abstract
Paraspinal Muscle Atrophy After Lumbar
Spine Surgery
S
inaP
ourtaheri, MD; K
iMonai
SSa, MD; e
lizabethl
orD, MD; r
eMia
jiboye, MD; a
uStinD
rySch;
K
ih
wang, MD; M
ichaelF
aloon, MD; K
uMarS
inha, MD; a
raShe
MaMi, MD
P
araspinal muscles are commonly affected during spine surgery.1 This is partly due to retraction or dissec-tion techniques, which can potentially re-sult in iatrogenic denervation, ischemic or thermal damage, and progression to even-tual atrophy of the paraspinal muscles.1-4 This may lead to pain and instability and contribute to poor clinical outcomes,in-creased morbidity, and surgical failures requiring revision surgery, which is an additional challenge for the treating sur-geon. Furthermore, disuse of the paraspi-nal muscles as a consequence of a lumbar fusion may also contribute to postopera-tive paraspinal muscle atrophy (PMA).1-3,5 Some authors have suggested that be-cause paraspinal muscles are supplied
by the posterior rami of the spinal nerves and do not have intersegmental innerva-tion, injury to these nerves potentially damages all the muscle bundles they in-nervate.6 Several studies have introduced surgical modifications to attempt to pre-serve the posterior rami and minimize potential postoperative PMA.4,5,7-12 These include modifying incision length, ex-posure techniques, retraction, and screw trajectory and using lower electrocautery settings.7-12 However, to the current au-Paraspinal muscles are commonly affected during spine surgery. The
pur-pose of this study was to assess the potential factors that contribute to para-spinal muscle atrophy (PMA) after lumbar spine surgery. A comprehensive review of the available English literature, including relevant abstracts and references of articles selected for review, was conducted to identify studies that reported PMA after spinal surgery. The amount of postoperative PMA was evaluated in (1) lumbar fusion vs nonfusion procedures; (2) posterior lumbar fusion vs anterior lumbar fusion; and (3) minimally invasive (MIS) posterior lumbar decompression and/or fusion vs non-MIS equivalent pro-cedures. In total, 12 studies that included 529 patients (262 men and 267 women) were reviewed. Of these, 365 patients had lumbar fusions and 164 had lumbar decompressions. There was a significantly higher mean post-operative volumetric PMA with fusion vs nonfusion procedures (P=.0001), with posterior fusion vs anterior fusion (P=.0001), and with conventional fusions vs MIS fusions (P=.001). There was no significant difference in mean volumetric lumbar PMA with MIS decompression vs non-MIS decompres-sion (P=.56). There was significantly higher postoperative PMA with lumbar spine fusions, posterior procedures, and non-MIS fusions. [Orthopedics.]
The authors are from UCLA/Orthopaedic In-stitute for Children (SP, EL, RA, AD), Department of Orthopaedic Surgery, David Geffen School of Medicine at UCLA, Santa Monica, California; and the School of Health and Medical Sciences (KI, KH, MF, KS, AE), Seton Hall University, South Orange Village, and the Department of Or-thopaedic Surgery, Saint Joseph Regional Medi-cal Center, Paterson, New Jersey.
Dr Pourtaheri, Dr Issa, Dr Lord, Dr Ajiboye, Mr Drysch, Dr Faloon, and Dr Sinha have no relevant financial relationships to disclose. Dr Hwang is on the speaker’s bureau of DePuy. Dr Emami is a paid consultant for and is on the speaker’s bureau of DePuy.
Correspondence should be addressed to: Sina Pourtaheri, MD, UCLA/Orthopaedic Institute for Children, Department of Orthopaedic Surgery, David Geffen School of Medicine at UCLA, 1250 16th St, Ste 3145B, Santa Monica, CA 90404 (spourtah@gmail.com).
