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The factors that influence the postoperative segmental range of motion after cervical artificial disc replacement
The Spine Journal 10 (2010) 689–696
Clinical Study
The factors that influence the postoperative segmental range of motion after cervical artificial disc replacement Kyung-Chung Kang, MD, Chong-Suh Lee, MD, Jeong-Hoon Han, MD, Sung-Soo Chung, MD* Department of Orthopaedic Surgery, Samsung Medical Center, Sungkyunkwan University School of Medicine, Ilwon-dong 50, Kangnam-Gu, Seoul 135-710, Korea Received 30 October 2009; revised 26 February 2010; accepted 8 April 2010
Abstract
BACKGROUND CONTEXT: Advantages of cervical artificial disc replacement (ADR) are to preserve segmental range of motion (ROM) and avoid adjacent segmental disease. To achieve successful outcome after cervical ADR, ROM maintenance is important, but few authors have investigated the factors that influence the postoperative segmental ROM. PURPOSE: To evaluate the factors that influence the postoperative segmental ROM after cervical ADR. STUDY DESIGN/SETTING: A retrospective clinical study. PATIENT SAMPLE: Forty-one consecutive cervical ADR cases were analyzed. OUTCOME MEASURES: Disc height, segmental and overall ROM, and clinical parameters checked with Neck Disability Index (NDI) and visual analog scale (VAS) in neck and arm pain were assessed. METHODS: There were 21 men and 20 women with a mean age of 45 years (range, 27–61 years). All cases were followed up for more than 2 years (range, 24–54 months; average, 31 months). Angles of the inserted implant on the immediate postoperative lateral radiographs, segmental and overall ROM (full flexion angle full extension angle), disc height increment (immediate postoperative disc height preoperative disc height), and adjacent segment changes at cephalad and caudal disc space were measured. Correlations between the factors and segmental ROM at last follow-up were analyzed. RESULTS: Mean preoperative NDI was improved from 61.0 preoperatively to 11.5 at last followup, and mean VAS in the neck pain decreased from 56.8 preoperatively to 11.8 postoperatively and arm pain decreased from 68.1 to 18.0. The mean preoperative segmental ROM changed from 7.463.2 preoperatively to 10.465.9 at last follow-up, and mean preoperative disc height increased from 6.461.0 (4.1–8.4) mm preoperatively to 7.961.0 (6.3–9.9) mm postoperatively. The segmental ROM at last follow-up was not significantly correlated with preoperative segmental and overall ROM, angle of inserted implant, VAS, or age (pO.05). However, the segmental ROM at last follow-up was significantly correlated with the disc height increment (p5.046, r50.374) and preoperative NDI (p5.026, r50.412). The patient group with the postoperative segmental ROM greater than 10 had a significantly lower mean preoperative disc height than the group with the segmental ROM less than 10 (p5.050). CONCLUSIONS: At a minimum of 2 years after cervical ADR, clinical outcomes were satisfactory in terms of function and pain scores. Within our results, the segmental ROM was not affected by preoperative ROM but postoperative disc height increment positively and preoperative disc height negatively. Ó 2010 Elsevier Inc. All rights reserved.
Keywords:
Cervical artificial disc replacement; Range of motion; Influencing factors
FDA device/drug status: not applicable. Author disclosures: SSC (research support: staff/materials, AO Spine Korea). This paper is partly supported by research sponsorship from AO Spine Korea, Ltd. 1529-9430/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.spinee.2010.04.016
* Corresponding author. Department of Orthopaedic Surgery, Samsung Medical Center, Sungkyunkwan University School of Medicine, IlwonDong 50, Kangnam-Gu, Seoul 135-710, Korea. Tel.: (82) 2-3410-0385; fax: (82) 2-3410-0061. E-mail address: [email protected] (S.-S. Chung)
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Context Given that maintaining/improving range of motion is a stated goal of cervical disc replacement, factors that impact such motion are being explored. Contribution In this retrospective case series, an increase in disc height (post-op relative to pre-op, up to limit of 3.9 mm) correlated with improved postoperative ROM. Implications While providing some interesting information, this article looks at a limited number of potential factors impacting ROM in relatively few patients. Causal relations cannot be concluded, nor can unstudied factors impacting motion (confounders) be excluded. Finally, the larger question still remains: does maintaining a minimum degree of motion improve a patient’s outcome? —The Editors
Introduction Although many reports have demonstrated the advantages of cervical artificial disc replacement (ADR) [1–5], few have identified the factors that influence the good postoperative segmental range of motion (ROM) at the implanted disc level [6,7]. The advantage of cervical ADR is to preserve the segmental ROM while avoiding the adjacent segmental disease [8–11]. Most patients who have undergone cervical ADR showed preserved or improved segmental ROM at final follow-up. However, not all patients achieved excellent results. Some cases showed a good segmental ROM immediately after surgery and then gradually deteriorated, and others with osteophytes around the inserted implants postoperatively showed substantially reduced segmental motion at final follow-up. Recently, some reports on the lumbar ADR have identified the factors that importantly affected the postoperative segmental ROM [12,13], but few have demonstrated correlations between influencing factors and postoperative segmental ROM after cervical ADR [14]. Accordingly, the purpose of this study was to identify those factors that affected the postoperative segmental ROM and to find a method of preventing the postoperative segmental ROM decreases after cervical ADR.
Methods Patient selection Forty-one consecutive cervical ADR cases were analyzed retrospectively. All cases were treated by two senior
authors (SSC and CSL) between July 2004 and April 2007 and were followed up for more than 2 years (range, 24–54 months; average, 31 months). There are 21 men and 20 women with a mean age of 45 years (range, 27–61 years). Two patients were treated at C3–C4, 4 patients at C4–C5, 26 patients at C5–C6, and 9 patients at C6–C7. Patients were divided into three groups by pathology: the radiculopathy group (28 patients, 68%), the myelopathy group (4 patients, 10%), and the combined group (9 patients, 22%).
Surgical indication and technique One-level symptomatic cervical disc diseases between C3–C4 and C6–C7 were included in our study, and the inclusion criteria were similar to those for anterior cervical decompression and fusion. Cases of soft disc herniation with radiculopathy or myelopathy and spondylotic radiculopathy were included, but cases of cervical instability, severe facet joint degeneration, deformity, severe spondylosis, and spondylotic myelopathy that were determined by the dynamic X-rays and magnetic resonance images were excluded. The surgical techniques were similar to those for a routine anterior cervical decompression and fusion, except that uncovertebral joints were preserved, to minimize the softtissue damage and bleeding and to avoid damage to the bony end plate. Because of the possibility of bone formation at the bleeding sites, soft-tissue bleeding was meticulously controlled, and the damaged bone area was covered with a bone wax. Although all surgeons tried to minimize the bone procedure, the osteophytes that were compressing nerve roots were removed with a power burr. The posterior longitudinal ligaments (PLLs) were completely removed only when they were torn preoperatively. Three types of artificial disc devices were used: Bryan discs (n56; Medtronic Sofamor Dadek, Memphis, TN, USA), Prodisc-C discs (n517; Synthes Spine, West Chester, PA, USA), and Mobi-C discs (n518; LDR Medical, Troyes, France). There was no surgeons’ preference in selecting types of implants for surgeries and also there were no differences in the postoperative management between surgeons or among the devices.
