The Concept of Lamina-Pedicle Perpendicularity: Part 2: Thoracic Spine

STUDY DESIGN

Retrospective radiographic study.

PURPOSE

The hypothesis of this study was that the pedicle axis (PA) is almost perpendicular to the interlaminar line (ILL) in the sagittal plane of the thoracic vertebrae. The objective of the current study was to define the thoracic lamina-PA inclination in order to verify the right-angle concept and to estimate the safety zones for sagittal inclination during pedicle screw insertion. The authors, to the best of their knowledge, are unaware of previous similar studies.

OVERVIEW OF LITERATURE

Based on the study's observations of different spinal disorders, including deformities, it was noted that following a sagittal cranial-caudal trajectory perpendicular to the ILL and joining the two adjacent thoracic vertebrae would work well at most vertebral levels.

METHODS

This was a retrospective study on the computed tomography (CT) chest scans of patients with no spinal pathologies. The ILL-PA, superior and inferior safe angles of the pedicle screw trajectories, and the exit zone of the screw perpendicular to the ILL were reviewed by two observers via three-dimensional multiplanar reconstruction mode of the Horos DICOM software (https://horosproject.org/).

RESULTS

The CT chest images of 30 consecutive patients (20 males and 10 females) with a mean age of 49.87±15.48 years (range, 24-74 years) were evaluated. The mean ILL-PA angle was almost orthogonal for all levels. This angle ranged between 86.21°±3.01° at D5 and 90.59°±2.72° at D10. The safety zones of the sagittal inclination of the pedicle screws were demonstrated. The results revealed that the least safe angle was when the screw was directed cranially along the middle part of the pedicle between 4.43°±0.75° at D8 and 6.94°±1.19° at D11.

CONCLUSIONS

The results of this study confirmed the ILL-PA angle perpendicularity in the thoracic spine at all levels. The ILL is a useful guide for pedicle screw sagittal inclination.

The Concept of Lamina-Pedicle Perpendicularity: Part 1. Lumbar Spine

Study Design

Retrospective radiographic study.

Purpose

We hypothesized that the pedicle is almost perpendicular to the interlaminar line in the sagittal plane of the lumbar vertebrae. The current study aimed to define the lumbar lamina–pedicle inclination to verify the right-angle concept and to estimate the safety zones of sagittal inclination during pedicle screw insertion. To the best of our knowledge there are no previous similar studies.

Overview of Literature

Based on our observations in different spinal disorders including deformities, we noted that following a sagittal (cranial–caudal) trajectory perpendicular to the interlaminar line joining the two adjacent vertebrae would work well in most of the vertebral levels.

Methods

This was a retrospective study on normal lumbar spine lateral radiographs of patients who presented with low back pain and were reviewed by two observers. Different inclination angles were constructed to estimate the safety zones of the pedicle screws’ sagittal inclination.

Results

Radiographs of 30 consecutive patients, 25 females and five males, with a mean age of 39.43±11.18 years, were studied. The mean angle of the interlaminar line and the pedicle axis was almost orthogonal at all the levels, with a range of 89.16°–94.63°, which was not affected by the lumbar sagittal profile. The safety zones of the pedicle screws were measured, and they revealed a safe sagittal range of 19.73°–24.40° if the screw was inserted from the pedicle axis, 21.03°–22.59° if inserted from the most cephalic part, and 13.31°–17.03° if inserted from the most caudal part.

Conclusions

Our results confirmed the perpendicularity of the interlaminar line with the pedicle axis in the lumbar spine at all the levels. The interlaminar line is a useful guide for pedicle screw sagittal inclination.

Prognosis of cervical myelopathy based on diffusion tensor imaging with artificial intelligence methods

Diffusion tensor imaging (DTI) has been proposed for the prognosis of cervical myelopathy (CM), but the manual analysis of DTI features is complicated and time consuming. This study evaluated the potential of artificial intelligence (AI) methods in the analysis of DTI for the prognosis of CM. Seventy-five patients who underwent surgical treatment for CM were recruited for DTI imaging and were divided into two groups based on their one-year follow-up recovery. The DTI features of fractional anisotropy, axial diffusivity, radial diffusivity, and mean diffusivity were extracted from DTI maps of all cervical levels. Conventional AI models using logistic regression (LR), k-nearest neighbors (KNN), and a radial basis function kernel support vector machine (RBF-SVM) were built using these DTI features. In addition, a deep learning model was applied to the DTI maps. Their performances were compared using 50 repeated 10-fold cross-validations. The accuracy of the classifications reached 74.2% ± 1.6% for LR, 85.6% ± 1.4% for KNN, 89.7% ± 1.6% for RBF-SVM, and 59.2% ± 3.8% for the deep leaning model. The RBF-SVM algorithm achieved the best accuracy, with sensitivity and specificity of 85.0% ± 3.4% and 92.4% ± 1.9% respectively. This finding indicates that AI methods are feasible and effective for DTI analysis for the prognosis of CM.

The dorsal skinfold chamber: A versatile tool for preclinical research in tissue engineering and regenerative medicine

Previous human study suggested that fresh-frozen intervertebral disc allograft transplantation can relieve neurological symptoms and restore segmental kinematics. Before wide clinical application, research into the pathophysiology of the postoperative disc allograft is needed. One important question that remains to be answered in disc allografting is the healing process of the host-graft interface and the subsequent change of the endplates. With the goat model for lumbar disc allografting, histology, micro-computed tomography analysis, scanning electron microscopy and energy-dispersive X-ray spectroscopy mapping were applied to evaluate the healing of the host-graft interfaces, the remodelling of subchondral bone, and the changes of the bony and cartilaginous endplates after transplantation. It was found that healing of the host-graft interfaces started at 1.5 months and was completed at 6 months by natural remodelling. This bony remodelling was also noted in the subchondral bone area after 6 months. The bony endplate was well preserved initially, but was gradually replaced by trabecular bone afterwards; on the other hand, the cartilaginous endplate became atrophic at 6 months and nearly disappeared at the final follow-up. Collectively, after intervertebral disc allograft transplantation, bony healing and remodelling were seen which ensured the stability and mobility of the disc-transplanted segment, but the integrity of bony and cartilaginous endplates was gradually lost and nearly disappeared finally.

Systemic blood plasma CCL5 and CXCL6: Potential biomarkers for human lumbar disc degeneration

Lumbar disc degeneration severity on magnetic resonance imaging (MRI) is associated with low back pain. Pro-inflammatory chemokines CCL5 and CXCL6 are released by induced degenerative discs, and CCL5 has been associated with discogenic back pain. A case-control study was performed, based on the Hong Kong Disc Degeneration Population-Based Cohort of Southern Chinese, to investigate if systemic levels of CCL5 and CXCL6 were elevated in subjects with disc degeneration compared to non-degenerated individuals. Eighty subjects were selected, 40 with no disc degeneration (control group; DDD score 0) and 40 with moderate/severe disc degeneration (disc degeneration group; DDD score ≥5) as noted on MRI. Subjects were matched for age, sex, body mass index and workload. Blood plasma samples were obtained from each individual, and levels of CCL5 and CXCL6 were measured. Secondary phenotypes of lumbar disc displacement and cervical disc changes were also assessed. CCL5 concentrations were significantly increased in the disc degeneration (mean: 19.8 ng/mL) compared to the control group (mean: 12.8 ng/mL) (p = 0.015). The degeneration group demonstrated higher levels of CXCL6 (mean: 56.9 pg/mL) compared to the control group (mean: 43.4 pg/mL) (p = 0.010). There was a trend towards elevated CCL5 levels with disc displacement in the degeneration group (p = 0.073). Cervical disc degeneration was not associated with elevated chemokine levels (p > 0.05). This is the first study to note that elevated systemic CCL5 and CXCL6 were associated with moderate/severe lumbar disc degeneration, further corroborating tissue studies of painful discs. These chemokines may be systemic biomarkers for the diagnosis and monitoring of disc degeneration.

A correlation study between in-brace correction, compliance to spinal orthosis and health-related quality of life of patients with Adolescent Idiopathic Scoliosis

BACKGROUND

It has been proposed that in-brace correction is the best guideline for prediction of the results of brace treatment for patients with Adolescent Idiopathic Scoliosis (AIS). However, bracing may be a stressful experience for patients and bracing non-compliance could be psychologically related. The purpose of this study was to assess the correlation between brace compliance, in-brace correction and QoL of patients with AIS.

