Keywords microdiscectomy - limited discectomy - long-term outcome - reoperation - Oswestry
disability index - ODI - lumbar disc herniation
Final level of evidence (LoE)—prognostic
Study design
Prospective cohort
Retrospective cohort
Case–control
Case series
x
Methods
Patients at similar point in course of treatment
x
F/U ≥ 85%
Similarity of treatment protocols for patient groups
x
Patients followed for long enough for outcomes to occur
x
Control for extraneous risk factors
Overall level of evidence
IV
The definitions of the different levels of evidence are available on page 166.
Study Rationale
Lower back pain (LBP) is the most frequently reported type of pain, affecting 29%
of the adult population in the United States,[1 ] resulting in an estimated $84.1 to $624.8 billion total costs for the U.S. health
care system.[2 ] Apart from nonspecific back pain, degenerative disease and disc herniation represent
the most common causes for LBP-related physician office consultations.[3 ] In fact, the majority of lumbar radicular pain symptoms is the result of a disc
herniation, defined as bulging of the nucleus pulposus through a fissure or tear within
the annulus fibrosus.[4 ] Although favorable outcomes have been demonstrated for both surgical and nonoperative
treatment options, patients who underwent open discectomy for lumbar disc herniation
(LDH) were shown to have better self-reported outcomes than conservatively treated
individuals.[5 ]
Due to the postulated advantages of reduced tissue invasiveness, limited blood loss,
a shorter duration of surgery, and a faster postoperative recovery, minimally invasive
microdiscectomy, often also referred to as limited discectomy, has been established
as an alternative to traditional, more aggressive open approaches in the treatment
of LDHs.[6 ] Nevertheless, based on previous study findings, controversies regarding the benefits
of a minimally invasive over an open surgical approach remain.[7 ]
[8 ]
[9 ]
[10 ] In a recently published long-term outcome analysis, limited microdiscectomy was
reported to be an effective surgical approach for the treatment of LDH. However, the
reported disc herniation recurrence rate was higher compared with previous studies
with a shorter follow-up period,[8 ] which warrants further follow-up investigations to assess the long-term efficacy
of this minimally invasive surgical approach.
Objective
The objective of this study was to assess the reoperation rate after microdiscectomy
for the treatment of LDH in patients with ≥ 5-year follow-up and identify demographic,
perioperative, and outcome-related differences between patients with and without a
reoperation.
Methods
Study Population
After obtaining the approval of the Institutional Review Board, the medical records,
physician office charts, operative reports, and radiographic imaging studies of patients
who had undergone minimally invasive microdiscectomy at a single institution between
March 1994 and December 2007 were retrospectively reviewed. All patients underwent
surgery for the treatment of single-level LDH in the setting of degenerative disc
disease with concomitant nerve root compression and radicular symptoms. The exclusion
criteria of the present study were defined as (1) a follow-up period of less than
5 years and (2) microdiscectomy as a revision surgery (see PPO table in online supplementary
material).
Baseline/Perioperative Characteristics
Data collection included gender, age at index surgery, body mass index (BMI), preoperative
neurological examination, and length of stay ([Table 1 ]). The sensory and motor neurological function was assessed both in the pre- and
the postoperative setting by a fellowship-trained spine surgeon. A sensory deficit
was defined as any change in the individual's sensory neurological function, including
numbness, para-/dysesthesias, and sensation of pins and needles, and a motor deficit
was defined as any change in the individual's muscle strength during the neurological
examination.
Table 1
Descriptive patient characteristics (n = 40)
Variable
Mean or N
SD or %
Min
Max
Age at surgery (y)
39.9
12.5
18
80
Gender
Female
16
40.0%
Male
24
60.0%
BMI (kg/m2 )
26.8
4.1
19.0
35.9
Neurological exam
Preoperative VAS (back)
4.8
3.2
0
10
Preoperative VAS (leg)
6.5
2.1
2
10
Preoperative sensory deficit
No
9
22.5%
Yes
31
77.5%
Preoperative motor deficit
No
12
30.0%
Yes
28
70.0%
Microdiscectomy level
L1–2
1
2.5%
L2–3
0
0.0%
L3–4
2
5.0%
L4–5
9
22.5%
L5-S1
28
70.0%
Length of surgery (min)
77.9
36.8
43
256
Days of hospitalization
1.7
1.2
1
7
Abbreviations: SD, standard deviation; VAS, visual analog scale.
