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How Accurately do Inexperienced Surgeons Place Thoracic Pedicle Screws with the Free Hand Technique?

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Written by Richard M. Schwend, MD, Ryan Bergeson, Selina Silva and Stacey Delucia

Poster from the 2006 SRS Annual Meeting

Purpose: To evaluate with real time direct observation what are the common errors made and whether these errors are recognized while they are occurring when inexperienced surgeons learn to place thoracic pedicle screws.

Methods: Three orthopaedic resident surgeons inexperienced in the straight ahead freehand technique received an introductory teaching session and utilized published visual charts (Lenke 2004). Six adult spines were used to harvest intact vertebral body specimens with rib heads removed. Each vertebral body was mounted on a clear plexiglass frame with only the posterior surface anatomy visible to the surgeon. The resident surgeon verbalized all perceived anatomical violations. An observer recorded in real time the accuracy of gearshift probe, flexible probe, tap and screw placement. A critically perforated screw was defined as greater than 2.0 mm outside the confines of the pedicle wall.

Results: 137 pedicles in 68 intact vertebral body specimens were instrumented with either a 4.2 or 5.2 mm screw selected based on the perceived pedicle diameter. 61/137 (45%) screws were not fully within the pedicle, most commonly due to a narrow pedicle diameter and were typically a noncritical perforation (48/61 (77%) vs 14/61 (23%) critical perforation). There were 13/61 (22%) perforations that were not perceived by the surgeon to be outside the pedicle. A total of 4/137 (3%) screws were felt to be placed safely but were critically perforated medially (average 3.8mm). Several screws were simultaneously outside pedicle wall both medial and lateral.

Conclusion: Inexperienced surgeons utilizing anatomic straight ahead insertion of thoracic pedicle screws generally were able to be have perforations less than 2mm. Screws most commonly were perforated due to narrow pedicle diameter, not poor starting point or technique. Most perforations were recognized immediately by the operator during probing and did not lead to major screw misdirection.

** The FDA has not cleared a drug and/or medical device described in this presentation (i.e., the drug or medical device is being discussed in an (off-label use.)

Comparison of the SRS-24 Individual Domain and Question

Domain and Question		American (n=100)	Japanese
(n=100)	p-value	Mean Score (SD)	Mean
Score (SD)
	Total Pain Domain	3.7(±0.8)	4.3
(±0.4)	p<0.0001*
	General Self-Image Domain	4.0 (±0.7)	3.5
(±0.5)	p<0.0001*
	General Function Domain	3.9 (±0.6)	4.2
(±0.5)	p<0.005*
	Activity Domain	4.5 (±0.8)
4.9 (±0.3)	p<0.0001*

1. The degree of pain you experience regularly.		3.8 (±1.3)	4.6
(±0.7)	p<0.0001*

2. The most severe degree of pain over the last month.		3.6 (±1.4)	4.5
(±0.9)	p<0.0001*

3. How would you feel about spending the rest of your life?		2.2 (±1.2)	2.5
(±0.8)	p<0.005*

4. What is your current level of leisurely activity?		4.5 (±0.7)	4.9
(±0.5)	p<0.0005*

5. How do you look in clothes?		3.6 (±1.0)	3.5
(±1.2)	p=0.4842

6. Do you experience back pain at rest?		3.6 (±1.3)	4.6
(±0.7)	p<0.0001*

7. What is your current level of work/school activity?		4.5 (±0.9)
4.8 (±0.5)	p<0.001*

8. What medications are you currently taking for your back?		4.7 (±0.5)	4.99
(±0.1)	p<0.001*

9. Does your back limit your ability around the house?		4.3 (±1.3)	4.9
(±0.4)	p<0.0001*

10. Have you taken any sick time from work/school?		4.5 (±1.1)	4.9
(±0.4)	p<0.0001*

11. Does your condition negatively affect your personal relationships?		4.5 (±1.1)	4.8
(±1.0)	p<0.01*

12. Are you or your family experiencing financial difficulties?		4.7 (±0.7)	4.8
(±0.7)	p<0.05*

13. Do you get out more or less than your friends?		2.8 (±0.9)	3.0
±1.0)	p=0.0657

14. Do you feel attractive?		3.6 (±1.0)
2.7 (±0.9)	p<0.001*

15. How would you rate your self-image?		3.7 (±1.2)	2.9
(±0.8)	p<0.0001*