Clinical evaluation For the clinical evaluation, the Neck Disability Index (NDI) and visual analog scale (VAS) in the neck and arm pain were assessed respectively. All patients were asked to complete questionnaires before surgery and at each follow-up examination. The NDI scores varied from 0 to 100, and the VAS ranged from 0 to 100. The preoperative NDI and VAS were compared with the scores at last follow-up.
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Fig. 1. (Left and Center) Segmental (C5–C6) and overall range of motion (ROM) (C2–C7) were measured using dynamic flexion and extension X-rays at a magnification of 2. (Right) Disc height increment on a lateral X-ray (original magnification 4).
Radiographic evaluation
Statistical analysis
Evaluations were performed preoperatively at 3, 6, and 12 months postoperatively and at last follow-up. The segmental (cephalad, implanted, and caudal disc levels) and overall ROM (C2–C7) were measured on the dynamic full flexion and extension X-rays, and angles of the inserted implants were measured on the immediate postoperative lateral X-rays [15,16]. Kyphotic angle was considered to be a positive value. The disc height on the lateral X-ray, which was defined as the distance from highest portion of the lower end plate in the cephalad vertebra to closest portion of the upper end plate in the caudal vertebra and the disc height increment (immediate postoperative disc height preoperative disc height) were checked (Fig. 1). Degrees of the facet joint degeneration were graded as 1 to 4 using the lumbar facet joint classification in the axial magnetic resonance images [17,18]. All radiographic measurements were carried out on a Picture Archiving and Communications System monitor (General Electric Inc., Chicago, IL, USA), and the angles and lengths were automatically calculated when a measurer drew lines in the interesting area. On the cephalad and caudal disc levels, decreases in the segmental motion and the disc height and bony spurs were also measured. Heterotopic ossifications in the operated segment were evaluated and classified using the grading system introduced by McAfee et al. (Grade 0–4) [19]. Patients with the segmental ROM #2 were considered to have a severe decrease in the segmental ROM and were assessed separately [20].
Statistical analyses were performed by a professional medical statistical consultant. Values are presented as the means6standard deviations. Differences between the preoperative and postoperative disc heights were analyzed by a paired t test and Wilcoxon signed rank test, and the differences between the preoperative and last follow-up segmental (cephalad, implanted, and caudal levels) and overall ROM were also analyzed. The correlations between the postoperative segmental ROM at the last follow-up and other influencing factors, including preoperative segmental and overall ROM, preoperative disc height, disc height increment, angle of the inserted implant, age, and preoperative NDI and VAS in the neck and arm pain were analyzed by a Pearson product-moment correlation coefficient. To identify the factors that influence the postoperative segmental ROM, the patients were divided into two groups (Group I and II) based on a segmental ROM at last follow up of !10 and $10 . This cutoff value was used because it was the average segmental ROM at last follow-up. The values of other influencing factors in these two groups were compared using the two-sample t test. The two-sample t test and the Kruskal-Wallis test were also used to compare the mean postoperative segmental ROMs of different types of artificial disc devices (Bryan, Prodisc-C, and Mobi-C), operated cervical levels (C3–C4, C4–C5, C5–C6, and C6–C7), degrees of facet degeneration, and with respect to PLL removal. Statistical significance was accepted for p value !.05.
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Fig. 2. Mean preoperative segmental range of motions (ROMs) of cephalad, implanted, and caudal levels and mean preoperative overall ROM were slightly increased postoperatively, but only preoperative segmental ROM of implanted level showed the significant difference with postoperative segmental ROM (p5.008). f/u, follow-up.
Inter- and intraobserver intraclass correlation coefficient (ICC) were also assessed for ROM and disc height.
Results Mean preoperative NDI was improved from 61.0 preoperatively to 11.5 postoperatively, mean VAS in neck pain decreased from 56.8 preoperatively to 11.8 postoperatively, and VAS in arm pain decreased from 68.1 to 18.0, respectively. Mean preoperative segmental ROM at the implanted level changed from 7.463.2 to 10.465.9 at last followup, and overall ROM changed from 43.1614.1 to 44.9622.1 . Mean preoperative disc height was increased significantly from 6.461.0 (4.1–8.4) to 7.961.0 (6.3–9.9)
mm immediately after surgery (p!.001) and then decreased to 7.460.9 (5.5–8.6) mm at last follow-up. Preoperative and last follow-up segmental ROM were significantly different, but no significant difference was found between the preoperative and last follow-up segmental ROMs of the cephalad and caudal levels or between overall ROMs at the implanted level (Fig. 2, Table 1). Segmental ROM at last follow-up was not found to be associated with preoperative segmental ROM or disc height (pO.05). However, the segmental ROM at last follow-up was significantly correlated with the disc height increment (p5.046, r50.374) and preoperative NDI (p5.026, r50.412) (Table 2). Group I (segmental ROM !10 at last follow-up) and group II (segmental ROM $10 at last follow-up) were
Table 1 Preoperative and postoperative values of influencing factors Influencing factors NDI (%) VAS in neck VAS in arm Seg. ROM ( ) Implanted Cephalad Caudal Overall ROM ( ) Disc height (mm)
Preoperative (mean6SD)
Immediate postoperative (mean6SD)
61.0618.3 56.8616.2 68.1621.4 7.463.2 8.865.2 6.464.5 43.1614.1 6.461.0
9.565.5 10.064.2 6.463.4 43.3614.8 7.961.0
Last follow-up (mean6SD)
Comparison analysis*: preop. vs. last f/u (p value)
11.568.1 11.8613.6 18.0618.8
!.001** !.001** !.001**
10.465.9 9.666.0 7.166.0 48.4622.1 7.460.9
.008** .489 .467 .166 !.001**
SD, standard deviation; preop., preoperative; f/u, follow-up; NDI, Neck Disability Index; VAS, visual analog scale; Seg. ROM, segmental range of motion. * Paired t test and Wilcoxon signed-rank test. ** p!.05.
