Review Question - QID 211938

Placement of an anterior cervical plate within 5 mm of the adjacent disc space had been reported to lead to accelerated adjacent segment disease.

Adjacent segment disease is the degeneration of the intact motion segment immediately above or below and fusion construct. Accelerated degeneration has been reported to occur in these regions due to altered spinal biomechanics with an annual risk of 3% per year or 30% at 10 years. The compensatory hypermobility of the adjacent segments is the theorized driving factor with other authors reporting a continuation of the originally present degenerative process. However, the placement of an anterior cervical plate within 5 mm of the adjacent disc space had been reported to cause accelerated adjacent segment disease.

Lawrence et al. performed a systematic review of factors associated with adjacent segment pathology following cervical spine arthrodesis. The authors deduced an annual incidence of clinically relevant adjacent segment disease (ASD) of 1.6% to 4.2% with reported risk factors for ASD being age <60 years at the time of surgery, fusion constructs that include 3-levels or less, and excluding C5-6 and C6-7 levels at the time of the index procedure. The authors concluded that ASD is a multifactorial process that spine surgeons must balance when considering treatment approaches for cervical degenerative disc disease.

Kim et al. performed a systematic review of adjacent segment ossification development following anterior cervical plating, total disc arthroplasty, and noninstrumented fusion. They reported an adjacent segment ossification rate of 41% - 64% following anterior plating with plate positioning <5 mm from the adjacent disc space being a risk factor during anterior plating. They concluded that there is insufficient evidence to make recommendations for the surgical treatment of adjacent segment ossification.

Alimi et al. performed a retrospective cohort study of 104 patients treated for cervical degenerative disc disease with either standard anterior cervical plating with fusion or interbody fusion with low-profile implants. They reported that patients receiving low-profile implants had a significant reduction in long-term postoperative dysphagia and significantly decreased prevertebral soft tissue swelling. They concluded that low-profile implants for anterior cervical discectomy and fusion result in similar functional outcomes with standard anterior plating with reduced risk of postoperative dysphagia.

Lee et al. performed a retrospective cohort study of cervical degenerative disc disease treated with either stand-alone cages, cage-and-plate constructs, or zero-profile anchored cages. They reported a significantly higher subsidence rate with the stand-alone cage constructs with the anchored cage and cage-and-plate constructs having greater preservation of cervical lordosis, segmental height, and fused segmental angle at 12-month follow-up. They concluded that anchored cages appear biomechanically superior to stand-alone cages for single-level anterior cervical discectomy and fusion, but consideration should be given to cage-and-plate constructs when increased postoperative motion stabilization is needed.

Duan et al. performed a meta-analysis comparing zero-profile cervical cages to anterior cervical plating for cervical degenerative disc disease. They reported that there was a significant decrease in postoperative dysphagia both at long-term and short-term follow-up, decreased intraoperative blood loss, increased improvement of Cobb angle in multi-level surgery, and higher subsidence rates compared to anterior cervical plating. They concluded that the use of zero-profile cages appears to be a safer and more effective construct than anterior cervical plating with decreased postoperative dysphagia and increased subsidence rate.

Figures A and B are the AP and lateral radiographs of the cervical spine with an anterior cervical plate and cage at the C4-5 level. Illustrations A and B are the radiographs of a zero-profile anchored cage at the C5-6 level.

Incorrect Answers:
Answer 1: The screw angle within the plate has not been associated with the development of adjacent segment disease.
Answer 3: The thickness of the anterior cervical plate has not been associated with the development of adjacent segment disease. Excessively thick plates can make the patient more prone to post-op dysphagia.
Answer 4: The length of the plate screws has not been associated with the development of adjacent segment disease. Rather, screw lengths >80% of the vertebral body AP diameter have been associated with lower pseudoarthrosis rates.
Answer 5: Interbody cage height has not been associated with the development of adjacent segment disease. However, excessively thick interbody cages have been associated with subsidence.