牧 聡

STUDY DESIGN: A retrospective study. OBJECTIVE: The aim of this study was to determine the publication rate and impact factors (IFs) among all abstracts presented at the 2010 and 2012 meetings of the International Society for the Study of Lumbar Spine (ISSLS). SUMMARY OF BACKGROUND DATA: The publication rate of abstracts presented at overseas meetings was reported to be around 50%. However, the publication rate and IFs of oral and poster presentations made at ISSLS meetings were unclear. Moreover, whether the publication rates and IFs differed for papers associated with oral or poster presentations at ISSLS meetings was unknown. METHODS: We investigated all 1126 abstracts (oral, special posters, general posters) presented at ISSLS meetings held between 2010 and 2012. PubMed was searched to identify publications and IFs were determined using journal citation reports. We also compared the publication rates and IFs between oral and poster presentations. RESULTS: The overall publication rate was 50.1% for three ISSLS meetings (564 publications/1126 abstracts). The overall publication rate for oral presentations, special posters, and general posters given in the 2010 to 2012 meetings was 62.0%, 48.3, and 46.6%, respectively. Overall, papers related to oral presentations had significantly higher publication rates than those of special and general posters (P = 0.0002). The average IFs of publications associated with abstracts presented at three ISSLS meetings was 2.802 for oral presentations, 2.593 for special posters, and 2.589 for general posters. There were no significant differences in average IFs between oral and poster presentations (P > 0.05). CONCLUSION: The publication rate for abstracts presented at ISSLS meetings was high and similar to publication rates for abstracts presented at other meetings concerning orthopedic and spine research. However, there was no significant difference in IFs between oral and poster presentations, suggesting that abstract evaluations cannot predict IFs of the eventual publication. LEVEL OF EVIDENCE: 4.

We report two cases of restenosis caused by the progression of thickness of ossification of the posterior longitudinal ligament (OPLL) seven and more years after laminoplasty, resulting in neurological deterioration needed for revision anterior decompressive surgeries. Neurological recovery after revision anterior excision of OPLL was poor. In both cases, the patients had progressive OPLL, with a non-ossified segment of the ossification foci, in common. After laminoplasty, they also both exhibited osseous fusion of the elevated laminae, but there was discontinuity at the interlaminar space at the peak level of OPLL. Discontinuity of the osseous fusion in the elevated laminae might cause mechanical stress increases at the non-ossified segment of the OPLL and could lead to the progression of OPLL. The present cases showed that long-term progression of OPLL can induce neurological deterioration even after sufficient posterior decompression by laminoplasty. Therefore, when considering risk factors that may be predictive of the progression of OPLL after laminoplasty, it is important to perform strict follow-up examination to check for progression to reduce the risk of myelopathy symptoms that are indicative of neurological deterioration.

Patients with multiple sclerosis present with focal lesions throughout the spinal cord. There is a clinical need for non-invasive measurements of spinal cord activity and functional organization in multiple sclerosis, given the cord's critical role in the disease. Recent reports of spontaneous blood oxygenation level-dependent fluctuations in the spinal cord using functional MRI suggest that, like the brain, cord activity at rest is organized into distinct, synchronized functional networks among grey matter regions, likely related to motor and sensory systems. Previous studies looking at stimulus-evoked activity in the spinal cord of patients with multiple sclerosis have demonstrated increased levels of activation as well as a more bilateral distribution of activity compared to controls. Functional connectivity studies of brain networks in multiple sclerosis have revealed widespread alterations, which may take on a dynamic trajectory over the course of the disease, with compensatory increases in connectivity followed by decreases associated with structural damage. We build upon this literature by examining functional connectivity in the spinal cord of patients with multiple sclerosis. Using ultra-high field 7 T imaging along with processing strategies for robust spinal cord functional MRI and lesion identification, the present study assessed functional connectivity within cervical cord grey matter of patients with relapsing-remitting multiple sclerosis (n = 22) compared to a large sample of healthy controls (n = 56). Patient anatomical images were rated for lesions by three independent raters, with consensus ratings revealing 19 of 22 patients presented with lesions somewhere in the imaged volume. Linear mixed models were used to assess effects of lesion location on functional connectivity. Analysis in control subjects demonstrated a robust pattern of connectivity among ventral grey matter regions as well as a distinct network among dorsal regions. A gender effect was also observed in controls whereby females demonstrated higher ventral network connectivity. Wilcoxon rank-sum tests detected no differences in average connectivity or power of low frequency fluctuations in patients compared to controls. The presence of lesions was, however, associated with local alterations in connectivity with differential effects depending on columnar location. The patient results suggest that spinal cord functional networks are generally intact in relapsing-remitting multiple sclerosis but that lesions are associated with focal abnormalities in intrinsic connectivity. These findings are discussed in light of the current literature on spinal cord functional MRI and the potential neurological underpinnings.

