Range of motion and adjacent level degeneration after lumbar total disc replacement

The Spine Journal 6 (2006) 242–247

Range of motion and adjacent level degeneration after lumbar total disc replacement Russel C. Huang, MDa,*, Patrick Tropiano, MDb, Thierry Marnay, MDc, Federico P. Girardi, MDa, Moe R. Lim, MDa, Frank P. Cammisa, Jr., MDa a Spine Surgery Service, Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021, USA Department of Orthopaedic Surgery, H^ opital CHU Nord, Chemin des Bourrelly, 13915 Marseille Cedex 20 France c Department of Orthopaedic Surgery, Clinique du Parc, 50 Rue Emile-Combes, Boite Postal 20, 34171 Castelnau-le-Lez, France b

Received 16 December 2004; accepted 10 April 2005

Abstract

BACKGROUND CONTEXT: There are no published studies on the relationship between total disc replacement (TDR) motion and the development of adjacent level degeneration (ALD). Because prevention of ALD is the underlying justification for TDR, studies investigating the validity of this concept are essential. PURPOSE: To examine the relationship between range of motion (ROM) and ALD 8.7 years after lumbar TDR. STUDY DESIGN/SETTING: Retrospective radiographic and chart review. PATIENT SAMPLE: Forty-two patients 8.7 years after lumbar TDR. OUTCOME MEASURES: Radiographic flexion-extension and ALD. Modified Stauffer-Coventry score. Oswestry Disability Questionnaire. Subjective patient ratings of back pain, leg pain, and disability. METHODS: We reviewed the flexion-extension radiographs of 42 patients 8.7 years after TDR. Cephalad adjacent levels were evaluated for degeneration: loss of disc space height, anterior osteophyte formation, or dynamic flexion-extension instability. Graphical analysis of motion and the prevalence of ALD was performed. A statistical relationship between ALD and clinical outcome was sought. RESULTS: Ten of 42 patients evaluated (24%) had radiographic ALD. The mean motion was 3.8  62.0  . The patients with ALD had mean motion of 1.6  61.3  whereas the patients without ALD had motion of 4.7  64.5  (p5.035). A clear relationship between motion and the presence of ALD at 8.7-year follow-up was observed. Patients with motion 5  or greater (n513) had a 0% prevalence of ALD. Patients with motion less than 5  (n529) had a 34% prevalence of ALD (p5.021, odds ratio 13.5). ALD had no statistically significant effect on clinical outcome although the sample size was small. CONCLUSIONS: At 8.7-year follow-up, the prevalence of ALD after TDR is higher in patients with motion less than 5  . The presence of ALD had no significant effect on clinical outcome, but the sample size was small. These data suggest that patients with significant ROM after lumbar TDR may have reduced risk for radiographic ALD. Ó 2006 Elsevier Inc. All rights reserved.

Keywords:

Disc replacement; Lumbar; Spine; Adjacent level degeneration; Junctional degeneration; Radiographic; Outcomes; Motion

FDA device/drug status: not applicable. Authors acknowledge financial relationships (TM inventor of the Prodisc 1 TDR implant, and consultant and stockholder for Spine Solutions, Inc.; FPG and FPC consultants and stockholders for Spine Solutions, Inc.) which may indirectly relate to the subject of this manuscript. * Corresponding author. Department of Orthopaedic Spine Surgery, Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021. Tel.: (212) 606-1634; fax: (212) 774-7130. E-mail address: [email protected] (R.C. Huang) 1529-9430/06/$ – see front matter Ó 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.spinee.2005.04.013

Introduction The fundamental rationale for performing total disc replacement (TDR) instead of fusion is preservation of motion. Theoretically, preservation of segmental motion may prevent the development of adjacent level degeneration (ALD) seen in long-term follow-up of fusions. No Class I or II data are currently available to support or refute this theory. It has been shown that some patients with

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lumbar TDR retain significant motion at short and midterm follow-up [1–6]. Furthermore, low TDR range of motion (ROM) is statistically associated with the development of radiographic ALD [6]. However, we are not aware of any published data that quantify the relationship between motion preservation and the development of ALD. Because new technologies bring with them new potential complications [7], the task of weighing the risk/ benefit profile of TDR is difficult. Until long-term data from randomized controlled trials of TDR versus fusion are available, the theory that motion preservation reduces ALD will remain unproven. However, retrospective studies may provide important preliminary information to clinicians. The purpose of this study is to examine the relationship between ROM and the development of ALD 7 to 11 years after TDR. Finally, the clinical impact of radiographic ALD after TDR is examined.

