Preservation of Motion at the Surgical Level after Minimally Invasive Posterior Cervical Foraminotomy

Objective : Although minimally invasive posterior cervical foraminotomy (MI-PCF) is an established approach for motion preservation, the outcomes are variable among patients. The objective of this study was to identify significant factors that influence motion preservation after MI-PCF. Methods : Forty-eight patients who had undergone MI-PCF between 2004 and 2012 on a total of 70 levels were studied. Cervical parameters measured using plain radiography included C2-7 plumb line, C2-7 Cobb angle, T1 slope, thoracic outlet angle, neck tilt, and disc height before and 24 months after surgery. The ratios of the remaining facet joints after MI-PCF were calculated postoperatively using computed tomography. Chang-es in the distance between interspinous processes (DISP) and the segmental angle (SA) before and after surgery were also measured. We deter-mined successful motion preservation with changes in DISP of <= 3 mm and in SA of <= 2 degrees. Results : The differences in preoperative and postoperative DISP and SA after MI-PCF were 0.03 +/- 3.95 mm and 0.34 +/- 4.46 degrees, respectively, fulfilling the criteria for successful motion preservation. However, the appropriate level of motion preservation is achieved in cases in which changes in pre-operative and postoperative DISP and SA motions are 55.7 and 57.1%, respectively. Based on preoperative and postoperative DISP, patients were divided into three groups, and the characteristics of each group were compared. Among these, the only statistically significant factor in motion pres-ervation was preoperative disc height (Pearson's correlation coefficient=0.658, p<0.001). The optimal disc height for motion preservation in regard to DISP ranges from 4.18 to 7.08 mm. Conclusion : MI-PCF is a widely accepted approach for motion preservation, although desirable radiographic outcomes were only achieved in ap-proximately half of the patients who had undergone the procedure. Since disc height appears to be a significant factor in motion preservation, sur-geons should consider disc height before performing MI-PCF.