Abstract
Background: Symptomatic lumbar degenerative disc disease is a
challenging entity to treat. The results of arthrodesis may be compromised in
the short term by pseudarthrosis and in the long term by pain at the
iliac-crest donor site and by junctional degeneration. Total disc replacement
has the potential to provide long-lasting relief to these patients. The
purpose of this study was to present the clinical and radiographic results
assessed seven to eleven years following a Prodisc total lumbar disc
replacement.
Methods: Sixty-four patients had single or multiple-level
implantation of a total lumbar disc replacement between 1990 and 1993. The
mean duration of follow-up was 8.7 years. Clinical results were evaluated by
assessing preoperative and postoperative lumbar pain, radiculopathy,
disability, and modified Stauffer-Coventry scores. Preoperative and
postoperative radiographs were evaluated as well. Subgroup analysis was
performed to determine if gender, an age of less than forty-five years,
previous surgery, or multilevel surgery had an effect on outcome.
Results: At an average of 8.7 years postoperatively, there were
significant improvements in the back-pain, radiculopathy, disability, and
modified Stauffer-Coventry scores. Thirty-three of the fifty-five patients
with sufficient follow-up had an excellent result, eight had a good result,
and fourteen had a poor result. Neither gender nor multilevel surgery affected
outcome. An age of less than forty-five years and prior lumbar surgery had
small but significant negative effects on outcome. Radiographs did not
demonstrate loosening, migration, or mechanical failure in any patient. Five
patients had approach-related complications.
Conclusions: The Prodisc lumbar total disc replacement appears to be
effective and safe for the treatment of symptomatic degenerative disc disease.
Gender and multilevel surgery did not affect the outcomes, whereas prior
lumbar surgery or an age of less than forty-five years was associated with
slightly worse outcomes. Longer follow-up of this cohort of patients and
randomized trials comparing disc replacement with arthrodesis are needed.
Level of Evidence: Therapeutic Level IV. See Instructions
to Authors for a complete description of levels of evidence.
Intervertebral disc degeneration is a major cause of pain and disability in
adults and is associated with large economic and social
costs1. The initial
treatment for lumbar degenerative disc disease is nonoperative, but that often
fails. The most common surgical treatment is arthrodesis, which can relieve
pain, eliminate segmental instability, maintain disc space height, preserve
sagittal balance, and halt further degeneration at the operatively treated
level. A recent randomized clinical trial demonstrated that, at the time of
short-term follow-up, lumbar arthrodesis was superior to nonoperative
management for the treatment of chronic low-back pain due to degenerative disc
disease2.
However, lumbar arthrodesis is not a perfect operation. In a meta-analysis
of forty-seven publications on lumbar arthrodesis, the rates of pseudarthrosis
and chronic pain at the iliac crest donor site were estimated to be 14% and
9%, respectively3.
Many postoperative protocols include cumbersome bracing. At the time of
long-term follow-up after intersegmental fusion, stress concentrations have
been found cephalad and caudad to the fused segments. Hypertrophic facet
arthropathy, dynamic instability, spinal stenosis, disc degeneration, and
osteophyte formation have all been reported to occur at levels adjacent to a
fusion. These pathological processes may result in pain and require revision
surgery in many
patients4-6.
Many investigators have attempted to develop intervertebral disc
prostheses7.
Although multiple studies have demonstrated good short-term clinical results
after lumbar total disc
replacement8-10,
to our knowledge none have included clinical follow-up of greater than 4.3
years11 after a
contemporary lumbar total disc replacement.
The purpose of this study was to report the clinical and radiographic
outcomes seven to eleven years following treatment with a first-generation
Prodisc lumbar total disc replacement (Aesculap, Tuttlingen, Germany). We also
sought to determine the patient factors that might affect the clinical
outcome.
Patient Characteristics
Sixty-four patients underwent single or multiple-level implantation of a
Prodisc lumbar total disc replacement between 1990 and 1993. Fifty-five (86%)
of the sixty-four patients in the original cohort had sufficient clinical and
radiographic follow-up for analysis and gave informed consent to participate
in this study. Of the patients who were not included in the follow-up
analysis, three had died from causes unrelated to the implantation surgery,
two could not be located for the follow-up evaluation, two refused to return
for the follow-up examination, and two did not complete all items of the
questionnaire. The ethical compliance of this study was certified by the
Committee on Medical Ethics of the Clinique du Parc.
