Journal of Spinal Disorders & Techniques
`Vol. 16, No. 4, pp. 362–368
`© 2003 Lippincott Williams & Wilkins, Inc., Philadelphia
`
`Lumbar Disc Replacement
`
`Preliminary Results with ProDisc II After a Minimum Follow-Up Period of 1 Year
`
`Patrick Tropiano, †Russel C. Huang, †Federico P. Girardi, and *Thierry Marnay
`
`Department of Orthopaedic Surgery, Hôpital CHU Nord, Marseille, and *Clinique du Parc, Department of
`Orthopaedic Surgery, Castelnau-le-Lez, France; and †Spine Surgery Service, Hospital for Special Surgery,
`New York, New York
`
`Summary: Total disc replacement has the potential to replace fusion as the gold stan-
`dard surgical treatment of degenerative disc disease. Potential advantages of disc re-
`placement over fusion include avoidance of pseudarthrosis, postoperative orthoses, and
`junctional degeneration. After observing satisfactory clinical results at 7–11 years’ fol-
`low-up with the ProDisc first-generation implant, a second-generation prosthesis was
`designed. This study is a prospective analysis of the early results of total disc replace-
`ment with the ProDisc II total disc prosthesis. Fifty-three patients had single-level or
`multilevel disc replacement and were evaluated clinically and radiographically preop-
`eratively and at mean 1.4-year follow-up. There were clinically and statistically signifi-
`cant improvements in back and leg pain Visual Analog Scale and Oswestry disability
`scores that were maintained at final follow-up. The clinical results of patients with
`single- and multilevel surgery were equivalent. Satisfactory results were achieved in 90%
`of patients who had previous lumbar surgery. Complications occurred in 9% of patients
`and included vertebral body fracture, transient radicular pain, implant malposition, and
`transient retrograde ejaculation. Three patients (6%) required reoperation to address
`complications. No mechanical failure of the implants or loosening was observed, and the
`prostheses retained motion. Randomized, prospective, long-term studies will be neces-
`sary to compare the effectiveness of arthrodesis with total disc replacement. Key
`Words: disc, replacement, prosthesis, lumbar
`
`INTRODUCTION
`
`Preserving the function of the motion segment rather
`than opting for arthrodesis seems intuitively to be a more
`favorable treatment option for several spinal disorders.
`The current gold standard treatment of painful degenera-
`tive disc disease of the lumbar spine that has failed non-
`surgical management is arthrodesis. Short-term clinical
`success rates as high as 80% have been reported with
`fusion techniques.1–3 Furthermore, a recent randomized,
`prospective trial found that the clinical success rate of
`
`Received January 15, 2003; accepted April 10, 2003.
`Address correspondence and reprint requests to Dr. Patrick Tropiano,
`Department of Orthopaedic Surgery, Hôpital CHU Nord, Chemin des
`Bourrelly, 13915 Marseille, Cedex 20, France. E-mail: ptropiano@
`ap-hm.fr
`
`surgical fusion was superior to that of nonsurgical man-
`agement.4 However, the incidence of pseudarthrosis and
`the need for postoperative orthoses after fusion surgery are
`distinct disadvantages. Furthermore, long-term elimina-
`tion of segmental motion leads to junctional degeneration
`and stenosis in some cases.5–8
`Since 1950, artificial disc technology has been devel-
`oped to recreate intervertebral disc function. Many design
`philosophies have evolved,9,10 such as low-friction sliding
`surfaces, spring systems, contained fluid-filled chambers,
`and disc of rubber or other elastomers, but the majority
`have not been used clinically.11 An ideal intervertebral
`disc prosthesis should restore disc space height and lor-
`dosis, restore segmental motion, generate physiologic ki-
`netics at the spinal triple joint complex, and serve as a
`shock absorber. If these goals are met, the clinical result
`
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`EXHIBIT 1016
`IPR2015-to be assigned
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`Preliminary Results with ProDisc II
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`should be elimination of pain from disc degeneration or
`from nerve compression, prevention of adjacent segment
`degeneration, and improvement of the patient’s functional
`status. Finally, a prosthetic disc must be biocompatible
`and durable for >40 years.
