Importance of computed tomography Hounsfield units in predicting S1 screw loosening after lumbosacral fusion

We investigated whether computed tomography (CT) Hounsfield unit (HU) values of the S1 screw trajectory can predict screw loosening after lumbosacral fixation. We analysed 102 patients (58 men and 44 women) who underwent L5-S1 interbody fusion between April 2018 and October 2019. We reviewed the characteristics of patients including body mass index, smoking, comorbidity with diabetes mellitus, and interbody fusion types. Bone mineral density (BMD) was obtained from the lumbar spine and total hip using dual-energy X-ray absorptiometry. Additionally, we reviewed the S1 screw lengths and diameters. HU values of both L1 vertebral bodies and bilateral S1 screw trajectories were measured on preoperative CT. At six months postoperatively, S1 screws on CT were assessed. Screws with a 1 mm or more radiolucent zone were defined as "loosening". Seventeen patients had loosened screws, and 85 patients did not. The patient characteristics did not significantly differ between the two groups. Both total hip BMD and L1 HU values were low in the loosening patient group (both p = 0.03). Of the 204 total S1 screws, 25 screws were loosened, and 179 screws were not. The screw length was short (p = 0.01), and the HU value of the S1 screw trajectory was low (p < 0.001) in the loosening screw group. Based on receiver operating characteristic analyses of these factors, the area under the curve of HU value of the S1 screw trajectory was the highest (0.79). Measuring the HU value of both the L1 vertebral body and S1 screw trajectory aids in predicting screw loosening.

Predictive biomarkers of ossification progression and bone metabolism dynamics in patients with cervical ossification of the posterior longitudinal ligament

PURPOSE

This study aimed to establish biomarkers to predict the progression of ossification by examining ossification volume and bone metabolism dynamics in patients with ossification of the posterior longitudinal ligament (OPLL).

METHODS

We assessed OPLL progression using computed tomography-based three-dimensional (3D) image analysis and examined bone metabolism dynamics in 107 patients with OPLL (men, 72; women, 35; mean age, 63.6 years). The volume of OPLL was calculated twice during the follow-up period, and OPLL progression was evaluated by the annual rate of ossification increase. Bone metabolism dynamics were assessed by routine blood tests and analysis of various serum biomarkers (including 25-hydroxyvitamin D, intact parathyroid hormone, fibroblast growth factor 23, intact N-terminal propeptide of type 1, tartrate-resistant acid phosphatase isoform 5b, sclerostin, and Dickkopf-1) and bone mineral density (BMD). Patients were classified into the progression (P) or non-progression (NP) group according to the annual rate of increase in previous 3D image analyses, and associated factors between these groups were compared.

RESULTS

The P and NP groups consisted of 29 patients (23 men and 6 women) and 78 patients (49 men and 29 women), respectively. Univariate analysis revealed significant differences in terms of age, body mass index, serum phosphorus, serum sclerostin, and BMD. In multivariate analysis, age, serum phosphorus, and serum sclerostin were identified as independent factors associated with OPLL progression.

CONCLUSION

Younger age, hypophosphatemia, and high serum sclerostin are risk factors for OPLL progression. Serum phosphorus and sclerostin could serve as important biomarkers for predicting ossification progression.

Neoadjuvant teriparatide therapy targeting the osteoporotic spine: influence of administration period from the perspective of bone histomorphometry

OBJECTIVE

Teriparatide (TPTD) is a potent promoter of early-stage osteogenesis and may be a useful adjuvant therapy to reduce complications related to bone fragility in spinal surgery patients with osteoporosis. However, effective neoadjuvant TPTD therapy regimens remain poorly understood. This study aimed to examine the effect of preoperative TPTD administration on cancellous bone with bone histomorphometry and to clarify the timing of preoperative TPTD administration for patients with spinal fusion and osteoporosis.