Furthermore, information about the preoperative visual analog scale (VAS) scores of
back and lower extremity pain were retrieved from the medical records. If the appropriate
score was not specified by the patient, the documented characterization of pain severity
was used to estimate the VAS score: “minimal,” “mild,” “moderate,” “quite significant,”
“quite strong,” and “severe” pain was defined as a VAS score of 1.5, 3, 6, 7, 8, and
9, respectively (preoperative back and leg pain estimation in 12.5% [n = 5] and 20.0% [n = 8] of patients, respectively).
Surgery-related data were collected on previous surgeries of the lumbar spine, surgically
addressed levels, intraoperative complications, postoperative clinical outcome, and
any requirements for add-on lumbar spine surgeries.
Surgical Technique
All included patients underwent surgery for single-level LDH with radicular lower
extremity symptoms. Minimally invasive microdiscectomy at the appropriate level was
performed according to a standardized institutional surgical protocol. In brief summary,
general anesthesia was induced, the patient secured in prone position to the surgical
table, and the spine approached via a posterior midline incision. After the removal
of the ligamentum flavum at the appropriate motion segment level, the compressed nerve
root was retracted and protected to safely remove all extruded disc segments. When
indicated, the annular lesion was further inspected and additional disc fragments
removed. Once the nerve root was found to be free of compression, the surgical field
was copiously irrigated and the wound closed. Finally, the patient was awakened from
anesthesia and transferred to the recovery room, after the motor strength of the lower
extremities had been evaluated.
Postoperative Clinical Outcome
Data on the short-term postoperative clinical outcome were retrieved from the patients'
medical records, and office notes, including the presence of residual radicular pain,
sensory, and motor deficits, as well as the need for additional lumbar spinal surgery
involving the level of the initial microdiscectomy.
Long-Term Clinical Outcome
Patients were called to assess their postoperative long-term clinical outcome after
a follow-up of at least 5 years after the index microdiscectomy. In addition to the
utilized telephone questionnaire, the Oswestry disability index (ODI) score[11 ] was obtained for each patient. Patients who were not available for the telephone
follow-up interview were considered as “lost to follow-up.”
Postoperative long-term outcome parameters that were assessed via the telephone questionnaire
included (1) the need for another back surgery after the microdiscectomy and (2) whether
the additional surgery was related to the index surgery, (3) the need for pain management
measures after the index surgery, (4) the back and leg pain severity at the time of
the telephone follow-up graded according to the VAS scoring system, (5) the presence
of additional symptoms apart from pain such as sensory and motor deficits reported
on a scale from 0 to 10 with 0 being no additional symptoms and 10 being the highest
severity of additional symptoms, (6) the degree of improvement as a result of the
index microdiscectomy, (7) the degree of satisfaction regarding the outcome of the
surgery reported on a scale from 0 to 10 with 0 being complete dissatisfaction and
10 being complete satisfaction, (8) the patient's opinion regarding undergoing the
same surgery again, (9) the ability to work after surgery, (10) the present working
status, and (11) the Oswestry low back pain disability index (ODI)—Version 1.0.
The used ODI questionnaire consisted of 10 questions regarding pain intensity and
the degree of pain over time, as well as the ability to perform personal care tasks,
lift weights, walk, sit, stand, sleep, travel, and participate in social life. The
percentage of disability was then calculated based on the patient's total ODI score
divided by the maximally achievable score (i.e., 50) for each patient.
Statistical Analysis
The results of descriptive data analysis are shown as means ± standard deviations
for continuous variables, and as frequencies and percentages for categorical variables.
