BACKGROUND
In this preliminary study we used a goat model to quantify pressure at an interbody bone graft interface. Although the study was designed to assess fusion status, the concept behind the technology could lead to early detection of implant failure and potential hazardous complications related to motion-preservation devices. The purpose of this study was to investigate the feasibility of in vivo pressure monitoring as a strategy to determine fusion status.

METHODS
Telemetric pressure transducers were implanted, and pressure at the bone graft interfaces of cervical interbody fusion autografts placed into living goats (Groups A and B) was evaluated. Group A constituted the 4-month survival group and Group B the 6-month survival group. One goat served as the study control (Group C) and was not implanted with a pressure transducer. An additional six cadaveric goat cervical spines (Group D) were obtained from a local slaughterhouse and implanted

with bone grafts and ventral plates and used for in vitro biomechanical comparison to the specimens from Groups A and B.

RESULTS
All goats demonstrated an increase in interface pressure within the first 10 days postoperatively, with the largest relative change in pressure occurring between the sixth and ninth days. The goats from Groups A and B had a 200% to 400% increase in relative pressure.

CONCLUSIONS
Although this was a pilot study to assess pressure as an indicator for a fusion or pseudarthrosis, the preliminary data suggest that early bone healing is detectable by an increase in pressure. Thus, pressure may serve as an indicator of fusion status by detecting altered biomechanical parameters.

Key Words Pseudarthrosis, biomechanics, pressure, vertebral endplate, cervical spine, goat, telemetric. SAS Journal. Winter 2008. 2:1–8. DOI: SASJ-2007-0102-RR

Lisa A. Ferrara, MS, Ilya Gordon, BS, Richard Schlenk, MD, Madeline Coquillette, Aaron J. Fleischman, PhD, Shuvo Roy, PhD, Daisuke Togawa, MD, PhD, Thomas W. Bauer, MD, PhD, and Edward C. Benzel, MD, FACS

From The Cleveland Clinic Foundation (Gordon, Schlenk, Coquillette, Fleischman, Roy, Togawa, Bauer, and Benzel) and OrthoKinetic Techologies, LLC (Ferrara).

The Cleveland Clinic Foundation (the "Clinic") holds a substantial equity ownership interest in OrthoMEMS, LLC ("OrthoMEMS") and is entitled to royalty payments from OrthoMEMS upon commercialization of OrthoMEMS's products. Authors Lisa Ferrara, Shuvo Roy, Aaron Fleischman, and Edward Benzel are entitled to a share of any such royalty payments and to a share of proceeds when the Clinic liquidates its equity ownership. Certain Clinic offi cials serve on the OrthoMEMS Board of Managers. Research related to OrthoMEMS's products, including early-stage research essential to the development of those products, has been conducted at the Clinic by individuals who hold a fi nancial stake in the successful outcome of that research.

Institutional and individual confl icts of interest in research are disclosed to, and reviewed and managed by, the Clinic's Confl icts of Interest Committee and are subject to approval by the Clinic's Institutional Review Board. The Clinic has retained independent monitors to review the protocols, subject enrollment and follow up, and data reporting and analysis of the research reported in this publication.

The treatment and euthanizing of animals in this study followed standardized protocol compliant with the Animal Review Committee for the Cleveland Clinic.

Address correspondence to Lisa A. Ferrara, MS, OrthoKinetic Technologies, LLC, 2790 Creekbridge Court, Southport, NC 28461,USA (email: lisa@orthokintech.com).

This paper was submitted on May 29, 2007, and accepted on October 27, 2007.