METHODS

In this longitudinal multicenter study, 57 patients with spinal fusion and osteoporosis, who consented to undergo iliac biopsy, were allocated to the following treatment groups: neoadjuvant TPTD therapy group (n = 42) and no neoadjuvant therapy (NTC) group (n = 15). Patients in the TPTD group were categorized into subgroups on the basis of duration of preoperative TPTD administration, as follows: 1 month (n = 9), 2 months (n = 8), 3 months (n = 9), 4 months (n = 7), and 6 months (n = 9). All patient samples were preoperatively double labeled with tetracycline, and iliac biopsies were performed during spinal fusion surgery. Histomorphometric analyses were performed on nondecalcified, thin-sliced specimens. Specimens were classified on the basis of TPTD administration duration and subsequently compared with those of the NTC group. Postoperative complications and Oswestry Disability Index scores were evaluated at 1 and 2 years after surgery.

RESULTS

There were no demographic differences between groups. Mineralizing surface/bone surface, a key parameter of dynamic bone formation, started to increase after 1 month of TPTD administration; this increase became significant after 3 months of administration and peaked at 4 months, with a 6-fold increase relative to that of the NTC group. The patients who received preoperative TPTD for 3 months or more had superior clinical results in terms of the osteoporotic complication rate and Oswestry Disability Index scores, except for bisphosphonate-pretreated patients.

CONCLUSIONS

When considering neoadjuvant TPTD therapy, the authors recommend at least 3 months of preoperative administration to provide a more substantial anabolic effect from the early postoperative stage.

Randomized trial of granulocyte colony-stimulating factor for spinal cord injury

Attenuation of the secondary injury of spinal cord injury (SCI) can suppress the spread of spinal cord tissue damage, possibly resulting in spinal cord sparing that can improve functional prognoses. Granulocyte colony-stimulating factor (G-CSF) is a haematological cytokine commonly used to treat neutropenia. Previous reports have shown that G-CSF promotes functional recovery in rodent models of SCI. Based on preclinical results, we conducted early phase clinical trials, showing safety/feasibility and suggestive efficacy. These lines of evidence demonstrate that G-CSF might have therapeutic benefits for acute SCI in humans. To confirm this efficacy and to obtain strong evidence for pharmaceutical approval of G-CSF therapy for SCI, we conducted a phase 3 clinical trial designed as a prospective, randomized, double-blinded and placebo-controlled comparative trial. The current trial included cervical SCI [severity of American Spinal Injury Association (ASIA) Impairment Scale (AIS) B or C] within 48 h after injury. Patients are randomly assigned to G-CSF and placebo groups. The G-CSF group was administered 400 μg/m²/day × 5 days of G-CSF in normal saline via intravenous infusion for five consecutive days. The placebo group was similarly administered a placebo. Allocation was concealed between blinded evaluators of efficacy/safety and those for laboratory data, as G-CSF markedly increases white blood cell counts that can reveal patient treatment. Efficacy and safety were evaluated by blinded observer. Our primary end point was changes in ASIA motor scores from baseline to 3 months after drug administration. Each group includes 44 patients (88 total patients). Our protocol was approved by the Pharmaceuticals and Medical Device Agency in Japan and this trial is funded by the Center for Clinical Trials, Japan Medical Association. There was no significant difference in the primary end point between the G-CSF and the placebo control groups. In contrast, one of the secondary end points showed that the ASIA motor score 6 months (P = 0.062) and 1 year (P = 0.073) after drug administration tend to be higher in the G-CSF group compared with the placebo control group. The present trial failed to show a significant effect of G-CSF in primary end point.

A case of advanced ankylosing spondylitis complicated with cervical myelopathy due to ossification of yellow ligament in which bone histomorphometry demonstrated delayed calcification

There is minimal information available about bone histomorphometric findings in patients with ankylosing spondylitis (AS). Herein, we report a case of advanced AS complicated with cervical myelopathy due to ossification of yellow ligament (OYL). A 37-year-old Japanese man who had been diagnosed with AS was administered adalimumab. Thirty-four months after adalimumab treatment, he reported upper extremity numbness, dexterity impairment and a spastic gait. Magnetic resonance imaging and computed tomography of the cervical spine revealed cervical cord compression at the C5/6 level due to OYL. After surgery including posterior spinal fusion and cervical cord decompression with iliac bone graft at C5 and C6 arches, these symptoms improved. Bone histomorphometry of his ilium revealed marked osteoid formation and reduced mineral apposition, suggesting a calcification disorder. In addition, 25-hydroxy vitamin D was abnormally low (<4 ng/mL), and at 148 pg/mL parathyroid hormone was higher than the reference value, indicating secondary hyperparathyroidism. This case warrants reporting because OYL was complicated with AS and bone histomorphometric findings in AS were evaluated.