Differences in pre- and postoperative VAS scores were assessed with paired t -tests. The association between each independent risk factor and the requirement for
additional lumbar spine surgery related to the index microdiscectomy was then assessed
using a bivariate analysis. Due to the small sample size, we were unable to perform
a multivariate analysis to control for potential confounding when comparing outcomes
between those with and without an additional lumbar surgery. Independent sample t -tests or nonparametric Mann–Whitney U tests were used for continuous risk factors, while chi-squared or Fisher exact tests
were used for categorical risk factors. Statistical significance was defined at the
level of α = 0.05. Data analysis was performed using SAS software version 9.3 (SAS
Institute Inc., Cary, North Carolina, United States).
Results
Study Population
Out of 203 microdiscectomy patients with a postoperative follow-up of at least 5 years,
8 patients did not meet the inclusion criteria of the present study, due to the index
microdiscectomy as a revision surgery ([Table 1 ]). Out of the remaining 195 eligible patients, 1 patient refused to participate in
the present study, resulting in a total of 194 potential subjects for follow-up. Forty-nine
patients had incomplete data, and another 105 patients were not available for the
telephone follow-up interview, resulting in a total of 40 patients (16 females, 24
males) available for analysis. The average patient age at surgery was 39.9 ± 12.5
years (range: 18–80), and the average BMI was 26.8 ± 4.1 kg/m2 (range: 19.0–35.9) ([Fig. 1 ]). During the preoperative neurological examination, all patients complained of lower
back and/or lower extremity pain. Preoperative VAS scores for lower back and lower
extremity pain were reported to be 4.8 ± 3.2 out of 10 (range: 0–10), and 6.5 ± 2.1
out of 10 (range: 2–10), respectively. Preoperative neurological examination of the
study population revealed a sensory deficit in 77.5% (n = 31) and a motor deficit in 70% (n = 28) of cases.
Fig. 1 Patient sampling and selection.
Surgical Details
Single-level lumbar microdiscectomy was performed by one of three fellowship-trained
spine surgeons at the levels L5–S1 (n = 28, 70%), L4–L5 (n = 9, 22.5%), L3–L4 (n = 2, 5.0%), and L1–L2 (n = 1, 2.5%). There were no patients with a surgery performed at the L2–L3 level. There
were no cases of a surgical procedure previously performed at the index microdiscectomy
level. The average length of surgery was 77.9 ± 36.8 minutes (range: 43.0–256.0) with
no reports of intraoperative complications, and the patients were discharged after
an average of 1.7 ± 1.2 days (range: 1–7).
Postoperative Clinical Outcome
In the early postoperative period (1.5 ± 1.0 months postoperatively on average, range:
0.2–6.3), 62.2% (23/37) of patients presented with residual radicular pain, 25.7%
(9/35) with a sensory deficit, and 8.1% (3/37) with a residual motor deficit, respectively.
After an average of 40.4 ± 40.1 months (range: 1–128), 25% of patients (10/40) required
further surgery at the lumbar spine, which involved the level of the initial microdiscectomy.
Out of 30 patients who did not undergo additional spine surgery, 10 patients (33.3%)
needed further pain management measures.
Long-Term Clinical Outcome
At the time of the long-term telephone follow-up, which was conducted after an average
of 11.1 ± 4.0 years (range: 5–19) after the microdiscectomy, the VAS scores for back
and leg pain were reported to be 2.1 ± 1.9 out of 10 (range: 0–9), and 1.6 ± 1.6 out
of 10 (range: 0–8), respectively, which was significantly lower compared with the
preoperative VAS scores (p < 0.001 and p < 0.001) ([Fig. 2 ]). The pre- to postoperative changes in the back and leg pain VAS scores were −2.7 ± 3.7
(range: −9–5) and −4.9 ± 2.6 (range: −9–1), respectively. The severity of other reported
symptoms in the back and lower extremities apart from pain were described as 1.7 ± 1.7
(range: 0–7) on average.
Fig. 2 At postoperative follow-up of 11.1 ± 4.0 years (range: 5–19), the VAS scores for
both back and leg pain were significantly lower, compared with the preoperative setting
(p < 0.001 and p < 0.001, respectively). The pre- to postoperative changes in the back and leg pain
VAS scores were −2.7 ± 3.7 (range: −9 to 5) and −4.9 ± 2.6 (range: −9 to 1), respectively.
