Correlation Between Quantitative Cage Pressure Measurements and Surgeons' Qualitative Tactile Assessments During...

A cadaveric study.

Measuring the pressure exerted on lumbar lateral interbody fusion (LLIF) cages and examining its correlation with a qualitative assessment of tactile feedback related to pullout strength during cage extraction to determine the optimal cage height.

No data exists on the relationship between the surgeon's tactile feedback related to pullout strength during the LLIF cage extraction and the cage pressures measured during surgery.

We used four cadavers to insert the original stress-measuring cages at the L2/3 to L4/5 levels (12 intervertebral spaces) using the oblique lumbar lateral approach. The intervertebral disk height (IDH) was measured before cage insertion. These stainless-steel stress-measuring cages were designed with the same shape as standard cages and included a built-in load cell to measure the stress applied. The cage heights were set at 8, 10, and 12 mm, and they were inserted sequentially from 8 mm, with stress measurements taken at each step. Four spine surgeons qualitatively evaluated the extraction strength using three rating categories ("loose," "appropriate," and "hard to extract"). After cage removal, endplate damage (ED) and anterior longitudinal ligament injury (ALLI) were checked. The anterior part of the vertebral body was dissected to expose the ALL, and it was checked for obvious injuries. In addition, a surgical probe is used to check for ED and ALLI.

The measured cage pressures were 45, 120, and 191 N for the "loose," "appropriate," and "hard to extract" ratings, respectively ( P < 0.001). ED was observed in five intervertebral spaces, whereas no ALLI was noted. The average maximum pressure when ED occurred was 127 N. The primary risk factor for ED was identified as the difference between the height of the inserted cage and IDH, with a cutoff value of 4.5 mm.

The appropriate extraction strength corresponded to a cage pressure of 120 N. A cage pressure ≥127 N posed a risk for ED. ED incidence was high when the difference between the IDH and the height of the inserted cage exceeded 4.5 mm.

Level 3.