Three-dimensional morphological analysis of cervical foraminal stenosis using dynamic flexion-extension computed tomography images

BACKGROUND

Morphological features of foraminal stenosis in cervical spondylotic radiculopathy and the adequate extent of facet resection in posterior cervical foraminotomy remain uncertain. Herein, we evaluated quantitatively foraminal widths in cervical spondylotic radiculopathy on dynamic flexion-extension computed tomography using a novel three-dimensional analysis method and determined the extent of facet resection in posterior cervical foraminotomy.

METHODS

Seventeen patients undergoing posterior cervical foraminotomy for cervical spondylotic radiculopathy were evaluated. A neuroforamen three-dimensional model was built from preoperative images of flexion-extension computed tomography myelography, and an ordinary cervical spine coordinate system and an original neuroforaminal coordinate system, were established. In the neuroforaminal coordinate system, minimum areas perpendicular to the long axis by the slices from inlet to outlet of neuroforamen and narrowest foraminal width in a slice of minimum area were measured. The location of the narrowest region from inlet of the foramen was calculated. Ratios of minimum and sufficient facet resection were obtained from the location of the narrowest region in the neuroforaminal coordinate system.

RESULTS

The narrowest foraminal widths (flexion/extension) in the cervical spine coordinate system and the neuroforaminal coordinate system were 2.9/2.3 and 2.6/1.9 mm, respectively. The mean values of the location of the narrowest region (flexion/extension) were 0.27/0.22 and 0.50/0.45 mm, respectively, and the narrowest region in the neuroforaminal coordinate system was located on the outer side than in the cervical spine coordinate system (p < 0.001). The ratios of minimum and sufficient facet resection were 23 ± 8% and 32 ± 9%, respectively.

CONCLUSIONS

The narrowest regions both in flexion and extension are located at the middle of the foramen based on the neuroforaminal coordinate system. Ordinary evaluation of axial computed tomography images likely underestimates the extent of facet resection, whereas certain extent of facet resection does not exceed 50% in cases with single-level cervical spondylotic radiculopathy.

STUDY DESIGN

A retrospective case control study.

A novel concept of posterior decompression and instrumented fusion with selective lordotic correction for cervical ossification of the posterior longitudinal ligament

PURPOSE

The recovery rate of Japanese Orthopedic Association (JOA) score with K-line (-) cervical ossification of the posterior longitudinal ligament (OPLL) for posterior decompression with in-situ fusion (PDF) tends to be lower than that of anterior decompression with fusion (ADF). However, ADF is a technically demanding operation and has ADF-specific complications. This prospective report introduced a novel concept of PDF with selective lordotic correction as well as prophylactic foraminal decompression.

METHODS

Six consecutive patients (four men and two women; mean age, 61.8 years) were included. PDF was performed, attempting to create cervical lordosis to acquire a posterior shift of the spinal cord, while preventing postoperative C5 palsy by prophylactic facetectomy and selective lordotic correction.

RESULTS

The mean recovery rate of JOA score at the final follow-up was 70.9 ± 20.3%. The mean C2-C7 angle preoperatively and at final follow-up was 5.5 ± 3.9° and 12.2 ± 4.8°, respectively. No symptomatic nerve root palsy, except one case with transient C7 root iatrogenic palsy, was found.

CONCLUSIONS

A novel concept of PDF with selective lordotic correction obtained recovery rates of JOA scores comparable to those of ADF. We believe that this method can improve PDF outcomes in patients with K-line (-) OPLL.

