Postoperative Spinal Deformities

Introduction

Spinal stability and maintenance of horizontal gaze are important to humans. Stability is defined as the spine’s ability to maintain its pattern of displacement such that no neurological deficit, major deformity, or incapacitating pain occurs under physiological loads. Spinal stability is necessary for the transfer of forces between the upper and lower limbs, to prevent the mechanical deterioration that occurs as a result of local compensatory mechanisms, and to protect neural structures. It is maintained through a complex multiarticular system comprised of vertebral bodies, intervertebral discs, posterior osseous elements, facet joints, interspinous ligaments, supraspinous ligaments, and paravertebral muscles. Gradual loss of stability, or in rare cases acute mechanical failure, results from disruption or degeneration of one or more of these structures. Loss of stability may occur because of several etiologies, including congenital anomalies, biological pathologies (i.e., tumor, infection, inflammation), degeneration, or for iatrogenic reasons. This chapter focuses primarily on spinal deformities that occur postoperatively. The etiologies of these deformities are diverse and include flatback syndrome, junctional kyphosis, postlaminectomy deformities, adjacent-level degeneration, postoperative instability, and pseudarthrosis. Additionally, other factors such as advancing age compromise bony structures and soft tissue, making these problems particularly challenging for the spine surgeon. Although postsurgical spinal deformities may be a consequence of the unavoidable natural history of spinal fusion or decompression, the majority of these deformities may be prevented by a fundamental understanding of sagittal balance parameters and surgical techniques to preserve spinal stability intraoperatively and to ensure proper alignment. Thus surgical strategies to avoid destabilizing the spine intraoperatively, as well as prevent intraoperative malalignment, are also addressed in detail in this chapter.

Loss of spinal stability manifests as an inability of the spine to maintain an adequate loadbearing capacity. Malalignment of the spine is a common manifestation of spinal instability and the hallmark of spinal deformity. Neglected spinal malalignment often progresses to marked functional limitation. Severe sagittal imbalance may render individuals socially and functionally debilitated, as it compromises maintenance of horizontal gaze. Thus, performing activities of daily living, including driving, swallowing, speaking, and upkeep of personal hygiene may become more difficult with worsening kyphosis. Glassman and colleagues demonstrated that quality of life is negatively affected by mild sagittal imbalance and is significantly compromised as sagittal imbalance increases. Progressive kyphosis is better tolerated in the thoracic spine and poorly tolerated in the cervical and lumbar spine. Although coronal imbalance is better tolerated than sagittal imbalance, coronal malalignment greater than 5 cm is associated with worsening pain, increased disability, and worse function. In addition to pain and poor general health, postoperative spinal deformity may result in acute or progressive neurological injury. ^, For example, Watanabe and colleagues reported that the neurological status of 20% of patients who sustained an acute proximal junctional fracture deteriorated from Frankel E to Frankel B. After proximal extension of the instrumentation and revision arthrodesis, these patients recovered to Frankel D. Thus all attempts should be made intraoperatively to both avoid destabilizing the spine and avoid instrumenting and fusing the spine in a misaligned position.

Decompression-Related Postoperative Spinal Deformities