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Table 2 Factors significantly correlated with segmental ROM of implanted level at last follow-up Minimum–maximum
Correlation* with seg. ROM at last f/u (p value)
Influencing factors
Mean6SD
Preoperative Seg. ROM ( ) Overall ROM ( ) Disc height (mm) NDI (%) VAS in neck VAS in arm
7.463.2 43.1614.1 6.461.0 61.0618.3 56.8616.2 68.1621.4
1.1–13.9 16.6–69.7 4.1–8.4 16–80 0–100 45–100
.905 .662 .075 .026** .371 .258
Immediate postoperative Disc height (mm) Disc height increment (mm) Age (y) Angle of inserted implant ( )
7.961.0 1.661.4 44.867.9 2.465.4
6.3–9.9 1.3–3.9 27–61 10.1–9.3
.538 .046** .835 .914
Correlation coefficient (r)
0.412
0.374
SD, standard deviation; Seg. ROM, segmental range of motion; NDI, Neck Disability Index; VAS, visual analog scale. * Pearson correlation. ** p!.05.
compared. The two groups were found to be significantly different with respect to preoperative disc height, preoperative NDI, and disc height increment (p5.050, .035, and .028, respectively; Table 3). The last follow-up segmental ROM was not found to be significantly affected by types of the artificial disc devices, operated cervical levels, degrees of facet degeneration, or different pathologies (p5.192, .711, .199, and .083, respectively, Kruskal-Wallis test) or whether the PLL had been removed or not (p5.292, two-sample t test). No additional operations were performed on cephalad and caudal segments during the follow-up period. Regarding cephalad segments, three retrolisthesis and five heterotopic ossification (#Grade 2) cases were showed at last followups, and three heterotopic ossification (#Grade 2) cases were detected in caudal segments. For operated segments, 23 patients (56.1%) had no heterotopic ossification. Grade 1 ossifications were present in four patients (9.8%) and heterotopic ossifications of Grade 2 and 3 were observed in six (14.6%) and five patients (12.2%), respectively. At last follow-ups, three patients (7.3%) had a spontaneous fusion. Among the 18 cases of heterotopic ossifications, 4, 3, and 11 cases were showed at postoperative 6, 12, and 24 months postoperatively, respectively. Three patients had a preoperative segmental ROM #2 . Among them, one patient showed a #2 segmental ROM continuously during the follow-up, but, the other two showed an increase of segmental ROM at 3 months postoperatively and maintained this increase throughout followup. At last follow-up, three patients had a segmental ROM at the implanted level of #2 and two of these had a greater than mean segmental ROM preoperatively but showed significant decreases of segmental ROM and bridging osteophytes at 1 year postoperatively (Table 4). The measurements of both ROM and disc height showed excellent reproducibility (interobserver: ROM: ICC, 0.885;
disc height: ICC, 0.945; intraobserver: ROM: ICC, 0.882; disc height: ICC, 0.938).
Discussion Few reports have been issued concerning correlations between variables and postoperative segmental ROM after cervical ADR. Peng et al. [14] suggested that patients with disc collapse of #4 mm with respect to preoperative disc height benefit more after ADR in terms of segmental ROM and concluded that the optimal range of postoperative disc heights in terms of maximizing segmental ROM is between 5 and 7 mm for the Prodisc-C prosthesis. On the Table 3 Values of factors found to influence postoperative segmental ROM in Group 1 (!10 of segmental ROM at last follow-up) and Group 2 ($10 of segmental ROM at last follow-up)
Influencing factors
Group I (n519) (mean6SD)
Group II (n522) (mean6SD)
Comparison analysis* (p value*)
Preoperative Seg. ROM ( ) Overall ROM ( ) Disc height (mm) NDI (%) VAS in neck VAS in arm
7.163.5 46.6613.7 6.761.0 57.1615.1 54.3614.2 61.4622.9
6.663.3 41.3612.1 6.061.0 69.4614.7 60.7613.3 74.3618.5
.655 .246 .050** .035** .151 .106
7.960.9 1.261.4
8.261.1 2.261.1
.379 .028**
42.166.7 1.266.0
46.168.0 2.666.0
Immediate postoperative Disc height (mm) Disc height increment (mm) Age (y) Angle of inserted implant ( )
.133 .499
SD, standard deviation; Seg. ROM, segmental range of motion; NDI, Neck Disability Index; VAS, visual analog scale. * t Test. ** p!.05.
Seg. ROM, segmental range of motion; PLL, posterior longitudinal ligament; NDI, Neck Disability Index; VAS, visual analog scale; f/u, follow-up; M, male; F, female; Radi., radiculopathy. * Seg. ROM at the last follow-up #2 .
1.2* 1.9* 0.3* 13.9 7.4 1.8 70 90 70 40 85 60 56 58 52 O O 0 2.6 3.2 7.9 8.5 8.4 9.3 6.3 7.1 6.9 5.3 7.5 7.9 5.9 5.2 Radi. Radi. Radi. Prodisc-C Mobi-C Mobi-C M F M
44 47 55
C5–C6 C5–C6 C5–C6 1 2 3
Preoperative Preoperative
Last f/u seg. Immediate PLL VAS VAS Seg. Diagnosis Implanted Cephalad Caudal postoperative Increment removal NDI (%) in neck in arm ROM ( ) ROM ( ) Implant type Operated No. Sex Age level
Disc height (mm)
Table 4 Characteristics of the three patients who experienced a severe decrease in seg. ROM at last follow-up (#2)
O O
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Postoperative bridging osteophyte
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other hand, Mehren et al. [21] and Leung et al. [22] showed a high prevalence of heterotopic ossification and found a correlation between heterotopic ossification and restriction of segmental ROM after cervical ADR. In addition, Bartels and Donk [23] described two cases with a bony spur and fusion around the cervical disc prosthesis using a Bryan disc prosthesis, although facet joints were completely normal, and the possibility of diffuse idiopathic skeletal hyperostosis had been excluded. They also prescribed a nonsteroidal antiinflammatory drug to prevent the early formation of bone matrix. In lumbar ADR, Yaszay et al. [12] reported that patients with greater disc collapse benefit more from ADR in terms of segmental ROM and proposed a standard for the postoperative anterior disc height. However, Siepe et al. [13] mentioned that if disc height is restored, ADR leads to a significant decrease in postoperative segmental ROM, particularly at the lumbosacral junction, and a higher preoperative disc height and segmental ROM had a beneficial effect on the postoperative segmental mobility. In the present study, mean preoperative segmental and overall ROM were either preserved or slightly increased after cervical ADR in most cases, but postoperative segmental ROM greatly decreased in a few cases. Many factors that could influence the postoperative segmental ROM were evaluated during the course of the study. Preoperative segmental or overall ROM, VAS, immediate postoperative disc height, and others were not found to be associated with postoperative segmental or overall ROM. On the other hand, disc height increments showed a significant correlation with segmental ROM at last follow-up. Common sense dictates that an excessive increase in disc height confers larger loads on operated segments and thus, is likely to reduce segmental ROM [24], but our study showed that disc height increments within an acceptable range could increase segmental ROM at more than 2-year follow-up after cervical ADR. In the present study, the maximum postoperative disc height increment was 3.9 mm, and thus, we conclude that if the immediate postoperative disc height is within the range represented by our results (6.3–9.9 mm), a disc height increment of !4.0 mm is acceptable, and postoperative segmental ROM is likely to be satisfactory after cervical ADR. Preoperative NDI also showed a significant correlation with segmental ROM at last follow-up, which means that segmental ROM at affected level was restricted because of its own disease or pathology, and that segmental ROM recovered normally after cervical ADR. Therefore, authors considered that postoperative segmental ROM at implanted level increased with increasing preoperative NDI. On the other hand, preoperative disc height was not significantly correlated with segmental ROM at last follow-up (p5.075), although patients with an excellent postoperative segmental ROM ($10 ) had significantly lower disc heights than patients with less than good postoperative segmental ROM (!10 ) (p5.050), which indicates that disc height can also influence postoperative segmental ROM.