Background: The K-line, which is a virtual line between the midpoints of the antero-posterior canal diameter at C2 and C7, can be useful for determination of surgical procedures for cervical ossification of the posterior longitudinal ligament (OPLL). Although K-line is originally measured with plain radiogram, computed tomography multiplanar reconstruction (CT-MPR) is applied for K-line measurement by several surgeons. The purpose of the present study was to analyze whether there is a difference in K-lines obtained from radiographs of standing patients and those obtained from CT-MPR images of supine patients. Methods: The present study included 65 patients with cervical OPLL underwent surgical treatment. We investigated the K-line (+ or -) before surgery, measured from lateral cervical spine radiographs taken in standing patients in a neutral position (X-P-based K-line) and CT-MPR mid-sagittal images obtained in supine patients (CT-based K-line). The X-P-based and CT-based K-lines were compared and differences between them were assessed. Results: The-X-P-based K-line was found to be (+) in 35 patients and (-) in 30 patients. Four of 35 patients with an X-P-based K-line (11%) showed a change from K-line (+) to (-) in CT-based K-line measurements. One of 30 patients with an X-P-based K-line (3%) showed a change from (-) to (+) in CT-based measurements. Conclusions: The K-line should be measured with plain radiogram of standing patients because X-P-based K-line and CT-based K-line can be different.

Background Total en bloc spondylectomy (TES) is potential radical resection surgery for spinal tumors. Surgical procedure of TES includes extremely wide detachment of surrounding soft tissue from pathological vertebra, resulting in impairment of blood supply. Moreover, massive dead space inevitably is made after vertebral body resection. Therefore deep surgical site infection (SSI) after TES could be intractable. To date, suitable treatment for deep SSI after TES has not been established. Case description A 72 years old man underwent TES of 12th thoracic level via single posterior approach for primary leiomyosarcoma. Postoperative additional irradiation was performed. One year after surgery, late infection around the cage occurred. We removed the cage followed by autologous iliac bone grafting, we treat the wound by open therapy and daily irrigation, followed by negative pressure wound therapy. Four-month later, we performed musculo-cutaneous flap using latissimus dorsi muscle with plastic surgeons. At the follow-up visit one year after flap surgery, no evidence of recurrence of infection was observed. Conclusion Musculo-cutaneous flap is one of treatment options to fill the dead space and to control deep SSI after TES.

STUDY DESIGN: A cross-sectional study. OBJECTIVE: The aim of this study was to quantify spinal cord dysfunction at the tract level in patients with cervical compressive myelopathy (CCM) using reduced field-of-view (rFOV) diffusion tensor imaging (DTI). SUMMARY OF BACKGROUND DATA: Although magnetic resonance imaging (MRI) is the standard used for radiological evaluation of CCM, information acquired by MRI does not necessarily reflect the severity of spinal cord disorder. There is a growing interest in developing imaging methods to quantify spinal cord dysfunction. To acquire high-resolution DTI, a new scheme using rFOV has been proposed. METHODS: We enrolled 10 healthy volunteers and 20 patients with CCM in this study. The participants were studied using a 3.0-T MRI system. For DTI acquisitions, diffusion-weighted spin-echo rFOV single-shot echo-planar imaging was used. Regions-of-interest (ROI) for the lateral column (LC) and posterior column (PC) tracts were determined on the basis of a map of fractional anisotropy (FA) of the spinal cord and FA values were measured. The FA of patients with CCM was compared with that of healthy controls and correlated with Japanese Orthopaedic Association (JOA) score. RESULTS: In LC and PC tracts, FA values in patients with CCM were significantly lower than in healthy volunteers. Total JOA scores correlated moderately with FA in LC and PC tracts. JOA subscores for motor dysfunction of the lower extremities correlated strongly with FA in LC and PC tracts. CONCLUSION: It is feasible to evaluate the cervical spinal cord at the tract level using rFOV DTI. Although FA values at the maximum compression level were not well correlated with total JOA scores, they were strongly correlated with JOA subscores for motor dysfunction of the lower extremities. Our findings suggest that FA reflects white matter dysfunction below the maximum compression level and FA can be used as an imaging biomarker of spinal cord dysfunction. LEVEL OF EVIDENCE: 4.