Improvement of symptoms in the postoperative setting compared with the preoperative
condition was stated by 37 out of 40 patients (92.5%). The majority of patients (31/40,
77.5%) reported “a lot of” improvement after surgery, whereas “moderate” or “little”
improvement was reported in 5% (2/40) and 10% (4/40) of patients, respectively. No
improvement or worsening of radiculopathy was reported in 2.5% (1/40) and 5% (2/40)
of patients, respectively. In terms of long-term overall patient satisfaction, the
average value was 9.1 ± 2.1 (range: 0–10), and 95.0% of patients (38/40) stated they
would undergo the same surgery again. Furthermore, 9 patients (22.5%) were unable
to work with respect to their spine condition, with 27 patients (67.5%) being employed
at the time of responding to the questionnaire. In only 1 of the 13 unemployment cases,
the reason for unemployment was related to the individual's spine condition. The results
of the ODI questionnaire indicated an average of 15.4 ± 20.7% (range: 0–80) at the
time of the telephone follow-up, which can be considered as “minimal disability.”[11 ]
Comparison of Patients with and without Additional Spine Surgery
The results of the detailed subanalysis comparing patients with and without additional
spine surgery are shown in [Table 2 ]. In summary, there were no statistically significant differences between both study
subpopulations, with regard to pre- and perioperative clinical data, only with regard
to the postoperative long-term clinical outcome. In the reoperation subcohort, the
reported outcome data were assessed at an average of 74.7 ± 52.5 months (range: 14–201)
after the revision surgery.
Table 2
Comparison of patients with or without reoperation after microdiscectomy
No add-on surgery (n = 30)
Add-on surgery (n = 10)
Variable
N
Mean or %
SD
N
Mean or %
SD
p value
Age at surgery (y)
40.3
12.9
38.8
11.7
0.595
Male gender
19
63%
5
50%
0.482
BMI (kg/m2 )
26.7
3.8
27.1
4.9
0.820
Neurological exam
Preoperative VAS (back)
4.3
2.9
6.3
3.7
0.082
Preoperative VAS (leg)
6.4
2.0
6.6
2.6
0.883
Preoperative sensory deficit
0.999
No
7
23%
2
20%
Yes
23
77%
8
80%
Preoperative motor deficit
0.693
No
10
33%
2
20%
Yes
20
67%
8
80%
Microdiscectomy level
0.100
L1–2
0
0%
1
10%
L2–3
0
0%
0
0%
L3–4
2
6.7%
0
0%
L4–5
5
17%
4
40%
L5-S1
23
77%
5
50%
Length of surgery (min)
77.4
40
79.9
23.2
0.300
Days of hospitalization
1.5
1.0
2.1
1.8
0.184
Telephone follow-up
Postoperative VAS (back)
1.8
1.7
2.9
2.1
0.117
Change from baseline VAS back
−2.5
3.2
−3.4
4.8
0.495
Postoperative VAS (leg)
1.5
1.5
1.9
1.6
0.295
Change from baseline VAS leg
−5.0
2.4
−4.7
3.4
0.950
Additional symptoms
1.2
1.0
3.3
2.3
0.005
Patient satisfaction
9.6
1.1
8.0
3.5
0.041
Ability to work
0.655
No
6
20%
3
30%
Yes
24
80%
7
70%
Oswestry disability index (%)
12.3%
18.2%
24.6%
25.7%
0.065
1. Pain intensity (0–5)
0.5
1.2
1.5
1.8
0.036
2. Personal care (0–5)
0.3
0.9
0.4
1.0
0.625
3. Lifting (0–5)
0.8
1.5
2.1
2.2
0.302
4. Walking (0–5)
0.4
1.0
0.6
1.3
0.282
5. Sitting (0–5)
0.8
1.2
0.9
1.3
0.959
6. Standing (0–5)
0.7
1.3
1.4
1.8
0.252
7. Sleeping (0–5)
0.3
0.9
1.5
1.8
0.006
8. Social life (0–5)
0.5
1.2
1.0
1.4
0.377
9. Traveling (0–5)
0.6
1.0
1.0
1.7
0.092
10. Changing pain (0–5)
1.2
1.7
1.9
1.9
0.261
Additional symptoms in the back and legs apart from pain were reported more frequently
by patients who had undergone additional spine surgery after the initial microdiscectomy,
which was statistically significant (p = 0.005). Furthermore, patient satisfaction was reported to be significantly higher
in patients who had not undergone a reoperation (p = 0.041). Although not statistically significant, there was a trend of both higher
pre- and postoperative VAS back pain scores in the reoperation study subpopulation
(p = 0.082, p = 0.117). The pre-to-postoperative change in the average VAS back pain scores was
comparable between patients with and without a reoperation (− 3.4 ± 4.8 and −2.5 ± 3.2
points difference, respectively; p = 0.495), which was also the case for the pre-to-postoperative change in the average
VAS leg pain scores (− 4.7 ± 3.4 and −5.0 ± 2.4 points difference, respectively; p = 0.950). Furthermore, the L4–L5 level was more frequently addressed in the reoperation
group (40 vs. 17%); however, this observed difference was not statistically significant
(p = 0.100).
