Table 7. Single-level versus multilevel C-ADR.

Pain and disability
Outcomes	Strength of evidence	Conclusions/comments
1. Overall success		Three studies reported various measures of overall success (Odom’s criteria, neurological success, composite measure) and found no statistical differences between treatment groups across 1 to 6 years of follow-up.
1. Pain		Measured a variety of ways (VAS, analgesic use, treatment intensity score) across four studies. Inconsistent results regarding the effectiveness of one surgery to provide better pain relief over the other.
3. NDI		No significant differences between single-level and multilevel C-ADR in NDI scores over 1 to 6 years follow-up as reported by four studies.
4. Quality of Life (SF-36 PCS and MCS)		No significant differences were reported between single-level and multilevel C-ADR at 1, 2, 4, or 6 years follow-up in two studies.
5. Patient satisfaction		Similar numbers of patients in both treatment groups were satisfied with their treatment and would repeat the procedure as reported by one study.
6. Return to work		Greater proportion of multilevel C-ADR patients returned to part-time or full-time work and at a quicker rate than single-level C-ADR patients in one study.

Complications
Outcomes	Strength of evidence	Conclusions/comments
1. Reoperation		Reoperation was reported by three studies, one of which reported a lower rate at 2 years following single-level compared with multilevel C-ADR, and two studies reported similar reoperation rates between the groups.
2. Heterotopic ossification		Two studies reported conflicting results for the rate of HO between groups.
3. Other complications		A significantly lower incidence of dysphagia was reported following single-level compared with multilevel C-ADR at 2 years in one study. Rates of revision, device subsidence or migration, infection, mortality, and other complications were similar between groups.