Clinical and Radiological Comparison of Semirigid (WavefleX) and Rigid System for the Lumbar Spine.

OBJECTIVE: Spinal fusion operation is an effective treatment in the spinal pathology, but it could change the physiological distribution of load at the instrumented and adjacent segments. This retrospective study compared the radiological and clinical outcomes of patients undergoing lumbar fusion with semirigid rods versus rigid rods system. METHODS: Using transpedicular fixation and posterior lumbar interbody fusion at the level of L4/L5, 20 patients were treated with semirigid rods (WavefleX, SR group), and 20 patients with rigid rods (titanium, RR group). Clinical and radiological outcomes were evaluated, including visual analog score for lower back pain and leg pain, Prolo functional and economic scores, statues of implanted instruments, fusion rate, and complications during 24-month follow-up. RESULTS: Clinical scores were significantly improved until postoperative 24-month follow-up as compared with preoperative scores in both groups (p<0.05), with similar levels of improvement observed at the same time points postoperatively between the 2 groups. Prolo economic scores were significantly improved in SR group compared to RR until 12 months, but this improvement became similar after 18 months. The overall fusion rate was 94.1% until the 24-month follow-up for both groups. No significant complication was observed in both groups. CONCLUSION: The results of the present study indicate that semirigid rods system with posterior lumbar interbody fusion showed similar clinical and radiological result with rigid rods system until 2 years after instrumentation. The WavefleX rods system, as a semirigid rods with unique characteristics, may be an effective alternative treatment for patients in lumbar fusion.

Quantitative Pfirrmann Disc Degeneration Grading System to Overcome the Limitation of Pfirrmann Disc Degeneration Grade.

OBJECTIVE: Pfirrmann disc degeneration grade is one of morphologic disc degeneration grading system and it was reliable on routine T2-weighted magnetic resonance (MR) images. The purpose of this study was to evaluate the agreement of Pfirrmann disc degeneration grade, and check the alternative technique of disc degeneration grading system. METHODS: Fifteen volunteers (4 medical doctors related to spinal disease, 2 medical doctors not related to spinal disease, 6 nurses in spinal hospital, and 3 para-medicines) were included in this study. Three different digitalized MR images were provided all volunteers, and they checked Pfirrmann disc degeneration grade of each disc levels after careful listening to explanation. Indeed, all volunteers checked the signal intensity of disc degeneration at the points of nucleus pulposus (NP), disc membrane, ligaments, fat, and air to modify the quantitative Pfirrmann disc degeneration grade. RESULTS: Total 225 grade results of Pfirrmann disc degeneration grade and 405 signal intensity results of quantitative Pfirrmann disc degeneration grade were analyzed. Average interobserver agreement was "moderate (mean±standard deviation, 0.575±0.251)" from poor to excellent. Completely agreed levels of Pfirrmann disc degeneration grade were only 4 levels (26.67%), and the disagreement levels were observed in 11 levels; two different grades in 8 levels (53.33%) and three different grades in 3 levels (20%). Quantitative Pfirrmann disc degeneration showed relatively cluster distribution with the interobserver deviations of 0.41-1.56 at the ratio of NP and disc membrane, and it showed relatively good cluster and distribution indicating that the proposed grading system has good discrimination ability. CONCLUSION: Pfirrmann disc degeneration grade showed the limitation of different interobserver results, but this limitation could be overcome by using quantitative techniques of MR signal intensity. Further evaluation is needed to access its advantage and reliabilities.

Biomechanical Comparisons of Pull Out Strengths After Pedicle Screw Augmentation with Hydroxyapatite, Calcium Phosphate, or Polymethylmethacrylate in the Cadaveric Spine.

