Dynamic plates in anterior cervical fusion surgery: graft settling and cervical alignment.

STUDY
DESIGN: Retrospective cohort.
OBJECTIVE: To evaluate the effect of graft subsidence associated with the use of dynamic cervical plates on cervical alignment and clinical outcome of patients undergoing anterior cervical decompression and fusion. SUMMARY AND BACKGROUND DATA: Dynamic cervical plates allow graft loading which may enhance fusion. However, subsidence of the bone graft may result in changes in cervical alignment. The extent of settling of the graft and its impact on cervical alignment has not been determined. Also whether such change in alignment has an impact on clinical outcome is not known.
METHODS: Fifty-five patients with spondylitic myelopathy or radiculopathy underwent anterior cervical decompression and fusion using a dynamic plate for stabilization (ABC, Braun/Aesculap). The surgical indications included myelopathy (n = 21), radiculopathy (n = 30), or myeloradiculopathy (n = 4). Regional and local cervical angles, graft subsidence, and fusion rates were assessed before surgery, immediately after surgery and at 6 months after surgery. Visual analogue scores for neck and radicular pain, Neck Disability Indexes, and Nurick grades for myelopathy were recorded. Patients were observed up for at least 6 months with a median of 14 months (range: 6-48 months).
RESULTS: Radicular pain improved by a median of 5 points (P < 0.0001), whereas Neck pain improved by a median score of 3 (P < 0.0001). A median improvement in Neck Disability Index score of 18 (P < 0.0001) was observed. Nurick grades improved in 68% of patients with myelopathy. Fusion was achieved in 96% of cases. The mean graft subsidence at 6 months was 1.7 mm (range: 0-6 mm). A change of local cervical angle toward lordosis of 5.8 degrees (P < 0.0001) was obtained as a result of surgery. However, there was a loss of 2.7 degrees of lordosis in the first 6 months following surgery (P = 0.001). The extent of subsidence correlated with the local loss of lordosis (P = 0.0003). There was no change in the regional cervical angle in the 6 months following surgery. There was no significant association between clinical outcome and changes in cervical angles.
CONCLUSION: Dynamic anterior cervical plating after anterior decompression and grafting provides comparable fusion rates to that reported following the use of rigid cervical plating. Immediate changes in cervical alignment towards lordosis are partially lost on follow-up. The loss of lordosis is related to the amount of graft settling.