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Purpose: Preoperative counting of thoracic and lumbar vertebrae is crucial in adolescent idiopathic scoliosis (AIS) due to reported anatomical variations and potential surgical site misidentification. This study investigated characteristics associated with the vertebral number variations AIS, particularly focusing on rib morphology., Methods: Based on three-dimensional computed tomography, patients were categorized into the non-variant number group, comprising individuals with 12 thoracic and 5 lumbar vertebrae, and the variant number group, comprising individuals with different numbers of vertebrae. Additionally, the most caudal rib morphology was classified as normal, unilateral, or hypoplastic., Results: A total of 359 patients were included in our study (41 males, 318 females, age: 16.3 ± 3.1 years), with 44 patients (12.3%) assigned to the variant number group. Logistic regression analysis identified unilateral ribs (odds ratio [OR]: 10.50) and lumbosacral transitional vertebrae (LSTV) (OR 6.49) as significant risk factors associated with variations. Further analysis revealed hypoplastic ribs as a significant risk factor associated with LSTV (OR: 4.58). 8 CONCLUSION: Our study suggests that abnormal rib morphology may be associated with vertebral number variations. Close attention to rib morphology is, therefore, warranted in cases with atypical vertebral numbers. Accordingly, to ensure surgical safety and accuracy, spine surgeons must communicate these variations to the surgical team, standardize nomenclature for describing them, and intraoperatively verify fusion levels with them., (© 2024. The Author(s), under exclusive licence to Scoliosis Research Society.)

Spinal fixation surgery has been increasingly performed in patients with osteoporosis. Romosozumab, a drug that was introduced in Japan recently, is known to possibly promote bone healing. However, few studies have reported the therapeutic effects of romosozumab in clinical practice in Japan. Therefore, here, we investigated the effects of romosozumab dosage on bone fusion promotion using an ovariectomized rat spinal fusion model. Eight-week-old female Sprague-Dawley rats were matched by body weight and divided into three groups: 1.0 romosozumab (R) group (Evenity®, 25 mg/kg), 1/10R group (Evenity®, 2.5 mg/kg), and control (C) group (saline). Subcutaneous injections were administered twice a week for 8 weeks postoperatively. Computed tomography scans were performed every 2 weeks from the time of surgery till 8 weeks postoperatively. The mean fusion rates in terms of volume were significantly higher in the R groups [1/10R, 1.0R] than in the C group from 4 weeks postoperatively. The rate of increase was significantly higher in the 1.0R group from 4 weeks postoperatively and in the 1/10R group from 6 weeks postoperatively, than in the C group. The proportion of trabecular bone area was approximately 1.5 times higher in the R groups than in the C group. No significant differences were observed between the R groups. Our results suggest that romosozumab stimulates bone growth at the graft site, and similar effects were achieved at 1/10 of the standard dosage., (© 2024 Orthopaedic Research Society.)

