Table 3.

Characteristics of Studies Included in Adjacent Level Surgery Analysis.

Study	Study Design	Inclusion Criteria	Exclusion Criteria	Sponsor	Definition of Adjacent Surgery	Arm	Sample Size	Technical Details	Age (mean and standard deviation unless otherwise stated)	Sex	NDI?	Reasons for adjacent surgery
NCT00389597 50	RCT	Single or 2 level spondylosis with radiculopathy and/or myelopathy with levels involved C3-C7	More than 2 levels, rigid segment, infection, osteoporosis, disc height <3mm, morbid obesity, Rheumatoid Arthritis, etc.	LDR Spine USA	Not reported	ACDF	186	ACDF with allograft and plate	44.0 ± 8.2 1 level 46.2 ± 8.0 2 level	44.4% male for 1-level, 57.1% male for 2-level	yes	Not fully reported, most common reason stated for both was “adjacent level disease or herniation”
						ADR	389	Mobi-C ADR	43.3 ± 9.2 1 level 45.3 ± 8.1 2 level	47.6% male for 1-level, 50.2% male for 2-level	yes
NCT00437190 51,52	RCT	Single level degenerative disc disease with radiculopathy or myelopathy at levels between C3 and C7	Deformity, diabetes requiring daily Insulin, morbid obesity, previous C-pine surgery, infection, steroid use.	Medtronic Spinal and Biologics	Surgery at adjacent level to index procedure	ACDF	221	Allograft Fusion and ATLANTIS™ Cervical Plate System	Not reported	Not reported	Yes	“Symptomatic adjacent level disease requiring surgery”
						ADR	242	BRYAN Cervical Disc Prosthesis	Not reported	Not reported	Yes	“Symptomatic adjacent level disease requiring surgery”
NCT00637156 53	RCT	Intractable radiculopathy and/or myelopathy with degenerative disc disease at 2 adjacent cervical levels from C3-C7	Other condition, smokers, pregnant patients, osteoporotic patients	Medtronic Spinal and Biologics	Any surgery at adjacent levels	ACDF	Historical Control from NCT00642876 5
						ADR	209	PRESTIGE LP device at 2 adjacent levels	47.1 (8.3)	44.0% male	Yes	Not reported
NCT00642876 54	RCT	Single-level cervical disc disease and at least 1 additional confirmatory neuroradiographic study, such as MRI or CT-enhanced myelography that showed findings consistent with clinical findings	-Cervical spinal conditions other than single-level symptomatic degenerative disc disease or evidence of instability. -Symptomatic disc disease at level C2–3 or C7–T1, a history of discitis, or a medical condition that required medication, such as steroids or nonsteroidal anti-inflammatory medications that could interfere with fusion.	Medtronic Spinal and Biologics	Any secondary surgery including revision at initial site that involved an adjacent level	ACDF	265	Allograft Fusion and ATLANTIS™ Cervical Plate System	43.9 (22-73)	46.0% male	Yes	Not reported
						ADR	276	PRESTIGE® Cervical Disc	43.3 (25-72)	46.4% male	Yes	Not reported
Lee et al. 2014 55,56	Retrospective series	Cervical spine surgery performed by the senior author (K.D.R.) for radiculopathy, myelopathy, or myeloradiculopathy between January 1999 and December 2010	Contiguous or mixed OPLL, patients undergoing revision within 12 months.	Soonchunhyang University Research Fund (No. 20150000)	Any surgery at adjacent level	ACDF	1038	One level arthrodesis were performed on 353 patients; 2 levels on 374 patients; 3 levels on 228 patients; 4 levels on 70 patients; 5 levels on 12 patients; and 6 levels on 1 patient	50 (22–89)	49.5% male	No	New radiographically correlated symptoms at a segment adjacent to previous anterior arthrodesis minimum 1 year after the index operation