Minimally invasive transforaminal lumbar interbody fusion: one surgeon's learning curve.

BACKGROUND CONTEXT: The published literature has not characterized the surgeon's learning curve with the technically demanding technique of a minimally invasive transforaminal lumbar interbody fusion (MIS TLIF).
PURPOSE: To characterize based on intra- and perioperative parameters, the learning curve for one spine surgeon during his initial phases of performing an MIS TLIF. STUDY DESIGN/
SETTING: Retrospective analysis of a single institution and single surgeon experience with the unilateral MIS TLIF technique between July 2008 and April 2011. PATIENT SAMPLE: Sixty-five consecutive patients, with at least 1 year of follow-up, who underwent a unilateral, single-level, index MIS TLIF for the diagnosis of degenerative disk disease or lumbar spinal stenosis with grade I or II spondylolisthesis were analyzed based on data obtained from the medical records and postoperative imaging (computed tomography). OUTCOME MEASURES: Postoperative radiographic assessment of fusion at 1 year via computed tomography. Surgical parameters of surgical time (skin-skin, minutes), anesthesia time (induction-extubation, minutes), estimated blood loss (mL), intravenous fluids during surgery (mL), intraoperative complications (durotomy), and postoperative complications (pseudarthrosis, implant failure, malpositioned implants, graft-related complications) were also assessed.
METHODS: The senior author's first 100 consecutive MIS TLIFs were evaluated initially. Patients undergoing revision or multilevel surgery were excluded leaving a total of 65 consecutive primary MIS TLIFs. The first 33 patients were compared with the second 32 patients in terms of radiographic arthrodesis rates, surgical parameters, and intra-/postoperative complications. A two-tailed Student t test was used to assess for differences between the two cohorts where a p value of less than or equal to .05 denoting statistical significance. Pearson's correlation coefficient was used to determine any association between the date of surgery and surgical time.
RESULTS: Average surgical time, estimated blood loss, intraoperative fluids, and duration of anesthesia was significantly longer in the first cohort (p<.05). There were no significant differences in intraoperative complications (two durotomies in both groups) or length of stay. There was no significant difference in postoperative complications at final follow-up based on computed tomography analysis (11 vs. 9, p=.649). In the first cohort, these complications included two cases of radiographic pseudarthrosis: one case of graft migration and one case of medial pedicle wall violation necessitating two revision surgeries. There were two cases of pseudarthrosis and one case of an early surgical site infection identified in the second group requiring three revision surgeries. Last, four cases of neuroforaminal bone growth were demonstrated, two in each cohort. Pearson's correlation coefficient demonstrated a negative correlation between the date of surgery and surgical time (r=-0.44; p<.001) estimated blood loss (r=-0.49; p<.001), duration of anesthesia (r=-0.41; p=.001), and intravenous fluids (r=-0.42; p=.001).
CONCLUSIONS: The MIS TLIF is a technically difficult procedure to the practicing spine surgeon with regard to intra- and perioperative parameters of surgical time, estimated blood loss, intravenous fluid, and duration of anesthesia. Operative time and proficiency improved with understanding the minimally invasive technique. Further studies are warranted to delineate the methods to minimize the complications associated with the learning curve.