イバンドロネー卜錠剤を投与した閉経後骨粗鬆症患者60例(平均75.0±7.1歳)を対象に、薬剤継続率、骨粗鬆症改善効果(骨吸収抑制および骨密度上昇)を検討した。薬剤継続率は投与後6ヵ月時点で76.7%(46例)であった。また、副作用発生頻度は11.7%(7例)で、インフルエンザ様症状3例、歯の違和感2例、内服後胃部不快感2例であった。副作用が発生した症例における薬剤継続率は57.1%であった。骨粗鬆症改善効果は、投与前に比べ投与後6ヵ月で骨吸収マーカーTRACP-5b値は有意に低下し、平均腰椎YAM値は有意に増加した。投与6ヵ月による骨密度レスポンス率(骨密度が増加した患者の割合)は95.7%であった。以上、イバンドロネート錠剤の高い薬剤継続率、骨粗鬆症改善効果(骨吸収抑制効果、骨密度上昇効果、骨密度レスポンス率)が示された。

An occipital condyle fracture (OCF) is a relatively rare trauma that is now increasingly diagnosed because of the wide availability of computed tomography. For nondisplaced OCFs, conservative treatment is generally recommended, and there is no previous report of a nondisplaced OCF requiring surgery. We report a patient who had a nondisplaced OCF with craniocervical misalignment (a condyle-C1 interval > 2.0 mm) and C1-C2 translation treated with a halo vest and occipitocervical fusion surgery. An 87-year-old Asian woman fell from a 4-meter height and hit her head. She was transferred to our emergency room. Computed tomography revealed a nondisplaced impaction OCF with a 2.5 mm occipital condyle-C1 interval and a 5 mm C1-C2 translation. The fracture pattern was considered stable. However, since craniocervical misalignment and C1-C2 translation were present, the patient was placed in a halo device, and we reduced the occipitoatlantoaxial joint, adjusting the halo ring position preoperatively. Confirming reduction of the atlantooccipital facet joint and the atlantoaxial joint by computed tomography, we performed an occipitocervical fusion. This is the first report of a nondisplaced OCF with craniocervical misalignment and C1-C2 translation that required surgical treatment. Clinicians should be aware of craniocervical misalignment and atlantoaxial instability even in Tuli type 1 OCFs.