METHODS

Fifty-five patients with a diagnosis of AIS were recruited. All were female and aged 10 years or above when a brace was prescribed, none had undergone prior treatment, and all had a Risser sign of 0-2 and a Cobb angle of 25-40°. The patients were examined in three consecutive visits with 4 to 6 months between each visit. The Chinese translated Trunk Appearance Perception Scale (TAPS), the Chinese translated Brace Questionnaires (BrQ) and the Chinese translated SRS-22 Questionnaires were used in the study. The in-brace Cobb angle, vertebral rotation and trunk listing were also measured. Patients' compliance, in-brace correction and patients' QoL were assessed. To identify the relationship among these three areas, logistic regression model and generalized linear model were used.

RESULT

For the compliance measure, a significant difference (p = 0.008) was detected on TAPS mean score difference between Visit 1 and Visit 2 in the least compliant group (0-8 hours) and the most compliant group (17-23 hours). In addition, a significant difference (p = 0.000) was detected on BrQ mean score difference between Visit 2 and Visit 3 in the least compliant group (0-8 hours) and the most compliant group (17-23 hours). For the orthosis effectiveness measure, no significant difference was detected between the three groups of bracing hours (0-8 hours, 9-16 hours, 17-23 hours) on in-brace correction (below 40% and 40% or above). For the QoL measure, no significant difference was detected between the two different in-brace correction groups (below 40% and 40% or above) on QoL as reflected by the TAPS, BrQ and SRS-22r mean scores.

CONCLUSION

The results showed a positive relationship between patients' brace wear compliance and patients' QoL. Poor compliance would cause a lower QoL.

Ten-year risk of osteoporotic fractures in postmenopausal Chinese women according to clinical risk factors and BMD T-scores: a prospective study

Independent risk factors for osteoporotic fracture were identified for a Southern Chinese postmenopausal population. Clinical risk factor assessment with or without BMD measurement was shown to be an effective predictor of 10-yr risk of osteoporotic fracture and provides a more accessible tool for patient evaluation.

INTRODUCTION

Asian-specific data on risk factors for osteoporosis remain sparse. However, risk factor assessment, in addition to BMD measurement, is increasingly recognized as a reliable predictor of absolute osteoporotic fracture risk. The purpose of this prospective study was to determine the specific independent risk factors for osteoporotic fracture and to predict the 10-yr risk of osteoporotic fracture in the postmenopausal Southern Chinese population.

MATERIALS AND METHODS

A total of 1435 community-dwelling, postmenopausal, treatment-naive women were recruited. Baseline demographic characteristics and clinical risk factors were obtained, and BMD at the spine and hip was measured. Subjects were followed for outcomes of incident low trauma fracture. Ten-year risk of osteoporotic fracture was predicted from the risk factor assessment and BMD measurement by Cox proportional hazards models.

RESULTS

The mean age of subjects was 63.4 +/- 8.3 yr. After 5.0 +/- 2.3 yr (range, 1.0-11.0 yr) of follow-up, 80 nontraumatic new fractures were reported during follow-up. Eight independent clinical risk factors identified at baseline were found to be significant predictors of osteoporotic fracture, with the most important being use of walking aids (RR, 4.2; 95% CI, 2.7-6.7; p < 0.001) and a history of fall (RR, 4.0; 95% CI, 2.5-6.2; p < 0.001). Other predictive factors included being homebound, calcium intake < 400 mg/d, age > 65 yr, history of fracture, and BMI < 19 kg/cm(2). Subjects with three to eight clinical risk factors had a predicted 10-year risk of osteoporotic fracture of 25%, which increased to 30% if they also had total hip BMD T-score <or= -2.5.

CONCLUSIONS

Clinical risk factor assessment, with or without BMD measurement, is a reliable predictor of 10-year risk of osteoporotic fracture and may be particularly useful in regions or primary care clinics without access to bone densitometry equipment.

Selection of floating-point or fixed-point for adaptive noise canceller in somatosensory evoked potential measurement

Adaptive noise canceller (ANC) has been used to improve signal to noise ratio (SNR) of somsatosensory evoked potential (SEP). In order to efficiently apply the ANC in hardware system, fixed-point algorithm based ANC can achieve fast, cost-efficient construction, and low-power consumption in FPGA design. However, it is still questionable whether the SNR improvement performance by fixed-point algorithm is as good as that by floating-point algorithm. This study is to compare the outputs of ANC by floating-point and fixed-point algorithm ANC when it was applied to SEP signals. The selection of step-size parameter (micro) was found different in fixed-point algorithm from floating-point algorithm. In this simulation study, the outputs of fixed-point ANC showed higher distortion from real SEP signals than that of floating-point ANC. However, the difference would be decreased with increasing micro value. In the optimal selection of micro, fixed-point ANC can get as good results as floating-point algorithm.

Time-frequency feature of intraoperative somatosensory evoked potential signals

The purpose of this paper is to investigate the time-frequency analysis of somatosensory evoked potentials (SEP) and its potential application to intraoperative spinal cord monitoring. In this study, SEP signals were recorded from 97 adolescent patients undergoing surgical correction of idiopathic scoliosis. The time-frequency distributions of SEP were observed during surgery by analysing averaged SEP signals with Short Time Fourier Transform (STFT). Main peak in time-frequency interpretation of SEP was measured in peak time, peak frequency and peak power. The changes of these parameters were compared with the changes of latency and amplitude. The results showed that changes in peak times and peak powers were found to correlate to the changes of latency and amplitude, respectively. However, the peak time showed more variability than the latency (p<0.01), while the peak power showed significantly lower variability than the amplitude (p<0.01). The peak frequency of SEP seems to be unchanged during surgery. Time-frequency analysis of SEP waveform gives stable and easily identifiable characteristics, and also shows higher specificity than amplitude and latency. Applying time-frequency analysis to SEP may improve the reliability of intraoperative spinal cord monitoring.

Bioactive bone cement as a principal fixture for spinal burst fracture: an in vitro biomechanical and morphologic study

STUDY DESIGN

An in vitro biomechanical and radiographic study to evaluate the properties of a newly developed bioactive bone cement for stabilization of the fractured spine, suitable for minimally invasive application.

OBJECTIVES

To determine the mechanical stability of the fractured spine after injection of the newly developed bioactive bone cement under quasi-static and cyclic loading regimens.

SUMMARY OF BACKGROUND DATA

Bone cement injection has been reported as a potentially useful, minimally invasive technique for treating vertebral body fracture or stabilizing osteoporosis. However, potential problems associated with the use of polymethylmethacrylate (PMMA) have prompted the search for alternative solutions. The use of bioactive bone cement as a potential replacement for PMMA has been reported.

METHODS

Biomechanical and radiographic analyses were used to test the mechanical stability of the fractured spine. The cement used was formed from hydroxyapatite powder containing strontium and bisphenol A diglycidylether dimethacrylate (D-GMA) resin. Twenty-six fresh porcine spine specimens (T10-L1) were divided into three groups: pilot, intact, and cemented. Spinal stiffness and failure strength were recorded in the intact group with the specimens flexed at 10 degrees. Uniform injuries were created in all specimens of the cemented group, and compressive loading was applied with 10 degrees of flexion until a fracture occurred. The bone cement was injected into the fractured spine, and stiffness was evaluated after 1 hour. Failure strength was also recorded after 3000 and 20,000 fatigue load cycles. Morphology of the specimens was observed and evaluated.

RESULTS

Results from a cell biocompatibility test indicated that the new bioactive bone cement was favorable for cell growth. Spinal stiffness significantly decreased after fracture (47.5% of intact condition). Instant stiffness of the spine recovered to 107.8% of the intact condition after bone cement injection. After 3000 and 20,000 cycles of fatigue loading, stiffness of the cemented spine was found to be 93.5% and 94.4% of intact stiffness, respectively (P < 0.05). Average failure strength of the spine was 5056 N (after 3000 cycles) and 5301 N (after 20,000 cycles) after bone cement injection and fatigue loading. Radiographs and cross-sectional observations indicated a good cement-bone bonding and fracture fill.

CONCLUSIONS

A new bioactive bone cement without cytotoxic effect has been developed. Results show that minimally invasive techniques to apply this cement to porcine spines results in augmentation of mild burst fractures such that the original stiffness and strength of the vertebra are recovered. This new cement therefore shows potential as an augmentation to traditional instrumentation in the surgical management of vertebral fractures. The potential for further clinical applications is currently under investigation.

Prevention of spinal cord injury with time-frequency analysis of evoked potentials: an experimental study

OBJECTIVES

To verify the applicability and validity of time-frequency analysis (TFA) of evoked potential (EP) signals in detecting the integrity of spinal cord function and preventing spinal cord injury.