Received: August 1, 2014; Accepted: Febru-ary 4, 2015.
thors’ knowledge, no previous study has attempted to quantify the amount of re-ported postoperative PMA or its potential contributors. Therefore, a systemic review may be valuable to inform spine surgeons and patients about the postoperative PMA phenomenon and the risk factors for post-operative PMA.
The purpose of this study was to assess the potential factors that contribute to PMA by examining the available literature on the topic. The amount of postoperative PMA was evaluated in (1) lumbar fusion com-pared with nonfusion procedures; (2) poste-rior lumbar fusion compared with anteposte-rior lumbar fusions; and (3) minimally invasive (MIS) posterior lumbar fusions compared with non-MIS equivalent procedures.
M
aterialsandM
ethodsA systematic review of the literature was performed to identify studies that re-ported PMA after lumbar spine surgery. In accordance with the PRISMA (preferred reporting items for systematic reviews and meta-analyses) guidelines,13 the electronic medical databases of PubMed, SCOPUS, EMBASE, CINAHL, and Web of Science were independently searched by 2 authors (S.P., K.I.) to identify all relevant reports of patients undergoing lumbar spine sur-gery with evidence Level I to IV. The key-words searched were paraspinal muscle,
paraspinal muscle atrophy, and PMA.
Only English-language full-text manu-scripts or abstracts that had quantified outcomes were reviewed. Following re-view of all relevant reports, the references of articles selected for review were further assessed to identify studies that were not captured in the initial database search. Eligibility Criteria for Study Inclusion
Inclusion criteria included (1) reports on PMA related to a lumbar spine proce-dure irrespective of the level of evidence; (2) studies with reported follow-up; and (3) reports that quantified the postopera-tive PMA. Exclusion criteria included (1) case reports; (2) studies that did not report
quantified outcomes; (3) studies with less than 6 months of follow-up, and (4) and non-English-language studies.
Assessment of Level of Evidence and Methodological Quality of the Studies
Two authors (S.P., K.I.) performed the initial literature search independently, and, after a consensus decision, all stud-ies included in the final analysis were se-lected. A third author’s (A.E.) opinion was obtained when a consensus decision could not be reached in the assessments. Level of evidence ratings were assigned to each study using criteria set by the Journal of
Bone and Joint Surgery for therapeutic
studies. In addition, 2 authors (S.P., K.I.) conducted a quality assessment for each of the studies selected for final analysis. Quality assessment of all the selected reports was made by using the 12-point Methodological Index for Non-random-ized Studies (MINORS) criteria. These criteria have been previously reported to have high test-retest, external and internal validity, and interobserver reliability.14-16 A modified 24-point quality assessment scale for observational studies was also used to analyze the methodological qual-ity of the studies in this study.17,18 Analysis
Mean weighted percent of PMA, im-mediate postoperative creatine phospho-kinase (CPK) levels, and radiographic outcomes were extracted, and weighted mean values according to the number of patients in each study were calculated. The volumetric postoperative PMA was defined as the percent volume of the mul-tifidus muscle that atrophied postopera-tively with respect to the multifidus’s ini-tial preoperative size. Iniini-tially, all lumbar spine fusions were evaluated as a single cohort, and outcomes were compared with all other procedures that did not involve a fusion. Afterward, outcomes in the fusion cohort were further substratified accord-ing to the surgical approach: anterior or posterior (posterolateral, transforaminal
lumbar interbody fusion [TLIF], and pos-terior lumbar interbody fusion [PLIF]). Furthermore, all outcomes were also substratified according to whether they were performed through MIS (paraspinal/ Wiltse) or non-MIS approaches.
All statistical analyses were performed using SPSS version 16 statistical software (IBM Corporation, Armonk, New York). The degree of postoperative volumetric PMA and elevations in postoperative CPK levels were stratified according to the ap-proach and surgical technique and ana-lyzed with the unpaired 2-tailed Student’s
t test. Results with a P value less than or equal to .05 were considered to be statisti-cally significant.
r
esultsStudy Identification
In total, 12 studies (Figure 1) evalu-ating 529 patients (262 men and 267 women) were analyzed in the final review (Table). Of these, 365 patients had lumbar spine fusions and 164 had lumbar decom-pressions without fusion. Radiographic analysis was with magnetic resonance imaging (MRI) in 9 studies and computed tomography in 3 studies.
