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Steven Casha, H. Andries Engelbrecht, Stephan J. DuPlessis and R. John Hurlbert

Object. Cervical laminoplasty is a recognized technique commonly used for multilevel posterior cervical decompression, and it is favored over laminectomy for maintaining spinal stability. Traditional hinge techniques, however, limit lateral exposure on one side and can limit dural exposure. The authors present their experience with a modified laminoplasty technique incorporating complete laminectomy and placement of titanium miniplate instrumentation. This method allows wide bilateral posterior decompression and unobscured dural access.

Methods. Twenty-eight patients (mean age 57 years) underwent cervical laminoplasty during a 4-year period. Twenty-seven patients presented with progressive cervical myelopathy. Seventeen patients (61%) had degenerative spondylotic stenosis; nine (32%) underwent resection of an intradural neoplasm. A mean of 3.5 levels were exposed and reconstructed. The follow-up period ranged from 4 months to 4 years (mean 15 months). The mean angular extension—flexion displacement measured between C-1 and C-7 was unchanged postoperatively, with preserved mobility across laminoplasty-treated segments in all patients. The anteroposterior diameter of the spinal canal increased 3.6 mm (27.2%) postoperatively (p = 0.004). In one patient an asymptomatic postoperative kyphosis developed. There were five cases of postoperative infection. One superficial infection resolved after intravenous antibiotic therapy alone, and four deep infections required surgical reexploration.

Conclusions. The advantages of this technique over other laminoplasty methods include wide lateral spinal canal and intradural access, as well as preserved motion with partial restoration of the posterior tension band.

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Heterotopic ossification and radiographic adjacent-segment disease after cervical disc arthroplasty

Presented at the 2019 AANS/CNS Joint Section on Disorders of the Spine and Peripheral Nerves

Michael M. H. Yang, Won Hyung A. Ryu, Steven Casha, Stephan DuPlessis, W. Bradley Jacobs and R. John Hurlbert

OBJECTIVE

Cervical disc arthroplasty (CDA) is an accepted motion-sparing technique associated with favorable patient outcomes. However, heterotopic ossification (HO) and adjacent-segment degeneration are poorly understood adverse events that can be observed after CDA. The purpose of this study was to retrospectively examine 1) the effect of the residual exposed endplate (REE) on HO, and 2) identify risk factors predicting radiographic adjacent-segment disease (rASD) in a consecutive cohort of CDA patients.

METHODS

A retrospective cohort study was performed on consecutive adult patients (≥ 18 years) who underwent 1- or 2-level CDA at the University of Calgary between 2002 and 2015 with > 1-year follow-up. REE was calculated by subtracting the anteroposterior (AP) diameter of the arthroplasty device from the native AP endplate diameter measured on lateral radiographs. HO was graded using the McAfee classification (low grade, 0–2; high grade, 3 and 4). Change in AP endplate diameter over time was measured at the index and adjacent levels to indicate progressive rASD.

RESULTS

Forty-five patients (58 levels) underwent CDA during the study period. The mean age was 46 years (SD 10 years). Twenty-six patients (58%) were male. The median follow-up was 29 months (IQR 42 months). Thirty-three patients (73%) underwent 1-level CDA. High-grade HO developed at 19 levels (33%). The mean REE was 2.4 mm in the high-grade HO group and 1.6 mm in the low-grade HO group (p = 0.02). On multivariable analysis, patients with REE > 2 mm had a 4.5-times-higher odds of developing high-grade HO (p = 0.02) than patients with REE ≤ 2 mm. No significant relationship was observed between the type of artificial disc and the development of high-grade HO (p = 0.1). RASD was more likely to develop in the lower cervical spine (p = 0.001) and increased with time (p < 0.001). The presence of an artificial disc was highly protective against degenerative changes at the index level of operation (p < 0.001) but did not influence degeneration in the adjacent segments.

CONCLUSIONS

In patients undergoing CDA, high-grade HO was predicted by REE. Therefore, maximizing the implant-endplate interface may help to reduce high-grade HO and preserve motion. RASD increases in an obligatory manner following CDA and is highly linked to specific levels (e.g., C6–7) rather than the presence or absence of an adjacent arthroplasty device. The presence of an artificial disc is, however, protective against further degenerative change at the index level of operation.