Does the size of the rod affect the surgical results in adolescent idiopathic scoliosis? 5.5-mm versus 6.35-mm rod.

BACKGROUND CONTEXT: Favorable clinical outcomes of surgical treatment with Cotrel-Dubousset instrumentation (CDI) or instrumentations that follow the principles of CDI, for adolescent idiopathic scoliosis (AIS) have been reported. However, there are few studies concerning the results with rods of different sizes. PURPOSE: To find out whether the rod size affects the surgical results for AIS. STUDY DESIGN: A retrospective cohort study based on the same spinal system with different sizes of rod. PATIENT SAMPLE: A consecutive series of 93 patients, who underwent posterior correction with posterior instrumentation and fusion for AIS, were included and retrospectively analyzed. OUTCOME MEASURES: Postoperative radiologic outcomes were evaluated using coronal curves, percentage of curve correction, and coronal global balance. METHODS: Ninety-three patients treated during the period January 2000 to December 2008 were included in this study; 48 patients were treated with the Cotrel-Dubousset Horizon (CDH) M10 system with a 6.35-mm rod from January 2000 through December 2004, and a CDH M8 was used with a 5.5-mm rod in another 45 patients from January 2005 through December 2008. The Cobb angle, Risser grade, coronal curves, flexibility of curve, percentage of curve correction, coronal global balance, operative time, and estimated blood loss were measured and analyzed. The same parameters were used when the patient was followed at the OPD. All of the patients underwent regular follow-up for at least 2 years. RESULTS: No statistical significance was observed in the demographic data, including age, sex, BMI, and Risser grade, between these 2 groups. The overall average percentage of correction was 60.0%±12.7%: 60.7%±12.5% for the CDH M10 group, and 59%±13.1% for the CDH M8 group. At the final follow-up, the overall average loss of correction was 4.8±3.9° for the CDH M10 group, and 4.3±4.0° for the CDH M8 group. The average percentage of correction at the final follow-up was 50.9%±15.1% for the CDH M10 group, and 51.1%±16.1% for the M8 group. No statistical significance could be observed in the radiologic parameters between these 2 groups. CONCLUSION: The radiologic results for the 5.5-mm rod and the 6.35-mm rod were comparable in terms of correction, loss of correction, and coronal global balance.

Polymethylmethacrylate augmentation of cannulated pedicle screws for fixation in osteoporotic spines and comparison of its clinical results and biomechanical characteristics with the needle injection method.

STUDY DESIGN: This is a retrospective study carried out to evaluate the clinical results of patients with osteoporosis and various spinal diseases treated surgically with polymethylmethacrylate (PMMA)-augmented cannulated pedicle screws, and to compare this method with the needle injection technique in terms of the clinical results and fixation strength. OBJECTIVES: To report a technique using PMMA-augmented cannulated pedicle screws for fixation in osteoporotic spines and to compare its clinical results and biomechanical characteristics with the needle injection technique. SUMMARY OF BACKGROUND DATA: Many studies have shown that PMMA-augmented pedicle screws can significantly increase the stiffness and strength of the screw. Various designs of cannulated screws have been used for cement augmentation in experimental studies; however, clinical reports using these screws in osteoporotic patients are rare. A practical and reliable technique and optimal screw design have not yet been established. METHODS: Forty-five patients (23 women, 22 men), mean age of 71.37 years (range, 53-94 y), with osteoporosis and various spinal diseases underwent spinal decompression and instrumentation with PMMA augmentation of cannulated pedicle screws. Preoperative and postoperative visual analog scale scores for pain and the Oswestry disability index questionnaire data were analyzed. Screw migration, which is the distance from the screw tip to the anterior cortex and the upper endplate of the vertebra, was also evaluated immediately after surgery and at the mean follow-up of 15.9 months. These clinical results were then compared with those reported for the needle injection technique. The pullout strength, insertional, and backout torque of these 2 techniques were compared using osteoporotic synthetic bone (0.12 g/cm). RESULTS: A total of 255 out of 283 cannulated screws were augmented with PMMA. The mean visual analog scale pain score of these patients improved from 9.5 to 3.1 (P<0.01) and the functional Oswestry disability index score improved from 71% to 28.9% (P<0.01). Kyphotic deformity of the compression fracture group (19 patients) was improved from an average of 9.38 to 3.27 degrees after surgery, and to 5.45 degrees at the final follow-up (P<0.01). There was no significant vertical screw migration when the screws' distances were compared just after the operation and at the final follow-up (P>0.01). However, significant horizontal screw migration was found in lesions below the L2 level (P<0.01). There was no major neurovascular injury, except in 1 patient, who had persistent left thigh pain due to cement leakage at the L1 level, and the symptom was controlled with analgesics. The clinical results of both techniques were satisfactory and there were no significant differences. Although the pullout strength and screw backout torque was significantly higher in the needle injection group (234.1 vs. 187.8 N, 1119.6 vs. 836.7 N mm, respectively), the operation time was shorter and the cement leakage rate was less in the cannulated pedicle screw group than that of the needle injection group (211.4 vs. 296.3 min, 14.05% vs. 26.2%, respectively). CONCLUSIONS: The technique of cannulated pedicle screws with PMMA augmentation used in this study can be an option for osteoporotic patients with various spinal diseases who require spinal instrumentation.

Fixation strength of PMMA-augmented pedicle screws after depth adjustment in a synthetic bone model of osteoporosis.

The purpose of this study was to determine the change of fixation strength after adjusting the height of polymethylmethacrylate (PMMA)-augmented pedicle screws.Cement-augmented cannulated pedicle screws with or without PMMA augmentation with a radial hole in the distal third of the screw thread were inserted into synthetic bone blocks used to model osteoporosis. Screws were left unchanged (in situ), screwed in 3 threads, or screwed out 3 threads. The change in screw height was made 24 hours after cement placement. Radiographs of the samples were taken before and after screw adjustment, and pullout strength testing was performed. In the cement group, a radiolucent cavity was present after screwing in due to the screw-cement complex migrating downward, whereas no obvious change in the boneicement complex existed after screwing out. Mean pullout strength was significantly higher in the groups with cement as compared to those without cement. However, in the cement groups, the screw-in group had the lowest mean pullout strength among 3 groups, and the mean pullout strength in the screw-out group was also significantly lower than that in the in situ group (P<.05).Adjustment of pedicle screw height after cement augmentation in a severely osteoporotic spine can significantly reduce the pullout strength of the screw.