Quality Assessment
The levels of evidence were as follows: 1 Level I, 2 Level II, 8 Level III, and 1 Level IV. Mean score for the 12 studies as per the modified quality assessment scale was 12 points (range, 8-17 points; maximum score, 22 points),17,18 whereas mean score for the MINORS scale was 13 points (range, 11-18 points; maximum score, 24 points).
Outcomes
Mean postoperative volumetric PMA was significantly higher in the fusion vs the nonfusion cohort (19.8%±11.3% vs 9.1%±6.9%, respectively; P=.0001)
(Ta-ble and Figure 2).
When outcomes were substratified according to the type of approach in the fusion cohort, mean postoperative
volu-metric PMA was significantly different between anterior and posterior procedures (6%±10% vs 24.7%±10.1%, respectively;
P=.0001) (Figure 3).
When fusion outcomes were sub-stratified according to MIS fusion vs non-MIS fusion, mean postoperative PMA was significantly lower in MIS fusions (10.2%±8.9% vs 24.7%±11.7%, respec-tively; P=.001).
When posterior nonfusion outcomes (ie, lumbar laminectomies/diskectomies) were substratified according to MIS de-compression and non-MIS decompres-sion, there were no significant differ-ences in the mean PMA (8.6%±4.3% vs 9.4%±10.2%, respectively).
d
iscussionParaspinal muscles are commonly af-fected during lumbar spine surgery due to retraction and dissection.1-3 Thus, postop-erative PMA may be an approach-related issue. With anterior procedures, the para-spinal muscles are not violated; there-fore, postoperative PMA may not occur. Similarly, with MIS approaches (para-spinal/Wiltse procedures) vs non-MIS approaches, there may be less paraspinal denervation and subsequent postopera-tive PMA. However, an additional culprit was noted in the current study because there was significant postoperative PMA with the standalone anterior lumbar in-terbody fusions. Also, when the cohorts were matched with respect to surgical approach, more postoperative PMA was seen in the fusion procedures than in the decompression-alone procedures. There-fore, the purpose of this study was to systematically assess the literature and quantify postoperative PMA as a result of disuse muscle atrophy from lumbar fusion and separately assess how much postop-erative PMA is an approach-related issue. There are several limitations to this study, which are potentially inherent in most systematic reviews. The authors were limited by the methodological quality of the original studies, length of
follow-up, and number of patients ana-lyzed in each study. Most studies were based on Level III or IV evidence, and quantification methods were not identical in all cases. Some of the studies did not report the different preoperative lumbar pathologies that necessitated the surgery, which may potentially affect the postop-erative outcomes. The physical therapy protocols were often not reported, and it is unlikely there was uniformity in the methods or duration of various modali-ties. Radiographic analyses were per-formed during different time frames, and inter- and intraobserver error margins for the radiographic outcomes were not rou-tinely reported. Medical comorbidities that could potentially affect the healing process, including diabetes mellitus and smoking, were not evaluated in any study. Despite these limitations, the authors be-lieve the results are valuable because, to their knowledge, no previous study has attempted to systematically quantify the amount of postoperative PMA according to surgical procedure.
The current study showed that an ad-dition of fusion (posterolateral or in-terbody) to lumbar surgery increased
the amount of postoperative PMA. This conclusion was supported by all studies. Disuse muscle atrophy after a lumbar fu-sion is significant. Suwa et al5 evaluated the amount of postoperative PMA in 42 patients who had received single-level laminectomy, 13 patients who had re-ceived multi-level laminectomy, and 34 patients who had received posterolateral fusion (PLF). Magnetic resonance imag-ing at 10-month follow-up showed PMA amounts of approximately 3% and 6.5% in the single-level and multi-level cohorts, respectively; however, the PLF cohort had approximately 11.5% PMA.