Materials and methods Patients From March 1990 to September 1993, 93 Prodisc (Aesculap AG & Co., Tuttlingen, Germany) total disc prostheses were implanted in 64 patients by a single surgeon (TM) at the Clinique du Parc (Castelnau-le-Lez, France). The indication for surgery was disc degeneration with discogenic back pain that had failed at least 6 months of nonsurgical management including anti-inflammatory medications, activity modification, and physical therapy. Diagnosis was based upon plain radiographs, magnetic resonance imaging, and history and physical examination. Discography was used in the minority of cases to help define symptomatic levels. It was the surgeon’s clinical practice to address all symptomatic degenerated levels at the time of the index operation. The current study was approved by the medical ethics committee of the Clinique du Parc. Patients gave informed consent to participate in the study at the most recent follow-up performed from May 1999 to January 2001. Of the 64 patients in the initial cohort, 3 were deceased, and 3 were lost to follow-up. Sixteen patients were excluded from this study because complete radiographic documentation was unavailable. Included in this study were 42 patients with a total of 60 Prodisc prostheses implanted. Because low-quality radiographs precluded the measurement of ROM in two prostheses implanted at L5-S1, a total of 58 Prodisc prostheses were evaluated in 42 patients. There were 23 male and 19 female patients. At time of surgery, the mean age was 45.268.6 years (range 25–65) and the mean weight was 72.4613.9 kg (range 52–102). The mean follow-up period was 8.761.0 years (range 6.9– 10.7). Twenty-one patients (50%) had a history of prior spine surgery. A total of 37 prior procedures were performed on these 20 patients including 21 discectomies, 2 decompressions for lumbar stenosis, and 14 other

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procedures (including thermocoagulation and chemonucleolysis). Twenty-seven patients had Prodisc implantation at one level, 12 had implantation at 2 levels, and 3 had implantation at 3 levels. There was one prosthesis placed at L2-L3, 5 placed at L3-L4, 32 placed at L4-L5, and 22 placed at L5-S1.

Radiographic evaluation Preoperative radiographs were not available. Postoperative active flexion-extension lateral radiographs taken at final follow-up were used to determine flexion-extension ROM and to evaluate for ALD as previously described [6]. Mean follow-up was 8.761.0 years (range 6.9–10.7). Flexion-extension ROM was measured by Cobb’s method at the junctional TDR, defined as the TDR immediately subjacent to the native disc. Measurements were performed by a single observer (RCH) who was not involved in patient selection, surgery, or follow-up. The intraobserver and interobserver reliability of Cobb’s method are high. The mean absolute difference between lumbar Cobb measurements performed by three independent observers (mean interclass correlation coefficient 0.87, mean intraclass correlation coefficient 0.93) is 1.4  [8]. The mean absolute difference between repeated Cobb measurements after lumbar TDR is 1.6  (intraobserver) and 1.8  (interobserver) (M. R. Lim, MD, unpublished data, December 2003). Cephalad adjacent nonoperated levels were examined for radiographic signs of ALD: loss of disc space height greater than or equal to 2 mm compared with adjacent normal discs (Fig. 1), anterior osteophyte formation projecting greater than 3 mm from the anterior surface of the vertebral body [9] (Fig. 2), or dynamic flexionextension instability of greater than 3.5 mm.

Fig. 1. Adjacent level degeneration: loss of disc space height.

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R.C. Huang et al. / The Spine Journal 6 (2006) 242–247 Table 2 Scoring of low back pain, leg pain, and disability Grade

Fig. 2. Adjacent level degeneration: anterior osteophytes.

