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PREVENTION OF IMPLANTS FAILURE IN SPINE SURGERY NOV..2022.ppt

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PREVENTION OF IMPLANTS FAILURE IN SPINE SURGERY NOV..2022.ppt

  1. 1. George Sapkas Emeritus Professor of Orthopaedics Prevention of Implants Failure in Adult Scoliosis Surgery
  2. 2. Spino – Pelvic Parameters
  3. 3. Incidence Angle (Duval-Beaupere) Normal Values No 709 subjects PI= 52.60 +- 10.4 (31 to 83.5) PT= 13 +- 6.8 SS=39.6 +- 7.9 There is no difference between Men and Women Normal Values PT should be <PI/2 SS should be > PI/2 Interpretation of Pelvic Parameters Anatomical Constant. Every one has his/her own Pelvic Incidence Angle for the whole life. (Stops Increased after Skeletal Maturity) It is a characteristic of the Sagittal width of Pelvis There is no good or bad PI
  4. 4. Gravity line and Sagittal Vertical Axis (SVA) Femoral head S1 Gravity Line Center of Gravity C7 Plumb SVA
  5. 5. Sagittal-Coronal balance - imbalance S1 Coronal imbalance Sagittal imbalance
  6. 6. Goals of surgical treatment • Restoration of sagittal and coronal balance in a patient with fixed spinal deformity • Achievement of solid arthrodesis • Rigid internal fixation to permit a brace- free mobilization • Relief of axial and radicular pain Devlin J.V., Surg. Techn. Odf the spine 2003
  7. 7. • The surgical treatment of sagittal and coronal imbalance is complex and demanding. • Long instrumentations and vertebral osteotomies are frequently needed to restore balance of the spine.
  8. 8. • Different types of vertebral osteotomies can be performed these include: o Ponte osteotomy (PO) o Smith–Peterson osteotomy (SPO) o Pedicle Subtraction Osteotomy (PSO) o Posterior Vertebral decancellation osteotomy (eggshell decancellation) o Posterior Vertebral Column resection (PVCR). o Anterior Osteotomy(ies) and Posterior Corrective osteotomy(ies) and stabilization
  9. 9. • A high rate of complications can be anticipated, especially when PSO or PVCR are performed: o reaching short-term rates of nearly 30 % and o different patterns of long-term failures and complications. PSO Keith H. Bridwell, et al Spine 2003
  10. 10. Implants Failure
  11. 11. • The literature related to: o Complications o failures o revisions • after surgery for sagittal and coronal imbalance is scarce. Failures and revisions in surgery for sagittal imbalance: analysis of factors influencing failure P. Berjano et al, Eur Spine J. 2013 Sagittal Decompensation After Corrective Osteotomy for Lumbar Degenerative Kyphosis Sang-Hun Lee, MD, et al, Spine 2011 Complications and Outcomes of Pedicle Subtraction Osteotomies for Fixed Sagittal Imbalance Keith H. Bridwell, et al Spine 2003
  12. 12. Insufficient correction P. Berjano et al, Eur Spine J. 2013 Davis L. Reames, MD, et al Spinal Disord Tech 2015 PJK Spondylodesia bellow the top of kyphosis
  13. 13. • The final sagittal balance obtained with surgery is a key factor in determining the success of the procedure. • Sagittal balance has been evaluated with these parameters: o Pelvic tilt o Gravity line and SVA 7.5cm
  14. 14. • A patient with an anteriorly displaced gravity line has, as a consequence: o increased mechanical stress on the posterior implant: o the translation of the mass anteriorly causes a)an increase in the moment arm of the trunk mass with respect to the rod. b) increasing the cyclic bending stress on it.
  15. 15. • Muscular fatigue o causes pain in a long-term muscular work, and o the deterioration of sagittal imbalance • can lead to a fatigue or • breakage of the implant.
  16. 16. 1year pop Additionally, • a) Tensile forces (that are worst resisted by the rods compared to neutral or compression forces) are increased posteriorly. • b) Tensile forces through the posterior graft cause bone resorption and reduce the chance of obtaining solid fusion
  17. 17. • A practical consequence is the need to perform o an adequate preoperative planning, with calculation of the site and o the amount of correction necessary to restore the position of the gravity line related to the spine.
  18. 18. • Intra-operative measurement of the amount of correction obtained before final tightening of the implants is necessary. • In most cases extra manipulation needed to obtain the desired correction.
  19. 19. Posterior column discontinuity in PSO P. Berjano et al, Eur Spine J. 2013
  20. 20. • The Pedicle Subtraction Osteotomy (PSO) is a very effective technique to increase lordosis. • With this wedge osteotomy it is possible to obtain a correction of as much as 35o per osteotomy site. 35o PSO
  21. 21. • Though it is a very powerful option to improve lumbar lordosis, PSO shows some limits. • One of these is the wide resection of the posterior bony elements needed to perform the osteotomy. Ibrahim Obeid et al Eur. Spine J. 2012
  22. 22. • This often results in a lack of continuity of the posterior elements. • This gap in the posterior column after the correction o can cause a failure of the postero-lateral fusion process, because o insufficient bony bed can be available to incorporate bone graft at the level of osteotomy Ibrahim Obeid et al Eur. Spine J. 2012
  23. 23. • An additional factor of instability is o the combination around the osteotomy level • the lack of continuity of posterior elements with • intact (flexible) discs around. Ibrahim Obeid et al Eur. Spine J. 2012
  24. 24. • This represents a scenario: o of huge instability o concentration of mechanical stress, o with stiff and long constructs above and below the osteotomy site and o an unprotected area where the rods take most of the mechanical stress at the osteotomy level. Ibrahim Obeid et al Eur. Spine J. 2012
