Tese de Doutoramento Medicina 2024 Faculdade de Ciências Médicas, Universidade NOVA de Lisboa

Unlike other vertebrates, human beings have the unique ability to maintain an upright position and bipedal locomotion, which is only possible due to the morphology of the human spine. However, this comes at a cost. With increased strain and stress in the lumbopelvic transition, there is a higher susceptibility to degenerative disc disease in the lower lumbar spine. Despite self adaptative and compensatory mechanisms, some pathologies may still need surgical treatment whenever adequate conservative measures have failed or are unsuitable. Spine surgery has always been challenging due to the spine's neurological and biomechanical complexity. In order to reduce tissue trauma, decrease complication rates, and improve functional recovery, minimally invasive surgical techniques have been developed throughout the years. However, advances in endoscopic spine surgery (ESS) further minimized tissue aggression, making its way into a new era in spine surgery. The benefits of ESS are well established, namely in the treatment of disc herniations and decompression surgeries. Furthermore, it has also shown promising results in lumbar interbody fusion surgeries. The most common approach in lumbar endoscopic assisted fusions is through the foramen, using an intraforaminal access. However, the lower lumbar spine, and particularly L5S1, poses several challenges to this technique due to the potential conflict with the iliac crest, the disc slope, the dorsal root ganglion, or the facet joint's morphology, remaining an open field for research. This thesis focuses on assessing the lumbopelvic morphology in different populations and investigates an innovative surgical technique to overcome the anatomical challenges for an endoscopic assisted intraforaminal lumbar interbody fusion (iLIF). Specifically, this research focuses on: 1) Detailing characteristics of lumbopelvic morphology; 2) Developing an anatomic-based transforaminal surgical approach to L5S1 iLIF to overcome the iliac crest limitation; 3) Analyzing treatment outcomes and complications of L5S1 transiliac iLIF. In PART I, we discuss the relevant topics to understand the scope of our thesis. Chapter 1 is dedicated to spine development and morphology. Chapter 2 focuses on bipedalism, sagittal balance, and intervertebral disc degeneration. Finally, Chapter 3 provides a historical perspective on minimally invasive spine surgery, particularly endoscopic spine surgery. In PART II, we develop the rationale and aims of this thesis. In PART III, we present the original research performed. In Chapter 1, we present a systematic review and meta-analysis on endoscopic assisted lumbar interbody fusion, providing a state-of-the art overview and underlining the gaps in knowledge regarding the approach to the lower lumbar spine (Paper I). Chapter 2 focuses on lumbopelvic anatomic and morphological correlations for a transforaminal endoscopic approach to the L5S1 disc space in asymptomatic and symptomatic (low back pain) individuals (Paper II). In line with the results presented in the previous chapters, in Chapter 3, we describe a transiliac approach for iLIF in L5S1. The results of a cadaver study are presented, reporting the feasibility and potential risks of the technique. Furthermore, we compare cage positioning after a suprailiac and transiliac endoscopic intraforaminal approach to L5S1 (Paper III). Finally, Chapter 4 describes the initial clinical experience with the transiliac iLIF technique, reporting preliminary outcomes and complications (Paper IV). We provide an overview of our work in PART IV, discussing the results, summarizing our conclusions, and looking into future prospects within this field. In short, our thesis suggests the following: First, iLIF for treating lumbar degenerative diseases has significantly less intraoperative blood loss and reduced length of hospital stay than minimally invasive transforaminal lumbar interbody fusion (MI-TLIF). Second, iLIF provides significant clinical improvement and high fusion rates at 12 months or later, without significant difference in complication rates compared to MI-TLIF. Third, a deep understanding of the patient's anatomy will increase surgical procedures' safety, accuracy, and effectiveness. Our results comprehensively characterize lumbosacral morphology for L5S1 transforaminal access, setting preliminary reference values for access and working angles, its correlation to the iliac crest, and reference values for skin incision planning. Forth, as traditionally measured, the projection of the highest point of the iliac crest does not correspond to the potential point of conflict with the transforaminal access to L5S1. Only in a small percentage of cases will the iliac crest eventually prevent this approach. Fith, in the subset of patients in which the iliac crest prevents transforaminal endoscopic access to L5S1, the transiliac iLIF is a feasible surgical technique. It allows us to overcome the limitations imposed by the iliac crest and, at the same time, preserve the major anatomic structures at risk. Also, the cage can be placed more centrally without compromising its anterior position in the lateral plane. Sixth, the first patients who underwent transiliac L5S1 iLIF reported good clinical outcomes and high fusion rates at 12 months. However, dysesthesia of the ipsilateral lower limb is a significant concern when programming this type of surgery. Therefore, special care must always be taken to prevent L5 doral root ganglion (DRG) injury by performing a wide facet removal and decompression. Previous experience in lumbar transforaminal ESS is mandatory. As we look to the future, the field of ESS will most surely continue to evolve, striving to achieve the best possible clinical outcomes to tackle the complexity of spine pathology. The path to predictive medicine will be established with the growing range of analytic parameters available, combined with the advancements in artificial intelligence, including machine learning and deep learning. More precise pre-operative planning and progressive incorporation of not only navigation and robotics but also augmented reality during surgical procedures will probably lead to improved patient outcomes and more personalized approaches in spine care