Introduction

Surgery for the management of degenerative disorders of the spinal column continues to evolve. Although a majority of these procedures address simple decompression of the neural elements, the use of spinal fusion has been rapidly increasing. Fusion has long been accepted as a means for managing complex spinal deformities and instability. However, the primary reason for its increasing frequency has been its application to the management of degenerative disc disease and the treatment of chronic low back pain. Although this application remains controversial among spinal surgeons, several studies have shown that fusion for degenerative disc disease at one or two levels can improve outcomes compared with the natural history of low back pain.^1,2

Although many patients do well after lumbar fusion surgery, some patients can develop further degeneration at spinal levels adjacent to the fusion. Numerous biomechanical studies have demonstrated an increase in mechanical stresses within motion segments adjacent to fused segments.^3–5 As adjacent segment degeneration progresses, additional surgery to decompress and stabilize the involved segments may be necessary. This results in increased morbidity and expense of care and can propagate the cycle of additional adjacent segment degeneration and the subsequent need for even more surgery.

This long-standing problem with adjacent segment degeneration has led many to investigate alternatives to spinal fusion as a means of reducing the mechanical stresses placed on these segments. In particular, the development of a variety of motion-sparing technologies has been enthusiastically embraced as the ideal technology to manage degenerative disorders of the spine while limiting the potential for adjacent segment degeneration.

Motion-sparing technology encompasses a spectrum of devices. The most common of these devices are artificial discs for both the lumbar and cervical regions. Other motion-sparing technologies include nucleus replacement devices, interspinous devices, facet replacement devices, and posterior lumbar dynamic stabilization devices.

Each of these devices allows for some motion at the operated levels, subsequently decreasing the mechanical stresses felt at adjacent levels.⁶ In theory, this may reduce the incidence of degeneration at adjacent segments caused by fusion, resulting in improved long-term patient outcomes. This technology is attractive to both spinal surgeons as well as informed patients who both recognize the theoretical advantages to a spine fusion alternative. However, these devices are costly, and many lack the long-term follow-up needed to justify the added expense.

Although motion-sparing technologies have been developed to reduce the long-term complications associated with fusion procedures, they are not immune from their own set of postoperative problems. This chapter reviews the complications that can occur through the use of motion-sparing technology, specifically lumbar artificial disc replacement (arthroplasty) and lumbar nucleus replacement (nucleoplasty).

Lumbar Arthroplasty

The search for a surgical alternative to fusion and a means of treating painful lumbar discs dates back several decades. The initial efforts to design and develop an artificial lumbar disc began in the 1950s. Numerous designs were created and patented with few reaching the level of clinical study because of limitations with biomaterial design, lack of appropriate surgical approaches, and inconclusive patient selection strategies.

These early failures with artificial disc technology gradually improved aided by advancements in the design and application of artificial hip and knee joints. In the early 1980s Shellnack and Buttner-Janz⁷ introduced the SB Charité lumbar artificial disc. The device used a sliding, unconstrained polyethylene core placed between two metallic endplates. When inserted into the affected disc space through an anterior surgical approach, it permitted relatively normal motion of the intervertebral segment.

After two early design changes, the SB Charité disc (DePuy Spine, Raynham, MA) eventually underwent a rigorous multicenter, prospective, randomized study with encouraging early and midterm results. It became the first lumbar disc device to receive Food and Drug Administration (FDA) approval. Widespread use of the device began in 2004. The ProDisc device (Synthes Spine, Paoli, PA) also received early FDA approval and is currently in use (Fig. 9-1). Several other lumbar disc replacement devices are currently in varying stages of design, development, clinical analysis, and approval.

Fig. 9-1 Lateral plain radiograph demonstrating proper positioning of a ProDisc lumbar arthroplasty device within the L5–S1 disc space.