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Pedicle screw fixation in osteoporotic fractures
This document discusses strategies for improving pedicle screw fixation in osteoporotic bone. It describes the advantages of pedicle screw constructs but notes their risk of failure in osteoporosis due to poor bone quality compromising screw fixation. It then presents a novel technique of using fenestrated, cement-augmented pedicle screws that allows cement injection through the screw after placement to strengthen fixation. Comparative studies show this technique increases pullout strength while decreasing the risks of cement leakage compared to traditional cement augmentation. The document concludes by discussing other approaches like expansive screws, bicortical purchase, and multiple levels of fixation that can further improve construct stability in osteoporotic patients.
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Introduction to spinal arthrodesis using pedicle screws in osteoporosis presented by Mohamed Mohi Eldin, MD.
Discusses the advantages of pedicle screw constructs: three-column fixation, short-segments instrumentation, and maintaining sagittal alignment.
Emphasizes that the key to performance is the strength of attachment to the spine, highlighting the need for solid fixation in quality trabecular bone.
Describes how aging affects bone mineral density (BMD), a key factor in spinal instrumentation failure, noting that poor BMD compromises screw fixation.
Stresses the inevitability of needing spinal decompression and stabilization in cases of osteoporosis and poor bone quality.
Introduction to the topic of secondary osteoporosis and its relevance.
Performance issues in osteoporotic patients, including complications like screw loosening and high failure risk due to screw pullout.
Methods to improve screw fixation in osteoporotic bone: cement augmentation, multiaxial screws, bicortical and iliac screws, among others.
Introduction of canulated, fenestrated, augmented screws and old attempts to enhance fixation through cement diffusion before screw insertion.
Describes complications of injecting PMMA, including thermal damage, difficulty in removal, and neurologic risks.
Proposes a novel concept of injecting PMMA through fenestrated screws to optimize cement distribution.
Discusses surgical planning for different techniques and shares important positions to avoid leakage during cement injection.
Details techniques for cement delivery, including viscosity management and fluoroscopic control to prevent leakage.
Combining techniques: discusses cement volumes for thoracic and lumbar screws with focus on safe injection practices.
Underlines importance of screw alignment and positioning for effective cement distribution and avoiding breaches.
Conducts comparative analysis between augmented fenestrated screws and standard screws, highlighting strength and safety.
Evaluates clinical safety comparing fenestrated vs. traditional techniques, emphasizing reduced risk of complications.
Analyzes cement leakage in traditional techniques vs. operatively efficient fenestrated technique, which allows easier screw placement.
Highlights the benefits of the fenestrated technique in terms of efficiency and presents tips to prevent extravasation.
Discusses the ergotropic effects of bone cement, including stability strengthening and other positive outcomes as compared to extended instrumentation.
Presents how expansive pedicle screws function and stresses the role of cement augmentation in improving pullout strength.
Explains bicortical screw benefits for improving strength and the associated risks of anterior structure damage.
Focuses on hydroxyapatite coating on screws to enhance screw-bone contact and pullout strength.
Explores the potential of using double screws in cadaver studies to improve fixation in osteoporotic vertebrae.
Discusses the benefit of multilevel constructs and extension of fusion to reduce failure risks.
Presents various case studies including spondylolisthesis and burst fractures, showcasing surgical techniques used.
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Pedicle screw fixation in osteoporotic fractures
- 1. Spinal Arthrodesis Using PedicleScrews in Osteoporosis Mohamed Mohi Eldin, MD, Professor of Neurosurgery, Faculty of Medicine, Cairo University, Egypt.
- 2. Pedicle Screw Constructs •Advantages: 1) Three-column fixation, 2) short-segments instrumentation, 3) Maintain sagittal alignment.
- 3. Performance of PedicleScrew Systems The key is strength of attachment to spine. Solid fixation (when screws are placed in dense, good-quality trabecular bone)
- 4. Aging population • Bonemineral density (BMD) is one of main factors related to spinal instrumentation failure. • In vitro: poor BMD compromises screw fixation.
