Objective. In functional electrophysiological imaging, signals are often contaminated by interference that can be of considerable magnitude compared to the signals of interest. This paper proposes a novel algorithm for removing such interferences that does not require separate noise measurements. Approach. The algorithm is based on a dual definition of the signal subspace in the spatial- and time-domains. Since the algorithm makes use of this duality, it is named the dual signal subspace projection (DSSP). The DSSP algorithm first projects the columns of the measured data matrix onto the inside and outside of the spatial-domain signal subspace, creating a set of two preprocessed data matrices. The intersection of the row spans of these two matrices is estimated as the time-domain interference subspace. The original data matrix is projected onto the subspace that is orthogonal to this interference subspace. Main results. The DSSP algorithm is validated by using the computer simulation, and using two sets of real biomagnetic data: spinal cord evoked field data measured from a healthy volunteer and magnetoencephalography data from a patient with a vagus nerve stimulator. Significance. The proposed DSSP algorithm is effective for removing overlapped interference in a wide variety of biomagnetic measurements.

Diagnosis of nervous system disease is greatly aided by functional assessments and imaging techniques that localize neural activity abnormalities. Electrophysiological methods are helpful but often insufficient to locate neural lesions precisely. One proposed noninvasive alternative is magnetoneurography (MNG); we have developed MNG of the spinal cord (magnetospinography, MSG). Using a 120-channel superconducting quantum interference device biomagnetometer system in a magnetically shielded room, cervical spinal cord evoked magnetic fields (SCEFs) were recorded after stimulation of the lower thoracic cord in healthy subjects and a patient with cervical spondylotic myelopathy and after median nerve stimulation in healthy subjects. Electrophysiological activities in the spinal cord were reconstructed from SCEFs and visualized by a spatial filter, a recursive null-steering beamformer. Here, we show for the first time that MSG with high spatial and temporal resolution can be used to map electrophysiological activities in the cervical spinal cord and spinal nerve.

Study Design.: Retrospective observational study. Objective.: To analyze a large consecutive cohort of patients who had undergone spinal instrumentation surgery, to characterize a patient population with surgical site infections (SSI), and to identify preoperative risk factors associated with SSI. Summary of Background Data.: Malnutrition is a risk factor for SSI in many health conditions; however, the evidence connecting preoperative malnutrition with SSI in spinal instrumentation surgery is limited because of the small number of retrospective studies. While the modified Glasgow prognostic score (mGPS), C-Reactive protein (CRP)–albumin ratio (CAR), controlling nutritional status index (CONUT), prognostic nutritional index (PNI), platelet–lymphocyte ratio (PLR), and neutrophil–lymphocyte ratio (NLR) are established methods for evaluating nutritious status, little has been reported on the predictive value of these indicators with respect to postoperative spinal infection. Methods.: We retrospectively investigated 384 patients who underwent spinal instrumentation surgery. We evaluated the significance of risk factors, including mGPS, CAR, CONUT, PNI, PLR, and NLR. We then performed stepwise logistic regression analysis to analyze the concurrent effects of various factors on the prevalence of SSI. Results.: Of the 384 patients analyzed, 14 were diagnosed with SSIs. Univariate analysis showed that preoperative BMI, lymphocyte count, albumin, erythrocyte sedimentation rate, CRP, CONUT, mGPS, CAR, and PNI were risk factors for SSI. Stepwise logistic regression analysis revealed that higher mGPS and lower BMI before surgery were independent risk factors for SSI. A receiver operating characteristic curve showed that the cut-off values of mGPS and BMI were 1 and 20.39, respectively. Conclusion.: The risk factors for SSI after spinal instrumentation surgery were mGPS more than or equal to 1 and BMI less than or equal to 20.39 kg/m². These findings could help to identify patients at higher risk of SSI after spinal instrumentation surgery. Level of Evidence: 4