  25. 25. Furthermore, after a PSO a)the osteotomized vertebral level cannot be instrumented with * pedicle screws, * sublaminar wires * hooks, bringing another factor of instability. b)If pseudoarthrosis occurs, the rods will inevitably break because o of cyclic load o and fatigue stress
  26. 26. Rod diameter P. Berjano et al, Eur Spine J. 2013
  27. 27. • The rods used in the degenerative pathology have been originally designed for adolescent deformity surgery. • The 5.5 mm diameter rods provide: o an adequate resistance to correction maneuvers during surgery and o can be easily bent in lordosis to connect the screws after PSO. 5.5 mm 6 mm
  28. 28. • The 6 mm diameter rods o have a greater stiffness and o resistance to breakage.
  29. 29. • The increased stiffness is insufficient when fusion is not obtained. • The continuous stress on the rods: o in case of post-operative unbalanced spine or o in case of pseudoarthrosis leads in any case to rod breakage.
  30. 30. Pe. Ag. F 72 3/10/22 1 yr F-up • Instrumentation will fail o if balance and o fusion are not obtained after surgery. • Six millimeter Co – Cr rods or double rods are however preferred in this kind of surgery, because of their greater resistance to fatigue stresses.
  31. 31. • Probably o a specific instrumentation for degenerative spine surgery, o with new materials o and geometry could improve the resistance of the rods, leading to a greater resistance to stresses. Titanium rod Co- Cr rod
  32. 32. Rod bending P. Berjano et al, Eur Spine J. 2013
  33. 33. • In order o to engage the rods on the screws o to provide adequate correction, o the surgeon frequently needs to perform an aggressive bending of the rods at the level of the osteotomy from straight rods.
  34. 34. • In specific cases like PSO o at the L4 level (the most frequent preference currently to reproduce the physiological curvature of the lumbar spine, that concentrates most of the lordosis between L4 and S1) o typically requires bending the rod nearly 90o in a short 4-cm segment.
  35. 35. • A short radius bending of the rod causes o compressive stress in the concavity and o distractive stress in the convexity, which can cause stress risers to form. Tensile forces Compressive forces
  36. 36. • The combination o of a short radius bending, o lever marks, o distractive forces, o increased flexion moment arm on the rod and o reduced stiffness of the spine at the level of the osteotomy o is probably the cause of the high observed incidence of rod breakage.
  37. 37. Insufficient distal foundation P. Berjano et al, Eur Spine J. 2013
  38. 38. Distal foundation 1st sacral vertebra
  39. 39. Distal foundation 1st sacral vertebra and Interbody Cages Diverted sacral screws TLIF S1 L2 TLIF L5 L4 L3
  40. 40. • Current strategy includes pelvic instrumentation in all cases of sagittal imbalance correction with surgery extending to S1. • This increases the lever on the pelvis and allows for more aggressive correction of the loss of lordosis, without increasing the risk of acute intraoperative or delayed failure of the fixation at S1
  41. 41. a)The different orientation in the axial plane of the divergent pelvic screws b)with respect to the S1 convergent screws c)is the key in increasing pullout resistance of the construct. Darryl Lau et al, Spine 2014
  42. 42. Proximal Junctional Kyphosis
  43. 43. Spinal deformities (Kyphosis – Scoliosis) related to osteoporosis
  44. 44. 82 82
  45. 45. Kyphotic deformity
  46. 46. Ponte osteotomies
  47. 47. Sacral – Iliac fixation
  48. 48. Tether system Hook Screws
  49. 49. Cemented vertebrae and double rods
  50. 50. Cemented vertebrae above spondylodesia
  51. 51. Conclusions
  52. 52. • Patients with o an SVA correction of 4cm with surgery did not need revision surgery o whereas those with PJK requiring revisions had SVA > 8 cm Han Jo Kim et al, Spine 2014 4.7cm
  53. 53. • Patients with insufficient correction had: o Sagittal Vertical Axis higher than 5 cm o Pelvic Tilt higher than 20o.
  54. 54. • Patients with Proximal Junctional Kyphosis (PJK) requiring revision o were older and o had higher postoperative lumbar lordosis (LL) and o larger SVA corrections than patients without PJK Han Jo Kim et al, Spine 2014 Darryl Lau et al, Spine 2014 Kyphoplasty
  55. 55. • In adult scoliosis, a)older patients with large corrections in their LL and SVA • b)were at high risk for developing PJK, • c)requiring revision surgery. Han Jo Kim et al, Spine 2014
  56. 56. • Long fusions, • a)often associated with vertebral osteotomies, b)are needed to restore an adequate alignment of the spine. P. Berjano et al, Eur. Spine Journal 2013
  57. 57. • Many factors can have a role o in the final outcomes and o can influence the risk of failure, o with need of revision surgery. P. Berjano et al, Eur. Spine Journal 2013 imbalanced balanced
  58. 58. • Adequate o preoperative planning and o calculation of the amount of correction needed is of paramount importance, o as is intra-operative measurement to assure the final achievement of planning. P. Berjano et al, Eur. Spine Journal 2013
  59. 59. • The choice of o rod diameter and o rod alloy and o a careful contouring, avoiding the creation of stress risers, P. Berjano et al, Eur. Spine Journal 2013
  60. 60. o restoration a)of bone continuity b)both in the posterior and anterior column, P. Berjano et al, Eur. Spine Journal 2013
  61. 61. o solid distal foundation with iliac screws in fusions extending to the sacrum, o are suggested to increase the chance of success. P. Berjano et al, Eur. Spine Journal 2013
  62. 62. • In future, design of specific implants for this pathology can provide o increased stability and o fusion rate. P. Berjano et al, Eur. Spine Journal 2013

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