This chapter will deal with postoperative imaging in patients with degenerative disc disease, the most frequent spine pathology requiring surgery.
There are several main categories of surgical procedures for treating degenerative lumbar spine conditions:
1. Disc excision
2. Laminectomy and partial facetectomy to relieve central, lateral, subarticular, or foraminal stenosis
3. Fusion procedures: posterolateral, posterior, or interbody (Figure 17-1)
4. Disc replacement surgery (Figure 17-2)
5. Fracture reduction and stabilization, including vertebro-plasty and kyphoplasty
6. Deformity correction
There are two types of interbody fusion procedures: posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF) (Figure 17-1). Fusion procedures are performed with autogenous bone graft or with allograft and are usually combined with spinal instrumentation (pedicle screws that are connected to rods or plates). Interbody cages are also used and may be implanted through a posterior or anterior approach.
The most frequent conditions that need to be evaluated in symptomatic patients after discectomy/laminectomy procedures are persistent or recurrent disc herniation, epidural hematoma, epidural fibrosis, spinal stenosis, instability, pars fracture, arachnoiditis, spinal infection, and dural tears. Plain X-rays and computerized tomography (CT) are the imaging procedures of choice for evaluating instability, pars fracture, and facet arthritis. The others are best evaluated nowadays by magnetic resonance imaging (MRI) with or without intravenous (IV) contrast medium.
The most frequent conditions that need to be evaluated in symptomatic patients after spinal instrumentation and fusion are residual stenosis at the operated level(s) or at an adjacent level, epidural hematoma, epidural scarring, infection, pseudoarthrosis, instability, misplaced instrumentation, failed instrumentation, and loosening of implants. Plain films and CT with or without myelography are applicable for most of these complications.
The modern most common surgical approach for cervical spondylosis is the anterior one. It allows a direct approach to the cervical spine and allows complete disc and osteophyte excision with decompression of the spinal cord. The procedure is usually completed with fusion of the operated segment, which is known as anterior cervical discectomy with fusion (ACDF) (Figure 17-3A), or with disc replacement (Figure 17-3B). An anterior cervical corpectomy may be considered if the site of epidural compression extends beyond the disc space. This approach has the advantage of allowing a thorough decompression, including the resection of osteophytes, and also improves fusion rates in cases where multilevel decompression is needed, such as in patients with multilevel spondylosis or ossification of the posterior longitudinal ligament (OPLL). Reconstruction of the spine is traditionally performed with a strut bone graft. A variety of strut-grafting techniques have been described, including a tricortical autogenous iliac crest bone graft or a fibular strut (autologous or allograft). The tricortical autogenous iliac crest bone graft is most often utilized for corpectomy of one or two levels, whereas autogenous fibular grafts may be required to reconstruct corpectomies of more than two levels. The structural stability of the cervical spine may be then supplemented with various anterior plates or external immobilization. Vertical titanium-mesh fusion (Harms) cages have been used to replace the resected vertebral body to avoid low fusion rates with allograft use and donor site morbidity with autograft harvesting (Figure 17-4). A "hybrid decompression fixation"
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