Spine surgery outcome in patients who sought compensation after a motor vehicle accident: a retrospective cohort study
Sarrami et al. BMC Surgery
Spine surgery outcome in patients who sought compensation after a motor vehicle accident: a retrospective cohort study
Pooria Sarrami 0 1
Rafael Ekmejian 1
Justine M. Naylor 1 2
Joseph Descallar 1 3
Robindro Chatterji 1
Ian A. Harris 1 2
0 Institute of Trauma and Injury Management, Agency for Clinical Innovation , Level 4, Sage Building, 67 Albert Avenue, Chatswood, Sydney, NSW 2067 , Australia
1 South Western Sydney Clinical School , UNSW, Sydney , Australia
2 South Western Sydney Local Health District, Liverpool Hospital , Liverpool , Australia
3 Ingham Institute for Applied Medical Research , Sydney , Australia
Background: Back and neck pain are common after road traffic injury and are treated by spine surgery in some cases. This study aimed to describe the outcomes of spine surgery in people who made an insurance claim after road traffic accidents without an associated spinal fracture or dislocation. Methods: This study was a retrospective cohort based on insurers' data of Compulsory Third Party (CTP) claims. File audit and data extraction were undertaken using a study-specific proforma. Primary outcomes were ongoing pain and symptoms, complications, return to work and pre-injury duties, and ongoing treatment 2 years following spine surgery. Secondary outcomes were health care costs based on data provided by the insurers. Results: After screening 766 files, 90 cases were included (female: 48; mean age: 46 years). Among the subjects who were working prior the injury, the rate of return to work was 37% and return to pre-injury duties was 23% 2 years following the surgery. The average number of appointments with health care professionals in the 1 year after surgery was 21, compared to 10 for the 1 year prior to surgery (p = 0.03). At 2 years following the initial surgery, 21% of claimants had undergone revision spine surgery; 68% reported ongoing back pain and 41% had ongoing radicular symptoms. The difference between costs 1 year before and after surgery (excluding surgical costs) was statistically significant (p = 0.04). Fusions surgery was associated with higher total costs than decompression alone. After adjusting for surgery type, lumbar surgery was associated with higher costs in the 1 year after surgery and total surgical costs compared to cervical surgery. Conclusions: The majority of claimants continued having clinical symptoms, continued using health care and did not return to work despite undertaking spine surgery.
Spine surgery; Decompression; Clinical outcome; Road traffic accidents; Compensation
Road traffic crash casualties are estimated to cost $17b
in Australia each year, with New South Wales (NSW)
having the highest total cost compared to other states
. Among the annual cost of road traffic crash
casualties, 56% are related to human costs, including: medical
treatment and rehabilitation; long-term care; labour in
the workplace and quality of life .
Back and neck pain are common after road traffic
injury . Recovery of back pain is lengthy and the median
time to claim closure is reported to be 505 days .
Post-accident neck and back pain are also predictors of
chronicity in whiplash after motor vehicle crashes [3–5].
A considerable number of patients who are involved in a
road traffic accident will pursue a compensation claim,
mostly through a Compulsory Third Party (CTP)
scheme. In NSW, CTP insurance covers all persons
involved in a motor vehicle crash on public roads who are
not at fault. Surgery is a one of the treatments used for
back pain [6–8] including following motor vehicle injury
and surgery costs can be covered by the CTP scheme for
© The Author(s). 2016 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver
(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Emerging evidence suggests seeking compensation can
be associated with poorer health outcomes . A previous
study retrospectively reviewed outcomes of spine surgery
for patients without fracture or dislocation in an Australian
worker’s compensation cohort. Data were collected from
WorkCover NSW and insurer agents and it was found 77%
of patients needed ongoing treatment 2 years post spine
surgery . However, there have been no reports on the
outcome of patients who undergo spine surgery under CTP
scheme after road traffic accidents. Therefore, this study
aimed to explore the outcomes of such patients.
Specifically, we aimed to determine rates of ongoing pain and
symptoms, complications and ongoing treatment and
health care use, and to determine predicting capability of
age, gender, surgery type, surgery location, and the
socioeconomic status of residential area.
We studied a retrospective cohort of claimants identified
using information from three insurers, covering 70% of
the CTP insurance market in the study location .