METHODS

The spinal cord was simulated during surgery in 20 mature rats by mechanically damaging the spinal cord. Cortical somatosensory evoked potential (CSEP), spinal somatosensory evoked potential (SSEP), cortical motor evoked potential (CMEP), and spinal cord evoked potential (SCEP) were used to monitor spinal cord function. Short time Fourier transform (STFT) was applied to the CSEP signal, and cone shaped distribution (CSD) was used as the TFA algorithm for SSEP, CMEP, and SCEP signals. The changes in the latency and amplitude of EP signals were measured in the time domain, and peak time, peak frequency, and peak power were measured in the time-frequency distribution (TFD).

RESULTS

The TFDs of EPs were found to concentrate in a certain location under normal conditions. When injury occurred, the energy decreased in peak power, and there was a greater dispersion of energy across the time-frequency range. Strong relations were found between latency and peak time, and amplitude and peak power. However, the change in peak power after injury was significantly larger than the corresponding change in amplitude (p<0.001 by ANOVA).

CONCLUSIONS

It was found that TFA of EPs provided an earlier and more sensitive indication of injury than time domain monitoring alone. It is suggested that TFA of EP signals should therefore be useful in preventing spinal cord injury during surgery.

Effect of stimulation parameters on intraoperative spinal cord evoked potential monitoring

The purpose of this study was to investigate the effects of the stimulus parameters on spinal cord evoked potential (SCEP) and to recommend a practical epidural stimulation protocol for intraoperative spinal cord monitoring. This prospective study compared the latencies and amplitudes of SCEP obtained on epidural stimulation of 30 patients with scoliosis under anesthesia using different stimulus pulse duration and stimulation rates. SCEP was found to be undetectable with shorter stimulus duration (<0.05 ms). The SCEP latencies did not show any significant difference among different stimulation parameters. However, the SCEP amplitude showed significant changes with differing stimulus durations. The SCEP amplitudes were found to significantly decrease when the pulse durations become shorter than 0.2 ms. Stimulus parameters showed significant effects on SCEP amplitude but not latency. Stimulus rates in the range of 21 to 61 Hz are equivalent for quick and reliable detection of SCEP. Considering the short latency of SCEP, a pulse duration of 0.2 ms is recommended for SCEP using epidural stimulation.

Evaluation of various evoked potential techniques for spinal cord monitoring during scoliosis surgery

STUDY DESIGN

This prospective study compared the outcomes of different evoked potential (EP) techniques for intraoperative spinal cord monitoring.

OBJECTIVES

To evaluate the reliability of different EP techniques administered during scoliosis surgery.

SUMMARY OF BACKGROUND DATA

A number of different methods of intraoperative spinal cord monitoring are available. Because each has its own advantages and limitations, multimodal spinal cord monitoring has been proposed to improve monitoring reliability.

MATERIALS AND METHODS

Cortical somatosensory-evoked potential (CSEP), cortical motor-evoked potential (CMEP), spinal somatosensory-evoked potential (SSEP), and spinal cord-evoked potential (SCEP) were applied simultaneously to 30 patients undergoing surgical correction for spinal deformity. The presence of the EP waveforms and their reproducibilities over separate tests were compared. In addition, the monitoring outcomes were evaluated with the clinical results.

RESULTS

Of the 30 patients, CSEP waveforms were successfully recorded in 28 cases (93%), SCEP in 25 cases (83%), CMEP in 24 cases (80%), and SSEP in 21 cases (70%). Latencies of each EP technique showed no significant variability. However, amplitudes showed significant differences between different techniques. SCEP and CMEP showed clearer waveforms of greater amplitude that could be detected faster than CSEP and SSEP waveforms. SCEP and SSEP waveforms were more easily influenced by the surgical procedure.

CONCLUSION

CSEP and CMEP are recommended for routine monitoring, so that both ascending and descending tracts are monitored. If adequate signals for either of these proposed monitoring methods cannot be easily obtained, SSEP can substitute for CSEP, whereas SCEP can substitute for CMEP.

Back muscle contraction patterns of patients with low back pain before and after rehabilitation treatment: an electromyographic evaluation

The aims of this study were to conduct a comparative investigation of muscle function between patients with low back pain (LBP) and healthy persons, and to determine whether intensive rehabilitation can change back muscle contraction synergy. Twenty healthy persons and 20 patients with chronic LBP were asked to perform symmetrical and asymmetric tasks. The patients with LBP were tested in the weeks immediately before and after 12 weeks of LBP rehabilitation. Tasks include "carrying" weights up and down and with a 45 degrees left rotation. Eight-channel surface electromyographic electrodes were placed on the surface of paraspinal muscles over the lumbar region. Correlations between the right and left corresponding muscles and between values before and after treatment were determined. Lifting capacity for patients with LBP were also measured before and after treatment. Results from electromyographic profiles showed that the muscle activity strategies varied between healthy persons and patients with LBP. The correlation coefficients for spinal muscles have shown very reproducible intrasubject muscle contraction synergies. Unbalanced electromyographic patterns found in patients with LBP given symmetrical tasks were not affected by rehabilitation treatment.

Effect of stimulus pulse duration on intraoperative somatosensory evoked potential (SEP) monitoring

The effect of the stimulus duration on the amplitude and latency of intraoperative somatosensory evoked potential (SEP) was studied in 30 patients with idiopathic scoliosis undergoing surgery. Constant current square-wave electrical stimulation was applied to the posterior tibial nerve at a rate of 5.1 Hz. The effects of both the pulse duration and the stimulus current density on the intraoperative SEP were evaluated. Amplitudes and latencies of SEP were analyzed by one-way parametric analysis of variance. SEP signal recording was found to be difficult if the stimulus duration was less than 0.05 ms. The stimulus duration had no significant effect on the latencies of the SEP, but the amplitude of the SEP showed significant changes with differing stimulus durations. The SEP amplitudes were found with significant increases in pulse durations less than 0.3 ms. Stimulus pulse duration has a significant effect on SEP amplitude, and this should be taken into consideration during intraoperative SEP monitoring. A pulse duration of 0.3 ms is recommended for SEP using posterior tibial nerve stimulation.

Comparison of time-frequency distribution techniques for analysis of spinal somatosensory evoked potential

Spinal somatosensory evoked potential (SSEP) has been employed to monitor the integrity of the spinal cord during surgery. To detect both temporal and spectral changes in SSEP waveforms, an investigation of the application of time-frequency analysis (TFA) techniques was conducted. SSEP signals from 30 scoliosis patients were analysed using different techniques; short time Fourier transform (STFT), Wigner-Ville distribution (WVD), Choi-Williams distribution (CWD), cone-shaped distribution (CSD) and adaptive spectrogram (ADS). The time-frequency distributions (TFD) computed using these methods were assessed and compared with each other. WVD, ADS, CSD and CWD showed better resolution than STFT. Comparing normalised peak widths, CSD showed the sharpest peak width (0.13+/-0.1) in the frequency dimension, and a mean peak width of 0.70+/-0.12 in the time dimension. Both WVD and CWD produced cross-term interference, distorting the TFA distribution, but this was not seen with CSD and ADS. CSD appeared to give a lower mean peak power bias (10.3%+/-6.2%) than ADS (41.8%+/-19.6%). Application of the CSD algorithm showed both good resolution and accurate spectrograms, and is therefore recommended as the most appropriate TFA technique for the analysis of SSEP signals.

Effectiveness of audio-biofeedback in postural training for adolescent idiopathic scoliosis patients

The possibility of using learned physiological responses in control of progressive adolescent idiopathic scoliosis (AIS) was investigated. Sixteen (16) AIS patients with progressing or high-risk curves (Cobb's angle between 25 degrees and 35 degrees at start and reducible by lateral bending) were fitted with a device with tone alarm for poor posture. In the first 18 months of application, 3 patients defaulted and 4 showed curve progression > 10 degrees (2 changed to rigid spinal orthoses and 2 underwent surgery). The curves for the other 9 patients were kept under control (within +/- 5 degrees of Cobb's angle) and 5 of them have reached skeletal maturity and terminated the application. The remaining 4 patients were still using the devices until skeletal maturity or curve progression. The curve control rate was 69%. A long-lasting active spinal control could be achieved through the patient's own spinal muscles. Nevertheless, before the postural training device could become a treatment modality, a long-term study for more AIS patients was necessary. This project is ongoing in the Duchess of Kent Children's Hospital, Sandy Bay, Hong Kong.

