Five-year clinical outcomes with endoscopic transforaminal foraminoplasty for symptomatic degenerative conditions of the lumbar spine: a comparative study of inside-out versus outside-in techniques

Anthony Yeung, Kai-Uwe Lewandrowski


Background: Foraminal stenosis is a condition that is underappreciated by traditionally trained surgeons because the entire foraminal zone is not adequately visualized with the translaminar approach unless extensive removal of the facet is performed to expose the extraforaminal zone. Its direct endoscopic visualization is feasible with the inside-out and outside-in endoscopic transforaminal technique. The authors analyzed the differences in long-term 5-year clinical outcomes of endoscopic transforaminal foraminoplasty for symptoms from lumbar foraminal stenosis to better establish clinical indications for each technique.
Methods: Long-term 5-year MacNab outcomes, VAS scores, complications, and unintended aftercare were analyzed in a series of 176 patients consisting of 86 inside-out (group 1) and 90 outside-in (group 2) patients treated for sciatica-type back and leg pain due to lumbar foraminal stenosis.
Results: At minimum 5-year follow-up, excellent results according to the MacNab criteria were obtained in 93 (52.8%) patients, good in 63 (35.8%), fair in 17 (9.7%), and poor in 3 (1.7%), respectively. The mean preoperative VAS was 6.87±1.96. The mean postoperative VAS was 3.15±1.59 and 2.98±1.75 at last follow-up, respectively. Both postoperative VAS and final follow-up VAS were statistically reduced at a significance level of P<0001. There were no major approach-, surgical- or anesthesia-related complications in this series. The vast majority of patients (112/176; 63.6% of the study population) did not require any additional interventional or surgical treatment following the index transforaminal endoscopic decompression. Postoperative dysesthesia due to irritation of the dorsal root ganglion (DRG) as a consequence of operation next to the DRG occurred in 17 patients (9.7%) and was the most common benign postoperative sequelae. There was a higher reoperation rate in the outside-in group (35.6%) than in the inside-out group (8.1%). The secondary fusion rate was also higher with the outside-in (8.9%) than with the inside-out technique (2.3%). Ultimately, the long-term clinical outcomes with the endoscopic transforaminal decompression procedure were favorable regardless of whether the inside-out or outside-in technique was used. These numbers were generated by two experienced endoscopic surgeons with thousands of case experience.
Conclusions: Patients with symptomatic foraminal stenosis may be treated successfully with either the inside-out or the outside-in selective endoscopic discectomy (SED™) method while maintaining favorable long-term outcomes with a 3.2× decreased need for secondary fusion at 5-year follow-up when compared to recently reported reoperation rates for traditional decompression/fusion. Long-term clinical outcomes with the inside-out technique were presumably better because of the ability to visualize and decompress underneath the dural sac, the ventral facet and the axilla known as the hidden zone of MacNab.