Hiroki Oba

Study of dural sac cross-sectional area in early and late phases after lumbar decompression surgery.

BACKGROUND CONTEXT Lumbar magnetic resonance imaging (MRI) in the early phase after lumbar decompression surgery sometimes reveals an absence in the expansion of the dural sac, regardless of the presence or absence of clinical symptoms; the reason for such a condition is often difficult to explain. There are some reports that compared the dural sac area between the preoperative and early postoperative phases; however, no report exists that compares the early and late phases after lumbar decompression surgery. PURPOSE The purpose of this study was to compare changes in the dural sac cross-sectional area (CSA) in the early and late phases after lumbar decompression surgery. Factors related to the insufficient increase in the postoperative dural sac CSA were also analyzed. STUDY DESIGN The dural sac CSA preoperatively and in the early and late phases after lumbar decompression surgery was analyzed retrospectively. PATIENT SAMPLE Of 105 patients who underwent lumbar decompression surgery and MRI within 1 week and again more than 1 month after surgery, 83 patients (38 men, 45 women; mean age 65.6 years) were included in this study. OUTCOME MEASURES Cross-sectional areas of the dural sac. METHODS The dural sac CSA was measured within 1 week (early phase) and more than 1 month (late phase) after surgery, using T2 axial plane MR images. The preoperative and the early and late postoperative CSAs were measured at the same site. The relationship between the dural sac area and age and presence of dural injury was also analyzed. RESULTS The mean area of the dural sac preoperatively and in the early and late postoperative phases was 71.2±4.9, 102.2±5.7, and 164.1±6.9 mm(2), respectively. The mean area increased significantly (p<.001) between the preoperative and postoperative early phases and between the early and late postoperative phases. The dural sac area in the early (p=.16) and late (p=.086) phases did not differ significantly between patients aged 75 years or more and those aged less than 75 years. In the case of lumbar spinal stenosis, patients with a preoperative dural sac area of less than 60 mm(2) showed a significantly (p<.001) smaller dural sac area in the early and late postoperative phases, compared with patients with a preoperative dural sac area of 60 mm(2) or more. No significant increase was observed in the dural sac area with regard to the presence or absence of dural injury. CONCLUSIONS The dural sac area increased significantly between the early and late postoperative phases. No significant difference in the dural sac CSA between the early and late postoperative phases was observed with regard to age or the presence/absence of dural sac injury. A smaller preoperative dural sac CSA resulted in a smaller dural sac CSA in the early and late postoperative phases.

Pedicle Screw Loosening after Posterior Spinal Fusion for Adolescent Idiopathic Scoliosis in Upper and Lower Instrumented Vertebrae Having Major Perforation

Study Design. A retrospective chart review. Objective. The aim of this study was to investigate the incidence and characteristics of screw loosening in surgically treated adolescent idiopathic scoliosis (AIS) patients. Summary of Background Data. Pedicle screws are widely used in posterior spinal fusion for AIS, although postoperative loosening can occur. However, few reports exist on screw loosening after pedicle screw fixation in young scoliosis patients and the etiology of loosening is not well known. Methods. One hundred twenty AIS patients (9 males, 111 females; mean age: 15.0 years) who had received pedicle screw fixation were retrospectively reviewed. All patients underwent routine computed tomography (CT) reconstruction scans at 6 months postoperatively to assess screw position, bony fusion, and the presence of screw loosening. The perforation status of each pedicle screw was assigned a grade of 0 to 3 using Rao classification. Results. Forty-three of 1624 (2.6%) screws showed evidence of loosening on CT. Screw loosening rates according to vertebral insertion level were upper instrumented vertebra (UIV): 9.6%; lower instrumented vertebra (LIV): 5.4%; one vertebra below the UIV: 1.8%; one vertebra above the LIV: 0.5%; two vertebrae below the UIV: 1.2%; and three vertebrae below the UIV: 0.9%. Screw loosening rates based on screw perforation grade were Grade 0: 1.4%; Grade 1: 3.1%; Grade 2: 15.5%; and Grade 3: 15.2%. Multivariate analysis revealed a distance from the UIV or LIV of one vertebra as well as the presence of major perforation to be independent factors affecting screw loosening. The odds ratios (ORs) of UIV/LIV insertion and major perforation were 73.4 and 17.2, respectively. When major perforations occurred in the UIV or LIV, the OR for loosening approached 1262. Conclusion. Pedicle screw loosening after posterior spinal fusion in AIS patients tend to occur in the UIV or LIV. Major screw perforation is also significantly associated with screw loosening. The risk of loosening becomes compounded when major perforations are present in the UIV or LIV. Level of Evidence: 4

