Fig. 12.1
Sixty-five-year-old female presented with 3 months of low back pain and right L5 radicular symptoms who was treated conservatively and required surgery. (a, b) Anterior–posterior and lateral plain radiographs of a grade I L4–5 degenerative spondylolisthesis with 4 mm of anterolisthesis. (c–e) T2 sagittal and coronal MRI image showing spinal stenosis and right facet joint internal cyst and intra-operative picture showing the actual cyst removed with the lamina during decompression
Fig. 12.2
Drawing of L4–5 facet stenosis. Illustration of a grade 2 L4–5 degenerative spondylolisthesis. (a) Oblique view of a grade 2 L4–5 degenerative spondylolisthesis demonstrating facet spondylosis, capsular hypertrophy, and foraminal narrowing that can affect both the exiting nerve root (L4) and the transversing nerve root (L5) is severe enough and associated with concurrent central stenosis. (b) Lateral view of L4–5 foraminal stenosis affecting the L4 and L5 nerve roots. (c) Posterior view showing wide decompression addressing bilateral foraminal stenosis and any central stenosis of all four potential nerve root compressive pathology. The restoration of the central canal and foraminal size is assisted by reduction of the spondylolisthesis by a variety of methods
Fig. 12.3
Drawing of L5–S1 spondylolisthesis. Illustration of a grade 2 L5–S1 isthmic spondylolisthesis. (a) Oblique view of a grade 2 L5–S1 isthmic spondylolisthesis demonstrating acquired facet spondylosis, capsular hypertrophy, and foraminal narrowing that affects the exiting L5 nerve and is often associated with concurrent central stenosis. (b) Lateral view of L5–S1 foraminal stenosis affecting the L5 nerve root. (c) Posterior view showing a wide decompression addressing bilateral foraminal stenosis and any central stenosis causing potential nerve root compressive pathology. The decompression needs to be carried out laterally along the entire path of the L5 nerve root to decompress any extra-foraminal stenosis. The restoration of the central canal and foraminal size is also assisted by reduction of the spondylolisthesis by a variety of methods
Indications for Surgical Treatment
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.
Surgical Techniques
Decompression
Patients who have a degenerative spondylolisthesis with symptomatic spinal stenosis that have not improved with medical/interventional treatment are potential candidates for decompression surgery [19]. Although rarely employed as an isolated procedure, decompression alone is also a viable procedure in certain populations including a stable spondylolisthesis that exhibits ankylosis or in older individuals who have serious co-morbidities where a more extensive surgical fusion would potentially be contraindicated. However, there is always the risk in a younger patient that they may develop further slippage or have worse long-term outcomes if they are not fused [5, 14, 16] (Fig. 12.4: Post-decompression worsening of slippage).
Fig. 12.4
Fifty-two-year-old female presented with severe low back pain and bilateral L5 radicular symptoms following a “Minimally Invasive Decompression.” (a, b) Lateral plain radiograph taken prior to index surgery with a grade I L4–5 degenerative spondylolisthesis with 1–2 mm of anterolisthesis and a recumbent MRI that deceptively shows a degenerative disc at L4–5 and no spondylolisthesis due to postural reduction. (c, d) T2 axial MRI image showing inflammatory bilateral facet synovial fluid and joint widening following the MIS procedure and a lateral plain radiograph showing post-operative iatrogenic L4–5 instability with a marked increase in anterolisthesis to 14 mm
The standard surgical technique is an open posterior decompression that is performed with the patient lying in the prone position either on a Wilson frame or on a Jackson table with all bone prominences well padded. Ensure that the abdomen hangs freely to allow blood to pool in the abdominal cavity. The use of the Jackson table will frequently result in postural reduction of mobile spondylolisthesis and will help minimize the venous congestion and blood pooling into the surgical field. A standard posterior mid-line incision is made through the skin, sub-cutaneous fat, fascia and muscle is carried down to the lamina. Regardless of which procedure is performed, laminectomy, laminotomy, most stenotic patients will improve as long as they are adequately decompressed [8]. The supraspinous ligaments, inter-spinous, and facet capsules should be preserved to maintain stability following the decompression. Once the levels of the decompressive laminotomies are verified with plain radiographs or fluoroscopy the hypertrophied inter-spinous and ligamentum flavum can be resected along with part of the lamina and any overgrown portion of the facet into the foramen. The central canal and foramen should be palpated with an appropriate probe to ensure the decompression is adequate. When necessary the decompression can be expanded to a complete laminectomy from pedicle to pedicle to adequately restore the spinal canal dimensions. However, this will tend to destabilize the spinal segment [7].
Dural tears can be a frequent complication during decompression of a degenerative spondylolisthesis when trying to enter into the spinal canal. The increased risk of dural tears is due to the narrowed canal and frequent adhesions that form between the juxtafacet cysts to the dura, which is itself commonly thinned in degenerative spondylolisthesis patients. There are four anatomical zones of dissection where dural tears are likely to occur: the caudal margin of the cranial lamina, cranial margin of the caudal lamina, herniated disc level, and medial aspect of the facet joint adjacent to the insertion of the hypertrophic ligamentum flavum [20]. The authors’ preference is to repair all dural tears primarily and have fibrin glue applied while with extensive tearing a dural patch can be employed. Although rarely employed as an isolated procedure in a patient with a degenerative spondylolisthesis, decompression is effective in stable slips where a full decompression and fusion is contraindicated due to significant co-morbidities.
Decompression with Fusion Without Instrumentation
A decompression and fusion has been shown to offer better clinical outcomes compared with decompression alone in spondylolisthesis patients [19, 21]. However, the fusion technique employed has been shown to have no difference in outcome over the other after 4-year follow-up [22]. In addition to the exposure for decompression, the paraspinal muscles are reflected out to the transverse process tips and the facet capsules removed and then decorticated. It is necessary to ensure there is a clear, unencumbered path from one transverse process to the other along the inter-transverse ligament. The proper preparation of this area is critical to obtaining a solid intra-transverse process fusion. Take care not to penetrate anterior to the inter-transverse ligament, as this will bring you into the retroperitoneal space and create a hole that your bone graft may fall into. During the dissection the facet artery should be cauterized at the decorticated facet and care must be taken not to disrupt the cephalad facets and their corresponding neurovascular bundles since they innervate a portion of the paraspinal muscles that will atrophy if denervated. Once the soft tissues have been adequately stripped free from the fusion surfaces, decorticate the remaining exposed bony surfaces of the transverse processes, pars, and facets and to the lower level transverse process and lay the bone graft material of choice along these surfaces and packed into the facets. Primary grafting material includes local products of decompression, iliac crest bone graft (ICBG), allograft, demineralized bone matrix (DBM), and biologics such as BMP-2 or 7 [23, 24]. Each of these has its benefits and drawbacks as far as effectiveness, complications, fusion success and cost profile and are frequently used in various combinations.
Decompression with Fusion and Instrumentation
To achieve a higher rate of fusion, pedicle screws and rod instrumentation are often recommended [6, 19]. The use of an interbody device for fusion and sagittal alignment is presented later in the book.