Objective: The goal of this study was to evaluate, using computed tomography (CT) and magnetic resonance imaging (MRI), patients who underwent oblique lateral interbody fusion (OLIF) using either expandable or static interbody spacers., Methods: Thirty-five patients with degenerative disc disease were surgically treated with one-level OLIF and were followed up for more than 6 months. The Static group consisted of 22 patients, and 13 patients were in the Expandable group. Intraoperative findings included operative time (min), blood loss (ml), and cage size. Low back pain, leg pain, and leg numbness were measured using the Japanese Orthopedic Association score, visual analogue score, and the Roland-Morris Disability Questionnaire. Radiologic evaluation using computed tomography (CT) and magnetic resonance imaging (MRI) allowed measurement of cage subsidence, cross-sectional area (CSA) of the dural sac, disc height, segmental lordosis, foraminal height, and foraminal CSA preoperatively and 6 months postoperatively., Results: The Expandable group had significantly larger cage height and lordosis than the Static group (P < 0.05). The Expandable group also had greater dural sac area expansion and enlargement of the intervertebral foramen, as well as better correction of vertebral body slip (P < 0.05). Cage subsidence was significantly lower in the Expandable group (P < 0.05). JOA and VAS scores for leg numbness were significantly better in the Expandable group (P < 0.05)., Conclusions: Compared with static spacers, expandable spacers significantly enlarged the dural sac area, corrected vertebral body slippage, expanded the intervertebral foramen, and achieved good indirect decompression while reducing cage subsidence, resulting in improvement in clinical symptoms., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Vacuum phenomenon is a commonly observed radiological entity in the degenerated intervertebral discs of the lumbar spine in the elderly population. The entity is frequently asymptomatic. Although disc herniation containing gas (DH-CoG) is commonly associated with the vacuum phenomenon, DH-CoG associated with clinical symptoms is a rare condition. There are very few reports which have histologically demonstrated the existence of the gas itself within DH-CoG. Herein, we report a rare case of a 65-year-old female with symptomatic DH-CoG at L5/S1. The patient was admitted to our hospital with a one-month history of pain in the left buttock and leg in addition to neurogenic claudication. Roentgenograms illustrated a degenerative lumbar spine with the vacuum phenomenon at the L5/S1 disc space. Computed tomography showed a round and low-density lesion within the spinal canal at left L5/S1. Additionally, a lesion characterized by an iso- and partially hypointense signal on T1 and hypointense signal on T2 was detected in magnetic resonance imaging (MRI) by the spin-echo method. The decision for posterior lumbar interbody fusion surgery using pedicle screws was made as the symptoms had not responded to the conservative treatment. After a degenerated prolapsed nucleus was carefully extracted, the specimen was sent to the laboratory for histopathological analysis. The prolapsed nucleus of DH-CoG histologically showed many small vacuoles containing degenerated mucopolysaccharides. The left leg pain drastically resolved on the first post-operative day, and no recurrence had been observed. Degenerated mucopolysaccharide may be a precursor of nitrogen or "the gas itself" in DH-CoG. Surgical intervention for DH-CoG should be considered if conservative treatment fails.

Study Design: Retrospective analysis of prospectively collected observational multicenter data., Objective: To compare the clinical results and rates of revision surgery after posterior lumbar interbody fusion (PLIF) and microendoscopic muscle-preserving interlaminar decompression (ME-MILD) in patients with single-level, mild degenerative lumbar spondylolisthesis (DLS) and follow-up of at least 5 years., Summary of Background Data: Surgery for symptomatic DLS remains controversial. Evaluating long-term results may reveal problems such as adjacent segmental diseases of the PLIF and decreased quality of life because of slippage and restenosis of the ME-MILD., Methods: We enrolled 116 patients who underwent PLIF (79 patients) or ME-MILD (37 patients). Operative times, blood losses, surgical complications, Short-Form 36 (SF-36), Japanese Orthopedic Association (JOA) score, the JOA Back Pain Questionnaire (JOABPEQ), visual analog scales (VAS), and Zurich Claudication Questionnaire (ZCQ) were evaluated., Results: PLIF was observed to require significantly longer operative times and entailed greater operative blood losses than did ME-MILD (151.1 vs. 119.9 min; 202.2 vs. 6.4 mL, respectively). Surgery-related complications were identified in 3 cases in the PLIF group and 2 cases in the ME-MILD group. Seventy-eight patients (50 and 28 patients in the PLIF and ME-MILD groups, respectively) were successfully followed-up for >5 years. The follow-up rate was 67.2%. No significant differences between the groups were found in terms of preoperative and postoperative JOA scores, postoperative JOABPEQ, VAS, or ZCQ. Significant improvements in JOA scores were observed in both groups. Significant improvements in the SF-36 were observed in all subscales except in role physical, general health, vitality, and mental health in the ME-MILD group. Revision surgical procedures were performed in 2 patients in the ME-MILD group and 4 patients in the PLIF group., Conclusions: PLIF and ME-MILD resulted in equivalent improvements in SF-36 and JOA scores. There were no differences in revision surgery rates among patients with single-level, mild DLS., Level of Evidence: Level III-a retrospective analysis.