Spinal cord MRI signal changes at 1 year after cervical decompression surgery is useful for predicting midterm clinical outcome: an observational study using propensity scores

BACKGROUND CONTEXT There is little information on the relationship between magnetic resonance imaging (MRI) T2-weighted high signal change (T2HSC) in the spinal cord and surgical outcome for cervical myelopathy. We therefore examined whether T2HSC regression at 1 year postoperatively reflected a 5-year prognosis after adjustment using propensity scores for potential confounding variables, which have been a disadvantage of earlier observational studies. PURPOSE The objective of this study was to clarify the usefulness of MRI signal changes for the prediction of midterm surgical outcome in patients with cervical myelopathy. STUDY DESIGN/SETTING This is a retrospective cohort study. PATIENT SAMPLE We recruited 137 patients with cervical myelopathy who had undergone surgery between 2007 and 2012 at a median age of 69 years (range: 39-87 years). OUTCOME MEASURES The outcome measures were the recovery rates of the Japanese Orthopaedic Association (JOA) scores and the visual analog scale (VAS) scores for complaints at several body regions. MATERIALS AND METHODS The subjects were divided according to the spinal MRI results at 1 year post surgery into the MRI regression group (Reg+ group, 37 cases) with fading of T2HSC, or the non-regression group (Reg- group, 100 cases) with either no change or an enlargement of T2HSC. The recovery rates of JOA scores from 1 to 5 years postoperatively along with the 5-year postoperative VAS scores were compared between the groups using t test. Outcome scores were adjusted for age, sex, diagnosis, symptom duration, and preoperative JOA score by the inverse probability weighting method using propensity scores. RESULTS The mean recovery rates in the Reg- group were 35.1%, 34.6%, 27.6%, 28.0%, and 30.1% from 1 to 5 years post surgery, respectively, whereas those in the Reg+ group were 52.0%, 52.0%, 51.1%, 49.0%, and 50.1%, respectively. The recovery rates in the Reg+ group were significantly higher at all observation points. At 5 years postoperatively, the VAS score for pain or numbnessin the arms or hands of the patients in the Reg+ group (24.7 mm) was significantly milder than that of the patients in the Reg- group (42.2 mm). CONCLUSIONS Spinal T2HSC improvement at 1 year postoperatively may predict a favorable recovery until up to 5 years after surgery.

Are pedicle screw perforation rates influenced by distance from the reference frame in multilevel registration using a computed tomography-based navigation system in the setting of scoliosis?

