Implant/fusion mass load sharing following implantation of spinal fixation: An in vitro study

Spinal fusion following surgery due to trauma or tumors requires stabilization using instrumentation. Biomechanical fusion of the spine depends on many factors including initial and long-term implant stability, proper implant location, and a responsible post-operative rehabilitation protocol. Successful fusion (clinical fusion) is achieved when the spinal levels unite into a single bone mass. At the present, the time frame and application of rehabilitation for the biological healing of the spine post-operatively remains an intuitive process. Theory states that as spinal fusion progresses, the loads carried by the implant will decrease in magnitude. Analysis of the spinal loads over time post-operatively will enable the clinician to gain an understanding of the rate of spinal fusion as well as develop optimum rehabilitation therapy. The objective of this research was to develop an understanding of the implant/fusion mass load sharing following implantation of a novel intraosseous spinal nail.; To accomplish this goal, a new thoracolumbar spinal nail has been developed that enables real time spinal load telemetry. Additionally, an allograft model was developed that simulates the temporal structural properties of an anterior allograft strut graft. The implant/fusion load sharing curve was analyzed following implantation of these systems. All biomechanical testing was performed using seven L1–L5 porcine spine segments with a corpectomy model.; Following biomechanical testing, three distinct modes of load sharing occurred. The fusion mass always carried the greatest percentage of the total load for the axial compression and torsional load cases. However, the implant always carried the greatest percentage of the total lateral bending load. The implant/fusion mass loading results suggest that the use of a telemeterized implant of this type would give the clinician a useful tool to recognize successful spinal fusion. Application of this device in conjunction with the load sharing curves can be used to quantify the spinal healing time frame. Consequently, the ability to enhance current post-operative protocols with respect to rehabilitation methodology can be achieved.