Quantitative radiographic analysis of foraminal re-stenosis after posterior cervical foraminotomy with laminoplasty

Few studies have performed detailed radiographic evaluation of the cause of recurrent cervical radiculopathy. In this study, we aimed to perform quantitative analyses of foraminal re-stenosis after posterior cervical foraminotomy (PCF) concomitant with laminoplasty. Seventy-eight consecutive patients (50 males and 28 females, mean age of 62 years at surgery) with cervical spondylotic radiculomyelopathy who underwent PCF concomitant with open-door laminoplasty were included. A total of 133 foramina undergoing PCF were radiographically evaluated using the following parameters: disc height, focal range of motion at the corresponding disc level, foraminal diameter (FD) and facet joint width (FJW) in the axial view on computed tomography, and re-stenosis rate (RR) of foramina. RR was calculated as follows: (foraminal regrowth at 2 years after surgery)/(foraminal enlargement immediate postoperatively) × 100% (RR2y). FDs preoperatively, postoperatively, and at 2-year follow-up were 2.2, 6.6, and 4.6 mm, respectively, and FJWs were 14.5, 9.0, and 10.6 mm, respectively. Both parameters significantly increased at the 2-year follow-up (p < 0.001). The mean RR2y was 42% (range, -16 to 108%). On logistic regression analysis of risk factors for higher RR2y (>50%), only preoperative posterior disc height (PDH) (OR = 0.33; 95% CI = 0.193-0.563; p < 0.001) was identified. Receiver operating characteristic curve analysis showed that the cut-off value of RR2y 50% was 1-mm PDH (AUC 0.73, sensitivity 52%, specificity 86%, p value < 0.001). After posterior foraminotomy with laminoplasty, the enlarged foraminal space gradually decreased during the 2-year follow-up. Foraminal re-stenosis was mainly due to bone regrowth of the resected facet joint, which is caused by disc degeneration with loss of PDH.

The Influence of Lumbar Muscle Volume on Curve Progression After Skeletal Maturity in Patients With Adolescent Idiopathic Scoliosis: A Long-Term Follow-up Study

STUDY DESIGN

A retrospective cohort study.

OBJECTIVES

To investigate the relationship between skeletal muscle status of the trunk and the progression of adolescent idiopathic scoliosis (AIS) during adulthood.

SUMMARY OF BACKGROUND DATA

To date, studies evaluating the risk factors for progression of AIS have principally focused on radiographic parameters.

METHODS

Eighty-two women with AIS managed conservatively, who had a major curve ≥30° at skeletal maturity (Risser grade ≥4), were enrolled. Patients had been followed-up, on average, over 23.5 years (range, 12-37 years) after skeletal maturity, and were ≥30-years-old at the time of the survey (mean, 40.1 years). The ratio of the cross-sectional area (CSA) and signal intensity (SI) of muscles (multifidus [MF], erector spinae [ES], and psoas major [PM]) were evaluated using axial T2-weighted magnetic resonance images at the level of L4.

RESULTS

The mean progression of the main thoracic and thoracolumbar/lumbar (TL/L) curves after skeletal maturity was 8.2° (mean annual rate of 0.4°) and 7.2° (mean annual rate of 0.3°), respectively. The mean CSA ratio was as follows: MF, 23.3%; ES, 79.6%; and PM, 40.5%. The mean SI ratio was as follows: MF, 34.9%; ES, 31.7%; and PM, 20.9%. On multivariate logistic regression, a higher SI ratio of the MF was predictive of a progression of the Cobb angle and translation of the apical vertebra, with a lower CSA ratio of the ES contributing to the progression of the Cobb angle for the TL/L curve.

CONCLUSIONS

In patients with AIS who have a major curve ≥30° at skeletal maturity, patients with greater TL/L curve progression have lower skeletal muscle volume and higher fatty degeneration of the lumbar extensor muscles in adulthood. However, further longitudinal or prospective studies are necessary to clarify the causal relationship between scoliosis progression and trunk muscular status.

LEVEL OF EVIDENCE

Level III, retrospective cohort study.