Clinical evaluation The patients were evaluated preoperatively by the surgeon (TM) and postoperatively by one of the authors (PT) and by a research assistant. The mean follow-up period was 8.761.0 years (range 6.9–10.7). Postoperative evaluators were not involved in patient selection, surgery, or postoperative care. Four scoring systems were used to evaluate patients preoperatively and postoperatively. A 20-point modified Stauffer-Coventry [5] score assessed pain, neurologic deficit, need for medication, disability, and psychiatric status (Table 1). Possible scores range from 0 (worst) to 20 (best). Three separate subjective areas were scored on 3-point scales preoperatively and postoperatively by the patients (Table 2): low back pain was graded as severe (3), moderate (2), mild (1), or absent (0); leg (radicular) pain was graded as severe (3), moderate (2), mild (1), or absent (0); and the ability to perform employment and activities of daily living was scored as normal (0), slightly limited (1), substantially impaired (2), or severely limited/impossible (3). The Oswestry Disability Questionnaire was administered only postoperatively because it was not in use at the senior author’s institution at the time of the initial surgeries. Statistical methods Graphical analysis was performed plotting the flexionextension ROM of the junctional TDR (x-axis) against the

Parameter

0

1

2

3

Low back pain Leg pain Disability

None None None

Mild Mild Slight

Moderate Moderate Significant

Severe Severe Severe

prevalence of radiographic ALD (y-axis). Patients were divided into those with ROM less than 5  and those with ROM of 5  or greater. Fisher’s exact testing was used to compare the prevalence of ALD between the two groups. To measure the impact of ALD on clinical outcome, patients were divided into groups based on the presence or absence of ALD. Preoperative characteristics and postoperative outcomes between groups were compared with Student t test (parametric data), Fisher’s exact test (dichotomous data), or Mann-Whitney test (ordinal data). The detectable alternative [10] was calculated for all data to determine whether sample size was sufficient to avoid type 2 error setting power at 0.80. All testing was two-tailed, and the alpha level for statistical significance was set at 0.05. All data analysis was performed using Microsoft Excel 2002 (Microsoft Inc., Redmond, WA), InStat 3.05 (GraphPad Software Inc., San Diego, CA), and PS 2.1.30 (William D. Dupont and Walton D. Plummer, Nashville, TN).

Results Of the 42 patients evaluated, 10 patients (24%) with radiographic ALD were identified. Four patients had loss of disc space height, three had anterior osteophyte formation, and three had both height loss and osteophyte formation. None had static or dynamic listhesis of greater than 3.5 mm. The mean ROM measured at all levels was 3.8  62.0  (range 0–18). The patients with ALD had a ROM of 1.6  61.3  (range 0–4) whereas the patients without ALD had ROM 4.7  64.5  (range 0–18, p!.035). A clear relationship between TDR ROM and the presence of ALD at 8.7-year follow-up was observed. Most notably, when patients were stratified by ROM, no

Table 1 Modified Stauffer-Coventry Score Grade Parameter

0

1

2

3

4

Low back pain Radicular pain Neurologic deficit Medication Day living activities Work status postoperatively

Permanent Permanent Major Major Impossible No work

Frequent Frequent

Frequently stopped

Moderate Effort Moderate None Normal Change

d d None d d Normal

Psychiatric status Total

Preoperative

Secondary to pathology

None

None None d d d Same work O6 months Change !3 months d

Moderate

d

Total 3 3 4 2 2 4 2 20

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Fig. 3. TOR motion and prevalence of adjacent level degeneration.

patients with ROM 5  or greater developed ALD. The overall prevalence of ALD was 24% but was higher in patients with less ROM (Fig. 3). When patients were divided into those with ROM 5  or greater (n513) and those with motion less than 5  (n529), the prevalence of ALD was 0% in the high ROM group and 34% in the low ROM group (p5.021, odds ratio 13.5). In patients with ALD, 100% had ROM less than 5  . In patients without ALD, 59% had ROM less than 5  . Radiographic ALD did not have a clear impact on clinical outcome. There were no statistically significant differences in preoperative age, weight, or gender between patients with or without ALD. Preoperative pain, disability, and modified Stauffer-Coventry scores were similar between groups (Table 3). Power study analysis showed that the sample size was sufficient to maintain the probability of beta error at less that 20% for preoperative age only. There were no statistically significant differences between groups in postoperative pain, disability, or modified Stauffer-Coventry scores (Table 4). Power study analysis showed that the sample size was sufficient to maintain the probability of beta error at less that 20% for postoperative disability and Stauffer-Coventry scores.

