Advances in Spinal Stabilization (Progress in Neurological Surgery, Vol. 16)

Dramatic changes in spinal stabilization have taken place in the last years and the pace of change continues to accelerate. This volume is an excellent mirror of the evolution of spinal stabilization. It brings together the latest and most comprehensive reviews in minimally-invasive and novel surgical approaches and spinal stabilization techniques. Highlights in new biomaterials including radiolucent, bioresorbable, and standard titanium are discussed by experts. Biological advances including the use of bone morphogenetic protein in anterior lumbar interbody fusion as well as computer-assisted image-guided surgical techniques are demonstrated. The section on instrumentation and technique represents the most up-to-date advances in surgical technique and management of spinal disorders. Illustrations included in each chapter document these excellent papers. Because it is a must for all surgeons performing spinal surgery to keep up-to-date in this fast moving field this book is indispensable reading for them. Neurosurgeons and orthopedic surgeons will find a wealth of information in this volume on the developments in surgical approaches, biomaterials and implants, and biological innovations.

Haid RW Jr, Subach BR, Rodts GE Jr (eds): Advances in Spinal Stabilization. Prog Neurol Surg. Basel, Karger, 2003, vol 16, pp 165 175

Cervical Lateral Mass Advances (S. 174-175)

Praveen V. Mummanenia, Vincent C. Traynelisb, Rick C. Sassoc

a Department of Neurosurgery, Emory University, Atlanta, Ga.,
b Division of Neurosurgery, University of Iowa, Iowa City, Iowa, and
c Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis Neurosurgical Group, Indianapolis, Ind., USA

Posterior cervical fixation utilizing lateral mass plates has been shown to be a safe and efficacious method to achieve cervical fusion [1 3]. Lateral mass plating is biomechanically superior to laminar wiring or clamping in limiting cervical motion [4 7]. In addition, unlike posterior laminar wiring or clamping, lateral mass plating does not require the presence of the posterior elements.

However, lateral mass plates have numerous drawbacks. They are difficult to contour, and the screw positions are dictated by the fixed plate entry holes. In addition, the screw trajectories are divergent from the plate entry holes, and the connection of the screw to the plate is not rigid. There is no space to pack autograft bone under the screw-plate connection. Screws placed medially or laterally cannot be captured by the plate. Successive screws cannot be compressed or distracted because of the fixed plate hole distances. Moreover, if the plate needs to be revised, the screws must be removed. Finally, most of the systems currently available do not easily allow for extension of fusion up to the occiput or down to the thoracic spine [8]. The ideal posterior cervical instrumentation system will address these shortfalls from the lateral mass plate systems. Currently, there are three commercially available systems that address the problems of lateral mass plates. These systems do allow for initial screw placement with subsequent rod contouring. The three systems are Starlock/Cervifix (Synthes USA, Paoli, Pa., USA), SUMMIT (DePuy Acromed, Raynham, Mass., USA), and VERTEX (Medtronic Sofamor Danek, Memphis, Tenn., USA).

Instrumentation

The three systems that allow for initial screw placement with subsequent rod attachment differ from each other in several ways.

Starlock/Cervifix Systems (Synthes)

Unlike the VERTEX and SUMMIT systems, the Starlock/Cervifix systems do not have polyaxial screw heads. These systems require the use of an intervening closed-loop eyebolt to connect the screw to the rod and, as a result, the connection of the rod to the screw is not a locked, rigid attachment. Starlock and Cervifix are two instrumentation sets from Synthes that have interchangeable hardware. Cervifix is more restrictive than Starlock because it requires the surgeon to place the lateral mass screws through closed loop eyebolts, which are already mounted on a rod. The closed-loop eyebolts have the capability of sliding up and down the rod, thus enabling the screws to be placed variably in the sagittal plane [9]. Starlock is an improved version of this system that requires attaching closed-loop eye bolts to standard lateral mass screws and then subsequently threading the rod through the closed-loop eyebolts. However, the threading of a contoured rod through closed-loop eyebolts can be tedious and sometimes impossible [9].

Both the Starlock and Cervifix systems have features that distinguish them from standard lateral mass plate systems. They both have occipital plate extensions to accommodate occipitocervical fusions and laminar hooks for use when lateral mass screw attachment is not possible. It is possible to accommodate thoracic pedicle screws into the systems with appropriate rod contouring and attachment of the closed-loop eyebolts to upper t