PEEK versus Silicon Interspinous Spacer for Reduction of Supradjacent Segment Degeneration following Decompression and Short-Segment Instrumentation for Degenerative Lumbar Spinal Stenosis

Table 4

Pfirrmann degeneration grade in MRI in the supradjacent segment preoperatively till the final observation.

Group	Preoperatively		Postoperatively (>3 years postop)
	II	III	II	III	IV	V
R (n=17)	8	9	8	7	0	2
S (n= 18)	7	11	7	9	1	1
C (n=20)	8	12	8	8	2	2

Cases with symptomatic ASD.