Takenori Oda

Mechanical Properties of the Human Cervical Spine as Shown by Three-dimensional Load–displacement Curves

Study Design. The mechanical properties of multilevel human cervical spines were investigated by applying pure rotational moments to each specimen and measuring multidirectional intervertebral motions. Objectives. To document intervertebral main and coupled motions of the cervical spine in the form of load–displacement curves. Summary of Background Data. Although a number of in vivo and in vitro studies have attempted to delineate normal movement patterns of the cervical spine, none has explored the complexity of the whole cervical spine as a three-dimensional structure. Methods. Sixteen human cadaveric specimens (C0–C7) were used for this study. Pure rotational moments of flexion–extension, bilateral axial torque, and bilateral lateral bending were applied using a specially designed loading fixture. The resulting intervertebral motions were recorded using stereophotogrammetry and depicted as a series of load–displacement curves. Results. The resulting load–displacement curves were found to be nonlinear, and both rotation and translation motions were coupled with main motions. With flexion–extension moment loading, the greatest degree of flexion occurred at C1–C2 (12.3°), whereas the greatest degree of extension was observed at C0–C1 (20.2°). With axial moment loading, rotation at C1–C2 was the largest recorded (56.7°). With lateral bending moments, the average range of motion for all vertebral levels was 7.9°. Conclusions. The findings of the present study are relevant to the clinical practice of examining motions of the cervical spine in three dimensions and to the understanding of spinal trauma and degenerative diseases.

Deep venous thrombosis after posterior spinal surgery.

Study Design. A prospective clinical study using venography to evaluate deep venous thrombosis after posterior spinal surgery. Objectives. To demonstrate the prevalence of deep venous thrombosis after posterior spinal surgery with no prophylaxis. Summary of Background Data. There have been few studies about the occurrence of deep venous thrombosis after spinal surgery in which venography was used for screening. Methods. Of the enrolled 134 patients undergoing posterior spinal surgery, 110 (82.1%) were examined with complete surveillance for deep venous thrombosis by venography. There were 64 males and 46 females. The average age at operation was 59.0 years (range, 14–86 years). The levels of the operation were cervical in 54, thoracic in 7, and lumbar in 49. All procedures were performed with patients under general anesthesia. Neither mechanical methods nor anticoagulation medications were used for prophylaxis against thromboembolism. Bilateral ascending venography was performed within 14 days after surgery. Results. There were no patients with clinical signs of deep venous thrombosis and pulmonary embolism. However, 17 patients (15.5%) showed venographic evidence of deep venous thrombosis, of whom 16 had distal thrombi, and only one had a proximal thrombus. Deep venous thrombosis was venographically evident in 3 (5.6%) of 54 patients who underwent cervical procedures, and it was evident in 13 (26.5%) of 49 patients who underwent lumbar procedures. This difference was statistical significant (&khgr;2 test, P = 0.003). Statistical comparison between patients who did and did not have deep venous thrombosis showed that age was statistically significant (Mann–Whitney test;P < 0.05). Conclusions. The prevalence of deep venous thrombosis after posterior spinal surgery is higher than generally recognized. Therefore, further study is necessary to clarify the appropriate method for screening and the effect of prophylaxis against thromboembolism after spinal surgery.

Surgical Outcomes of Posterior Lumbar Interbody Fusion in Elderly Patients

BACKGROUND We are aware of no reports on the surgical results of posterior lumbar interbody fusion in elderly patients. The purpose of this study was to investigate the clinical and radiographic results of posterior lumbar interbody fusion with pedicle screws in patients older than seventy years of age and compare them with results in younger patients. We also investigated the association between the clinical and radiographic results. METHODS The study included 101 patients who had been followed for at least three years after posterior lumbar interbody fusion with pedicle screws for the treatment of L4-L5 degenerative spondylolisthesis. The average follow-up period was fifty months. The patients were divided into two groups according to their age at the time of the operation: Group 1 included thirty-one patients who were seventy years of age or older (average age, seventy-four years) at the time of the operation, and Group 2 included seventy patients who were less than seventy years old (average age, fifty-nine years). Preoperative and postoperative status (according to the Japanese Orthopaedic Association scoring system) and postoperative complications were compared between the two groups. Postoperative radiographic features, including fusion status and segmental lordosis, were also examined. RESULTS No significant differences in preoperative and postoperative scores were observed between the two age groups, with the numbers available. General complications were found in Group 1. However, the prevalence of adjacent segment degeneration in Group 1 was lower than that in Group 2. The radiographic results revealed no significant difference in the prevalence of segmental lordosis, with the numbers available. There was no nonunion in either group. Although the prevalence of either collapsed union or delayed union in Group 1 was significantly higher than that in Group 2 (p = 0.034), the fusion results such as union in situ, collapsed union, and delayed union did not appear to affect the postoperative clinical results in this study. CONCLUSIONS No obvious differences in the clinical results were observed between the age groups with the numbers available. Postoperative adjacent segment degeneration was less frequent and collapsed union and delayed union were more common in the elderly group. The fusion results did not appear to affect the postoperative clinical results in this study.

