Kuniyoshi Abumi

An in vitro human cadaveric study investigating the biomechanical properties of the thoracic spine.

Study Design. An in vitro human cadaveric study comparing the effects of anterior and posterior sequential destabilization conditions on thoracic functional unit mechanics was studied. Objectives. To investigate the biomechanical properties of the human thoracic spine. Summary of Background Data. Few studies have addressed the mechanical role of the costovertebral joints under torsion in the stability of the human thoracic spine. Methods. Sixteen functional spinal units with intact costovertebral joints were obtained from six human cadavers and randomized into two groups based on destabilization procedures: Group 1, anterior to posterior sequential resection; and Group 2, posterior to anterior sequential destabilization. Biomechanical testing was performed after each destabilization procedure, and the range of motion under maximum load was calculated. Results. Group 1: Under flexion–extension, lateral bending, and axial rotation loading, discectomy increased the range of motion by 193%, 74%, and 111%, respectively. Moreover, subsequent right rib head resection further increased the range of motion by 81%, 84%, and 72%, respectively. Group 2: Under all loading conditions laminectomy + medial facetectomy resulted in a 22–30% increase in range of motion. Subsequent total facetectomy led to an additional 15–28% increase in range of motion. Conclusion. The rib head joints serve as stabilizing structures to the human thoracic spine in the sagittal, coronal, and transverse planes. In anterior scoliosis surgery additional rib head resection after discectomy may achieve greater curve and rib hump correction. The lateral portion of the facet joints plays an important role in providing spinal stability and should be preserved to minimize postoperative kyphotic deformity and segmental instability when performing decompressive wide laminectomy.

Artificial intervertebral disc replacement using bioactive three-dimensional fabric: design, development, and preliminary animal study.

Study Design. A new artificial intervertebral disc was developed, and its intrinsic biomechanical properties, bioactivity, and the effectiveness as a total disc replacement were evaluated in vitro and in vivo. Objectives. To introduce a new artificial intervertebral disc and to evaluate the in vitro mechanical properties, fusion capacity to bone, and segmental biomechanics in the total intervertebral disc replacement using a sheep lumbar spine. Summary of Background Data. The loss of biologic fusion at the bone–implant interface and prosthetic failures have been reported in previous artificial discs. There have been no clinically applicable discs with detailed experimental testing of in vivo mechanics and interface fusion capacity. Methods. The artificial intervertebral disc consists of a triaxial three-dimensional fabric (3-DF) woven with an ultra-high molecular weight polyethylene fiber, and spray-coated bioactive ceramics on the disc surface. The arrangement of weave properties was designed to produce mechanical behavior nearly equivalent to the natural intervertebral disc. Total intervertebral disc replacement at L2–L3 and L4–L5 was performed using 3-DF disc with or without internal fixation in a sheep lumbar spine model. The segmental biomechanics and interface histology were evaluated after surgery at 4 and 6 months. Results. The tensile-compressive and torsional properties of prototype 3-DF were nearly equivalent to those of human lumbar disc. The lumbar segments replaced with 3-DF disc alone showed a significant decrease of flexion–extension range of motion to 28% of control values as well as partial bony fusion at 6 months. However, the use of temporary fixation provided a nearly physiologic mobility of the spinal segment after implant removal as well as excellent bone–disc fusion at 6 months. Conclusion. An artificial intervertebral disc using a three-dimensional fabric demonstrated excellent in vitro and in vivo performance in both biomechanics and interface histology. There is a potential for future clinical application.

Clinical outcome of posterolateral endoscopic surgery for pyogenic spondylodiscitis: results of 15 patients with serious comorbid conditions.

