TABLE 3.

Sites of Iliac Vein Compression and Extent of thrombosis of Case Groups

Groups	Cases	Sites of IVC by DSA				Extent of Thrombosis by US
		Right Ahead of the L4–5 Disc*	Left Front of the L5	Right Ahead of the L5	Right Front of the L5	Limited to the Iliac Vein	Extended to the Femoral Vein	Extended to the Popliteal Vein
oMTS	22	4 (18%)	0	4 (18%)	14 (64%)	0	6 (27%)	16 (73%)
dMTS	33	9 (26%)	3 (9%)	18 (56%)	3 (9%)	6 (18%)	10 (30%)	17 (52%)
oIVCS	14	0	0	0	0	4 (29%)	6 (43%)	4 (29%)
Test	69	χ2 = 19.305, P < 0.001				— P = 0.033†

dMTS indicates low lumbar degeneration-related May-Thurner syndrome; DSA, digital subtraction angiography; IVC, iliac vein compression; oIVCS, other cause iliac vein compression; oMTS, May-Thurner syndrome; US, ultrasound sonography.

^*the L4–5 disc, the disc between the fourth lumbar and the fifth lumbar.

^†Fisher precise algorithm.