- 5. For a spinesurgeon It is unavoidable to require spinal decompression & stabilization for osteoporosis or other decreased bone quality
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- 7. Performance of pediclescrews In osteoporotic patients potential complications screw loosening, migration, or pullout, compromising outcome Screw-bone interface stripped easily during screw tapping and insertion
- 8. Pedicle screws useis relatively contraindicated in osteoporosis because of: • High risk of failure (screw pullout) • Damage caused by such pullouts can complicate revision surgeries.
- 9. How to improvepedicle screw fixation in osteoporotic bone 1. Augmentation with cement 2. Multiaxial expandable pedicle screw 3. Bicortical sacral screws for the sacrum 4. Bilateral iliac screws for the pelvis 5. Hydroxyapatite Coating of screws 6. Double screws (Only in cadavers) 7. Multiple levels 8. Increase points of fixation
- 10. Spinal Arthrodesis Using Cannulated,Fenestrated, Augmented Screws
- 11. Old Attempts To enhancepedicle screw fixation Passive diffusion of cement into the vertebral body and pedicle immediately prior to screw insertion
- 12. Injecting PMMA throughthe pedicle before inserting the screw • Time consuming • Screws not designed to be used with PMMA • Risk of PMMA leakage
- 13. PMMA traditional techniqueRisks • Extravasation (fractured cortex) • Thermal damage, • Difficult removal, • Potential for major neurologic compromise • Rare fatal fat embolism
- 14. However • Time couldbe diminished • Avoidance of extrusion could be done by Altering delivery of PMMA through a fenestrated pedicle screw.
- 15. Cannulated Screw withDistal Fenestrations (a novel-concept) After screw insertion, cement can be injected and will distribute evenly around the thread of the screw
- 16. The cement isextruded through the fenestrations to fill the spaces inside the osteoporotic cancellous bone; Under fluoroscopic guidance
- 17. Depending on thesurgical plan Either – A pure bilateral percutaneous pedicle screw arthrodesis – A combination of unilateral percutaneous with a contralateral miniopen (modified Wiltse).
- 18. For the PurePercutaneous Fenestrated Screw Placement The position of holes, as far as possible from posterior wall (to prevent leakage)
- 19. After augmentation, changeof screw position is no longer possible Trial of placement of the rod should be done before cement injection to avoid positioning issues after cement injection.
- 20. • PMMA bonecement is delivered through – the cement cannula within the screws – Cement delivery system connected by connector. • To prevent cement leakage, the injection is done in a higher viscosity state (started 5 minutes after mixing).
- 21. • Injection mustbe done under fluoroscopic control to immediately stop the injection in case of cement extravasations – anterior, – posterior, or – into an adjacent disc
- 22. Test, Try, Inject,Fix & Lock
- 23. For combination ofunilateral percutaneous with a contralateral Miniopen Techniques When a central canal decompression or an interbody fusion (LIF) is planned
- 24. Cement Volume injected intoeach screw • Varies from 1.5 to 3mL. – The ideal amount is 2mL. – The safer amount • 1.0 cc for the thoracic spine • 1.5 cc for the lumbar spine • Greater volume did not lead to higher pullout strength.
- 25. An optimal positioningof the fenestrated pedicle screws • The length of screw is important, as far as possible from the posterior wall. • Placed in middle of pedicle to avoid cortical breaches • An optimal alignment with pedicle with good convergent trajectory.
- 26. The Location &Dispersion of Cement • The fenestrations, whether partial or full, led to a more optimal distribution of cement inside the vertebrae
- 27. Typical bone cement distributionin lumbar spine Micro-CT showing the interdigitation of the bone cement within the vertebral body
- 28. When compared withstandard pedicle screws without PMMA Augmented fenestrated screws showed increased pullout strength in osteoporosis
- 29. When Compared to TraditionalTechnique • Cement injection increases pull-out strength (200%) in both • The fenestrated cement technique required more power until failure Cross-section
- 30. Comparing Clinical Safety •The fenestrated technique decrease the risk of nerve injury significantly – small numbers of pedicle wall violations – no extrusion of cement into spinal canal • Medial wall violations in traditional delivery technique with PMMA extrusion into the canal.