Correction method for determining anteroposterior diameter of the cervical spinal canal on lateral radiographs

SUMMARY

Measurement of the anteroposterior diameter of the cervical spinal canal may prove unreliable because of the rotatory effect of degenerative disease. Nevertheless, this measuring error may be corrected by performing dual midpoint measurements between the posterior vertebral body and spinolaminar line when less than 10 degrees of rotation is present.

A novel injectable bioactive bone cement for spinal surgery: a developmental and preclinical study

The injection of bone cement by minimally invasive techniques for the treatment of vertebral body fractures or for stabilization of an osteoporotic vertebral body is regarded as promising in spinal surgery. The purpose of this study was to develop a novel injectable bioactive bone cement to address such concerns. The cement was composed mainly of strontium-containing hydroxyapatite (Sr-HA) filler and Bisphenol A Diglycidylether Dimethacrylate (D-GMA) resin. The Sr-HA filler was prepared by precipitation and calcination, then analyzed with Fourier transform infrared (FTIR) spectra and X-ray diffraction (XRD) patterns. Samples of strontium-containing hydroxyapatite cement (SrHAC) were formed by a combination of powder filler and resin matrix, with the setting time and peak temperature recorded. Cell relative growth rate (RGR), Tetrazolium bromide (MTT), and haemolysis tests were used to detect initial in vitro biocompatibility of the new cement. In vitro spinal biomechanical testing and morphological observation after bone cement injection were performed on pig spines. Results indicate that the setting time and peak temperature of the cement was 15 min and 55 degrees C, respectively. Cytotoxicity of the cement was class 1 (no cytotoxicity) and haemolysis was 1% (no haemolysis). Stiffness after cement injection and fatigue loading were 112% and 95% of the intact bone, respectively, which is similar to that of natural bone. Radiopacity of SrHAC allowed easy radiographic imaging. The use of SrHAC cement is, thus, promising in spinal surgery.

Loosening of sacral screw fixation under in vitro fatigue loading

Sacral screw fixation is frequently used for fusion of the lower lumbar spine, but sacral screws appear to offer less secure fixation than lumbar pedicle screws, and failure due to loosening under fatigue loading is common. The aim of this study was to examine in vitro the stability of medial and lateral bicortical and unicortical sacral screw fixation under a physiologically relevant fatigue-loading pattern. Bone mineral density, screw insertion torque, and screw-fixation stiffness were measured prior to cyclic loading between 40 and 400 N compression at 2 Hz for 20,000 cycles. The screw-fixation stiffness was measured every 500 cycles, and the axial pullout strength of the screws was recorded following loading. All of the lateral insertions loosened under the applied loading, but some of the medial insertions remained stable. Medial insertions proved stiffer and stronger than lateral insertions, and bicortical fixations were stronger than unicortical fixations. Bone mineral density and insertion torque were correlated with screw stiffness and pullout strength, although better correlation was found for insertion torque than bone mineral density. Bone mineral density is a good preoperative indicator of sacral screw-fixation strength, and insertion torque is a good intraoperative indicator. An insertion torque greater than 1.5 Nm is suggested as an indicative value for a stable medial unicortical insertion, whereas an insertion torque greater than 2 Nm suggests a stable medial bicortical insertion. It appears that, apart from the choice of technique (screw orientation and depth), minimizing the load on the screws during the initial part of the fusion process is also critical to maintain stability of the fused section and to obtain a solid fusion mass.

Bone mineral density variations along the lumbosacral spine

Vertebral bone quality is essential in vertebral strength and the stability of spinal screw fixation. A major factor of bone quality is the density of bone mineral and its distribution throughout the bone. There have been studies regarding bone mineral density variations in the cervical and thoracolumbar spine, but bone mineral density variations in the lumbosacral spine have not been documented. The purpose of the current study was to quantify bone mineral density variations at different lumbosacral levels and within vertebra, especially along the pathways of lumbar pedicle screws. Bone mineral density variations within the vertebrae along the lumbosacral spine were measured in 13 specimens from young male cadavers using peripheral quantitative computed tomography. Measurements included bone mineral density variations at different lumbosacral levels and in transverse layers and vertical columns within each vertebral body. These original data showed that the bone mineral density increased gradually from lumbar to S1 vertebrae, possibly reflecting a caudally increasing load on different lumbosacral levels. The highest bone mineral density in the lumbosacral spine is found at the pedicles and regions closest to pedicle bases, supporting the use of pedicle screw fixation.

Lung function reference values in Chinese children and adolescents in Hong Kong. II. Prediction equations for plethysmographic lung volumes

As part of a comprehensive evaluation of lung function in Hong Kong Chinese children and adolescents, over a thousand healthy subjects aged 7-19 yr from seven schools were recruited for lung function testing that included spirometry and, in many cases, lung subdivision measurements. Lung function tests were performed using SensorMedics Automated Body Plethysmograph according to published standards. Of these, 551 subjects (219 males), aged 8-19 yr, had satisfactory lung subdivision indices recorded. Analysis for the values of lung subdivisions including total lung capacity (TLC), residual volume (RV), and functional residual capacity (FRC) demonstrated that standing height and sitting height were the best predictors of lung volumes. After allowing for standing height or sitting height in the regression models for lung volumes, age at examination was the second best parameter, although its inclusion into the equations contributed to less than 1% of explained variance for boys and 3% for girls. These are the first reported data in international literature on reference values for lung subdivisions in Chinese children and adolescents.

Effectiveness and biomechanics of spinal orthoses in the treatment of adolescent idiopathic scoliosis (AIS)

In this prospective study, the effectiveness and biomechanical factors of spinal orthoses in the treatment of moderate adolescent idiopathic scoliosis (AIS) patients were investigated. In the first 20 months of orthotic treatment, the values of standing AP Cobb's angle, apical vertebral rotation, lumbar lordosis as well as thoracic kyphosis showed significant reduction (P<0.05), however, the angle of trunk inclination and trunk listing did not. The values of those reducible parameters reached their lowest values within the first 12 months of orthotic treatment and then the values gradually increased but they were still below the pre-brace values. The mean pressure of The pressure pads was found to be 7.09 +/- 1.77 kPa (53.2 +/- 13.3 mmHg) while the mean tension of the straps was 26.8 +/- 5.2N. The standing AP Cobb's angle strongly correlated with the pad pressure (correlation coefficient=0.931, p<(.05) and strap tension (correlation coefficient=0.914, p<0.05). The strap tension and pad pressure strongly correlated and the correlation coefficient was 0.873 (p<0.05). This suggests that in the consideration of biomechanical function of spinal orthoses, the focus may be upon how tightly the orthosis was fastened and if the location and direction of the pressure pads are the correct. Therefore, for enhancing independent standard tension should be set in each strap, and regular and close monitoring is needed.

Lung function reference values in Chinese children and adolescents in Hong Kong. I. Spirometric values and comparison with other populations

As part of a comprehensive evaluation of lung function in Hong Kong-born Chinese children and adolescents, this study was conducted to determine updated prediction equations for spirometry, to evaluate the secular changes of lung function during the past decade, and to compare these results with other data sets. The results are based on 852 (392 male, 460 female) healthy students, age 7 to 19 yr, recruited from seven schools in Hong Kong. All were born and lived in Hong Kong, nonsmokers, free from past or present symptoms or diseases affecting the respiratory tract. A body plethysmograph was used to record lung function measurements. Natural logarithmic values of lung volumes and body height were used in the final regression model. Prediction equations for FVC, FEV(1), and maximal expiratory flow at 50% of the FVC (MEF(50)) for both sexes are presented, with standing height as the dependent variable. Compared with Hong Kong data from 1985, the results show a significant increase in height-corrected FVC and FEV(1) in both boys and girls, over the whole height range. Compared with recent data of whites, FVC in boys were 8 to 10% lower in the study population, and the difference increased to 12% above the 165 cm height ranges, while FVC in Chinese girls had similar or only slightly lower predicted values. FEV(1) values showed a similar pattern with lesser difference between the two ethnic groups. Compared with recent data from Chinese children in Singapore, a similar pattern with overall lesser difference of the two populations was present in boys, whereas there was no significant difference between girls in the two places. Our findings support the conclusion that exogenous factors may contribute significantly to the differences in lung function values among ethnic groups and that it is important to examine normative values of various populations for secular trends.