Claimants were 18 years or older and had undergone
spinal surgery after a road collision during 2005–2011 and
were treated under CTP insurance. Those with acute
fracture-dislocations were excluded, as these conditions
represent a different population to those treated for
ongoing, chronic pain after injury . File audit and data
extraction were undertaken by three researchers using a
study-specific proforma (See Additional file 1).
Primary outcomes were ongoing pain and symptoms,
opioid consumption, revision surgery, return to work
(RTW), return to pre-injury duties (PID) 2 years
following spine surgery. In addition, healthcare use (e.g.
physiotherapy, pain management, hydrotherapy) was
measured and compared 1 year before and after surgery.
Secondary outcomes were health care costs (total health
care costs insurers spent on the subjects and costs 1 year
before surgery and 1 year after surgery) based on data
provided by the insurers.
Insurers’ data systems varied; one relied on paper files
and Australian Medical Association (AMA) codes and
two relied on electronic files and Abbreviated Injury
Scale (AIS) codes. Therefore, strategies to identify cases
were different for each insurer. To identify cases with
spine surgery, two comprehensive lists of AMA and AIS
codes were used (See Appendix). Presence of a surgical
procedure could not be determined via automated
systems and was done manually by screening patients’ files.
However, the process of screening was facilitated based
on the dates of significant payments (more than $2000)
as it was assumed that spinal surgery in Australia could
not be performed for less than $2000. Claimants’ files,
including reports of imaging studies, were examined and
cases were excluded if there was any indication of
fractures or dislocations. Socio-demographic data (age,
gender, and postcode), car collision history (position at
the time of car collision and seat belt use), data related
to surgery (surgery type and location), health care use
and RTW status were gathered from the files.
Claimants studied in this research could have
undertaken spine surgery only if insurers’ medical assessments
indicated their back pain and symptoms are mainly
attributable to the recent car accident rather than any
prior spine issues. For this reason, claimants’ past history
was not included in data analysis.
Rates of ongoing back pain and ongoing radicular
symptoms, obtained from claimants’ files, during 2 years
following surgery were recorded. In addition, the rates of opioid
consumption before and after surgery were recorded.
McNemar test was used to compare the rate of opioid
consumption in claimants before and after surgery.
Rate of return to work (RTW) and return to pre-injury
duties (PID) during 2 years after surgery were explored
among the subjects who were working either part-time or
full time before the accident. RTW indicated that subjects
were working in any capacity after surgery, while PID
indicated that subjects were working at the same level
(part-time or full-time) as they did before the accident.
These two rates were recorded as binary variables.
In order to explore health care use, the number of
appointments that the subjects had with health care
professionals for services such as physiotherapy, pain clinic,
hydrotherapy and psychotherapy in the 1 year prior to the
surgery were considered and was compared with the
number of appointments in the same claimants 1 year after
surgery using paired t-test it. Only those participants who
had 1 year or more between the car accident and the
surgery were included for that part of the analysis compared
before and after surgery. All participants had data related
to at least 2 years after surgery. In addition, the rate of
revision surgery 2 years after the initial surgery was
recorded. Revision surgery was defined as repeat surgery
(of any type) to the same spine region of the initial surgery
(cervical or lumbar) for ongoing symptoms (and not for
any new incidence or pathology).
Data related to health care costs included total health
care costs that insurers paid for each claimant and costs
insurers paid in the 1 year before and after surgery. Total
health care costs included all payments made by the
insurers for treatment of each subject, including outpatient
services, consultations fees, medication costs, hospital
fees, surgeon fees, implant costs and inpatient costs. Total
health care costs did not include non-health related
payments. Costs 1 year before surgery and 1 year after surgery
did not include costs directly related to surgery (surgeon
fees, inpatient costs, implant costs and hospital costs).
Acute health care costs at public hospitals are covered by
the NSW Motor Accidents Authority (MAA) and are not
included in the health care costs before surgery. Costs in
the 1 year before surgery were compared with costs in the
same claimants in 1 year after surgery using paired t-test.
We analysed whether age, gender, surgery type, surgery
location and the Socio-Economic Indexes for Areas
(SEIFA; calculated based on subjects’ residential postcode)
were associated with each of the outcomes. Surgery type
was considered as either fusion (with or without
decompression) or decompression alone. Univariate logistic
regression was used to determine if there were associations
between the predictors and binary categorical outcomes
(improved back pain, work status, revision surgery, and
opioid use after surgery). Negative binomial regression
was used to analyse the number of times health care was
used after surgery as a count. Data analyses were
performed using SAS 6.1 (Cary, NC, USA).