OBJECTIVE: In vertebrae with low bone mineral densities pull out strength is often poor, thus various substances have been used to fill screw holes before screw placement for corrective spine surgery. We performed biomechanical cadaveric studies to compare nonaugmented pedicle screws versus hydroxyapatite, calcium phosphate, or polymethylmethacrylate augmented pedicle screws for screw tightening torques and pull out strengths in spine procedures requiring bone screw insertion. METHODS: Seven human cadaveric T10-L1 spines with 28 vertebral bodies were examined by x-ray to exclude bony abnormalities. Dual-energy x-ray absorptiometry scans evaluated bone mineral densities. Twenty of 28 vertebrae underwent ipsilateral fluoroscopic placement of 6-mm holes augmented with hydroxyapatite, calcium phosphate, or polymethylmethacrylate, followed by transpedicular screw placements. Controls were pedicle screw placements in the contralateral hemivertebrae without augmentation. All groups were evaluated for axial pull out strength using a biomechanical loading frame. RESULTS: Mean pedicle screw axial pull out strength compared with controls increased by 12.5% in hydroxyapatite augmented hemivertebrae (P = 0.600) and by 14.9% in calcium phosphate augmented hemivertebrae (P = 0.234), but the increase was not significant for either method. Pull out strength of polymethylmethacrylate versus hydroxyapatite augmented pedicle screws was 60.8% higher (P = 0.028). CONCLUSIONS: Hydroxyapatite and calcium phosphate augmentation in osteoporotic vertebrae showed a trend toward increased pedicle screw pull out strength versus controls. Pedicle screw pull out force of polymethylmethacrylate in the insertion stage was higher than that of hydroxyapatite. However, hydroxyapatite is likely a better clinical alternative to polymethylmethacrylate, as hydroxyapatite augmentation, unlike polymethylmethacrylate augmentation, stimulates bone growth and can be revised.

Usefulness of Simple Rod Rotation to Correct Curve of Adolescent Idiopathic Scoliosis.

OBJECTIVE: To correct apical vertebral rotation for adolescent idiopathic scoliosis (AIS), direct vertebral derotation (DVD) or simple rod rotation (SRR) might be considered. The aim of the present study is to introduce the surgical experiences of AIS by a Korean neurosurgeon and to evaluate the effectiveness of SRR for apical vertebral rotation. METHODS: A total of 9 patients (1 male and 8 females) underwent scoliosis surgery by a neurosurgeon of our hospital. The Lenke classifications of the patients were 1 of 1B, 2 of 1C, 1 of 2A, 1 of 2C, 3 of 5C and 1 of 6C. Surgery was done by manner of simple rod rotation on the concave side and in situ coronal bending. Coronal Cobb's angles, vertebral rotation angles and SRS-22 were measured on a plain standing X-ray and CT before and after surgery. RESULTS: The mean follow up period was 25.7 months (range : 5-52). The mean number of screw positioning level was nine (6-12). The mean age was 16.4 years (range : 13-25) at surgery. The mean Risser grade was 3.7±0.9. The apical vertebral rotation measured from the CT scans was 25.8±8.5° vs. 9.3±6.7° (p<0.001) and the Coronal Cobb's angle was 53.7±10.4° vs. 15.4±6.5° (p<0.001) preoperatively and postoperative, respectively. The SRS-22 improved from 71.9 preoperatively to 90.3 postoperatively. There were no complications related with the operations. CONCLUSION: SRR with pedicle screw instrumentation could be corrected successfully by axial rotation without complications. SRR might serve as a good option to correct AIS deformed curves of AIS.

Biomechanical comparison of cervical fixation via transarticular facet screws without rods versus lateral mass screws with rods.