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Severe restrictions in segmental ROM preoperatively were not always found to be associated with decreases in segmental ROM after cervical ADR. In the present study, only one of three patients with a severe decrease of segmental ROM preoperatively experienced a severe decrease in segmental ROM at last follow-up. On the other hand, none of four patients with a disc height of !5 mm preoperatively experienced a severe decrease in segmental ROM postoperatively. The patients with a preoperative lowest segment ROM (#2 ) or disc height (!5 mm) do not always show the significant decrease of postoperative segmental ROM. Within our results, these indications may not be absolute contraindications to cervical ADR. At last follow-ups, three patients almost had a fused segment (postoperative segmental ROM #2 ), and two of these had the bridging osteophyte around the implanted level at 1 year postoperatively. One of the three showed a preoperative severe decrease in segmental ROM. However, no other preoperative factors were found to be correlated with severe postoperative decreases in segmental ROM. We believe the factors that influence a decrease in segmental ROM after cervical ADR will be determined by future larger-scale studies. In the present study, we did not consider an implant height as a disc height in the operated segment and introduced a new easy method in radiographic measurement of disc height because a real disc height is dependent on the topography of the upper and lower end plates, although the same implant was inserted. There were some limitations in this study. A longer follow-up is necessary, and the ADR group was not compared with a fusion or other controlled group. These are inherent weaknesses of our study; however, our study was uniquely focused on factors affecting the postoperative segment ROM after cervical ADR and statistically significant differences could be obtained within our cases. Furthermore, the three different types of artificial discs involved might have introduced bias, although we did confirm that these devices were nonsignificantly different in terms of segmental ROM and disc height at last follow-ups. Finally, the radiographic measurement used may have introduced unacceptable inter- and intraobserver errors. In an effort to minimize these errors, we introduced a simple method to estimate disc height and had all measurements taken twice by two orthopedic surgeons using magnified X-ray images. With this effort, we could measure both the ROM and disc height with excellent reproducibility.
Conclusion After a minimum 2-year follow-up after cervical ADR, clinical outcomes were satisfactory in terms of pain and function scores. The maintenance of segmental ROM was found to be unaffected by preoperative ROM or VAS but to be positively influenced by postoperative disc height
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increments and preoperative NDI. Within our results, enough postoperative disc height increment is thought to be essential to improve segmental ROM. However, a larger-scale study is needed to identify the factors that influence postoperative decreases in segmental ROM after cervical ADR. References [1] Shin DA, Yi S, Yoon do H, et al. Artificial disc replacement combined with fusion versus two-level fusion in cervical two-level disc disease. Spine 2009;34:1153–9; discussion 60–1. [2] Rohl K, Rohrich F. Artificial disc versus spinal fusion in the treatment of cervical spine degenerations in tetraplegics: a comparison of clinical results. Spinal Cord 2009;47:705–8. [3] Kim SW, Limson MA, Kim SB, et al. Comparison of radiographic changes after ACDF versus Bryan disc arthroplasty in single and bi-level cases. Eur Spine J 2009;18:218–31. [4] Goffin J, Van Calenbergh F, van Loon J, et al. Intermediate follow-up after treatment of degenerative disc disease with the Bryan Cervical Disc Prosthesis: single-level and bi-level. Spine 2003;28:2673–8. [5] Sasso RC, Smucker JD, Hacker RJ, Heller JG. Artificial disc versus fusion: a prospective, randomized study with 2-year follow-up on 99 patients. Spine 2007;32:2933–40; discussion 41–2. [6] Rundell SA, Auerbach JD, Balderston RA, Kurtz SM. Total disc replacement positioning affects facet contact forces and vertebral body strains. Spine 2008;33:2510–7. [7] Palissery V, Mulholland RC, McNally DS. The implications of stress patterns in the vertebral body under axial support of an artificial implant. Med Eng Phys 2009;31:833–7. [8] Pickett GE, Rouleau JP, Duggal N. Kinematic analysis of the cervical spine following implantation of an artificial cervical disc. Spine 2005;30:1949–54. [9] Murrey D, Janssen M, Delamarter R, et al. Results of the prospective, randomized, controlled multicenter Food and Drug Administration investigational device exemption study of the ProDisc-C total disc replacement versus anterior discectomy and fusion for the treatment of 1-level symptomatic cervical disc disease. Spine J 2009;9: 275–86. [10] Hilibrand AS, Carlson GD, Palumbo MA, et al. Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis. J Bone Joint Surg Am 1999;81:519–28. [11] Park JB, Cho YS, Riew KD. Development of adjacent-level ossification in patients with an anterior cervical plate. J Bone Joint Surg Am 2005;87:558–63. [12] Yaszay B, Bendo JA, Goldstein JA, et al. Effect of intervertebral disc height on postoperative motion and outcomes after ProDisc-L lumbar disc replacement. Spine 2008;33:508–12; discussion 13. [13] Siepe CJ, Hitzl W, Meschede P, et al. Interdependence between disc space height, range of motion and clinical outcome in total lumbar disc replacement. Spine 2009;34:904–16. [14] Peng CW, Quirnoa M, Bendo JA, et al. Effect of intervertebral disc height on postoperative motion and clinical outcomes after Prodisc-C cervical disc replacement. Spine J 2009;9:551–5. [15] Lim MR, Girardi FP, Zhang K, et al. Measurement of total disc replacement radiographic range of motion: a comparison of two techniques. J Spinal Disord Tech 2005;18:252–6. [16] Hayes MA, Howard TC, Gruel CR, Kopta JA. Roentgenographic evaluation of lumbar spine flexion-extension in asymptomatic individuals. Spine 1989;14:327–31. [17] Fujiwara A, Tamai K, An HS, et al. Orientation and osteoarthritis of the lumbar facet joint. Clin Orthop Relat Res 2001;385:88–94. [18] Fujiwara A, Tamai K, Yamato M, et al. The relationship between facet joint osteoarthritis and disc degeneration of the lumbar spine: an MRI study. Eur Spine J 1999;8:396–401.
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[19] McAfee PC, Cunningham BW, Devine J, et al. Classification of heterotopic ossification (HO) in artificial disk replacement. J Spinal Disord Tech 2003;16:384–9. [20] Auerbach JD, Jones KJ, Fras CI, et al. The prevalence of indications and contraindications to cervical total disc replacement. Spine J 2008;8:711–6. [21] Mehren C, Suchomel P, Grochulla F, et al. Heterotopic ossification in total cervical artificial disc replacement. Spine 2006;31:2802–6.
