brief review of pedicle screw fixation of thoracic and lumbar spine

1. DR. BEN TUNGOE
CENTRAL INSTITUTE OF ORTHOPEDICS,
SAFDARJUNG HOSPITAL; NEW DELHI
PEDICLE SCREWS FIXATION OF
THORACO-LUMBAR SPINE

2. LEARNING OBJECTIVES
 BRIEF ANATOMY OF THORACIC AND LUMBAR
VERTEBRA
 PEDICLE ANATOMY
 PEDICLE SCREW AND ITS PROPERTIES
 ENTRY POINTS FOR THORACIC AND LUMBAR
SPINE
 PECULARITIES IN UPPER THORACIC VERTEBRA
FIXATION
 DIFFERENT TECHNIQUES
 COMPLICATIONS
 TIPS FOR GOOD FIXATION

3. THORACIC VERTEBRA

4. THORACIC VERTEBRA
 TYPICAL VERTEBRA:
 medium-sized, heart shaped vertebral bodies
 medium-sized vertebral canals
 prominent transverse processes with costal facets
 long spinous processes angulating downwards
 ATYPICAL VERTEBRA:
 T1 and T9 to T12 are considered atypical
vertebrae. T1 bears some resemblance to low
cervical vertebrae. T9 has no inferior demifacet. T10
often, but not always, shares features with T11
and T12.

5. LUMBAR VERTEBRA

6. LUMBAR VERTEBRA
 body: kidney shaped, convex anteriorly, flattened posteriorly;
resulting vertebral canal is triangular in cross-section
 pedicles: project directly posteriorly, attached to the upper half
of the body
 transverse processes: spatulate, project laterally on both
sides; L3 most often has the longest transverse processes of
the lumbar spine, a fact that can be used to number the
vertebrae
 lamina: broad, thick, overlap minimally
 articular processes (superior and inferior): lie at the lateral
angle of the laminae (junction with pedicle), connected via the
pars interarticularis
 spinous process: single, short, thick, roughly
horizontal, hatchet-shaped (upper border is straight, lower
border curves down)
 L1 to L4 are considered typical lumbar vertebrae, whereas due

9.  The widest pedicles are at L5 and narrowest at T5 in
the horizontal plane.
 The widest pedicles in the sagittal plane were at T11,
and the narrowest are at T1.
 In the sagittal plane, the pedicles angle caudad at L5
and cephalad at L3-T1

12. Some noteworthy points to remember
 The respective facet joint space and the middle of the
transverse process are the most important reference
points.
 The pedicles of the thoracic and lumbar vertebrae
are tubelike bony structures that connect the anterior
and posterior columns of the spine.
 Medial to the medial wall of the pedicle lies the dural
sac.
 Inferior to the medial wall of the pedicle is the nerve
root in the neural foramen.
 The lumbar roots usually are situated in the upper
third of the foramen; it is more dangerous to
penetrate the pedicle medially or inferiorly as

13. PRE-OPASSESSMENT
Assess individual spinal anatomy by:
1.high-quality antero-posterior and lateral
radiographs of the lumbar and thoracic spine.
2. Axial CT at the level of the pedicle.

14. Commonly used techniques
 (1) the intersection technique,
 (2) the pars interarticularis technique,
 (3) the mammillary process technique

15. INTERSECTION TECHNIQUE
 The intersection
technique is perhaps
the most commonly
used method of
localizing the pedicle.
 It involves dropping a
line from the lateral
aspect of the facet
joint, which intersects a
line that bisects the
transverse process at
a spot overlying the
pedicle

16. Note:
 The pars interarticularis is the area of bone where
the pedicle connects to the lamina.
 Because the laminae and the pars interarticularis
can be identified easily at surgery, they provide
landmarks by which a pedicular drill starting point
can be made.
 The mammillary process technique is based on a
small prominence of bone at the base of the
transverse process.
 This mammillary process can be used as a starting
point for transpedicular drilling.
 Mamillary process starting point is lateral than the
intersection technique starting point, which also is
more lateral than the pars interarticularis starting
point.

17. LUMBAR SPINE: ENTRY POINTS

18. Lumbar pedicle screw entry points

19. THORACIC SPINE: ENTRY POINTS

21. STEPS: OPENING THE CORTEX

22. CRANIO CAUDALANGULATION

23. MEDIO LATERAL INCLINATION

24. SCREW INSERTION

26. T1-T3 PEDICLE SCREW FIXATION

27. GENERAL CONSIDERATIONS

28. PITFALLS

29. ENTRY POINTS

30. OPENING OF THE CORTEX

31. MEDIO-LATERAL INCLINATION

32. CRANIO-CAUDALANGULATION

33. CRANIO-CAUDALANGULATION

34. PREPARATION OF THE PEDICLE

35. SCREW INSERTION

39. BREACH OF THE PEDICLE

43. INCREASING PULL OUT STRENGTH
OF SCREWS

44. OTHER TECHNIQUES

48. PEARLS FOR GOOD FIXATION

49. PEARLS FOR GOOD FIXATION
 There are three basic concepts that are important to the
biomechanics of pedicle screw-based instrumentation.
 First, the outer diameter of the screw determines
pullout strength, while the inner diameter determines
fatigue strength.
 Secondly, when inserting a pedicle screw, the dorsal
cortex of the spine should not be violated and the
screws on each side should converge and be of good
length.
 Thirdly, fixation can be augmented in cases of severe
osteoporosis or revision.
 A trajectory parallel or caudal to the superior endplate
can minimize breakage of the screw from repeated axial
loading.
 Straight insertion of the pedicle screw in the mid-sagittal
plane provides the strongest stability.
 Rotational stability can be improved by adding
transverse connectors.

50. References:
 Campell’s Operative Orthopedics 12th Edition
 AO Surgical Reference
(https://www2.aofoundation.org/wps/portal/surgery)
 Spine Surgery-Tricks of the Trade; 3rd edition (Alexander R
Vaccaro)