Bone Mineral Density After Spinal Fusion Surgery for Adolescent Idiopathic Scoliosis at a Minimum 20-Year Follow-up

STUDY DESIGN

A retrospective, long-term follow-up study.

OBJECTIVE

We investigated the incidence and risk factors for osteopenia at a minimum of 20 years after spinal instrumented fusion for adolescent idiopathic scoliosis (AIS).

SUMMARY OF BACKGROUND DATA

Surgically treated AIS patients may be likely to have osteopenia in adulthood because the association between AIS and osteopenia has been well documented. However, the long-term results of AIS surgery on BMD have not been evaluated.

METHODS

Twenty-one (19 women; mean age, 45.3 years) of 45 consecutive patients with AIS who underwent spinal instrumented fusion surgery between 1973 and 1994 consented to inclusion in the current analysis. Based on their T scores for bone mineral density (BMD) of the left hip, participants were divided into an osteopenia/osteoporosis group (group P, T score < -1.0) and a normal group (group N, T score ≥ -1.0). Z scores of the left hip were used for analyses of the association between bone mineral status and individual factors.

RESULTS

Eleven participants (52.4%) were categorized into group P. Mean body weight (kg) at survey (46.6 vs. 56.8) and mean body mass index (BMI) at both surgery (17.2 vs. 19.5) and survey (18.7 vs. 23.2) were significantly lower in group P than in group N (p < .05). Moreover, body weight at survey (Spearman rank correlation coefficient, r_S = 0.49), as well as BMI at both surgery (r_S = 0.67) and survey (r_S = 0.61) demonstrated positive correlations with the Z-score (p < .05).

CONCLUSION

More than half of the participants had osteopenia or osteoporosis, and both preoperative and postoperative low BMI were risk factors for osteopenia in adulthood.

LEVEL OF EVIDENCE

Level IV.

En Bloc Spondylectomy for Spinal Metastases: Detailed Oncological Outcomes at a Minimum of 2 Years after Surgery

Study Design

Retrospective case series.

Purpose

To investigate the oncological outcomes, including distant relapse, after en bloc spondylectomy (EBS) for spinal metastases in patients with a minimum of 2-year follow-up.

Overview of Literature

Although EBS has been reported to be locally curative and extend survival in select patients with spinal metastases, detailed reports regarding the control of distant relapse after EBS are lacking.

Methods

We conducted a retrospective review of 18 consecutive patients (median age at EBS, 62 years; range, 40–77 years) who underwent EBS for spinal metastases between 1991 and 2015. The primary cancer sites included the kidney (n=7), thyroid (n=4), liver (n=3), and other locations (n=4). Survival rates were estimated using the Kaplan–Meier method, and groups were compared using the log-rank method.

Results

The median operative time and intraoperative blood loss were 767.5 minutes and 2,375 g, respectively. Twelve patients (66.7%) experienced perioperative complications. Five patients (27.8%) experienced local recurrence of the tumor at a median of 12.5 months after EBS, four of which had a positive resection margin status. Thirteen patients (72.2%) experienced distant relapse at a median of 21 months after EBS. The estimated median survival period after distant relapse was 20 months (95% confidence interval, 0.71–39.29 months). No association was found between resection margin status and distant relapse. Overall, the 2-year, 5-year, and 10-year survival rates after EBS were 72.2%, 48.8%, and 27.1%, respectively. Importantly, the era in which EBS was performed did not impact the oncological outcomes.

Conclusions

Our results suggest that EBS by itself, even if margin-free, cannot prevent further dissemination, which occurred in >70% of patients at a median of 21 months after EBS. These results should be considered and conveyed to patients for clinical decision-making.

Study protocol for the G-SPIRIT trial: a randomised, placebo-controlled, double-blinded phase III trial of granulocyte colony-stimulating factor-mediated neuroprotection for acute spinal cord injury

INTRODUCTION

Granulocyte colony-stimulating factor (G-CSF) is generally used for neutropaenia. Previous experimental studies revealed that G-CSF promoted neurological recovery after spinal cord injury (SCI). Next, we moved to early phase of clinical trials. In a phase I/IIa trial, no adverse events were observed. Next, we conducted a non-randomised, non-blinded, comparative trial, which suggested the efficacy of G-CSF for promoting neurological recovery. Based on those results, we are now performing a phase III trial.