OBJECTIVE Fusion surgery with instrumentation is a widely accepted treatment for cervical spine pathologies. The authors propose a novel technique for subaxial cervical fusion surgery using paravertebral foramen screws (PVFS). The authors consider that PVFS have equal or greater biomechanical strength than lateral mass screws (LMS). The authors' goals of this study were to conduct a biomechanical study of PVFS, to investigate the suitability of PVFS as salvage fixation for failed LMS, and to describe this novel technique. METHODS The authors harvested 24 human cervical spine vertebrae (C3-6) from 6 fresh-frozen cadaver specimens from donors whose mean age was 84.3 ± 10.4 years at death. For each vertebra, one side was chosen randomly for PVFS and the other for LMS. For PVFS, a 3.2-mm drill with a stopper was advanced under lateral fluoroscopic imaging. The drill stopper was set to 12 mm, which was considered sufficiently short not to breach the transverse foramen. The drill was directed from 20° to 25° medially so that the screw could purchase the relatively hard cancellous bone around the entry zone of the pedicle. The hole was tapped and a 4.5-mm-diameter × 12-mm screw was inserted. For LMS, 3.5-mm-diameter × 14-mm screws were inserted into the lateral mass of C3-6. The pullout strength of each screw was measured. After pullout testing of LMS, a drill was inserted into the screw hole and the superior cortex of the lateral mass was pried to cause a fracture through the screw hole, simulating intraoperative fracture of the lateral mass. After the procedure, PVFS for salvage (sPVFS) were inserted on the same side and pullout strength was measured. RESULTS The CT scans obtained after screw insertion revealed no sign of pedicle breaching, violation of the transverse foramen, or fracture of the lateral mass. A total of 69 screws were tested (23 PVFS, 23 LMS, and 23 sPVFS). One vertebra was not used because of a fracture that occurred while the specimen was prepared. The mean bone mineral density of the specimens was 0.29 ± 0.10 g/cm3. The mean pullout strength was 234 ± 114 N for PVFS, 158 ± 91 N for LMS, and 195 ± 125 N for sPVFS. The pullout strength for PVFS tended to be greater than that for LMS. However, the difference was not quite significant (p = 0.06). CONCLUSIONS The authors introduce a novel fixation technique for the subaxial cervical spine. This study suggests that PVFS tend to provide stronger fixation than LMS for initial applications and fixation equal to LMS for salvage applications. If placement of LMS fails, PVFS can serve as a salvage fixation technique.

PURPOSE: The aim of this study was to assess the potential role of diffusion tensor imaging (DTI) as a predictor of surgical outcomes in patients with cervical compressive myelopathy (CCM). Surgical decompression is often recommended for symptomatic CCM. It is important to know the prognosis of surgical outcomes and to recommend appropriate timing for surgery. METHODS: We enrolled 26 patients with CCM who underwent surgery. The Japanese Orthopaedic Association (JOA) score for cervical myelopathy was evaluated before and 6 months after surgery. Surgical outcomes were regarded as good if there was a change in JOA score of three points or more, or the recovery rate of JOA score was 50% or more. The patients were examined using a 3.0 T magnetic resonance system before surgery. Measured diffusion parameters were fractional anisotropy (FA) and mean diffusivity (MD). The correlations between DTI parameters and surgical outcomes were analyzed. RESULTS: Both change and recovery rate of JOA score moderately correlated with FA. Furthermore, the area under the receiver-operator characteristic curve based on FA for prognostic precision of surgical outcomes indicates that FA is a good predictive factor. The cut-off values of FA for predicting good surgical outcomes evaluated by change and recovery rate of JOA score were 0.65 and 0.57, respectively. Neither change nor recovery rate of JOA score correlated with MD. CONCLUSIONS: FA in spinal cord DTI can moderately predict surgical outcomes. DTI can serve as a supplementary tool for decision-making to guide surgical intervention in patients with CCM.

How aging affects the spinal cord at a molecular level is unclear. The aim of this study was to explore spinal cord aging-related proteins that may be involved in pathological mechanisms of age-related changes in the spinal cord. Spinal cords of 2-year-old and 8-week-old female Sprague-Dawley rats were dissected from the animals. Protein samples were subjected to 2-dimentional polyacrylamide gel electrophoresis followed by mass spectrometry. Screened proteins were further investigated with immunohistochemistry and Western blotting. Among the screened proteins, we selected α-crystallin B-subunit (αB-crystallin) and peripherin for further investigation because these proteins were previously reported to be related to central nervous system pathologies. Immunohistochemistry and Western blotting revealed significant upregulation of αB-crystallin and peripherin expression in aged rat spinal cord. Further exploration is needed to elucidate the precise mechanism and potential role of these upregulated proteins in spinal cord aging processes.