Objective: The purpose of this study is to disclose the characteristic symptoms and signs in L2, L3 and L4 nerve root disturbance., Materials and Methods: Fifty eight patients who underwent lateral herniotomy were analyzed. Breakdowns are 15 patients with L2/3 lateral disc herniation (group A), 20 patients with L3/4 lateral disc herniation (group B), and 23 patients with L4/5 lateral disc herniation (group C). The following items were examined: 1) localization of the subjective pain and numbness, 2) objective neurological findings, including deep tendon reflex, manual muscle strength (MMT), straight leg raising test (SLRT) and femoral nerve stretch test (FNST)., Results: In group A, subjective pain and/or numbness was present in the thigh aspect, proximal to the knee joint in all patients. In group B, 80% of the patients had subjective pain and/or numbness in the medial site of the knee joint. In group C, the subjective pain and/or numbness was localized in various aspects of the lower extremity. Weakness in the iliopsoas, the femoral quadriceps, and the anterior tibial muscle were observed in 60-95%, 27-70%, 0-43% of three groups, respectively. Depression or absence of the patella tendon reflex was present in 27-100% of three groups. SLRT and FNST were positive in 13-87% and 91-95% of three groups., Conclusion: Symptomatic levels of nerve root disturbance in the upper lumbar spine could not be accurately identified by objective neurological findings alone. Pain and/or numbness localized in the thigh area proximal to the knee joint is a specific sign of L2 nerve root disturbance. Either subjective pain or numbness in the medial knee joint aspect is another key sign which strongly suggests L3 nerve root disturbance., (Copyright © 2016 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.)

Objectives: To determine the validity of posterior lumbar interbody fusion (PLIF) using a titanium cage filled with excised facet joint bone and a pedicle screw for degenerative spondylolisthesis., Methods: PLIF using a titanium cage filled with excised facet joint bone and a pedicle screw was performed in 28 consecutive patients (men 10, women 18). The mean age of the patients was 60 years (range, 52 to 75 y) at the time of surgery. The mean follow-up period was 2.3 years (range, 2.0 to 4.5 y). The operation was done at L3/4 in 5, L4/5 in 20, and L3/4/5 in 3 patients. The mean operative bleeding was 318+/-151 g (mean+/-standard deviation), and the mean operative time was 3.34+/-0.57 hours per fixed segment. Clinical outcome was assessed by Denis' Pain and Work scale. Radiologic assessment was done using Boxell's method. Fusion outcome was assessed using an established criteria., Results: On Pain scale, 20 and 8 patients were rated P4 and P5 before surgery, and 11, 12, 2, 2, and 1 patients were rated P1, P2, P3, P4, and P5 at final follow-up, respectively. On Work scale (for only physical labors), 12 and 9 patients were rated W4 and W5, before surgery, and 12, 5, 1, and 3 patients were rated W1, W2, W3 and W5 at final follow-up, respectively. There was significant difference in clinical outcome (P<0.01, Wilcoxon singled-rank test) The mean %Slip and Slip Angle was 17.9+/-8.1% and 3.9+/-5.8 degrees before surgery. The mean % Slip and Slip Angle was 5.4+/-4.4% and -2.0+/-4.8 degrees at final follow-up. There was a significant difference between the values (P<0.01, paired t test). "Union" and "probable union" was determined in 29 (93.5%) and 2 (6.5%) of 31 operated segments at 2.3 years (range, 2.0 to 4.5 y), postoperatively., Conclusions: PLIF using a titanium cage filled with excised facet joint bone and a pedicle screw provided a satisfactory clinical outcome and an excellent union rate without harvesting and grafting the autologous iliac bone.

