Heterotopic ossification after cervical total disc replacement: determination by CT and effects on clinical outcomes

Clinical article

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Heterotopic ossification (HO) after cervical total disc replacement (TDR) has been reported to impede artificial disc motion. In all previously reported cases of HO, assessment was based on plain radiographs. The authors hypothesized that CT scan is a more sensitive and accurate detector. The aims of this study were to assess the actual incidence of HO and its effect on outcome in a cohort of patients undergoing cervical TDR with the Bryan disc and to compare HO detection by means of plain radiographs and CT.


The authors retrospectively assessed data from medical records, radiological studies, and clinical evaluations of patients who underwent 1- or 2-level cervical TDR with the Bryan disc and were followed up for more than 12 months. The presence and grading of HO according to the McAfee classification were assessed by CT scan, and these findings were compared with findings on plain radiographs. Thirty-six patients (mean age 46.61 ± 7.24 years; range 29–60 years; 21 men and 15 women) who underwent Bryan TDR at 52 levels were included in the study. The mean duration of CT follow-up was 19.03 ± 4.64 months; the mean duration of clinical follow-up was 26.78 ± 7.20 months.


On the basis of CT, HO was identified in 18 (50%) of 36 patients and 25 (48.1%) of 52 levels treated. Grade 1 HO was present in 9 of the levels treated (17.3%), Grade 2 in 13 levels (25.0%), Grade 3 in 2 levels (3.8%), and Grade 4 in 1 level (1.9%). Nineteen (76%) of the 25 affected levels were in patients who had undergone 2-level TDR. There was no significant association with patient sex or disc pathology. There was a tendency for HO development among older patients, but this finding was not statistically significant (mean age 48.8 ± 6.8 in patients with HO vs 44.4 ± 7.2 in those without HO, p = 0.065). Although HO was found in 25 levels, 96.2% of the treated levels (50 of 52) had segmental range of motion on dynamic (flexion and extension) radiographs. The concordance between HO grading by CT and radiography was high, with an intraclass correlation coefficient of 0.822 (lower limit of 95% CI: 0.710, p < 0.001). Patients who had HO had the same clinical success rate as those who did not (94.4% vs 94.4%, p = 1.00). The visual analog scale scores for neck and arm pain were significantly improved in both the HO and the non-HO group.


The rate of HO detected by CT scan in this cohort of patients undergoing cervical TDR with a Bryan disc was 48.1% per level treated and 50% per patient with minimal limitation of segmental motion (96.2% of levels remained mobile), but plain radiograph is an acceptable detection tool. Two-level surgery has a higher risk of HO, although development of HO does not affect clinical outcome.

Abbreviations used in this paper: ACDF = anterior cervical discectomy and fusion; ASD = adjacent-segment disease; HO = heterotopic ossification; NSAID = nonsteroidal antiinflammatory drug; TDR = total disc replacement; VAS = visual analog scale.

Article Information

Address correspondence to: Jau-Ching Wu, M.D., Neural Regeneration Center, Department of Neurosurgery, Neurological Institute, Taipei Veterans General Hospital, Room 509, 17F, No. 201, Shih-Pai Road, Sec. 2, Beitou, Taipei 11217, Taiwan. email: jauching@gmail.com.

Please include this information when citing this paper: published online February 4, 2011; DOI: 10.3171/2010.11.SPINE10444.

© AANS, except where prohibited by US copyright law.



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    Bar graph showing distribution of treated levels and presence of HO by level.

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    Mean VAS scores for neck and arm pain. Error bars represent SDs. Asterisk represents significant difference compared with preoperative level for both the HO and the non-HO groups (p < 0.001 and p < 0.001, respectively). There were no significant between-group differences at 12 and 24 months after surgery.

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    Plain radiographs and CT images obtained in a 59-year-old female patient. A and B: Preoperative anterior-posterior (A) and neutral lateral (B) radiographs showing a normal cervical lordotic curve and alignment. C and D: Postoperative lateral extension (C) and flexion (D) radiographs demonstrating Grade 4 HO at the C4–5 level (white arrow) with loss of segmental mobility and Grade 2 HO at the C5–6 level (black arrowhead) with preserved segmental mobility. E and F: Right (E) and left (F) sides of the sagittal reformatted CT imaging study obtained 18 months after C4–5 and C5–6 TDR. G and H: The axial CT images at the C4–5 (G) and C5–6 (H) levels confirming the ventral and dorsal bridging ossification, HO (Grade 4), and showing the dorsal Grade 2 HO (black arrow) at the C5–6 level, which was not seen on plain radiographs.

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    Dynamic plain radiographs and CT scans obtained in a 40-year-old female patient 20 months after C5–6 and C6–7 TDR. A and B: Lateral extension (A) and flexion (B) radiographs showing loss of segmental mobility at the C6–7 level and Grade 2 HO (black arrows). C–E: Sagittal (C) and coronal (D) reformatted CT scan and axial CT scan (E) demonstrating arthrodesis in the left C6–7 facet (white arrows) with immobilization of the C6–7 segment.



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