lewandrowski.qxp 24/4/08 10:09 Page 51
Pre-operative Planning for Endoscopic Lumbar Foraminal Decompression
outcome at final follow-up. Our success rate was similar to clinical
Figure 8: Clinical Outcomes with Entry Zone Stenosis Using
success rates
19
and to success rates reported by patients undergoing
Modified McNab Criteria
laminectomy for spinal stenosis.
20
8
The importance of pre-operative planning of transforaminal
endoscopic removal of herniated discs has been stressed by Lee et al.,
6
who suggested a classification based on the location of a migrated
disc fragment.
18
According to pre-operative sagittal MRI images, he
defined four zones depending on the direction and distance from the
4
disc space as follows: zone 1 – from the inferior margin of the upper
P
a
tients
pedicle to 3mm below the inferior margin of the upper pedicle; zone
2 – from 3mm below the inferior margin of the upper pedicle to
2
the inferior margin of the upper vertebral body; zone 3 – from the
superior margin of the lower vertebral body to the centre of the lower
pedicle; and zone 4 – from the centre to the the inferior margin of the
0
lower pedicle.
Excellent Good outcome Poor + fair
Over 50 Under 50
In this study we employed previously published radiographic
Note: clinical failures occurred significantly more frequently in patients over 50 years of age (see Table 2).
classification systems
14,15
in pre-operative decision-making for patients
Figure 9: Clinical Outcomes with Middle Zone Stenosis Using
with symptomatic foraminal stenosis, and correlated them with clinical
Modified McNab Criteria
outcomes according to the modified McNab criteria.
13
In 1988, Lee
published on a three-zone classification of the neuroforamen by
4
dividing it into entry, middle and exit zone.
14
In 1995, Hasegawa
defined the height of the neuroforamen of 5mm or more as normal.
15
3
He suggested that a reduced height of 3–4mm is suggestive of spinal
stenosis and that a height of 2mm or less is associated with nerve root
compression approximately 80% of the time. 2
P
a
tients
As demonstrated by this study, the application of radiographic grading
systems of foraminal stenosis may assist in selecting appropriate
1
surgical candidates for the procedure. Our results indicated that
patients with stenosis in the entry zone of the neuroforamen fared
0
worse than those with stenosis in the middle and exit zone. These Excellent Good outcome Poor + fair
types of stenotic lesions should perhaps be avoided until advanced
Over 50 Under 50
endoscopic instrumentation such as the Morgenstern endoscopic
Figure 10: Clinical Outcomes with Exit Zone Stenosis Using
spinal stenosis system become widely available. These newer Modified McNab Criteria
instrumentation sets include reamers, chisels and awls that may be
4
positioned under direct visualisation through the centre working
channel of the endoscope, and thus may allow a more sophisticated
endoscopic decompression.
3
Conclusion
Foraminal decompression is feasible through the percutaneous 2
P
a
tients
transforaminal endoscopic approach and works well in patients with
bony stenosis in the mid- and exit zone of the neuroforamen.
Decompressive surgery through a laminectomy approach should be
1
considered for neuroforaminal stenosis in the entry zone. Regardless
of the instrumentation, pre-operative classification of the
0
neuroforamen into three zones may prove useful in the pre-operative Excellent Good outcome Poor + fair
patient selection process. ■
Over 50 Under 50
1. Yeung AT, Yeung CA, Orthop Clin North Am, 2007;38(3): 8. Schubert M, Hoogland T, Oper Orthop Traumatol, 15. Hasegawa T, et al., J Bone Joint Surg Am, 1995;77(1):32–8.
363–72. 2005;17(6):641–61. 16. Kim MJ, et al., Surg Neurol, 2007;68(6):623–31.
2. Tsou PM, et al., Spine J, 2004;4(5):564–73. 9. Schaller B, Eur Spine J, 2004;13(3):193–8. 17. Ahn Y, et al., Spine, 2004;29(16):E326–32.
3. Tsou PM, Yeung AT, Spine J, 2002;2(1):41–8. 10. Mullin BB, et al., J Spinal Disord, 1996;9(2):107–16. 18. Lee S, et al., Eur Spine J, 2007;16(3):431–7.
4. Yeung AT, Yeung CA, Surg Technol Int, 2003;11:255–63. 11. Papagelopoulos PJ, et al., Spine, 1997;22(4):442–51. 19. Fokter SK, Yerby SA, Eur Spine J, 2006;15(11):1661–9.
5. Kambin P, et al., J Neurosurg, 1996;84:462–7. 12. Mullin BB, et al., J Spinal Disord, 1996;9(2):107–16. 20. Sengupta DK, Herkowitz HN, Orthop Clin North Am,
6. Kambin P, O’Brien E, Zhou L, Clin Orthop, 1998;347:150–67 13. Macnab I, J Bone Joint Surg Am, 1971;53:891–903. 2003;34(2):281–95.
7. Hoogland T, et al., Spine, 2006;15;31(24):E890–97. 14. Lee CK, et al., Spine, 1988;13(3):313–20.
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