`Today, two main families of disc prostheses exist: the
`disc nucleus replacement devices and the total disc re-
`placement devices. The first-generation ProDisc (Aescu-
`lap AG & Co., Tuttlingen, Germany) total disc replace-
`ment prosthesis was created in 1989 and implanted in 64
`patients between March 1990 and September 1993. It was
`an investigational device and its implantation required a
`long and difficult learning curve, but mean 8.7-year (range
`7–11 years) follow-up has confirmed its effectiveness and
`safety.12 The ProDisc II (Aesculap AG & Co.) implant
`incorporates several implant and instrumentation design
`improvements and was launched in the European market
`in December 1999. The purpose of the current study is to
`report the preliminary clinical and radiographic outcomes
`of patients who had ProDisc II disc replacement.
`
`MATERIALS AND METHODS
`
`Implant Design
`
`The ProDisc II (Fig. 1) consists of two cobalt-
`chromium endplates coated with a titanium plasmapore
`bone ingrowth surface. A convex polyethylene core acts
`as a bearing surface and shock absorber. A modular lock-
`ing system secures the polyethylene core to the caudal
`endplate, leaving two moving parts. The endplates have
`central anchoring keels to provide immediate stability for
`optimal bone ingrowth. The ProDisc II instrumentation is
`used to create a precise groove in the vertebral endplates
`for implant insertion, to lock the polyethylene core into the
`caudal endplate, and to insert the implant precisely. The
`device is modular, so the surgeon can customize the im-
`plant to each patient’s unique anatomy. There are two
`endplate sizes (medium and large), three heights (10, 12,
`and 14 mm), and two lordosis angles (6° and 11°).
`
`Patients and Surgical Protocol
`
`Between December 1999 and December 2001, 53 pa-
`tients who had previously undergone ProDisc II implan-
`tation by one surgeon underwent clinical and radiographic
`evaluation after a mean follow-up period of 1.4 years
`(range 1–2 years). There were 18 men and 35 women with
`a mean age of 45 years (range 28–67 years). Preoperative
`diagnoses included disc degeneration (33 patients) and
`failed spine surgery (20 patients), and all the patients had
`at least 6 months of severe back pain and had failed non-
`
`surgical treatment. Exclusion criteria are summarized in
`Table 1. Thirty-three patients (62%) had no prior surgery,
`11 patients (21%) had one prior surgery, and 9 patients
`(17%) had two or more prior surgeries. The types of prior
`surgery included discectomy, partial laminectomy, and
`thermocoagulation.
`The operated level was L5–S1 in 27 patients and L4–L5
`in 13 patients. Eleven patients had disc prostheses im-
`planted at two vertebral levels (L4–L5 and L5–S1 in nine,
`L3–L4 and L4–L5 in two). Two patients had implantation
`at three vertebral levels (L3–L4, L4–L5, and L5–S1). The
`anterior surgical approach was retroperitoneal in 48 cases
`(90%) and transperitoneal in 5 cases (10%). The transperi-
`toneal approach was preferred in cases of obesity or pre-
`vious anterior surgery. The mean operative time was 104
`minutes (range 32–250 minutes), and the mean hospital
`stay was 9 days (range 4–31 days). Low molecular weight
`heparin was administered as thromboembolic prophylaxis
`for the first 21 postoperative days. One month after sur-
`gery, all the patients began physiotherapy. No patient
`wore an orthosis postoperatively. Patients were advanced
`as tolerated to unrestricted activities beginning 1 month
`after surgery.
`
`Clinical Evaluation
`
`The patients were clinically evaluated by one of the
`authors and by a research assistant at 3 months, 6 months,
`and at final follow-up (minimum 1 year). Neither evalu-
`ator participated in patient selection, surgery, or postop-
`erative care. Back and leg pain intensities were indepen-
`dently evaluated using the Visual Analog Scale (VAS)
`modified from the work of Million et al.13 Pain intensity
`was scored from severe interference10 to no interference.1
`Scores were interpreted as excellent (1–2.49), good (2.5–
`4.99), fair (5–7.49), or poor (7.5–10). Disability was esti-
`mated using the Oswestry Disability Questionnaire.14
`Three additional criteria were analyzed on qualitative
`scales as follows:
`
`• Quality of life was defined on a scale of 1–4: normal,
`slightly limited, hindered, or severely limited/impossible.
`• Return to work was documented on a scale of 1–4:
`normal, slightly limited, hindered, or severely
`limited/impossible.
`• Patient satisfaction with the surgical procedure was re-
`corded as entirely satisfied, satisfied, or not satisfied.