Longitudinal study of spinal deformity in Duchenne muscular dystrophy.

Summary: To investigate the natural course of the spinal deformity in Duchenne muscular dystrophy (DMD) and its clinical relevance, longitudinal series of spinal radiographs and medical records of 46 patients with DMD were reviewed. The natural course of the deformity was classified into three types; type 1 (n = 21), unremittent progression of scoliosis with kyphosis; type 2 (n = 18), transition from kyphosis to lordosis before age 15 years; and type 3 (n = 7), less deformity without prominent longitudinal changes. Age at loss of ambulatory ability was not a predictor of type. Neither was the age at which the Cobb angle was 30° correlated with the rate of subsequent progression. Because the spinal deformity always progresses, we consider spinal surgery justifiable in type 1, when a certain strict indication exists, such as spinal deformity >30° and age <15 years in patients with >35% predicted value of vital capacity. In type 2, operation may be necessary in patients in whom Cobb angle will progress unremittently. There is no surgical indication for patients with type 3.

Experimental study of atlas injuries. I. Biomechanical analysis of their mechanisms and fracture patterns.

Understanding injury mechanisms is important for the prevention, diagnosis, and treatment of spinal injuries. Using 10 fresh cadaveric human spine specimens of occiput to C3, clinically similar injuries of the atlas (C1) were produced with high-speed (4.4 m/sec) axial compression. The traumatic event was biomechanically monitored. The resulting injuries were studied with radiography, computed tomography, and a multidirectional instability test. The average compressive failure force was 3,050 N for specimens impacted in neutral posture (n= 437) and 2,100 N for those in extended posture (n-282). Corresponding values for the impulse were 34.9 Nsec (n=8.3) and 17.6 Nsec (n=18). Average instability for both groups, as measured by the neutral zone and range of motion, increased by 90% and 44%, respectively, in flexion-extension and 20% in lateral bending, but not in axial rotation. These findings confirm the clinical observations.

Transections of the C1-c2 Joint Capsular Ligaments in the Cadaveric Spine

The purpose of this study was to examine the mechanical function of the C1-C2 capsular ligaments. Physiologic torques of up to 1.5 Nm were applied to human fresh cadaveric specimens (C0-C1-C2-C3) in three dimensions, and the three-dimensional motion of C1 relative to C2 was recorded. Two groups of cadaveric specimens were used to study the effect of two different sequential ligamentous transections. In the first group (n = 4), the transection of the left capsular ligament was followed by transection of the right capsular ligament. In the second group (n = 10), the transection of the left capsular ligament was preceded by transection of the left and right alar and transverse ligaments. The greatest changes in motion occurred in axial rotation to the side opposite the transection. In the first group, left capsular transections resulted in a significant increase in axial rotation range of motion to the right of 1°. After the right capsular ligament was transected, there was a further significant increase of 1.8° to the left and 1.0° to the right. Lateral bending to the left also increased significantly by 1.5° after both ligaments were cut. In the second group, with the nonfunctional alar and transverse ligaments, transection of the left capsular ligament resulted in greater increases in range of motion: 3.3° to the right and 1.3° to the left. Lateral bending to the right also increased significantly by 4.2°.

Accuracy of Atlantoaxial Transarticular Screw Insertion

Study Design. The accuracy and safety of atlantoaxial transarticular screw insertion were evaluated in clinical cases. Objectives. To evaluate the accuracy and safety of atlantoaxial transarticular screw insertion under lateral fluoroscopic monitoring without opening the joint. Summary of Background Data. Atlantoaxial transarticular screw fixation has been reported to be biomechanically superior to posterior atlantoaxial wiring techniques. Several clinical series have been reported in the literature. In some reports, the risk of screw insertion in this technique has been pointed out. Materials and Methods. Fifty-six consecutive patients with atlantoaxial instability were treated by transarticular screw fixation. One hundred twelve screw insertions in these 56 patients were assessed by surgical record and computed tomographic examination. One screw could not be inserted because of the difficulty of adequate placement during operation; 111 screws were therefore inserted. Adequate position was defined as when the screw perforated the lateral atlantoaxial joint. Results. In this series, neither vertebral artery injury nor spinal cord injury was experienced clinically. One guide wire was broken during drilling with a cannulated drill. Computed tomographic examination demonstrated that 106 screws perforated the atlantoaxial joint. Therefore, 95.5% of screws were adequately positioned. There were two screws positioned lateral to the joint, two medially, and one anteroinferiorly to the joint. Conclusions. Atlantoaxial transarticular screw insertion using image intensifier without opening the lateral joint was performed safely, but not accurately, in all cases.

