3 Posterior Retractor Systems

Mohammed Abbas, Benjamin Khechen, Brittany E. Haws, Ankur S. Narain, Fady Hijji, Kaitlyn L. Cardinal, Jordan A. Guntin, and Kern Singh

3 Posterior Retractor Systems

3.1 Introduction

3.1.1 Retractor Components

Retraction systems are composed of various components, including tubular dilators, frames, retractors, illumination devices, and camera sources. Tubular dilators are thin-walled tubular structures that are used to obtain spinal access via splitting of the muscle fascicles. In order to split the necessary muscles during surgical exposure, a series of concentric dilators are sequentially introduced. ¹ Frames are metal or plastic constructs that allow for the connection and anchoring of retractor components to the surgical bed. In expandable systems, frames often contain the necessary inputs for adjustment of retractor size. The retractor apparatus can be composed of a tubular structure or bladed system. Tubular retractors, like tubular dilators, are thin walled to provide even pressure distribution on nearby musculature. ¹ Due to their shape, they also provide a defined surgical corridor. Bladed retractors, unlike tubular retractors, require muscle tension to remain in position. ¹ Additionally, these retractors allow for retraction in the cranial-caudal and medial-lateral planes. Various blade lengths and shapes are available to provide adequate retraction depth and orientation based on the surgical anatomy. Finally, illumination and camera systems can be fixed to the retraction frame or retractor apparatus to improve visualization in the appropriate surgical scenarios.

3.1.2 Types of Retraction Systems

Fixed versus Expandable Systems

Fixed retraction systems are those that are not adjustable in the cranial-caudal or medial-lateral planes after insertion into the target tissue. These retractors are typically composed of anodized metal and are available as tubular or bladed systems. These systems are partially or completely radiolucent, allowing for acquisition of fluoroscopic images without interference of retractor components. The benefits of a fixed tubular system include minimal muscle creep and limitation of the pressure placed on the surrounding paraspinal musculature due to consistent tube size. While fixed systems have retractors of varying lengths, complete replacement of the retractor apparatus is necessary if adjustment to sizing is required. Expandable systems, on the other hand, contain mechanisms that allow for adjustment of retractor orientation in the cranial-caudal and medial-lateral planes. As such, any repositioning required to adjust the degree of surgical exposure does not require removal of the retractor apparatus. However, muscle creep can occur and a larger retraction field is necessary, increasing the surgical dissection.

Pedicle-Screw–Based Systems

Pedicle-screw–based retraction systems are used in cases of degenerative disease or trauma requiring pedicle screw and rod constructs for fixation or reduction. These systems are composed of percutaneous retractor towers attached to pedicle screws at a fixation point. While a variety of retraction towers are currently available (▶ Fig. 3.1), the standard setup involves a simple tower that connects to the pedicle screw tulip. ² Floppy towers utilize a soft, malleable sleeve that provides an enhanced view of the surgical field. ² Reduction towers, currently the most utilized type, are associated with screws containing an extended internal thread which allows for greater ability to reduce deformities. ² Overall, advantages of pedicle-screw–based systems include decreased retractor migration due to fixation of the construct to the screw, and improved visualization of anatomic landmarks. However, pedicle fracture and screw subsidence are possibilities, as distraction across the screws is often used to facilitate visualization and interbody placement.

**Fig. 3.1 (a)** Standard retraction tower. **(b)** Floppy retraction tower.

3.1.3 Complications

While minimally invasive surgery decreases iatrogenic tissue trauma due to smaller exposures, utilization of tubular dilators and retractions systems is associated with a unique set of complications. Misplacement of retraction systems, regardless of the specific minimally invasive spine (MIS) procedure performed, is associated with transient neurologic deficits including numbness, paraesthesia, and pain. ³ ^, ⁴ The use of tubular retractors also reduces tactile feedback and the overall surgical exposure, consequently increasing the risk of iatrogenic injuries and difficulty with resolving intraoperative issues. ¹

3.2 Static Retractor Systems

**Table 3.1** DePuy Synthes SPOTLIGHT^® Access System
Design
Retractor system Fixed	Retractor apparatus Radiolucent tube	Design feature 360° light access

Modular aspects and variations
Port diameters 12, 15, 18, 21, 24 mm	Port lengths 30–140 mm (10-mm increments)

Procedures
MIS TLIF, MIS posterior decompression
Radiographs unavailable
Compatible devices
DePuy Synthes T-PAL™ Interbody Spacer System, VIPER^® 2 MIS Spine System

**Table 3.2** Medtronic METRx® II System
Design
Retractor system Fixed	Retractor apparatus Radiolucent tube		Design feature Retractor available with 20° beveled tip permits docking onto the lamina

Modular aspects and variations
Retractor dimensions and composition					Dilator diameter
Composition	Beveled stainless	Straight stainless	Beveled disposable	Straight disposable	5.3, 9.4, 12.8, 14.6 mm, 16.8–24.8 mm (2-mm increments)
Widths	14, 16, 18, 20 mm	22, 26 mm	18 mm	22, 26 mm
Lengths	30–90 mm (10-mm increments)

Procedures
MIS TLIF, MIS posterior decompression
Radiographs unavailable
Compatible devices
Medtronic CD Horizon® Posterior Stabilization System

**Table 3.3** RTI Surgical Clarity® MIS Port System
Design
Retractor system Fixed	Retractor apparatus Radiolucent tube	Design feature Aluminum ports with dual-light access

Modular aspects and variations
Retractor tube diameters: 18, 22, and 26 mm	Retractor tube lengths: 50–120 mm (10-mm increments)

Procedures
MIS TLIF, MIS posterior decompression

Compatible devices
RTI Surgical Streamline® MIS Spinal Fixation System, Bullet-tip, and T-Plus™ Interbody Cages

**Table 3.4** Zimmer Biomet Viewline™ Tube Retraction System
Design
Retractor system Fixed	Retractor apparatus Radiolucent tube	Design feature Rotating accessory arm with dual-light ports

Modular aspects and variations
Retractor tube diameter 18, 22, and 26 mm	Retractor tube length 40–120 mm (10-mm increments)

Procedures
MIS TLIF, MIS posterior decompression
Radiographs unavailable
Compatible devices
Zimmer Biomet PathFinder NXT®, minimally invasive pedicle screw system, and TM Ardis® Interbody System