Tuberculosis of the spine in the new millennium

Tuberculosis of the spine is probably one of the earliest diseases to have affected the human race. Over the past few decades, the epidemiology, pathology, natural history and diagnostic methodology have been well studied. The multinational prospective study on the efficacy of conservative chemotherapy and surgical treatment coordinated by the Medical Research Council has just completed a final 15-year follow-up report. Although it appears from this study that conservative treatment is as effective as surgical intervention for earlier and milder diseases, there are still reservations on the effect of such treatment at much longer follow-ups and for more severe diseases. Further developments in diagnosis using molecular genetic techniques, more effective antibiotics and more aggressive surgical protocols in the next millennium may help in solving the problems of late severe deformity and paraplegia in the debilitated immunocompromised patients.

Variability of somatosensory-evoked potentials in different stages of scoliosis surgery

STUDY DESIGN

A comparison of the latencies and amplitudes of the somatosensory-evoked potential in different stages of scoliosis surgery.

OBJECTIVES

To investigate the normal variability of the somatosensory-evoked potential at different stages of scoliosis surgery and to improve the reliability of spinal cord monitoring.

SUMMARY OF BACKGROUND DATA

False alarms in intra-operative spinal cord monitoring have been reported when the somatosensory-evoked potential measured before skin incision was used as the reference baseline value. However, the normal variability during different stages of surgery and the specificity of somatosensory-evoked potential is not well documented.

METHODS

The somatosensory-evoked potential of 90 patients who underwent surgical correction for idiopathic scoliosis was monitored intraoperatively, with stimuli applied to the posterior tibial nerve. The amplitudes and latencies of the somatosensory-evoked potential were recorded over Cz'-Fz and Cv-Fz. The values of latencies and amplitudes and their percentage variabilities were analyzed.

RESULTS

The values of latencies and their percentage variabilities did not differ significantly from each other in different stages of surgery. The values of amplitudes between different stages showed statistically significant differences. In particular, the amplitude of the somatosensory-evoked potential was found to be significantly decreased after exposure of the spine when compared with the amplitude before skin incision.

CONCLUSION

Some variability in latencies and amplitudes between different stages of scoliosis surgery is normal. These results suggest that the somatosensory-evoked potential when the spine is exposed may be used as the reference baseline to determine whether somatosensory-evoked potentials are subnormal at the subsequent stages of surgery.

Comparison of CMV, RSV, SV40 viral and Vlambda1 cellular promoters in B and T lymphoid and non-lymphoid cell lines

Determining the activity of viral and cellular regulatory elements in B or T lymphoid cell lines would facilitate appropriate utilization of the regulatory sequences for gene transfer- and expression-dependent applications. We have compared the activity of the CMV, RSV and SV40 viral promoter/enhancers as well as the Vlambda1 cellular promoter, in three B cell lines (REH, SMS-SB, C3P), three T cell lines (CEM, Jurkat, ST-F10), and two non-lymphoid cell lines (K-562, HeLa) using the luciferase reporter gene. In B cell lines, the activity of the CMV promoter/enhancer construct was the highest ranging from 10- to 113-fold greater than that of SV40. In contrast, in T cell lines the RSV promoter/enhancer activity was 11-65-fold higher than that of SV40. The Vlambda1 promoter activity was close to that of SV40 promoter/enhancer in most of the cell lines tested. We conclude that CMV and RSV promoter/enhancers contain stronger regulatory elements than do the SV40 and Vlambda1 for expression of genes in lymphoid cell lines.

Stability of the whole lumbar spine after multilevel fenestration and discectomy

STUDY DESIGN

An investigation of the in vitro biomechanical effects of multilevel fenestrations and discectomies on the behavior of whole lumbar spine motion, using a material testing system (Instron 1341, Instron Limited, High Wycombe, England) and Elite three-dimensional motion analysis system (BTS, Milano, Italy).

OBJECTIVES

To investigate the effects of multilevel fenestrations and discectomies on the stability of the whole lumbar spine, including segmental stiffness and sagittal (horizontal and vertical) translation.

SUMMARY OF BACKGROUND DATA

In the management of lumbar spinal stenosis, wide decompressive laminectomy with partial or total facetectomy has been the standard procedure for multilevel nerve decompression. Main complications with these procedures have been instability and chronic pain syndrome. Multilevel fenestration with undermining enlargement of the spinal canal has been selected for multilevel nerve decompression in recent years. However, the biomechanical effects of multilevel fenestration and discectomy have been controversial and difficult to validate. This study investigated the in vitro biomechanical effects of multilevel fenestrations and discectomies on motion behavior of the whole lumbar spine.

METHODS

Seven fresh human specimens from L1 to sacrum were used in this study. The fenestrations and discectomies consisted of L3-L4 bilateral fenestration, L4-L5 bilateral fenestration, L5-S1 bilateral fenestration, L4-L5 discectomy, and L5-S1 discectomy. Flexion, lateral bending, and axial rotation (torsion) loading were applied. Ranges of motion were determined two-dimensionally by the Elite system with an infrared camera. The postoperation results were compared with the intact conditions.

RESULTS

After multiple fenestrations, the sagittal ranges of motion at L4-L5 increased by 18% anteroposteriorly and 16% vertically under the flexion loads. At L5-S1, the motions increased by 19% and 45%, respectively. After fenestrations and discectomies, the ranges of motion in the sagittal plane increased by 28% horizontally and 71% vertically at L4-L5, and 14% and 166% at L5-S1. Motion increases were statistically significant (P < 0.05) in vertical translations. However, after the multilevel surgeries, no significant motions were found in each of the lumbar segments during lateral bending and axial rotation.

CONCLUSIONS

The results demonstrate that multilevel fenestrations and discectomies affect lumbar spinal stability in flexion, but have no effect on the stability of the lumbar spine in lateral bending or axial rotation.

Kinematics of the chest cage and spine during breathing in healthy individuals and in patients with adolescent idiopathic scoliosis

STUDY DESIGN

The lung function test by a Plethysmograph enabled calculations to be made of the total lung capacity and vital capacity. A Motion Analysis System (Elite, BTS Inc., Milano, Italy) was used to observe and record chest cage and spinal movements and as to correlate lung function with the chest cage and spine kinematics.

OBJECTIVES

To determine the three-dimensional kinematics and the shape and size changes of the chest cage and thoracic spine motion during deep breathing in healthy and scoliotic individuals.

SUMMARY OF BACKGROUND DATA

Lateral flexion plus rotation of the involved vertebrae around a vertical axis causing a decrease in lung function is the main disfigurement of scoliosis. Reports show that even after spinal fusion, reduced vital capacity associated with an increased residual volume are detected. Factors such as angle of scoliosis, length of the spinal column involved, and duration of the deformity influence pulmonary function but do not significantly affect its reduction. Mechanical inefficiency during breathing has not been studied.

METHODS

Three-dimensional kinematics of the chest cage and spine during breathing were studied in 41 scoliotic patients and in 20 healthy individuals. Three-dimensional chest cage motions relative to the spine and thoracic spine motions relative to T12 were calculated. To examine stiffness of the spine, lateral bending angles were calculated. The lung function test, which including spirometry and lung subdivision, also was performed for the scoliotic patients.

RESULTS

Significant differences (P < 0.05) were found in the movements of the upper level of the chest cage in anteroposterior and vertical directions, ranging from 16.7 to 28.6 mm in healthy individuals and from 12.1 to 24.2 mm in scoliotic patients. The thoracic spine displayed two-dimensional movements posteriorly and vertically during breathing, whereas less movement was seen in scoliotic patients. In addition, overall the scoliotic spine showed signs of stiffness in lateral bending.

CONCLUSIONS

The range of movement of the chest cage and spine is more limited in the scoliotic cases. This overall stiffness of the chest cage and the spine may contribute to the mechanical inefficiency and impairment of pulmonary function found in scoliotic patients.

