Ventral Cervical Plating: Dynamic versus Static Debate

Raqeeb Haque

Maxwell Boakye

Michael G. Kaiser

Brian Y. Hwang

Regis W. Haid Jr.

Ventral cervical fusion was developed in the 1950s and early 1960s and involved stand-alone structural grafts with no instrumentation (1, 2 and 3). The fusion rates for uninstrumented ventral cervical surgery generally averaged above 80% with satisfactory results (4,5). However, these surgical techniques were associated with significant graft-related complications such as graft dislocation and subsidence, as well as unacceptable rates of kyphotic deformity and pseudoarthrosis (6, 7, 8, 9, 10 and 11). To reduce the incidence of these complications, internal cervical fixation is an option in order to provide initial stability and reduce graft-related complications (7,12).

In 1964, Bohler (13) first reported the use of ventral cervical plating and screw fixation in a cervical spinal trauma case. Since then, ventral cervical plating has gained widespread acceptance for the treatment of various cervical spine pathologies (14), leading to a threefold increase in the number of surgical cases performed in the United States with ventral cervical fusion and plating between 1985 and 1996 (15). The regularity with which ventral cervical fixation is performed with interbody fusion has made the indications for both synonymous: (a) to restore clinical and radiographic spinal stability, (b) to maintain cervical alignment, (c) to prevent deformity, and (d) to alleviate pain (14). Ventral cervical instrumentation is used to treat degenerative disk disease, cervical stenosis, traumatic or acquired cervical instability, fractures, and infectious neoplastic lesions of the spine (14,16, 17, 18, 19, 20 and 21). Relative contraindications include anomalies of the vertebral body, severe osteoporosis, and infection. A stand-alone ventral construct is also contraindicated in the presence of significant dorsal element destruction (22,23).

Well-designed randomized control trials establishing the benefits of ventral cervical plating are lacking; nevertheless, ventral plate fixation has been reported to increase fusion rates following single and multilevel discectomies (24, 25, 26, 27, 28, 29, 30 and 31) (Table 128.1) and corpectomies (20,32,37) (Table 128.2). Kaiser et al. (30) reviewed 251 cases and reported that the fusion rates for one- and two-level anterior cervical discectomy and fusion (ACDF) with a static plate were 96% and 91%, respectively, compared with 90% and 72% for one- and two-level ACDFs without fixation. Figure 128.1 demonstrates anterior cervical plate placement with interbody fusion. Ventral cervical instrumentation is also thought to decrease requirement for external immobilization and expedite return to work with reduced indirect costs to the patient and society (29,31,38, 39, 40, 41 and 42). Retrospective reviews and case series have demonstrated a decrease in graft-related surgical complications, rate of spinal deformities, and incidence of pseudoarthrosis (7,10,14,30,43,44) (Fig. 128.2). Although the link between radiographic fusion and clinical outcome remains controversial, anterior cervical plates appear to favorably affect outcome following ventral cervical surgery (29,31,43, 44 and 45).

EVOLUTION/CLASSIFICATION OF VENTRAL CERVICAL PLATING

A wide variety of anterior cervical plating systems have been developed since Bohler introduced his device in 1964. Unprecedented expansion of available devices, particularly in the past decade, has provided the surgeon with a wide variety of implants for the diverse surgical indications (45). The Cervical Spine Study Group proposed a classification system for ventral cervical plating devices based on the interaction between the plate and vertebral body screw (45) (Fig. 128.3). Although it was not based on biomechanical testing, the classification scheme proved to be useful in categorizing the modern array of cervical plating options and outlining the evolution of ventral cervical plate development. Current generation plates have been divided into two broad categories. Plates that allow intended motion between the screw and plate and allow variability in the direction of screw placement are known as “dynamic” plates. Plates that require a predetermined, fixed trajectory during screw insertion and eliminate any motion at this interface are known as “constrained” or “static” plates (45).

Early generation cervical plating systems developed in the 1980s featured unrestricted screw backout design that allowed motion at the screw-plate interface (7,45). The
plating devices markedly reduced graft-associated complications following anterior cervical discectomies (8,10). The design of the unrestricted screw was also thought to increase the chance of fusion by exposing the graft to greater compressive forces (46,47). However, the design also led to high rates of implant-related complications such as screw back out and breakage (40,48). The requirement of bicortical purchase of the screws, through the dorsal cortical wall, to reduce the risk of instrumentation failure, made the technique technically more challenging and introduced the potential for dural penetration and subsequent neurologic complications (14).

TABLE 128.1 Outcomes of Anterior Cervical Diskectomies with or without Anterior Cervical Plate Fixation

		Single-level Fusion Rate		Two-level Fusion Rate			Graft-related Complication
Authors	Number of Patients	No Plate (%)	Plate (%)	No Plate (%)	Plate (%)	Plate-related Complication (%)	No Plate (%)	Plate (%)
Kostuik et al. (1993) (24)	42	—	—	—	100	17	—	2.3
Connolly et al. (1996) (29)	43	100	100	70	100	24	5.5	0
Shapiro (1996) (25)	188	—	100	—	100	2.2	8	0
Schneeberger et al. (1999) (26) 35	—	100	—	87	0	—	0
Wang et al. (1999) (31)	80	92	95	—	—	0	—	—
Wang et al. (2000) (43)	60	—	—	75	100	0	25	0
Bose (2001) (27)	37	—	—	—	100	0	—	0
Kaiser et al. (2002) (30)	540	90	96	72	91	1.3	6	0
Boakye et al. (2005) (28)	24	—	100	—	100	0	—	0