Laminoplasty (LMP) is a widely accepted surgical procedure for ossification of the posterior longitudinal ligament (OPLL) of the cervical spine. Progression of OPLL can occur in the long term after LMP. The aim of the present study was to determine whether addition of the instrumented fusion, (posterior decompression with instrumented fusion [PDF]), can suppress progression of OPLL or not. The present study included 50 patients who underwent LMP (n=23) or PDF (n=27) for OPLL of the cervical spine. We performed open door laminoplasty. PDF surgery was performed by double-door laminoplasty followed by instrumented fusion. We observed the non-ossified segment of the OPLL and measured the thickness of the OPLL at the thickest segment with pre- and postoperative sagittal CT multi-planar reconstruction images. Postoperative CT scan revealed fusion of the non-ossified segment of the OPLL was obtained in 4/23 patients (17%) in the LPM group and in 23/27 patients (85%) in the PDF group, showing a significant difference between both groups (p=0.003). Progression of the thickness of the OPLL in the PDF group (-0.1±0.4mm) was significantly smaller than in the LMP group (0.6±0.7mm, p=0.0002). The proportion of patients showing the decrease in thickness of OPLL was significantly larger in the PDF group (6/27 patients; 22%) than in the LMP group (0/23 patients; 0%, p=0.05). In conclusion, PDF surgery can suppress the thickening of OPLL.

BACKGROUND: Patients with cervical compression myelopathy (CCM) generally present bilateral neurological symptoms in their extremities. However, a substantial portion of patients with CCM exhibit laterality of neurological symptoms. The aim of this study was to assess the correlation between intrinsic structural damage and laterality of symptoms using spinal cord diffusion tensor imaging (DTI) of the corticospinal tract. METHODS: We enrolled 10 healthy volunteers and 40 patients with CCM in this study. We evaluated motor function using the American Spinal Injury Association (ASIA) motor score for left and right extremities. For DTI acquisitions, a 3.0-T magnetic resonance imaging system with diffusion-weighted spin-echo sequence was used. Regions-of-interest in the lateral column tracts were determined. We determined the correlations between fractional anisotropy (FA) and ASIA motor scores. An FA asymmetry index was calculated using left and right regions-of-interest. RESULTS: Four patients exhibited laterality of symptoms in their extremities, for which left and right ASIA scores correlated moderately with FA in the left and right lateral columns, respectively (left: ρ = 0.64, P < 0.001; right: ρ = 0.67, P < 0.001). The area under the receiver-operator characteristic curve showed that the FA asymmetry index indicated laterality of symptoms. CONCLUSIONS: Using tract-specific DTI, we demonstrated that microstructural damages in the left and right corticospinal tracts correlated with corresponding neurological symptoms in the ipsilateral side and the FA asymmetry index could indicate laterality in neurological symptoms of patients with CCM.

STUDY DESIGN: Retrospective case-control study. PURPOSE: To determine whether kissing spine is a risk factor for recurrence of sciatica after lumbar posterior decompression using a spinous process floating approach. OVERVIEW OF LITERATURE: Kissing spine is defined by apposition and sclerotic change of the facing spinous processes as shown in X-ray images, and is often accompanied by marked disc degeneration and decrement of disc height. If kissing spine significantly contributes to weight bearing and the stability of the lumbar spine, trauma to the spinous process might induce a breakdown of lumbar spine stability after posterior decompression surgery in cases of kissing spine. METHODS: The present study included 161 patients who had undergone posterior decompression surgery for lumbar canal stenosis using a spinous process floating approaches. We defined recurrence of sciatica as that resolved after initial surgery and then recurred. Kissing spine was defined as sclerotic change and the apposition of the spinous process in a plain radiogram. Preoperative foraminal stenosis was determined by the decrease of perineural fat intensity detected by parasagittal T1-weighted magnetic resonance imaging. Preoperative percentage slip, segmental range of motion, and segmental scoliosis were analyzed in preoperative radiographs. Univariate analysis followed by stepwise logistic regression analysis determined factors independently associated with recurrence of sciatica. RESULTS: Stepwise logistic regression revealed kissing spine (p=0.024; odds ratio, 3.80) and foraminal stenosis (p<0.01; odds ratio, 17.89) as independent risk factors for the recurrence of sciatica after posterior lumbar spinal decompression with spinous process floating procedures for lumbar spinal canal stenosis. CONCLUSIONS: When a patient shows kissing spine and concomitant subclinical foraminal stenosis at the affected level, we should sufficiently discuss the selection of an appropriate surgical procedure.