Evaluation of a new calcaneal quantitative ultrasound system and determination of normative ultrasound values in southern Chinese women

Quantitative ultrasound (QUS) assessment at the calcaneus has been found to be a safe and reliable method for evaluating skeletal status. The present study aimed at evaluating the precision of the Sahara bone ultrasound densitometer and to determine the normative QUS data in healthy southern Chinese women. Broadband ultrasound attenuation (BUA), speed of sound (SOS) and qualitative ultrasound index (QUI) were determined. The long-term in vitro precision of the Sahara machine over 6 months was 4.6% for BUA and 0.39% for SOS. The short-term in vivo precision was 3.2 +/- 1.3% for BUA, 0.3 +/- 0.2% for SOS and 1.8 +/- 1.0% for QUI. The standardized precision for BUA, SOS and QUI was 4.4, 3.8 and 2.2 respectively. The normative data were determined in 1086 healthy subjects. Postmenopausal women had significantly lower BUA, SOS and QUI levels than the premenopausal women. Significant negative correlations were observed between QUS indices and age. Bone mineral density (BMD) assessments was performed on 349 of these subjects. BUA correlated significantly with lumbar spine BMD (r = 0.326) and femoral neck BMD (r = 0.395). Similar correlations were observed between SOS, QUI and BMD, with r values ranging between 0.446 to 0.522. Despite the fact that Chinese women have significantly lower BMD values than Caucasian women, the mean BUA values for pre- and postmenopausal Chinese women (73 +/- 18 and 59 +/- 18 dB/MHz respectively) were almost the same as those reported for Caucasian women. These normative data will be useful in the assessment of southern Chinese women with fracture risk.

Quantitative ultrasound and symptomatic vertebral fracture risk in Chinese women

Quantitative ultrasound (QUS) is emerging as a simple, inexpensive and noninvasive method for assessing bone quality and assessing fracture risk. We assessed the usefulness of a contact calcaneal ultrasonometer by studying normal premenopausal women (group I, n = 53), normal postmenopausal women (group II, n = 198), and osteoporotic women without (group III, n = 141) and with vertebral fractures (group IV, n = 53). The osteoporotic subjects had a T-score of the spine or hip neck bone mineral density (BMD) <-2.5 based on the local Chinese peak young mean values. When compared with postmenopausal controls, mean broadband ultrasound attenuation (BUA), speed of sound (SOS), and quantitative ultrasound index (QUI) were 26%, 2.1% and 25% lower in women with vertebral fractures (p all <0.005). The correlation coefficients between QUS parameters and BMD of the spine and hip ranged between 0.4 and 0.5. The ability of the QUS to discriminate between patients groups was determined based on the mean value of normal premenopausal women in group I. The mean T-score for women with fractures was -2.87 +/- 1.02 for BUA, -2.54 +/- 0.79 for SOS, -3.17 +/- 0.70 for QUI, -2.65 +/- 0.86 for L2-4 BMD and -2.53 +/- 0.66 for hip neck BMD. After adjustment for age and body mass index, the odds ratio of vertebral fracture was 1.71 (95% CI 1.2-2.6) for each 1 SD reduction in BUA, 2.72 (1.3-5.3) for SOS, 2.58 (1.4-4.6) for QUI, 2.33 (1.6-3.3) for L2-4 BMD, 2.09 (1. 37-3.20) for femoral neck BMD and 1.88 (1.34-2.92) for total hip BMD. The association between the QUS parameters and vertebral fracture risk persisted even adjustment for BMD. The area under the receiver operating characteristic curve for BUA for vertebral fracture was 0. 92, for SOS, QUI, L2-4 BMD and femoral neck BMD was 0.95, and for total hip was 0.91.

Age-related osteoporosis in Chinese: an evaluation of the response of intestinal calcium absorption and calcitropic hormones to dietary calcium deprivation

BACKGROUND

Age-related osteoporosis may be associated with inefficient intestinal calcium absorption and bone remodeling.

OBJECTIVE

We investigated the pathogenesis of age-related osteoporosis in Chinese women with habitual low calcium intakes.

DESIGN

We studied the response of intestinal calcium absorption, calcitropic hormones, and biochemical bone markers to graded dietary calcium deprivation.

RESULTS

The osteoporotic subjects (n = 25) had higher urinary calcium excretion (P < 0.05) and lower plasma 1,25-dihydroxyvitamin D concentrations (P < 0.02) than did age-matched control women (n = 25). Parathyroid hormone was not significantly different from that in age-matched control women but was significantly higher than in young women (n = 15, P < 0.05). Fractional 45Ca absorption was approximately 61% in all 3 groups when the diet was unmodified and increased to 71%, 69%, and 68% in the osteoporotic subjects, age-matched control women, and young women, respectively, when dietary calcium was reduced to 300 mg/d. When the osteoporotic women were calcium deprived, serum 1,25-dihydroxyvitamin D failed to increase but urinary calcium excretion persisted. In contrast, supplementation with 1200 mg Ca resulted in a lowering of parathyroid hormone (P < 0.005 compared with the unmodified diet) and 1,25-dihydroxyvitamin D (P < 0.01) and decreased fractional 45Ca absorption (P < 0.01), suggesting that the increased calcium intake was associated with a potent compensatory ability of the intestine and calcitropic hormones to adapt. Calcium supplementation lowered osteocalcin (P < 0.05) but not alkaline phosphatase, which remained elevated in the osteoporotic subjects at all stages.

CONCLUSIONS

Elderly osteoporotic women had reduced 1,25-dihydroxyvitamin D production, excessive urinary calcium loss, and high bone turnover. The Chinese women had exceptionally potent intestinal calcium absorption.

Assessment of scoliosis correction in relation to flexibility using the fulcrum bending correction index

STUDY DESIGN

A prospective study on adolescent idiopathic scoliosis to assess a new method of describing frontal plane correction.

OBJECTIVE

To assess the difference between using the correction rate and using the new fulcrum bending correction index when describing scoliosis correction.

SUMMARY OF BACKGROUND DATA

A description of the outcome of scoliosis surgery based on the correction rate does not take into account the curve's flexibility.

METHODS

The fulcrum bending correction index is calculated by dividing the correction rate by the fulcrum flexibility (based on the fulcrum bending radiograph) and is expressed as a percentage. The fulcrum bending correction index was compared with the correction rate in 35 patients with adolescent idiopathic scoliosis undergoing surgical correction. These patients were divided into a stiff and a flexible group based on a fulcrum flexibility of 50% to show the advantage of the fulcrum bending correction index over the correction rate.

RESULTS

The difference in correction rate between the flexible (66%) and the stiff group (45%) was significant (P < 0.05). The difference in the fulcrum bending correction index between the flexible (96%) and the stiff group (107%) was not significant (P = 0.2).

CONCLUSIONS

The fulcrum bending correction index takes into account the curve flexibility and is therefore better than the correction rate for comparing curve correction and use of instrumentation systems between different series of patients. A fulcrum bending correction index of close to 100% suggests that the instrumentation has taken up all the flexibility revealed by the fulcrum bending radiograph. It is recommended that the fulcrum bending correction index be used in the future as part of the postoperative assessment of frontal plane correction in cases of thoracic scoliosis.

Costal osteochondroma. A rare cause of spinal cord compression

STUDY DESIGN

Report of a rare cause of spinal cord compression: costal osteochondroma.

OBJECTIVE

To describe a very rare cause of spinal cord compression, costal osteochondroma, which was present in a 16-year-old girl with a history of hereditary multiple exostoses.

SUMMARY OF BACKGROUND DATA

Only four cases of expansion of costal osteochondroma into the spinal canal through an intervertebral foramen have been reported previously.

METHODS AND RESULTS

The origin of the osteochondroma at the head of the right 12th rib, the invasion of the spinal canal through the right T12-L1 intervertebral foramen, and the compression of the spinal cord were shown on computed tomography and magnetic resonance imaging. The exact extent of the osteochondroma, particularly the cartilage cap, was delineated accurately by magnetic resonance imaging. Complete excision followed by full recovery occurred 19 months after surgery.

CONCLUSION

Magnetic resonance imaging is the preferred method of investigation in cases of osteochondroma related to spine, because it allows for better pre-operative planning and helps to prevent incomplete excision of the tumor.

Radiographic assessment of pedicle hook placement

STUDY DESIGN

A cadaveric study of the changes in the radiographic morphology of the thoracic pedicle with vertebral rotation.

OBJECTIVE

To study the effect of vertebral rotation on the assessment of pedicle hook placement by determining the radiographic anatomy of the pedicle and its relation to the pedicle hook.

SUMMARY OF BACKGROUND DATA

It is commonly assumed that the oval pedicle shadow seen on spine radiographs is formed by the waist of the pedicle. The postoperative assessment of pedicle hook position is based on this assumption.

METHODS

Thoracic cadaveric vertebrae between T5 and T8 were studied, with wire markers placed at the waist, the pedicle-facet junction, and the pedicle-body junction. Thoracic pedicle hooks were placed in the correct position and offset to one side. Radiographs of the vertebral body were taken from 0 degree to 30 degrees of rotation with reference to the sagittal plane.