Retrospective observational study. We investigated whether bone turnover markers could be a useful indicator for prediction of nonunion. Nonunion is a major complication of lumbar spinal fusion surgery. However, the involvement of bone turnover in the process of bony union in spinal fusion surgery is poorly understood. Of the 74 patients analyzed, 13 were diagnosed with nonunion. We evaluated the significance of the following risk factors: age, gender, number of fused segments, serum levels of total alkaline phosphatase, procollagen type 1 amino-terminal propeptide (P1NP), tartrate-resistant acid phosphatase 5b (TRACP-5b), and albumin, and history of diabetes mellitus, cigarette smoking, or alcohol use. We also defined the Bone Turnover Ratio (BTR) as a value that equals serum TRACP-5b concentration divided by serum P1NP concentration to evaluate patients’ individual bone turnover balance and investigated the significance of BTR as a risk factor. Univariate analysis showed that older age, malnutrition, and lower P1NP are risk factors for nonunion. Stepwise logistic regression analysis revealed that in the presence of lower P1NP, higher TRACP-5b becomes a risk factor. Furthermore, we identified BTR as the most significant risk factor for nonunion. The optimum cut-off value of BTR by receiver-operating characteristic curve was 11.74. These findings show a relationship between bone turnover and nonunion after spinal fusion surgery. The measurement of bone turnover markers could potentially be used to predict nonunion after spinal fusion surgery. 4

To establish a method to measure cauda equina action fields (CEAFs) and visualize the electrical activities of the cauda equina in a broadly aged group of healthy adults. Using a 124-channel magnetospinography (MSG) system with superconducting interference devices, the CEAFs of 43 healthy volunteers (22-64 years of age) were measured after stimulation of the peroneal nerve at the knee. Reconstructed currents were obtained from the CEAFs and superimposed on the X-ray image. Conduction velocities were also calculated from the waveform of the reconstructed currents. The reconstructed currents were successfully visualized. They flowed into the L5/S1 foramen about 8.25-8.95 ms after the stimulation and propagated cranially along the spinal canal. In 32 subjects (74%), the conduction velocities of the reconstructed currents in the cauda equina could be calculated from the peak latency at the L2-L5 level. MSG visualized the electrical activity of the cauda equina after peroneal nerve stimulation in healthy adults. In addition, the conduction velocities of the reconstructed currents in the cauda equina could be calculated, despite previously being difficult to measure. MSG has the potential to be a novel and noninvasive functional examination for lumbar spinal disease.

In patients with ossification of the posterior longitudinal ligament (OPLL) in the cervical spine, it is well known that the thoracic ossified lesions often coexist with the cervical lesions and can cause severe myelopathy. However, the prevalence of OPLL at each level of the thoracic and lumbar spinal segments is unknown. The aims of this study were to investigate how often OPLL occurs at each level in the thoracolumbar spine in patients with a radiological diagnosis of cervical OPLL and to identify the spinal levels most likely to develop ossification. Data were collected from 20 institutions in Japan. Three hundred and twenty-two patients with a diagnosis of cervical OPLL were included. The OPLL index (OP index), defined as the sum of the vertebral body and intervertebral disc levels where OPLL is present, was used to determine disease severity. An OP index ≥20 was defined as severe OPLL. The prevalence of OPLL at each level of the thoracic and lumbar spinal segments was calculated. Women were more likely to have ossified lesions in the thoracolumbar spine than men. Severe OPLL was significantly more common in women than in men (20% vs. 4.5%). For thoracic vertebral OPLL, the most frequently affected was the T1 segment in both men and women, followed by the T1/2 and T3/4 intervertebral levels in men and women, respectively. Ossified lesions were frequently seen at the intervertebral and vertebral levels around the cervicothoracic and thoracolumbar junctions in men with severe OPLL, whereas OPLL was more diffusely distributed in the thoracic spine in women with severe OPLL. Thoracolumbar OPLL occurred most often at T1 in men and at T3/4 in women. In severe OPLL cases, although ossified lesions were frequently seen at the intervertebral and vertebral levels around the cervicothoracic and thoracolumbar junctions in men, OPLL could be observed more diffusely in the thoracic spine in women.