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out instability. Therefore, there is not a single surgical solution that may address the totality of the disease spectrum.

While many patients with lumbar stenosis will benefit from laminectomy alone, there are many who will still have mechanical back pain or develop recurrent disease [45–47]. In these patients, stabilization may offer additional bene­fits. In the case of Coflex, decompression may be performed. Clinical evidence supports significant advantages in clinical outcomes, maintenance of spinal motion, reduced back and leg pain, and preservation of foraminal height in the Coflex procedure over decompression alone and decom­pression with fusion [48–53]. In the case of Superion, the primary goal is to relieve symptom­atic lumbar stenosis in patients with moderate stenosis. By virtue of lack of surgical fixation, this device allows some degree of maintenance of motion but, unlike interlaminar stabilization, the maintenance of motion is not the intended mech­anism of action.

Grade II or greater spondylolisthesis

Isthmic spondylolisthesis or spondylolysis (pars fracture)

Degenerative lumbar scoliosis (Cobb angle of greater than 25°)

With ILS, the decompression will be accom­plished via direct laminectomy. Therefore, the preoperative considerations center around whether the patient would benefit from post­laminectomy stabilization to improve mechani­cal back pain and prevent recurrent stenosis and foraminal collapse. In the case of grossly unsta­ble patients or patients with moderate to severe spinal deformity, fusion remains the gold stan­dard for stabilization. Also, if the act of decom­pression will destabilize the spinal segment or if the degree of decompression requires exces­sive laminar removal, then ILS may not be feasible.

serving portions of the lamina for engagement with the U-shaped Coflex device. The ligamentum flavum is resected as part of the decompression and to ensure the device can seat properly in the interlaminar space. It is recommended that the decompression be performed with the patient in a prone neutral position to ensure that the decom­pression is adequate for symptomatic relief but not so extensive as to preclude placement of the device.

The Superion interspinous process spacer is the only interspinous motion-preserving device cur­rently available for use in the USA. The surgical technique relies upon an indirect decompression of the spinal canal via the introduction of seg­mental distraction by leveraging off the spinous processes. The patient is placed in a prone posi­tion and a midline skin incision is made over the segment of interest. An incision is made through the fascia and supraspinous ligament, and dila­tors are used to introduce a cannula into the mid­line interspinous space. An intraspinous gauge is then passed through the cannula and used to select the appropriate size for implantation. The titanium implant is then inserted through the can­nula and has two cam lobes which are deployed inferiorly and superiorly to encompass the corre­sponding spinous processes. Figure 25.5 pro­vides an illustration of the surgical technique.

The complications associated with this technique include wound related issues, inadequate lami­nectomy and decompression, and poor patient selection including those who ultimately require a fusion due to their instability. Less common adverse events include a 2.8% incidence of device-related failures requiring revision and a

Potential adverse events of this procedure pri­marily involve ineffective treatment and/or spi­nous process fracture. At 2-year follow-up, there was a 23.2% incidence of reoperations or revi­sions reported in the FDA trial data. Additionally, there was a 12.1% incidence of spinous process fracture and a 13.2% incidence of postoperative epidural steroid injection or nerve block at index level [54, 55]. Avoidance of therapeutic failure is most likely tied to proper patient selection and dependence on bone integrity to maintain spinal distraction.

5. Tencer AF, Self J, Allen BL, Drummond D. Design

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21. Boucher HH. A method of spinal fusion. J Bone Joint Surg Br. 1959;41-B(2):248–59.

22. Mitchell SM, Hsu WK. Lumbar pedicle cortical bone trajectory screw: indications and surgical technique. Contemporary Spine Surgery. 2016;17(1):1–5.

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with the lumbar plexus lying between them. The psoas muscle descends anterolaterally, deep to the inguinal ligament, where it is joined by the iliacus muscle and together they insert into the lesser trochanter of the femur. Together they are referred to as iliopsoas muscle. As it progresses inferiorly from approximately the L1 level, the diameter of the psoas muscle steadily increases as it is contributed to by insertions at each subse­quent level. The psoas major muscle receives innervations from the second to fourth lumbar spinal nerves as tiny intrinsic branches off the femoral nerve. The main action of the psoas mus­cle is hip flexion. In approximately 50% of the population, there is a smaller accompanying muscle lying on its ventromedial surface known as the psoas minor. It originates from the antero­lateral surface of the twelfth thoracic and first lumbar vertebrae and the intervertebral disc between them. The psoas minor muscle ends in a long flat tendon that inserts into the superior ramus of the pubis. A branch of the first or sec­ond lumbar spinal nerve innervates it, and its action is to assist in upward rotation of the hip.

The ilioinguinal nerve innervates the skin at the base of the penis and upper scrotum in males and the skin of the mons pubis and labia majora in females.

The furcal (meaning forked) nerve is an indepen­dent nerve with its own ventral and dorsal root­lets. It most commonly arises at the L4 level followed by L3 level as the second most common location, but it can be present at any lumbar level except for L1. It generally follows the L4 nerve in parallel through the neural foramina and is located superior and ventral to it extraforami­nally. It forks and gives off branches to the obtu­rator nerve, the femoral nerve, and the lumbosacral trunk serving as a link between lum­bar and sacral plexus (Fig. 26.1). Compression of this nerve is responsible for atypical presentation of sciatica/radicular symptoms or for double nerve root contribution in unilateral radiculopa­thy [13]. Clinical presentation may differ from radiographic imaging on the CT myelogram or MRI. Sensory distribution may not exactly fol­low dermatomal patterns corresponding to the appropriate level of disc herniation. Because of its location, it can be easily injured during lateral transpsoas approaches.