We investigated the relationships between tumor necrosis factor (TNF) gene polymorphism, circulating TNF-alpha (TNF-alpha) concentrations, and bone mineral density (BMD) in the lumbar spine. TNF gene polymorphisms studied were the Nco I polymorphism within the first intron of TNF-beta (TNF-beta) and three single nucleotide polymorphisms in the promoter region of the TNF-alpha gene, at positions -857, -863, and -1031. Allelic variants of the TNF gene were identified using restriction fragment length polymorphism (RFLP) analysis in 177 postmenopausal Japanese women within 10 years after menopause, aged 56.4 +/- 4.5 years (mean +/- SD). A significantly higher prevalence of the alleles TNF-alpha-863A (20.3% versus 9.9%) and TNF-alpha-1031C (21.3% versus 12.4%) was seen in the low BMD group (Z-score < 0, n = 91) than in the high BMD group (0 < Z-score, n = 86). In genotype analysis, although difference did not reach a significant level, women with the rarest allelic variants, i.e., homozygous TNFbl, TNF-alpha-863A, and TNF-alpha-1031C, showed the lowest BMD Z-scores. Women with another rarest allelic variant, TNF-alpha-857T/T had significantly lower BMD Z-scores than did women with TNF-alpha-857C/T or -857C/C. The BMD Z-score decreased significantly with an increase in the total number of such rare alleles. Serum concentrations of TNF-alpha did not differ significantly among groups divided by genotypes. Multiple linear regression analysis revealed that the total number of rare alleles, in addition to the body mass index and the number of years since menopause, was an independent predictor of the BMD. These presumptive functional polymorphisms of the TNF gene may be associated with the lumbar spine BMD in early postmenopausal Japanese women.

Background Context: Some biomechanical studies have demonstrated that bone mineral density of the lumbar spine (BMD) affects the stability of pedicle screws in vitro., Purpose: To investigate influence of BMD on loosening and related failure of pedicle screws in vivo., Study Design/setting: A clinical study of 52 patients who underwent pedicle screw fixation augmenting posterior lumbar interbody fusion (PLIF)., Patient Sample: There were 13 men and 39 women, with an average age of 63 years (range, 45-76 years) at the time of operation. The mean follow-up period was 2.8 years (range, 2-6 years)., Outcome Measures: Relationship between BMD, screw loosening, and its related failures were statistically analyzed., Methods: BMD was measured by the dual energy X-ray absorptiometry (DEXA) method. Radiographic assessments were done by the first author and independently by another orthopedist who was not informed of the values of BMD., Results: The mean BMD of all patients was 0.879 +/- 0.215 (mean +/- S.D.) g/cm2. The mean BMD in patients with and without screw loosening was 0.720 +/- 0.078 g/cm2 (n=11) and 0.922 +/- 0.221 g/cm2 (n=41). There was a significant difference between the mean BMD of patients with and without screw loosening (P<.01). The mean BMD of patients with "union," "nonunion" and "undetermined union" was 0.934 +/- 0.210 g/cm2 (n=40), 0.674 +/- 0.104 g/cm2 (n=4) and 0.710 +/- 0.116 g/cm2 (n=8), respectively. The mean BMD of patients with "union" was significantly greater than those with "nonunion" and "undetermined union" (P<.05)., Conclusion: It could be concluded that BMD has a close relation with the stability of pedicle screws in vivo, and BMD value below 0.674 +/- 0.104 g/cm2 suggests a potential increased risk of "nonunion" when pedicle screw fixation is performed in conjunction with PLIF.