Each patient had radiographic evidence of degenerative disc disease and had
had severe lumbar pain despite nonoperative treatment for a minimum of six
months prior to the index procedure. Exclusion criteria included facet
arthrosis, central or lateral recess stenosis, osteoporosis, sagittal or
coronal plane deformity, postoperative absence of posterior elements, and a
sequestrated herniated nucleus pulposus that could not be decompressed from an
anterior approach. There were thirty men and twenty-five women with an average
age of forty-six years (range, twenty-five to sixty-five years) at the time of
surgery. Twenty-seven patients (49%) had had no prior lumbar surgery, ten
patients (18%) had had one prior operation, and eighteen patients (33%) had
had two, three, or four prior operations. The prior operations included
discectomy, laminotomy, percutaneous nucleotomy, chemonucleolysis, and
thermocoagulation. A total of seventy-eight prostheses were implanted in the
fifty-five patients. Thirty-five patients had a one-level implantation;
seventeen, a two-level implantation; and three, a three-level implantation
(Table I). Seven patients
underwent additional surgical procedures during the same surgical session;
these operations included an L5-S1 arthrodesis with an L4-L5 lumbar total disc
replacement in six patients and an L5-S1 arthrodesis adjacent to L3-L4 and
L4-L5 lumbar total disc replacements in one patient.
Preoperatively, forty-six (84%) of the fifty-five patients were employed:
twelve were sedentary workers, and thirty-four were manual laborers. Of the
forty-six employed patients, twenty-two were on medical leave from work
because of back pain. Of the nine unemployed patients, two were receiving
disability benefits and one was retired.
Implant Design
The first-generation Prodisc lumbar total disc replacement consists of two
titanium-alloy end plates and a polyethylene core
(Fig. 1). The implants are
manufactured in four sizes, three heights, and two lordosis angles. Each end
plate is coated with a titanium-plasma ingrowth surface and has two keels to
provide primary stability. The convex polyethylene core is securely mated to
the inferior titanium end plate and provides a congruent ball-and-socket
articulation.
Surgical Protocol
Forty-five patients (82%) were treated through a retroperitoneal approach
and ten, through a transperitoneal approach. The transperitoneal approach was
preferred for obese patients or patients who had had previous anterior
surgery. Anterior anulotomy and nucleotomy back to the posterior anular fibers
was performed. The end-plate cartilage was removed, but the mechanical
integrity of the osseous end plates was carefully preserved. The patients were
mobilized out of bed on the first postoperative day. No patient wore a brace
postoperatively. Running, jumping, heavy lifting, twisting, and bending at the
waist were restricted until the third postoperative month.
Clinical Evaluation
The patients were evaluated preoperatively by the surgeon who treated them
(T.M.) and postoperatively by another one of the authors (P.T.) and by a
research assistant, neither of whom were involved in the patient selection,
surgery, or postoperative care. The average follow-up period was 104 months
(8.7 years), with a range of eighty-five to 128 months.
Four scoring systems were used to evaluate the patients preoperatively and
postoperatively. A 20-point modified
Stauffer-Coventry11
score, ranging from 0 (worst) to 20 (best), was used to assess pain,
neurologic deficits, need for medication, disability, and psychiatric status
(see Appendix). Absolute scores were converted into relative improvement
scores by dividing the actual improvement by the maximum possible improvement.
A result was rated as excellent when the relative improvement score was
>70%, good when it was between 60% and 70%, and poor when it was <60%.
Three separate subjective areas were scored on 3-point scales preoperatively
and postoperatively by the patients (see Appendix): low-back pain was graded
as severe (3 points), moderate (2 points), mild (1 point), or absent (0
points); lower-limb (radicular) pain was graded as severe (3 points), moderate
(2 points), mild (1 point), or absent (0 points); and the ability to perform
work-related activities and activities of daily living was scored as normal (0
points), slightly limited (1 point), substantially impaired (2 points), or
severely limited or impossible (3 points). Finally, it was noted whether the
patient was entirely satisfied, satisfied, or not satisfied with the result of
the surgical procedure.
Several patient factors, including younger age (less than forty-five
years), gender, previous lumbar surgery, and multilevel disc implantation,
were evaluated to determine their effect on outcome. Student t testing
(parametric), Wilcoxon matched-pairs signed-ranks testing (ordinal, paired),
and Mann-Whitney testing (ordinal, unpaired) were performed with significance
defined as p < 0.05. All data analysis was performed with Microsoft Excel
97 software (Microsoft, Redmond, Washington) and InStat 3 software (GraphPad
Software, San Diego, California).
Radiographic Evaluation
Standing anteroposterior and lateral radiographs, lateral flexion-extension
radiographs, magnetic resonance images, and computed tomography scans were
assessed for periprosthetic radiolucent lines, implant migration, mechanical
failure (dissociation or fracture), and wear of the polyethylene bearing. The
height of the polyethylene core was measured on standing lateral radiographs
made immediately after the surgery and at the final evaluation; the width of
the subjacent vertebral end plate was used to correct for differences in
magnification between radiographs.