Study Design. Clinical results of posterolateral endoscopic debridement and irrigation followed by percutaneous drainage for pyogenic spondylodiscitis were analyzed. Objectives. To report clinical results of transforaminal endoscopic surgery for pyogenic spondylodiscitis and to evaluate the effectiveness of this procedure in treatment of pyogenic spinal infections. Summary of Background Data. Pyogenic spinal infections have been increasing due to the development of medical treatment for patients with comorbid medical problems. Common treatments for spinal infections are administration of antibiotics or surgical debridement with bone grafts. There have been no reports, however, regarding the clinical outcome of posterolateral endoscopic treatment for pyogenic spinal infections. Methods. Fifteen consecutive patients with pyogenic spondylodiscitis in the thoracic or lumbar spine were enrolled. Preoperative antibiotic treatment had failed in all the patients. The procedures consisted of posterolateral endoscopic debridement and irrigation followed by percutaneous drainage through single portal under the combination of local and intravenous anesthesia. Pain response using visual analog scale (VAS, 0–100 mm), inflammation parameters, and duration of antibiotic therapy were investigated. Radiologic evaluation focused on bony fusion, local kyphosis, disc height reduction, and abscess formation. Results. All patients showed immediate pain reduction after surgery. Averaged VAS for pain was 86 before surgery and 25 at postoperative 1 week. Average of CRP was 4.00 mg/dL before surgery and 1.88 mg/dL at postoperative 1 week. Averaged duration of antibiotics therapy was 3.7 weeks. Spinal fusion was obtained in 13 patients. Two patients with neurologic deficits due to epidural abscess returned to normal. Preoperative psoas abscess in 6 patients disappeared after surgery on MRI. Conclusions. Posterolateral spinal endoscopic debridement and irrigation brought immediate pain reduction and good clinical results to patients who had comorbid medical problems and had pyogenic spondylodiscitis.

Cervical spine injuries associated with lateral mass and facet joint fractures: new classification and surgical treatment with pedicle screw fixation

To clarify the injury pattern, initial spinal instability, degree of discoligamentous injuries in cervical lateral mass and facet joint fractures, we retrospectively analyzed radiological parameters and introduced a new classification for these injuries. Surgical treatment was performed with cervical pedicle screw fixation (CPS), and overall neurological and radiological outcome was evaluated with a minimum follow-up period of 2xa0years. Lateral mass fractures were divided into the following four subtypes: separation, comminution, split, and traumatic spondylolysis. The sagittal and frontal alignments were evaluated at both mainly injured and adjacent spinal segments on radiographs. The initial discoligamentous injuries were investigated on magnetic resonance imaging in terms of their frequencies, subtype of injuries, and involved spinal levels. Anterior translation of fractured vertebra was demonstrated in 77% of lateral mass fractures, while 24% of anterior translation was observed, even in cephalad-adjacent vertebrae. On magnetic resonance imaging, signal changes in anterior longitudinal ligament (ALL) and intervertebral disc were demonstrated in 76% of caudal segments and 24% of cephalad segments adjacent to fractured vertebra of lateral mass fractures. The subtype analyses of lateral mass fractures demonstrated high rates of anterior translation in separation, split, and traumatic spondylolisthesis, as well as significant coronal malalignment in comminution and split types (p<0.05). Thirty-one patients underwent surgical treatments using a cervical pedicle screw fixation. The CPS provided the superior capability of deformity correction without pseudoarthrosis, as well as excellent neurological recovery. The average numbers of stabilized segments were minimized without serious complications. In separation, facet joint fracture, and fractures with mild lateral mass comminution, the single level posterior fixation can be considered. The significant unstable injuries of split and comminution type with coronal malalignment can be treated with exclusive two-level posterior stabilization with CPS. The initial evaluation of fracture subtypes helps to successfully minimize the stabilized spinal segment.

Bone ingrowth fixation of artificial intervertebral disc consisting of bioceramic-coated three-dimensional fabric.

Study Design. The bone-bonding characteristic of the new artificial intervertebral disc consisting of bioceramic-coated three-dimensional fabric was evaluated mechanically and histologically in an in vivo sheep model. Objectives. To investigate the mechanical properties and the histologic appearance of the interface between the three-dimensional fabric disc and the vertebral body, and to evaluate these alterations in vivo under a spinal segmentally mobile condition. Summary of Background Data. Bone ingrowth to the bioceramic-coated three-dimensional fabric surface had been demonstrated already under a stable environment in preliminary animal studies. Methods. For this study, 20 sheep underwent two-level lumbar intervertebral disc replacement with three-dimensional fabric discs (Group I) or bioceramic spacers as a comparative material (Group II). All operative segments were stabilized temporarily with spinal instrumentation for the initial ingrown phase. Four animals each were killed at 4, 6, 15, and 24 months in Group I and at 6 months in Group II, and the operative segments were subjected to either a detachment test or histologic evaluation. Results. The interfacial tensile strength at 6 months was significantly higher in Group I than in Group II. No significant decrease in tensile strength was detected until 24 months after surgery in Group I. Histologically, bone ingrowth to the three-dimensional fabric surface was observed 4 months after surgery, and no aseptic loosening occurred until 24 months after surgery. Conclusions. The findings show that the three-dimensional fabric disc was firmly fixed to the vertebral body by bone ingrowth, and that this biologic fixation was preserved even under the spinal segmentally mobile condition.