BACKGROUND CONTEXT Pedicle screw fixation is commonly employed for the surgical correction of scoliosis but carries a risk of serious neurovascular or visceral structure events during screw insertion. To avoid these complications, we have been using a computed tomography (CT)-based navigation system during pedicle screw placement. As this could also prolong operation time, multilevel registration for pedicle screw insertion for posterior scoliosis surgery was developed to register three consecutive vertebrae in a single time with CT-based navigation. The reference frame was set either at the caudal end of three consecutive vertebrae or at one or two vertebrae inferior to the most caudal registered vertebra, and then pedicle screws were inserted into the three consecutive registered vertebrae and into the one or two adjacent vertebrae. OBJECTIVES This study investigated the perforation rates of vertebrae at zero, one, two, three, or four or more levels above or below the vertebra at which the reference frame was set. STUDY DESIGN This is a retrospective, single-center, single-surgeon study. PATIENT SAMPLE One hundred sixty-one scoliosis patients who had undergone pedicle screw fixation were reviewed. OUTCOME MEASURES Screw perforation rates were evaluated by postoperative CT. MATERIALS AND METHODS We evaluated 161 scoliosis patients (34 boys and 127 girls; mean±standard deviation age: 14.6±2.8 years) who underwent pedicle screw fixation guided by a CT-based navigation system between March 2006 and December 2015. RESULTS A total of 2,203 pedicle screws were inserted into T2-L5 using multilevel registration with CT-based navigation. The overall perforation rates for Grade 1, 2, or 3, Grade 2 or 3 (major perforations), and Grade 3 perforations (violations) were as follows: vertebrae at which the reference frame was set: 15.9%, 6.1%, and 2.5%; one vertebra above or below the reference frame vertebra: 16.5%, 4.0%, and 1.2%; two vertebrae above or below the reference frame vertebra: 20.7%, 8.7%, and 2.3%; three vertebrae above or below the reference frame vertebra: 23.8%, 7.9%, and 3.5%; and four vertebrae or more above/below the reference frame vertebra: 25.4%, 9.5%, and 4.1%, respectively. Fisher exact test was performed to detect significant differences among the above five groups. With regard to Grade 1, 2, or 3 perforations, the rates of screw perforation for three and four vertebrae or more above or below the reference frame vertebra were significantly larger than that for vertebrae at the reference frame (both p<.01). No significant differences were found for Grade 3 perforations (violations) among the groups. CONCLUSIONS In multilevel registration of three consecutive vertebrae, the accuracy of screw insertion into vertebrae at which the reference frame was not set was not significantly inferior to that in vertebrae at which the reference frame was set with regard to major perforation rate. Including minor perforations, however, a distance of three vertebrae or more above or below the reference frame vertebra produced significantly more frequent perforations.

Optimal cervical screw insertion angle determined by means of computed tomography scans pre- and postoperatively

BACKGROUND CONTEXT Cervical pedicle screw (CPS) insertion is technically demanding and carries a risk of serious neurovascular complications when screws perforate. To avoid such serious risks, we currently perform CPS insertion using a computed tomography (CT)-guided navigation system. However, there remains a low probability of screw perforation during CPS insertion that is affected by factors such as CPS insertion angle and anatomical pedicle transverse angle (PTA). PURPOSE This study aimed to understand the perforation tendencies of CPS insertion angles in relation to anatomical PTA. STUDY DESIGN This is a retrospective chart review. PATIENT SAMPLE The study enrolled 151 consecutive patients (95 men and 56 women, with a mean age of 64.6 years). OUTCOME MEASURES Anatomical PTA and CPS insertion angles were evaluated by axial CT images. METHODS The medical records of 151 consecutive patients who underwent CPS insertion using a CT-based navigation system were reviewed. We examined the relationships between PTA and CPS insertion angle on axial CT images according to vertebral level. RESULTS The average preoperative PTA at each vertebral level was 32.1° for C2, 41.5° for C3, 41.0° for C4, 39.4° for C5, 34.4° for C6, and 27.3° for C7. Corresponding CT-determined pedicle screw insertion angles were 24.9°, 31.3°, 28.7°, 27.8°, 28.0°, and 26.0°, respectively. The CPS insertion angles at C2-C6 were significantly smaller than those for PTA (p<.01). In evaluations of angle thresholds from C3 to C5 that predicted a higher risk of perforation, the receiver operating characteristic curve analysis determined CPS insertion angles of <24.5° and >36.5° for the identification of lateral and medial perforations, respectively. CONCLUSION For CPS insertion into the C3-C5 pedicles using CT, there is an increased likelihood of lateral or medial perforation for insertion angles of <24.5° or >36.5°, respectively.