With regard to the ODI questionnaire, the pain intensity was more severe in the reoperation
group (p = 0.036). Furthermore, the severity of pain-related sleep disturbances was significantly
higher in patients who had undergone add-on surgery (p = 0.006). Although not statistically significant, there was a trend of a more severe
pain-related inability to travel (p = 0.092) in patients who had undergone a reoperation, in addition to a trend toward
a higher total ODI score (24.6 ± 25.7 vs. 12.3 ± 18.2%, p = 0.065).
Discussion
Minimally invasive microdiscectomy has been established as an alternative to traditional,
more aggressive open approaches for the treatment of LDH, which is based on proposed
advantages including reduced tissue invasiveness, limited blood loss, a shorter duration
of surgery, and a faster postoperative recovery.[6 ]
[7 ]
[8 ]
[9 ]
[10 ] Although microdiscectomy was previously suggested to result in a favorable postoperative
outcome, the reported rate of recurrent disc herniations was higher in some long-term
follow-up studies compared with investigations with a shorter follow-up period.[8 ]
[12 ] Therefore, the aim of the present study was to evaluate the rate of revision surgery,
as well as the long-term outcome after microdiscectomy for the treatment of LDH in
patients with a minimum postoperative follow-up of 5 years. An illustrative case presentation
of a reoperation is shown in [Fig. 3A–D ].
Fig. 3 A 45-year-old female patient presented to the physician office complaining of lower
back pain (VAS: 10/10) radiating to the right lower extremity (VAS: 9/10), and a sensory
deficit in the L5–S1 distribution. (A) A preoperative computed tomography (CT) imaging
study depicted a lumbar disc herniation with central disc protrusion at the L5–S1
level, in addition to a mild retrolisthesis. The patient underwent a single-level
microdiscectomy at L5–S1 supplemented by fat-graft placement, and was discharged after
2 days. At her first postoperative office consultation, the symptoms of a sensory
deficit in the L5–S1 distribution had resolved, and her back and leg pain had improved,
with VAS scores of 4/10 and 1/10, respectively. Due to recurrent radicular symptoms,
a magnetic resonance (MR) image was performed 39 months after the index microdiscectomy,
which depicted a right paracentral disc herniation at the L5–S1 level, in addition
to a severely decreased disc height with posterior bulging of the L4–L5 disc (B) causing
mild thecal sac compression, and a slightly progressive right scoliosis with 12 degrees,
measured between L1 and L5 (C). Forty months after the initial microdiscectomy at
L5–S1, the patient underwent a posterior decompression from L4 to S1, neurolysis of
the L5 and S1 nerve roots, bilateral lateral fusion and posterior instrumentation
from L4 to S1, as well as two-level posterior lumbar interbody fusion at L4–L5 and
L5–S1 (D). At a postoperative telephone follow-up of 78 months, the reported VAS scores
for back and leg pain were both 1/10 with an absence of other radicular symptoms apart
from back or leg pain.
