OBJECTIVE: To test the following hypotheses: (i) anterior cervical discetomy and fusion (ACDF) using stand-alone interbody spacers will significantly reduce the range of motion from intact spine; and (ii) the use of a static or a rotational-dynamic plate will significantly augment the stability of stand-alone interbody spacers, with similar beneficial effect when compared to each other.METHODS: Eleven human cadaveric subaxial cervical spines (age: 48.2 ± 5.4 years) were tested under the following sequence: (i) intact spine; (ii) ACDF at C -C using a stand-alone interbody spacer; (iii) ACDF at C -C and insertion of an interbody spacer (two-level construct); and (iv) randomized placement of either a two-level locking static plate or a rotational-dynamic plate.RESULTS: Insertion of stand-alone cage at C -C and C -C caused a significant decrease in the range of motion compared to intact spine (P < 0.05). Placement of both the locking and the rotational dynamic plate further reduced the range of motion at C -C and C -C compared to stand-alone cage (P < 0.01). No significant differences in range of motion restriction at either C -C or C -C were found when the two plating systems were compared (P > 0.05).CONCLUSIONS: Cervical stand-alone interbody spacers caused significant restriction in the range of motion. Both plates significantly augmented the stability of stand-alone interbody spacers, with similar stabilizing effect.