OBJECTIVE: Transarticular facet screws restore biomechanical stability to the cervical spine when posterior cervical anatomy has been compromised. This study compares the more recent, less invasive, and briefer transarticular facet screw system without rods with the lateral mass screw system with rods. METHODS: For this study, 6 human cervical spines were obtained from cadavers. Transarticular facet screws without rods were inserted bilaterally into the inferior articular facets at the C5-C6 and C5-C6-C7 levels. Lateral mass screws with rods were inserted bilaterally at the same levels using Magerl's technique. All specimens underwent range of motion (ROM) testing by a material testing machine for flexion, extension, lateral bending, and axial rotation. RESULTS: Both fixation methods, transarticular facet screws without rods and lateral mass screws with rods, reduced all ROM measurements and increased spinal stiffness. No statistically significant differences between the 2 stabilization methods were found in ROM measurements for 1-level insertions. However, in 2-level insertions, ROM for the nonrod transarticular facet screw group was significantly increased for flexion-extension and lateral bending. CONCLUSIONS: Transarticular facet screws without rods and lateral mass screws with rods had similar biomechanical stability in single-level insertions. For 2-level insertions, transarticular facet screws without rods are a valid option in cervical spine repair.

A Multi-center Clinical Study of Posterior Lumbar Interbody Fusion with the Expandable Stand-alone Cage (Tyche(R) Cage) for Degenerative Lumbar Spinal Disorders.

OBJECTIVE: This multi-center clinical study was designed to determine the long-term results of patients who received a one-level posterior lumbar interbody fusion with expandable cage (Tyche(R) cage) for degenerative spinal diseases during the same period in each hospital. METHODS: Fifty-seven patients with low back pain who had a one-level posterior lumbar interbody fusion using a newly designed expandable cage were enrolled in this study at five centers from June 2003 to December 2004 and followed up for 24 months. Pain improvement was checked with a Visual Analogue Scale (VAS) and their disability was evaluated with the Oswestry Disability Index. Radiographs were obtained before and after surgery. At the final follow-up, dynamic stability, quality of bone fusion, interveretebral disc height, and lumbar lordosis were assessed. In some cases, a lumbar computed tomography scan was also obtained. RESULTS: The mean VAS score of back pain was improved from 6.44 points preoperatively to 0.44 at the final visit and the score of sciatica was reduced from 4.84 to 0.26. Also, the Oswestry Disability Index was improved from 32.62 points preoperatively to 18.25 at the final visit. The fusion rate was 92.5%. Intervertebral disc height, recorded as 9.94+/-2.69 mm before surgery was increased to 12.23+/-3.31 mm at postoperative 1 month and was stabilized at 11.43+/-2.23 mm on final visit. The segmental angle of lordosis was changed significantly from 3.54+/-3.70 degrees before surgery to 6.37+/-3.97 degrees by 24 months postoperative, and total lumbar lordosis was 20.37+/-11.30 degrees preoperatively and 24.71+/-11.70 degrees at 24 months postoperative. CONCLUSION: There have been no special complications regarding the expandable cage during the follow-up period and the results of this study demonstrates a high fusion rate and clinical success.

Radiological considerations of posterior cervical lateral mass fixation using plate and screw.

The aim of this study is to determine whether the posterior cervical fusion methods with the plate-screw system applied to the lateral mass of cervical spine are radiologically safe to patients. The lateral cervical X-rays and CT scans were done on 40 normal adults without cervical problem. Based on Roy-Camille and Magerl's method, the theological trajectory of screw was shown on films and the parameters were measured. The study based on Roy-Camille's method showed less than one percent chance of injury on the facet joint and the mean depth of the screw to be 10.5 +/- 1.4 mm. On the other hand, Magerl's method showed the mean depth of screw to be 11.9 +/- 1.5 mm which is slightly larger than that of Roy-Camille's method and no chance of facet injury occurred. A reduced lateral angle of screw (19.6 +/- 3.5 degrees C) performed with the concept based on Magerl's method resulted a longer depth of screw (13.5 +/- 2.1 mm). Both Roy-Camille and Magerl's methods seemed to be radiologically safe to normal persons. However, the authors recommend the reduced lateral angle (19.6 +/- 3.5 degrees C) of screw based on the Magerl's method more than an original Magerl's methods.