METHODS AND ANALYSIS

The objective of this study is to evaluate the efficacy of G-CSF for acute SCI. The study design is a prospective, multicentre, randomised, double-blinded, placebo-controlled comparative study. The current trial includes cervical SCI (severity of American Spinal Injury Association (ASIA) Impairment Scale B/C) within 48 hours after injury. Patients are randomly assigned to G-CSF and placebo groups. The G-CSF group is administered 400 µg/m²/day×5 days of G-CSF in normal saline via intravenous infusion for 5 consecutive days. The placebo group is similarly administered a placebo. Our primary endpoint is changes in ASIA motor scores from baseline to 3 months. Each group includes 44 patients (88 total patients).

ETHICS AND DISSEMINATION

The study will be conducted according to the principles of the World Medical Association Declaration of Helsinki and in accordance with the Japanese Medical Research Involving Human Subjects Act and other guidelines, regulations and Acts. Results of the clinical study will be submitted to the head of the respective clinical study site as a report after conclusion of the clinical study by the sponsor-investigator. Even if the results are not favourable despite conducting the clinical study properly, the data will be published as a paper.

TRIAL REGISTRATION NUMBER

UMIN000018752.

Risk factors for surgical site infection following spinal instrumentation surgery

BACKGROUND

In spinal instrumentation surgeries, surgical site infection (SSI) is one of the complications to be avoided. However, spinal instrumentation surgeries have a higher rate of SSI than other clean orthopedic surgeries. The purpose of this study was to investigate the risk factors for SSI following spinal instrumentation surgeries and contribute to the prevention of SSIs by identifying high-risk patients.

METHODS

Records of 431 patients who underwent spinal instrumentation surgeries from 2011 to 2014 with a minimum follow-up period of 90 days were retrospectively reviewed. Associations of SSI with various preoperative, operative, and postoperative factors were statistically analyzed with univariate and stepwise multivariate logistic regression analysis.

RESULTS

Deep or superficial SSIs were observed in 15 patients (3.5%). Univariate analysis revealed significant association of SSI with diabetes mellitus (odds ratio [OR] 4.7, 95% confidence interval [CI] 1.5-14.4; p = 0.012) and serum albumin ≤3.5 g/dl (OR 3.35, 95% CI 1.1-10.38, p = 0.012). The number of regular medications prescribed in patients with SSI (8.2 ± 5.4) was significantly more than that in patients without SSI (3.8 ± 4.4) (p = 0.001), and the cut-off value of the number of medications was 7, as derived from receiver operating characteristics analysis. Multivariate analysis revealed that the number of regular medications ≥7 was an independent risk factor significantly associated with SSIs (OR 7.3, 95% CI 2.3-24.0, p = 0.001).

CONCLUSIONS

Our study demonstrated that an important risk factor for SSI after spinal instrumentation surgery was number of regular medications ≥7. Number of regular medications is a simple and valuable risk index for SSI, which reflects the influence of medications and comorbidities.

Natural history of the ossification of cervical posterior longitudinal ligament: a three dimensional analysis

PURPOSE

Three-dimensional (3D) imaging using computed tomography (CT) has made it possible to accurately evaluate ossification of the posterior longitudinal ligament (OPLL). Recently, we developed a novel technique to measure ossification volume using the 3D analysis. The purpose of this study was to investigate the natural course of OPLL and the risk factors for volume progression.

METHODS

Forty-one patients (22 males and 19 females) diagnosed with cervical OPLL who had been non-surgically treated were included in this study. We evaluated clinical examination, radiological findings, and the volume of ossified lesions during at least 1-year intervals. Furthermore, we performed risk factor analysis for OPLL volume progression.