RESULTS

The radiographic morphology of the pedicle changes with vertebral rotation; it also differs between the concave and the convex side of a scoliotic spine. With rotation of less than 20 degrees, the pedicle shadow is formed by the waist on both sides. With 30 degrees of rotation, the concave pedicle shadow is formed by the pedicle-facet junction, whereas on the convex side, it is over-lapped by the transverse process shadow. A laterally misplaced hook on the convex side and a medially misplaced hook on the concave side can appear correctly located with vertebral rotation.

CONCLUSION

The oval pedicle shadow is not simply represented by the waist of the pedicle. An understanding of the changes in radiographic morphology with rotation is necessary for the assessment of thoracic pedicle hook location after surgery.

Prediction of correction of scoliosis with use of the fulcrum bending radiograph

We used a new method to assess spinal flexibility in thirty patients who were to be managed operatively for adolescent idiopathic scoliosis. The method involves placing the patient in the lateral decubitus position and bent over a fulcrum (a radiolucent padded cylinder) so that the spine is passively hinged open. For thoracic curves the fulcrum is centered under the rib corresponding to the apex of the curve, and for lumbar curves the fulcrum is placed directly under the apex. The preoperative workup for the thirty patients included an anteroposterior radiograph made with the patient standing, a lateral-bending radiograph made with the patient supine, and the new fulcrum bending radiograph. All patients were treated with posterior spinal arthrodesis with segmental spinal instrumentation. The degree of flexibility obtained with the traditional and new methods was compared with the degree of correction observed on the radiograph made, with the patient standing, one week after the operation. Preoperatively, the mean Cobb angle was 58 degrees on the anteroposterior radiograph made with the patient standing, 31 degrees on the lateral-bending radiograph made with the patient supine, and 24 degrees on the fulcrum bending radiograph. The mean angle was 25 degrees on the anteroposterior radiograph made one week postoperatively, so the mean correction was 57 per cent. The difference between the mean angle on the lateral-bending radiograph and that on the postoperative radiograph was significant (p < 0.001); however, the mean angle measured on the preoperative fulcrum bending radiograph and the postoperative angle were almost identical. We found the fulcrum bending radiograph to be more predictive of the degree of flexibility and correctability than the lateral-bending radiograph in this group of patients who had segmental spinal instrumentation for correction of idiopathic scoliosis.

Intervertebral disc autografting in a bipedal animal model

Fusion of the spine while restoring stability of the spinal segment, fails to preserve spinal mobility. Long term complications of accelerated degeneration in the neighboring segments have been reported. The present study explores the possibility of intervertebral disc autografting in a bipedal animal model by isolating a lumbar disc together with the adjacent end plates and repositioning it with minimal internal fixation. Fourteen Rhesus monkeys were sacrificed at 2, 4, 6, and 12 months after surgery and the grafted discs were examined radiologically, biochemically, pathologically, and biomechanically. Healing of the bony end plate was seen between 2 to 4 months postoperatively. There was early loss of disc height at 2 and 4 months but there was a suggestion of some reconstitution up to 12 months. There was minimal evidence of gross degeneration at all stages. Gradual loss of water content was found in the annulus and the nucleus. The nucleus pulposus seemed to be able to reaccumulate proteoglycan after an initial drop in the first 4 months. There was significant increase in hydroxyproline content in the annulus fibrosus and the nucleus pulposus. Biomechanically, the grafted disc showed hypermobility in the first 4 months but gradually became stabilized with time. Results from this study suggested that a fresh intervertebral disc autograft could survive a period of ischemia. Although the physiology of the disc was deranged, it was able to preserve a certain degree of segmental mobility without sacrificing stability. Further studies are required to validate these results and the field of disc allografting should be explored.

Applications of bone scintigraphy in ankylosing spondylitis

Eighteen bone scintisans performed in 14 patients with ankylosing spondylitis were reviewed. In young patients with low back pain, positive serology, and indeterminate radiographs, quantitative sacroiliac joint assessment and the presence of typical uptake patterns, particularly costovertebral, were useful in suggesting the diagnosis. Scintigraphy was helpful in the early detection of pseudoarthrosis complicating long-standing disease, especially in patients presenting with recurrent back pain. Selective application of bone scintigraphy aids the diagnosis of ankylosing spondylitis and its potential complications.

Spinal stenosis above a healed tuberculous kyphosis. A case report

STUDY DESIGN

This case report illustrates two patients with paraplegia of late onset resulting from cord compression in the hyperlordotic thoracic or thoracolumbar spine proximal to a healed tuberculous kyphosis.

OBJECTIVES

The objective of this paper is to highlight that degenerative stenosis of the thoracic spine proximal to a healed stable kyphosis can be a cause of paraplegia of healed disease.

SUMMARY OF BACKGROUND DATA

Paraplegia resulting from tuberculosis of the spine can be of early or late onset. Early onset paraplegia is usually a result of cord compression by active disease. Late onset paraplegia can be due to disease reactivation, bony ridge compression, or unstable kyphosis. To our knowledge, compression of the cord proximal to a healed, stable kyphosis giving rise to paraplegia has never been reported.

METHODS

Patient 1 presented with symptoms of spinal claudication and progressive paraparesis. He was found to have spinal stenosis in the hyperlordotic thoracolumbar spine proximal to a healed lumbosacral tuberculous kyphosis. Patient 2 presented with a 2-year history of progressive paraplegia. Imaging revealed cord compression at the hyperlordotic T10-11 segment by disc protrusion, and facet hypertrophy.

RESULTS

Laminectomy successfully relieved the first patient of all symptoms but the second patient had significant deterioration of the neurologic status after surgery.

CONCLUSION

Compensatory hyperlordosis of the thoracic or thoracolumbar spine commonly occurs in patients with severe tuberculous thoracolumbar or lumbosacral kyphosis. Degenerative spinal stenosis and cord compression at such hyperlordotic segment can cause late onset paraplegia. The blood supply of these chronically compressed cords is precarious and the risk of surgery is high.

Effects of short anterior lumbar interbody fusion on biomechanics of neighboring unfused segments

STUDY DESIGN

Segmental mobility and intradiscal pressure were measured and the data compared in six cadaveric lumbar spine specimens before and after in vitro simulated single level L4-5 and double level L4-5-S1 anterior interbody fusions.

OBJECTIVE

The experimental objective was to study the biomechanical effects of single level L4-5 and double level L4-5-S1 anterior interbody fusions on the neighboring unfused segments.

SUMMARY OF BACKGROUND DATA

The relationship between the local rigidity created by fusion mass and accelerated degeneration reported at the neighboring unfused intervertebral discs is not clear.

METHODS

Six cadaveric lumbar spine specimens were biomechanically tested in flexion and extension. Segmental mobility and intradiscal pressure of the specimens were measured before and after in vitro simulation of single level L4-5 and double level L4-5-S1 anterior interbody fusions.

RESULTS

The mobility of the motion segments immediately above and below an L4-5 fusion was increased in flexion. When the L5-S1 segment was also fused, the loss of segmental motion in both flexion and extension at the L4-5 and L5-S1 were compensated for by increased motion in all levels above the fusion. In both flexion and extension, the intradiscal pressures of all unfused intervertebral discs were increased after a single level L4-5 fusion and this increase was even more marked after a double level L4-5-S1 fusion.

CONCLUSIONS

There is no evidence that the neighboring unfused segments are loaded beyond their physiological limits due to the fusion. However, the neighboring unfused segments have to work more frequently toward the extremes of their functional ranges of motion after fusion and these effects will be more marked after a double level L4-5-S1 fusion.

A 68-year-old man with gradual onset of low-back pain

The following case is presented to illustrate the roentgenographic and clinical findings of a condition of interest to orthopedic surgeons. The initial history, physical findings, and roentgenographic examinations are noted on this page. The clinical and roentgenographic diagnoses are presented on the following pages.

Relation of spinal and thoracic cage deformities and their flexibilities with altered pulmonary functions in adolescent idiopathic scoliosis

STUDY DESIGN

Seventy patients (average age, 13.8 years) with adolescent idiopathic right thoracic scoliosis had full assessment of pulmonary functions and radiographic evaluation of spinal and thoracic cage deformities and their flexibilities.

OBJECTIVES

To determine how measurements of spinal and thoracic cage deformities related to pulmonary function.

SUMMARY OF BACKGROUND DATA

Pulmonary functions have been evaluated in relation to lateral curvature of the spine in most of the published studies. Scoliosis is a three-dimensional deformity. There is a need to evaluate these changes in pulmonary functions, reflecting not only spinal curvature but also rotational deformity, thoracic cage deformity, and their flexibilities.