Dropped head syndrome (DHS) is characterized by apparent neck extensor muscle weakness and difficulty extending the neck to raise the head against gravity. The aim of the present study was to elucidate possible risk factors for DHS after cervical laminoplasty. Five patients who developed DHS after cervical laminoplasty (DHS group) and twenty age-matched patients who underwent laminoplasty without DHS after surgery (control group) were compared. The surgical procedure was single-door laminoplasty with strut grafting using resected spinous processes or hydroxyapatite spacers from C3 to C6 or C7. Analyses of preoperative images including the C2-C7 angle, C7-T1 kyphosis, T1 tilt, center of gravity line from the head-C7 sagittal vertical axis (CGH-C7 SVA) were performed on lateral plain cervical spine radiographs. Preoperative T2-weighted MRI at the C5 vertebral level was used to measure the cross-sectional area of the deep extensor muscles. Widths of the lateral gutters were assessed postoperatively using CT scans of the C5 vertebral body. The average preoperative C2-C7 angle was significantly smaller in the DHS group compared with the control group. The average preoperative C7-T1 angle was significantly larger in the DHS group compared with the control group. The average preoperative CGH-C7 SVA was significantly larger in the DHS group compared with the control group. In conclusion, patients with more pronounced preoperative C2-C7 kyphosis, C7-T1 kyphosis, and CGH-C7 SVA are more likely to develop DHS following laminoplasty.

We investigated the outcome of posterior decompression and instrumented fusion (PDF) surgery for patients with K-line (-) ossification of the posterior longitudinal ligament (OPLL) of the cervical spine, who may have a poor surgical prognosis. We retrospectively analyzed the outcome of a series of 27 patients who underwent PDF without correction of cervical alignment for K-line (-) OPLL and were followed-up for at least 1 year after surgery. We had performed double-door laminoplasty followed by posterior instrumented fusion without excessive correction of cervical spine alignment. The preoperative Japanese Orthopedic Association (JOA) score for cervical myelopathy was 8.0 points and postoperative JOA score was 11.9 points on average. The mean JOA score recovery rate was 43.6%. The average C2-C7 angle was 2.2° preoperatively and 3.1° postoperatively. The average maximum occupation ratio of OPLL was 56.7%. In conclusion, PDF without correcting cervical alignment for patients with K-line (-) OPLL showed moderate neurological recovery, which was acceptable considering K-line (-) predicts poor surgical outcomes. Thus, PDF is a surgical option for such patients with OPLL.

STUDY DESIGN: Retrospective case series. PURPOSE: To elucidate the impact of postoperative occiput-C2 (O-C2) angle change on subaxial cervical alignment. OVERVIEW OF LITERATURE: In the case of occipito-upper cervical fixation surgery, it is recommended that the O-C2 angle should be set larger than the preoperative value postoperatively. METHODS: The present study included 17 patients who underwent occipito-upper cervical spine (above C4) posterior fixation surgery for atlantoaxial subluxation of various etiologies. Plain lateral cervical radiographs in a neutral position at standing were obtained and the O-C2 angle and subaxial lordosis angle (the angle between the endplates of the lowest instrumented vertebra (LIV) and C7 vertebrae) were measured preoperatively and postoperatively soon after surgery and ambulation and at the final follow-up visit. RESULTS: There was a significant negative correlation between the average postoperative alteration of O-C2 angle (DO-C2) and the average postoperative alteration of subaxial lordosis angle (Dsubaxial lordosis angle) (r=-0.47, p=0.03). CONCLUSIONS: There was a negative correlation between DO-C2 and Dsubaxial lordosis angles. This suggests that decrease of mid-to lower-cervical lordosis acts as a compensatory mechanism for lordotic correction between the occiput and C2. In occipito-cervical fusion surgery, care must be taken to avoid excessive O-C2 angle correction because it might induce mid-to-lower cervical compensatory decrease of lordosis.