In the first round of data collection, three insurers
provided access to 321 cases that potentially had spine
surgery during 2010–11. After screening 321 files from the
three insurers, 31 cases were included. As the number of
the included claimants was low, an ethics amendment
was obtained and the study inclusion period was
extended to include subjects having surgery during 2005 to
2011. One of the insurers did not continue its
collaboration with the study due to their resource limitations. A
further 445 cases from the remaining two insurers were
screened and 59 cases were included from the other two
insurers. The reasons for exclusion were: not identifying
any record of spine surgery (82%), spine fracture (15%),
surgery performed outside of designated time period of
this study (4%) and age under 18 (1%). Figure 1
illustrates the overall process of screening and inclusion.
The exclusion was only due to ineligibility.
Of the 90 included claimants, 48 were female (53%).
The mean age at the time of claim was 46 years (SD:
11.9, range: 23 to 73). The majority of subjects were the
driver of their car at the time of accident (68%). The rest
were passengers (22%), motorcyclists (6%) or pedestrians
(3%) (Table 1).
For those who could use a seat belt, 96% claimed they
used it at the time of accident. Included claimants were
from wide range socioeconomic statuses based on the
postcode of their living place.
Decompression was the most common type of surgery
performed (56%), followed by the combination of fusion
and decompression (34%) and fusion alone (10%).
Approximately half of the procedures were undertaken on
the lumbar spine (52%), the rest were on the cervical
spine. The surgery levels ranked from the highest
frequency were: C5/6 (22%), L4/5 (21%), multiple levels
(20%), L5/S1 (19%), C6/7 (13%) and other single levels
(4%). The mean time between accident and spine
surgery was 386 days (SD: 271, range: 41 to 1552).
Insurer one provided health care costs data of 41 cases
out of 42 cases; however, insurer two provided cost data
for only 16 cases (of 42 cases), because the insurer paid
a lump sum for the remaining participants and could
not separate health care costs. Insurer three, who did
not participate in round 2, provided access to cost data
of all 6 cases. The average total health care cost per
patient was $59,145 (SD: 35,817; range: $11,064 to
$164,189). The total health care cost by surgery type
was: decompression surgery $47,875; fusion surgery
$60,130 and decompression and fusion together $75,016.
Fig. 1 Flowchart of screening and inclusion process
Table 1 Demographic information of the claimants included in the study
Age less than 35
Age between 36 and 50
Age between 51 and 65
Age more than 66
Outcome of claimants after spine surgery
In 68% of claimants, there were reports of ongoing back
pain 2 years following surgery. Similarly, 41% of
participants had ongoing radicular symptoms following
surgery. In addition, opioid consumption did not
statistically change after surgery (Table 2). Opioid use
was not able to be determined in all claimants. The
missing data indicates we have identified the minimum
rate of opioid use. Before surgery 48% (23/48) of
participants used opioids and after surgery this figure was 57%
(39/68). Statistically these was no significant difference
between these rates (McNemar test, p = 0.80, Table 2).
Before the accident, 78% of the claimants were
working either full-time or part-time. This rate was reduced
to 37% after the accident and did not change after
surgery (Table 3). Among the subjects who were working
either part-time or full-time prior the injury, the rate of
RTW was 37% and return to PID was 23% 2 years
following the surgery.
Claimants had on average 10 appointments with
health care professionals for services such as
physiotherapy, pain clinic, hydrotherapy and psychotherapy in the
1 year prior to the surgery, while they averaged 21
appointments in the 1 year after surgery (Tables 3 and 4).
This difference is statistically significant (paired sample
t-test, p = 0.03). During the 2 years following the initial
surgery, 21% of patients had undergone revision surgery.
Average health care costs that the insurers paid for
claimants in the 1 year before surgery was $2289, while
this figure during the 1 year after surgery was $4.271
(Table 3). The difference between before and after
surgery health care costs was statistically significant (paired
sample t-test, p = 0.04). The calculated costs before and
after surgery did not include costs directly related to
surgery, such as surgeon fees, implant fees or hospital costs.
