Quantification of Multifidus Atrophy and Fatty Infiltration Following a Minimally Invasive Microdiscectomy

Ehsan Tabaraee; Junyoung Ahn; Daniel D. Bohl; Frank M. Phillips; Kern Singh

doi:10.14444/2025

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Fig. 1
41 year-old male presents with a herniated nucleus pulposus at L4-5. Preoperative axial T1-weighted MRI image demonstrates lean cross-sectional area measurements at the index level (L4-5).
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Fig. 2
Postoperative axial T1-weighted MRI image demonstrates total and lean cross-sectional measurements at the index level (L4-5).

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Table 1

Patient Characteristics, Operative Levels, and Timing for Primary 1-level MIS Lumbar Decompression.

	MIS (n = 24)
Age (Years, SD)	47.8 (14.2)
Female (n)	58.3% (14)
Operative Levels (%, n)
L2L3	4.2% (1)
L3L4	12.5% (3)
L4L5	58.3% (14)
L5S1	25.0% (6)
Time between Surgery and MRI
Preoperative MRI (Days, SD)	61.1 (55.4)
Postoperative MRI (Days, SD)	182.5 (194.4)

MIS: Minimally Invasive; SD: Standard Deviation; MRI: Magnetic Resonance Imaging.

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Table 2

MRI-Documented Changes in Multifidus Muscle Following Primary 1-Level MIS Lumbar Decompression.

	Ipsilateral
	Multifidus Total Cross Sectional Area (mm²)				Multifidus Lean Cross Sectional Area (mm²)
Level	Preoperative	Postoperative	% Change	pvalue	Preoperative	Postoperative	% Change	pvalue
Supra Disc	794.0±233.0	811.6±259.0	+2.0%	0.38	582.0±203.0	569.3±232.7	− 3.1%	0.52
Supra Pedicle	953.4±290.0	957.4±341.5	− 1.3%	0.91	688.1±283.2	660.5±270.0	− 2.9%	0.37
Index	1047.4±246.2	1000.3±238.7	− 4.9%	<0.01	726.2±234.4	680.4±221.6	− 6.2%	<0.05
Infra Pedicle	1148.3±288.9	1088.6±278.0	− 5.3%	0.08	738.0±234.1	641.7±213.2	− 13.0%	<0.01
Infra Disc ^†	1135.5±245.8	1117.3±269.1	− 1.6%	0.66	743.0±230.8	600.3±209.5	− 18.6%	<0.01
	Contralateral
	Multifidus Total Cross Sectional Area (mm²)				Multifidus Lean Cross Sectional Area (mm²)
Level	Preoperative	Postoperative	% Change	pvalue	Preoperative	Postoperative	% Change	pvalue
Supra Disc	787.9±224.5	778.3±212.7	− 0.5%	0.65	582.2±207.3	574.3±205.7	− 1.4%	0.57
Supra Pedicle	961.3±315.0	936.5±323.5	− 0.8%	0.52	714.4±283.2	673.8±267.0	− 4.4%	0.17
Index	1029.9±239.6	1021.5±213.9	+ 0.4%	0.71	707.1±206.1	671.6±193.3	− 4.2%	0.052
Infra Pedicle	1121.7±264.4	1138.7±282.3	+ 1.7%	0.52	721.7±216.1	706.2±204.5	− 0.1%	0.55
Infra Disc ^†	1117.4±215.4	1131.9±243.3	+ 1.1%	0.59	734.6±206.3	698.5±212.3	− 4.4%	0.15
	Ipsilateral
	Multifidus Psoas T1 Signal Intensity Ratio				Lean CSA to Total CSA Ratio
Level	Preoperative	Postoperative	% Change	pvalue	Preoperative	Postoperative	% Change	pvalue
Supra Disc	1.81±0.63	1.98±0.72	+ 26.0%	0.43	0.73±0.10	0.69±0.11	− 5.2%	<0.05
Supra Pedicle	1.91±0.69	2.06±0.80	+ 21.7%	0.53	0.71±0.14	0.69±0.10	− 1.5%	0.33
Index	2.23±0.91	2.27±0.89	+ 21.8%	0.90	0.69±0.11	0.67±0.12	− 1.2%	0.47
Infra Pedicle	2.35±0.93	2.68±1.20	+ 35.0%	0.32	0.65±0.12	0.59±0.11	− 8.4%	<0.01
Infra Disc ^†	2.76±1.24	3.42±1.82	+ 51.7%	0.25	0.66±0.14	0.55±0.16	− 17.2%	<0.001
	Contralateral
	Multifidus Psoas T1 Signal Intensity Ratio				Lean CSA to Total CSA Ratio
Level	Preoperative	Postoperative	% Change	pvalue	Preoperative	Postoperative	% Change	pvalue
Supra Disc	1.83±0.65	1.98±0.69	+ 22.6%	0.49	0.73±0.12	0.73±0.11	− 0.3%	0.59
Supra Pedicle	1.90±0.69	1.94±0.64	+ 15.2%	0.81	0.75±0.19	0.72±0.10	0%	0.41
Index	2.20±0.93	2.41±0.80	+ 33.9%	0.47	0.69±0.11	0.65±0.10	− 3.8%	0.09
Infra Pedicle	2.48±1.04	2.65±1.03	+ 27.9%	0.61	0.64±0.11	0.63±0.12	− 1.9%	0.37
Infra Disc ^†	2.80±1.31	3.24±1.75	+ 45.7%	0.44	0.66±0.13	0.62±0.14	− 5.3%	<0.05

↵† Patients whose operative levels included S1 were excluded from measurement at the inferior disc level. MIS: Minimally Invasive; MRI: Magnetic Resonance Imaging; Supra: Superior; Infra: Inferior; CSA: Cross Sectional Area.