Discussion These data demonstrate that at mean 8.7-year follow-up, the prevalence of ALD after TDR is higher in patients with less ROM. The prevalence of ALD was statistically lower in patients with flexion-extension motion of at least 5  . In our patients, ROM less than 5  was necessary but not sufficient for the development of ALD because 59% of patients without ALD had ROM less than 5  . We are aware of no studies in the current literature that closely address the relationship between TDR ROM and radiographic ALD. This information may prove useful in the design and clinical evaluation of nonfusion technologies in spine surgery. Nonfusion technologies including TDR, nucleus pulposus replacements, and soft stabilization devices are designed to maintain segmental ROM and theoretically may reduce the incidence of ALD relative to fusion. These implants and techniques are currently generating high levels of interest in the spine surgery community, but our enthusiasm should be tempered by the fact that no wellcontrolled studies have proven that nonfusion technology can prevent the development of ALD. Kanayama et al. [11] retrospectively reviewed 45 nonrandomized patients who

Table 3 Preoperative patient data in patients with or without adjacent level degeneration (ALD) Group

Age

Weight

Gender

Low back pain

Leg pain

Disability

Stauffer-Coventry

With ALD Without ALD p value Detectable alternative

49.767.7 43.968.6 0.065 4.3*

74.1616.6 71.3613.3 0.62 6.9

50.0% male 54.8% male 1.0 29%

2.8060.42 2.7460.58 0.99 0.27

2.5060.97 2.5260.96 0.89 0.48

3.2060.42 2.8760.88 0.40 0.40

7.4063.2 6.9763.3 0.75 1.6

* Detectable alternative less than observed difference between groups.

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Table 4 Postoperative patient data in patients with or without adjacent level degeneration (ALD) Group

Low back pain

Leg pain

Disability

ODQ

Stauffer-Coventry

With ALD Without ALD p value Detectable alternative

1.6060.52 1.2960.90 0.28 0.41

0.7061.16 0.6560.80 0.81 0.44

2.1060.88 1.6060.67 0.11 0.38*

22.4619.6 16.4614.4 0.47 8.0

15.263.2 16.562.3 0.29 * 1.3

ODQ5Oswestry Disability Questionnaire. * Detectable alternative less than observed difference between groups.

had Graf ligamentoplasty (n518) or instrumented posterolateral fusion (n527) at L4-5. At minimum 5-year followup, the rate of reoperation for ALD was 19% (5 of 27) in the fusion group and 6% (1 of 18) in the ligamentoplasty group. Interestingly, the rate of radiographic ALD was higher in the fusion group at all levels from L1 to the sacrum, suggesting that the fusion group in this nonrandomized study may have been predisposed to degenerative disc disease. Nevertheless these data and ours suggest that nonfusion technology may have efficacy in preventing ALD. The prevalence and clinical significance of ALD after fusion surgery are controversial issues in spine surgery because of variation in diagnostic criteria, follow-up periods, and patient age in published series. Furthermore, it is difficult to make generalizations about the incidence of ALD after fusions because the specific level studied (L4-5 vs. L5-S1, for example) as well as the location and length of the adjacent fusion mass are likely important variables. Finally, it is impossible to prove whether adjacent level degenerative changes result directly from fusion or are a part of the natural history of degenerative spine disease and may have occurred even in the absence of a fusion. The reported prevalence of radiographic ALD after lumbar fusion in long-term follow-up studies varies widely depending on the length of follow-up, diagnostic criteria, and imaging methods [9,12–16]. Penta et al. [12] found that 32% (17 of 52) of patients had adjacent level degenerative changes on magnetic resonance imaging 10 years after anterior lumbar interbody fusion. Kumar et al. [15] showed that 30 years after one- or two-level lumbar fusion, 36% (10 of 28) of patients had disc space narrowing and 43% (12 of 28) had osteophytes. Finally, Miyakoshi et al. [16] detected loss of disc height in 100% (45 of 45) of patients 6 years after L4-L5 posterior lumbar interbody fusion. It is impossible to make direct comparisons between these studies and the current study. The clinical significance of ALD has also been debated. It has been clearly shown that radiographic degenerative changes of the spine are nearly universal in old age and are often asymptomatic [17,18]. Several studies of post-fusion ALD have suggested that these radiographic changes may likewise be asymptomatic [9,12,15,16]. We were not able to demonstrate a statistically significant effect of radiographic ALD on clinical outcome, but for most parameters we