In their previously published meta-analysis on recurrent disc herniations after disc
removal, McGirt et al reviewed 54 studies including a total of 13,359 patients and
compared the postoperative outcomes after a limited versus an aggressive approach
to lumbar discectomy. In their subanalysis assessing persistent or recurrent back/leg
pain after a minimum of 2 years postoperatively, the authors reported a cumulative
incidence of 11.6% (range: 7–16%) for limited versus 27.9% (range: 19–36%) for aggressive
discectomy.[12 ] According to the results of the present study, the rate of reoperation related to
the index microdiscectomy was 25%, which is higher than the recently reported rate
of 18.5% by Soliman et al. However, the average postoperative follow-up period of
the quoted study was 7.2 years, which is approximately 3.5 years shorter than in the
present study.[8 ] According to the findings of a recent prospective cohort study on 108 patients,
a large size of the annular defect and little removal of disc material were identified
as risk factors for a same-level recurrent disc herniation after lumbar discectomy.
However, discectomy was performed by five surgeons, each from a distinct institution,
according to a surgeon-preference based, nonstandardized protocol, ranging from removal
of the herniated fragment only to intradiscal curettage with subtotal discectomy.[13 ] Their results are similar to the findings of Carragee et al, who identified the
lowest reherniation and reoperation rates for patients with a disc fragment and a
small annular fissure, both reported to be 1%.[14 ] In their retrospective analysis, Yorimitsu et al highlighted the favorable long-term
outcome after standard discectomy for the treatment of LDH. According to their findings
regarding the activities of daily living, assessed utilizing the Japanese Orthopedic
Association scoring system, the degree of disability was higher for activities such
as leaning forward and lifting heavy objects compared with others.[15 ]
In the present study population, a reoperation was performed after an average interval
of 40.4 ± 40.1 months (range: 1–128). In only 2 out of 10 cases, the reoperation was
performed within the first 12 months and in only 3 out of 10 cases within the first
24 months after surgery. As already suggested in a previous study,[8 ] it is hard to define whether a reoperation was necessary due to inefficacy of the
initial surgical attempt, or due to the progression of the degenerative spine disease
itself. We believe that in the study subjects with a reoperation after an interval
of more than 24 months, degenerative disease progression was the predominant cause
for symptom recurrence as opposed to surgical failure. By comparing patients with
and without a reoperation after the index microdiscectomy, we were able to identify
a difference in the postoperative long-term outcome. According to our data, statistically
significant differences between both study subgroups were observed regarding the presence
of additional symptoms apart from back or leg pain, the degree of patient satisfaction,
the severity of pain-related sleep disturbances, and the patient-reported pain intensity
as scored according to the ODI in the postoperative setting. Nevertheless, it needs
to be highlighted that it remains unclear whether these differences were observed
because of the performance of an additional lumbar spine surgery or a more advanced
disease at baseline in the reoperation subcohort, as reflected by a trend toward a
higher preoperative back pain severity. Interestingly, the pre-to-postoperative differences
in the average VAS back and leg pain scores were comparable between patients with
and without a reoperation. There were no statistically significant differences between
both study subpopulations, with regard to pre- and perioperative clinical data.
To capture all reoperations that were performed at an outside institution, patients
were asked about any other related spine surgery after the index microdiscectomy as
part of the long-term follow-up questionnaire. Furthermore, since the data collection
were completed before hypothesizing a potential difference in the postoperative long-term
outcome between both study subpopulations, data acquisition was performed in an unbiased
way. In fact, data collection was performed by a coauthor without any conflicts of
interest who was not involved in the patient care. Moreover, besides retrospectively
collected data, patient reported data were evaluated in the statistical analysis.
