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The Learning Curve in Foraminal Endoscopic Discectomy: Experience Needed to Achieve a 90% Success Rate

Rudolf Morgenstern, MD, PhD,1 Christian Morgenstern,2 Dipl-Ing, Anthony T. Yeung, MD3

1Centro Médico Teknon, Barcelona, Spain 2Universitat Politècnica de Catalunya, Barcelona, Spain 3Squaw Peak Surgical Facility, Phoenix, AZ



We sought to construct a general methodology for objectively quantifying the learning curve associated with any surgical technique and to determine the number of cases needed to achieve a success rate of 90% for the technique of transforaminal endoscopic lumbar discectomy. To our knowledge, no other studies have observed the learning curve of endoscopic lumbar discectomy by transforaminal approach.


We studied the learning curve of 1 orthopedic surgeon who had had experience performing open spine surgery and knee and shoulder arthroscopic surgery, but not endoscopic spine surgery. We studied 144 patients who had an endoscopic lumbar discectomy by transforaminal approach (using the Yeung Endoscopic Surgery System). We evaluated results with modified MacNab criteria and used a questionnaire to determine the patients’ satisfaction with the surgery. The average follow-up period was 24 months. We used an algorithm, analyzing the patient outcome and the surgical time evolution, to determine the case at which a success rate of 90% good/excellent results was reached.


The cut for the calculated learning curve was placed at case no. 72; i.e., the results in the first 72 cases were 75% good/excellent, 18% fair, and 7% poor, and the results in the following 72 cases were 90.3% good/excellent, 9.7% fair, and 0% poor.


A methodology to calculate the learning curve of a surgical procedure was developed. A learning curve of 72 cases was needed to reach the goal of 90% of good/excellent results for transforaminal endoscopic lumbar discectomy.

Clinical Relevance

The method developed to establish the learning curve of a surgical procedure, based on outcome and surgical time, may be used to assess any new procedure. With respect to the transforaminal endoscopic technique, the determination of a specific number of cases (72) needed to master (achieve 90% excellent/good results) could help orient surgeons willing to adopt this technique.

Foraminal endoscopic lumbar discectomy, learning curve, transforaminal approach
Volume 1 Issue 3