`
`Radiographic Evaluation
`
`Preoperative evaluation included standing anteroposte-
`rior (AP) and lateral radiographs, lateral flexion-extension
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`FIGURE 1. The ProDisc II prosthesis provides a 20° arc of
`motion in flexion-extension and lateral bending. Physiologic an-
`terior translation occurs during flexion. A, Lateral bending; B,
`flexion with physiologic anterior translation; C, extension.
`
`radiographs, magnetic resonance imaging, and computed
`tomography scans. Postoperative evaluation consisted of
`standing AP and lateral radiographs and flexion-extension
`lateral radiographs. Lumbar lordosis was measured preop-
`eratively and at final follow-up by Cobb’s method from
`the superior endplate of T12 to the superior endplate of S1.
`Discography was performed in cases of multilevel dis-
`copathy to better define symptomatic levels. Follow-up
`radiographs were assessed for implant position, interface
`ingrowth, angular motion on lateral flexion-extension
`views, and degenerative changes in the adjacent motion
`segments.
`
`RESULTS
`
`Patient satisfaction was reported as entirely satisfied in
`46 patients (87%), satisfied in 7 (13%), and not satisfied in
`0 (0%). The resumption of work and activities of daily
`living (ADLs) was reported as full in 38 cases (72%) and
`as slightly limited in 15 (28%). Seven patients with work-
`ers’ compensation stated they could not work, but their
`ADLs were only slightly limited.
`Table 2 compares the average preoperative back and leg
`VAS scores compared with the scores obtained at 3
`months, 6 months, and last follow-up. Statistical analysis
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`TABLE 1. Exclusion criteria
`
`TABLE 2. Pre- and postoperative VAS back and leg pain
`scores and Oswestry disability scores
`
`General exclusion criteria
`䡲 Known chronic disease of major organ system (eg, cardiac failure,
`hepatitis, diabetes)
`䡲 History of local infection
`䡲 Pregnancy
`Specific exclusion criteria
`䡲 Associated facet degeneration (eg, significant bony central canal
`stenosis, deformation of facet articulations, osteophyte formation,
`severe articular degeneration)
`䡲 History of abdominal or retroperitoneal surgery near planned
`anterior approach
`䡲 Osteoporosis or osteopenia
`䡲 Structural spinal deformities (eg, scoliosis, kyphosis)
`䡲 Absence (postoperative) of posterior elements (eg, after
`laminectomy and facetectomy)
`
`showed a significant improvement for back and leg pain at
`final follow-up (P < 10−6, paired t test). The data showed
`a significant improvement in back pain after the third
`month, which remained stable with time until the last fol-
`low-up (P < 10−6, paired t test). Statistical analysis dem-
`onstrated progressive improvement of radicular pain with
`significant differences between preoperative and 3 months
`(P < 10−6, paired t test) and between 3 and 6 months (P <
`10−3, paired t test). The improvement was stable between
`6 months and final follow-up. The Oswestry disability
`score improved from a preoperative mean of 56% (severe
`
`FIGURE 2. Three-level ProDisc II implantation. A 55-year-old
`man with segmental instability at L3–L4, failed discectomy at L4–
`L5 and L5–S1, and severe low back pain. Excellent clinical out-
`come at 16-month follow-up.
`
`Preoperative
`
`3 mo
`postoperative
`
`6 mo
`postoperative
`
`Mean 1.4-y
`follow-up
`
`VAS lumbar
`VAS radicular
`Oswestry
`
`7.4 ± 2.5
`6.7 ± 2.99
`56 ± 8.21
`
`1.8 ± 2.14a
`2.8 ± 3.15a
`30 ± 10.11a
`
`1.4 ± 2.23a
`1.6 ± 2.83a
`18 ± 9.92a
`
`1.3 ± 1.78a
`1.9 ± 2.59a
`14 ± 7.38a
`
`Student’s t test compares preoperative with postoperative data. Values
`are ±SD.
`aP < 0.05.
`
`disability) to a mean of 30% after 3 months (P < 10−6,
`paired t test), a mean of 18% after 6 months (P < 10−6,
`paired t test), and a mean of 0.14% (minimal disability)
`after 1.4 years (P < 10−6, paired t test).
`The comparison between patients operated on at one
`level and those with multilevel disc replacement (Fig. 2) is
`summarized in Table 3. There was no significant differ-
`ence in the improvement of the VAS or Oswestry scores
`between the two groups. Ninety-seven percent of patients
`(32/33) with no previous surgery reported satisfactory re-
`sults compared with 90% (10/11) of those who had pre-
`vious lumbar surgery.