The accurate interpretation of the presented findings requires the consideration of
the study's limitations. The fact that there was a large proportion of patients who
either did not meet the inclusion criteria of the present study or were lost to follow-up
represents the main limitation of the present study, due to a potential follow-up
bias. To evaluate the potential for bias in the results due to missing data of unavailable
patients, we compared demographic and surgical details between the study population
(n = 40) and patients who were not available for statistical analysis (n = 163). Out of the 163 “not available” patients, basic demographic and surgical details
were available for 140 patients. There were no significant differences between the
study population and the 140 patients who were not available for analysis in terms
of the age at surgery (p = 0.752), height (p = 0.626), weight (p = 0.468), BMI (p = 0.134), sex (p > 0.999), or microdiscectomy level (p = 0.090). There was a statistical difference in terms of the side of the surgical
approach (right- vs. left-sided approach) with a p value of 0.046 (not shown). Another limitation of the present study is that not all
patients had available VAS scores reported in the medical records, and that missing
VAS scores needed to be retrieved from the documented patient history and estimated
based on the individual description of the pain severity. Despite the fact that only
a small proportion of preoperative VAS scores needed to be estimated (preoperative
back and leg pain estimation in 12.5% [n = 5] and 20.0% [n = 8] of patients, respectively), and that all pain scores were collected by a single
independent co-author without any conflict of interest, the reported mean VAS scores
for each subcohort need to be seen as estimated values when interpreting the reported
findings. Moreover, the observed postoperative differences in some of the ODI questions
between patients with and without a reoperation may be biased by the missing and therefore
unknown preoperative ODI scores.
Finally, with regard to the subanalysis comparing patients with and without a reoperation
after the index microdiscectomy, it needs to be stated that patients in the reoperation
subgroup may have a poorer long-term outcome either because they had a reoperation
or because they had greater disability or more advanced disease at baseline. In fact,
it appears that the reoperation subgroup presented with a trend toward a higher back
pain severity already in the preoperative setting. Follow-up studies with available
preoperative ODI scores and a larger sample size are warranted to investigate the
trend toward a poorer clinical long-term outcome in the reoperation subgroup, as reflected
in the ODI score and the degree of patient satisfaction.
Summary and Conclusion
In conclusion, according to our findings, a minimally invasive approach for the treatment
of LDH results in a favorable postoperative long-term outcome in the majority of cases.
However, the reoperation rate in our series was higher as previously reported in investigations
with a generally shorter postoperative follow-up period. Although there were neither
pre- nor perioperative statistically significant, clinical differences between patients
with and without a reoperation related to the index microdiscectomy, our findings
suggest a potential difference with regard to the long-term outcome, as reflected
in the ODI score. However, further follow-up studies with available preoperative ODI
scores and a larger sample size are warranted to investigate whether these differences
were observed because of the performance of an additional lumbar spine surgery or
a more advanced disease at baseline in the reoperation subcohort.
This article was accepted after robust discussions among EBSJ reviewers. The authors were able to address the concerns raised and acceptance was
granted in light of the thought-provoking insights gained by this article with its
strengths being long-term follow-up and study of a consistently applied intervention
in form of minimally invasive microdiscectomy. The questions posed were simple yet
of high interest: long-term outcomes and reoperation rates.
There were two important methodological concerns: Even though this is a retrospective
study where the majority of the data came from the medical records, the issue of follow-up
bias is just as important. It is not appropriate to have an exclusion criteria that
pertains to data collected after a person is treated. For example, missing data or
subjects not available for a telephone interview are akin to a subject who is enrolled
prospectively that cannot be contacted and hence “lost to follow-up.” It is an important
distinction. Inclusion/exclusion criteria pertain to the generalizability of the results.
Patients who ordinarily would be eligible but did not contribute to the results should
be treated separately and unfortunately contribute to the potential for follow-up
bias. That is why is it so important to provide the data on the similarities between
these groups which was done well in this study. That technically means the follow-up
rate will be less than 25%. The problem with follow-up bias is that it may not be
random. That is, people who cannot be reached by phone may have been more or less
likely to have had a reoperation or more or less likely to have a poor outcome. We
will not know for sure.
The other important issue is the comparison between those who have reoperation and
those who do not with respect to long-term outcomes. It is not entirely clear if the
authors are implying these patients do worse because they had an operation or worse
because they had greater disability or more advanced disease as baseline. The data
does not support either theory. In fact, it appears that the reoperation group presented
with more back pain and there were some other differences like preoperative motor
deficit and discectomy levels. Statistical significance is probably less important
with such a small sample size. The absolute differences are worth noting and may explain
why the reoperation group had less satisfaction as well as lower ODI scores. Without
a preoperative ODI score, we, however, have no way of knowing what the follow-up score
represents.
EBSJ commends the authors for a worthy effort and being willing to publish less than perfect
results to allow us more realistic outcomes prognostication and patient counseling.