An equally important determinant of postoperative PMA may be the surgical approach, specifically anterior vs poste-rior lumbar surgery. There is a paucity of literature on the anterior approach; how-ever, all studies that evaluated this con-cept showed that posterior lumbar fusion cohorts had more postoperative PMA. Therefore, by going anteriorly, where none of the paraspinal muscles are disrupt-ed, there may be less postoperative PMA. Motosuneya et al4 compared PMA in 11 patients who had received anterior lumbar interbody fusion (ALIF) with 19 patients
Table
Summar
y of P
at
ient Demographics and Sur
gic al Charac ter ist ics Stud y Pr eoper ati ve Diagnosis Vertebr al Le vel Inv olv ement Tr eatment
Total No. of Patients Mean Age (Range), y
Ev aluation Mean Follo w-up (Range), mo
Mean Change in Paraspinal Muscle
Volume Kim et al 2 Spond ylolytic d ylolisthesis: 79% Degener ati ve d ylolisthesis: 10.5% For aminal stenosis: 10.5% L4-L5: 37% L5-S1: 52.5% L4-L5-S1: 10.5%
Group I: OPF Group II: PPF
19 52 (35 to 72) MRI 21 (18 to 31) OPF: -31.5%±25% PPF: -3.5%±25% Hyun et al 12 Degener ati ve
tions of lumbar spine
-Group I: P
ar
amedian interfascial
(MIS) Group II: Midline approac
h 26 52 (26 to 69) CT 12
Group I: 17.3%±1.8% Group II: 15.2%±1.3% Group III: 4.5%±1.1%
Motosuney a et al 4 Single-lev el gener ati ve lumbar disease L3-4: 16% L4-5: 79.5% L5-S1: 18% Group I: ALIF
Group II: PLIF Group III: PLF Group IV
: LAM Group V : LO VE 49 (36 to 63) MRI (16 to 19) Group I: -6%±1%
Group II: -12%±1% Group III: -16%±1.3% Group IV
: -6%±1.3% Group V : -4%±0.6% Suw a et al 5 -Group I: Single-interlaminar -lev el laminectom y
Group II: 13 multiple-interlaminar
-
lev
el laminectom
y
Group III: 34 PLF procedures
89
56
(21 to 82)
MRI
10
Group I: -3% Group II: -6.5%
Group III: -11.5%
W
atanabe et al23 Spinal stenosis Degener
ati
ve
d
ylolisthesis
L3-L4 L4-L5 Group I: Modified spinous split- ting fusion (n=18) Group II: Con
ventional fusion (n=16) 44 70 MRI 1 MIS: 24%±15% Open: 43%±22% Fan et al 19 Isthmic spond thesis (22%) Degener ati ve d ylolisthesis (46%)
Lumbar disk hernia- tion (8%) Spinal stenosis with instability (24%) L3-L4: 1.7% L4-L5: 69.5% L5-S1: 28.8%
Group I: MIS fusion Group II: Con
ventional open fusion 59 53 MRI 12 MIS: 12.2% CO: 36.8% Tsutsumimo -to et al 24 Single-lev el stenosis Degener ati ve d ylolisthesis L4-L5: 100% Lumbar degener ati ve spond listhesis 20 62 (39 to 76) MRI 14 CO: 36.8%±12.3% MIS: 12.2%±4.5% Remes et al 25 Isthmic spond thesis L4-L5: 43% L5-S1: 57% Group I: PLF Group II: ALF Group III: CF 67 14.5 (9 to 19.5) MRI (6 to 18)
who had received either PLF (n=11) or PLIF (n=8). At a mean 16-month follow-up, they reported that mean PMA in the anterior fusion cohort was approximately 6%, compared with 12% to 16% in the posterior fusion cohorts.
