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OBJECTIVELittle is known about the risk factors for postoperative subaxial cervical kyphosis following craniovertebral junction (CVJ) fixation. The object of this study was to evaluate postoperative changes in cervical alignment and to identify the risk factors for postoperative kyphotic change in the subaxial cervical spine after CVJ fixation.METHODSOne hundred fifteen patients were retrospectively analyzed for postoperative subaxial kyphosis after CVJ fixation. Relations between subaxial kyphosis and radiological risk factors, including segmental angles and ranges of motion (ROMs) at C0–1, C1–2, and C2–7, and clinical factors, such as age, sex, etiology, occipital fixation, extensor muscle resection at C2, additional C1–2 posterior wiring, and subaxial laminoplasty, were investigated. Univariate and multivariate logistic regression analyses were conducted to identify the risk factors for postoperative kyphotic changes in the subaxial cervical spine.RESULTSThe C2–7 angle change was more than −10° in 30 (26.1%) of the 115 patients. Risk factor analysis showed CVJ fixation combined with subaxial laminoplasty (OR 9.336, 95% CI 1.484–58.734, p = 0.017) and a small ROM at the C0–1 segment (OR 0.836, 95% CI 0.757–0.923, p < 0.01) were related to postoperative subaxial kyphotic change. On the other hand, age, sex, resection of the C2 extensor muscle, rheumatoid arthritis, additional C1–2 posterior wiring, and postoperative segmental angles were not risk factors for postoperative subaxial kyphosisCONCLUSIONSSubaxial alignment change is not uncommon after CVJ fixation. Muscle detachment at the C2 spinous process was not a risk factor of kyphotic change. The study findings suggest that a small ROM at the C0–1 segment with or without occipital fixation and combined subaxial laminoplasty are risk factors for subaxial kyphotic change.

BACKGROUND Cervical spine deformity negatively affects patients’ quality of life. Pedicle subtraction osteotomy (PSO) has reported to correct cervical deformity but it is challenging and carries a significant risk of morbidity. OBJECTIVE To report transdiscal C7 PSO with a strut graft for the correction of sagittal and coronal imbalance in patients with fixed cervical deformity. METHODS After standard exposure, the spine was instrumented from C2 to T3. T1 subtotal laminectomy, and C6 to C7 total laminectomies were necessary for C7 PSO. Osteotomy was initiated with removal of C6–7 and C7–T1 facet joints to isolate C7 pedicles and identify bilateral C7/C8 roots. Bilateral C7 pediculectomies and transdiscal PSO were performed. A rectangular strut allograft was then inserted into the PSO site. The location of the strut graft was used as a fulcrum of sagittal and coronal correction. The head fixator was released and the head was extended under intraoperative neuromonitoring, and then detailed sagittal and coronal balances were controlled by compressing or distracting between the pedicle screws above and below the osteotomy. RESULTS This technique was applied in 2 patients with fixed subaxial cervical deformities. Transdiscal PSO could add more amount of correction and provide the additional fusion surface. The strut graft prevented sagittal translation, foraminal narrowing, and excessive focal cord kinking during PSO. Both patients showed radiologic and clinical improvements after surgery, and no neurovascular complication occurred after the surgery. CONCLUSION Transdiscal C7 PSO with a strut graft placement provided a safe way of correcting sagittal and coronal imbalance simultaneously and reduced neurological complication by preventing sagittal translation, foraminal narrowing and spinal cord kinking.