[22] Leung C, Casey AT, Goffin J, et al. Clinical significance of heterotopic ossification in cervical disc replacement: a prospective multicenter clinical trial. Neurosurgery 2005;57:759–63; discussion 759–63. [23] Bartels RH, Donk R. Fusion around cervical disc prosthesis: case report. Neurosurgery 2005;57:E194; discussion E. [24] Liu J, Ebraheim NA, Haman SP, et al. How the increase of the cervical disc space height affects the facet joint: an anatomy study. Spine 2006;31:E350–4.
Clinical Study
The factors that influence the postoperative segmental range of motion after cervical artificial disc replacement Kyung-Chung Kang, MD, Chong-Suh Lee, MD, Jeong-Hoon Han, MD, Sung-Soo Chung, MD* Department of Orthopaedic Surgery, Samsung Medical Center, Sungkyunkwan University School of Medicine, Ilwon-dong 50, Kangnam-Gu, Seoul 135-710, Korea Received 30 October 2009; revised 26 February 2010; accepted 8 April 2010
Abstract
BACKGROUND CONTEXT: Advantages of cervical artificial disc replacement (ADR) are to preserve segmental range of motion (ROM) and avoid adjacent segmental disease. To achieve successful outcome after cervical ADR, ROM maintenance is important, but few authors have investigated the factors that influence the postoperative segmental ROM. PURPOSE: To evaluate the factors that influence the postoperative segmental ROM after cervical ADR. STUDY DESIGN/SETTING: A retrospective clinical study. PATIENT SAMPLE: Forty-one consecutive cervical ADR cases were analyzed. OUTCOME MEASURES: Disc height, segmental and overall ROM, and clinical parameters checked with Neck Disability Index (NDI) and visual analog scale (VAS) in neck and arm pain were assessed. METHODS: There were 21 men and 20 women with a mean age of 45 years (range, 27–61 years). All cases were followed up for more than 2 years (range, 24–54 months; average, 31 months). Angles of the inserted implant on the immediate postoperative lateral radiographs, segmental and overall ROM (full flexion angle full extension angle), disc height increment (immediate postoperative disc height preoperative disc height), and adjacent segment changes at cephalad and caudal disc space were measured. Correlations between the factors and segmental ROM at last follow-up were analyzed. RESULTS: Mean preoperative NDI was improved from 61.0 preoperatively to 11.5 at last followup, and mean VAS in the neck pain decreased from 56.8 preoperatively to 11.8 postoperatively and arm pain decreased from 68.1 to 18.0. The mean preoperative segmental ROM changed from 7.463.2 preoperatively to 10.465.9 at last follow-up, and mean preoperative disc height increased from 6.461.0 (4.1–8.4) mm preoperatively to 7.961.0 (6.3–9.9) mm postoperatively. The segmental ROM at last follow-up was not significantly correlated with preoperative segmental and overall ROM, angle of inserted implant, VAS, or age (pO.05). However, the segmental ROM at last follow-up was significantly correlated with the disc height increment (p5.046, r50.374) and preoperative NDI (p5.026, r50.412). The patient group with the postoperative segmental ROM greater than 10 had a significantly lower mean preoperative disc height than the group with the segmental ROM less than 10 (p5.050). CONCLUSIONS: At a minimum of 2 years after cervical ADR, clinical outcomes were satisfactory in terms of function and pain scores. Within our results, the segmental ROM was not affected by preoperative ROM but postoperative disc height increment positively and preoperative disc height negatively. Ó 2010 Elsevier Inc. All rights reserved.
Keywords:
Cervical artificial disc replacement; Range of motion; Influencing factors
FDA device/drug status: not applicable. Author disclosures: SSC (research support: staff/materials, AO Spine Korea). This paper is partly supported by research sponsorship from AO Spine Korea, Ltd. 1529-9430/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.spinee.2010.04.016
* Corresponding author. Department of Orthopaedic Surgery, Samsung Medical Center, Sungkyunkwan University School of Medicine, IlwonDong 50, Kangnam-Gu, Seoul 135-710, Korea. Tel.: (82) 2-3410-0385; fax: (82) 2-3410-0061. E-mail address: [email protected] (S.-S. Chung)
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Context Given that maintaining/improving range of motion is a stated goal of cervical disc replacement, factors that impact such motion are being explored. Contribution In this retrospective case series, an increase in disc height (post-op relative to pre-op, up to limit of 3.9 mm) correlated with improved postoperative ROM. Implications While providing some interesting information, this article looks at a limited number of potential factors impacting ROM in relatively few patients. Causal relations cannot be concluded, nor can unstudied factors impacting motion (confounders) be excluded. Finally, the larger question still remains: does maintaining a minimum degree of motion improve a patient’s outcome? —The Editors
Introduction Although many reports have demonstrated the advantages of cervical artificial disc replacement (ADR) [1–5], few have identified the factors that influence the good postoperative segmental range of motion (ROM) at the implanted disc level [6,7]. The advantage of cervical ADR is to preserve the segmental ROM while avoiding the adjacent segmental disease [8–11]. Most patients who have undergone cervical ADR showed preserved or improved segmental ROM at final follow-up. However, not all patients achieved excellent results. Some cases showed a good segmental ROM immediately after surgery and then gradually deteriorated, and others with osteophytes around the inserted implants postoperatively showed substantially reduced segmental motion at final follow-up. Recently, some reports on the lumbar ADR have identified the factors that importantly affected the postoperative segmental ROM [12,13], but few have demonstrated correlations between influencing factors and postoperative segmental ROM after cervical ADR [14]. Accordingly, the purpose of this study was to identify those factors that affected the postoperative segmental ROM and to find a method of preventing the postoperative segmental ROM decreases after cervical ADR.
Methods Patient selection Forty-one consecutive cervical ADR cases were analyzed retrospectively. All cases were treated by two senior
authors (SSC and CSL) between July 2004 and April 2007 and were followed up for more than 2 years (range, 24–54 months; average, 31 months). There are 21 men and 20 women with a mean age of 45 years (range, 27–61 years). Two patients were treated at C3–C4, 4 patients at C4–C5, 26 patients at C5–C6, and 9 patients at C6–C7. Patients were divided into three groups by pathology: the radiculopathy group (28 patients, 68%), the myelopathy group (4 patients, 10%), and the combined group (9 patients, 22%).