A current topic of discussion is whether MIS lumbar surgery results in less postoperative PMA when compared with conventional techniques (eg, stan-dard midline, open lumbar procedures). Most of the studies that evaluated this concept showed less postoperative PMA after an MIS procedure. Kim et al2 evalu-ated the amount of PMA in 11 patients who had received open pedicle screw fixation (OPF) compared with 8 patients who had received percutaneous pedicle screw fixation (PPF). The indications for surgery were degenerative and isthmic spondylolisthesis. All patients underwent interbody fusion (ALIF or PLIF) as well. Magnetic resonance imaging evaluation
Table
Summar
y of P
at
ient Demographics and Sur
gic al Charac ter ist ics Stud y Pr eoper ati ve Diagnosis Vertebr al Le vel Inv olv ement Tr eatment
Total No. of Patients Mean Age (Range), y
Ev aluation Mean Follo w-up (Range), mo
Mean Change in Paraspinal Muscle
Volume Kim et al 28 -Group I: Unilater al par aspinal
dissection with cutting of the spinous process (posterior decompression) Group II: Modified bilater
al
decompression via hemilami- nectom
y (MIS) (posterior
compression) Group III: Modified bilater
al
decompression via spinous process splitting (MIS) (posterior decompression)
71 53 (19 to 81) CT >24 Con ventional: -24%±6% to -38%±9% MIS: -3%±7% to 15%±8% Hartwig et al 26 Symptomatic degen- er ati ve disk disease L4-L5: 100% Cir
cumferential lumbar fusion
20 64.5 (45 to 85) CT 6 MIS: 0.9±0.8 (atroph y score) Open: 1.4±1.1 (atroph y score) Mori et al 20 Degener ati ve d ylolisthesis L3-L4: 5.5% L4-L5: 94.5% Group I: Modified spinous splitting fusion (n=27) Group II: Con
ventional fusion (n=26) 53 63.5 (44 to 79) MRI 12 Modified: -2%±8% Open: -13%±7% Stev ens et al 27 -L4-L5: 100%
Group I: MIS PLF Group II: Con
ventional PLF 12 51.5 MRI (24 to 96) T2 relaxation time: MIS: 47 ms CF: 90 ms Abbr eviations: ALF , anterior fusion; ALIF
, anterior lumbar interbody fusion; CF
, cir
cumfer
ential fusion; CO, con
ventional; CT
, computed tomo
gr
aphy; LAM, laminectomy or
fenestr
ation; LO
VE, Lo
ve’
s nucleotomy; MIS, minimally in
vasive; MRI, ma gnetic r esonance ima ging; OPF , open pedicle scr ew fixation; PLF , poster olater al fusion; PLIF , posterior
lumbar interbody fusion; PPF
, per
cutaneous pedicle scr
ew fixation.
(cont’
d)
Figure 2: Comparison of mean paraspinal
muscu-lar atrophy between fusion and nonfusion proce-dures.
Figure 3: Comparison of anterior and nonanterior
showed that the mean PMA in the ORF cohort was approximately 31.5%, com-pared with 3.5% in the PPF cohort. Fan et al19 compared PMA in 16 patients who had undergone PLIF using an MIS ap-proach with 16 patients who had under-gone a conventional open approach. Us-ing MRI evaluations, they reported that the mean PMA in the MIS cohort was approximately 12.2%, compared with 36.8% in the conventional open cohort. Few studies have attempted to correlate clinical outcomes with postoperative PMA using other metrics.19-22
c
onclusionAccording to the findings of the cur-rent study, lumbar spinal fusions were associated with significantly higher post-operative PMA vs decompressions alone. Anterior lumbar procedures resulted in less PMA than equivalent posterior pro-cedures. Furthermore, there may be less postoperative PMA in MIS fusions com-pared with non-MIS fusions. Further pro-spective studies are necessary to evaluate potential correlations of PMA with clini-cal and patient-reported outcomes.
r
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