`In patients who had implantation at L5–S1, the flexion-
`extension range of motion averaged 8° (range 2–12°) at
`the operated level. In patients who had implantation at L4–
`L5, the range of motion averaged 10° (range 8–18°) (Fig.
`3). The mean lumbar lordosis was 56.7° before surgery
`(range 30–72°) and 61.9° at final follow-up (range 46–72°).
`There was no significant difference in lordosis after disc
`replacement. No radiolucent or sclerotic lines were noted in
`response to the presence of the implant. There was no peri-
`annular ossification noted and no mechanical implant fail-
`ures. No degenerative changes were seen at the levels ad-
`jacent to the disc replacement or at the facet joints.
`Complications occurred in five patients (9%) and con-
`sisted of one case of postoperative vertebral body fracture,
`two cases of implant malposition, and two cases of per-
`sistent radicular pain without radiographically evident
`neural compression. The reoperation rate in this series was
`6% (3/53). The vertebral body fracture occurred after L5–
`
`TABLE 3. Comparison of patients with one-level or
`multilevel disc replacement on VAS back and leg pain scores
`and Oswestry disability scores
`
`One level
`(n ⳱ 40)
`
`Multilevel
`(n ⳱ 13)
`
`Student’s
`t test
`
`VAS lumbar preoperative
`VAS lumbar last follow-up
`VAS radicular preoperative
`VAS radicular last follow-up
`Oswestry preoperative
`Oswestry last follow-up
`
`7.4 ± 2.26
`1.3 ± 1.74
`6.5 ± 3.11
`2.2 ± 2.81
`27 ± 8.4
`8 ± 8.07
`
`7.4 ± 3.39
`1.3 ± 2.06
`7.4 ± 2.47
`1.2 ± 1.9
`31 ± 7.05
`5 ± 4.72
`
`NS
`NS
`NS
`NS
`NS
`NS
`
`Values are ±SD.
`
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`ther degeneration results in deterioration of intervertebral
`stability, loss of the disc height, foraminal and central
`stenosis, and facet arthropathy. Many prosthetic devices
`have been designed: some with the goal of restoring lost
`disc biomechanics (ie, motion) and others with the pur-
`pose of restoring nuclear function and promoting potential
`healing of the annulus fibrosus.17 In cases of advanced
`disc degeneration, total disc replacement is the only way
`to restore motion and to avoid fusion. Few devices have
`been tested clinically, and only two, the SB Charité pros-
`thesis (Waldemar Link, Hamburg, Germany)18 and the
`ProDisc prosthesis,12 have >5 years of clinical follow-up.
`The reported clinical and radiographic results of the
`ProDisc first-generation implant were acceptable at 7- to
`11-year follow-up.12 Therefore, the second-generation
`ProDisc II was based upon the same principles as the
`first-generation implant, but with several modifications in
`the implant and instrumentation to allow for easier im-
`plantation. The purpose of this article is to report the clini-
`cal outcome of ProDisc II implantation by comparing pre-
`operative and follow-up data. The improvements in leg
`and back pain are theoretically the result of disc height
`restoration, indirect foraminal decompression, removal of
`the degenerated disc material, and maintained sagittal bal-
`ance of the spine. In the current series, 94% of patients had
`good clinical results without reoperation. This is compa-
`rable with the results of Lemaire et al19 but superior to the
`results of David18 who reported 77% excellent and good
`results and Cinnotti et al20 with only 63% satisfactory
`results. These discrepancies could be related to differences
`in patient assessment or patient selection or to the retro-
`spective study design.
`The results of our subset of multilevel disc implanta-
`tions suggest that the ProDisc II can be used at two or
`three contiguous levels. Because of the monoconvex con-
`figuration of the polyethylene core, this prosthesis can be
`inserted safely as the intersegmental distraction required is
`considerably less than is needed to implant a biconvex
`core such as in the SB Charité prosthesis. This was con-
`firmed by Cinotti et al20 and David21 who reported that the
`SB Charité III prosthesis was not suitable for implantation
`at two contiguous levels. The ProDisc II appears to be
`
`TABLE 4. Clinical results in five patients who had
`surgical complications
`
`Preoperative
`
`3 mo
`postoperative
`
`6 mo
`postoperative
`
`Final
`follow-up
`
`7.9 ± 2.65
`VAS lumbar
`VAS radicular 6.1 ± 2.8
`Oswestry
`64 ± 13.23
`
`3.6 ± 4.8a
`5.5 ± 4.8
`50 ± 17.67
`
`0.8 ± 0.98a
`0.8 ± 0.72a
`20 ± 9.61a
`
`0.6 ± 0.78a
`1.3 ± 0.92a
`14 ± 8.49a
`
`Student’s t test compares preoperative with postoperative data. Values
`are ±SD.