Surgical indication and technique One-level symptomatic cervical disc diseases between C3–C4 and C6–C7 were included in our study, and the inclusion criteria were similar to those for anterior cervical decompression and fusion. Cases of soft disc herniation with radiculopathy or myelopathy and spondylotic radiculopathy were included, but cases of cervical instability, severe facet joint degeneration, deformity, severe spondylosis, and spondylotic myelopathy that were determined by the dynamic X-rays and magnetic resonance images were excluded. The surgical techniques were similar to those for a routine anterior cervical decompression and fusion, except that uncovertebral joints were preserved, to minimize the softtissue damage and bleeding and to avoid damage to the bony end plate. Because of the possibility of bone formation at the bleeding sites, soft-tissue bleeding was meticulously controlled, and the damaged bone area was covered with a bone wax. Although all surgeons tried to minimize the bone procedure, the osteophytes that were compressing nerve roots were removed with a power burr. The posterior longitudinal ligaments (PLLs) were completely removed only when they were torn preoperatively. Three types of artificial disc devices were used: Bryan discs (n56; Medtronic Sofamor Dadek, Memphis, TN, USA), Prodisc-C discs (n517; Synthes Spine, West Chester, PA, USA), and Mobi-C discs (n518; LDR Medical, Troyes, France). There was no surgeons’ preference in selecting types of implants for surgeries and also there were no differences in the postoperative management between surgeons or among the devices.
Clinical evaluation For the clinical evaluation, the Neck Disability Index (NDI) and visual analog scale (VAS) in the neck and arm pain were assessed respectively. All patients were asked to complete questionnaires before surgery and at each follow-up examination. The NDI scores varied from 0 to 100, and the VAS ranged from 0 to 100. The preoperative NDI and VAS were compared with the scores at last follow-up.
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Fig. 1. (Left and Center) Segmental (C5–C6) and overall range of motion (ROM) (C2–C7) were measured using dynamic flexion and extension X-rays at a magnification of 2. (Right) Disc height increment on a lateral X-ray (original magnification 4).
Radiographic evaluation
Statistical analysis
Evaluations were performed preoperatively at 3, 6, and 12 months postoperatively and at last follow-up. The segmental (cephalad, implanted, and caudal disc levels) and overall ROM (C2–C7) were measured on the dynamic full flexion and extension X-rays, and angles of the inserted implants were measured on the immediate postoperative lateral X-rays [15,16]. Kyphotic angle was considered to be a positive value. The disc height on the lateral X-ray, which was defined as the distance from highest portion of the lower end plate in the cephalad vertebra to closest portion of the upper end plate in the caudal vertebra and the disc height increment (immediate postoperative disc height preoperative disc height) were checked (Fig. 1). Degrees of the facet joint degeneration were graded as 1 to 4 using the lumbar facet joint classification in the axial magnetic resonance images [17,18]. All radiographic measurements were carried out on a Picture Archiving and Communications System monitor (General Electric Inc., Chicago, IL, USA), and the angles and lengths were automatically calculated when a measurer drew lines in the interesting area. On the cephalad and caudal disc levels, decreases in the segmental motion and the disc height and bony spurs were also measured. Heterotopic ossifications in the operated segment were evaluated and classified using the grading system introduced by McAfee et al. (Grade 0–4) [19]. Patients with the segmental ROM #2 were considered to have a severe decrease in the segmental ROM and were assessed separately [20].
Statistical analyses were performed by a professional medical statistical consultant. Values are presented as the means6standard deviations. Differences between the preoperative and postoperative disc heights were analyzed by a paired t test and Wilcoxon signed rank test, and the differences between the preoperative and last follow-up segmental (cephalad, implanted, and caudal levels) and overall ROM were also analyzed. The correlations between the postoperative segmental ROM at the last follow-up and other influencing factors, including preoperative segmental and overall ROM, preoperative disc height, disc height increment, angle of the inserted implant, age, and preoperative NDI and VAS in the neck and arm pain were analyzed by a Pearson product-moment correlation coefficient. To identify the factors that influence the postoperative segmental ROM, the patients were divided into two groups (Group I and II) based on a segmental ROM at last follow up of !10 and $10 . This cutoff value was used because it was the average segmental ROM at last follow-up. The values of other influencing factors in these two groups were compared using the two-sample t test. The two-sample t test and the Kruskal-Wallis test were also used to compare the mean postoperative segmental ROMs of different types of artificial disc devices (Bryan, Prodisc-C, and Mobi-C), operated cervical levels (C3–C4, C4–C5, C5–C6, and C6–C7), degrees of facet degeneration, and with respect to PLL removal. Statistical significance was accepted for p value !.05.
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Fig. 2. Mean preoperative segmental range of motions (ROMs) of cephalad, implanted, and caudal levels and mean preoperative overall ROM were slightly increased postoperatively, but only preoperative segmental ROM of implanted level showed the significant difference with postoperative segmental ROM (p5.008). f/u, follow-up.
Inter- and intraobserver intraclass correlation coefficient (ICC) were also assessed for ROM and disc height.
Results Mean preoperative NDI was improved from 61.0 preoperatively to 11.5 postoperatively, mean VAS in neck pain decreased from 56.8 preoperatively to 11.8 postoperatively, and VAS in arm pain decreased from 68.1 to 18.0, respectively. Mean preoperative segmental ROM at the implanted level changed from 7.463.2 to 10.465.9 at last followup, and overall ROM changed from 43.1614.1 to 44.9622.1 . Mean preoperative disc height was increased significantly from 6.461.0 (4.1–8.4) to 7.961.0 (6.3–9.9)
mm immediately after surgery (p!.001) and then decreased to 7.460.9 (5.5–8.6) mm at last follow-up. Preoperative and last follow-up segmental ROM were significantly different, but no significant difference was found between the preoperative and last follow-up segmental ROMs of the cephalad and caudal levels or between overall ROMs at the implanted level (Fig. 2, Table 1). Segmental ROM at last follow-up was not found to be associated with preoperative segmental ROM or disc height (pO.05). However, the segmental ROM at last follow-up was significantly correlated with the disc height increment (p5.046, r50.374) and preoperative NDI (p5.026, r50.412) (Table 2). Group I (segmental ROM !10 at last follow-up) and group II (segmental ROM $10 at last follow-up) were
Table 1 Preoperative and postoperative values of influencing factors Influencing factors NDI (%) VAS in neck VAS in arm Seg. ROM ( ) Implanted Cephalad Caudal Overall ROM ( ) Disc height (mm)
Preoperative (mean6SD)
Immediate postoperative (mean6SD)
61.0618.3 56.8616.2 68.1621.4 7.463.2 8.865.2 6.464.5 43.1614.1 6.461.0
9.565.5 10.064.2 6.463.4 43.3614.8 7.961.0
Last follow-up (mean6SD)
Comparison analysis*: preop. vs. last f/u (p value)
11.568.1 11.8613.6 18.0618.8
!.001** !.001** !.001**
10.465.9 9.666.0 7.166.0 48.4622.1 7.460.9
.008** .489 .467 .166 !.001**
SD, standard deviation; preop., preoperative; f/u, follow-up; NDI, Neck Disability Index; VAS, visual analog scale; Seg. ROM, segmental range of motion. * Paired t test and Wilcoxon signed-rank test. ** p!.05.
