Effects of disc height and distractive forces on graft compression in an anterior cervical corpectomy model.

Study Design: An in vitro biomechanical study using a calibrated distractor and a subminiature load cell in a cadaveric cervical corpectomy construct.

Objective: To study the inter-relationships of defect height, graft height, and compressive and distractive forces in an anterior cervical corpectomy model.

Summary Of Background Data: The effects of graft size on compressive and distractive forces in cervical corpectomy remain unknown. Larger grafts afford neural decompression through anterior column distraction, but may subject the graft and vertebral bodies to excessive loads, increasing graft fracture, and subsidence risk.

Methods: The intended corpectomy defect was measured radiographically in 17 specimens. A C6 corpectomy was performed and the specimens embedded in polyester resin. A distractive force was applied through a strain gauge fitted distractor to allow introduction of allograft struts fixed to a subminiature load cell. After distraction was removed, immediate compressive force was measured. The specimen was then placed in a loading frame to simulate head weight.

Results: Distractive forces of 36.65, 70.90, and 118.10 N were required to insert 23, 25, and 27 mm grafts, respectively. On removal of this distraction, immediate compressive loads of 2.87, 4.74, and 8.95 N were noted. No statistically significant relationship between the intended corpectomy height and graft distraction forces was found. A statistically significant relationship was observed between distractive force required for graft insertion and immediate graft compressive force. Distractive force was also significantly related to the compressive force borne by the loaded strut graft.

Conclusion: Significantly higher distractive and compressive forces were recorded with larger grafts. Intended corpectomy height was not an accurate predictor of graft loads.