`aP < 0.05.
`
`5 of 7
`
`FIGURE 3. Flexion-extension radiographs of a disc prosthesis at
`L4–L5. The segmental motion was 12°.
`
`S1 disc replacement in a 52-year-old woman with unrec-
`ognized osteopenia. She had an impacted L5 endplate
`fracture 3 weeks after surgery and was revised to an L5–
`S1 anterior fusion with prosthesis removal. This case was
`scored as a poor result despite improvement of the back
`and leg pain. In two cases, lateral implant malposition
`with back pain required revision at 6–8 weeks. In one of
`these cases, the patient had retrograde ejaculation after the
`second surgery. The primary approach was transperito-
`neal, and the second was retroperitoneal. At the most re-
`cent follow-up, 8 months after the last surgery, resolution
`of retrograde ejaculation was reported. Finally, the two
`patients with radicular pain were treated with medication.
`Those patients had previous discectomies. The radicular
`pain improved after 3 months in the first case and 5
`months in the second. The clinical results of the patients
`with complications are presented in Table 4.
`
`DISCUSSION
`
`Since Fernström’s first report of disc replacement in
`1966,15 there has been much interest in the development
`and perfection of intervertebral disc replacement. Disc de-
`generation, a major contributor to chronic low back pain,
`is thought to occur with the loss of nuclear hydrostatic
`pressure and the release of inflammatory products.16 Fur-
`
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`Preliminary Results with ProDisc II
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`367
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`uniquely suited for the treatment of multilevel disc degen-
`eration. Notably, clinical results were also good in patients
`with previous failed back surgery.
`The functional status of the patients was significantly
`improved after disc replacement. Despite good clinical
`outcomes, the Oswestry scores show that many patients
`avoid carrying any significant weight after disc replace-
`ment surgery. This could result from a desire to protect the
`spine or from secondary gain. The improvement of func-
`tional status was progressive over time and took 1 year to
`stabilize.
`In this series, the average patient age was 45 years, but
`seven patients were older than 50 years, with the oldest at
`67 years. In this group of patients, age did not adversely
`affect the clinical or radiographic outcomes. This is in
`accordance with the results of Sott and Harrison22 who
`reported that advanced age was not a contraindication to
`lumbar disc replacement as long as facet arthropathy and
`osteoporosis are excluded.
`The prostheses in the current study had an average flex-
`ion-extension range of motion of 9°. A significantly lower
`range of motion was observed in the first-generation im-
`plant at 8.7-year follow-up, with a mean range of motion
`of 5.5° (unpublished data). This difference may have been
`observed because of changes in the implant and implan-
`tation technique or because of the longer follow-up period.
`Only longer follow-up of the ProDisc II prosthesis can de-
`termine if range of motion will decrease or be maintained.
`A previous study of sagittal balance after disc replace-
`ment23 has suggested that the ProDisc II can restore sag-
`ittal balance and protect the junctional disc by improving
`sagittal orientation. The ProDisc II slightly increased glob-
`al lumbar lordosis. These results are concordant with those
`of Lemaire et al19 who reported an increase of lumbar
`lordosis. The increase in lordosis is related to the lordotic
`shape of the prosthesis, and the change in sagittal balance
`results from adaptation of the lumbar spine above the im-
`planted level. It is not known whether these changes in
`sagittal alignment will protect the rest of the spine against
`degeneration, and longer follow-up may help illuminate
`this issue.
`In this series, the complications associated with disc
`replacement were not directly related to the device but
`resulted from errors in judgment and technique on the part
`of the surgeon (ie, patient selection, positioning of the
`prosthesis) and from the anterior approach. Any new sur-
`gical technology or device is associated with a learning
`curve. Osteopenia should be considered a contraindication
`to disc replacement. Patients who have had previous pos-
`terior surgery should be apprised of the risk of postopera-
`tive radicular pain. Nerve root traction by postoperative
`fibrosis may limit the surgeon’s ability to restore disc
`height and may require posterior surgery for root decom-
`
`pression if the pain is persistent. Retrograde ejaculation
`after L5–S1 access remains an unsolved problem. Fortu-
`nately, it is usually a transient problem and may be avoid-
`able through more careful dissection of the presacral area
`and by preferential right-sided access. In this series, there
`were no vascular complications.
