Postoperative Spine

Introduction

Imaging plays an important role in the assessment of the postoperative spine. The main objectives of imaging are to evaluate the alignment of the spinal column, the position of implants and the status of fusion or fracture healing, and to demonstrate potential complications in case of persistent or new postoperative symptoms. Postsurgical appearances may be complex, and knowledge of indications for surgery, type of the procedure, hardware and biomaterials used and pertinent clinical information is essential to avoid misinterpretation. In this chapter we discuss principles of spinal surgery and briefly review its potential complications with emphasis on the ones most often encountered in radiological practice.

Principles of Spinal Surgery

The goals of spinal surgery can be broadly categorised into three main groups:

• 1.

  Decompression of neural structures: for example, by removal of herniated disc material, widening of a stenosed spinal canal or removal of a displaced fracture fragment.

• 2.

  Stabilisation of the spinal column in order to reduce pain caused by motion segments, to ensure stability after a fracture or resection of spinal elements, to prevent progression of deformity or to reduce its degree.

• 3.

  Excision of spinal tumours.

In order to achieve decompression, several surgical techniques are employed, usually in combination. Removal of intervertebral disc material is performed by discectomy or minimally invasive microdiscectomy; access to a herniated disc may require removal of the margins of the lamina (laminotomy), unilateral laminar resection (hemilaminectomy) and resection of the ligamentum flavum (flavectomy). Techniques used in spinal canal decompression include laminoplasty (osteotomy of one lamina with contralateral partial osteotomy to allow the formation of a unilateral gap), bilateral laminectomy with the removal of the posterior elements and deroofing of the spinal canal and/or facetectomy (excision of a part or entire facet joint). Neural foraminal decompression is achieved by foraminotomy. More extensive techniques used in the management of traumatic fractures and primary or metastatic spinal tumours include resection of one or both pedicles (pediculectomy), vertebral body (corpectomy) or entire vertebra (vertebrectomy).

Stabilisation can be the primary goal of surgery, or can be performed in combination with decompressive or excision procedures that impair spine stability. In the majority of cases, a stabilisation procedure consists of instrumentation and bone grafting. Types of fixation devices used include translaminar or facet screws, and transpedicular screws in conjunction with rods, plates, hooks, wires or clamps. It is important to realise that metalwork, although usually left in place indefinitely, is only relied upon for temporary support until uninterrupted osseous union is achieved. Bone fusion can be promoted by a variety of graft materials. Autologous bone grafts are most often harvested from the iliac crest, another part of the spine, or for purely cortical bone, from the tibia or fibula. Ground-up (morselised) cancellous bone chips are used to promote osteogenesis ( Fig. 51.1A ), while cortical bone is used for structural support (see Fig. 51.1B and C ). Allograft bone substitutes are obtained from the tissue bank and include femoral rings, fibular struts and bone chips that can be used on their own or to supplement autografts. Synthetic graft substitutes include recombinant bone morphogenetic protein (BMP), demineralised bone matrix (DBX) and ceramics (tricalcium phosphate, hydroxyapatite or calcium sulphate), available in a variety of forms and consistencies. Increasingly, synthetic cages manufactured from metal (titanium or tantalum) or non-metallic radiolucent material, such as carbon composite polymers, polyether ether ketone (PEEK) or bioabsorbable polylactic acid (PLA), are used instead of cortical bone for structural support in vertebral interbody fusion procedures (see Fig. 51.1D–F ). Such implants provide immediate load-bearing capacity while fusion occurs in their core packed with autologous cancellous bone, allograft or synthetic bone substitute.

Spinal surgery can be performed from anterior, posterior or combined approaches. An anterior approach is primarily used in the cervical spine for procedures such as anterior cervical discectomy and fusion (ACDF), and anterior instrumentation for corpectomy, peg fracture fixation with anterior screws, cervical foraminotomy and disc replacement. The traditional open anterior approach in the lumbar spine has been more difficult, but with increasing use of minimally invasive surgery (MIS) and endoscopic surgical techniques this route is now more frequently used: for example, for anterior lumbar interbody fusion (ALIF). A posterior approach is used in discectomy, foraminotomy, spinal canal decompression, various types of fixation using pedicle, translaminar or transfacet screws, and insertion of interspinous spacers, as well as posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF). Anterior and posterior approaches can be combined in ‘360° fusion’ procedures in which anterior interbody fusion is accompanied by posterior stabilisation with translaminar or pedicle screws, and facet joint or intertransversal fixation. Scoliosis correction surgery may require an anterior or posterior approach, depending on individual anatomical considerations and involved spinal segment.