Iliac crest reconstruction with a bioactive ceramic spacer

This study aimed to investigate the long-term clinical results of the apatite wollastonite-containing glass ceramic (AWGC) iliac spacer and to discuss its efficacy in reconstruction of the bone graft donor site at the iliac crest. Thirty-one patients were studied for more than 10xa0years. All patients underwent anterior spinal fusion using autogenous tricortical iliac bone graft. After harvest of tricortical iliac bone graft, an AWGC iliac spacer ranging from 15xa0mm to 70xa0mm in length was press-fitted into the gap. Long-term clinical results were obtained from radiological and blood examinations. Thirty patients (97%) were satisfied with the spacer. There was new bone formation around the spacer on the radiograph. There was no abnormal silicon concentration in blood examinations. AWGC iliac spacer appears to be useful in the reconstruction of harvested iliac crest. New bone formation occurs, reducing the defect size.

A biomechanical analysis of metastatic vertebral collapse of the thoracic spine: a sheep model study.

Study Design. This is a biomechanical study using sheep thoracic spine to investigate the probability of mechanical failure of the thoracic spine with various sizes or locations of tumor metastasis. Objective. The objectives of this study were to investigate biomechanical effects of not only tumor sizes within the thoracic vertebral body but also its involvement of other spinal components on the probability of mechanical failures of the thoracic spine. Summary of Background Data. There have been no experimental studies concerning mechanical influences of destruction of costovertebral joint or posterior elements as well as vertebral body on the load-bearing capacity of the thoracic spine. Methods. Ninety-nine fresh sheep thoracic spine specimens with ribs were used (T7–T9, T10–T12). Within vertebral bodies of 39 specimens, only trabecular defects were created in different sizes. In other 48 specimens, not only vertebral body defects that were 40% to the cross-sectional area of the vertebral body but also additional destruction of costovertebral joint, pedicle, and facet joint were created. All specimens were subjected to destructive biomechanical testing. Results. The failure load decreased as the defect size in the vertebral body increased. A negative linear correlation was observed between the failure load and the size of vertebral body defect (r2 = 0.782). With 40% cross-sectional defect in the vertebral body, additional costovertebral joint destruction brought 25% reduction of the failure load, which was statistically significant. Conclusion. The load-bearing capacity of metastasized vertebrae in the thoracic spine was proportionally decreased when the defect size in the vertebral body increased. Destruction of costovertebral joint significantly increased the probability of vertebral collapse.

Static and dynamic analysis of five anterior instrumentation systems for thoracolumbar scoliosis

Study Design. A nondestructive biomechanical investigation among five anterior spinal instrumentation systems for scoliosis. Objectives. The purpose of this study is to analyze the static and dynamic biomechanical stability of five different systems. Summary of Background Data. Although a variety of anterior spinal instrumentation systems for scoliosis are available, very few attempts have been made at comparative biomechanical studies. Methods. Thirty calf spines were underwent static biomechanical tests, including flexion–extension, axial rotation, and lateral bending loading modes in the multisegmental spinal model. Five anterior instrumentation systems included: 1) Texas Scottish Rite Hospital system; 2) Bad Wildungen Metz; 3) anterior ISOLA; 4) Cotrel–Dubousset Hoph; and 5) Kaneda Anterior Scoliosis System. The initial and postfatigue stability after a cyclic loading test were analyzed by measuring the range of motion at instrumented segments compared to the intact within the same specimen (% to intact). Results. Two-rod systems showed a significant decrease in range of motion compared to one-rod systems in flexion–extension (P < 0.001) and axial rotation (P < 0.05). In lateral bending, all systems demonstrated a significant decrease in range of motion of less than 40% to the intact (P < 0.001). After cyclical loading test, all systems increased in range of motion. In flexion–extension, one-rod systems depicted a significant increase in range of motion, compared to two-rod systems (P < 0.05). Conclusions. In the initial stability analysis, two-rod systems are superior to one-rod systems. For one-rod systems, repeated physiologic loading may result in reduced stability in flexion–extension.

An investigational study on the healing process of anterior spinal arthrodesis using a bioactive ceramic spacer and the change in load-sharing of spinal instrumentation.