Experimental study of Atlas injuries. II : Relevance to clinical diagnosis and treatment

Atlas injuries were produced in vitro and evaluated by radiographic examinations and anatomic studies from a clinical viewpoint. Ten cadaveric human upper cervical spine specimens were subjected to a high-speed axial impact. Injuries to the atlas consisted of six bursting fractures, two ruptures of the transverse ligament, one four-part fracture without a prominent bursting, and one posterior arch fracture. The major soft tissue injury involved the transverse ligament. There were five bony avulsions and three midsubstance tears. In this study, computed tomographic examinations clearly demonstrated the sites of fracture and bony avulsions of the transverse ligament. The best diagnostic tool for function of the transverse ligament was determined to be the atlantodental interval on flexion radiographs. Axial traction force reduced a bursting fracture of the atlas ring. The in vitro atlas injury model gives useful information for clinical diagnosis and treatment.

Lamina horizontalization and facet tropism as the risk factors for adjacent segment degeneration after PLIF.

Study Design. A retrospective case-control study. Objective. To clarify associations between both lamina horizontalization and facet tropism and adjacent segment degeneration (ASD). Summary of Background Data. We have previously reported coexistence of lamina horizontalization and facet tropism adjacent to the cranial fusion segment as risk factors for ASD. Methods. Subjects comprised 20 patients who underwent additional surgery for ASD after L4/5 posterior lumbar interbody fusion (PLIF) for L4 degenerative spondylolisthesis. Patients who underwent additional surgery for ASD (ASD group) were divided into 2 groups according to the duration until additional surgery: early group (n = 13), additional surgery ≤3 years after primary surgery; and late group (n = 7), additional surgery >3 years after primary surgery. As a control group, 20 age- and sex-matched patients who underwent L4/5 PLIF and could be followed for ≥5 years without ASD were selected. Lamina inclination angle at L3 and facet tropism at L3/4 in each group were measured 3 times by 3 individuals blinded to clinical results. Associations between clinical results and these risk factors and influences of these factors for periods up to the occurrence of ASD were investigated. Results. All ASD was observed in the cranial adjacent segment and the most common condition at additional surgery was spondylolisthesis (n = 15, 75%). Lamina inclination angle was significantly higher in the ASD group than in the control group. ASD was observed in 86% of patients with lamina inclination >130°. In addition, facet tropism was more significant in the early group than in the late and control groups. ASD was observed ≤3 years after primary surgery in all patients with both lamina inclination >130° and facet tropism >10°. Conclusion. Preexisting lamina horizontalization at the cranial fusion segment seems to affect ASD, and coexistence of lamina horizontalization and facet tropism seems to accelerate ASD after PLIF.

Surgical outcomes of posterior lumbar interbody fusion in elderly patients. Surgical technique.

BACKGROUND We are aware of no reports on the surgical results of posterior lumbar interbody fusion in elderly patients. The purpose of this study was to investigate the clinical and radiographic results of posterior lumbar interbody fusion with pedicle screws in patients older than seventy years of age and compare them with results in younger patients. We also investigated the association between the clinical and radiographic results. METHODS The study included 101 patients who had been followed for at least three years after posterior lumbar interbody fusion with pedicle screws for the treatment of L4-L5 degenerative spondylolisthesis. The average follow-up period was fifty months. The patients were divided into two groups according to their age at the time of the operation: Group 1 included thirty-one patients who were seventy years of age or older (average age, seventy-four years) at the time of the operation, and Group 2 included seventy patients who were less than seventy years old (average age, fifty-nine years). Preoperative and postoperative status (according to the Japanese Orthopaedic Association scoring system) and postoperative complications were compared between the two groups. Postoperative radiographic features, including fusion status and segmental lordosis, were also examined. RESULTS No significant differences in preoperative and postoperative scores were observed between the two age groups, with the numbers available. General complications were found in Group 1. However, the prevalence of adjacent segment degeneration in Group 1 was lower than that in Group 2. The radiographic results revealed no significant difference in the prevalence of segmental lordosis, with the numbers available. There was no nonunion in either group. Although the prevalence of either collapsed union or delayed union in Group 1 was significantly higher than that in Group 2 (p = 0.034), the fusion results such as union in situ, collapsed union, and delayed union did not appear to affect the postoperative clinical results in this study. CONCLUSIONS No obvious differences in the clinical results were observed between the age groups with the numbers available. Postoperative adjacent segment degeneration was less frequent and collapsed union and delayed union were more common in the elderly group. The fusion results did not appear to affect the postoperative clinical results in this study.