Clinical Results
Thirty-three (60%) of the fifty-five patients had an excellent result
(relative improvement score, >70%), eight (15%) had a good result (relative
improvement score, 60% to 70%), and fourteen (25%) had a poor result (relative
improvement score, <60%). There were significant postoperative improvements
(p < 0.0001) in the modified Stauffer-Coventry, low-back-pain,
lower-limb-pain, and disability scores
(Table II). The mean modified
Stauffer-Coventry score was 7.0 of 20 points preoperatively and 16.1 of 20
points postoperatively. Forty-three of the fifty-five patients rated the
low-back pain as severe preoperatively, and fifty patients rated it as
moderate, mild, or absent at the time of final follow-up
(Fig. 2). Thirty-eight patients
had severe lower-limb pain preoperatively compared with two at the time of the
last-follow-up. Of the forty-eight patients who had had preoperative
lower-limb pain, forty-three had no or mild pain at the time of the last
follow-up (Fig. 3).
Preoperatively, forty-six of the fifty-five patients were substantially or
severely impaired with regard to their ability to perform work-related
activities or activities of daily living, whereas, at the time of the last
follow-up, forty-four patients had a normal or slightly impaired ability and
eleven had a moderately or severely impaired ability
(Fig. 4).
Of the twenty-four patients who had been employed full-time before the
surgery, thirteen (54%) were employed, six were retired, four were receiving
disability benefits, and one was on sick leave from employment at the time of
final follow-up. Of the eight patients who had been unemployed or receiving
disability benefits before the surgery, one was still receiving disability
benefits, two were still unemployed, and five were retired at the time of
final follow-up. Finally, thirty-five patients (64%) reported that they were
entirely satisfied with the result of the surgery, fifteen reported that they
were satisfied, and five were not satisfied.
The results of the analysis of the effects of age, gender, previous lumbar
surgery, and multilevel disc implantation are shown in the Appendix. Briefly,
patients who were forty-five years of age or older had better postoperative
modified Stauffer-Coventry scores (p = 0.006) and higher relative improvement
scores (p = 0.005). Although, preoperatively, women considered themselves to
be more disabled than did men (p = 0.005), there were no significant
differences in postoperative outcome based on gender. Patients who had had
previous lumbar surgery had inferior postoperative modified Stauffer-Coventry
scores (p = 0.042) and relative improvement scores (p = 0.045). Finally, with
the numbers available, there were no significant differences in outcome
between single and multiple-level implantations.
Of the seven patients who had had both disc replacement and an adjacent
arthrodesis during the same operation, five had a relative improvement score
of >70% and two had a relative improvement score of <60%. Three of the
five patients who were not satisfied with the result of the index surgery
subsequently underwent an arthrodesis with posterior instrumentation and
retention of the prosthesis. These patients all had had multiple previous
operations. One patient underwent the arthrodesis at five years after the disc
replacement, and the other two patients, at three years.
Radiographic Results
No periprosthetic radiolucencies, migration, or mechanical failures were
noted at the time of the last follow-up
(Fig. 5). There was no
substantial decrease in the mean height of the polyethylene bearing between
the immediate postoperative and final radiographs. Seventeen patients (31%)
had intraoperative penetration of the implant through the posterior part of
the superior and/or inferior end plates and into the vertebral body. The
end-plate penetration was =2 mm in fifteen patients and >2 mm in two.
End-plate penetration had no significant effect on clinical outcome, with the
numbers available. A spontaneous interbody fusion developed at the level of
the implantation in one patient with end-plate penetration.
Complications
Five patients (9%) had surgical complications, consisting of one deep
venous thrombosis, one iliac vein laceration that was repaired primarily, one
transient retrograde ejaculation, and two incisional hernias. No complication
was related to the prosthesis itself. Five patients had increased radicular
pain postoperatively, without radiographically apparent neural compression.
Their pain was attributed to nerve root traction resulting from intervertebral
distraction in the setting of postoperative epidural fibrosis. These patients,
who all had had previous discectomies, were treated with medication. The
radicular pain had resolved by three months postoperatively in all
patients.
Lumbar arthrodesis is the most commonly performed procedure for patients
with painful degenerative disc disease for which nonoperative management has
failed12. Despite
excellent short-term clinical success rates approaching 80% in series ranging
in size from fifty-one to sixty-nine
patients13-15,
lumbar arthrodesis is an imperfect procedure. One long-term study of patients
treated with lumbar arthrodesis showed that 44% (twenty-seven of sixty-one)
had back pain, 53% (thirty-three of sixty-two) were using medications for back
pain, and 15% (nine of sixty-two) had required additional lumbar surgery at a
mean of thirty-three years
postoperatively16.
Total disc replacement has numerous potential advantages, including the
avoidance of pseudarthrosis, postoperative bracing, and the development of
junctional degeneration. Because candidates for lumbar total disc replacement
are often young, a successful disc-replacement prosthesis must endure decades
of high loading without mechanical failure. To our knowledge, we are the first
to report the seven to eleven-year results of a contemporary lumbar total disc
replacement. We consider this to be medium-term follow-up, and it is essential
that follow-up of this cohort be continued in the decades to come.
