Table 1.

Comparison of the hydroxyapatite cages with other cages used in ACDF.

Type of Cage	Material	Fusion Rate	Time to Achieve Solid Fusion	Subsidence Rate	Disadvantages
Autograft	Natural bone harvested from iliac bone	85–100% [102]	~6 months [96]	~0% [96]	morbidity at the donor site, increased blood loss, limited amount
Standard cages
TMC Cage	Titanium	94–96% [113,118]	5–7 months [93]	From 4 to 22% [93,113,115]	difficulty in radiographic assessment, stress shielding effect [93,113]
PEEK Cage	Polyetheretherketone	88–100% [94]	7–8 months [120]	From 9.8% to 14.3% [115]	lack of osteointegration of the cage, difficulty in radiographic assessment [94]
Hydroxyapatite cages
nHA/PA66 Cage	Nanohydroxyapatite infiltrating into polyamide 66	97%–98% [113,115,118]	-	From 2 to 10.6% [38,113,115,116,117,118]	difficult radiographic assessment of solid fusion, but easier compared with TMC [113]
Hydroxyapatite/PEEK Cage	Composite of 80% PEEK and 20% calcium hydroxyapatite	~100% [120]	3–5 months [120]	-	lack of clinical studies, difficulty in radiographic assessment