Introduction: Clinical outcomes on one-level cervical disc replacement (CDR) as alternative to fusion are very encouraging. Because fusing multilevel causes more loss of motion, the concept of motion preservation by CDR seems more appealing in multilevel degenerative disc disease (DDD) than in one-level. But there are very few biomechanical studies evaluating the kinematics of two-level CDR and hybrid constructs. The aim of the present study was to evaluate the multidirectional kinematics of a two-level CDR and hybrid construct with CDR adjacent to integrated plate spacer (IPS), compared to two-level fusion using a selectively constrained CDR.
Methods: Seven cadaveric cervical spines (C3-T1) were tested in the following sequence (Figure 1): 1) Intact; 2) Two-level CDR (CDR C5-C7); 3) Hybrid (CDR C5-C6 + IPS C6-C7); and 4) Two-level Fusion (IPS C5-C7). Range of motion at both implanted and adjacent level, and center of rotation in sagittal plane were calculated.
Results: At the level of implantation, motion was preserved in flexion-extension (102%) and axial rotation (96%), and tended to decrease in lateral bending (79%), with two-level CDR. The findings also revealed that two-level CDR and hybrid construct did not significantly change adjacent level kinematics compared to the intact condition, whereas the two-level fusion construct demonstrated a significant increase in flexibility at the adjacent level. The location of center of rotation in the sagittal plane at C5-C6 and C6-C7 for the two-level CDR construct was similar to that of the intact condition.
Conclusions: Two-level CDR construct tended to imitate a motion profile similar to the intact condition in flexion-extension and axial rotation but had a tendency to reduce motion in lateral bending. The results of this study agree with those observed in previous in vitro biomechanical studies. Hybrid constructs may be used as a surgical alternative for treating two-level cervical DDD.
Patient Care: Our research will help surgeon general to choose the most effective treatment for patients suffering from two-level degenerative disc disease
Learning Objectives: By the conclusion of this session, participants should be able to identify an effective treatment for treating two-level degenerative disc disease.