Table 2 Cross-tabulation of opioid use before and after surgery
Opioid use before surgery
There were no significant associations between the
potential predictors and work capacity, health care use,
ongoing pain, rates of revision surgery or opioid use.
There were no significant associations between age,
gender, SEIFA deciles, or surgery type and costs 1 year
after surgery. However, after adjusting for surgery type,
surgery location (lumbar versus cervical spine) was
found to be a predictor of costs after surgery (p = 0.04).
The average costs during 1 year after surgery for
claimants with lumbar surgery was $8784, while for cervical
surgery it was $4201.
There were no significant associations between age,
gender and SEIFA deciles with total costs. However, surgery
type was a predictor of total costs (p = 0.02; average total
cost for decompression: $50,550 and for fusion with and
without decompression: $71,543). Surgery location was
also identified as a predictor of total costs (p = 0.02;
average total cost for lumbar surgery: $68,030; and for
cervical surgery: $55,482).
In this study, undertaking spine surgery under CTP
compensation after motor vehicle trauma, compared to
pre-surgery, was associated with increased health care
use, high rates of ongoing pain and low rates of return
to pre injury duties at 2 years post-surgery, and
increased non-surgical health care costs 1 year after
surgery. The rate of revision surgery observed here (21%)
was in the range of previous studies that reported 9.2 to
27% [6, 11, 12]. The rate of RTW was 43%, which is
similar to other studies that have reported 26 to 50%
RTW [6, 12].
These results are similar to several other studies that
reported poor outcomes of spine surgery under workers’
compensation for spine conditions without fracture or
dislocation [6, 11, 12]. Studies undertaken on workers’
compensation cohorts have been criticised for
considering a specific population with particular types of
occupation ; however, this criticism is not applicable to this
study as claimants did not belong to a particular
working group. Results of this study are similar to previous
studies indicating that spine surgery does not reliably
improve RTW or reduce pain or health care use in
patients with no fracture or dislocation.
It is notable that patients can have more routine
appointments with allied health services post-operatively
with the aim of achieving a better outcome, which does
not necessarily reflect failure or inadequacy of surgical
treatment. Nevertheless this increased health care use
indicates that the cost of surgical therapies for claimants
and/or insurers is not limited to the direct costs.
In addition, while spine surgery is a costly procedure, it
also led to a further increase in claimants’ health care
costs after surgery due to further use of health services
such as physiotherapy. The lack of improvement may be
due to the complex nature of chronic pain which is related
to physiological, psychological and social factors .
The decision for surgery should be based on shared
decision making with patients that includes providing
information on surgery outcomes. Therefore, reliable
information is needed regarding the outcomes of surgery.
The retrospective research methodology employed in
this study had the advantage of ease of access to
available data in a relatively short-time, however, this method
imposed limitations. Insurers could not provide cost
data related to 27 cases. In addition, files did not include
the needed information in some cases, for example 17
files did not have adequate data on work status of
claimants. These missing data were random and we do not
Before and after surgery: 29
Before surgery: 48
After surgery: 68
have any reason to assume the missing values would be
systematically different from the available data. For each
spine surgery outcome, the patient population have
varying sample sizes since this information was not available
in every patient (Table 3). This would lead to reduced
statistical power when analysing the association between
predictors and outcomes. In addition, relying on the
insurance data for, we have not access to potential health
care use and costs that claimants may have had out of
the insurance system. Due to our reliance on medical
notes submitted to insurers, it is likely that we have
underestimated the complications, such as revision
surgery, as these may have occurred outside the
A lack of control group is another limitation of
retrospective studies like this. While we have observed a lack
of improvement in the claimants we cannot ascertain
the outcome of those who did not undergo surgery. It is
also notable that we could not use standardised tools to
measure the quantity of pain before and after surgery;
we could only compare existence of pain based on the
contemporaneous medical notes reported whether the
patients felt better, worse or not changed. In addition,
we did not have access to claimants’ history before the
injury, including use of opioids, which may influence
some of the outcomes measured.
Despite the limitation of the method of retrospective
inspection of claimants’ files, insurers can be a valuable
source of data for similar studies. However, in order to
make recommendations and address the existing
uncertainties on the application of spinal surgery for
claimants who have pain following a motor vehicle accident,
there is a need for more rigorous methods such as
randomised control trials,  prospective cohort
studies or registries.