- 31. Comparing location ofcement • In the fenestrated technique, the cement confined to vertebral body with NO proximal migration (screw as a plug) • Even in the presence of pedicle wall violation during insertion.
- 32. Cement Leakage in traditionaldelivery technique The PMMA is pushed against the walls of the pedicle during screw insertion, allowing cement to extrude from any violation into spinal canal.
- 33. Operative efficiency ofthe fenestrated delivery technique • In traditional technique, – Number of pedicle screws is limited by how fast the cement hardens vs. how fast a surgeon can place screws by hand. • In fenestrated technique, – all screws are placed prior to mixing the cement so cement is injected through pre-placed screws much easier.
- 34. The fenestrated techniqueappears to save both time and money
- 35. 7 Tips toprevent cement extravasations 1. Optimal positioning of screws 2. Good preoperative CT planning (to select correct diameter) 3. No injection if: – Breaches suspected – Bicortical screw fixation 4. Start injection when high viscosity obtained 5. Injection under fluoroscopic control (immediate control) 6. Controlled delivery system 7. Avoid to inject high volume of cement
- 36. Despite this caution 33%of radiological cement extravasation; however, non-symptomatic
- 37. Avoid breakage ofthe cement bridges between the screw & bone • Before injecting cement: – Fixation system locked – Rods tested in position • After injecting cement: – No torsion movement should be applied to screws
- 38. Ergotropic effects ofbone cement on pedicle screw fixation • Strengthen screws stability (long-term) • Restore height of vertebra • Reduce canal compression • Correction of kyphosis • Neurological function recovery. • Reduce screw loosening and vertebral collapse.
- 39. Cement augmentation versus extendedinstrumentation Lengthening instrumentation results in higher increase of stability during fatigue testing in osteoporotic spine compared with cement augmentation.
- 40. Failure of Cement- Augmented Pedicle Screwsin the Osteoporotic Spine
- 41. Expansive Pedicle Screwsfor Severe Osteoporosis before and after expansion
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- 43. Expansive screws afterexpansion (A) 6-slit screw with 16-mm EEL (B) 6-slit screw with 22-mm EEL.
- 44. • Increase inboth the number of slits and the extent of screw expansion had little impact on the screw-anchoring strength. • Cement augmentation is the most influential factor for improving screw pullout strength for expansive pedicle screws. The Effects of Screw Design and Cement Augmentation
- 45. Various cemented screws afterpullout tests Left to right: • solid, • 4-slit with 16-mm, • 4-slit with 22-mm, • 6-slit with 16-mm, • 6-slit with 22-mm.
- 46. Bicortical purchase • Thecortex is stronger than cancellous bone in normal and osteoporotic vertebrae, • Logically stronger than cortical-cancellous purchase, • Improve pullout strength from 20% to 50%, depending on – patient’s vertebrae, – screw dimensions, – screw type
- 47. Bicortical screw increasesrisk of damage to various anterior structures usually used only at the S1 level (avoiding damage to the aorta and vena cava)
- 48. Hydroxyapatite Coating ofscrews • Improving pedicle screw-bone contact, • Improving bone ingrowth, and mineralization • Increasing screw pullout strength • Require significantly greater insertional torque than uncoated screws
- 49. Double screws (Only incadaveric studies) Because pedicles of osteoporotic vertebrae are often larger than those of non-osteoporotic vertebra, it may be possible to implant two small-diameter pedicle screws into one pedicle to improve fixation.
- 50. Multiple levels andpoints of fixation • Cement augmentation of most rostral pedicle screws can also help avoid failure in multilevel constructs • Extension of the fusion to the sacrum/ilium can reduce the potential high risk for failure of constructs ending with pedicle screws at L5.
- 51. Case Presentations Miniopen correction/reductionof 2nd degree L4,5 Spondylolithesis in osteoporotic with Interbody cage & Augmentation of Fenestraed Screws
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