`There are no reports of mechanical failure or polyeth-
`ylene core dislocation of the first- or second-generation
`ProDiscs. The polyethylene core is locked into the caudal
`endplate during surgery, leaving only two movable parts.
`In contrast to the SB Charité prosthesis,24–26 subluxation
`or dislocation of the polyethylene core cannot occur with
`the ProDisc II. The ProDisc II, with one midline keel,
`provides immediate stability for bone ingrowth. With the
`SB Charité III, primary stability is achieved by distraction
`and axial preloading, potentially increasing the risk of
`loosening and dislocation.20
`Biomechanically, the ProDisc is constrained in AP and
`lateral shear but unconstrained in axial rotation. This im-
`plant was inspired by the work of Fick,27 Lysell,28 Gonon
`et al,29 and Louis.30 Axial rotation is unconstrained, and
`the axis rotation of the cephalad endplate is angled pos-
`teriorly in the neutral position due to the intradiscal lor-
`dosis of the prosthesis. This is consistent with the physi-
`ologic axis of rotation.30 The instantaneous axis of
`rotation of flexion-extension and lateral bending is situ-
`ated slightly posterior and inferior to the center of the
`inferior vertebral endplate, as described by White and Pan-
`jabi.31 Lateral bending and flexion-extension therefore oc-
`cur in combination with facet rotation.
`The ProDisc II prosthesis permits a 20° arc of motion in
`flexion-extension and in lateral bending. The design of
`any disc prosthesis is obviously a compromise between
`physiologic intervertebral disc function and currently
`available materials and technology. We believe that the
`ProDisc II maintains near-physiologic kinetics of the
`three-joint complex.30,32 Conversely, the SB Charité pos-
`sibly provides a larger range of motion but requires more
`distraction during implantation and is not constrained.19
`The stability of an unconstrained implant must be supple-
`mented by the facet joints. This could cause accelerated
`degeneration if facets are subjected to excessive horizontal
`shear forces. The constrained ProDisc II absorbs the shear
`forces and may protect the facet joints.
`We believe that the best indications for the use of the
`ProDisc II are single- or multilevel lumbar discopathy
`with disc collapse and intersegmental hypermobile insta-
`bility without significant posterior changes (ie, no major
`degenerative or postoperative alterations of spinous pro-
`cess, laminae, or facet joints) in patients between the ages
`of 18 and 60 years. Secondary indications include patients
`with lateral recess stenosis due to disc degeneration and
`loss of disc space height, patients with single- or multi-
`
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`level postdiscectomy syndrome or failed back surgery
`syndrome, and patients with discopathy adjacent to a fu-
`sion. These secondary indications should currently be re-
`garded as relative indications and require a larger patient
`cohort for confirmation.
`Because disc replacement is not complicated by pseud-
`arthrosis and long-term junctional degeneration may be
`avoided by maintenance of segmental motion, we believe
`that total disc replacement may one day be the surgical
`treatment of choice for degenerative disc disease. Prospec-
`tive, randomized trials of fusion compared with disc re-
`placement are currently underway in Europe and the
`United States, and we eagerly await the results of those
`studies.
`
`CONCLUSION
`
`Total disc replacement in our series of 53 patients with
`the ProDisc II prosthesis has good clinical results as mea-
`sured by pre- and postoperative VAS and Oswestry
`scores. There were clinically and statistically significant
`improvements in VAS and Oswestry scores over the first
`6 months after surgery, and these were maintained at mean
`1.4-year follow-up. Patients with multilevel surgery had
`equivalent results. Satisfactory results were achieved in
`90% of patients who had previous lumbar surgery. Com-
`plications occurred in 9% of patients and included verte-
`bral body fracture, transient radicular pain, implant mal-
`position, and transient retrograde ejaculation. Three
`patients (6%) required reoperation to address complica-
`tions.
`
`Acknowledgments; The authors gratefully acknowledge
`the assistance of Ms. Nathalie Larive, BS, and Ms. Pascale
`Munoz, BS.
`
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