Future studies should utilise prospective research
methods and include additional dimensions such as
patients’ expectation of surgery  and psychological
predictors . As previous studies have reported that
the outcome of spine surgery varies between diagnostic
subgroups , outcomes of different groups of patients
should be compared in those with and without using
compensation. In addition, patient reported outcomes of
revision surgeries could also be investigated.
Table 3 Comparison of claimants’ status before and after surgery
Average health care costs during one year
Percentage of claimants using opioids
Average number of appointments with health services during one year
Before and after surgery: 23
This study does not support the use of spine surgery
under CTP compensation for claimants without a
fracture or dislocation. Comparative studies are required
to determine the relative effectiveness of surgery in this
environment. Until such data are available, based on the
high costs of surgery and the limited benefits for this
particular patient group, utilisation of other pathways of
care is suggested.
Injury codes used to identify potential cases with spine
AMA (Australian Medical Association) codes
MT030, MT050, MT055, MT060, MT070, MT080,
MT090, MT100, MT110, MT130, MT140, MT145,
MT150, MT160, MT170, MT180, MT190, MT200,
MT210, MT220, MT230, MT240, MT250, MT260,
MT270, MT280, MT290, MT300, MT310, MT320,
MT330, MT340, LT045, LT055, LT075, LT135, LT145,
LT155, LT165, LT175, LT185, LT195, LT205, LT215.
AIS (Abbreviated Injury Scale) codes
Cervical spine: 650299.2, 650200.2, 651202.2, 650203.3,
650205.3, 630260.2, 640278.1.
Thoracic spine: 650499.2, 650400.2, 650402.2, 650403.3,
650405.3, 630499.2, 640478.4.
Lumbar spine: 650699.2, 650600.2, 650602.2, 650603.3,
Additional file 1: Study-specific proforma. (DOCX 51 kb)
AIS: Abbreviated injury scale; AMA: Australian Medical Association;
CTP: Compulsory Third Party; MAA: Motor Accidents Authority; NSW: New
South Wales; PID: Pre-injury duties; RTW: Return to work; SEIFA:
SocioEconomic Indexes for Areas
This study has been funded by the Motor Accident Authority (MAA) New
South Wales (NSW), Australia. The funder had no role in study design, data
collection and analysis, decision to publish, or preparation of the manuscript.
PS, RE, JN, and IH were responsible for the design of the study; PS, RE and
RC collected the data, PS and JD analysed the data. All authors were
involved in drafting the manuscript and revising it critically and have
approved the final version.
Pooria Sarrami is a Conjoint Senior lecturer at the SWS Clinical School and a
Research Fellow at the Institute of Trauma and Injury Management, NSW
Agency for Clinical Innovation. He has a doctoral degree in medicine (2001)
and a PhD in Sociology (2009). His broad expertise includes the study of
social aspects of health and medicine for more than a decade.
Rafael Ekmejian is a final year medical student at the University of New
South Wales. He is the founder of Society of Medical Innovation at UNSW.
Justine Naylor is the Principal Senior Research Fellow for Orthopaedics for
South West Sydney Local Health District, and a Conjoint Associate Professor
at UNSW. She has extensive post-doctoral research experience in the
orthopaedic and musculoskeletal fields.
Joseph Descallar is a biostatistician at the Ingham Institute for Applied
Medical Research, Liverpool, NSW, Australia and a conjoint lecturer at the
South Western Sydney Clinical School, UNSW Australia, Liverpool, NSW. He
has a Bachelor of Science (2008) and a Masters of Biostatistics (2011). He has
co-authored peer reviewed articles in several health related areas including
Orthopaedics, Oncology, Psychology, and Cardiology.
Robindro Chatterji is a final year medical student at the University of New South
Wales due to receive a BMed M.D. in 2016. He has interests in medical education,
clinical research and patient-centred care. He has had prior experience clinical
work with Indigenous Australians and has published research in the fields of
respiratory physiology and surgery. His current work focusses on data collection
methods in hip and knee arthroplasty.
Ian Harris is an orthopaedic surgeon clinical researcher with interests in
trauma and surgical outcomes. He is Professor of Orthopaedic Surgery at
Consent for publication
1. Connelly LB , Supangan R. The economic costs of road traffic crashes: Australia, states and territories . Accid Anal Prev . 2006 ; 38 ( 6 ): 1087 - 93 .