evaluated, sample size was insufficient to avoid type 2 error. There are numerous series reported in the literature of patients who have required surgical treatment for ALD [13,19–24]. Therefore, avoidance of ALD after spine surgery is a rational objective if the short- and long-term safety profile of TDR implants proves similar to fusion. Long-term follow-up is essential to understand ALD. In most cases, ALD develops many years after fusion surgery. Schlegel et al. [21] reviewed 58 patients who presented with symptomatic post-fusion ALD after good short-term (minimum 2-year) outcomes. The mean symptom-free interval was 13.1 years. Because isolated lumbar degenerative disc disease amenable to TDR is typically a disease of young patients, it is incumbent upon the orthopedic community to follow patients with TDRs for decades. Many investigators have found a high level of variability between patients in preservation of motion after TDR [6]. Why some patients retain significant TDR ROM and others do not is a mystery. This variability probably results from a combination of patient-dependent and patient-independent factors. Patient-dependent factors include preoperative ROM, facet joint integrity, gender [6], and genetic predisposition for segmental mobility. In patients with advanced preoperative disc space collapse, contracture of spinal ligaments and facet capsules may reduce postoperative motion. Females may be more likely to have low postoperative TDR motion [6]. Patient-independent factors include implant design [25], implant size, surgical technique, and implant positioning [3,26]. Placement of an implant that is too large or too anterior reduces postoperative motion. Excessive decortication of the end plates may release osteogenic factors or cells, promoting ankylosis. The current study suggests that preservation of motion may reduce radiographic ALD, and other studies have suggested that motion preservation may improve clinical outcome [27]. In the future, improvements in patient selection, implant designs, and surgical technique may permit surgeons to restore segmental motion in a more predictable fashion, and thereby to reduce the incidence of ALD. There are many limitations to the current study. These results may not be generalizable to all TDR implants and other motion-preserving technologies. The results of the current study are based upon the first generation Prodisc implant which has been superseded by the currently

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available second generation implant. Differences between TDR implants with regard to kinematics, constraint, location of instantaneous axis of rotation, and radius of curvature will likely affect their long-term performance [25]. Preoperative radiographs were not available. Although it was the surgeon’s practice to surgically address all significantly degenerated levels, we cannot prove that all adjacent discs were radiographically normal at baseline. We have demonstrated an association between low TDR ROM and ALD, but it is impossible to prove causation. One alternative explanation for the statistical association we observed is that patients with radiographic ALD had more back pain and voluntarily restricted their motion during flexion-extension radiographs. It is also possible that a third variable (genetic predisposition, for example) affected both the propensity for degenerative disc disease and TDR ROM. Finally, our study suffered from a relatively small sample size. Despite these limitations, it is certainly plausible that there is a relationship between motion preservation and the prevention of ALD. In conclusion, the current study demonstrates that 8.7 years after TDR, patients with at least 5  of flexionextension ROM have a significantly lower prevalence of radiographic ALD. We were not able to detect a statistically significant effect of ALD on clinical outcome, but the sample size was small. This information should prove useful in the design and clinical evaluation of TDR and other motion-preserving technologies. Longer-term followup of this and other patient cohorts is essential to define the role of nonfusion technology in spine surgery. References [1] Tropiano P, Huang RC, Girardi FP, et al. Lumbar disc replacement: preliminary results with ProDisc II after a minimum follow-up period of 1 year. J Spinal Disord Tech 2003;16:362–8. [2] Bertagnoli R, Kumar S. Indications for full prosthetic disc arthroplasty: a correlation of clinical outcome against a variety of indications. Eur Spine J 2002;11(Suppl. 2):S131–6. [3] Cinotti G, David T, Postacchini F. Results of disc prosthesis after a minimum follow-up period of 2 years. Spine 1996;21:995–1000. [4] Zeegers WS, Bohnen LM, Laaper M, et al. Artificial disc replacement with the modular type SB Charite III: 2-year results in 50 prospectively studied patients. Eur Spine J 1999;8:210–7. [5] Lemaire JP, Skalli W, Lavaste F, et al. Intervertebral disc prosthesis: results and prospects for the year 2000. Clin Orthop 1997;337:64–76. [6] Huang RC, Girardi FP, Cammisa FP Jr, et al. Long-term flexionextension range of motion of the prodisc total disc replacement. J Spinal Disord Tech 2003;16:435–40. [7] Huang RC, Girardi FP, Lim MR, et al. Advantages and disadvantages of nonfusion technology in spine surgery. Orthop Clin North Am 2005;36:263–9.

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