Pressure Dynamics on Intervertebral Disc Cages in TLIF: A Cadaver Study

Objective This study aimed to quantify the change in pressure on the cage during compression manipulation in lumbar interbody fusion. While the procedure involves applying compression between pedicle screws to press the cage against the endplate, the exact compression force remains elusive. We hypothesize that an intact facet joint might serve as a fulcrum, potentially reducing cage pressure. Methods Pressure on the intervertebral disc cage was measured during compression manipulation in four donor cadavers undergoing lumbar interbody fusion. Unilateral facetectomy models with both normal and parallel compression and bilateral facetectomy models were included. A transforaminal lumbar interbody fusion (TLIF) cage with a built-in load cell measured the compression force. Results Pressure data from 14 discs indicated a consistent pre-compression pressure average of 68.16N. Following compression, pressures increased to 125.99N and 140.84N for normal and parallel compression post-unilateral facetectomy, respectively, and to 154.58N and 150.46N for bilateral models. A strong linear correlation (correlation coefficient: 0.967, P < 0.0001) between pre- and post-compression pressures emphasized the necessity of sufficient pre-compression pressure for achieving desired post-compression outcomes. None of the data showed a decrease in compression force to the cage with the compression maneuver. Conclusion Both normal and parallel compression maneuvers effectively increased the pressure on the cage, irrespective of the facet joint resection status. Compression manipulation consistently enhanced compressive force on the cage. However, when baseline pressure is low, the manipulation might not yield significant increases in compression force. This underlines the essential role of meticulous pre-compression preparation in enhancing surgical outcomes.