Study Design. Ceramic anterior lumbar interbody arthrodesis was performed using an in vivo sheep model. Observations of fusion status and the load-sharing of spinal instrumentation were studied at sequential intervals for 1 year after surgery. Objectives. To elucidate the healing process of spinal arthrodesis performed with a bioactive ceramic spacer and the change in load-sharing of anterior spinal instrumentation. Summary of Background Data. With the improved development of spinal instrumentation, anterior spinal arthrodesis has become a standard spinal reconstruction technique; however, the mechanistic basis underlying the healing process is not well documented. Moreover, it remains unclear how load-distribution through the fusion mass and spinal instrumentation change throughout the healing process. Methods. Using 24 sheep, a two-level anterior lumbar interbody fusion (L2–L3, L4–L5) was performed using a smooth surface and a porous surface-modified bioactive ceramic, with each segment instrumented using a one-rod anterior spinal instrumentation system. Four animals each were killed at 2, 4, 8, 12, 24, and 52 weeks after surgery. Postmortem analysis included quantification of anterior rod strain under multidirectional flexibility testing and radiographic and histologic analyses of the arthrodesed segments. Results. From 0 to 8 weeks after surgery, the bending strain of the rod gradually decreased despite no obvious bone formation. From 8 to 24 weeks after surgery, the rod strain markedly decreased with the development of bridging trabeculated bone formation between vertebral bodies. After 24 weeks after surgery, minimal changes were observed in rod strain; however, the fusion mass volumetrically increased with corresponding facet joint atrophy. The porous surface-modification of ceramic did not influence the histologic healing process, despite the improvement of interface osseous union rate. Conclusions. In anterior spinal arthrodesis, spinal instrumentation is mainly exposed to bending stress, with decreased load-sharing with corresponding development of the spinal fusion. Continuous bone remodeling of the anterior fusion mass results in concurrent decreases in spinal instrumentation and posterior spinal element load-transmission. The principal healing mechanism of ceramic anterior interbody spinal fusion is not an osseous union between the ceramic and vertebral body, but bridging bone formation around the ceramic, which directly connects the vertebral bodies above and below the disc.

Cervical spine injuries associated with lateral mass and facet joint fractures

Abstract Purpose of study: The objectives of this study were to analyze the surgical results of cervical spine injuries associated with lateral mass and facet joint fractures retrospectively and to clarify the surgical indication and treatment strategies for these injuries. Methods used: From 1991 to 1999, 30 patients including 20 lateral mass fractures and 8 facet joint fractures received surgical treatments in our institution. The average age at surgery was 46 years. The injury types according to Allens classification were compressive-extension in 26, lateral flexion in 3, and distractive-flexion in 1 patient. All patients, except one who required osteosynthesis for the separation fracture of the lateral mass, received exclusive posterior fusion with cervical pedicle screw system. From X-rays and magnetic resonance imaging (MRI) analyses, the fractures were classified into subtypes. The translation of fractured and adjacent vertebrae in the sagittal and coronal planes, vertebral body destruction and signal changes of disc and spinal ligaments (ALL, PLL, SSL and ISL) on MRI were evaluated. The number of stabilized segments and the spinal alignment were also evaluated at follow-up. of findings: The lateral mass fractures were divided into the following four subtypes: separation fracture in 11, comminution type in 4, split type in 5 and traumatic spondylolysis in 2. The superior and inferior articular process fractures and combination of both fractures were seen in six, one and one patient, respectively. The anterior translation of fractured vertebra was demonstrated in 77% of lateral mass fractures, whereas 24% and 10% of anterior translation was observed even in cephalad and caudal adjacent vertebrae, respectively. The alignment change in coronal plane was detected in 33% of lateral mass fractures. On MRI, the signal changes in ALL and disc were demonstrated in 76% and 25% of caudal and cephalad segments adjacent to fractured vertebra, respectively. The number of stabilized segments were 1.4, 1.67 and 2 in separation, comminution and split type, respectively. The fusion was completely achieved in all patients. However, the preservation of spinal segments resulted in fusion with the mild anterior translation in six patients. Relationship between findings and existing knowledge: Little is known about the detailed fracture type of lateral mass/facet fractures, initial instability, and a frequency of soft tissue injury. This study first analyzed these parameters. Overall significance of findings: The evaluation of spinal instability as well as the assessment of soft tissue injury on initial MRI was essential for the diagnosis and treatment of lateral mass and facet fractures. We successfully saved the stabilized segments in separation fractures or fractures with mild comminution based on the adjacent disc and ligaments evaluation. However, severely comminuted lateral mass fractures with coronal plane malalignment required two-level posterior fixation. The exclusive posterior stabilization with cervical pedicle screw system provides a short fusion as well as a normal spinal alignment even in the lateral mass fractures with severe spinal instability. Disclosures: Device or drug: cervical pedicle screw. Status: not approved. Conflict of interest: No conflicts.