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Table 2 Factors significantly correlated with segmental ROM of implanted level at last follow-up Minimum–maximum
Correlation* with seg. ROM at last f/u (p value)
Influencing factors
Mean6SD
Preoperative Seg. ROM ( ) Overall ROM ( ) Disc height (mm) NDI (%) VAS in neck VAS in arm
7.463.2 43.1614.1 6.461.0 61.0618.3 56.8616.2 68.1621.4
1.1–13.9 16.6–69.7 4.1–8.4 16–80 0–100 45–100
.905 .662 .075 .026** .371 .258
Immediate postoperative Disc height (mm) Disc height increment (mm) Age (y) Angle of inserted implant ( )
7.961.0 1.661.4 44.867.9 2.465.4
6.3–9.9 1.3–3.9 27–61 10.1–9.3
.538 .046** .835 .914
Correlation coefficient (r)
0.412
0.374
SD, standard deviation; Seg. ROM, segmental range of motion; NDI, Neck Disability Index; VAS, visual analog scale. * Pearson correlation. ** p!.05.
compared. The two groups were found to be significantly different with respect to preoperative disc height, preoperative NDI, and disc height increment (p5.050, .035, and .028, respectively; Table 3). The last follow-up segmental ROM was not found to be significantly affected by types of the artificial disc devices, operated cervical levels, degrees of facet degeneration, or different pathologies (p5.192, .711, .199, and .083, respectively, Kruskal-Wallis test) or whether the PLL had been removed or not (p5.292, two-sample t test). No additional operations were performed on cephalad and caudal segments during the follow-up period. Regarding cephalad segments, three retrolisthesis and five heterotopic ossification (#Grade 2) cases were showed at last followups, and three heterotopic ossification (#Grade 2) cases were detected in caudal segments. For operated segments, 23 patients (56.1%) had no heterotopic ossification. Grade 1 ossifications were present in four patients (9.8%) and heterotopic ossifications of Grade 2 and 3 were observed in six (14.6%) and five patients (12.2%), respectively. At last follow-ups, three patients (7.3%) had a spontaneous fusion. Among the 18 cases of heterotopic ossifications, 4, 3, and 11 cases were showed at postoperative 6, 12, and 24 months postoperatively, respectively. Three patients had a preoperative segmental ROM #2 . Among them, one patient showed a #2 segmental ROM continuously during the follow-up, but, the other two showed an increase of segmental ROM at 3 months postoperatively and maintained this increase throughout followup. At last follow-up, three patients had a segmental ROM at the implanted level of #2 and two of these had a greater than mean segmental ROM preoperatively but showed significant decreases of segmental ROM and bridging osteophytes at 1 year postoperatively (Table 4). The measurements of both ROM and disc height showed excellent reproducibility (interobserver: ROM: ICC, 0.885;
disc height: ICC, 0.945; intraobserver: ROM: ICC, 0.882; disc height: ICC, 0.938).
Discussion Few reports have been issued concerning correlations between variables and postoperative segmental ROM after cervical ADR. Peng et al. [14] suggested that patients with disc collapse of #4 mm with respect to preoperative disc height benefit more after ADR in terms of segmental ROM and concluded that the optimal range of postoperative disc heights in terms of maximizing segmental ROM is between 5 and 7 mm for the Prodisc-C prosthesis. On the Table 3 Values of factors found to influence postoperative segmental ROM in Group 1 (!10 of segmental ROM at last follow-up) and Group 2 ($10 of segmental ROM at last follow-up)
Influencing factors
Group I (n519) (mean6SD)
Group II (n522) (mean6SD)
Comparison analysis* (p value*)
Preoperative Seg. ROM ( ) Overall ROM ( ) Disc height (mm) NDI (%) VAS in neck VAS in arm
7.163.5 46.6613.7 6.761.0 57.1615.1 54.3614.2 61.4622.9
6.663.3 41.3612.1 6.061.0 69.4614.7 60.7613.3 74.3618.5
.655 .246 .050** .035** .151 .106
7.960.9 1.261.4
8.261.1 2.261.1
.379 .028**
42.166.7 1.266.0
46.168.0 2.666.0
Immediate postoperative Disc height (mm) Disc height increment (mm) Age (y) Angle of inserted implant ( )
.133 .499
SD, standard deviation; Seg. ROM, segmental range of motion; NDI, Neck Disability Index; VAS, visual analog scale. * t Test. ** p!.05.
Seg. ROM, segmental range of motion; PLL, posterior longitudinal ligament; NDI, Neck Disability Index; VAS, visual analog scale; f/u, follow-up; M, male; F, female; Radi., radiculopathy. * Seg. ROM at the last follow-up #2 .
1.2* 1.9* 0.3* 13.9 7.4 1.8 70 90 70 40 85 60 56 58 52 O O 0 2.6 3.2 7.9 8.5 8.4 9.3 6.3 7.1 6.9 5.3 7.5 7.9 5.9 5.2 Radi. Radi. Radi. Prodisc-C Mobi-C Mobi-C M F M
44 47 55
C5–C6 C5–C6 C5–C6 1 2 3
Preoperative Preoperative
Last f/u seg. Immediate PLL VAS VAS Seg. Diagnosis Implanted Cephalad Caudal postoperative Increment removal NDI (%) in neck in arm ROM ( ) ROM ( ) Implant type Operated No. Sex Age level
Disc height (mm)
Table 4 Characteristics of the three patients who experienced a severe decrease in seg. ROM at last follow-up (#2)
O O
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Postoperative bridging osteophyte
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other hand, Mehren et al. [21] and Leung et al. [22] showed a high prevalence of heterotopic ossification and found a correlation between heterotopic ossification and restriction of segmental ROM after cervical ADR. In addition, Bartels and Donk [23] described two cases with a bony spur and fusion around the cervical disc prosthesis using a Bryan disc prosthesis, although facet joints were completely normal, and the possibility of diffuse idiopathic skeletal hyperostosis had been excluded. They also prescribed a nonsteroidal antiinflammatory drug to prevent the early formation of bone matrix. In lumbar ADR, Yaszay et al. [12] reported that patients with greater disc collapse benefit more from ADR in terms of segmental ROM and proposed a standard for the postoperative anterior disc height. However, Siepe et al. [13] mentioned that if disc height is restored, ADR leads to a significant decrease in postoperative segmental ROM, particularly at the lumbosacral junction, and a higher preoperative disc height and segmental ROM had a beneficial effect on the postoperative segmental mobility. In the present study, mean preoperative segmental and overall ROM were either preserved or slightly increased after cervical ADR in most cases, but postoperative segmental ROM greatly decreased in a few cases. Many factors that could influence the postoperative segmental ROM were evaluated during the course of the study. Preoperative segmental or overall ROM, VAS, immediate postoperative disc height, and others were not found to be associated with postoperative segmental or overall ROM. On the other hand, disc height increments showed a significant correlation with segmental ROM at last follow-up. Common sense dictates that an excessive increase in disc height confers larger loads on operated segments and thus, is likely to reduce segmental ROM [24], but our study showed that disc height increments within an acceptable range could increase segmental ROM at more than 2-year follow-up after cervical ADR. In the present study, the maximum postoperative disc height increment was 3.9 mm, and thus, we conclude that if the immediate postoperative disc height is within the range represented by our results (6.3–9.9 mm), a disc height increment of !4.0 mm is acceptable, and postoperative segmental ROM is likely to be satisfactory after cervical ADR. Preoperative NDI also showed a significant correlation with segmental ROM at last follow-up, which means that segmental ROM at affected level was restricted because of its own disease or pathology, and that segmental ROM recovered normally after cervical ADR. Therefore, authors considered that postoperative segmental ROM at implanted level increased with increasing preoperative NDI. On the other hand, preoperative disc height was not significantly correlated with segmental ROM at last follow-up (p5.075), although patients with an excellent postoperative segmental ROM ($10 ) had significantly lower disc heights than patients with less than good postoperative segmental ROM (!10 ) (p5.050), which indicates that disc height can also influence postoperative segmental ROM.
