The high incidence of radiculopathy demonstrates the importance of the need for thorough decompression. The strong indications for surgery include: progressive neurological deficits such as severe radiculopathy, weakness, intractable pain, the loss of bowel/bladder control, or rarely acute cauda equina syndrome. The relative indications include intractable back pain, sagittal imbalance, failure of 3–6 months of conservative care, intolerable radiculopathy, or severe interference with the activities of daily living that affect the patient’s quality of life. If surgery is decided upon there are a variety of procedures available including decompression, decompression with/without dynamic stabilization, or decompression with fusion. There is evidence to support that the addition of a fusion to the decompression improves outcomes when surgically treating a spondylolisthesis. There are a wide variety of options available to fuse a spondylolisthesis following decompression including posterolateral, TLIF, anterior, and direct lateral, and all can be combined with various forms of cages and pedicular instrumentation to improve the fusion rates and the durability of the outcomes of the procedures. There also are various inter-spinous process devices available to distract the lamina and concurrently the foramen thus improving radicular symptoms [4–13]. Finally, there are a wide variety of currently available materials available to facilitate the fusions including autograft, allograft, ceramics, and the bone morphogenetic proteins since a successful fusion remains critical to the success of the surgery. This chapter focuses on decompression and fusion without and with instrumentation.

In 1991, Herkowitz led the way with the first prospective, randomized study comparing an L3–4 or L4–5 degenerative spondylolisthesis with stenosis undergoing a decompressive laminectomy compared to a laminectomy with arthrodesis in 50 patients. The study showed that the patients whom demonstrated inter-transverse process fusion had superior outcomes when back and leg pain was evaluated [5]. A follow-up study by Fischgrund comparing fusion success in degenerative spondylolisthesis with and without instrumentation found that of the 67/76 patients available at 2-year follow-up fusion occurred in 82 % of instrumented cases as compared to only 45 % of non-instrumented cases (P = 0.0015). However, clinical outcome was excellent or good in 76 % of patients with instrumentation and 85 % without instrumentation (P = 0.45). The authors concluded that instrumentation significantly improves fusions but not necessarily patient outcomes [6]. One shortcoming of the study is that the 2-year follow-up period in this study may not be significantly long enough to delineate long-term clinical outcomes benefit of using instrumentation to improve the fusion rate. However, a review of Fischgrund’s original series with an average of a 7.8-year follow-up by Kornblum et al. [14] showed those with single-level spondylolisthesis and spinal stenosis treated with posterior decompression and fusion using autograft showed a solid fusion in only 46 % of the patients (22/47). In contrast, the clinical outcome data of the 86 % of the patients who had a solid fusion were good or excellent while those with a pseudarthrosis had only 56 % reporting good or excellent result. This study showed that a solid fusion provides improved outcomes and longer lasting results. Since instrumentation increases a fusion success most surgeons recommended using instrumentation concurrently with a posterolateral fusion to improve the long-term results. Although instrumentation raises the success of a lumbar spinal fusion certain factors have been identified that decrease the fusion rate even with instrumentation including high disc spaces and segmental kyphosis [15].

The question of whether or not to reduce a degenerative spondylolisthesis by indirect or direct means was evaluated in a study by Montgomery where the pre- and post-operative standing lateral lumbosacral radiographs were compared following the indirect, passive correction of 25 patients with single-level spondylolisthesis following positioning on the operating table. The percentage slip decreased from 24 to 15 to 6 % on standing flexion, extension, and intra-operative lateral radiographs, respectively (P < 0.001). In both instances, standing and operative positioning, the reduction was not dependent on grade of slip, slip angle, or degenerative disc disease (DDD) [4].

Spine Patient Outcomes Research Trial (SPORT) was a prospective evaluation of patients with degenerative spondylolisthesis that has reported 2-year [16] and 4-year outcomes [17]. The study was critiqued for allowing severely symptomatic patients in the conservative treatment group to cross over to the surgical treatment group, producing both an intent-to-treat and as-treated analysis of the data. In the as-treated analysis, SPORT demonstrated that patients who underwent decompression and concurrent fusion achieved substantially greater improvement in pain and function compared to those treated nonoperatively at 2- and 4-year follow-up periods. The study has shown durability of improvements with surgical treatment in patients with lumbar disc herniations at 8-year follow-up [18], and analysis of patients with degenerative spondylolisthesis with 8-year follow-up is pending.