The records of 14 patients with malignant or aggressive benign vertebral tumors of the thoracolumbar spine who underwent total spondylectomy (TS) were evaluated retrospectively. Total spondylectomy was performed by bisecting the affected vertebra through the pedicle using fine threadwire saws and removing the vertebra en bloc through the posterior procedure alone or the one-stage anteroposterior combined procedure. Remarkable pain relief and ambulation after surgery were achieved in all 14 patients. No serious complications occurred. Nerve roots were sacrificed in seven cases. A marginal surgical margin was achieved in 10 cases and an intralesional surgical margin was achieved in four. At the site of the osteotomized pedicle, the surgical margin was marginal, with the possibility of tumor-cell contamination in 10 cases. Local recurrence was found in three cases of posterior total spondylectomy at 0.3 to 3.5 years (mean, 3.2 years) follow-up evaluation at the other site of the osteotomized pedicle. These results suggest that this type of total spondylectomy is effective in controlling local recurrence without incurring major complications and is a clinically useful procedure.

Study Design: Review of the clinical and radiologic records of patients who underwent one-level posterior lumbar interbody fusion (PLIF) at L4-L5., Objective: To determine whether adjacent intervertebral disc degeneration after PLIF affects the clinical results, and whether preoperative caudal disc (L5-S1) degeneration affects postoperative clinical results., Summary of Background Data: There is little reliable information in the literature regarding clinical results and adjacent disc degeneration after PLIF., Methods: Forty-five patients who underwent L4-L5 PLIF for spondylolisthesis with more than 5 years of postoperative observation were included in this study. PLIF was performed in conjunction with posterior instrumentation. The posterior lumbar intervertebral grafting was performed using both autograft and a ceramic spacer. Intervertebral disc heights at L2-L3, L3-L4, and L5-S1 were measured before and after surgery. The patients were divided into two groups based on the presence or absence of the preoperative L5-S1 narrowing. Correlation between clinical status evaluated by the recovery rate of the Japanese Orthopedic Association (JOA) score and disc heights were determined., Results: All intervertebral disc heights adjacent to the fusion decreased after surgery (P < 0.05). However, no significant correlation was seen between clinical results estimated by the recovery rate and postoperative disc narrowing. There was also no significant difference in clinical results between patients with or without preoperative L5-S1 narrowing., Conclusions: There is no evidence from the results that postoperative narrowing of the adjacent disc and preoperative narrowing of the L5-S1 disc affects the clinical outcome of L4-L5 PLIF.

Study Design: An investigation of the relation between intraoperative insertional torque of pedicle screws, bone mineral density of the vertebra, and development of screw loosening in vivo., Objectives: To determine the usefulness of intraoperative measurement of the insertional torque of pedicle screws., Summary of Background Data: Some biomechanical studies have demonstrated that the insertional torque is highly correlated with bone mineral density and the stability of pedicle screws in vitro., Methods: Pedicle screw fixation was performed with posterior lumbar interbody fusion in 62 consecutive patients. The mean age of the patients at the time of surgery was 58 years. The insertional torque of pedicle screws was measured intraoperatively in all patients. The mean follow-up period was 2.7 years., Results: The mean insertional torque was 1.28 +/- 0.37 Nm in patients with screw loosening and 1.50 +/- 0. 40 Nm in patients without the problem. The mean insertional torque in patients with compression fractures in the upper vertebra adjacent to the fixed segment was 0.83 +/- 0.23 Nm. There was no significant difference between the mean insertional torque in patients with screw loosening and those without the condition. The mean insertional torque in patients without screw loosening was significantly greater than in patients with compression fractures (P < 0.01). A high correlation was found between insertional torque and bone mineral density (P < 0.01)., Conclusions: Although a high correlation was found between the insertional torque of pedicle screws and bone mineral density in vivo, the insertional torque could not objectively predict screw loosening.

We report a case of a lumbar teratoma in a 50-year-old woman. The teratoma showed a dumb-bell-type expansion at the level of the left L3/4 foramen with massive erosion of the L3 vertebral body. MRI revealed inhomogeneous signal changes in the tumor, which were histologically compatible with a mixture of bone, muscle, fat, and cyst containing sebaceous material. Complete resection of the tumor and spinal arthrodesis with pedicle screw fixation was necessary to obtain stability of the affected spinal segment.