Rigid Occipitocervical Instrumented Fusion for Atlantoaxial Instability in an 18-month-old Toddler with Brachytelephalangic Chondrodysplasia Punctata: A Case Report

Study Design. Case report. Objective. We report here on an 18-month-old boy with brachytelephalangic chondrodysplasia punctata (BCDP), whose atlantoaxial instability was successfully managed with occipitocervical instrumented fusion (OCF) using screw and rod instrumentations. Summary of Background Data. Recently, there have been a number of reports on BCDP with early onset of cervical myelopathy. Surgical OCF is a vital intervention to salvage affected individuals from the life-threatening morbidity. Despite recent advancement of instrumentation techniques, however, rigid OCF is technically demanding in very young children with small and fragile osseous elements. To our best knowledge, this is the first report on application of the instrumentation technique to a toddler patient with BCDP. Methods. A 16-month-old boy with BCDP presented with tetraplegia and swallow obstacle. Hypoplasia of the odontoid process and atlantoaxial instability were present in lateral radiographs. T2-weighted magnetic resonance (MR) images revealed a high signal region in the spinal cord at the C1-2 and C7-T1 levels. Cervical computed tomography (CT) showed that the pedicles and lateral masses in the cervical spine were small and immature, but the laminae were comparatively thick. Results. One week before surgery, the patient was fitted with a Halo-body jacket. We performed plate-rod placement with occipital cortical screws and C2/C3 interlaminar screws, and added an autogenous bone graft using the right 8 and 9 ribs. Rigid fixation of the occipito-cervical spine was completed successfully without major complications. Postoperative halo-body jacket immobilization was continued for 3 months, after which Aspen collar was fitted. CT confirmed occipitocervical bone fusion at 6 months after surgery. Mild clinical improvements in motor power of the affected muscles and swallowing were witnessed at 1 year postoperatively. Conclusion. Rigid fixation using screw, rod, and occipital plate instrumentation was successful in an 18-month-old toddler with BCDP and atlantoaxial instability. Bone fusion was achieved at postoperative 6 months. Level of Evidence: 5

Early Postoperative Magnetic Resonance Imaging in Detecting Radicular Pain After Lumbar Decompression Surgery: Retrospective Study of the Relationship Between Dural Sac Cross-sectional Area and Postoperative Radicular Pain.

Study Design: A retrospective analysis. Objective: To evaluate the association between early postoperative dural sac cross-sectional area (DCSA) and radicular pain. Summary of Background Data: The correlation between postoperative magnetic resonance imaging (MRI) findings and postoperative neurological symptoms after lumbar decompression surgery is controversial. Methods: This study included 115 patients who underwent lumbar decompression surgery followed by MRI within 7 days postoperatively. There were 46 patients with early postoperative radicular pain, regardless of whether the pain was mild or similar to that before surgery. The intervertebral level with the smallest DCSA was identified on MRI and compared preoperatively and postoperatively. Risk factors for postoperative radicular pain were determined using univariate and multivariate analyses. Subanalysis according to absence/presence of a residual suction drain also was performed. Results: Multivariate regression analysis showed that smaller postoperative DCSA was significantly associated with early postoperative radicular pain (per −10 mm2; odds ratio, 1.26). The best cutoff value for radicular pain was early postoperative DCSA of 67.7 mm2. Even with a cutoff value of <70 mm2, sensitivity and specificity are 74.3% and 75.0%, respectively. Early postoperative DCSA was significantly larger before suction drain removal than after (119.7±10.1 vs. 93.9±5.4 mm2). Conclusions: Smaller DCSA in the early postoperative period was associated with radicular pain after lumbar decompression surgery. The best cutoff value for postoperative radicular pain was 67.7 mm2. Absence of a suction drain at the time of early postoperative MRI was related to smaller DCSA.