Differences between 1- and 2-level cervical arthroplasty: more heterotopic ossification in 2-level disc replacement

Clinical article

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The most currently accepted indication for cervical arthroplasty is 1- or 2-level degenerative disc disease (DDD) refractory to medical treatment. However, the randomized and controlled clinical trials by the US FDA investigational device exemption studies only compared cervical arthroplasty with anterior cervical discectomy and fusion for 1-level disease. Theoretically, 2-level cervical spondylosis usually implicates more advanced degeneration, whereas the 1-level DDD can be caused by merely a soft-disc herniation. This study aimed to investigate the differences between 1- and 2-level cervical arthroplasty.


The authors analyzed data obtained in 87 consecutive patients who underwent 1- or 2-level cervical arthroplasty with Bryan disc. The patients were divided into the 1-level and the 2-level treatment groups. Clinical outcomes were measured using the visual analog scale (VAS) for the neck and arm pain and the Neck Disability Index (NDI), with a minimum follow-up of 30 months. Radiographic outcomes were evaluated on both radiographs and CT scans.


The study analyzed 98 levels of Bryan cervical arthroplasty in 70 patients (80.5%) who completed the evaluations in a mean follow-up period of 46.21 ± 9.85 months. There were 22 females (31.4%) and 48 males (68.6%), whose mean age was 46.57 ± 10.07 years at the time of surgery. The 1-level group had 42 patients (60.0%), while the 2-level group had 28 patients (40.0%). Patients in the 1-level group were younger than those in the 2-level group (mean 45.00 vs 48.93 years, p = 0.111 [not significant]). Proportional sex compositions and perioperative prescription of nonsteroidal antiinflammatory drugs were also similar in both groups (p = 0.227 and p = 1.000). The 2-level group had significantly greater EBL during surgery than the 1-level group (220.80 vs 111.89 ml, p = 0.024). Heterotopic ossification was identified more frequently in the 2-level group than the 1-level group (75.0% vs 40.5%, p = 0.009). Although most of the artificial discs remained mobile during the follow up, the 2-level group had fewer mobile discs (100% and 85.7%, p = 0.022) than the 1-level group. However, in both groups, the clinical outcomes measured by VAS for neck pain, VAS for arm pain, and NDI all significantly improved after surgery compared with that preoperatively, and there were no significant differences between the groups at any point of evaluation (that is, at 3, 6, 12, and 24 months after surgery).


Clinical outcomes of 1- and 2-level cervical arthroplasty were similar at 46 months after surgery, and patients in both groups had significantly improved compared with preoperative status. However, there was a significantly higher rate of heterotopic ossification formation and less mobility of the Bryan disc in patients who underwent 2-level arthroplasty. Although mobility to date has been maintained in the vast majority (94.3%) of patients, the long-term effects of heterotopic ossification warrant further investigation.

Abbreviations used in this paper:ACDF = anterior cervical discectomy and fusion; DDD = degenerative disc disease; EBL = estimated blood loss; FDA-IDE = FDA investigational device exemption; HO = heterotopic ossification; NDI = Neck Disability Index; NSAID nonsteroidal antiinflammatory drug; VAS = visual analog scale.

Article Information

* Drs. JC Wu and Huang contributed equally to this work.

Address correspondence to: Chin-Chu Ko, M.D., Department of Neurosurgery, Neurological Institute, Taipei Veterans General Hospital, Room 509, 17F, No. 201, Shih-Pai Road, Sec. 2, Beitou, Taipei 11217, Taiwan. email: hansamu0627@gmail.com.

Please include this information when citing this paper: published online March 23, 2012; DOI: 10.3171/2012.2.SPINE111066.

© AANS, except where prohibited by US copyright law.



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    Radiographs (A–C) and CT scans (D and E) obtained in a 23-year-old man who underwent Bryan arthroplasty at C5–6. There was no HO formation at 24 months postoperatively. AP = anteroposterior.

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    Radiographs (A–C) and CT scans (D–F) obtained in a 45-year-old woman who underwent Bryan cervical arthroplasty at C4–5 and C5–6. There was no HO formation at 23 months postoperatively.

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    Radiographs (A–C) and CT scans (D–F) acquired in a 34-year-old man who underwent Bryan cervical arthroplasty at C5–6 and C6–7. The arrows indicate the formation of HOs at 24 months postoperatively.

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    Comparison of the clinical outcomes between the 1- and 2-level Bryan cervical arthroplasty groups at up to 24 months postoperatively. In both groups the VAS neck pain, VAS arm pain, and NDI scores all significantly improved after surgery compared with preoperative scores. Moreover, there were no significant intergroup differences at each time point of evaluation (that is, preoperatively, at 3, 6, 12, and 24 months postoperatively).

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    Comparison of the clinical outcomes between the patients with and without the formation of HOs after Bryan cervical arthroplasty. In both groups the VAS neck pain, VAS arm pain, and NDI scores were significantly improved after surgery compared with preoperative scores. Moreover, there were no significant intergroup differences at each time point of evaluation (that is, preoperatively, at 3, 6, 12, and 24 months postoperatively).



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