Eight cases of solitary spinal metastasis with neurological deficit in thoracolumbar spine in which total en bloc spondylectomy (TS) was performed by bisecting the affected vertebra through both pedicles using fine thread wire saws were reviewed. Patient age ranged from 40 to 78 (mean, 62) years. Primary lesions were in the lung (2), kidney (2), thyroid (3) and prostate (1). TS was performed through a posterior approach in 5 cases (T6-7, T12, L2, L2 and L2-3) and through a one-stage anterior and posterior combined approach in the others (L2, L3 and L4). The spine was reconstructed with a ceramic vertebral prosthesis and a pedicle screw fixation system in 5 cases, and with augmented anterior spinal instruments in 3 cases. There were neither surgical complications nor surgical mortality. All patients became ambulatory and pain-free after surgery. Histologically, a marginal surgical margin was achieved in only one case. The other 7 cases had intralesional margin at the osteotomized pedicles. Four patients died from causes unrelated to local recurrence 4 to 44 (mean, 19) months after surgery. Effectiveness of surgery was maintained until death in all 4 of these patients. Asymptomatic local recurrence occurred in 2 patients with renal cancer at 10 and 33 months after surgery. These preliminary results suggest that TS for solitary spinal metastasis can achieve good control of local recurrence without major complications and is clinically acceptable surgery.

We retrospectively evaluated neurological and other complications related to posterior lumbar interbody fusion (PLIF) performed by facet joint excision and pedicle screw fixation, in 148 consecutive patients with degenerative disorders. Their mean age at surgery was 59 (19-80) years. The mean follow-up period was 3 (2-6.5) years. Overall, 91 complications in 75 cases were observed. Although no permanent neural damage was detected, transient neural palsy occurred in 8% of the cases. Dural tear, partial misplacement, loosening, breakage of the pedicle screw and loss of correction were seen in 6, 6, 4, 1 and 1 of the cases, respectively. Deep infection of the fused segment developed in 2 cases. We conclude that PLIF, performed by facet joint excision and pedicle screw fixation, demonstrated a very low incidence of osteosynthesis failure, such as screw loosening, breakage and loss of correction. However, the high incidence of other complications, particularly neurological impairment, is still a disadvantage of this technically-demanding procedure.

Study Design: Nine patients with thoracolumbar burst fractures associated with horizontal fractures in the posterior column were studied retrospectively., Objectives: To clarify the clinical and radiographic findings and evaluate the postoperative results for this type of fracture., Summary of Background Data: It is not well recognized that burst fractures occasionally are accompanied by horizontal fractures of the posterior column such as those that result from seatbelt-type injuries. This type of burst fracture differs from flexion-distraction injuries combined with burst fracture, which are accompanied by horizontal fractures not only in the posterior but also in the middle column. Radiographic features of these two different types of injuries are very similar to each other, and their differentiation in diagnosis and treatment has not been recognized clearly., Methods: Patients were reviewed using a combination of clinical records, follow-up examination, and radiographic data (computed tomography [CT], plain radiographs, and tomographs). Anterior spinal fusion was performed in eight patients using the Kaneda device (Mizuhoika Tokyo, Japan), and one was treated by posterior fusion with pedicle screw fixation. The average follow-up period was 4 years., Results: Patients with fractures of this type represented 21% of the 48 patients with thoracolumbar burst fractures. The injury was sustained by falling in all nine patients. All of the burst fractures were Denis' type B. The horizontal fracture was located at the lamina and spinous process in the posterior column of the upper vertebra adjacent to the involved vertebra in all nine patients. The integrity of the ligamentous structures of the middle column, such as the posterior longitudinal ligament, the periosteum, and the outermost anulus, was confirmed at surgery in eight patients, although not in the patient who underwent posterior fusion. One patient required surgery because of progression of kyphotic deformity during conservative treatment. Solid fusion with no complications was noted in all patients., Conclusion: This type of burst fracture is not accompanied by ligamentous injuries because of distraction force in the middle column, which is not present in flexion-distraction injuries, but it seems to be more unstable than burst fractures with no horizontal splitting of the posterior column and requires surgical stabilization.

