Implant complications, fusion, loss of lordosis, and outcome after anterior cervical plating with dynamic or rigid plates: two-year results of a multi-centric, randomized, controlled study.

STUDY DESIGN: Prospective, controlled, randomized, multicenter study. OBJECTIVE: To analyze implant complications and speed. SUMMARY OF BACKGROUND DATA: Rigid plate designs, in which the screws are locked to the plate, are in common use and thought to provide more fixation than dynamic designs, in which the screws may glide when the graft is settling. The aim of the study is to analyze (1) implant complications, (2) speed of fusion, (3) loss of lordosis, and (4) clinical outcome in both types of plates. METHODS: One hundred thirty-two patients were included and assigned by randomization to one of the groups in which they received a routine anterior cervical discectomy and autograft fusion with either a dynamic plate (ABC, study group) or a rigid plate (CSLP, control group). At discharge, after 3 and 6 months and finally after 2 years, implant complications, segmental mobility, absence of radiolucencies, absence of bone sclerosis, evidence of bridging trabecular bone, loss of lordosis, Visual Analog Scale (VAS) and Neck Disability Score were recorded. All radiographic measurements were performed by an independent radiologist. RESULTS: There have been 4 patients with implant complications within the control group and no implant complications within the study group, P = 0.045. Mean segmental mobility before discharge for the study group was 1.7 mm, 1.4 mm after 3 months, 0.8 mm after 6 months, and 0.4 mm after 2 years. For the control group, these values were 1.0, 1.8, 1.6, and 0.5 mm. The difference at 6 months between both groups was significant (P = 0.024). Neither absence of radiolucencies, nor absence of sclerosis, nor evidence of bridging bone showed significant differences between the 2 groups through the postoperative follow-up (P > 0.05). The loss of segmental lordosis for the study group with respect to intraoperative radiograph was 1.3 degrees at discharge and 4.3 degrees after 2 years. For the control group, these values were 0.9 degrees , 0.7 degrees . The difference at 2 years was significant (P = 0.003). Clinical postoperative outcome (VAS and ODI) was not different between the 2 groups through the postoperative follow-up (P > 0.05). CONCLUSION: Dynamic cervical plate designs provide less implant complications (no patient) compared with rigid plate designs (4 patients). Speed of fusion was faster in the presence of a dynamic plate. However, loss of segmental lordosis is significantly higher if dynamic plates are used, which did not result in differences regarding clinical outcome between dynamic and constrained plates after 2 years. Thus, dynamic plates should be considered to be the preferred treatment option because of the lower risk for implant failure-related revision surgery.

Fusion and failure following anterior cervical plating with dynamic or rigid plates: 6-months results of a multi-centric, prospective, randomized, controlled study.

Anterior cervical plate fixation is an approved surgical technique for cervical spine stabilization in the presence of anterior cervical instability. Rigid plate design with screws rigidly locked to the plate is widely used and is thought to provide a better fixation for the treated spinal segment than a dynamic design in which the screws may slide when the graft is settling. Recent biomechanical studies showed that dynamic anterior plates provide a better graft loading possibly leading to accelerated spinal fusion with a lower incidence of implant complications. This, however, was investigated in vitro and does not necessarily mean to be the case in vivo, as well. Thus, the two major aspects of this study were to compare the speed of bone fusion and the rate of implant complications using either rigid- or dynamic plates. The study design is prospective, randomized, controlled, and multi-centric, having been approved by respective ethic committees of all participating sites. One hundred and thirty-two patients were included in this study and randomly assigned to one of the two groups, both undergoing routine level-1- or level-2 anterior cervical discectomy with autograft fusion receiving either a dynamic plate with screws being locked in ap - position (ABC, Aesculap, Germany), or a rigid plate (CSLP, Synthes, Switzerland). Segmental mobility and implant complications were compared after 3- and 6 months, respectively. All measurements were performed by an independent radiologist. Mobility results after 6 months were available for 77 patients (43 ABC/34 CSLP). Mean segmental mobility for the ABC group was 1.7 mm at the time of discharge, 1.4 mm after 3 months, and 0.8 mm after 6 months. For the CSLP- group the measurements were 1.0, 1.8, and 1.7 mm, respectively. The differences of mean segmental mobility were statistically significant between both groups after 6 months (P = 0.02). Four patients of the CSLP-group demonstrated surgical hardware complications, whereas no implant complications were observed within the ABC-group (P = 0.0375). Dynamic plate designs provided a faster fusion of the cervical spine compared with rigid plate designs after prior spinal surgery. Moreover, the rate of implant complications was lower within the group of patients receiving a dynamic plate. These interim results refer to a follow-up period of 6 months after prior spinal surgery. Further investigations will be performed 2 years postoperatively.