Using a Combination of Intralaminar and Pedicular Screw Constructs for Enhancement of Spinal Stability and Maintenance of Correction in Patients With Sagittal Imbalance: Clinical Applications and Finite Element Analysis.

STUDY DESIGN: Case series and finite element analysis. OBJECTIVE: To report the clinical results of using intralaminar screw-rod (ILS) constructs as supplements to regular pedicle screw (PS) constructs in "high risk for implant failure" patients and to report the results of a finite element analysis (FEA) of this new instrumentation technique. SUMMARY OF BACKGROUND DATA: Despite advances in surgery and implantation techniques, osteoporosis, obesity, revision surgeries, and neuromuscular conditions (such as the Parkinson disease) are challenges against achieving solid arthrodesis and maintaining correction. Additional fixation strategies must be considered in these patients. There is only one study in the literature suggesting that ILS can be used as alternative anchor points and/or to increase fixation strength in conjunction with the PSs. MATERIALS AND METHODS: Five patients (3 male and 2 female) with mechanical comorbidities underwent PS+ILS to treat sagittal imbalance. In radiologic analysis, thoracic kyphosis, lumbar lordosis, and sagittal vertical axis were analyzed. FEA of ILS augmentation technique were carried out.Four different models were created: (1) the full-construct model with ILS+PS 2 levels above and below the osteotomy of T10; (2) only PS 2 levels above and below T10; (3) ILS+PS 1 level above and below the osteotomy; and (4) short-segment PS with only PSs 1 level above and below the osteotomy. The stress/load distributions on the implants in vertebrae were analyzed. RESULTS: The mean age of the patients included in this study was 41 years and the mean follow-up was 28.2 months. A total of 87 PSs and 39 ILSs were used. Both sagittal vertical axis and kyphosis angles showed significant improvements maintained at the latest follow-up. No pseudarthrosis or instrumentation failures were observed. FEA indicated that addition of ILS construct to a PS construct enabled decreased load bearing and increased implant life. CONCLUSIONS: Addition of an ILS construct to PS construct decreases osteotomy line deformation and reduces stress on pedicle fixation points, and the combination improves fixation stability over the conventional PS-rod technique.

The use of intralaminar screws in patients with spinal deformity.

STUDY DESIGN: Retrospective study. OBJECTIVE: To demonstrate that intralaminar screws (ILS) can be used as supplements in spinal deformity surgery in the thoracic and lumbar levels in pediatric and adult patients. SUMMARY OF BACKGROUND DATA: Rigid posterior fixation of the spine is generally accomplished using pedicle screws, hooks, or wires. ILSs are useful tools when other spinal fixation techniques have failed or the bony anatomy precludes hook or screw placement. MATERIALS AND METHODS: All spinal deformity patients (primary/revision) operated between 2007 and 2011 were retrospectively reviewed. The patients with ILS were included in the study. The anteroposterior and lateral standing x-rays were evaluated in terms of preoperative and postoperative coronal and sagittal deformities. The number and level of ILS, intraoperative complications, and postoperative complications were noted. RESULTS: There were 20 patients (12 male and 8 female). The mean age was 21.75 years. The mean follow-up period was 17.4 months. Fifty-seven ILS were inserted. Seventeen screws were used in the uppermost to lowermost levels. Forty screws were used in the middle. There was 1 lamina fracture and screw pull out (1.75%). There were 3 canal violations (corrected intraoperative) and 2 instrument prominences which required implant removal. The mean preoperative/postoperative cobb angles were 78.5 degrees/27.8 degrees and the mean preoperative/postoperative kyphosis angles were 57.2 degrees/32.5 degrees, respectively. The loss of correction was 1.2 degrees. There were no neurological deficits and no instrument failures. CONCLUSIONS: ILS are safe and effective when used in deformity correction. However, biomechanical studies and randomized controlled trials are needed to conclude whether ILS will be considered a first-line technique, or will remain a technique for salvage situations.