Study Design: This study investigated the outcome of anterior decompression and stabilization for "unstable" burst fractures without initial neurologic deficits in the thoracolumbar spine., Objective: To determine the pain and work status of the patients, who underwent the anterior decompression and stabilization, to evaluate the relationship between residual back pain and the degree of kyphosis, and to analyze the advantages and disadvantages of surgery for burst fractures without initial neurologic deficits in the thoracolumbar spine., Summary of Background Data: A retrospective review was conducted on 45 patients with unstable burst fractures in the thoracolumbar spine treated by anterior decompression and stabilization in our institutions from 1982 to 1993. Nineteen patients were available for this study. Ten patients were men and 9 were women. Their age at surgery ranged from 15 to 76 years (average, 46 years). The duration of follow-up ranged from 24 to 84 months (average follow-up, 54 months)., Methods: All clinical charts and radiologic data of these patients were reviewed by the first author. Their pain, work, and employment statuses were assessed by the scales proposed by Denis in 1984., Results: Nine patients were rated P1, 7 were rated P2, 2 were rated P3, 1 was rated P5, 11 were rated W1, 3 were W2, 1 was W3, and 4 were rated W5. Even the physical laborers' return to work averaged 5 months after surgery (range, 3-12 months). The postoperative kyphotic angle ranged from -6 degrees to 45 degrees (average, 11 degrees), and it remained -5 degrees to 45 degrees (average, 12 degrees) at final follow-up. There was no statistical correlation between the kyphotic angle and the pain scale., Conclusions: Anterior decompression and stabilization for unstable burst fracture without initial neurologic deficits in the thoracolumbar spine has some advantages in the view of anatomical reduction and rigid stability that allows patients an early rehabilitation, return to work, and gainful employment.

The isthmic diameter of the vertebral pedicle is an important dimension affecting the stability of transpedicular screwing. The isthmic diameter of the pedicle was measured in the lumbar spines of 18 Japanese cadavers (10 male, 8 female) by axial computed tomographic (CT) scan and directly with calipers. In L1 and L2, there was no significant difference between the average value of the isthmic diameter as determined by the two methods (Student's t-test). However, in L3-5, the average value of the isthmic diameter as determined by axial CT scan was significantly greater than that given by caliper measurement. In view of the fact that caudally the longitudinal axis of the pedicle diverges towards the mid-line of the vertebral body in the coronal plane, the plane of the CT scan cannot be parallel to the real isthmic diameter of the pedicle. Therefore, it is suggested that below L2 the diameter as determined by axial CT scanning is greater than the real isthmic diameter.

The influence of bone mineral density on the stability of transpedicle screwing was studied in the human cadaveric lumbar vertebrae. The pull-out force correlated with bone mineral density. The tilting moment (load needed to tilt the screw 4 degrees cranially at the screw-plate junction) and the cut-up force (load needed to tip the end plate up by the screw) correlated with bone mineral density. A correlation was also found between the maximum insertion torque of the screw and bone mineral density. The maximum insertion torque correlated with the pull-out force, the tilting moment, and the cut-up force. In the cyclic tilting test (200 cycles), the mean value of the tilting moment at the 200th cycle was 67.4 +/- 6.1%, compared with the first cycle. The results suggest that preoperative measurement of BMD is necessary for transpedicle screwing in osteoporotic cases, and that the cyclic tilting motion decrease its mechanical stability. The authors have also concluded that the maximum insertion torque could predict the mechanical stability.