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Severe restrictions in segmental ROM preoperatively were not always found to be associated with decreases in segmental ROM after cervical ADR. In the present study, only one of three patients with a severe decrease of segmental ROM preoperatively experienced a severe decrease in segmental ROM at last follow-up. On the other hand, none of four patients with a disc height of !5 mm preoperatively experienced a severe decrease in segmental ROM postoperatively. The patients with a preoperative lowest segment ROM (#2 ) or disc height (!5 mm) do not always show the significant decrease of postoperative segmental ROM. Within our results, these indications may not be absolute contraindications to cervical ADR. At last follow-ups, three patients almost had a fused segment (postoperative segmental ROM #2 ), and two of these had the bridging osteophyte around the implanted level at 1 year postoperatively. One of the three showed a preoperative severe decrease in segmental ROM. However, no other preoperative factors were found to be correlated with severe postoperative decreases in segmental ROM. We believe the factors that influence a decrease in segmental ROM after cervical ADR will be determined by future larger-scale studies. In the present study, we did not consider an implant height as a disc height in the operated segment and introduced a new easy method in radiographic measurement of disc height because a real disc height is dependent on the topography of the upper and lower end plates, although the same implant was inserted. There were some limitations in this study. A longer follow-up is necessary, and the ADR group was not compared with a fusion or other controlled group. These are inherent weaknesses of our study; however, our study was uniquely focused on factors affecting the postoperative segment ROM after cervical ADR and statistically significant differences could be obtained within our cases. Furthermore, the three different types of artificial discs involved might have introduced bias, although we did confirm that these devices were nonsignificantly different in terms of segmental ROM and disc height at last follow-ups. Finally, the radiographic measurement used may have introduced unacceptable inter- and intraobserver errors. In an effort to minimize these errors, we introduced a simple method to estimate disc height and had all measurements taken twice by two orthopedic surgeons using magnified X-ray images. With this effort, we could measure both the ROM and disc height with excellent reproducibility.
Conclusion After a minimum 2-year follow-up after cervical ADR, clinical outcomes were satisfactory in terms of pain and function scores. The maintenance of segmental ROM was found to be unaffected by preoperative ROM or VAS but to be positively influenced by postoperative disc height
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increments and preoperative NDI. Within our results, enough postoperative disc height increment is thought to be essential to improve segmental ROM. However, a larger-scale study is needed to identify the factors that influence postoperative decreases in segmental ROM after cervical ADR. References [1] Shin DA, Yi S, Yoon do H, et al. Artificial disc replacement combined with fusion versus two-level fusion in cervical two-level disc disease. Spine 2009;34:1153–9; discussion 60–1. [2] Rohl K, Rohrich F. Artificial disc versus spinal fusion in the treatment of cervical spine degenerations in tetraplegics: a comparison of clinical results. Spinal Cord 2009;47:705–8. [3] Kim SW, Limson MA, Kim SB, et al. Comparison of radiographic changes after ACDF versus Bryan disc arthroplasty in single and bi-level cases. Eur Spine J 2009;18:218–31. [4] Goffin J, Van Calenbergh F, van Loon J, et al. Intermediate follow-up after treatment of degenerative disc disease with the Bryan Cervical Disc Prosthesis: single-level and bi-level. Spine 2003;28:2673–8. [5] Sasso RC, Smucker JD, Hacker RJ, Heller JG. Artificial disc versus fusion: a prospective, randomized study with 2-year follow-up on 99 patients. Spine 2007;32:2933–40; discussion 41–2. [6] Rundell SA, Auerbach JD, Balderston RA, Kurtz SM. Total disc replacement positioning affects facet contact forces and vertebral body strains. Spine 2008;33:2510–7. [7] Palissery V, Mulholland RC, McNally DS. The implications of stress patterns in the vertebral body under axial support of an artificial implant. Med Eng Phys 2009;31:833–7. [8] Pickett GE, Rouleau JP, Duggal N. Kinematic analysis of the cervical spine following implantation of an artificial cervical disc. Spine 2005;30:1949–54. [9] Murrey D, Janssen M, Delamarter R, et al. Results of the prospective, randomized, controlled multicenter Food and Drug Administration investigational device exemption study of the ProDisc-C total disc replacement versus anterior discectomy and fusion for the treatment of 1-level symptomatic cervical disc disease. Spine J 2009;9: 275–86. [10] Hilibrand AS, Carlson GD, Palumbo MA, et al. Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis. J Bone Joint Surg Am 1999;81:519–28. [11] Park JB, Cho YS, Riew KD. Development of adjacent-level ossification in patients with an anterior cervical plate. J Bone Joint Surg Am 2005;87:558–63. [12] Yaszay B, Bendo JA, Goldstein JA, et al. Effect of intervertebral disc height on postoperative motion and outcomes after ProDisc-L lumbar disc replacement. Spine 2008;33:508–12; discussion 13. [13] Siepe CJ, Hitzl W, Meschede P, et al. Interdependence between disc space height, range of motion and clinical outcome in total lumbar disc replacement. Spine 2009;34:904–16. [14] Peng CW, Quirnoa M, Bendo JA, et al. Effect of intervertebral disc height on postoperative motion and clinical outcomes after Prodisc-C cervical disc replacement. Spine J 2009;9:551–5. [15] Lim MR, Girardi FP, Zhang K, et al. Measurement of total disc replacement radiographic range of motion: a comparison of two techniques. J Spinal Disord Tech 2005;18:252–6. [16] Hayes MA, Howard TC, Gruel CR, Kopta JA. Roentgenographic evaluation of lumbar spine flexion-extension in asymptomatic individuals. Spine 1989;14:327–31. [17] Fujiwara A, Tamai K, An HS, et al. Orientation and osteoarthritis of the lumbar facet joint. Clin Orthop Relat Res 2001;385:88–94. [18] Fujiwara A, Tamai K, Yamato M, et al. The relationship between facet joint osteoarthritis and disc degeneration of the lumbar spine: an MRI study. Eur Spine J 1999;8:396–401.
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