The surgical learning curve and accuracy of minimally invasive lumbar pedicle screw placement using CT based computer-assisted navigation plus continuous electromyography monitoring – a retrospective review of 627 screws in 150 patients

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Fig. 1
Pedicle screw malposition and adjustment learning curve.
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Fig. 2
Intraoperative CT imaging after L5-S1 TLIF, demonstrating an inferior breach of the cortex of the S1 pedicle by <2mm.

Table 1

Surgical procedures.

Procedure	Number of patients	Procedure and level	Number of patients
Single level TLIF	124	TLIF – L3-L4	2
		TLIF – L4-L5	60
		TLIF – L5-S1	62
2 level TLIF	15	TLIF – L3-L5	1
		TLIF – L4-S1	14
Single level PLIF	5	PLIF – L4-L5	1
		PLIF – L5-S1	4
Posterolateral fixation	6	Postero-lateral Fixation – T11-L1	1
		Postero-lateral Fixation – L4-L5	2
		Postero-lateral Fixation – L5-S1	1
		Postero-lateral Fixation – L4-S1	2
Total cases	150		150

Table 2

Complication learning curve – Pedicle access trajectory malposition and adjustment due to EMG monitoring.

	First 50 April 2008 – Mar 2010	Second 50 May 2010 – August 2011	Third 50 Sept 2011 – October 2012	Total
Cases adjusted due to EMG	8/50 cases = 16%	6/50 cases = 12%	3/50 cases = 6%	17/150 cases = 11.3%
Pedicle access trajectories adjusted due to EMG	9/216 screws = 4.2%	7/209 screws = 3.3%	3/202 screws = 1.5%	19/627 screws = 3.0%

Table 3

Complication learning curve – Screw malposition and adjustment due to intraoperative CT.

	First 50 April 2008 – Mar 2010	Second 50 May 2010 – August 2011	Third 50 Sept 2011 – October 2012	Total
Screws adjusted due to CT	4/216 screws = 1.9%	3/209 screws = 1.4%	1/202 screws = 0.5%	8/627 screws = 1.3%
TOTAL adjusted trajectories + Screws (EMG + CT)	11/216 screws = 5.1%	9/209 screws = 4.3%	4/202 screws = 2.0%	24/627 screws = 3.8%

Note: Some adjusted screws were malpositioned on intraoperative CT, as well as EMG signal positive.