The longest previous follow-up study of a contemporary lumbar total disc
replacement, of which we are aware, was reported by Lemaire et
al.11. In their
study, 105 patients were evaluated with use of the modified Stauffer-Coventry
score fifty-one months following treatment with the SB Charité implant
(Waldemar Link, Hamburg, Germany). Using the same criteria that we used in the
current study, they found that 79% of their patients had a relative
improvement score of >70% (excellent), 6% had a score of 60% to 70% (good),
and 15% had a score of <60% (poor). Complications occurred in 10% (eleven)
of the 105 patients.
It is difficult to directly compare the results of lumbar total disc
replacement with those of arthrodesis for the treatment of degenerative disc
disease. Penta and
Fraser17 reported
on 103 patients who had been followed for ten to twelve years following
anterior lumbar interbody arthrodesis. Seventy-eight percent (ninety-eight) of
the original cohort of 125 patients had the surgery for treatment of
discogenic back pain. Not including those who had nonunion, 10% of the 103
patients who were followed had complications. Seventy-eight percent of the 103
patients reported that they had "complete relief" or "a good
deal of relief." According to the Low-Back Outcome
Score18, 68%
(seventy) of the 103 patients had a "fair" result or better.
Twenty-two percent (twenty-nine) of the 129 treated levels failed to fuse.
Given the differences in patient-evaluation techniques between our study and
the one by Penta and Fraser, it is impossible to determine whether fusion or
lumbar total disc replacement provides superior results. In fact, since it may
take more than a decade for symptomatic junctional degeneration to develop
after a fusion19,
longer follow-up periods may be necessary to distinguish between the two
techniques even in randomized prospective studies.
We believe that the Prodisc device can be used successfully at two or three
contiguous levels. Some authors have reported that they had not observed
problems with multilevel implantation of SB Charité
devices11; however,
they did not compare single and multiple-level subgroups as we did in the
current study. Cinotti et
al.9 reported that
the SB Charité prosthesis is not suitable for implantation at two
contiguous levels. When it is implanted at two levels, adequate distraction
may be difficult to achieve at the second level, resulting in an undersized or
anteriorly located prosthesis. Because of the monoconvex configuration of the
Prodisc polyethylene core, the intersegmental distraction required for
insertion of the Prodisc replacement is probably less than that needed for
insertion of the biconvex core of the SB Charité replacement. Twenty of
our fifty-five patients had multilevel implantation, and their clinical
results were similar to those of the single-level implantations.
Five patients with previous, failed back surgery experienced notable
radicular pain after implantation of the Prodisc replacement, possibly because
of epidural fibrosis resulting in nerve root traction after intervertebral
distraction. The pain resolved spontaneously in all five patients after three
months of observation. This complication occurred in five of the twenty-eight
patients who had had previous lumbar surgery.
After an average of 8.7 years, polyethylene wear was not evident on plain
radiographs. Although compressive loads in the lumbar spine are high, the
previously
reported9-11,20
arcs of flexion-extension have been small, averaging 4° to 10°. The
accuracy of our technique for wear assessment is unknown, but it is likely
that radiostereometric analysis is the most sensitive technique. Postmortem
recovery of prostheses could also provide useful information regarding wear
and bone ingrowth, but this information has not been reported, to our
knowledge. Currently it is unknown whether osteolysis will occur after lumbar
total disc replacement, but we are encouraged by the absence of
radiographically apparent osteolysis in our patients at seven to eleven years
postoperatively. Although metal and polyethylene lumbar total disc
replacements were first implanted in the early 1980s, we are aware of only one
reported case of presumed osteolysis after lumbar total disc replacement; this
occurred thirteen years after placement of an SB Charité lumbar total
disc
replacement21.
The current study had all of the limitations inherent to nonrandomized case
series. We cannot make any definitive statements regarding the outcomes of
lumbar total disc replacement compared with those of nonoperative treatment or
arthrodesis. The data reflect the results associated with a single implant
type and may be different for other designs of lumbar total disc
replacement22.
Furthermore, the study would be more useful if validated outcomes instruments
had been used. Nevertheless, our data indicate that the prosthesis is safe,
with an acceptably low rate of complications at seven to eleven years
postoperatively, and that its efficacy appears promising and should be tested
in a randomized prospective trial.
Tables showing the modified Stauffer-Conventry scores; scores for low-back
pain, lower-limb pain, and disability; and subgroup analysis by age, gender,
prior lumbar surgery, and multilevel disc implantation are available with the
electronic versions of this article, on our web site at
(go to
the article citation and click on "Supplementary Material") and on
our quarterly CD-ROM (call our subscription department, at 781-449-9780, to
order the CD-ROM). ?
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