2. Cassidy JD , Carroll L , Côté P , Berglund A , Nygren Å . Low back pain after traffic collisions: a population-based cohort study . Spine . 2003 ; 28 ( 10 ): 1002 - 9 .
3. Barnsley L. Whiplash after motor vehicle crashes . BMJ: Br Med J . 2013 ; 347 :f5966.
4. Walton DM , Macdermid JC , Giorgianni AA , Mascarenhas JC , West SC , Zammit CA . Risk factors for persistent problems following acute whiplash injury: update of a systematic review and meta-analysis . J Orthop Sports Phys Ther . 2013 ; 43 ( 2 ): 31 - 43 .
5. Carroll LJ , Holm LW , Hogg-Johnson S , Cote P , Cassidy JD , Haldeman S , Nordin M , Hurwitz EL , Carragee EJ , van der Velde G , et al. Course and prognostic factors for neck pain in whiplash-associated disorders (WAD): results of the Bone and Joint Decade 2000-2010 Task Force on Neck Pain and Its Associated Disorders . Spine. 2008 ; 33 ( 4 Suppl): S83 - 92 .
6. Harris IA , Dantanarayana N , Naylor JM . Spine surgery outcomes in a workers' compensation cohort . ANZ J Surg . 2012 ; 82 ( 9 ): 625 - 9 .
7. Murgatroyd DF , Cameron ID , Harris IA . Understanding the effect of compensation on recovery from severe motor vehicle crash injuries: a qualitative study . Injury Prevention . 2011 ; 17 ( 4 ): 222 - 7 .
8. Harris IA , Murgatroyd DF , Cameron ID , Young JM , Solomon MJ . The effect of compensation on health care utilisation in a trauma cohort . Med J Aust . 2009 ; 190 ( 11 ): 619 - 22 .
9. Harris I , Mulford J , Solomon M , van Gelder JM , Young J. Association between compensation status and outcome after surgery: a meta-analysis . JAMA . 2005 ; 293 ( 13 ): 1644 - 52 .
10. State Insurance Regulatory Authority. Compulsory Third Party 2014 Scheme Performance Report , accessible from https://www.opengov. nsw.gov.au/ publications/15266 (access date: 1 Dec 2016 ); 2015
11. Juratli SM , Franklin GM , Mirza SK , Wickizer TM , Fulton-Kehoe D. Lumbar fusion outcomes in Washington State workers' compensation . Spine . 2006 ; 31 ( 23 ): 2715 - 23 .
12. Nguyen TH , Randolph DC , Talmage J , Succop P , Travis R. Long-term outcomes of lumbar fusion among workers' compensation subjects: a historical cohort study . Spine . 2011 ; 36 ( 4 ): 320 - 31 .
13. Quan GM , Wilde P. Re : Spine surgery outcomes in a workers' compensation cohort . ANZ J Surg . 2013 ; 83 ( 1-2 ): 96 .
14. Turk DC , Wilson HD , Cahana A. Treatment of chronic non-cancer pain . Lancet . 2011 ; 377 ( 9784 ): 2226 - 35 .
15. Chou R , Loeser JD , Owens DK , Rosenquist RW , Atlas SJ , Baisden J , Carragee EJ , Grabois M , Murphy DR , Resnick DK . Interventional therapies, surgery, and interdisciplinary rehabilitation for low back pain: an evidence-based clinical practice guideline from the American Pain Society . Spine. 2009 ; 34 ( 10 ): 1066 - 77 .
16. Soroceanu A , Ching A , Abdu W , McGuire K. Relationship between preoperative expectations, satisfaction, and functional outcomes in patients undergoing lumbar and cervical spine surgery: a multicenter study . Spine . 2012 ; 37 ( 2 ): E103 - 8 .
17. Trief PM , Grant W , Fredrickson B. A prospective study of psychological predictors of lumbar surgery outcome . Spine . 2000 ; 25 ( 20 ): 2616 - 21 .
18. Glassman SD , Carreon LY , Djurasovic M , Dimar JR , Johnson JR , Puno RM , Campbell MJ. Lumbar fusion outcomes stratified by specific diagnostic indication . Spine J . 2009 ; 9 ( 1 ): 13 - 21 .