We enrolled 100 patients who underwent preoperative CT angiography before cervical spine instrumentation and investigated the morphology of the C2 pedicle from the perspective of pedicle screw (PS) trajectory using volume rendering and multiplanar reconstruction. The narrowest portion of the pedicle was identified as the pedicle isthmus. Safe C2 PS insertion was regarded to be not feasible when the height of the medullary cavity of the pedicle isthmus and/or width of the medullary cavity of the pedicle isthmus was ⩽4mm. Forty-five (22.5%) pedicles were ⩽4mm in width, and safe insertion of a PS was determined to be not feasible. Among these, seven pedicles were ⩽4mm in both height and width. The remaining 38 pedicles were ⩽4mm in width with heights >4mm. There was no pedicle with a width >4mm and height <4mm. In other words, short pedicles were always concomitantly narrow. Therefore, the seven pedicles ⩽4mm in both height and width were considered to be morphologically narrow. The heights of the pedicle isthmus were not limited by the vertebral artery groove (VAG) and safe C2 PS insertion can be considered feasible where the VAG is marginally cranial, whereas the widths of the pedicle isthmus are limited by the VAG. Therefore, safe C2 PS insertion is precluded only when the VAG courses cranially and medially. It is a medially-shifted, rather than a high-riding, vertebral artery that precludes safe C2 PS insertion. Therefore to avoid vertebral artery injury an axial CT scan, parallel to the pedicle axis, should be evaluated before C2 PS insertion.

PURPOSE: The K-line, which is a virtual line that connects the midpoints of the anteroposterior diameter of the spinal canal at C2 and C7 in a plain lateral radiogram, is a useful preoperative predictive indicator for sufficient decompression by laminoplasty (LMP) for ossification of the posterior longitudinal ligament (OPLL). K-line is defined as (+) when the peak of OPLL does not exceed the K-line, and is defined as (-) when the peak of OPLL exceeds the K-line. For patients with K-line (-) OPLL, LMP often results in poor outcome. The aim of the present study was to compare the clinical outcome of LMP, posterior decompression with instrumented fusion (PDF) and anterior decompression and fusion (ADF) for patients with K-line (-) OPLL. METHODS: The present study included patients who underwent surgical treatment including LMP, PDF and ADF for K-line (-) cervical OPLL. We retrospectively compared the clinical outcome of those patients in terms of Japanese Orthopedic Association score (JOA score) recovery rate. RESULTS: JOA score recovery rate was significantly higher in the ADF group compared with that in the LMP group and the PDF group. The JOA score recovery rate in the PDF group was significantly higher than that in the LMP group. CONCLUSIONS: LMP should not be used for K-line (-) cervical OPLL. ADF is one of the suitable surgical treatments for K-line (-) OPLL. Both ADF and PDF are applicable for K-line (-) OPLL according to indications set by each institute and surgical decisions.

Posterior decompression with instrumented fusion (PDF) surgery has been previously reported as a relatively safe surgical procedure for any type of thoracic ossification of the longitudinal ligament (OPLL). However, mid- to long-term outcomes are still unclear. The aim of the present study was to elucidate the mid- to long-term clinical outcome of PDF surgery for thoracic OPLL patients. The present study included 20 patients who had undergone PDF for thoracic OPLL and were followed for at least 5years. Increment change and recovery rate of the Japanese Orthopaedic Association (JOA) score were assessed. Revision surgery during the follow-up period was also recorded. Average JOA scores were 3.5 preoperatively and 7.1 at final follow-up. The average improvement in JOA score was 3.8 points and the average recovery rate was 47.0%. The JOA score showed gradual increase after surgery, and took 9months to reach peak recovery. As for neurological complications, two patients suffered postoperative paralysis, but both recovered without intervention. Six revision surgeries in four patients were related to OPLL. Additional anterior thoracic decompression for remaining ossification at the same level of PDF surgery was performed in one patient. Decompression surgery for deterioration of symptoms of pre-existing cervical OPLL was performed in three patients. One patient had undergone lumbar and cervical PDF surgery for de novo ossification foci of the lumbar and cervical spine. PDF surgery for thoracic OPLL is thus considered a relatively safe and stable surgical procedure considering the mid- to long-term outcomes.