Zi-xiang Wu MD

Purpose. To investigate the clinical abstractnd radiographic outcome of multi-axial expandable pedicle screws (MEPS) in patients with osteoporosis. Methods. One hundred and twenty-!ve consecutive patients received MEPS from the UPASS spinal !xation system to obtain thorocolumbar or lumbosacral stabilization. All patients underwent bone mineral density (BMD) scans. "e indications for use of the MEPS were spinal diseases with severe osteoporosis (degenerative diseases 46 cases, compression fractures 28 cases, lumbar tuberculosis 27 cases and revision spine surgery 24 cases). "e pre-operative and three months post-operative functional evaluations were graded with JOA and VAS scoring system. One week, six months and 12 months a#er surgery, plain !lm and three-dimensional CT scans were obtained to evaluate the spinal fusion and !xation e$ectiveness of MEPS. Results "e mean follow-up period was 18 months (ranged from 6 to 33 months). All patients su$ered from severely osteoporosis with a decrease of 25.3% in BMD. "e preoperative JOA and VAS scores were 11.3±3.0 and 6.7±1.8 mm, respectively. "ree months a#er operation, the JOA and VAS scores were 25.2±2.0 and 2.3±1.7 mm. "e recovery rate was 78.1±11.5% and the clinical results were satisfying. "ere were no instances of screw loosening or pullout of the MEPS and the screw-bone interface was excellent. "e radiographic results showed that bone healing, both around the screws and inter-vertebral, was achieved. Conclusion In osteoporosis spine surgery, excellent bone-screw interface and !xation strength can be achieved by using MEPS. MEPS are a novel approach to increase the pedicle screw !xation in osteoporotic and revision spine surgeries. ORIGINAL RESEARCH © 2010 CIM Clin Inv E368 Correspondence to: Professor Hong-xun Sang Institude of Orthopaedics, Xijing Hospital, No.17 Changlexi Road, Xi’an Shaanxi Province P.R.China 710032 Fax: 86-29-84771012 E-mail: [email protected] Clin Invest Med 2010; 33 (6): E368-E374. !e transpedical "xation technique is the most important and useful method in the posterior "xation of the spine. It can be inserted into virtually any level of the thoracic and lumbar spine and provides three-column stability. !e "xation strength of the pedicle screws depends on the bone mineral density so e#cacy of the pedicle screw in patients with low bone density is a concern. Among the elderly patients, osteoporosis is the most common metabolic bone disorder. Osteoporotic patients requiring spinal instrumentation as treatment for instability or deformity are in high risk of internal "xation failure. Surgical remedies currently in practice include increasing the diameter and/or length of the pedicle screw [1] or, in cases of severe bone loss, "lling in the void with such materials as polymethylmethacrylate (PMMA) or calcium phosphate cement (CPC) [2-4]. !ese strategies, however, have numerous drawbacks, including increased risks of pedicle fracture with resultant neural injury with larger screws, anterior body penetration with ensuing vascular or visceral injury with longer screws [5], or problems associated with a non-absorbable foreign body in the spinal canal [6-8]. A better solution for increasing pedicle screw "xation may be the use of an alternate screw design. Cook et al. [9] have developed expandable pedicle screws (Omega21 spinal "xation system, EBI, L.P., Parsippany, New Jersey) that could increase the bone "xation strength signi"cantly, especially in the osteoporotic spine. Clinical results showed that the expandable screws are ideal in problematic situations of bone compromised by osteoporosis or pedicle screw revision, providing clinical results similar to those expected in normal bone and primary surgery [10]. !e Omega21 spinal "xation system, however, has a uniaxial-designed that is limited by the spine curvature and requires more operation technique and clinical experience than conventional screws. Multi-axial heads have made the pedicle screw more versatile, particularly improving ease of connecting rod application; however, there are no published reports describing the use of multi-axial expandable pedicle screws (MEPS). !e purpose of this study was to investigate the clinical and radiographic outcomes of MEPS in patients with osteoporosis. !e attainment of solid fusion was evaluated using dynamic radiographs, as well as three-dimensional CT, to evaluate its clinical stability and reliability. Complications related to the instrumentation were also evaluated. Materials and Methods !e newly designed MEPS (Shandong Weigao Orthopedic Device Co., Limited, Shandong, China) is barrel-shaped, with an outer diameter of 6.5 mm (and 7.0 mm), a 2.5 mm bore and a 3 mm pitch. MEPS has a curvate head, a two-piece interlocking coupling element that mounts about the curvate head, and a rod-receiving cylindrical body with a tapered socket into which both the screw and the interlocking coupling element are securely nested. !e anterior half of the screw is split lengthwise by a groove to form two anterior "ns. A smaller gauge can be inserted into the interior of MEPS and opens the "ns concentrically as it is advanced: this system increases the diameter of the expanding screw tip by approximately 2.0 mm (Fig. 1). !e diameter of the posterior portion of the screw remains constant in order to prevent the fracture of the pedicle during the expansion of the screw.