RESULTS

The mean ossification volume was 2047.4 ± 1437.3 mm³ in the first examination and 2201.0 ± 1524.1 mm³ in the final examination, indicating a significant increase during the follow-up period (p < 0.001). The mean annual rate of lesion increase was 4.1 ± 2.7%. Univariate regression analysis demonstrated significant relationships between the annual rate of lesion increase and age (β = -0.48; p = 0.001), body weight (BW) (β = 0.36; p = 0.02), and body mass index (BMI) (β = 0.35; p = 0.03). Furthermore, age was the only significant predictor of OPLL progression (R² = 0.23; p = 0.001) in multivariate liner regression analysis.

CONCLUSIONS

Younger age, higher BW, and higher BMI are predictors of OPLL progression. Younger age is the most significant predictor in non-surgically treated patients.

False-negative transcranial motor evoked potentials (TcMEPs) during surgery for congenital lumbar kyphoscoliosis: a case report

INTRODUCTION

Transcranial motor evoked potential (TcMEP) monitoring is the gold standard for intra-operative neurological monitoring (IOM) of motor pathways during complex spine surgery because of its high sensitivity and specificity. However, although it is very low, the rate of false-negatives in TcMEP monitoring is not zero. Therefore, over-reliance on TcMEP monitoring can cause potentially preventable motor deficits.

CASE PRESENTATION

We report a case of motor deficits due to nerve root stretch after surgical correction of a congenital lumbar kyphoscoliosis in a 56-year-old woman. TcMEPs did not show any significant changes during surgery, whereas free-run electromyography (EMG) demonstrated a long-lasting train activity in the left quadriceps femoris muscle (QF) after correction at the osteotomy area. According to the normal findings on TcMEP monitoring, we did not release the correction. Postoperatively, a significant decrease (grade 2-) in the manual muscle test for the left QF and iliopsoas muscle and hypesthesia of the left anterior thigh was revealed. Fortunately, muscle strength was fully recovered without revision surgery at 6 months postoperatively; however, numbness in the left anterior thigh persisted at 2 years after surgery.

DISCUSSION

Our report suggests that the possibility of false-negative TcMEPs should be kept in mind, especially during surgery with a risk of nerve root injury. When abnormal findings in the free-run EMG, including long-lasting train activity, are observed, surgeons should consider performing appropriate responses, such as the release of the correction, even when no substantial changes are seen in the TcMEPs.

Preservation of donor cornea prevents corneal allograft rejection by inhibiting induction of alloimmunity

To determine whether preservation of the donor cornea prevents allograft rejection, orthotopic corneal transplantation was performed using corneas preserved in storage medium (Optisol-GS((R))). Donor corneas harvested from C3H/He (H-2(k)) mice and B10.D2 (H-2(d)) mice were preserved in storage medium for 0, 3, 7 and 14 days, and then transplanted into the corneal beds of the recipient BALB/c (H-2(d)) mice. Graft survival was determined clinically and histologically. The expression of major histocompatibility complex (MHC) molecules in the preserved corneas was analysed by immunohistochemistry and Western blotting. Donor-specific cytotoxic T lymphocyte (CTL) and delayed-type hypersensitivity (DTH) responses were assessed 3 weeks after grafting. Active suppression of DTH in the recipient mice was also examined 3 weeks after grafting. The survival of 14 day preserved allografts was significantly higher than that of the non-preserved allografts in both MHC and minor histocompatibility (H) antigens, and minor H only disparate combination. The recipients of the preserved allografts failed to induce both CTL and DTH. The active suppression of DTH was not acquired in these recipients. The expression of donor-derived MHC class I antigens was markedly reduced in the corneas after preservation. Preservation of the donor cornea had a remarkable effect on the prevention of corneal allograft rejection. Since the preserved allografts failed to induce donor-specific CTL and DTH, and active suppression of DTH was not acquired in the recipients, the prevention of allo-rejection is due to a failure of allo-sensitization. These results indicate that the reduction of MHC class I antigens and minor H antigens expression in the preserved grafts induces a failure of allo-sensitization and leads to the high rate of acceptance in corneal allografts.