present study aims to clarify the influence of the interosseous talocalcaneal ligament (ITCL) injury associated with injury to the lateral ankle ligaments on the ankle-subtalar joint complex motion under conditions of physiologic loading. We conducted mechanical tests using five fresh cadaveric lower extremities. Each specimen was mounted in the loading device and an axial cyclic load from 9.8 to 686 N was applied. Three-dimensional rotations of the ankle and the subtalar joint were measured simultaneously by a linkage electric goniometer. Mechanical tests were repeated after sectioning of the anterior talofibular ligament (ATFL), and again after additional sectioning of the ITCL. In the intact condition, the ankle and the subtalar joints rotated consistently with increase of the load. The predominant rotations were plantar flexion and adduction at the ankle joint, with some eversion demonstrated at the subtalar joint. Although ATFL sectioning did not significantly change the motion of the two joints, additional sectioning of the ITCL significantly increased adduction and total rotation of the ankle joint. The present study demonstrated that a combined injury of the ATFL and the ITCL can induce anterolateral rotatory instability of the ankle joint under conditions of axial loading.

The dynamic role of buttress reconstruction after maxillectomy

Background: The purpose of this study was to investigate the dynamic effect of maxillary reconstruction after partial resection of the maxilla. Methods: On a personal computer, three-dimensional maxilla models were designed based on computed tomographic data obtained from 10 edentulous skull models. Simulation surgery was performed on each model, creating 10 pairs of half-removed maxilla models and corresponding models after reconstruction with a rib. The three different patterns seen in the 10 models were termed normal maxilla, half-removed maxilla, and reconstructed maxilla. After an implant was fixed on the molar region of each model, a 300-N vertical load and a 50-N horizontal load were applied. Using finite element analysis software, the deviation and stress on each model were calculated and compared between different model patterns. Results: Regarding deformity of the maxilla, when a vertical load was applied, no significant difference was observed among the three model patterns. However, a difference was observed in response to a horizontal load in that there was a tendency for deformation to occur, with that of half-removed maxilla being the greatest followed by reconstructed and normal maxilla. Regarding stresses around the implant, when the vertical and horizontal loads were applied, no significant difference was observed among the three model patterns in maximum stress around the implant. Conclusions: A buttress reconstruction is effective in increasing the stability of the maxilla against a horizontal load. However, the maximum stress around the implant in the molar region is unaffected whether or not removal or reconstruction is performed.

Three-dimensional motion of the upper cervical spine in rheumatoid arthritis

Rheumatoid arthritis frequently contributes to instability of the upper cervical spine. Rotational instability of the upper cervical spine was evaluated in rheumatoid arthritis patients using biplanar x-ray photogrammetry. Three-dimensional cervical motion and the instantaneous axis of rotation of the atlas relative to the axis were evaluated in normal and rheumatoid arthritis patients during axial rotation in the horizontal plane. Anterior atlantoaxial subluxation did not increase during axial head rotation in either the atlantoaxial subluxation or the vertical subluxation groups, while the instantaneous axes of rotation were distributed posteriorly in the dens in the RA-normal group, but were widely scattered in the atlantoaxial subluxation group.

Double-bar application decreases postoperative pain after the Nuss procedure

OBJECTIVE This biomechanical study aims to elucidate whether additional bar application increases postoperative pain after the Nuss procedure for pectus excavatum. METHODS Clinical evaluation: The intensity of postoperative pain was compared between patients for whom a single-bar was used (single-bar group: n = 14) and those for whom double bars (double-bar group: n = 10) were used to correct the thoracic deformity. The evaluation was performed by referring to the frequency with which local anesthetics were self-injected in a patient-controlled anesthetic system and how many days were needed for the patients to resume ambulation. Theoretical evaluation: An original simulation system for the Nuss procedure was developed by producing 3-dimensional finite element analysis models from computed tomographic data of patients with pectus excavatum. With this system, single-bar and double-bar placement was simulated separately for the thorax models of the double-bar group. The stresses occurring on the thoraces were then compared between the two situations. RESULTS Clinical evaluation: Self-injection of local anesthetic was more frequent for the single-bar group than for the double-bar group; single-bar patients restarted ambulation later than the double-bar group. Theoretical evaluation: Stresses on the thoraces were smaller when double bars were applied than when a single bar was applied. CONCLUSIONS Performing double-bar placement decreases postoperative pain. Therefore, surgeons should not hesitate to perform double-bar correction in patients in whom the deformity extends to multiple intercostal spaces, requiring correction of the thorax shape at multiple sites.

Quantitative analysis of cell detachment by shear stress

It is important to enhance adhesive force of cells to scaffolds in a field of tissue engineering. In this study, we developed a new system that can evaluate detachment force of cells with ease. A cone and plate-type viscometer provides a well-defined homogeneous laminar flow and consists of simple structure. Therefore, the system was based on a modified cone and plate-type viscometer equipped with an upright epifluorescence microscope. The fixation of diverse biomaterials, i.e. plate-, membranous- and porous-shaped materials to the system was enabled possible. In addition, small volume of medium, small number of cells, and small piece of material were enough to evaluate cell detachment by shear stress. By using the newly developed apparatus, the phenomena of cell detachment were quantitatively analyzed with ease. Therefore, our apparatus should be a useful instrument to develop and evaluate the materials that are expected to enhance endothelialization.