318

320

6–9]. Despite these drawbacks, PSF techniques

322

that may be more painful, leading to a longer recovery and protracted use of pain medications

30, 31]. Rigid interspinous fixation devices may

29]. In addi-

Spinous process fixation devices are versatile and can be utilized to provide stabilization to promote fusion in a number of clinical scenarios. These

The technique for SPF is relatively straightfor­ward as the anatomy is familiar and the applica­tion of the device is not typically challenging. However, there are some important consider­ations in planning, technical nuances, and some minor variations depending on the particular device. Contraindications include pars defects and osteoporosis. However, in the aging spine, there may be a significant differential between the density of the posterior elements and the vertebral bodies, favoring posterior fixation (Table 25.2).

A midline incision 4–5 cm in length is planned over the rostral and caudal spinous processes to be fixated. It is important to remember that the rostral spinous process will be in the axial plane

The supraspinous ligament may be removed or left intact based on the surgeon’s preference. Preservation of this structure is important for the application of some motion-sparing devices like X-Stop that require it to remain contained within the interspinous space. However, for SPF devices that provide rigid stabilization by attaching to the spinous processes themselves, it may be resected. Further, for translating SPF devices that provide distraction and compression, it is removed with a Leksell rongeur. Next, the interspinous space is measured with calipers or trials in order to select the appropriately sized device that will maxi­mally fill the space. For the translating SPF devices, this is not necessary, since the device may be expanded to fit this space prior to engag­ing the spinous processes (Fig. 25.3a). In either case, the instruments used to prepare the interspi­nous space or the translating SPF devices can be used to apply distractive forces. Careful visual inspection, tactile feedback, and the surgeon’s judgment are all critical in preventing fracture or weakening of the spinous processes through these maneuvers. The plates on either side of the midline are then compressed so that the spikes integral to the medial aspect of the plates engage the cortical bone of the spinous processes (Fig. 25.3b). Care must be taken to avoid over­compression, as this may fracture or weaken these structures as well. At this point, some devices are self-locking and others require subse­quent steps to lock the device to the spinous processes.

• For the devices that allow for distraction and compression across the interspace, forces should be applied with caution to avoid frac­ture or weakening of the spinous processes.

symptoms of degenerative spinal disease with MIS and without fusion. While multiple devices have been introduced, only a limited number are available in the US market. The two most influ­ential dynamic MSTs, the Wallis Interspinous Device (Abbott Spine, Abbott Park, IL) intro­duced for treatment of patients with recurrent disc herniations and the X-stop Interspinous Spacer (Medtronic, Memphis, TN) for mild to moderate stenosis, are no longer available for clinical use. Another device, Diam (Medtronic, Memphis, TN), intended for use as an indirect decompression device for spinal stenosis, failed to receive FDA clearance for use in the USA. Despite these early failures, there are sig­nificant benefits to be gained by exploiting the posterior midline for motion preserving stabiliza­tion devices.

Interlaminar and interspinous motion-

preserving devices represent an evolution of