METHODS

Radiographic measurements obtained from anteroposterior and lateral standing and anteroposterior supine bending radiographs included lateral curvature, vertebral rotation, kyphosis, maximum sternovertebral distance, and apical rib-vertebral angles. Using previous measurements, the flexibility of the curve, vertebral rotation, and rib-vertebral angle were calculated. A pulmonary function assessment was performed using a computerized pulmonary function system (5000V; Gould, Dayton, Ohio). We analyzed pulmonary functions in relation to deformity.

RESULTS

Measurements reflecting spinal deformities obtained from anteroposterior radiographs, such as Cobb angle, vertebral rotation, and vertebral rotation flexibility, were significantly correlated with the percent of predicted values of vital capacity and forced vital capacity, whereas kyphosis measured from lateral radiographs was significantly correlated with absolute values of residual volume, total lung capacity, functional residual capacity, and forced expiratory flow from 25-75% of the forced vital capacity (FEF25-75). Of the measurements reflecting thoracic cage deformity obtained from anteroposterior radiographs, rib-vertebral angle asymmetry (measured from supine bending radiographs) showed significant correlation with the percent of predicted values of vital capacity, forced vital capacity, and functional residual capacity, whereas the sternovertebral distance that was measured from lateral radiographs correlated significantly with absolute values of vital capacity, total lung capacity, forced vital capacity, and FEF25-75.

CONCLUSIONS

Deformities in coronal and transverse plane influence changes in pulmonary functions expressed as the percent of predicted values, whereas sagittal plane deformities influence mainly those absolute volumes in which residual volume is a component. It is suggested that rotational flexibility combined with other deformities could be evaluated in future studies on prediction of pulmonary function from the measurements of the deformity.

Evaluation of deformities and pulmonary function in adolescent idiopathic right thoracic scoliosis

Seventy patients with adolescent idiopathic right thoracic scoliosis had full assessment of their pulmonary function using a computerised pulmonary function system. Their mean age at evaluation was 13.8 years. The following measurements were obtained from anteroposterior and lateral standing and antero-posterior supine bending radiographs: lateral curvature, vertebral rotation, kyphosis, maximum sterno-vertebral distance and apical rib-vertebral angles. Using the above measurements, the flexibility of curve, vertebral rotation and rib-vertebral angle asymmetry were calculated. Patients were classified into three groups on the basis of their predicted vital capacity, to determine whether radiological features of deformity can help identify patients with compromised pulmonary function. The mean Cobb angle and vertebral rotation for the 70 patients were 50 degrees (range 35-100 degrees) and 22 degrees (range 1-44 degrees) respectively. The mean flexibility of curve and vertebral rotation were 52% and 49% respectively. Mean thoracic kyphosis was 25 degrees, ranging from -7 to 55 degrees. Of the patients with Cobb angle less than 90 degrees, 71% had vital capacity less than 80% of predicted values, and of these, 18% had marked compromise of vital capacity (less than 60% of predicted values). Mean values of Cobb angle, vertebral rotational flexibility, kyphosis, rib-vertebral angle asymmetry (in standing as well as supine bending radiographs) differed significantly between patients with more than 80% of predicted vital capacity and those with 60% or less of predicted values. Radiological features indicative of better pulmonary function were: rotational flexibility exceeding 55%, rib-vertebral angle asymmetry (standing) less than 25 degrees and kyphosis greater than 15 degrees. Two deformity parameters--that give a better prediction of pulmonary function than the widely used Cobb angle, vertebral rotational flexibility and rib-vertebral angle asymmetry--were identified in this study.

Cord compression caused by multiple disc herniations and intraspinal cyst in Scheuermann's disease

STUDY DESIGN

The design for this article is a case report.

OBJECTIVES

Reported is the case of a patient with Scheuermann's disease who experienced spastic paraparesis caused by multilevel disc herniations and intraspinal meningeal cyst occurring together.

SUMMARY OF BACKGROUND DATA

Although Scheuermann's disease is associated with disc degeneration and calcification, multilevel disc herniations causing neurologic deficit is exceedingly rare.

METHODS

A patient diagnosed with Scheuermann's disease was evaluated by laboratory tests and radiographs because of paresthesin in bilateral lower extremities.

RESULTS

Evaluation revealed a "cyst" that was separated from the proper subarachnoid space and a disc herniation.

CONCLUSIONS

Intraspinal cyst and multilevel disc herniations could coexist in Scheuermann's disease. Both could contribute to cord compression. Drainage of the cyst, anterior decompression of the disc herniations, and interbody fusion to stabilize the diseased segments produced good results after 2 years.

Sacral insufficiency fractures. Spectrum of radiological features

Clinical and radiological features of 22 Chinese patients with sacral insufficiency fractures were reviewed. Twenty-one were postmenopausal women. Other risk factors were external pelvic radiotherapy (eight) and total hip replacement (two). Severe low back pain was the most common presenting complaint. Fractures initially were demonstrated by bone scintigraphy in 21 and computed tomography (CT) in seven patients. Concomitant parasymphyseal and pubic rami fractures were detected in 17 and 10 patients, respectively. Follow-up assessment by CT and bone scintigraphy in five patients showed various stages of fracture healing. Recognition of the radiological patterns of this entity is emphasized.

Lumbar spinal mobility after short anterior interbody fusion

STUDY DESIGN

Segmental deformations of the lumbar spine in asymptomatic volunteers measured radiologically were compared with those in patients who underwent anterior interbody fusion.

OBJECTIVE

To determine the effects of anterior lumbar interbody fusion on the juxta-fused segments.

SUMMARY OF BACKGROUND DATA

Stiffness of a spinal segment after fusion was thought to be the cause of the degeneration process at the juxta-fused segments.

METHODS

Segmental deformations of the lumbar spine, from maximum extension to maximum flexion, in 30 asymptomatic volunteers and 52 pain-free patients who had single-level L4-L5 or double-level L4-S1 fusion were measured and compared.

RESULTS

The total flexibility of the lumbar spine was decreased after a single-level fusion and further decreased after double-level fusions. The segmental deformations of the juxta-fused segments also were decreased after either a single- or double-level fusion.

CONCLUSIONS

During normal flexion and extension of the lumbar spine, the juxta-fused segments were not deformed beyond their physiological limits after fusion. Thus, accelerated degeneration observed at a juxta-fused segment is unlikely to be attributable to hypermobility.

Radiologic case. Clinics in diagnostic imaging (1). Ankylosing spondylitis with complication of pseudoarthrosis

A 41-year-old Chinese woman with quiescent ankylosing spondylitis presented with increasingly severe, recurrent back pain. The thoracolumbar junction was focally tender on palpation. Radiographs and computerised tomography demonstrated T12/L1 pseudoarthrosis. Excision of pseudoarthrosis, followed by anterior and posterior spinal fusion were performed with good results. The clinical features, pathogenesis, and management of this complication are discussed. Imaging of pseudoarthrosis in ankylosing spondylitis is emphasized.

Vertebral growth after posterior spinal fusion for idiopathic scoliosis in skeletally immature adolescents. The effect of growth on spinal deformity

We studied 29 girls and one boy with adolescent idiopathic scoliosis who were at Risser grade 0 at the time of posterior spinal fusion and were followed until maturity (mean 7.8 years). We used serial radiographs to measure the ratio of disc to vertebral height in the fused segments and to detect differential anterior spinal growth and assess its effect on scoliosis, vertebral rotation, kyphosis, and rib-vertebral-angle difference (RVAD). From one year after surgery to the latest review, the percentage anterior disc height decreased by nearly one-half and the percentage posterior disc height by nearly one-third in the fused segments (p < 0.001). There was a 4 degree increase in mean Cobb angle (p < 0.001), 11 patients (37%) having an increase of between 6 degrees and 10 degrees. There was a significant increase in mean apical rotation by 2 degrees (p = 0.003), and four patients (13%) had an increase of between 6 degrees and 16 degrees. There was little change in kyphosis. There was an increase in mean RVAD by 4 degrees (p = 0.003), seven patients (23%) showing a reduction by 1 degree to 7 degrees, and 11 (37%) increases of between 6 degrees and 16 degrees. Spinal growth occurs after posterior fusion in adolescents who are skeletally immature, as a result of continued anterior vertebral growth. There is some progression of scoliosis, vertebral rotation, and RVAD, but little change in kyphosis. The increase in deformity is not enough to warrant the use of combined anterior and posterior fusion. The findings are relevant to the management of progressive curves, the timing and extent of surgery, and the prognosis for progression of deformity in this group of patients.